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Another idiot wanting to build too big a printer

Posted by gsport 
Another idiot wanting to build too big a printer
August 10, 2017 12:14PM
A few years back I built a Prusa i2 derivative and have been printing things on that quite happily using Slic3r and pronterface.

But now I want to print some bigger stuff. I've done experiments with printing in sections and gluing together the results, but that hasn't been great and wont work for the new stuff I want to print so...

I want to build a new printer to take advantage of all the improvements that have come along in the last few years, with a build volume of 650 x 750 x 250.

Now I have been doing some research and reading and I know this is "too big" but in my defence I haven't just rounded up to 1m x 1m x 1m and I am happy to use a big(ish) nozzle and thick(ish) layers and I don't plan on filling that build volume, more building low things that have lots of holes in them and have extremities that need to be printed.

I want to print modest sized things in Nylon and then the big things can be whatever is easiest/cheapest, probably PLA. The big things are completely flat bottomed if that helps.


So my provisional plan is to do a box with 20 x 40 V-slot along the top edges as the X axis with a motor for each side and 2 carriages with mini wheels. Then the link between these two carriages is another section of 20 x 40 V-slot with another carriage on it for the Y axis holding the extruder. Both of these would be belt driven. So like a coreXY or H-bot but with just direct drive and the Y axis motor mounted on the end of the Y carriage thing.

The bed is then raised and lowered as the Z axis on 3 biggish bits of threaded bar (M12 maybe), resting on combined thrust/radial bearing units at the base, radial bearings at the top and then a coupling to a motor each.

3mm Hot end/extruder e3D v6 and direct drive titan (not aero) to help keep weight off.

Electronics either Smoothie or Duet?


So my questions/help needed:-

1. How rubbish does this sound? I'm not bad on the old mechanical side so I can build something pretty rigid OK.

2. What do I need to get nylon printing nicely (apart from the all metal hot end)

3. Build plate? How much heating will I need? I've never needed more than 60 degrees on my current printer (with glass surface) to get prints to stick in PLA but Nylon is new to me. As it wont move much and can be heavy I wondered about slate, but I suspect this is daft. Otherwise is there somewhere to buy aluminium plate and borosilicate glass at a decent price? (I'm in the UK so ideally UK places for any stuff would be good). Another thing I wondered about was heating an aluminum bed from quite a way below with a hot air gun or fan heater.

4. Can I use 2 steppers for the X axis and 3 for the Z and just wire them in parallel like they are on my Prusa i2 (Z axis) or is this terrible in some way?

5. My plan is to keep the weight off the head wherever possible, use the small 21oz Nema17 stepper for the extruder (relying on the gearing to help make this adequate), then the next size up for the Y axis stepper (which is moving weight too but has 2 belts and motors to move it) and then biggies for the X axis and Z axis motors. Is a 21oz 17 going to be OK with the titan to feed material fast on a 0.6 nozzle and 0.3/0.4 layer height?

6. I'd like to just order all the bits from Ooznest to make my life easier, but it really adds up with all these bits, and they don't do the duet or ordinary cheap T-slot for the non rail sections, are there any other good UK places to order?

Many thanks for any help and for reading all this waffle.

George
Re: Another idiot wanting to build too big a printer
August 10, 2017 12:51PM
Not sure what you mean, this Erectorbot Fused Filament Fabrication 3D Printer has Build Size: 6096 x 2133.6 x 1828.9 mm or 23 cubic meters with mechanical printing speeds 1000mm/sec, this printer uses a .70 tip. (They called it a tip 'I would have called it a nozzle')

DUS Architects and Fiction Factory Fused Filament Fabrication 2.2 x 2.2 x 3.5 m
Traktus 3D Fused Filament Fabrication 1000 mm diameter x 1900 mm high (max top center 2100 mm) It can print with a resolution of 0.05 mm and a speed of 300mm/sec.


This one here may be more to your liking.
BigRep Fused Filament Fabrication 980 x 1050 x 1100 mm [www.youtube.com]

I would build it and print with a .8mm or 1.0 mm nozzle using 3mm filament. You could even make your own nozzle by boring out the 1.0mm to a 1.2 - 1.6mm nozzle, while printing with a layer height of 1/2 or even 1/4 the nozzle bore thus increasing your print speeds based on the fact that you fill widths are wider. Of course you may need to redesign the hot-end. I would increase the number of heaters, using two 12v heaters in series for 24V for a single hot-end, one for each side of the heater block for a more consistent heat source without overheating the filament. Maybe even a larger heater block to help maintain a consistent heat source.

Edited 14 time(s). Last edit at 08/10/2017 02:03PM by Roberts_Clif.
Re: Another idiot wanting to build too big a printer
August 10, 2017 04:57PM
I don't consider myself an expert on the mechanical side of things. but here is my 2p worth:

1. Bed: with a bed of that size, you lose the advantages of removable glass beds (i.e. being to swap them easily to start another print quickly, and being able to put the bed + print in the fridge/freezer if it is difficult to separate them). So I suggest you use a cast aluminium tool plate (to guarantee flatness) and your favourite print surface on top of that (PEI, PrintBite, Polycarbonate, Kapton tape etc. - although I've no idea how well these work with Nylon). See [www.aluminiumwarehouse.co.uk].

2. Bed heater: I usually reckon on 0.4W heating power per sq cm to be sure you can reach 120C reasonable quickly. If the bed is especially thick (which it may need to be, given its size), you may want to go higher. At the power levels this comes to, the only practical option is an AC mains silicone bed heater controlled from the electronics by an SSR. There are companies that will make a silicone heater to your own size, voltage and power specifications e.g. Shenzen Ali Brother Technology and I am told also Keenovo. Use a bed heater at least 15mm smaller all round that the bed plate to allow for fixings to the bed plate. Consider whether your bed plate may need additional support near the centre, in which case you may need 2 separate silicone heaters to leave room for it.

3. It's usually better to wire stepper motors in series than in parallel, although it depends on the current rating of your stepper drivers, the current rating of your stepper motors, and what power supply voltage you are using (don't even consider using 12V for a printer of that size, use 24V).

4. Driving the leadscrews: Use either one motor driving all 3 via a belt drive, or 3 motors driven from independent drivers. The problem with using 3 motors driven in series or parallel is that sometimes when you power the printer off an on again, they will get out of sync. With 3 motors driven independently and a Z probe, you can do automatic bed levelling (and I do mean leveling, not compensation) by adjusting the motors to get the bed level. RepRapFirmware on the Duets supports this. But of course you need a total of 6 drivers, assuming single extrusion. A Duet WiFi or Duet Ethernet + DueX2 expansion board will give you 7. If you don't want to buy the DueX2 you could consider using a cheap Pololu-style external driver for the extruder drive, if your electronics skills are up to it.

5. Two Y motors: if they are constrained to move together by a belt, no problem as long as the belt does not permit an error of 4 full steps between them. If not, then you risk them going out of sync again.

6. You can buy the Duet and accessories direct from the UK manufacturer at duet3d.com.

7. For a 3:1 geared extruder such as the Titan and 1.75mm filament, I suggest a motor with 20-25Ncm torque at rated current. You may get away with lower, I haven't tried. Also I haven't tried the really high extrusion rates that you are likely to need. I presume you will use Titan Aero + Volcano.

8. For printing Nylon I am guessing that you will need a heated chamber, although I've never printed Nylon so I could be wrong. If you enclose the printer, the bed heater may provide sufficient heat without the need for a separate chamber heater.

9. I buy T-slot from Motedis. They ship from Germany but they have a UK web site.

HTH David



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Another idiot wanting to build too big a printer
August 11, 2017 06:02AM
I would go for a CoreXY machine, I'm building one with a 400x400x300 range and I could easily see it scaled up a bit more. For the bed I use tooling plate. I choose 400x400 (plate is slightly bigger to fit mountings to) because I can fit 4 200x200 hot end plates. In your case going for 600x800 would allow for 12(!) of those standard plates. Hmmmm, you'll need a nice power source... Better look into a custom silicone heater, 240V or 115V depending on your location. I had some made by an AliEpress supplier which offers standard sizes, but mentions to welcome custom inquiries. Not too expensive.

Hugo
Re: Another idiot wanting to build too big a printer
August 11, 2017 08:08AM
Quote
Roberts_Clif
Not sure what you mean, this Erectorbot Fused Filament Fabrication 3D Printer has Build Size: 6096 x 2133.6 x 1828.9 mm or 23 cubic meters with mechanical printing speeds 1000mm/sec, this printer uses a .70 tip. (They called it a tip 'I would have called it a nozzle')

DUS Architects and Fiction Factory Fused Filament Fabrication 2.2 x 2.2 x 3.5 m
Traktus 3D Fused Filament Fabrication 1000 mm diameter x 1900 mm high (max top center 2100 mm) It can print with a resolution of 0.05 mm and a speed of 300mm/sec.


This one here may be more to your liking.
BigRep Fused Filament Fabrication 980 x 1050 x 1100 mm [www.youtube.com]

I would build it and print with a .8mm or 1.0 mm nozzle using 3mm filament. You could even make your own nozzle by boring out the 1.0mm to a 1.2 - 1.6mm nozzle, while printing with a layer height of 1/2 or even 1/4 the nozzle bore thus increasing your print speeds based on the fact that you fill widths are wider. Of course you may need to redesign the hot-end. I would increase the number of heaters, using two 12v heaters in series for 24V for a single hot-end, one for each side of the heater block for a more consistent heat source without overheating the filament. Maybe even a larger heater block to help maintain a consistent heat source.

Thanks for sharing that, sorry if my title seemed silly, I just wanted to make it clear that I have been searching previous posts on the subject.
I know it is possible or I wouldn't be trying.

George
Re: Another idiot wanting to build too big a printer
August 11, 2017 08:23AM
Quote
gsport

Thanks for sharing that, sorry if my title seemed silly, I just wanted to make it clear that I have been searching previous posts on the subject.
I know it is possible or I wouldn't be trying.

George

I knew you had, wanted to show you BigRep but I got carried away, an keep on typing.

I too want to make my 3D printers larger, Thought would start with an upward jump to 600mm. Which is going to require a more support, as I have a Goal post style printer.
Two uprights suspended only by Y axis clamps.

Edited 1 time(s). Last edit at 08/11/2017 08:42AM by Roberts_Clif.
Re: Another idiot wanting to build too big a printer
August 11, 2017 09:01AM
Quote
dc42
I don't consider myself an expert on the mechanical side of things. but here is my 2p worth:

1. Bed: with a bed of that size, you lose the advantages of removable glass beds (i.e. being to swap them easily to start another print quickly, and being able to put the bed + print in the fridge/freezer if it is difficult to separate them). So I suggest you use a cast aluminium tool plate (to guarantee flatness) and your favourite print surface on top of that (PEI, PrintBite, Polycarbonate, Kapton tape etc. - although I've no idea how well these work with Nylon). See [www.aluminiumwarehouse.co.uk].

2. Bed heater: I usually reckon on 0.4W heating power per sq cm to be sure you can reach 120C reasonable quickly. If the bed is especially thick (which it may need to be, given its size), you may want to go higher. At the power levels this comes to, the only practical option is an AC mains silicone bed heater controlled from the electronics by an SSR. There are companies that will make a silicone heater to your own size, voltage and power specifications e.g. Shenzen Ali Brother Technology and I am told also Keenovo. Use a bed heater at least 15mm smaller all round that the bed plate to allow for fixings to the bed plate. Consider whether your bed plate may need additional support near the centre, in which case you may need 2 separate silicone heaters to leave room for it.

3. It's usually better to wire stepper motors in series than in parallel, although it depends on the current rating of your stepper drivers, the current rating of your stepper motors, and what power supply voltage you are using (don't even consider using 12V for a printer of that size, use 24V).

4. Driving the leadscrews: Use either one motor driving all 3 via a belt drive, or 3 motors driven from independent drivers. The problem with using 3 motors driven in series or parallel is that sometimes when you power the printer off an on again, they will get out of sync. With 3 motors driven independently and a Z probe, you can do automatic bed levelling (and I do mean leveling, not compensation) by adjusting the motors to get the bed level. RepRapFirmware on the Duets supports this. But of course you need a total of 6 drivers, assuming single extrusion. A Duet WiFi or Duet Ethernet + DueX2 expansion board will give you 7. If you don't want to buy the DueX2 you could consider using a cheap Pololu-style external driver for the extruder drive, if your electronics skills are up to it.

5. Two Y motors: if they are constrained to move together by a belt, no problem as long as the belt does not permit an error of 4 full steps between them. If not, then you risk them going out of sync again.

6. You can buy the Duet and accessories direct from the UK manufacturer at duet3d.com.

7. For a 3:1 geared extruder such as the Titan and 1.75mm filament, I suggest a motor with 20-25Ncm torque at rated current. You may get away with lower, I haven't tried. Also I haven't tried the really high extrusion rates that you are likely to need. I presume you will use Titan Aero + Volcano.

8. For printing Nylon I am guessing that you will need a heated chamber, although I've never printed Nylon so I could be wrong. If you enclose the printer, the bed heater may provide sufficient heat without the need for a separate chamber heater.

9. I buy T-slot from Motedis. They ship from Germany but they have a UK web site.

HTH David


Thanks for the reply.

1. I'm not worried about a fast turn around on prints, so the removable bed isnt a worry, I've looked at big slabs of aluminium for the bed and that may be an option later but I have found a very flat bit of marble that I think might be good. Its much more rigid than aluminium though obviously not as conductive.

2. For heat I am increasingly liking the idea of just bunging a fan heater underneath and monitoring it manually to see what it settles at, this will have the benefit of heating the enclosure in general. I can always add a controlled heat bed as well to fine tune, or just replace the fan heater with a heat mat later.

3. I am definitely assuming 24 volts for everything. Both the Smoothie board and the Duet will do 24volt and the Smoothie board will do 2Amps per stepper and the Duet 2.8A so I was hoping that would be enough to drive multiple steppers. Please excuse my slowness, but I dont see how running steppers in series would work. Wouldn't that halve the voltage?

4. I would definitely like to do the automatic bed leveling but it represents a big cost for the duet and the expansion board. I was thinking of using a probe to "check" before each print and then just leveling with the 3 motors by turning the odd leadscrew by hand. I havent had any noticable issues with my dual Z motors on the current machine so if I have to make the odd correcting between prints that isnt a big deal, but obviously if I might lose significant levelness during a print that would be much worse.

6. Thanks, I first saw the duet on the think3dprint website at £107 so when I realised that was not available the jump to £160 is a bit of a shock. Adding the extension board at another £100 is a big add on to save a few minutes of bed leveling manually each time?

7. Given the big nozzle size and print layer thickness I was going to stick with 3mm. Do you think the small motor will still be up to this?

8. I think some heat will help with nylon but people aren't reporting it as essential, the main thing seems to be keeping the filament dry. I am planning on keeping it semi enclosed but am worried about the heat the motors can stand. The spec sheets suggest 50 degrees as a maximum, do you know if this can be pushed at all or what happens when exceeded?

9. Thanks, I'lll look into that.

George
Re: Another idiot wanting to build too big a printer
August 11, 2017 09:06AM
Quote
Roberts_Clif
Quote
gsport

Thanks for sharing that, sorry if my title seemed silly, I just wanted to make it clear that I have been searching previous posts on the subject.
I know it is possible or I wouldn't be trying.

George

I knew you had, wanted to show you BigRep but I got carried away, an keep on typing.

I too want to make my 3D printers larger, Thought would start with an upward jump to 600mm. Which is going to require a more support, as I have a Goal post style printer.
Two uprights suspended only by Y axis clamps.

You can always triangulate to the top to help those Y axis clamps, my worry would be the longer screws and guides bending/vibrating.

George
Re: Another idiot wanting to build too big a printer
August 11, 2017 09:09AM
Quote
HugoW
I would go for a CoreXY machine, I'm building one with a 400x400x300 range and I could easily see it scaled up a bit more. For the bed I use tooling plate. I choose 400x400 (plate is slightly bigger to fit mountings to) because I can fit 4 200x200 hot end plates. In your case going for 600x800 would allow for 12(!) of those standard plates. Hmmmm, you'll need a nice power source... Better look into a custom silicone heater, 240V or 115V depending on your location. I had some made by an AliEpress supplier which offers standard sizes, but mentions to welcome custom inquiries. Not too expensive.

Hugo

Thanks. I'll definitely look into those if my budget fan heater idea doesn't pan out. Should be easy enough to experiment before building the actual machine.

George
Re: Another idiot wanting to build too big a printer
August 11, 2017 05:19PM
Quote
gsport
3. I am definitely assuming 24 volts for everything. Both the Smoothie board and the Duet will do 24volt and the Smoothie board will do 2Amps per stepper and the Duet 2.8A so I was hoping that would be enough to drive multiple steppers. Please excuse my slowness, but I dont see how running steppers in series would work. Wouldn't that halve the voltage?

Yes, but this is usually better than halving the current, unless you deliberately choose weak low-current motors.

Quote
gsport
4. I would definitely like to do the automatic bed leveling but it represents a big cost for the duet and the expansion board. I was thinking of using a probe to "check" before each print and then just leveling with the 3 motors by turning the odd leadscrew by hand. I havent had any noticable issues with my dual Z motors on the current machine so if I have to make the odd correcting between prints that isnt a big deal, but obviously if I might lose significant levelness during a print that would be much worse.

The same facility that does auto bed levelling on the Duet can be used to tell you how much to adjust your levelling screws (or leadscrews) by if you don't have multiple Z motors.

Quote
gsport
6. Thanks, I first saw the duet on the think3dprint website at £107 so when I realised that was not available the jump to £160 is a bit of a shock. Adding the extension board at another £100 is a big add on to save a few minutes of bed leveling manually each time?

Re the £160, you must be including carriage and VAT. Last time I compared prices, the Duet WiFi was slightly cheaper than a Smoothieboard 5XL + the 5V regulator that it needs. The Due X2 expansion board isn't £100, it's £57.50 + VAT.

Quote
gsport
7. Given the big nozzle size and print layer thickness I was going to stick with 3mm. Do you think the small motor will still be up to this?

I've never used 3mm filament so I can't answer that.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Another idiot wanting to build too big a printer
August 11, 2017 05:58PM
Quote
dc42
Quote
gsport
3. I am definitely assuming 24 volts for everything. Both the Smoothie board and the Duet will do 24volt and the Smoothie board will do 2Amps per stepper and the Duet 2.8A so I was hoping that would be enough to drive multiple steppers. Please excuse my slowness, but I dont see how running steppers in series would work. Wouldn't that halve the voltage?

Yes, but this is usually better than halving the current, unless you deliberately choose weak low-current motors.

Quote
gsport
4. I would definitely like to do the automatic bed leveling but it represents a big cost for the duet and the expansion board. I was thinking of using a probe to "check" before each print and then just leveling with the 3 motors by turning the odd leadscrew by hand. I havent had any noticable issues with my dual Z motors on the current machine so if I have to make the odd correcting between prints that isnt a big deal, but obviously if I might lose significant levelness during a print that would be much worse.

The same facility that does auto bed levelling on the Duet can be used to tell you how much to adjust your levelling screws (or leadscrews) by if you don't have multiple Z motors.

Quote
gsport
6. Thanks, I first saw the duet on the think3dprint website at £107 so when I realised that was not available the jump to £160 is a bit of a shock. Adding the extension board at another £100 is a big add on to save a few minutes of bed leveling manually each time?

Re the £160, you must be including carriage and VAT. Last time I compared prices, the Duet WiFi was slightly cheaper than a Smoothieboard 5XL + the 5V regulator that it needs. The Due X2 expansion board isn't £100, it's £57.50 + VAT.

Quote
gsport
7. Given the big nozzle size and print layer thickness I was going to stick with 3mm. Do you think the small motor will still be up to this?

I've never used 3mm filament so I can't answer that.

Thanks for the further info. Hadn't realised there was a +2 version of the Deux board at a lower price, you have to select that from the drop down box then it takes money off the price which is the reverse of what I am used to seeing on websites (to be honest I found the website rather confusing to navigate, sometimes it suggests an add on of a heaterblock but you cant find that through menus?). That does make it a lot less intimidating price wise but its still a huge chunk of my budget. Might make sense for me to just get the Duet and try running the motors from the same driver and I can always add the Deux2 later.
The electronics are one of my biggest areas of uncertainty, do you by any chance have a link to a clear review/demonstration of the Duet? Currently I've been leaning towards the Smoothie board just because I can get it from ooznest at the same time as most of the other parts.

George
Re: Another idiot wanting to build too big a printer
August 12, 2017 03:18AM
You can find descriptions of various printers using Duets at [www.duet3d.com]. There are a few reviews of the Duet WiFi around including this one [youtu.be].

PS - Smoothieboard 5XC from Ooznest inc. voltage regulator is £168 inc VAT. Duet WiFi/Duet Ethernet are both £144 inc. VAT. So I was right, the Duets do cost less, despite the advantages they offer. I didn't check carriage costs. The Duet Ethernet price will increase by £10+VAT at the start of next month.

Edited 1 time(s). Last edit at 08/12/2017 04:51AM by dc42.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Another idiot wanting to build too big a printer
August 12, 2017 03:39PM
Mechanics of the machine aside, what about the thermal expansion of the materials?

If you think of a .5 meter object, depending on the exact material you select, it may be quite a bit longer (thermal expansion) at the temp it comes out of the nozzle than at room temp. If the material you select has a thermal coefficient vastly different from the bed material or at room temp, you may print a potato chip. This may be worse if you plan to cover most of the bed with a thin layer?

If you print a .3 x .5 meter oval, it will contract at different amounts along the axis as opposed to just missing the scale of the thing, it may pucker up.

I think that little objects can cope with the expansion better, there is just less distance x temp to stress them and make them curl.

The material of the machine itself will also change size depending on the temp, some clearances may need to be adjusted. This is also less of a problem with smaller machines.
Re: Another idiot wanting to build too big a printer
August 12, 2017 04:51PM
Quote
kengineer
Mechanics of the machine aside, what about the thermal expansion of the materials?

If you think of a .5 meter object, depending on the exact material you select, it may be quite a bit longer (thermal expansion) at the temp it comes out of the nozzle than at room temp. If the material you select has a thermal coefficient vastly different from the bed material or at room temp, you may print a potato chip. This may be worse if you plan to cover most of the bed with a thin layer?

If you print a .3 x .5 meter oval, it will contract at different amounts along the axis as opposed to just missing the scale of the thing, it may pucker up.

I think that little objects can cope with the expansion better, there is just less distance x temp to stress them and make them curl.

The material of the machine itself will also change size depending on the temp, some clearances may need to be adjusted. This is also less of a problem with smaller machines.

This is a very good point. This is already a problem on "normal" sized prints so on a print half a meter long its likely to be an even bigger problem. I guess it is going to come down to the thermal expansion of the material in use which is not likely to be very linear. So if the plastic in use expands slightly as it goes from liquid to solid (which I have a feeling is the case with crystaline polymers) and then contracts as it cools, then if I can keep the build chamber at the right temperature then hopefully it wont be too bad. Also got to think that as the part gets bigger the amount of freshly extruded material is in a lower ratio compared to the already cooled volume, so maybe it actually gets better?

Only really one way to find out...

George
Re: Another idiot wanting to build too big a printer
August 12, 2017 04:54PM
Quote
dc42
You can find descriptions of various printers using Duets at [www.duet3d.com]. There are a few reviews of the Duet WiFi around including this one [youtu.be].

PS - Smoothieboard 5XC from Ooznest inc. voltage regulator is £168 inc VAT. Duet WiFi/Duet Ethernet are both £144 inc. VAT. So I was right, the Duets do cost less, despite the advantages they offer. I didn't check carriage costs. The Duet Ethernet price will increase by £10+VAT at the start of next month.

Thanks, I'd seen that video, was hoping for something that talked about the initial setup, the warnings about connecting via USB and creating a ground loop, but having to do that to do the initial setup had me a bit spooked so a walk through would be nice.

George
Re: Another idiot wanting to build too big a printer
August 12, 2017 10:23PM
Quote
gsport
Quote
kengineer
Mechanics of the machine aside, what about the thermal expansion of the materials?

If you think of a .5 meter object, depending on the exact material you select, it may be quite a bit longer (thermal expansion) at the temp it comes out of the nozzle than at room temp. If the material you select has a thermal coefficient vastly different from the bed material or at room temp, you may print a potato chip. This may be worse if you plan to cover most of the bed with a thin layer?

If you print a .3 x .5 meter oval, it will contract at different amounts along the axis as opposed to just missing the scale of the thing, it may pucker up.

I think that little objects can cope with the expansion better, there is just less distance x temp to stress them and make them curl.

The material of the machine itself will also change size depending on the temp, some clearances may need to be adjusted. This is also less of a problem with smaller machines.

This is a very good point. This is already a problem on "normal" sized prints so on a print half a meter long its likely to be an even bigger problem. I guess it is going to come down to the thermal expansion of the material in use which is not likely to be very linear. So if the plastic in use expands slightly as it goes from liquid to solid (which I have a feeling is the case with crystaline polymers) and then contracts as it cools, then if I can keep the build chamber at the right temperature then hopefully it wont be too bad. Also got to think that as the part gets bigger the amount of freshly extruded material is in a lower ratio compared to the already cooled volume, so maybe it actually gets better?

Only really one way to find out...

George

George,

It will get much worse with a larger thing. The material, as it comes out of the nozzle, is much different size than it will be at even an elevated enclosure temp.

If you check the thermal coefficient of your selected material on a website like matweb.com , you may be stunned a how much the material size changes per inch per degree. The longer the part, the greater the change will be. It will shrink one dimension on the short side and shrink a larger dimension on the longer side.

At 100 ° C, any aluminum printer parts will be .004" longer than at room temp. if the total length is around a meter. Steel will be somewhat better.

I only bring this up so that you can consider how to comp it, if you see it happen.

Maybe a bowl-like print would be able to resist being sheared from the plate if the attachment area was smaller? Maybe compliant build plate material that could yield? Maybe print on velvet? OK, maybe not....

I am also interested in what others think of this as a possible problem. I print up to 275mm things and any input on compensating for the thermal size changes would be interesting.
Re: Another idiot wanting to build too big a printer
August 13, 2017 09:42AM
Its definitely going to be a consideration, but I don't think it is something that can be solved on paper in advance (at least with the resources I have to hand). The problem is that the coefficient of thermal expansion is not linear and goes completely out the window once the material actually undergoes a phase change from liquid to solid.
I'm currently planning to use marble as my build platform as I happen to have a big flat slab of it already, and this has a coefficient of thermal expansion probably half that of the aluminium and quite likely even better than cast iron, but I dont think this is really a huge factor as it should remain at a constant temperature (near enough) throughout the build anyway.

The curling issue is to my mind mostly because the first few layers are constrained from contracting by a very rigid bed, but subsequent layers have a less rigid "part" to constrain them. One way to overcome this might be to print everything on "support material" so that the initial 5-10 layers or so are very flexible, then the part proper is on a flexible "bed" so it can shrink a similar amount on every layer.

The other obvious solution is to have everything at a very high temperature until the build is finished. So if the material solidifies at 150C but only cools to 100C (for example) in the build chamber then that is obviously going to be a lot less room for contraction, AND being above the vicat softening temperature it should sort itself out easily. However we then hit issues with the print potentially collapsing into a puddle and either removing the electronics from the build volume or having ones that can take it. Currently I only plan to have motors and Z probe etc in the build volume but would be good to know what they can take. 50C build will probably help a lot and the steppers at least say they can take this.

Edited 1 time(s). Last edit at 08/13/2017 09:47AM by gsport.
Re: Another idiot wanting to build too big a printer
August 14, 2017 02:58AM
I've reasonable experience with building/designing/servicing additive manufacturing machines but far less so with the extrusion printers. I'm having to learning fast and considering a similar path to yourself. This is my 2p worth, more experienced fused filament users are likely to expand further or indeed rule out some of these comments!

I'm currently building a 300x300x300mm core xy based d-bot for work with a view to up size in a couple of years after I've had a chance to prove the basics. I was a little concerned that if you look at the design from a nit-picking / over engineering perspective I would end up building a machine which has a far smaller operating window (in terms of tolerating unexpected errors, component wear, etc...) before even considering the complications of the larger printing including potential gotchas like the residual stress built into the printed parts and maybe the cooler temperature of the material on the previous layer when depositing the next layer. I believe the BAAM machine that printed the cars had additions like graphite to try and control the temperature a little more and even physically beat the deposited bead flat. This however was using a nozzle (/hose) that was millimetres wide fed by a traditional screw pellet extruder!

With regard the residual stress print strategy can help here. Lots of work has been done in this area to try and address the problem with metal additive manufacturing machines. They have it far worse! In a former employment I saw a build with simple dog bone tensile test parts built flat but thin edge down (large surface in the x-z plane) curl a 20mm aluminium substrate!

Thermal issues are probably most economically tackled by the heated chamber that others have suggested. The potential pitfall here is assuming the frame will move in a linear fashion rather than potentially twisting and wrecking the nozzle to build plate alignment. If you were putting plenty of effort into this then perhaps some PT100 temperature sensors on the main chassis components and have an additional system warn you if the current rate of change in temperature is likely to exceed a set limit and perhaps track the change in temperature from start to finish. Warning about differential temperatures across the machine at a specific time would be more difficult as you are then going to struggle with calibration issues. If cost allows, and the expected working temperature range allows materials like carbon fibre sheet and tubing could be a good choice for the chassis as this has little thermal movement. Invar is often use in high precision equipment but it is far from cheap.

I'm guessing you are expecting builds that last a few days on this system. A back up power supply to see you through power dips and short power cuts of a few minutes would be worth considering. There are a few dual head systems about. While the builders are often considering these for multiple materials it would be well worth considering these for redundancy. If the system detects a failure with the first head (or ran out of filament) you would have a spools amount of time to get to the print before it was interrupted. The longer the pause in printing the worse any visual or mechanical weakness will be.

Electrical safety. I would suggest picking wiring so that the expected loading is around 80% of the rated load of the cable. In addition I would check that at the expected loading there is no more than 10% voltage drop along the cable run - including the earth path back to the PSU. I would pay some attention to fusing but remember this is to protect from the likely hood of a short causing wires burning and starting a fire, rather than protecting electronics. With the exception of current controlled devices (eg the steppers) in an ideal world at least any wire coming out of the control box should be overload protected in some way. This is especially so for wires that are moved lots. Earth bond as much of the metal work as practical, but be aware that this can be a return path for current in the event of a component failure, and so should ideally be at least equal to the cross sectional area of the wires coming out of the PSUs and into the printer electronics and hardware. Don't forget to earth bod the steppers, especially those mounted in printed components as static build up could be an issue. I am currently replacing the OEM control board on a commercial printer with a Duet and some of the wiring in that is undersized in my opinion. Using a ribbon cable and doubling up on the conductors may work fine for most of the of the time but there are two connections that need to remain good for that to be safe. If one conductor begins to fail the other will immediately over current. If you have a single conductor and a connection begins to fail then the conductor conducts less.

Fire safety. Perhaps the heated enclosure should be designed include a fire detection and at best extinguishing system?

Fumes. With small builds you can get away with the fumes to an extent. I've been on the receiving end of some polymer extrusion fumes that knocked me a bit giddy for a day and got on my chest for a week or so more. I would consider extraction, but this would add challenges to the design of a heated enclosure.

I'd certainly spend more time looking at what others have reported on their big build before up scaling the d-bot, but I would be interested in keeping the platform still and moving the head up. This would allow the platform to be built very rigidly, keep more of the high current wires (and sometimes mains voltage) still, and keep the big source of heat in a constant position. If the heater is slowly getting lower in you system then the thermal issues would be quite complex and possibly very with build rate adding yet another parameter to the problem.

Edited 3 time(s). Last edit at 08/14/2017 03:06AM by WesBrooks.
Re: Another idiot wanting to build too big a printer
August 14, 2017 08:42AM
Quote
WesBrooks
I've reasonable experience with building/designing/servicing additive manufacturing machines but far less so with the extrusion printers. I'm having to learning fast and considering a similar path to yourself. This is my 2p worth, more experienced fused filament users are likely to expand further or indeed rule out some of these comments!

I'm currently building a 300x300x300mm core xy based d-bot for work with a view to up size in a couple of years after I've had a chance to prove the basics. I was a little concerned that if you look at the design from a nit-picking / over engineering perspective I would end up building a machine which has a far smaller operating window (in terms of tolerating unexpected errors, component wear, etc...) before even considering the complications of the larger printing including potential gotchas like the residual stress built into the printed parts and maybe the cooler temperature of the material on the previous layer when depositing the next layer. I believe the BAAM machine that printed the cars had additions like graphite to try and control the temperature a little more and even physically beat the deposited bead flat. This however was using a nozzle (/hose) that was millimetres wide fed by a traditional screw pellet extruder!

With regard the residual stress print strategy can help here. Lots of work has been done in this area to try and address the problem with metal additive manufacturing machines. They have it far worse! In a former employment I saw a build with simple dog bone tensile test parts built flat but thin edge down (large surface in the x-z plane) curl a 20mm aluminium substrate!

Thermal issues are probably most economically tackled by the heated chamber that others have suggested. The potential pitfall here is assuming the frame will move in a linear fashion rather than potentially twisting and wrecking the nozzle to build plate alignment. If you were putting plenty of effort into this then perhaps some PT100 temperature sensors on the main chassis components and have an additional system warn you if the current rate of change in temperature is likely to exceed a set limit and perhaps track the change in temperature from start to finish. Warning about differential temperatures across the machine at a specific time would be more difficult as you are then going to struggle with calibration issues. If cost allows, and the expected working temperature range allows materials like carbon fibre sheet and tubing could be a good choice for the chassis as this has little thermal movement. Invar is often use in high precision equipment but it is far from cheap.

I'm guessing you are expecting builds that last a few days on this system. A back up power supply to see you through power dips and short power cuts of a few minutes would be worth considering. There are a few dual head systems about. While the builders are often considering these for multiple materials it would be well worth considering these for redundancy. If the system detects a failure with the first head (or ran out of filament) you would have a spools amount of time to get to the print before it was interrupted. The longer the pause in printing the worse any visual or mechanical weakness will be.

Electrical safety. I would suggest picking wiring so that the expected loading is around 80% of the rated load of the cable. In addition I would check that at the expected loading there is no more than 10% voltage drop along the cable run - including the earth path back to the PSU. I would pay some attention to fusing but remember this is to protect from the likely hood of a short causing wires burning and starting a fire, rather than protecting electronics. With the exception of current controlled devices (eg the steppers) in an ideal world at least any wire coming out of the control box should be overload protected in some way. This is especially so for wires that are moved lots. Earth bond as much of the metal work as practical, but be aware that this can be a return path for current in the event of a component failure, and so should ideally be at least equal to the cross sectional area of the wires coming out of the PSUs and into the printer electronics and hardware. Don't forget to earth bod the steppers, especially those mounted in printed components as static build up could be an issue. I am currently replacing the OEM control board on a commercial printer with a Duet and some of the wiring in that is undersized in my opinion. Using a ribbon cable and doubling up on the conductors may work fine for most of the of the time but there are two connections that need to remain good for that to be safe. If one conductor begins to fail the other will immediately over current. If you have a single conductor and a connection begins to fail then the conductor conducts less.

Fire safety. Perhaps the heated enclosure should be designed include a fire detection and at best extinguishing system?

Fumes. With small builds you can get away with the fumes to an extent. I've been on the receiving end of some polymer extrusion fumes that knocked me a bit giddy for a day and got on my chest for a week or so more. I would consider extraction, but this would add challenges to the design of a heated enclosure.

I'd certainly spend more time looking at what others have reported on their big build before up scaling the d-bot, but I would be interested in keeping the platform still and moving the head up. This would allow the platform to be built very rigidly, keep more of the high current wires (and sometimes mains voltage) still, and keep the big source of heat in a constant position. If the heater is slowly getting lower in you system then the thermal issues would be quite complex and possibly very with build rate adding yet another parameter to the problem.

Thanks for taking the time to write that. I hadn't really considered the implications of the longer cable runs but surely the increase from 0.7m (as I have on my current machine) to 1 - 1.5m is not going to be huge (though I appreciate we are dealing with quite low voltages sometimes)?

I'm not too worried about thermal effects on the frame, I was planning on boxing everything in with plywood which is pretty good over these modest temperature ranges and should resist movement well.

I'm hoping that my build times wont be multiple days. I'm looking at a large nozzle and thickish layers and my intended parts aren't that much heavier than a big build would be on a 220x220 platform, just more spread out.

Good point about carbon fibre. I actually have quite a lot of spare resin and cloth knocking about so I had planned to reinforce the main moving gantry beam with it if I see any vibration there. However, what would be really nice is if someone did a pulltrusion of the V-slot, not sure how well it would wear but even a T-slot profile with added rails would be very light.

George
Re: Another idiot wanting to build too big a printer
August 14, 2017 08:57AM
I think there have been a few people trying the carbon fibre tubes as rods. I think they wear much faster but would be significantly lighter than the steel equivalents.

Here's a good link for calculating voltage drop:

[www.12voltplanet.co.uk]

...and a rough guide on resistance per unit of length:

[www.engineeringtoolbox.com]

These issues will only really start to raise there head if you pull near the full rating of the cable.

Edit: Changed link to a better current capacity website!

Edited 1 time(s). Last edit at 08/14/2017 09:03AM by WesBrooks.
Re: Another idiot wanting to build too big a printer
August 14, 2017 09:03AM
Quote
kengineer
Quote
gsport
Quote
kengineer
Mechanics of the machine aside, what about the thermal expansion of the materials?

If you think of a .5 meter object, depending on the exact material you select, it may be quite a bit longer (thermal expansion) at the temp it comes out of the nozzle than at room temp. If the material you select has a thermal coefficient vastly different from the bed material or at room temp, you may print a potato chip. This may be worse if you plan to cover most of the bed with a thin layer?

If you print a .3 x .5 meter oval, it will contract at different amounts along the axis as opposed to just missing the scale of the thing, it may pucker up.

I think that little objects can cope with the expansion better, there is just less distance x temp to stress them and make them curl.

The material of the machine itself will also change size depending on the temp, some clearances may need to be adjusted. This is also less of a problem with smaller machines.

This is a very good point. This is already a problem on "normal" sized prints so on a print half a meter long its likely to be an even bigger problem. I guess it is going to come down to the thermal expansion of the material in use which is not likely to be very linear. So if the plastic in use expands slightly as it goes from liquid to solid (which I have a feeling is the case with crystaline polymers) and then contracts as it cools, then if I can keep the build chamber at the right temperature then hopefully it wont be too bad. Also got to think that as the part gets bigger the amount of freshly extruded material is in a lower ratio compared to the already cooled volume, so maybe it actually gets better?

Only really one way to find out...

George

George,

It will get much worse with a larger thing. The material, as it comes out of the nozzle, is much different size than it will be at even an elevated enclosure temp.

If you check the thermal coefficient of your selected material on a website like matweb.com , you may be stunned a how much the material size changes per inch per degree. The longer the part, the greater the change will be. It will shrink one dimension on the short side and shrink a larger dimension on the longer side.

At 100 ° C, any aluminum printer parts will be .004" longer than at room temp. if the total length is around a meter. Steel will be somewhat better.

I only bring this up so that you can consider how to comp it, if you see it happen.

Maybe a bowl-like print would be able to resist being sheared from the plate if the attachment area was smaller? Maybe compliant build plate material that could yield? Maybe print on velvet? OK, maybe not....

I am also interested in what others think of this as a possible problem. I print up to 275mm things and any input on compensating for the thermal size changes would be interesting.

I realised later that there might be a simple way to get an approximate idea of shrinkage effects.

Looking at tables for injection moulding shrinkage allowance like this:- Shrinkage rates

Then ABS is at 0.6% and nylon 6 is at 1.2% (no number for PLA unfortunately on this chart). PET looks like a really good bet at 0.4%.

These will be shrinkage from moulding (which wont be quite as hot as we tend to extrude I would guess) to room temperature (say 20C), so if we then use the coefficient of thermal expansion to make an adjustment for say a 40degree build chamber then hopefully that gives us a good approximation to what we might see.

(And in line with what Wesbrooks was saying any fibre filled material is way less prone to shrinkage)

So for Nylon 6 Shrinkage is 1.2% then expansion from 20-40C is 0.0001 x 20 which is 0.2%. So we can expect a shrinkage to deal with during printing of 1%.

PET seems to be quoting at about 0.000040 so that's about 0.08% so shrinkage to deal with during print would be just 0.32%, or a third that of Nylon 6.

If the chamber temperature could be kept nearer 100C then shrinkage would be very low even with Nylon, but I cant see that being practical for me.

Using fibre filled material looks like the best bet, but not a cheap option.
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