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All Advices with Building Larger 3D printer

Posted by dynamitetalks 
All Advices with Building Larger 3D printer
December 30, 2016 01:35PM
Hello Everyone.

I've decided to build a larger 3D printer for printing robotic prototypes and concept models. looking at something with a build size of 85 L x 85 W x 60/70 H Or a build of around 1m X 1m X 1m

I've done some research the last few days and compiled it in this document with a lot of questions. I hope experienced people will help answering all my doubts. I also hope this process can help others to scale up a 3D printer build in the future.
I'll add more to the document tomorrow, I am not done.

Feel free to add comments in the google docs document or post it here in the thread.

[docs.google.com]

Edited 1 time(s). Last edit at 12/30/2016 01:39PM by dynamitetalks.
Re: All Advices with Building Larger 3D printer
December 30, 2016 03:11PM
I don't consider myself an expert on 3D printer mechanics, but here goes:

- Choose either a bed moving in the Z axis only, or a fixed bed and a gantry moving in the Z axis

- With a CoreXY or H-Bot design, I think a single high-torque Nema 17 stepper motor should be adequate for each of X and Y at the size you are talking about.

- You need a flat bed. Cast aluminium tool plate appears to be the preferred option. I normally like to put a removable glass sheet on top of the bed, however when the bed is large this is of limited value because it it difficult to handle and it won't fit in the fridge or freezer.

- For a large heated bed, AC mains power is the only practical option. You can get a bed heater made to your own size/voltage/power specifications inexpensively from this supplier [www.aliexpress.com]. Remember to get a heater smaller than the bed by about 15mm all round to allow space for fixing the bed to a frame. For a very large bed that needs bracing underneath, 4 separate heaters could be used. Preferably, use a separate thermistor in contact with the bed plate, not a thermistor embedded in the heater.

- Number of Z motors: keeping multiple Z motors in sync when you power a printer off and on is a problem in all current firmwares. However, we will have a solution to this in RepRapFirmware for the Duet WiFi (and the forthcoming Duet Ethernet) soon, although you may need to use 24V power for it to work well. Normally, 3 point support for the bed is considered best. However, when the bed gets really large it is difficult to keep it sufficiently rigid with 3-point support, and then 4-point support is better.

Edited 1 time(s). Last edit at 12/30/2016 03:15PM by dc42.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: All Advices with Building Larger 3D printer
December 30, 2016 03:31PM
What are you going to print with it?
Re: All Advices with Building Larger 3D printer
December 30, 2016 03:57PM
I have found that it can be difficult to get prints off a 300 mm x 300 mm bed. If you print large objects on a 1m x 1m bed you will probably have difficulty getting them off the bed when the print is finished.

A few years ago when seeking a replacement for the very expensive foam that Stratasys used to use in older printers, I discovered that PIR foam building insulation works fine. PIR is fire resistant and does not decompose at printer nozzle temperatures. It costs $15 for a 4' x 8' x 1" (even less for 1/2") thick sheet at Home Depot stores. One of the greatest benefits of using PIR for a large print bed is that it requires no heat, no matter what filament material you use. The extruder injects the plastic into tiny voids in the foam, forming a mechanical bond. That means you don't need the expensive heater or the power to run it or the electronics to drive it. You also don't have to accurately level the bed before printing, so the bed support structure is very simple. When you print, you set the nozzle about 1 mm into the surface of the foam, and use a raft when you slice. The raft will create a flat, level surface for the print. When it's time to remove the print, if it won't let go of the bed, just cut or break the foam off.

Yes the foam adds to the cost of a big print, but it is a small percentage of the cost of filament.

You can easily test PIR foam- use double sided tape and stick a small piece on your printer's bed and print on it.

Here's a print I made as a test years ago:

[vimeo.com]
[vimeo.com]

Edited 1 time(s). Last edit at 12/30/2016 03:58PM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: All Advices with Building Larger 3D printer
December 30, 2016 07:47PM
I've been doing some research into large format printing myself. It sounds like you are planning on sticking with a filament fed machine, so you don't need to worry about the intricacies of a pellet fed extruder. That being said, you'll still run into issues that most with smaller printers don't have to concern themselves with. When you are printing such large parts, your build times will be significantly longer, and you'll also go through a lot more filament, so find a good source for spools that are at least 5-10kg or more depending on your average part size. With a spool that large you will also want to make sure you have some sort of feed mechanism, as that's a lot for a little nema 17 stepper to feed. While you're at it, I would look into closed loop steppers or even servos as you will be able to push your machine harder and not worry about lost steps. Leadshine, coolmuscle and clearpath are a few companies you could look at for relatively affordable motors.

An H-Bot or core XY would be a safe bet for a machine of this size. When it comes to choosing linear bearings and screws, don't be afraid to go a little larger. I have found in some cases it may even be cheaper to use a size up as small linear bearings require small precision components, and those can get expensive. As far as cost goes, give yourself a reasonable budget too. A machine this size is in a different league than a small rep rap.
Re: All Advices with Building Larger 3D printer
December 30, 2016 09:06PM
Quote
dc42
- Number of Z motors: keeping multiple Z motors in sync when you power a printer off and on is a problem in all current firmwares. However, we will have a solution to this in RepRapFirmware for the Duet WiFi (and the forthcoming Duet Ethernet) soon, although you may need to use 24V power for it to work well.

Please explain how this solution works dc42. I'm using 2 high torque Nema 23 motors turning 4 screws to move the XY carriage along the Z axis of the 550mm x 750mm x 800mm Core XY printer I'm building. The bed is fixed. Thanks...TP.
Re: All Advices with Building Larger 3D printer
December 31, 2016 03:33AM
The main reason multiple Z motors get out of sync is that when you power them up, the motor currents are energized in a particular way and the motors have to jump to the nearest multiple of 4 full steps that matches the current. If the motors are not close to such a position, then the two motors may jump in opposite directions.

We can avoid this issue in two ways. One is detect impending loss of power, and move the bed down or the gantry up to one of those multiples of 4 full steps before turning the motors off. So they are in the right position when you power them up again. Another is to detect impending loss of power and record the current microstep position in flash memory; then when the motors are turned on again after power up, the motor drivers can be set to the same microstep position before energizing the motors.

The above will work if the motors do not move significantly when they are powered down. I think this should be the case if you use leadscrews with a fairly fine pitch. The Duet WiFi has the necessary on-board power moniltor.

If the motors cannot be relied on to hold position to within about 1 full step when powered off, a different approach is needed. Use a separate driver for each motor. Normally the drivers will be driven in sync; but after Z homing, the Z probe will be used to measure the bed tilt and the motors will be driven independently to correct it. To avoid having to do this in between prints, after a print is finished the motor currents are reduced to idle hold instead of turning them off completely (RepRapFirmware already supports this).

These approaches can be extended to 3 or even 4 motors.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: All Advices with Building Larger 3D printer
December 31, 2016 07:14PM
As currently designed my printer will use 5 belts to tie 2 Z axis motors and 4 corner screws together. Will it be necessary to sync the motors with belts using the approach you described? I have a Duet WiFi waiting on the shelf for this printer....I assume the solution will be a firmware upgrade...yes? Thanks...TP.

Re: All Advices with Building Larger 3D printer
January 01, 2017 04:54AM
The approaches I described are designed to overcome the problems you get when multiple motors are used. It will be a firmware upgrade. You could use leadscrews driven directly from the motors, with some caveats: you lose the opportunity to do gearing by using different pulley sizes, and the stepper motor bearings need to be capable of taking the weight of the bed. Also the second approach I described requires one driver per Z motor, so with more than 2 motors you would need a expansion board as well as the Duet WiFi.

I don't think syncing motors with belts would be wise. You would need to get the pulley positions on the shafts exactly right so that the motors don't fight, and then thermal expansion could alter that. A single motor would be easier to manage.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: All Advices with Building Larger 3D printer
January 01, 2017 01:25PM
I did order the expansion board with my Duet Wifi and I also have external drivers for each Z axis motor. I like the idea of not having to use the 3 connecting belts to sync the motors; using just 1 belt and motor at each end to drive the two corner shafts is much cleaner. In my example all the drive pulleys are the same 40 tooth. Also the weight of my XY carriage is carried by the 4 shafts; each supported at the bottom by separate bearings and locking collars. The motors carry no weight. Please let us know when the dual motor firmware solution is available. Thanks for your help...TP.

Edited 1 time(s). Last edit at 01/01/2017 01:26PM by simspeed.
Re: All Advices with Building Larger 3D printer
January 04, 2017 06:26PM
Thanks To everyone who have helped with advices and responded.

I've been busy with everyday life and will find time in the weekend.

I did a quick frame assembly in CAD and can now see that 4040 and 4080 will be the frame parts, Unless I find a good price on squaretubes and decides to go with that.
I'll either use 1 threaded acme 16mm rod in each end of the bedframe with two 16mm rods or use 4 threaded acme 16mm rods at each corner. I've to decide that in the weekend.

Also in the weekend I'll try to play with the brushed closed loop software and some brushed motors or I'll use Nema23 stepper motors for the build.

I've sourced some 3d CAD parts around from grabcad & thingiverse, Mcmaster and other companies.
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