Temperature around, in and under a print
Posted by Fiddler
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Temperature around, in and under a print May 06, 2014 03:58PM |
Registered: 10 years ago Posts: 38 |
I am trying to get my head around why sometimes a print will curl up from the bed, apart from the obvious one that it didnt quite stick well enough (or is that the only reason!!)
I have an off the shelf Ormerod, standard bed, 0.3mm nozzle and iamburny's new gears.
I am printing PLA and start with a bed temp of 65, dropping to 45; nozzle starting at 185 dropping to 175.
I print onto glass coated with a thin layer of very dilute pva.
All good and getting good results usually.
Kim has produced a a magnificent fan housing which reduces "backdraft" and which I assume blows cool air at the nozzle extrusion, setting it quicker allowing better bridges etc.
Iamburny has produced a fan support which replaces one of the Z bearing mounts and aims a fan at the bed.
Sorry for the rambling but I am trying to get the logic right in my head.
You need a reasonably hot bed and hot filament initially so the extrusion "sticks" to the bed
You dont need as hot a bed for later layers as the extrusion has already stuck and will only come unstuck (in my experience) when the bed cools to room temp.
The bed is kept warm so the model base does not begin to warp and retains adhesion to the bed ?
The extrusion is pumped out at about 180* and is cooled rapidly by all our assorted fans
The model retains a certain amount of heat especially if it is relatively thick/dense.
My very junior school knowledge of expansion/contraction suggests:
the base of the model is kept constantly warm by the heated bed while the core of the model gradually cools down
The core of the model will gradually contract as it gets cooler, pulling the warm base of the model up, aided by the base of the model being kept warm and relatively expanded in comparison to the cooler core.
Wont all our cooling fans exacerbate the problem of warping?
If we use fans to cool the model why is Backdraft a bad thing?
Should we turn off the bed heat after layer 1?
Should we turn off the cooling fans except for bridging?
Should the fan only be there to keep the hot end assembly getting too warm?
Sorry about the rambling posting but I was trying to explain to my son why I was fitting iamburny's Z bearing Extra Cooling Fan Mount and we were confusing each other.
I would be very interested in anyone else's thoughts
Tim
I have an off the shelf Ormerod, standard bed, 0.3mm nozzle and iamburny's new gears.
I am printing PLA and start with a bed temp of 65, dropping to 45; nozzle starting at 185 dropping to 175.
I print onto glass coated with a thin layer of very dilute pva.
All good and getting good results usually.
Kim has produced a a magnificent fan housing which reduces "backdraft" and which I assume blows cool air at the nozzle extrusion, setting it quicker allowing better bridges etc.
Iamburny has produced a fan support which replaces one of the Z bearing mounts and aims a fan at the bed.
Sorry for the rambling but I am trying to get the logic right in my head.
You need a reasonably hot bed and hot filament initially so the extrusion "sticks" to the bed
You dont need as hot a bed for later layers as the extrusion has already stuck and will only come unstuck (in my experience) when the bed cools to room temp.
The bed is kept warm so the model base does not begin to warp and retains adhesion to the bed ?
The extrusion is pumped out at about 180* and is cooled rapidly by all our assorted fans
The model retains a certain amount of heat especially if it is relatively thick/dense.
My very junior school knowledge of expansion/contraction suggests:
the base of the model is kept constantly warm by the heated bed while the core of the model gradually cools down
The core of the model will gradually contract as it gets cooler, pulling the warm base of the model up, aided by the base of the model being kept warm and relatively expanded in comparison to the cooler core.
Wont all our cooling fans exacerbate the problem of warping?
If we use fans to cool the model why is Backdraft a bad thing?
Should we turn off the bed heat after layer 1?
Should we turn off the cooling fans except for bridging?
Should the fan only be there to keep the hot end assembly getting too warm?
Sorry about the rambling posting but I was trying to explain to my son why I was fitting iamburny's Z bearing Extra Cooling Fan Mount and we were confusing each other.
I would be very interested in anyone else's thoughts
Tim
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Re: Temperature around, in and under a print May 06, 2014 04:35PM |
Registered: 10 years ago Posts: 859 |
Hi Tim, thanks for the compliment....
Ok, my fan duct is aimed towards printing PLA mainly, and by cooling the the hot plastic as soon as possible but not to allow excess (BackWash Cold Air) hit the print. Hence the fan/s (you can fit two if you wish, to increase bridging) directs any BackWash up into the air away from the print.
No BackWash can hit the print and cause Warping... On the Big Blue there is also an Exhaust pipe to vent off some air if you want to do more delicate things that don't involve bridging, and you will see less stranding, as the molten plastic melts the layer below. Cover the Exhaust to increase cooling,, uncover it to reduce it. Using the Big Blue 360 you can bridge inexcess of 80mm in any direction with the exhaust closed.... Straingely, I had someone message me recently, asking for help as with a BB he was only getting good bridges in certain directions.
I msged him back suggesting he look at the nozzles, and ensure they were clear.. A day later I got a msg back saying, it was all now perfect, and that some how he'd managed to nearly block one of the nozzles with the HotEnd cabling.... lol so it's all good. He's now doing long bridges in all directions.
BackWash kills big prints dead, as the edges/corners of the print get worst affected, and that leads to warping, where a corner lifts, and the more you print the worst it gets.
When you print a Big Blue (if), you will see I put a pillar near the recess for DCs probe connectors. This pillar was put there to hold the corner down while printing for exactly the same reason.... A large bulk of plastic, in mid air away from the HotBed, tends to cool at the bottom, and gets hot at the top, then that cools and pulls on the plastic (ie warping)... hence the pillar.
Kim
Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete
Ok, my fan duct is aimed towards printing PLA mainly, and by cooling the the hot plastic as soon as possible but not to allow excess (BackWash Cold Air) hit the print. Hence the fan/s (you can fit two if you wish, to increase bridging) directs any BackWash up into the air away from the print.
No BackWash can hit the print and cause Warping... On the Big Blue there is also an Exhaust pipe to vent off some air if you want to do more delicate things that don't involve bridging, and you will see less stranding, as the molten plastic melts the layer below. Cover the Exhaust to increase cooling,, uncover it to reduce it. Using the Big Blue 360 you can bridge inexcess of 80mm in any direction with the exhaust closed.... Straingely, I had someone message me recently, asking for help as with a BB he was only getting good bridges in certain directions.
I msged him back suggesting he look at the nozzles, and ensure they were clear.. A day later I got a msg back saying, it was all now perfect, and that some how he'd managed to nearly block one of the nozzles with the HotEnd cabling.... lol so it's all good. He's now doing long bridges in all directions.
BackWash kills big prints dead, as the edges/corners of the print get worst affected, and that leads to warping, where a corner lifts, and the more you print the worst it gets.
When you print a Big Blue (if), you will see I put a pillar near the recess for DCs probe connectors. This pillar was put there to hold the corner down while printing for exactly the same reason.... A large bulk of plastic, in mid air away from the HotBed, tends to cool at the bottom, and gets hot at the top, then that cools and pulls on the plastic (ie warping)... hence the pillar.
Kim
Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete
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Re: Temperature around, in and under a print May 06, 2014 04:35PM |
Registered: 10 years ago Posts: 2,472 |
As I've stated in other posts elsewhere, the most common culprit for warping in my experience seems to be draughts. Keep the printer shielded from all draughts, and try to keep the ambient temperature above 20 deg C for ABS printing as well. Setting Slic3r (or Cura) to print a raft around the print also helps for problem prints.
Cooling the extruded filament makes bridging better, but I should think that the cooling air should be directed onto a pretty narrow area around the nozzle only, and a fan that blows over the entire print might help bridging but I suspect that it will also make warping more likely (but I have done no experimentation so it's only an educated guess). Also, whilst cooling the filament may make better bridges, it seems logical that it will also cause the bonding to the lower layer to be weaker which could cause delamination later, so my preference would be to have the cooling fan turned off except when bridging (which you can set Slic3r to do if you have a separate fan controlled from the Duet).
Dave
(#106)
Cooling the extruded filament makes bridging better, but I should think that the cooling air should be directed onto a pretty narrow area around the nozzle only, and a fan that blows over the entire print might help bridging but I suspect that it will also make warping more likely (but I have done no experimentation so it's only an educated guess). Also, whilst cooling the filament may make better bridges, it seems logical that it will also cause the bonding to the lower layer to be weaker which could cause delamination later, so my preference would be to have the cooling fan turned off except when bridging (which you can set Slic3r to do if you have a separate fan controlled from the Duet).
Dave
(#106)
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Re: Temperature around, in and under a print May 06, 2014 05:36PM |
Registered: 10 years ago Posts: 14,672 |
I think you are asking for trouble cooling the bed from 65 to 45C after the first layer. The differential contraction between the glass and the print will encourage it to come unstuck. I suggest you keep the temperature at 65C throughout, unless you can use a lower initial temperature. Also, I suggest you try without the extra fan.
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].
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].
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Re: Temperature around, in and under a print May 06, 2014 06:38PM |
Registered: 12 years ago Posts: 1,611 |
Yes, too much cooling! Keep the bed temperature up. We usually have the bed set to 57C for the whole print. The fan backwash can be an issue for some people, and I don't think you'll need extra cooling.
The heated bed isn't just there to stick the first layer down; it's to stop subsequent layers cooling and pulling the part up at the corners. PLA has a 'glass transition' temperature of around 60C (and a melting point of around 170C), which is where it changes from a solid to a semi-solid; it's this temperature we want to keep the plastic at, then let the whole thing cool together at the end of a print. That way, in theory, there shouldn't be stresses through the print that are trying to pull it apart, or up from the bed. This is more successful in some cases than others, though, and as a print gets taller, you can't help that upper layers will be little effected by the bed temperature. PLA, and ABS, do most of their shrinking below their glass transition temperature (ABS shrinks more than PLA, which is why it can be more temperamental), which is why we need to keep the temperature up. ABS glass transition temperature is around 100C.
You could print on a cold bed, and so long as each layer was fully cooled before the next layer went on, and the first layer sticks well, there would only be one layer cooling and shrinking at a time. So as the layers built up, there would be *less* chance of warping, as there is strength to resist it in the lower layers. The trick is to find something that you can print on, and stick to, when cold... We're experimenting with 0.6mm thick PVC adhesive sheet, which works well for small objects. I haven't had a chance to try it with any object larger than the z-lower-mount yet, though, but it was fine with that.
A 'trick' to get good print attachment to the bed is to print the first layer a little low, to squash the first layer onto the bed. Generally, printing the first layer a little low is much better than printing a little high; if it's high, it will have weak attachment to the bed. You can usually tell; if you see space between the infill on the first layer, the nozzle is too high. You can adjust the Z height during printing (albeit rather brutally) by turning the z-driven-gear in the correct direction, even though it may be moving. The motor will just skip, but you can then move the Z height up or down as needed.
Ian
RepRapPro tech support
The heated bed isn't just there to stick the first layer down; it's to stop subsequent layers cooling and pulling the part up at the corners. PLA has a 'glass transition' temperature of around 60C (and a melting point of around 170C), which is where it changes from a solid to a semi-solid; it's this temperature we want to keep the plastic at, then let the whole thing cool together at the end of a print. That way, in theory, there shouldn't be stresses through the print that are trying to pull it apart, or up from the bed. This is more successful in some cases than others, though, and as a print gets taller, you can't help that upper layers will be little effected by the bed temperature. PLA, and ABS, do most of their shrinking below their glass transition temperature (ABS shrinks more than PLA, which is why it can be more temperamental), which is why we need to keep the temperature up. ABS glass transition temperature is around 100C.
You could print on a cold bed, and so long as each layer was fully cooled before the next layer went on, and the first layer sticks well, there would only be one layer cooling and shrinking at a time. So as the layers built up, there would be *less* chance of warping, as there is strength to resist it in the lower layers. The trick is to find something that you can print on, and stick to, when cold... We're experimenting with 0.6mm thick PVC adhesive sheet, which works well for small objects. I haven't had a chance to try it with any object larger than the z-lower-mount yet, though, but it was fine with that.
A 'trick' to get good print attachment to the bed is to print the first layer a little low, to squash the first layer onto the bed. Generally, printing the first layer a little low is much better than printing a little high; if it's high, it will have weak attachment to the bed. You can usually tell; if you see space between the infill on the first layer, the nozzle is too high. You can adjust the Z height during printing (albeit rather brutally) by turning the z-driven-gear in the correct direction, even though it may be moving. The motor will just skip, but you can then move the Z height up or down as needed.
Ian
RepRapPro tech support
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Re: Temperature around, in and under a print May 07, 2014 01:52AM |
Registered: 10 years ago Posts: 101 |
Just a quick comment from my experience.
I always place a big cardboard box over the printer, when I print ABS - otherwise I get warping and. Together with a 10 or 15mm wide brim it has so far pretty much solved my warping problems.
The cardboard-box is just a quick-and-dirty solution for an enclosure - but it does the job :-)
When printing PLA, I never use the box, and I have only had a few prints with a slight warping.
Best regards,
Carsten
I always place a big cardboard box over the printer, when I print ABS - otherwise I get warping and. Together with a 10 or 15mm wide brim it has so far pretty much solved my warping problems.
The cardboard-box is just a quick-and-dirty solution for an enclosure - but it does the job :-)
When printing PLA, I never use the box, and I have only had a few prints with a slight warping.
Best regards,
Carsten
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Re: Temperature around, in and under a print May 07, 2014 03:52AM |
Registered: 10 years ago Posts: 38 |
Thanks all for your replies.
I think I now have it.
Take off the new bed fan - shame it looks quite cool.
Print out Kims big blue
Keep my bed at 57* all through the print.
And
Work out how to control the X fan. It goes on when I turn on the PSU and will not be controlled by M106 S0 or M107, I might have it wired wrong?
Tim
I think I now have it.
Take off the new bed fan - shame it looks quite cool.
Print out Kims big blue
Keep my bed at 57* all through the print.
And
Work out how to control the X fan. It goes on when I turn on the PSU and will not be controlled by M106 S0 or M107, I might have it wired wrong?
Tim
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Re: Temperature around, in and under a print May 07, 2014 05:48AM |
Registered: 12 years ago Posts: 1,611 |
If you're using the current firmware, 057a, the 'FAN0' output is on all the time, and not controllable. dc42 has added control of this to his firmware (though we have to add the caveat that this must be regarded as experimental, as we haven't tested it), and the soon-to-be released 065 has fan control implemented.
Ian
RepRapPro tech support
Ian
RepRapPro tech support
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Re: Temperature around, in and under a print May 07, 2014 06:02AM |
Registered: 10 years ago Posts: 378 |
The fan control works if you have a firmware that supports it, and connect it to the FAN0 header (it's wired straight to +12V/GND in the installation instructions). I connected mine like that, mostly to be able to turn it off sometimes when not actually printing. You can then use it to control cooling airflow during print, but you have to be careful not to run it "too little", since not enough cooling for the hotend will make it "overheat" and jam.
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Re: Temperature around, in and under a print May 07, 2014 06:45AM |
Registered: 10 years ago Posts: 859 |
@jstck If you use my Big Blue, then ANY air from the fan gets directed over the HeatSink which is the purpose of the Baffle plate you see in the HeatSink Chamber. To reduce the cooling just uncover the Exhaust, and have the Fan on a low setting (if you have Fan Speed Control).
Just a thought on this Fan Control.... If the Fan was connected via a Diode to the PWM signal, and an Electrolitic Capacitor in Parrallel to supply the Fan, I recon we'd have better control of the Fan...... It'ss a cheap and dirty way of doing it I guess, but I would have thought it would work....
Kim
Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete
Just a thought on this Fan Control.... If the Fan was connected via a Diode to the PWM signal, and an Electrolitic Capacitor in Parrallel to supply the Fan, I recon we'd have better control of the Fan...... It'ss a cheap and dirty way of doing it I guess, but I would have thought it would work....
Kim
Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete
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Re: Temperature around, in and under a print May 07, 2014 06:54AM |
Registered: 12 years ago Posts: 1,611 |
065 official firmware has just been released! I told you it was soon-to-be-released...
[github.com]
There will be a blog post soon regarding the changes that have been made. We have still to implement some of dc42's latest changes in this firmware version, because we have to test any changes we make.
Ian
RepRapPro tech support
[github.com]
There will be a blog post soon regarding the changes that have been made. We have still to implement some of dc42's latest changes in this firmware version, because we have to test any changes we make.
Ian
RepRapPro tech support
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