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Heat Compensated Bed Support First Test

Re: Heat Compensated Bed Support First Test
March 04, 2016 06:38PM
Wow that's good. A maximum deviation of about .04mm? What's the temperature variation from corner to middle in the high temperature test? It occurred to me that any thermal expansion of the dti probe would add to the measured difference between the hotter centre and presumably cooler corners.
Ira
Re: Heat Compensated Bed Support First Test
March 04, 2016 08:31PM
Not a clue if this might help, but if you heated the edges of the plate and let the heat carry to the center would that change the thermal stress enough to matter? If you have more than one heater connected you might try disconnecting one and see if that changes the flatness pattern.

Ira
Re: Heat Compensated Bed Support First Test
March 04, 2016 09:14PM
I just bought my first linear guide, not sure where I'm going to use it yet, but its got me thinking...
I'm wondering if it could be possible, to run a lead(or ball screw) through dead center and have bed pivot around it for aligning,
building a mechanism, to adjust screw height both ends(including motor, or some other arrangement /flex drive), so it could slope bed,
or just plain 12mm rod throgh center, and have lead screw close to linear block
then if I could support say left of bed with guide block, which maybe needs a pin for bed to rotate,
still not figured out if this rail to would need to slope, not done any cad on it yet, just tossing the idea around.
Might not need bed on springs & screws,
Maybe incorporate these rod ends, or the other male type, a mix of left & right hand threads to help with locking tight(or not).


Edited 6 time(s). Last edit at 03/04/2016 09:53PM by MechaBits.
Re: Heat Compensated Bed Support First Test
March 04, 2016 11:31PM
Quote
JamesK
Wow that's good. A maximum deviation of about .04mm? What's the temperature variation from corner to middle in the high temperature test? It occurred to me that any thermal expansion of the dti probe would add to the measured difference between the hotter centre and presumably cooler corners.

I previously had problems with the measurements while heated- I was getting inconsistent results. I have run the test a few times now and the results are repeatable within +/-10 um which is probably the basic precision of the gauge. Maybe the way it was mounted on the extruder carriage was affecting it the first time. The probe appears to be a pretty high grade stainless steel and the heat doesn't creep very far up during the duration of the test.

I don't know the temperature variation yet. I'll get a picture of the bed with a FLIR camera, possibly later this week. A couple people at the makerspace have them, so I may be able to borrow one.

Quote
Ira
Not a clue if this might help, but if you heated the edges of the plate and let the heat carry to the center would that change the thermal stress enough to matter? If you have more than one heater connected you might try disconnecting one and see if that changes the flatness pattern.

It's just one heater. It may be that just putting a little insulation around the edge of the plate would reduce the heat loos there and provide a more even temperature closer to the edges of the plate.

I'm not sure how much longer I want to pursue this. It's flat enough to print just about edge to edge and I have other things I want to work on, so I'm going to try a couple test prints and see if removing the springs from the leveling screws has returned the print quality to the previous near-perfection. If the quality looks degraded I'll put the undercarriage back into the previous configuration, otherwise I'll leave it as-is.

Edited 1 time(s). Last edit at 03/04/2016 11:41PM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Heat Compensated Bed Support First Test
April 27, 2016 11:49AM
I just replaced the broken glass bed on a Taz 3 printer at the makerspace with a 1/4" cast tooling plate bed (and 3 point leveling) using the original heater and ran into the guy with the FLIR camera last night. I heated the bed to 70C for a HIPS test print and we took a FLIR picture when the bed had reached final temperature. The camera was set to read out in degrees F. The new bed plate is 305 mm square, and the heater is 240 W IRIC. The two bright horizontal lines are the IR reflections of the X axis guide rails, not hot spots.



We also took a picture of Son of MegaMax at 105C, but he hasn't emailed the picture to me yet. I'll post it as soon as I get it.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Attachments:
open | download - report.pdf (591.6 KB)
Re: Heat Compensated Bed Support First Test
April 27, 2016 03:01PM
Is this a pure case of sag?

Have seen this in supports for telescope mirrors
Many support points behind a parabolic mirror
in a newtonian configuration much better than just 3
clamps keeping mirror in mount also effect it.
Sag changes with temperature --- some cool mirrors with fan before use
mirror at ambient makes for a good long sharp image session

Perhaps supports somewhat like this:



confused smiley
Re: Heat Compensated Bed Support First Test
April 27, 2016 03:31PM
It might be, but I suspect it is caused in part by the lesser expansion around the cooler perimeter of the plate compared to the greater expansion at the central, warmer area of the plate. I previously suspected the support screws of causing some bowing because the expanding plate would apply lateral pressure to the screws, but the redesigned (eliminated) undercarriage that allows the plate to expand without creating any lateral force still shows a slight bowing of the plate when heated.

My measurements made with a dial gauge attached to the extruder carriage include any sag that may occur in the X and Y axes and printer frame as well as distortion of the bed surface. It seems that all bed surfaces appear to bow upward. A sagging Y axis would make the bed appear to bow downward. A sagging X axis / frame would make the bed appear to bow upward. So I suspect it's a combo of frame flex, X axis sag, and maybe a little plate distortion due to heating.

It would probably be best to look at the difference between the room temperature and heated measurements to see the effect of heating the bed alone, assuming everything else remains the same.

Whatever the cause, it isn't severe enough to prevent almost edge to edge printing, so for me the matter is closed- I have bigger fish to fry.

Here's a picture of Son of MegaMax heated to 105C (with a few small prints on the bed plate):




Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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