Heavy parts & Platform Deflection?

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zemlin
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Location: Indianapolis, Indiana

Heavy parts & Platform Deflection?

Post by zemlin » Sat Mar 18, 2017 2:17 pm

I recently printed some big parts - .65 kg of PETG. Almost 8" OD and 4" tall. The first layer is consistent across the part so I'll assume the bed is level. The platform is bare MIC6 aluminum, so it should be flat. Layer thickness was .25mm. Dimensional accuracy is important on these parts in all 3 axes.

On the finished part X and Y dimensions look great. On the Z axis I get about .9mm, .035" of taper from one side to the other.

My first though was that the weight of the part was causing the bed to deflect. It doesn't take much force on the bed plate to deflect the platform. One would think, however, that the minimum deflection would be near the screw and maximum deflection would be at the far side of the cantilever opposite the screw. The one part I still have on hand shows the opposite. The tall side of the part is near the screw and the short side is opposite the screw.

I saw the same sort of taper on ABS parts of similar size, but much lighter, so I'm not convinced that it's weight, but with the Z-Axis rail arrangement, I haven't figured out how this could be an alignment issue.

I'll be working on finding the cause of this. Has anyone else ever looked into this, or do you get large, heavy parts that are consistent in the Z-Axis?

86bg
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Joined: Fri Mar 17, 2017 1:46 am

Re: Heavy parts & Platform Deflection?

Post by 86bg » Sun Mar 26, 2017 12:35 am

not sure why it would deflect on that side unless it has to do with how the bead forms on the side which is slowly gaining nozzle gap distance (right). Measure the x0 and xMAX on the bed with a height gauge if you have one then throw the part on and measure it again

M3Jim
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Re: Heavy parts & Platform Deflection?

Post by M3Jim » Thu Mar 30, 2017 5:23 pm

Are you still using the 3 point leveling system with the springs? I could see where you would get the result you are seeing with that setup. If the CG of the part is in the center, the 2 center aligned supports would deflect slightly, but the right hand one would remain in its original position. That would cause the bed to deflect CCW (looking at it from the front) and you might get the taper that you are getting.

Jim

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zemlin
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Location: Indianapolis, Indiana

Re: Heavy parts & Platform Deflection?

Post by zemlin » Thu Mar 30, 2017 6:48 pm

M3Jim wrote:Are you still using the 3 point leveling system with the springs? I could see where you would get the result you are seeing with that setup. If the CG of the part is in the center, the 2 center aligned supports would deflect slightly, but the right hand one would remain in its original position. That would cause the bed to deflect CCW (looking at it from the front) and you might get the taper that you are getting.

Jim
I have a Rev E printer, so 4-point, no springs.

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