M2 Build Plates Slowly Deforming

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EricPeterson
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M2 Build Plates Slowly Deforming

Post by EricPeterson » Fri Jun 24, 2016 4:03 pm

We have two M2s. One started as a V3b and has been upgraded to a V4, and the newer started life as a V4. The earlier unit had the obsolete bed strain relief and has the larger lead vertical screw. Unit #2 has the finer pitch vertical screw and the bed strain relief with the convolute-sheathed cable.

Both units started out with beautifully flat build plates. Over time unit #2 developed a pronounced saddle shape to the build bed -- a dip about .008" to .012" across the plate's shorter dimension. Flipping and turning the glass doesn't change it any. I could adjust extruder gap at the ends, but I'd always have too much gap in the middle... or I could gap it down a bit too tight at the ends and have acceptable gap in the middle. Finally it got so bad I had to build up a layer of tape across the aluminum plate's shorter centerline. That fixed it completely for a while, but now the gap is coming back, indicating even further deformation of the plate.

The gap matters because we have a lot of fixtures printed on a regular basis that have a lot of features -- mostly holes and pass-throughs -- that start right on the build surface. Motion of the nozzle -- I have a 1mm retraction programmed, but Simplify3D apparently doesn't always apply it between moves -- during the first layer lay-down tends to disturb those features and ruin the print early if the gap isn't close enough to really stick the first plastic onto the tape.

Unit #1, with far more time on it, developed the saddle-shaped plate after unit #2, but it's worse now. I had to start using a tape spacer sooner as the deformation developed and it already needs more layers of tape to get into adjustment at all.

I am well aware that putting the tape under the glass is likely making it worse by placing the plate under additional deformation forces... but short of re-bending the plate or replacing it, there's really been no choice.

I know I've read comments about this before but I can't find them at the moment.

We've run about 40 1kg spools of PLA and ABS through the printers, mostly ABS with a bed temp set to 100. I don't have the hard numbers, but unit #1, which developed the problem later than the newer machine, ran more PLA than ABS and thus has likely had its bed sitting at 70 most of the time, the total time running at 100 probably less than the time unit #2 has had its bed running at 100. Unit #2 got put on the production floor with a flat panel, too, so the cell leads just dial in the tools they need for the next day's setups and let the machine run overnight..... so while unit #2 is much newer, it might actually be catching up to unit #1 in total hours. All this makes me think the deformation is directly related to the amount of time the machines run with their beds set to 100 degrees.

Anyone try re-flattening the bed? I'm thinking of putting them in fixtures in a press and easing the centers back up. Or is it easier just to replace the bed and heating element? For as much as these things have saved us in what we would have spent on Delrin tooling, that would still be a trivial expense.

- ep

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Jules
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Re: M2 Build Plates Slowly Deforming

Post by Jules » Fri Jun 24, 2016 4:36 pm

Considered a MIC6 plate? Perfectly flat and stay that way. (Not the cheapest in the world, but it will be the only time you need to purchase it.) :)

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ednisley
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Re: M2 Build Plates Slowly Deforming

Post by ednisley » Fri Jun 24, 2016 5:31 pm

EricPeterson wrote: Flipping and turning the glass doesn't change it any
Then it's probably not the glass...

I'd suspect the X axis gantries have bowed downward as a result of belt tension; perhaps you have those belts cranked a bit too tight.

If you have access to a good straightedge (*), check it against a surface plate, then put it atop the X axis linear slide and backlight the edge. If it's bowed downward, you'll see a gently bellied line of light marking the problem. You can probably measure the center with feeler gauges if you're so inclined, although I wouldn't trust the absolute accuracy.

A 12 mil gap = 0.3 mm, so you can (probably) make up for it with a thicker first layer and careful Z offset adjustment. Split the difference so the center is 0.15 mm low (Z=+0.15) and the edges are 0.15 high (Z=-0.15) with respect to Z=0.0 in the middle. Then slice the model with a 0.30 mm first layer, regardless of what you're using above that, to get enough plastic to fill the low regions; this is not the place for a finicky 0.10 mm first layer.

The first layer will be 0.45 mm thick in the middle and 0.15 mm thick along the edges, but that's survivable with a 0.30 mm nominal layer thickness. Once that layer's in place, the top surface will be pretty nearly flat and you can continue as usual, probably without any Z lift (which is different than "retraction", which deals with pulling the filament back at the end of a thread).

All that depends on getting the overall platform alignment Just Right, too, because you don't want to also compensate for diagonal corners being too high / too low.

Go for excellent alignment, set the Z=0 point to split the bow in half, use a thicker first layer, and you'll be pretty close to perfect.

(*) Not the usual Harbor Freight grade we all use around the shop... [grin]

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jimc
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Re: M2 Build Plates Slowly Deforming

Post by jimc » Fri Jun 24, 2016 11:19 pm

ed is absolutely right. 99% is your x gantry is bowing down. this is directly related to the amt of belt tension you have as well. the tighter you make the belt the more of a downward bow it will have. you need to shim the linear rail, not the bed.

EricPeterson
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Re: M2 Build Plates Slowly Deforming

Post by EricPeterson » Sat Jun 25, 2016 1:35 am

I had not considered the possibility that the gantry frame would bow. I would never have guessed that a composite beam formed from the aluminum gantry and the steel linear way would bend that significantly under an axial load that's so close to the beam's long axis, causing a relatively small moment. Or that it would worsen over time when another soft metal piece is heated from one side repeatedly nearby.

Well, I'm going to chalk this one up gratefully to We Should Only Stop Learning When We're Dead.

The bowing deformation of the aluminum gantry as can be checked from below with a straightedge is significant.

I do run the belt quite tight. I had problems with large parts on the order of 1.5 lb and up causing the belts to slip even after running the x-y speeds down to 3000 to 5000 from the default 12,000 -- I think -- in S3D. Running tighter and dropping the speeds finally fixed those issues.

Shimming the linear way is a patch. The right thing to do is to make the area moment of the composite beam greater by adding a third beam component under the gantry. An I-beam would be great, but I know of no such miniature I-beam sections. What I can find is a nice miniature channel. While it would be tempting to install it with the holes for the linear way mounting screws passing through the center of the U, mounting it sideways will throw more area more distant from the neutral axis, supporting more resistance to the bending moment.

Thank you people, very much.

I shall report back with my results.

- ep

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ednisley
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Re: M2 Build Plates Slowly Deforming

Post by ednisley » Sat Jun 25, 2016 2:20 am

EricPeterson wrote: adding a third beam component under the gantry
Remember there's very very very little clearance under there, particularly with a V4 hot end and the Y axis at the far end of its + travel.

Double-check for, mmm, negative clearance between your reinforcement and the platform gimcrackery...

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insta
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Re: M2 Build Plates Slowly Deforming

Post by insta » Sat Jun 25, 2016 2:54 am

EricPeterson wrote:I had not considered the possibility that the gantry frame would bow. I would never have guessed that a composite beam formed from the aluminum gantry and the steel linear way would bend that significantly under an axial load that's so close to the beam's long axis, causing a relatively small moment. Or that it would worsen over time when another soft metal piece is heated from one side repeatedly nearby.

Well, I'm going to chalk this one up gratefully to We Should Only Stop Learning When We're Dead.

The bowing deformation of the aluminum gantry as can be checked from below with a straightedge is significant.

I do run the belt quite tight. I had problems with large parts on the order of 1.5 lb and up causing the belts to slip even after running the x-y speeds down to 3000 to 5000 from the default 12,000 -- I think -- in S3D. Running tighter and dropping the speeds finally fixed those issues.

Shimming the linear way is a patch. The right thing to do is to make the area moment of the composite beam greater by adding a third beam component under the gantry. An I-beam would be great, but I know of no such miniature I-beam sections. What I can find is a nice miniature channel. While it would be tempting to install it with the holes for the linear way mounting screws passing through the center of the U, mounting it sideways will throw more area more distant from the neutral axis, supporting more resistance to the bending moment.

Thank you people, very much.

I shall report back with my results.

- ep
You might have had skipped steps on large parts. You can lower the acceleration and run higher travel speeds, it's acceleration that causes skipping, not overall speed.
Custom 3D printing for you or your business -- quote [at] pingring.org

EricPeterson
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Re: M2 Build Plates Slowly Deforming

Post by EricPeterson » Thu Jul 28, 2016 8:41 pm

Of course. I was being imprecise. I've lowered the speeds per various recommendations and the accelerations months ago.

EricPeterson
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Re: M2 Build Plates Slowly Deforming

Post by EricPeterson » Thu Jul 28, 2016 8:49 pm

Here is the post describing my fix.

viewtopic.php?f=10&t=3957

EricPeterson
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Re: M2 Build Plates Slowly Deforming

Post by EricPeterson » Mon Sep 18, 2017 3:42 pm

Ah, old post, new information.

My original post concerned apparent deformation in the long axis of the build plate. I was advised that it was more likely deformation in the frame and linear way.

There WAS deformation in the long axis' linear way. I fixed that by adding a miniature I-beam below the vertically traveling frame whose threaded holes replaced all the nuts holding the linear way's track down, discussed and linked elsewhere.

Comments to the effect that people thought I was discussing the short axis are moot. I have no significant deformation in the short axis, in either the build plate or the linear way.

I'd noticed a decrease in print reliability lately. And nozzle gap was getting VERY hard to adjust. It was beginning to look like the build plate was deforming again, bowing along the long axis.

A belt failure during a long print gave me the opportunity to tear down the printer. The aluminum build plate backed by the heater is most assuredly deforming over time along the long axis. A straight-edge indicates that there's almost no deformation along the shot axis, but the bow along the long axis has raised the ends with respect to the center almost .050!!!

I fixed it with Universal Tool #4 -- three short lengths of 2x4 -- and a press, warping the plate back into flat from below. One edge required adjustments separate from the other edge, as the bowing wasn't uniform.

Does anyone else have this kind of wear and tear on an M2? We've run more than 50 kilos of plastic through this unit. It's on its second set of fans, fourth extrusion motor mount -- my revised more durable piece is posted elsewhere -- third nozzle, and now on its fourth long axis belt.

- ep

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