Heated Bed bowing (doming)

[BigBadBry]

Hey guys. So I've been having trouble with builds where parts extent out toward the edges of the build area. Specifically, I can't seem to keep anything stuck down out there, and adjusting the Z yields a really close proximity in the center and a situation where the first bead seems too thin (see through). At first I thought the problem was my glass being bowed but after measuring the heck out of everything with a dial indicator, i can see the source is actually the heater plate itself.

Each measured set starts with 0 calibration at center. Negative measurements in the corners or along the edges indicate a surface that is closer to the table, whereas positive numbers represent measurements toward the sky. I measured each corner and each center of any given rail.


Glass Side A (center high)
[-0.011].......[-0.005].......[-0.010]
[-0.005].......[0.00]..........[-0.002]
[-0.007].......[-0.002].......[-0.006]

Same glass, side B (center still high)
[-0.011].......[-0.008].......[-0.010]
[-0.005].......[0.00].........[-0.003]
[-0.008].......[-0.003].......[-0.008]

Heater Plate alone (no glass, much more significant bow with center high)
[-0.015].......[-0.010].......[-0.011]
[-0.006].......[0.00]..........[-0.002]
[-0.014].......[-0.008].......[-0.012]

Granted, you can see that I am not "perfectly" leveled but in most cases you can see the bow by averaging the extremities along any given axis and comparing that value to the center.

So my question is, what are you guys seeing on your plates? Would this deviation (maximum 0.010 of the glass) be significant enough to cause the lower bond to the glass that I am seeing on larger builds, or something well within working range?

[jimc]

i have had glass plates and tooling aluminum plate. every piece of glass i have ever had had been high in the middle like that on both sides. i dont know what it is but it just seems that way. if your x belt is too tight it can slightly bow down the top rail of the machine. i have done it just to see and you can easily bow the top rail down in the small amts we are talking here. as far as plates go my aluminum plate is however much flatter than the glass is by far. i think glass just isnt manufactured to that degree of accuracy. my mic6 plate is milled on both sides making it flat but even that isnt perfect.

[BigBadBry]

I would imagine a solid plate of aluminum has some heft to it, wouldn't that affect the Y travel (all that extra mass to move back and forth)?

I think in another thread you had mentioned McMaster being the source but I didnt see any applicable "tool plates" listed in there... what do they call them?

[jimc]

Its mic6 tooling plate

[jereywolf]

Based on Jim's results, I also replaced my glass with aluminum and it's now flat within .005".

I went with a cheaper option though and got just a plate (not machined).

I had them cut it to 8" x 10"

http://www.speedymetals.com/pc-2406-836 ... plate.aspx

[BigBadBry]

Bummer, Even with mic6 plate, until you get to thicknesses over .625", they max deviation is still no less than .015" (at least with Alcoa anyway).

https://www.alcoa.com/mill_products/catalog/mic-6.pdf

Kind of seems like its a luck-of-the-draw sort of thing...


Do you guys have to do anything different in terms of bed prep with stock aluminum? I would imagine extracting a part with a flat razor (on Aluminum) wouldn't be wise right?

[jimc]

that spec is not what your looking for. that spec is just the thickness deviation over an 8 foot sheet. thickenss deviation doesnt matter anyway. on our 8x10" beds if the plate is thicker on one side than another then you just level the bed. its when the plate is warped thats the problem. the mic6 is perfectly flat. the luck of the draw is in who you buy it from. if they have the sheets leaning against the wall somewhere then its going to be warped. so far the ones that have come from mcmaster have been good. the most i have had one out was .1mm in the middle which i easily straightened out in 30 sec with 2 blocks of wood and a c-clamp. i cant remember where i got that one from. someplace online.

[BigBadBry]

I can see that McMaster carries 8x12, did you manage to find 8x10 in another section or did you have it cut down? (Im referring to McMaster's stuff)

[jimc]

I cut it to size here then i glass bead one side