How To Flatten A Plate

A

atunguyd

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Hi All, can any of the experts among you give me a hand with something?

I am working on a 3D printer that I have built up, the bed that things are built on is made from aluminum plate with a heater built in under it, the plate is about 210 x 210mm and 3mm thick.

For the printer this bed needs to be a flat as possible and it is mounted in the machine with bolts at each corner, the bolts attach through springs which allow one to level the bed by adjusting the mounting bolts.

Problem is that being thin aluminum the bed has been manufactured with a bow in it leading up from each corner toward the centre.

I mounted it flat on my milling table and took a light surface cut with a 50mm index face mill but I was not thinking and all I achieved doing this was to flatten it with the clamps, face mill it and then reintroduce the bow when the clamps were removed (I think it is even worse now).

I am looking at ideas on how to now flatten it more correctly.

What I have come up with so far is the following:

Taking two sturdy pieces of aluminum bars longer than the plate I tapped holes in each bar and mounted the plate to this bar using its mounting holes. The bars in turn were clamped to the milling table. This now in mind has the plate secured to the table but still allows it to keep it's natural bow.

I then plan on face milling it again like this (very lite cut, almost like a lathe spring cut), which I am hoping with make the top flat even though the bottom may be slightly bowed (when in use it does not get much pressure on it, only light plastic parts are built on it).

I started this tonight but the chatter was terrible and amplifier so much by the plate that I decided to try again tomorrow as making such a racket at midnight is very neighbor unfriendly.

In the mean time maybe some of you may have a better idea on how to go about this?

Thanks

Anthony
 
Absolutely and it's fairly inexpensive on eBay !
 
not really an option as this plate has a heater element already glued to one side of it so I need to keep using this plat, just somehow get it flat.
 
atunguyd said:
not really an option as this plate has a heater element already glued to one side of it so I need to keep using this plat, just somehow get it flat.
Click to expand...

Unless the built-in heater also includes the controller, that doesn't have to be a problem.

There are plenty of inexpensive heating elements intended for electronic assemblies available - you just need to match the resistance of the new element to the old element and make sure that the power ratings are compatible. ("Minco" is a company that comes to mind back when I used heaters for temperature controlling electronic gear some decades ago.)

Not trying to make your life any harder but honestly, flattening a piece of plate that is less than 1/8 inch thick by machining it is not something that I'd want to do. If you can straighten it by bending, well that's a possibility ... of course it could also make it worse :(
 
In that case it is as flat as the manufacturer meant it to be, program the errors out if possible.
You may also try turning the heater on for several hours and then letting it cool slowly to see if that stress relieves the platen and try milling it afterwards. Wrought aluminum plate has never been very flat in my 30 years of experience using it

Good Luck
 
Yeah thanks but I also live in a third world country, we just recently had a 4 month long postal strike and I am only now getting items from ebay that I bought in November so purchasing on ebay or internationally is pretty much out.

I am going to retry that light skimming cut and may even try applying pressure on the center while supporting the corners only and hopefully relieve some of the bend. Worse situation is I need to buy a new plate hey :)
 
you could try hand scraping the plate flat,
there will be temperature variations that may affect the absolute flatness.
i'm sure with some forethought a solution can be had.
 
Is there any way to support the center of the plate when it's mounted in your 3D printer, so that the screws pull the corners downward? This might allow the sides to bow upward between the screws, but the net effect should average out a bit flatter than just letting the center of the plate go where it wants to.

I don't know if you have room to add a stiff frame around the periphery of the plate, but this could also help.
 
atunguyd said:
not really an option as this plate has a heater element already glued to one side of it so I need to keep using this plat, just somehow get it flat.
Click to expand...
Glue it to something flat and thick enough to be reasonably stiff.
 
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