# Milling a plate to be flat



## Dynahoe Dave (Sep 18, 2019)

I have a piece of aluminum plate, about 8.5" square, .250" thick.  It's not flat- is it possible to mill the face / faces to get it flat?
How would this best be done?   I have a J-head Bridgeport mill.

The main thing I'm trying to get is how to clamp it - but the common way, obviously, the clamps get in the way...


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## ErichKeane (Sep 18, 2019)

What about putting it in a vise?  You can usually put the jaw of the moving side on the 'back', which increases your clamping area, and gives you the top of the vise as a spot to put it on.

From there, a flycutter or a face mill, depending on how many passes you want to take.


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## petertha (Sep 18, 2019)

Hopefully this 'toe clamp' search on YouTube will pre-populate. Otherwise just type it in.





						toe clamps - YouTube
					

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.




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## Dynahoe Dave (Sep 18, 2019)

Oh, I knew there had to be something!  Thank you!


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## benmychree (Sep 19, 2019)

There may be so many stresses in a piece like that that you never will be able to get it truly flat.


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## mmcmdl (Sep 20, 2019)

benmychree said:


> There may be so many stresses in a piece like that that you never will be able to get it truly flat.



Agree with that . I would think a vacuum chuck and shims would be the way to go , but you'll also be introducing more stress into the plate when cutting . Stress relieving would help , but truly flat would probably be impossible .


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## derf (Sep 20, 2019)

I don't know how flat it needs to be, but your best bet is to lap it on a flat surface.


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## epanzella (Sep 20, 2019)

This is a tuff nut but standoffs on the back of the piece will help when clamping it. If the back side is not flat the piece will bend when you clamp it then obviously the front side won't be flat when you machine it.


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## Cadillac (Sep 20, 2019)

Something like these go directly in t slots on table. They work great.


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## Illinoyance (Sep 21, 2019)

How you clamp it has a large effect on your ability to get it flat. Edge clamps that touch above the neutral axis will tend to bow the metal down.  Those that touch the work below the neutral axis will tend to bow it up.  Any locked in stress, as from rolling, will cause the metal to move whenever you cut it.  If you need flat plate buy Mic6


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## bob308 (Sep 21, 2019)

severial ways to tackle this. one I would put in my shaper. two clamp it in a 4 jaw chuck. face it off in the lathe or clamp the chuck to the mill table and mill it flat.


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## homebrewed (Sep 22, 2019)

I recently made a fixture plate out of 6061 and was looking at the same problem.  Since it was extruded material I expected stresses that would cause warping when I fly-cut the bottom and top surfaces.  In addition, the piece, as received, was warped.  I thought about drilling and countersinking the 2 mounting holes on each side of the plate, then screwing the plate down and fly-cutting it:  but the plate was stiff enough to cause concern about repeatability of the hold-down forces to ensure a planar surface every time I mounted it to the table.  It looked to me like the best approach was to sequentially flatten both sides, but the problem was how to do this and avoid spring-back when the plate was un-clamped.

To solve this, I made two  low-profile clamps out of square steel stock.  Both were a little less in height than the plate I was making, and both were drilled and counter-sunk for hex head mounting bolts, to attach them to my mill table.  One of them then was flipped 90 degrees and drilled/tapped for two 10-24 set screws.  I bolted the "plain" clamp to one side of the table, placed the workpiece I wanted to flatten on the table and pushed it into firm contact with the clamp.  The other clamp was loosely installed on the opposite side of the table, with the set screws protruding about .1 inch, pushed into firm contact with the plate-to-be and bolted in place.  I tightened the set screws to hold the plate firmly in place and fly-cut the plate.  Flipped it over and did the other side.

The clamping arrangement did not impose any additional forces that would warp the plate -- they all were in line with the top and bottom surfaces of the plate.  The internal stresses of the plate were the only forces distorting the plate.  I figured that the plate WOULD warp after being machined, but the effect would be small enough to address with the clamping forces used to bolt the plate down.  This turned out to be the case -- when installed the plate was flat enough for my purposes, anyway.  For more exacting requirements it might be possible to improve things even more by repeating the sequence of milling the front and back.


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## ezduzit (Sep 22, 2019)

Dynahoe Dave said:


> ...is it possible to mill the face / faces to get it flat?...



Simply put, no. Buy flat material.


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## Dynahoe Dave (Sep 24, 2019)

Wow!  All of the replies.   I used some square unistrut washers to make "fake" low profile edge clamps.  The held it ok.
Milled off about .020" to get a cut across the entire face.  But Near the end, I discovered that in some areas, every time I passed the cutter over it, it took a hare more metal off.  But not every where.  So it must have been warping more as I made each pass.  And this is all with one locked setting for the depth / vertical.  So yes, I have ordered flat stock that has specs for flatness.  The project is for my 3D printer - the stock bed is made from what must be just ordinary 1/4" thick aluminum.  It's dished at least .020"  I have 5 of these that I maintain, between the work owned ones, and mine.  Every one has a different warp to the build plate.  It causes problems with the first layerd of prints - they don't stay stuck, it matters where you place small parts on the bed, etc.  The first 2 [for work] I made new plates out of 3/8" specified plate from McMaster, but it was EXPENSIVE.  I just got my own printers, and figured I'd try the mill on the original plate, since it seemed like it could work, and I'm not making $ with them...  I also recently got feedback from another 3D printer forum, someone found a source [direct from a metal supply house] for similar speced metal for a fraction of the price, so I decided to give it a try.  Those should show up next week.

I still learned stuff trying this, also, trammed the mill, it wasn't off much, but I had most of the 8x8" plate flat with no line between passes that I could feel a step.  So that's a good thing too.


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## RJSakowski (Sep 24, 2019)

Take a look at this thread. https://www.hobby-machinist.com/thr...-1-lb-aluminum-plate-drops.79805/#post-685368
They have 1/4" MIC6 plate for a super cheap price. At around $3.60 a sq. ft. compared to McMster $54, it's a bargain even if you have to buy $30 worth.


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## Dynahoe Dave (Sep 25, 2019)

I bookmarked that metal place!  Thank you.


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