How to flatten a piece of 1/4" Aluminum Plate?


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Old 03-02-16, 12:52 AM
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How to flatten a piece of 1/4" Aluminum Plate?

I am in the throes of doing some woodworking.
I am building some of the tools I need to accomplish this.
My current project is putting together a router table extension for my tablesaw.
I am using a 8" X 13" piece of 1/4" aluminum plate as the router plate.
This piece of aluminum has a slight curvature through the 8" dimension.
It is probably only 1 or 2mm high in the center.
But, it is enough for the plate to rock a bit in its recess in the table top.
I could shim the recess.
but, that has drawbacks as far as keeping a smooth transition between the plate and the table top along all the edges.
I want to flatten the piece so that it lays in its recess without any rocking movement.

I do not have access to a good metalworking facility or tools.
I'm reluctant to try beating it to try flattening it.
That has never worked to my satisfaction in the past with other metal types.
And my suspicion is that the aluminum will quite elastic and tend to spring back very strongly after being hit, making it very hard to control.

How about heating and quenching to shrink one side of the plate?
Or, other suggestions?
 
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Old 03-02-16, 01:21 AM
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You could pay a machine shop to flatten it or sandwich is between 2 pieces of wood & set one of the tires from your car on it over night.
 
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Old 03-02-16, 03:52 AM
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Another way would be with a shop press.
Put the piece on two 1 x 1 strips of wood on either side of the bow with the high side up.
Press the high side untill slightly deflected in the opposite direction then release press.
Do this a little at a time untill it's straight.

If you don't have a press it could be a good excuse to buy an inexpensive one at a store like Harbor Freight or have a macine shop do this for you.
Another option is to rig up a lever using a long 2x4 and press down on it a bit at a time.
 
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Old 03-02-16, 04:06 AM
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The heating approach will not work with AL as it is too good of a conductor of heat, 5 times better than steel. The block of wood and the weight of the car approach will work, but you will want to over bend it slightly. Instead of just two flat pieces of wood, add small shims to each edge of the metal on one side and another small shim in the middle on the other side. Sandwich this between the two pieces of wood and apply weight, the car works if you don't have a press.

The trick is judging how thick to make the shims to obtain the right amount of bend after it flexes back. Start with thin shims and judge how wide they should be. measure the current deflection so you can compare after each attempt to determine your progress.

Bud
 
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Old 03-02-16, 04:41 AM
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It is difficult to flatten sheet material even with the proper tools. I'm guessing your pieces curled when they were sheered. Often it takes rolling it in the direction of it's current curve to put a constant radius bend in the plate (yes, initially making it worse). Then carefully roll it in the opposite direction to flatten.

Hammering to flatten is difficult especially with aluminum as a hammer will dent the material and leave tiny zones of stretched metal. Placing a piece of scrap wood over the area can help. I don't like using a car. 1 that amount of weight is not needed and 2 it's not controllable. Try placing support blocks under the low areas and a block on top and carefully hammer. You will have to go past the "level" or flat point to account for the elasticity of the metal as it will spring back a bit.

Best if wanting flat material is to buy or get flat material. Sheering often imparts a potato chip to small relatively thick pieces, but it's a quick cut. If you have a sheet of flat material to start with sawing, plasma or laser cutting out the piece you need will do a better job maintaining it's flatness.
 
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Old 03-02-16, 02:54 PM
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OK, thanks folks.
I had a small bench top 6 ton hydraulic press that I sold off, 2 or 3 years ago, rather than move it from Alaska to Hawai'i.
I used it for pressing u-joints and other shade-tree mechanic projects.
Now, for the first time in my life because of aging joints, I've begun to hire it out.
I might be able to justify acquiring another press for this project and other similar ones that will probably be coming up in the future.

HF cannot or will not compete with Amazon when shipping to AK or HI.
I'm thinking that another cheap $120 "Amazon Special" 6-ton would be big enough to do this job.
Agree - disagree?
 
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Old 03-02-16, 02:59 PM
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A machine shop should do it for far less than $120.

I don't crawl under my vehicles much any more.
No crawling would be necessary.
 
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Old 03-02-16, 03:21 PM
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Sorry Pulpo,
I edited my post and removed what you quoted.

Finding goods and services here on Big Island is about like trying to find the same in Alaska 25 years ago before the big box stores began moving in. Plus, a trip into town is a 50 mi. RT at the highest fuel prices in the country.

I figure that I'd only spend an extra $25 to $30 and have the press left over when I'm done, if I bought it.
I have to admit that I am a tool-head also.
He who dies with the most tools wins!
 
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Old 03-02-16, 03:47 PM
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Honestly, it's only aluminum which is easy to manipulate.
Take two strips of wood 1 x 1 inch square and as long as the aluminum, lay them on a flat sturdy surface spaced apart and put the piece of aluminum on it.
Take a bit wider strip of wood and place it on top of the aluminum.
Take a medium weight hammer and gently strike the piece of wood on top of the aluminum.
Note the effect and increase force in small increments untill you get the desired results.

I kmow this sounds a bit rough but is how a lot of metalworking is done.....restoring vintage cars for one.
 
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Old 03-02-16, 03:49 PM
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I don't see how a press will help any or do anything that a few blocks of wood and a hammer won't.
 
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Old 03-03-16, 01:19 PM
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Thanks Folks

OK, I've got it.
I needed some heads to bounce this off of.
I really didn't trust hammering it straight to get a good job done.
I've had problems trying to do that on thinner pieces, ending up with unusable "wavy and frilly" pieces.

I pulled out my trusty 4# hammer and gave it a fair number of moderate whacks on each end and in the middle, checking it after every couple of smacks.
Got it pretty close, then lightly sanded the middle of the ends of the recess.
All the rocker is gone.

I can now drill the plate for the router, make the fence for it, then start routing the banding for the plywood edges.
M'Lady's getting antsy for me to get this cabinet project finished.
She wants the garage back for her car.
 
 

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