How would you machine this?

[maclaren]

On top of that most abrasive cutting wheels are about 1/8 at most 3/16" which means you be making a lot more passes than two.

Its not a very good Idea to use an abrasive blade to cut aluminum. There are carbide tipped blades that are specifically meant to cut aluminum and other non-ferrous metals. Here is a link to the blade that I'm talking about.Non-Ferrous Metal Saw Blade


The most accurate way to do this would be do mill it on a manual vertical mill.

Almost any way you do it you will have to do multiple passes. There are vertical mills out there with beds longer then 60" but they are few and far between.

If you want to minimize the number of passes that you wil have to make. You could make a really big vise out of two pieces of precision ground bar stock The first one you would drill holes in and then bolt to one of the slots of the mill. If you buy a precision ground flat stock bar you should be able to find one that will key into the t-slot of the vertical mill that you are using. The second bar you would use as the moveable jaw and use cam action clamps to move the moveable jaw into the fixed jaw. Like the ones found here http://www.miteebite.com/products/multi-fixture_e.html

The other approach is to use multiple vises. The big thing is that you need to set it up to be as even as possible across the vises. An easy way to do this would be to clamp the vises on to a piece of bar stock and then using a test indicator to run along the edge of the bar and adjust the vises until the dial does not move along the length of the bar.

The biggest problem with this machining task is that you will be turning a ridged piece of box tubing into a not as ridged piece of channel. So in order to compensate for the material that you are removing you will need to make a couple of blocks that you can slide inside the tubing so that you have something to clamp down to so that the tubing does not deform under the clamping pressure. If the sides of the tubing bend in under the clamping pressure that would cause the .75" slot the you mill to become wider once you release the clamping pressure.

I would also mill the slot in two passes. I would not use a .75" cutter I would use a .5" cutter over two passes. This allows you to compensate for clamping deformation, and actual cutter size.


It would be even more accurate to mill this on a horizontal mill using a slitting saw. But good luck on finding one I don't know anyone that has one. But there are vertical to horizontal adapters for bridgeport mills that you can buy.

I have mill long slots in pieces of tubing and had to move and reclamp multiple times and it turned out fine it just took forever.


What type of tolerance are you trying to hold?

If you are planning on using this piece of box tubing in an elevator design it is not a bad idea to design in a degree of play so that the elevator does not bind as it goes up and down. Also please note that this piece of channel that you are making could easily deform under dynamic load and duing the competition.

I understand the desire to hold as tight of tolerance on machined parts as possible but just make sure that you don't design yourself into a corner by demanding that they stay that way.

I guess the moral of this story is that it is possible to make it as accruate as you want to pay for.