Thinning down sheetmetal

Video that describes the process:
Thinning down sheetmetal
((Link opens on Youtube in new window.)

At my dayjob we often have to prototype sheetmetal parts where we usualy have the contour lasercut, WEDM-cut or milled on the cnc – The problem: In some cases we don’t have the matching sheetmetal thickness especially when the material is only available in large batches or on a coil.

What to do if you need a piece of 0,9mm stainless steel sheetmetal?

Surfacegrinding sheetmetal works, but with non-magnetic materials it can be a problem. Facemilling on a vacuumchuck can also be very tricky.
In some cases it works well to superglue the sheetmetal to a freshly surfaced piece of aluminium and then face the sheetmetal to thickness.

But there is another technique, where we use the property of a climbcutting endmill to our advantage: It pushes the part thats cut away from the cutter.

My foreman showed me this technique years ago and since then I used it countless times with excellent results.

The sheetmetal is clamped in the vise, sticking out above the jaws, with a backing plate.

Thinning the material down is just a matter of taking climb cuts:

During climbcutting the material gets pushed against the backing plate, even if the sheetmetal is not perfectly flat.

A endmill with a large number of flutes works best, the more flutes are engaged in the cut at all time, the better it works. I usually try to use at least a sixflute endmill.

As this is a climbcut, you have to be careful on a manual machine. Due to the backlash in the feedscrew we are limited to shallow cuts – Don’t go above 0,1…0,5mm side engagement.
If you are running a cnc machine with ballscrews, you are on the safe side.

The sheetmetal can be unclamped, measured and reclamped without loosing any precision.

The finish we get that way can be pretty good.

This technique is somewhat limited in regards of material size, but with a long endmill you can thin down quite large pieces of material. And you can even thin down long strips of material in multiple passes.

Also, it is not a problem to mill one half of the part, flip it around and mill the other side.

That way, completely finished sheetmetal parts, for example punched or lasercut can be reduced in thickness. Here is an example in 1mm steel sheetmetal:

This is done in two setups. Cutting the first side:

Turning the part upside down, cutting the second half:

The accuracy to be achieved with this technique can be quite good, here i shot for 0,8mm:

Of course this also works with plastics:

1mm ABS thinned down to 0,5mm