[bgator220]

Hello All,

I have a few pieces I want to produce in the thousands on my 3-axis cnc mill. There are mostly 1/4" 6061, a few are 1/8" 6061, and dimensions of 3"x3" or 6"x4". They need to be planed on both sides and be milled and chamfer on one. They eventually will be anodized.

I am finding that bolting the pieces down is very time consuming and also does not make the pieces look so good as they have hold down holes in them.

My goal is to have a sheet of aluminum that I can put on an electromagnetic chuck and put a 1/8" steel plate where cuts do not need to be made. Plane the piece, flip plane, and then put steel pieces that are slightly inset of the part profile in position. Then I can proceed to mill the aluminum part out.

Cutting speeds will be pretty high, 40-70 inches per minute with 1/4" bit.

Is that even possible? Is there a more simpler way to eliminate hold down holes and speed up production.

Also any recommendations on good electromagnet chucks? My budget is 1500 and I want to get something with a window of 12x12.

Appreciate any input.

Thanks,
Steve

[Geof]

Very, very little chance that it will work. The steel will be separated from the magnetic chuck by the thickness of the aluminum plate and the magnetic hold will be greatly reduced.

Do some experimenting to see the influence of even a small separation between the magnetic materials. Get a really good rare earth magnet and you will find you cannot pull directly of a piece of steel, you have to slide it off. Then put some thing aluminum between it and the steel and you will find a 1/32" separation reduces the magnetic attraction dramatically.

[mcv300]

Have you thought about vacuum clamping system ?

It is not too expensive. I see it is discussed somewhere in the forum

[bgator220]

I do understand that magnetic strengths are reduced exponentially as the distance increases, but thought that electromagnets put out significantly more pull than rare earth magnets? Anyone with any experience have any idea? Even if I could do a setup with like this with just 1/8" material it would be great. Can anyone recommend a good electromagnetic chuck brand? I may just get one and see how it works out, Im sure I can find other uses for it.

I have not really considered vacuum chuck as Ive been told they require a lot of effort to change the seals for the piece your doing and cannot take heavy cuts, is that not correct?

[jsheerin]

Whether or not you get more pull force out of an electromagnet compared to neodymium magnets would depend on the specific design of the magnetic circuit. If you have the same size and geometry of steel in the circuit and you magnetically saturate the steel, then the force would be the same. That is common practice in designing loudspeakers (where I worked with magnetics). I don't know if that's the case for magnetic chucks.

[underthetire]

Vacuum tables work great. 50-75 inches per minute is very mild, you shouldn't have any hold down problems.

[Geof]

Nine squares inches at the maximum vacuum theoretically possible (14.7psi) gives only 132lbs of clamping.

Tewnty four square inches is better but even that is not a lot at 353.

But in practice it is not likely the vacuum will be more like 10psi so these maximums will never be reached.

[wildwestpat]

A magnetic chuck for a milling operation is fraught with danger as the side thrust can cause the work to move. These chucks are normally used for surface grinding not milling or turning operations where the side forces can be considerable.

Suggest you use tool makers buttons to define the position and then use either a cam excentric on opposite faces or a toggle clamps. This would be normal tool room practice with the buttons and the excentric or toggle clamps mounted on a sub plate which is in turn held down using the 'Tee' slots and matching fixings. If the numbers are very large a pneumatic clamp would soon earn its keep as a replacement for the excentrics or toggle clamps.

Regards - Pat