[tmt_92021]

what's the best way to hold down large thin sheets of aluminum for machining? Thanks.

[Runner4404spd]

double sided tape

[DEAN]

How about that Mitee-Grip stuff from Mitee-Bite

[mxtras]

A vacuum table is another option.

Scott

[JPMach]

Where is a good source of thin double sided tape?

How hard can you mill a part without worying about it lifting? Say a 1/4" endmill in 1/8" material.

JP

[DEAN]

Home depot has the wide carpet double sided tape.

[tomc3700]

what's the best way to hold down large thin sheets of aluminum for machining? Thanks.

You can sandwitch it between 2 pcs of thin scrap wood and strap it to
your table.



Tom C.

[cdlenterprises]

How thin? How big? What do you have to do to the parts? It's pretty tough to beat vacuum when dealing with thin stuff. Whether you use vacuum or double sided tape I would go easy with the feedrates. One trick we used to use was use an end mill with a left hand helix (right hand cut, left hand helix). The helix angle will actually push the part down vs. pulling it up like a standard helix.

[mxtras]

Another option is that if the finished part has any holes, drill/bore them first, then anchor the panel to a fixture/board through those holes.

If not, then find three or four locations outside the perimeter of the finished profile and anchor the plate down to the machine in those areas. Then, when profiling the shape from the plate, simply leave a small tab in place near each anchor point that will keep the part in place. Snip the tab off and sand that spot.

Scott

[psychomill]

All of the above are good suggestions... add to that, moving clamps around.

One trick we used to use was use an end mill with a left hand helix (right hand cut, left hand helix). The helix angle will actually push the part down vs. pulling it up like a standard helix.

Huh?

Left hand or right hand helix will exert the same "pulling force". It's the helix angle that will change this somewhat. Actually, it alters the direction of the cutting force. The only way a left hand helix will push down (so to speak) is if you still ran it in M3 (normal) spindle rotation. But then again, you might as well buy standard tooling and run it in M4 (reverse rotation). But that won't help you much for tool life, finishes and will probably launch the part.

Something to consider to get the chip and part to "go down" is the use of router tooling like from Onsrud. They make down cut spiral flutes that will change the force direction.

For the most part though, a good vacuum chuck or tape will suffice....

:cheers:

[cdlenterprises]

[QUOTE=psychomill;208058]
Huh?
...The only way a left hand helix will push down (so to speak) is if you still ran it in M3 (normal) spindle rotation. But then again, you might as well buy standard tooling and run it in M4 (reverse rotation).

www.mscdirect.com look at page 388 lower left hand corner Item #81864324 Putnam HSS LHS(left hand spiral)RHC(right hand cut) end mill. If you bought standard tooling and ran it in reverse then your not cutting are you? Hence the left hand spiral(pushes down as you say) with the right hand cut(cuts like we need) It was a long time ago, but I'm pretty sure that this was the type of cutter we used to push the part down onto the fixture plate

:cheers:

[keebler303]

yes left hand spiral cutters are available and are meant to cut in the standard direction. They are meant for applications where you want to push the chips through the part for some reason. ie through-cutting where there is a space below the workpiece for the chips to fall.

Matt

[JPMach]

right hand cut left hand spiral bits are common in wood bits as this keeps the top from spliting out. A local tool company (Vortex) even makes compression bits (mainly for laminetes or composites) that sometimes work for stacks but will not do anything for a single thin sheet.

I will have try the double stick tape, have done moving clamps and all that and they just kinda suck in my opinion. They work, they just suck. Vac plates are good if the part is large enough, but when you start putting holes in then you have to basically gasket around each hole or the vac is gone.

JP

[psychomill]

If you bought standard tooling and ran it in reverse then your not cutting are you?

Exactly... being sarcarstic, ... sorry....hence the following sentence from that statement in my post..

Of course, the picture from the MSC catalog wrong. It shows a LHS/LHC tool. But, as I read your post again, I think we're talking about the same thing here so I won't further.... :cheers:

My only point was that simply getting a left hand cutter doesn't mean you're going to push the chip down. I have lots of them and all the chips come up. But with a RHC (LHS) tool or "down spiral" fluted tool, the chips then move down. You can also buy RHS/LHC tools. All depends on which way you want to go.... hows that for a "mess"

Vac plates are good if the part is large enough, but when you start putting holes in then you have to basically gasket around each hole or the vac is gone.

Not necessarily. It's all in how the contact plate ( the faceplate the the part sits on ) is built. Depending on how you run your vacuum channels/chamber, you can drill thru the part and not affect the vacuum.

:cheers:

[SRT Mike]

All the options have +'s and -'s. Vacuum is probably best if the part will support it (doesn't work for small parts).

We had a sheet of copper about .02 thick that had to have an intricate shape cut into it - read: MAJOR PITA to machine. What we did on the advice of someone here is make a plate with a groove cut into it with a 1/8" ball endmill that followed the cuts in the copper. This served as a relief cut for the 1/16" endmill we cut the copper with.

Then we cut the piece of copper, put the fixture on a hot plate and heated it up. Then take a stick of hot-melt glue and smear it around, then stick the copper sheet on it and let it cool. Machines beautifully and provided it stays cool (it did) the glue doesn't melt. Make 2 or 3 fixtures and have one warming, one machining, one cooling and you can keep 'em going at a good clip. To remove, put it back on the hot plate until it's free then drop the copper sheet with hot glue all over it into a 5 gallon bucket filled with acetone. Leave it for a few hours and the hot glue just flakes off. The part stays perfectly flat, cheap to do, holds intricate parts very well, and if you are careful you can even re-use the glue. The fixture looked a bit ugly after a few hundred pieces but drop it in acetone overnight and it looked good as new.