First Piece cut in Aluminum

[BarryB]

Hey folks, I'm doing an installation piece about femme fatale profiles.  This is the first piece I've every cut in aluminum and notice some strange properties of aluminum that I'm hoping you guys can recommend ways around.  First off, here's the piece and also another showing the aluminum place, how I've mounted it, and cutting.


http://www.3dmation.com/images/First_AL/al_setup.jpg

The plate is seperated from the table by about 4 mm, and the plate is 2.3 mm.  When I cut, I'm cutting at .35mm depth at a time, and it's humming along.  As it starts to cut through, the aluminum starts to bend up and have sway.  At near the end of the process the piece bounces around a bit and breaks the bit.  Any idea how to make it so it doesn't do that?

[ostie01]

Hi, try to shorten your endmill, the shorter, the better.


Try to leave some tabs along the cut, this will prevent the part from hitting the tool.

If you could spray some WD-40 when cutting. this will also help the tool, not much, this is not very good about smoke ans vapor.

Jeff

[BarryB]

Thanks, I'll give it a try.

Barry

[RICH]

Here is a few thoughts for holding and avoiding the al bending.
- Use double sided carpet tape to attach the al to a firm base ( use a scrap piece of 1/4" al plate)
-Use epoxy glue , and then to remove it from the support metal plate , just heat it up with lighter and it will lift
- You can also use crazy glue, just a few touches , not the whole al plate

FWIW,
RICH

[GeorgeRace]

I do a lot of aluminum cutting, making parts for experimental airplanes.
I always use a piece of MDF under my aluminum sheet.  I cut parts from 1 X 1 inches up to 12 X 15 inches from aluminum of .016, .025, .032, .060, and .125.  In all cases I never cut more than .035 in depth.  I use only 2 flute carbide bits, usually between .09375 and .125 in diameter.  
What I find most critical is the RPM of the tool and the linear cutting speed.  If the tool RPM is too high and or the cutting speed is too fast you develop a lot of heat at the site of the cut.  This causes the aluminum to "bubble" upward at the site of the cut, due to the heating and swelling of the aluminum around the cut.  I have a simple test to test if the cutting speeds are right.  I simply run my finger along the cut, just BEHIND the cutting tool.  If the metal is just warm to the touch, and there is no swelling of the metal, all is going well.  I typically use cutting speeds of around 2000 to 2400 RPM and linear cutting speeds of no higher than 10 inches per minute.
I have tried 4 flute cutters and they just are not suitable to cutting aluminum sheet.  Actually the best cuts and lowest temps when cutting come from single flute carbide cutters.  They have long life and do a very clean cool cut.  
I forgot to mention, I hold the material in place with 3 or 4 "Clamp Down" devices around the perimeter of the sheet being cut.  I use ones made by Incra, they really work very well
Hope this help some,
George

[BarryB]

Thanks everybody's responses are great and I'm sorting through them now.  I'm sure I'll be able to complete the project now without breaking any more bits;)

[BarryB]

George you've made my day with recommending those Incra clamps.  No more drilling holes in my stock for clamping, that's a pain!

Btw, I'm off to the bit dealer tomorrow.  I broke my last one today, and will get a shorter one, say 15 mm exposed should do it, at least I'm hoping.

[GeorgeRace]

Hi Barry:
Glad to be of help.
I don't remember exactly where, but you can get the Incra hold downs for a bit less than directly from Incra.
Either Amazon.Com or ebay, I don't remember which.

The only problem I have had with them is that after a lot of use you may end up pulling the nut out of the knob.  I have a source for an exact replacement that costs a great big .75 each!  Was thinking about building some, but for the cost of them and the good quality of their extrusion I don't think it would pay.

They are very nice and really do work well.  There are pictures on my site of them in use.

http://www.mrrace.com/Products/  

George

[rcaffin]

The plate is seperated from the table by about 4 mm, and the plate is 2.3 mm.  When I cut, I'm cutting at .35mm depth at a time, and it's humming along.  As it starts to cut through, the aluminum starts to bend up and have sway.  At near the end of the process the piece bounces around a bit and breaks the bit.

The Al sheet should be clamped down very firmly onto a sacrificial layer. Air gaps are a big no-no. Multiple clamps.
The cutter should be as short as possible.

Cheers

[BarryB]

Thanks for everybody's help.  I thought I should post some progress.  I've shortened the length of the bit, as well as reduced the speed of the spindle.  I've had to reduce the feed rate a lot so I don't break bits, and I've broken about 4 to figure this out;)

I've got the clamps on order and will do the sacrificial layer and stock clamping on it next.  I think that'll reduce the noise and probably even allow me increase the feed rate a bit.

Anyway, here's some more pieces.  Oh, I put tabs on everything so it holds the pieces in place.  I can trim it down with a dremel easily.



Barry