[ex-egll]

Hi, I am fairly new at this hobby and after getting all the toys setup and some g-code put together I started to make chips.

One issue I am having is with clamping the work piece, for example I want to mill a 3" flywheel from a 3.5" square by .25" of Aluminum. I can clamp the Aluminum to the table on top of a piece of sacrificial wood and start milling but when it comes down to final pass the cutout will start to move as the bottom layer of metal is removed, this will at least put a an unwanted "dent" in the flywheel or at worse bury the mill into the flywheel.

Any suggestions?

ex-egll

[Dylwad]

Clamp the stock down, machine the inside features first, than clamp the inside and machine the outside features.

Or leave tabs holding the part to the clamped stock, and break/file the tabs off when your done.

For small aluminum parts I routinely super glue the stock down to wood or corian that's clamped to the bed, machine and soak in acetone or heat the part up to release the glue.

Workholding is one of those things you have to learn by experience, and a little but of trial and error.

Having a solid sacrificial board that you can drill and tap into goes a long way too.

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[rlockwood]

Put some carpet tape between the section of material that will become the flywheel and the sacrificial board. It wont be enough to hold the piece in place during machining, but should be plenty to prevent it from moving around during the final pass around the profile.

[ex-egll]

Thanks for the responses. I figured it would be an exercise in creativity. It's amazing, in this world of .0001 accuracy that there is still a place for carpet tape.

One thing about this hobby is that it keeps the brain cells out of retirement! Computer construction, Computer programming, electronic design and construction, technical drawing etc etc. One day I may even get my first model built. I figure the first year will be used to create a mound of chips and wreck a few machine bits, then I can get into the serious job of building something!

[aarggh]

I extensively use double sided sisalation tape for almost all small machining jobs that clamping is an issue or inconvenient. Even on alu, so long as it doesn't get too hot, it just doesn't move at all.

cheers, Ian

[CS900]

Another option, which i do quite frequently, is not to mill all the way thru the stock. Leave .005 or so material at the bottom of the part. Then you can use a deburing tool or similar to break thru the leftover after it's finished being milled. This is nice becasue you can just clamp it directly to the table, and not worry about the part breaking free on the final pass.