Need Help!- plate fixture!

[buggie]

need help to make a fixture to flycut a plate 8x11 .5" thick plate of silver, right now im holding it on two vise's but getting alot of chatter because of flexing. oh by the way im machining this on a hass tm p1 cnc mill.

[Geof]

Why are you flycutting in a CNC mill?

[rmorton]

Try making a small vacuum chuck. You can also use double sided tape to help hold the part to your bottom plate. Sounds crazy but it works.

[Jason S]

Or you could use t-slot toe clamps.


http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=51487556

[ALLtra Mach]

cam locks or mitee mites on a solid fixture plate.

[Jason S]

Toe clamps will hold the part "down" when tightening.

[kojack]

put a thicker piece under it ... just slightly less wide

I cut .250 thick all the time I stick 1inch or better under

@ 15 inches long all the chatter goes away

[scadvice]

Ideally you should make a vacuum chuck, especially if you are doing more than one piece. But a second alterative is to fly cut a one inch thick plate of aluminum, mic 6 it you got it (6061 if not) and cut a step down at 90 deg from the cut direction edges ( .040 or .05 will work). Then press three soft dowel pins spaced in in a big triangle in the cut surface with only .05 or .06 height above the milled surface. These, after you are sure the plate is absolutely flat, you will mill down to around .020 to .015. Next get some good sheet wax with med. to med. hard hardness (MSC catalog) and heat the plate in an oven with the wax sheet on it and the silver plate beside it ( not on yet). When it reaches temp., (check for the melting temp do not go too much over that!) carefully place the silver plate on the wax sheet, and as soon as it will set against the edge. Let it start cooling down. BTW - make sure to wash both pieces with alcohol or acetone first. Also a weight ( not to heavy and also heated) placed on top of the silver plate will help to assure seating on the top of the pins.
Make sure you clean all the excess wax from the mounting plate bottom and clamp to table, but only lightly, to avoid distortion.
Silver is a bit gummy. What type of cutter are you using? Single point is best with a very small radius and high rake angle to prevent chip build up. Use a small diameter cutter if you can, less chance of chattering. Some people use a mounted diamond chip to cut it, I have not. Coolant at around 5 to 6% mix. Some coolants will stain. If you are using oil, ( oil misting works mineral oil 5 or 10 wt if you can get it) melt and pour an extra bead of wax around the edges to prevent weakening of the wax bond by the oil.