[Smackre]

I am Machining the end of a peice of plastic. The wall of the tube is only like 0.06" thick. But when I go to machine the tube into the right contour my bits are just blowing the tube up. Is there a better way to machine this on my cnc router? I am using a 0.500" up cut spiral router bit.

Thanks Eric,

[Geof]

What kind of plastic is it? This can make a big difference.

[LeeWay]

It should also be clamped very tightly. Difficult to do without a purpose built fixture.

[One of Many]

You might try a smaller cutter and no helix, but a true forth axis would keep the cutter from needing to break through a side wall. A core filler and OD clamping sleeve or collar can stablize the tube enough to assist in the cut. Plunge cutting the exit point first, can minimize cutting through a side wall too.

A cheesy 4th axis simulation I have used, consisted of an air-bearing with a collet assembly to grip the tube. The back side of the air-bearing followed a contour profile to be copied into the tube end coming out of the collet. An air router spindle was stationary at the collet end. Slide the tube in and grip it with the collet, feed the airbearing up to the cutter and stylus position, rotate a couple turns for a clean profile. Simple with no electronics. The hardest part was making the initial profile to mount on the air-bearing collar.



Sounds like acrylic? That stuff is quite brittle. Good luck if it is! LOL!

DC

[Smackre]

I am unsure what kind of plastic it is. I just know everthing I get close to it with my 1/2" tool it wants to shatter. Most likely because its hard and thin.

[Geof]

If it is transparent it will most likely be acrylic, Plexiglas or Perspex. This comes in two types; cast and extruded. Sometimes you can tell that it is extruded because the ends are not flat and the surface is smooth but sometimes has striations or undulations that you can see with reflected light. Cast often has square smooth ends and is very smooth and flat because it is cast and polished; it is also much more expensive.

Good luck machining extruded it is almost not worth trying. Even if you are successful it will likely stress crack very soon adjacent to the cut.

Cast acrylic can be machined successfully but you need to support it well; spread your clamping around not just in one area. For a tube grip it inside another tube and just have the area you a working on protruding.

The tooling for acrylic should have no top rake which is diificult to obtain with milling cutters. At the very least use low helix or straight flute cutters.

Also plan your cut direction carefully; all plastics are flexible and conventional milling will often pull them into the cut, climb milling is much better.