Seeking advice on how to counterbore a lot of soft plastic tubes

**Steve_hamilton** · 08-20-2020, 06:27 PM

Pretty new to CNC and thought I'd ask to see if there's a good/easier/more efficient way to do my job. Particularly looking for advice on the best way to design/use fixtures (or any other way!) to make this job easier.

I'm trying to counterbore 8 holes into sides of a 3/4" plastic (cellulose acetate butyrate - fairly easy to machine) tube. Then mill to length. The counterbores are used to sit M2 machine screws in - and counterbore should be +- 0.1mm tolerance in depth. 7 holes on top, 1 on bottom.

I've got a couple of M2 counterbore step drill bits - so can do the counterbore and hole in one operation.

However, clamping the tube down squeezes it slightly thus making it difficult to get consistent counterbore depth. To get around this, one idea I've had is to make a stop for the step drill and just let it run down to the depth of step, setting it so the tube is squeezed slightly. However, the stop contacting surface may mar the surface so I'm wondering about some kind of bearing/freemoving stop.

After clamping and cutting top side, I'd think to rotate tube and do counterbore on bottom side. To get easy/fast alignment print a jig with an aligning pin that locks onto the previous counterbores, and then change to endmill and mill the ends.

I am thinking to make a fixture to hold 10 tubes at once and do all top counterbores (and then switch in tubes until all top counterbores done on all tubes), then rotate tubes and do bottom counterbores, then mill the ends.

However, I'm curious how someone more experienced would do this - I'm selftaught and well aware I lack experience.

I have 200 of these tubes to do initially, then another thousand. For making fixtures I have my router (but it's only 30x20cm bed), a large SLA resin printer, and general hand tools. I don't have a rotary axis.

Any advice/ideas?
Thanks

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