Newbie looking at 6040 (China CNC) for polypropylene 15mm sheet

**JOGARA** · 14-09-2017

Think I'll try that probe and soft jaws. Though I'll machine my stock on a sacrificial so my outer is perfect. I can then probe and machine my internals.

The problem with vac plate is that I mill through my part so will end up losing vacuum. Only way around that is 2nd op so might as well just mill out like I already am in 2 stages.

**Zeeflyboy** · 14-09-2017

Originally Posted by JOGARA

Think I'll try that probe and soft jaws. Though I'll machine my stock on a sacrificial so my outer is perfect. I can then probe and machine my internals.

The problem with vac plate is that I mill through my part so will end up losing vacuum. Only way around that is 2nd op so might as well just mill out like I already am in 2 stages.

Well with a custom vac fixture plate you could account for where the part will be cut through I'm sure.

Something I sometimes do for a tricky to hold down part is leave 0.3 - 0.4mm of stock at the bottom to help hold it in place (I guess like a tab, but all the way around), then just run a cut with a smaller bit that doesn't go too near the side wall to release the part, trim away the excess and then put a chamfer on the back side to clean it all up.

**Desertboy** · 14-09-2017

Vac table and jig is the way forward ;)

I'm doing a simple vac table with the idea that any repeated parts I'll jig up for to reduce the time it take to align parts. Seems to me 90% of the time you spend on cnc is aligning the part not the machining. Jig up correctly and you can reduce that alignment time the better the jig the less time you spend resetting the part. After all if you're repeating cuts you only need to generate the gcode once.