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Using live center for machining plastics (POM)

S

Schjell

Aluminum
Joined
Jan 16, 2020
Hi,
Is it be acceptable to "ram" the hydraulic tailstock live center into the end of the faced off stock when machining soft plastics such as POM-C or PEHD? It would free up one live tool slot in the turret or save time if I don't need to machine a center hole first. My only concern is that perhaps it's not good for the live center bearings, but again I will be setting the hydraulic pressure anyways..
 
You will need a very free running live centre in order for the almost non-existent friction between the part and the centre to overcome the friction in the seals and bearings in the live centre.

It's likely that in most cases if you do this you'll find that the centre just won't spin.

Also be careful which plastics you do this to. Nylon for example is liable to just split up the middle like a wooden log.
 
The only plastic I've been consistently able to pull that trick with is PTFE, and only small diameter work at that, for unless rammed in far too hard you get very little area riding in on the centre itself.

I turn very very little UHMWPE or soft ABS (can't recall) the grade

If you need a centre drill and are short of turret space find a way of mounting it in (say) a turning tool shank and program that in.
 
You don't need the center to dig into the material for support.

Use a flat face center, as big as your part profile will allow.

The larger diameter will stop the center from spinning in your part, and you shouldn't have enough radial load to shift it.
 
ManualEd said:
You don't need the center to dig into the material for support.

Use a flat face center, as big as your part profile will allow.

The larger diameter will stop the center from spinning in your part, and you shouldn't have enough radial load to shift it.
Click to expand...

Thanks for that piece of advice!
Think I'll try out the flat face center proposal by machining a disk that fits snugly onto my live center.
I'm happy I asked - I'm new to big CNC lathes, but I've done it a lot on a smaller manual lathe.
Thought I'd start acting a bit more professional in the workshop now that I've got myself a "serious" machine:-)

Note: Going to keep the scruffy manual lathe hidden in the back of the shop though - think for a lot of minor stuff it's just easier to get things done in a hurry on a manual lathe.
 
Thanks Limy - might go for that proposal - got a few shank positions that are available!
A flat center never crossed my mind though, as mentioned further down in the comments. Will try that first I think.
 
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