Threading plastic / inserts

What can you tell me about threading say Delrin.

I've hand threaded M8 and M10, but now I'm thinking about largish scale CNC prodcution of a part that requires 8x M4 threads by approx 10mm (or maybe 4x 25mm through).

First, can you auto cut the thread on CNC. I guess you can, but how common is it for someone to have that capability (I'm imagining a stepper motor for a spindle). Or are there other ways?


Or are press fit inserts the answer? What sort of pull out loads would I get from these:

http://www.insertsdirect.com/acatalo...t-inserts.html
http://www.insertsdirect.com/acatalo...it-insert.html

Hi Jim,

There are brass inserts available such as these http://uk.rs-online.com/web/p/insert...tent-_-0278562
When they have a screw put into them, they wedge outwards for a tight fit. RS don't give out any info on the pull-out forces as this would depend on the tolerances on the hole and the material they are in.

I have used them successfully in oak (M3 size inserts).

Cheers,

Rob

Quote:

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Originally Posted by jimbowley

Or are press fit inserts the answer? What sort of pull out loads would I get from these:

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Could you use these headed types inserted in such a way that the force is trying to pull the head through ?
You could of course recess the head so it's flush with the surface.

http://www.insertsdirect.com/acatalo...it-insert.html

It's not so neat using headed ones but could be done. That's why I'm interested in the straight ones. I'll have to get some data or samples and give them a try.

How would I make the needed 5.4mm hole all the way through 25mm thick delrin? Would that simply be a 3mm mill (or 4mm ?) I'm not familiar with sizes yet and how deep you can go, so much to learn.

Quote:

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Originally Posted by jimbowley

How would I make the needed 5.4mm hole all the way through 25mm thick delrin? Would that simply be a 3mm mill (or 4mm ?) I'm not familiar with sizes yet and how deep you can go, so much to learn.

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Yes you could use a smaller end mill, it would spiral down to make the required hole, there are several strategies for hole drilling.
These are the drilling operation parameters for Cambam for example; http://www.cambam.info/doc/0.9.7/cam/Drill.aspx
The cutter size would have to such that the chips could evacuate the hole easily.

Quote:

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Originally Posted by jimbowley

How would I make the needed 5.4mm hole all the way through 25mm thick delrin? Would that simply be a 3mm mill (or 4mm ?) I'm not familiar with sizes yet and how deep you can go, so much to learn.

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You could just buy a 5.4mm drill http://www.tooled-up.com/product/tro...i_YaApN58P8HAQ

..Clive

yes, I'm aware of drills :)

What I didn't spell out was that to use the suggested headed inserts I would have to go all the way through my material 25mm and then counterbore it, and that ideally needs to be done with the same tool that can profile that face as well.

Whereas with the unheaded insert I just need to mill (or drill) to a depth of about 10mm with no counterbore.

Rob, the expanding type unheaded inserts look like the ones for me.

I'd seen those so I don't know why I didn't mention those in the first place! I think it might have been because I didn't like the look of the non-expanding unheaded ones, so they were on my mind when I posted !

I've just thought, you could use those unheaded ones in counterbored holes, giving a more compact design than headed ones.

But the barbs on them do suggest they are for one-sided operation.

Anyway, i've requested pull-out data for use in delrin.