Machining glass-filled nylon

[JCash]

Hello,

I'm going to be drilling a few holes in glass-filled nylon using a manual milling machine.

I need 16x 25/64 through holes and 16x 1/4-20 tapped holes 0.5" deep.

I've seen that this material is very abrasive and carbide tools are recommended. Would carbide-tipped tools work for such a small batch size?

And is tapping directly into the nylon a poor idea, or is there a type of threaded insert that would be more reliable for pull-out resistance?

I don't see a coolant system on the mill. What techniques can I use to keep the temp down during drilling as I've heard that can warp the material?

Thank you.

 

[DavidScott]

HHS will work fine for that many but mark them as dull. Go slow speeds and it won't get too hot.

 

[claya]

Carbide tipped should be fine so long it is ground sharp. HSS will work, but will dull faster. Plan on the holes cutting undersize. Nylon tends to shrink when drilling & tapping. Any form of coolant will help.

 

[JCash]

Ok great. Thanks for the responses.

The mill has no automatic feed. Should I put pressure on the bit to drive it through or press more lightly?

Also, any advice on tapping vs. inserts?

 

[DavidScott]

With softer plastics you want big chip loads and slow spindle speeds so keep this in mind hand feeding. It depends on how much strength you need if you want inserts, but nylon taps quite well.

How much glass fill? I am thinking 10%, if 30%+ then the threads won't be as strong.

 

[JCash]

Thanks David.

The plastic is actually pretty hard (85D). Not sure if that changes what you recommend.

I talked to the manufacturer about the glassfill%. They will get back to me but expressed that there was a decent risk of cracking if I drilled into these.

Is this true? Would pilot holes or other techniques help me minimize that risk?

 

[Limy Sami]

Keep your tapping speed very low, or it will gauge too tight.......... and carbide taps are the way to go, .......... if it's gotta be HSS - I'd allow at least 4 taps.

That's what worked for me, YMMV

 

[DavidScott]

Talking nylon is the same as saying aluminum, there is a big range of properties possible. Still, I would be surprised to have it brittle enough to crack. Let us know what they say about it.

 

[???]

I machined a lot of prototypes in 30% GF and used air blast to clear the chips, obviously be careful where you blow them. I drilled and tapped with standard HSS drills and taps, however we tended to fit inserts using a heated tip on the Bridgeport most of the time. The tooling does get dull. One thing to watch out for is too deep a cut, material will pull out of the surface if you have a tall thin piece left at the end of a cut.

 

[Joe Gwinn]

Plain or soda water as a coolant, to prevent melting, is probably a very good idea. Beware any coolant containing oil.

 

[strokersix]

Thread forming screws can work in GF nylon. There are various types. Tri-lobe style is what I've used most recently in 30%GF nylon.

I don't know if this fits what you need to do or not. You would have to test it. I think screw installation speed matters and not typically reusable.

 

[ratbldr427]

Plastics don't transfer heat very well.I believe that is where the cracking comes from. So sharp free cutting tools helps and peck drill deep holes don't let the drill dwell and slower speeds. Coolent is good insurance. If you use inserts I would pick a coarse threaded insert over a Heli-coil, something like a Keen-sert.

 

[DavidScott]

Beware any coolant containing oil.

Why? Nylon is very safe from chemical attack and used in transmissions and engines bathed in hot oil.

 

[Joe Gwinn]

Why? Nylon is very safe from chemical attack and used in transmissions and engines bathed in hot oil.

True, but the discussion encompassed all kunds or plastics, not just nylon, so one must consider oil tolerance. It's a checklist item. For nylon, it's not a problem, for the right kinds of oil.