Helicoil problem in Delrin

[ranchak]

I'm having a problem installing 6-32 helicoils in .250 Delrin. I have a brand new screw forming tap, holes were drilled on the mill, tapped with a hand tapper. Some helicoils will install easily and others will "wind" down skipping a thread along the way. I think the problem is the size of the helicoil being installed, but this is a guess. Any suggestions?

[heli-coil]

Dear ,
Derlin as much I understand is one of latest polymers in use for Aerospace parts, electronic & communication devices.
Lets admit that after all its a plastic and not a metal. Fine plastic threads can deflect easily compared to metal threads.
UNC 6-32 is a small fine pitch size of aproximately 0.8mm thread pitch.

The possible causes are that a ? mark shaped helicoil insertion tool is in use.
OR a plain mandrel type prewinder insertion tool is in use , these type of tools don't guide the helicoil wire properly & could make them jump over in case of relatively flexible thread flanks in derlin.

Best to use a Threaded mandrel TYPE-II prewinder of HeliCoil Part # 7551-06 to prevent thread jump over.

Further a marginally better shaped thus stronger thread in derlin can be created by using serial taps ; rough first & then finish.
Somewhat significant thread flank strength improvement can be observed by using thread forming / Roll taps . ( check derlin physical property on permanent deformation)

You can download HeliCoil technical catalog from website www.helicoil.in for further information & support.

Regards
Adarsh Shishoo

[qfjsy]

Thanks, I also saw a website http://www.xhcljx.com/eng

[MadMax]

The full on expensive insertion tools work a fair bit better than the winding keys. If you're in a pinch, I find it helps to tap a small bit of round brass with your helicoil tap and use that as a pre tensioner. Basically turn the insert into the brass bit and wind it down so it pokes out the end a couple turns before twisting it into the softer material. If you skip a thread in the brass bit, you don't damage the potentially more expensive part and if it does turn thru, then it will hold the insert tight around the twist key and aid it's insertion into the delrin part. A bit of light aluminum tapping oil in the brass bit can also help.

There's lots of precedent for helicoil inserts in delrin. You're not pushing the limits of the material.

[ranchak]

I actually have some of the insertion tools although I think that the ends are worn. I need to take a better look at them and repair them. I bought some helicoil kits and used the winding keys and had much better luck.