11 replies to this topic

[1984mini25]

What size tap do you need for a 5/16" unc helicoil?

 

As the tap that came in the kit is now in two half's...

[Pigeonto]

Into ally or iron ?

[1984mini25]

Into iron, although I didn't think there would be any difference?

 

As I was helicoiling 2 of the thermostat threads on a spare head, done the first one with no problems, went to do the second and broke/snapped the tap.

[Gremlin]

Have you managed to get the broken bit out?

[1984mini25]

luckily the tap snapped diagonally in half and I'd only just started cutting the thread, so I had plenty for a pair of mole grips to grip onto and unscrew it.

[Pigeonto]

Into iron, although I didn't think there would be any difference?

I don't normally drill when in ally if the thread is completely smoothed out, just tap straight into it.Sorry,my stuff isn't here so cant check

[Dan]

  Taps for Helicoils are unique I believe.  The section of the diamond wire doesn't make the outer thread up to a standard size, or even if they do the thread count would be wrong for that size.  You will need to order the right one from an engineering supplier.

[Pigeonto]

Apologies OP, I read that as 'what tapping dill is needed for 5/16" UNC helicoil'
Dan, you are of course correct, they're unique. In this instance, 18 tpi, the tap is around 3/8" diameter but the tpi on a std 3/8" UNC is 16 so no good.

[1984mini25]

Plus my all now broken tap had stamped on it is 5/16 unc 18, witch it can't be as that's the internal tread size of the helicoil. It's looking like the easiest, although not cheapest option is buying a second helicoil kit if I can't find the right tap separately.

[Dan]

  Yes, it's the tap for a 5/16" UNC Helicoil so that's what's written on it.  It's unique.  You will be able to get one from the supplier that sold you the kit but it would probably take longer to order in than a whole new kit.

[1984mini25]

I originally bought the kit off eBay a few years back, so asking the supplier might be a bit of a problem.

 

anyways I popped off to a local country fair yesterday, with one stall/trader selling nothing but taps, dies, helicoils, nuts, bolts, etc. he did also happen to have a few helicoil taps, unfortunately in every size but the one I needed. but then I did manage to pick up a few other taps I'd been after and a pitch gauge.

 

today I've been comparing a measuring the broken 5/16 helicoil tap. In the kit is a 21/16 drill bit, witch I work out as being 8.33mm and measuring the thread pitch of the tap I get 1.50. Witch if I'm correct an m10 thread needs a 8.5mm drill bit and also has a thread pitch of 1.50. So I'm half tempted to drill a 8.5mm hole and tap it and see if the 5/16" helicoil works.

[Deejayry]

I originally bought the kit off eBay a few years back, so asking the supplier might be a bit of a problem.

 

anyways I popped off to a local country fair yesterday, with one stall/trader selling nothing but taps, dies, helicoils, nuts, bolts, etc. he did also happen to have a few helicoil taps, unfortunately in every size but the one I needed. but then I did manage to pick up a few other taps I'd been after and a pitch gauge.

 

today I've been comparing a measuring the broken 5/16 helicoil tap. In the kit is a 21/16 drill bit, witch I work out as being 8.33mm and measuring the thread pitch of the tap I get 1.50. Witch if I'm correct an m10 thread needs a 8.5mm drill bit and also has a thread pitch of 1.50. So I'm half tempted to drill a 8.5mm hole and tap it and see if the 5/16" helicoil works.

 

Personally i would hold out until you can find the correct helicoil tap, but i am a bit retentive when it comes to tapping threads.

 

there is an alternative to a helicoil, which is effectively a sleeve with both an internal and external thread, the internal thread would be the 5/16 unc and the external thread would be a standard thread usually one or two sizes up so a 3/8unc or 1/2unc for your purpose, unfortunately i cannot remember the name of the product, i have bought them from demon tweeks in the past but they no longer seem to stock them.

Edited by Deejayry, 27 August 2013 - 09:00 PM.