Helicoils

[Worty]

Sorry guys, but I can't get my head around helicoiling.  I need to helicoil stripped threads M9x1.25.  So:

*What drill size do I need?
*What size tap do I need?

It's getting my head around original size of hole, what to drill out to, and what tap to use for the helicoil I'm using.  Some have suggested you subtract the pitch? from the bolt size (so M9x1.25 would be a 7.75mm drill) but a drill that size would surely go straight through a 9mm bolt hole??

Sorry for being a bit thick on this, but I've always struggled with this issue.

Cheers all!

[Triton Thrasher]

A Helicoil kit contains the drill bit and the tap.

[Worty]

Cheers TT, but I'd like to know how it all works.  I've tried looking at charts, etc, but struggle to get a full picture.  I have taps, dies, drills, helicoils, threaded inserts and have tried doing this before with some success, but it's still trial and error.  I sure if I get the principles, it'd be a cinch.

[morris]

All your information here;
https://tinyurl.com/3v2xe88x
Page 18-23

[Worty]

Cheers Morris.  I'll take the info and experiment on an old piece of metal.  The application is for a cast iron bearing carrier on my car, and the thread is for one of the caliper slide pins.  I reckon I need to drill out to a size around 1.25mm less than the total diameter of the helicoil, then tap out to suit.  Of course, getting the kit means that one doesn't need to think about all this.  On the other hand, if I knew the drill diameter and tap diameter, I could use what I have.

The only drawback is that I think helicoil use a special tap which accommodates their inserts, although I have managed to get the inserts into threads I've cut myself??

I think using threaded inserts may be no go as I think they need larger holes (not sure).  I don't have loads of metal to work with, so helicoil seems favourite at present.

Cheers guys

[muskrat]

G'day Worty.
M9 is a weird size!
https://www.threadtoolsupply.com/m9x125-helical-insert-repair-kit.html
Helicoils need their special tap. So to get the original thread back the drill would need to be slightly bigger at 3/8" and at a guess the tap would be m11x1.25 so is a special tap for that helicoil. Not one you can buy at the local hardware store.
Cheers

[berger]

worty have you thought about scrap yard for a replacement part? before spending on things you will use once ---- AGAIN

[groily]

Not sure how little material there is there worty - you say there's not much.
But  . . . the hole diameter for the 9mm thread would have been 7.8mm and the tpi is close to 20.
If there is the surrounding material, possibly drill to 8.3mm and tap with a bog standard 3/8" x 20 BSF tap? That would mean the plain hole being 0.5mm /20 thou oversize.
Major thread diameter of 9mm is 0.354"; 3/8" is 0.375".
So there's really not a lot in it, and maybe no more metal lost than if drilling oversize for a helicoil (although I haven't checked Morris' link for the exact specs of the 9mm helicoil tap etc.)
Just a thought, anyway  . . .

[berger]

worty as i understand this you are wanting to thread a hole in a brake caliper for one of the pins that it slides on?? if so you have to be 100 % accurate with this threading job. even if it isn't this you still have to be 100% accurate , how are you going to set it up to drill it?

[Rex]

Just to reiterate, the Helicoil kit contains the necessary drill bit and tap to reclaim the thread.
There is no "I could use what I've got" in regard to the tap required.
One thing I've learnt over the years is to always use a pillar drill if at all possible, and with the piece securely fixed to the table.
My now-departed Sunbeam S8 sump plate had had the studs Helicoiled free-hand, and they were as crooked as a red-neck's teeth.

[Swarfcut]

  Worty. Got to thinking more about this conundrum. If it's the hub thread for the caliper sliding pins, this is one repair that needs to be 100% accurate to ensure the  pins are parallel and the caliper will slide. Assuming here the pins stay in place, caliper slides  on the pins.

 But on a safety note, far better to replace the hub carrier for peace of mind. I know it is only a pulled thread, but it has probably the most important job and as such not to be trifled with. Even if anyone can offer a repair, the hub carrier will have to come off to ensure accuracy...hand held won't do..... and at that stage you're more than half way labour wise to fitting an undamaged replacement.

 Those pins are usually pretty tight, and usually sealed with locking compound. In the future, removal of the pins for maintenance will most likely bring out the helicoil and the process will have to be repeated...more expense.

 Swarfy.

[Worty]

Thanks all.  I do have a pillar drill so would use that if needed.  As for the other comments, all points taken.  The carrier is a spare I bought from a scrappy for £20.  It cleaned up well and came with a decent bearing, it's just one of the pin slider threads that's a bit iffy.  I reckon I have about 60% thread on one, and 90% on the other.  I reckon I should test the pin in both to see if it torques up prior to drilling out anything.

The idea  of getting a  couple of hubs was to clean up in preparation for replacing the front wheel bearings - which are a bolt on affair.  Because the bolts are awkward and tought to get out, and awkward to clean the bearing housing.  The idea was to whip of the old hub and shove the replacement on with the bearing all set up.   I know this may sound a bit unnecessary to some, but we need the car every day so repair time/cost needs to be kept to a minimum.  Incidentally, the new shafts seem to be fine, and no need for wheel alignment either.

[ellis]

Hi wortluck,
You need to buy yourself a ZEUS precision book.
Buck & Hickman Ltd sell them in the UK.

ELLIS

[Triton Thrasher]

Hi wortluck,
You need to buy yourself a ZEUS precision book.
Buck & Hickman Ltd sell them in the UK.

ELLIS

http://www.moonshiners.org.uk/MZ/zeus.pdf

[Lone Wolf]

Hi wortluck,

http://www.moonshiners.org.uk/MZ/zeus.pdf

Wotcha.

I'd forgotten all about that.