Helicoil taps?

[Lakc]

I need to install one helicoil insert for a m10x1.5 thread. Mcmaster wants $20 for the tap. I see they list 12.5mm as outside diameter for the helicoil.
Is there anything special about the tap where I couldnt reproduce it? I can probably make a 12.5x1.5 homemade tap on my lathe, or 1/2x17tpi for that matter. Is there possibly some mystery outer diameter dimension to the tap that is critical?

 

[IronHorse]

The way I understand it, the taps are custom sized for the insert. I have had success with the Import/NoName type of repair kits, and they are a lot cheaper

 

[doc1955]

If you have room you could use a thin wall keensert they use standard tap sizes.
http://www.carrlane.com/Catalog/index.cfm/28025071F0B221118070C1C513E111D081B0006280B1713050245221E0107070F1A3C3B28535246595B

 

[Blogwitch]

Jeff,

After fitting thousands of inserts in my time, I can assure you that the tap is not a standard.

The pitch or TPI remains the same as the original size, but the OD can vary, even between manufacturers, as they all seem to want to sell their own inserts. They vary sometimes on the thickness of the insert threads.

If you want to try to make your own tap, first screw a bolt of the correct size into the insert, then very carefully measure the OD of the insert, and cut the thread crest of the tap to that figure, but the pitch or TPI to the original sized hole. I have never done it myself, but I see no reason why that shouldn't work.


Bogs

 

[Lakc]

After fitting thousands of inserts in my time, I can assure you that the tap is not a standard.

The way I understand it, the taps are custom sized for the insert. I have had success with the Import/NoName type of repair kits, and they are a lot cheaper

Thanks folks, that's what I was afraid of. Good idea on the measuring there Bogs, I will have to keep that in mind.

If you have room you could use a thin wall keensert they use standard tap sizes.

I do not know if I have room, but that's a lot cheaper plan then the helicoil, and only about .1" larger. Thanks!

 

[Ned Ludd]

Hi Guys,
If I might add a small fly in the ointment to Bogs' tip, Helicoil coils are larger than the threaded hole they are designed to fit. This oversize, or spring, is what is meant to hold them in the workpiece. I feel measuring might be a problem, while holding the coil compressed enough for a true size to be measured.

If I might a Helicoil tip of my own, increase the size of the "nick" at the point where the tag is meant to break. So often the tag does not break cleanly and jams on the bolt when you later try to unscrew it.

Another tip is to make your own coil inserting tool from a bolt of the right size, rather than using the standard forked tool. If you are not careful, using the standard inserter allows the coil to jump a thread, but using a tool with a thread on it prevents this from happening. To make your own inserter, file the end of the bolt to just over the diameter by one pitch deep. Wind a coil on and see where any corner rounding is necessary to catch the tag. I have to admit that I haven't fitted any Helicoils for more than 10 years, so this tool might now be the standard, in which case please ignore the above.
Ned