HeliCoil to make hole smaller? 1

[extrudedfeature]

Hello All,

Ive made a rather stupid and annoying mistake when specifying a tapped hole which should have been M4, but is infact M5. Am I right in thinking I can use a m4 helicoil to reduce the size of the thread. I know this is not the typical use for a helicoil but i'm in need of a solution rather swiftly.

Thanks in advance.

 

[ctopher]

Plug the hole and re-tap.

Chris, CSWA
SolidWorks '15
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[KENAT]

Are you proposing to drop a Heli-Coil insert straight into the M5 hole to end up with an M4 threaded hole? Doesn't that way but quick Google search didn't give a simple answer for me to share.

Or are you proposing drilling & re-tapping to accept an M4 helicoil insert?

Not sure typical Heli-Coil will work but there due to the little material you have to remove but there are other types of thread inserts that may.

http://www.mcmaster.com/#standard-threaded-inserts/=zr0mhn

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[JohnRBaker]

NO, that's not going to work. At least not for course Metric threads as the pitch of M5 and M4 threads are NOT the same.

Now what you can try to do is use the Helicoil as it's intended to be used, that is by drilling out the original hole and use THE Helicoil tap to create a new 'threaded' hole to accept the M4 Helicoil, if that's even possible since Helicoils are generally intended to 'repair' a damaged threaded-hole with a LIKE-SIZED THREAD. If you have an M5 threaded hole there may not be enough material left to even allow you to drill and chase a properly-sized threaded-hole for the M4 helicoil insert.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[monkeydog]

I am not familiar with metric threads, so that this with a grain of salt.
Have you looked into "Twinserts"?

http://www.stanleyengineeredfastening.com/sites/

http://www.emhartamericas.com/files/downloads/helicoil-oversize-and-twinsert-inserts.pdf

 

[ornerynorsk]

Use a solid replacement insert instead of a helicoil. More material must be drilled out, which is desirable in your case, and the inserts make use of standard tap sizes, rather than needing to buy a special tap. McMaster Carr, for starters.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[drawoh]

extrudedfeature,

Just for the heck of it once, I tapped a 1/4-20UNC hole, then I re-tapped it and I installed a 10-32UNF helical thread insert. The resulting thread feels fairly strong. On a non-critical application, I might do this.

The solid replacement inserts sound like a good idea. Carr Lane carries them too. You can also search for Keenserts.

--
JHG

 

[NBrink]

For reasons that really don't bear getting into (something, something, something, college student without the right tools for the job), I drove a Volvo for ~100,000 miles with several exhaust header studs going into helicoils.

I wouldn't go closing up an exchanger or anything with them, but they do hold up well...

http://www.linkedin.com/pub/nathan-brink/35/861/18

 

[rb1957]

helicoils, in the right place, for the right reason, are fine. Filling an over-size hole is probably not one of them (good reasons).

Filling a M5 hole and re-tapping for M4 won't leave much material behind (in the filler0.

choices ...
1) live with the M5 bolt (change the mating part), or
2) drill out the M5 hole to something like M8, fill with an interference fit plug, drill and tap.

another day in paradise, or is paradise one day closer ?

 

[RolMec]

I'd ask, at least, and specifically when you're talking bigger numbers.
Boellhoff (OEM of Helicoil, no rel.) does have an option where the thread is cold formed instead of cut. So it might just work if your material allows that and if the forming works and the residual strength after "helicoiling" covers your requirements.
And, somebody manufacturing this kind of thing perhaps has seen the same issue already & could point you towards a solution.
For small numbers, I'd redrill bigger, insert a plug etc as above, by others.
Regards
R.

 

[tbuelna]

I agree with ornerynorsk, use a sufficiently oversize solid key-lock insert and redrill/tap the M4 threads in the insert body. Make sure the insert is large enough in diameter to leave sufficient wall thickness after drilling/tapping the new M4 threads. Also make sure the rework leaves adequate edge margin for your application.

 

[extrudedfeature]

Thanks for all the advice and help on this matter. I eventually gave up on the idea of heli-coils as it became clear this would not work. The solution came in the form of a thread reducing insert provided by a company called memfast.co.uk.

The process involved drilling the hole to 5mmØ, tapping for M6 and and using a 6M/M4 thread reducer with a little thread-lock.

Thanks for all the replies hopefully someone will find the solution helpful.