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HT bolt mod safe?
goodguydrew - 11/2/11 at 11:15 AM

Is it safe to extend to thread length of a high tensile bolt?
I was thinking i could do this to make a replacement disc to hub bolt for a std mk4 cortina caliper.
If anyone has a single bolt I would be grateful.
I have a picture of the missing bolt in my photo archive.
Thanks.

[Edited on 11/2/11 by goodguydrew]

mcerd1 - 11/2/11 at 11:24 AM

a standard HSS die might not cut it - can you not get a fully threaded bolt (/setscrew)


or whats the spec of the bolt ?
(i.e. - dia, pitch, total length, thread length and grade)

designer - 11/2/11 at 12:12 PM

Any bolt should never have their thread extended.

Quality bolts have their threads rolled, cutting causes stress raisers.

Mr Whippy - 11/2/11 at 12:33 PM

you should replace it with a longer one

there are many online bolt suppliers who will be able to send you one, usually next day

goodguydrew - 11/2/11 at 01:07 PM

Thanks for the advice.

I need an M10, shank length 25mm, thread length 19mm.
15mm across the hex head flats.
High tensile.

britishtrident - 11/2/11 at 02:18 PM

quote:
Originally posted by designer
Any bolt should never have their thread extended.

Quality bolts have their threads rolled, cutting causes stress raisers.


In automotive application rolled threads are only used in very few instances, apart from Escort Mk2 track rods the big exception was the old Rolls-Royce company who specified rolled threads for every bolt and stud. Aapart from the strength considerations anyone working on one of these cars one could appreciate the difference when the time came to remove any part, 99 times out of 100 a bolt with a rolled thread will not be seized in no matter how long it has been in place, even the bolts holding the exhaust manifolds in place on an 25 year old Silver Shadow engine.

[Edited on 11/2/11 by britishtrident]

blakep82 - 11/2/11 at 02:23 PM

i forget how it works with bolts, but theres a particular sort of 'formula' for thread and shank lengths. i think its something like 1 third of the lenth threaded, 2 thirds unthreaded, or the other way around.

either way, contact your chosen supplier and ask them for one with the required unthreaded length, then you can shorten it, but i wouldn't extend

britishtrident - 11/2/11 at 07:07 PM

Reality Check Guys



Set Screw


[Edited on 11/2/11 by britishtrident]

mcerd1 - 11/2/11 at 07:20 PM

quote:
Originally posted by goodguydrew
Thanks for the advice.

I need an M10, shank length 25mm, thread length 19mm.
15mm across the hex head flats.
High tensile.


is Grade 8.8 enough or are the rest all 10.9's ?

an M10x25 setscrew is common in 8.8 = linky
(not sure about the head size, but if you were worried about it affecting the balance you could always buy a whole set )

[Edited on 11/2/2011 by mcerd1]

goodguydrew - 11/2/11 at 08:16 PM

It should be a 10.9, thats what it says on the head. Initially I didn't realise that was the strength spec.
I bought an 8.8 set screw of the right length, but thought the lack of unthreaded shank might be an issue, as it could be taking a large side loading.

britishtrident - 11/2/11 at 09:00 PM

quote:
Originally posted by goodguydrew
It should be a 10.9, thats what it says on the head. Initially I didn't realise that was the strength spec.
I bought an 8.8 set screw of the right length, but thought the lack of unthreaded shank might be an issue, as it could be taking a large side loading.



If the bolts are tight theyaren't really loaded in shear, it is the friction between the surfaces that transmits the torque.

mcerd1 - 11/2/11 at 11:33 PM

10.9 is probably OTT (ford use them on almost everything...)

but you can get them if it would make you any happier or failing that you can easy get 12.9 (even stronger) fully theaded ones if you look for ones with allen key heads (normally called 'socket cap heads' or 'cap heads' if your searching for them)

(if your really stuck I can ask our supplier, but they won't be cheap unless you want hundreds of them )

[Edited on 11/2/2011 by mcerd1]