helicoil use

[treequip]

ooh bugger - i get you CJ

the bolt was (or atleast looks like a 10 mm /m10)

went to 3/8ths as that was what was available in the kit.

 

not much of an engineer i'm afraid so learning by my mistakes.

 

3/8ths but what thread?

[Dean O]

god knows - does it say on the tap?

[C.J]

How about a longer bolt with a new nut behind the captive nut ?

[treequip]

god knows - does it say on the tap?

 

It will be on the helicoil set somewhere, it will say 3/8 followed by bsp/bsf/unc/unf or something like that

[Dean O]

i guess I could find this number out then and take it to a fastners then and still use the helicoil then.

[treequip]

Assuming you have fitted the heicoil any decent engineering factor will provide you a bolt to suit, won’t be his biggest sale of the day though. Take the heliciol kit with you for reference.

[Dean O]

thanks guys

[Treewolf]

The taps for helicoils are "standard" sizes, in that it is possible to go out and buy taps from a variety of manufacturers for threaded inserts, but they are not the same size as the tap that would be used for the same thread if an insert was not being used.

 

The insert taps will be the same thread form and same number of threads per inch as the bolt or screw thread, but will be significantly larger in diameter.

 

Unless the chipper is prehistoric, it is likely that the original bolts (or setscrews) were M10 (which is approx 3/8" diameter). An M10 threaded insert tap will be approximately 11.5mm diameter (the root diameter of the tap will be approximately the outside diameter of the original thread form).

 

If you have used a tap from a 3/8 helicoil kit, although the hole will now be approx 1/2 diameter the number of TPI will correspond with a 3/8" bolt not a 1/2" bolt. Although you haven't stated what thread form you used, in the case of BsW, BSF, UNC, and UNF the threads-per-inch there is a huge difference in TPI between the two sizes - a 1/2 screw simply won't fit.

 

Your only solution is to fit the insert and then get the right sized bolt or setscrew for the insert.

 

It is likely that the tap you used will be marked 3/8" and then the number of TPI. Unless you have got hold of something really freaky (like British Standard Cycle or British Naval threads) it will be one of the following (the numbers are the number of threads per inch for each thread form at 3/8" diameter):-

 

BSW - British Standard Whitworth - 16 TPI

BSF - British Standard Fine series - 20 TPI

UNC - Unified Coarse series - 16 TPI

UNF - Unified Fine series - 24 TPI

 

Note that the BS threads use a 55 degree thread angle and the Unified threads a 60 degree thread angle, and hence they are not interchangeable (if the tap is marked "3/8 - 16" there should be an additional marking to indicate the thread form).

 

If you can read the markings off the tap, check the length of fastener you need and simply ask for the apprioprate fastener (remember a bolt has a blind or unthreaded portion between the head and the thread, a setscrew is threaded throughout its entire length).

 

You may also consider putting some loctite or similar threadlocking compound on the outside of the insert before fitting it. It is not essential but can help avoid dislodging it in future.

[Dean O]

thanks treewolf

popped out today to try and get hold of the right kit to complete the job but couldnt find imperial sizes.

nearest option was m14 fine (for spark plugs)

didnt think it was worth drilling and tapping for m16.

 

ended up buying some m12 threaded bar and drilling stright through the frame and out the other side to get it sorted for monday.

 

but thanks for all the help

[slack ma girdle]

If you can't weld, then look up your local fitter/ agricultral engineer in the yellow pages. You will probably suffer a small amount of scorn/ abuse, but they will be able to explain what you have done wrong and how to fix it. Cost should be minimal, as it will only take a couple of minuites to weld a new nut in place.

Good luck