Hello

[numbnuts]

Hi all, from a panelbeater and very amateur engineer.

Could someone please explain to me how to size the threads on a double bulkhead fixed bowden cable. The one on my digger that operates the blade has snapped and I can order an aftermarket one mail order @£15.00 as opposed to £165 + Vat for the genuine one, hence the need for your knowledge please.

Both ends of the cable are symmetrical and have threaded ends taking 8mm nuts and the bulkhead fixings on the cable sleeve take 17mm nuts. I presume that just because the nuts are 8mm and 17mm that does not correspond to any definative sizing of the threads?

Any help much appreciated in layman's term please!


P.S. I should have said that the nut sizes are not necessarily 8mm and 17mm but the size of spanner required to remove them.

[PinkertonD]

Hi and welcome to the forum.

An 8mm wrench (spanner) would be for an M5 thread, as in 5mm diameter.
A 17mm wrench would be for an M10 thread, as in 10mm.

To my knowledge there are no set "standards" for cable end fittings etc. The sizes would probably be defined by the diameter of the actual inner cable and the loads it is expected to control.

An after market cable should do fine providing the cable materials are the same or similar. Inner cables can be steel, stainless steel or synthetic materials such as Nylon. The inner can be many smaller strands twisted together like electrical wire, or it can be a single solid strand, sometimes covered in a Nylon, Teflon or Polypropylene sheath.

If the bulkhead connection is welded or permanently attached to the bulkhead then you will need to match the thread pitch of the original M10. There is a range of pitches possible for the threads of both ends.

The same thread provision applies to the M5 end.

However, if both ends are held in place by nuts either side of a fixed plate with a simple through-hole then just use nuts to suit the threads that come with the after market cable ends.

[numbnuts]

Good Man! Thank you for taking the time and effort to reply. Many thanks.

I believe the after market suppliers offer light, medium, and heavy use cables so will go for medium and use my oiler regularly. All other requirements are sussed. The bulkhead fixings are not so much a problem as access is possible on both sides of each fixing,but it is the cable ends I was more particular about as they screw into olive type fixings and the 8mm nuts are the lock nuts. I did rethread the broken end on the origional cable but because the cable was so seized could not get my oiler onto the cable to free it without breaking it again.

Would I now be correct in thinking that 8mm nut = dia 5mm threaded section and that could be deduced by calipers over the threaded section? I have the TPI from rethreading below the broken section and trying the undamaged nut over my repair attempts and into it's holder.

I'll check back tomorrow as off to work. Many thanks again.

[PinkertonD]

Would I now be correct in thinking that 8mm nut = dia 5mm threaded section and that could be deduced by calipers over the threaded section?

Happy to help.

Yes, the M5 (in this example) diameter is measured with calipers over the outside diameter of the "bolt" portion. The nut across-flat size is never used in conjunction with the fastener itself, only the Spanners.

The nomenclature for Metric bolts is to start with an "M" then follow with the thread diameter, followed by Pitch in Decimal-mm and then length.

M5 x 0.8 x 40

A 5mm outside diameter bolt with 0.8mm Pitch and 40mm long.

[numbnuts]

Again many thanks for the comprehensive answer. I'll recheck the pitch from the die I used on my repair attempt on the undamaged end, and take all the other required measurements. I can now order a cable.

I did do an OND in mech eng about 25 years ago, but after having to get a private tutor to explain things like calculus realised that progressing further might be beyond me.

[PinkertonD]

Again, happy to help. One of my favorite things to bitch and whine about is lack of provided information in requests for assistance. Given that, I am compelled (driven??) to respond with detail.

>> I can now order a cable.

I am going out on a limb here, but your use of "Spanner" suggests you may be in the UK. If so, with the money you save buying the after-market cable, you can buy me a Theakston's the next time I am in town.

Don't count yourself out on Calculus, it is a mystery to most practical minds. I think in 40 years of Engineering I may have had to use Calculus maybe twice. I think it is included (along with Descriptive Geometry) in courses by Sadists in the Engineering Curriculum departments.