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Bolt Material?

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Peter Bell07/12/2017 07:35:50
228 forum posts
111 photos

As part of the ongoing restoration of a 1916 loco I want to get some replacement bolts made to suit various reamed holes to attach the axle horns to the frames. The bolts are around 20mm dia and 30mm long.

Not sure what material to get these bolts machined from but readily available EN8 or EN19t springs to mind. Googling suggests these are suitable.

Can anyone with experience of bolt material/manufacturing confirm our selection or suggest any other readily available alternatives?

Thanks Peter

Chris Evans 607/12/2017 07:44:13
1174 forum posts

EN19T or EN24T should be suitable. This was used a lot by a bolt manufacturing company I worked next door to, I miss being able to scrounge offcuts !

roy entwistle07/12/2017 09:00:23
830 forum posts

Peter If you are in UK a 1916 loco will most likely be imperial


Mick B107/12/2017 09:21:58
494 forum posts
28 photos

EN8 can be difficult to bring to a good finish, and die-cut threads can have a tendency to tear and chip.

Speedy Builder507/12/2017 10:40:30
1470 forum posts
99 photos

Them is dumpy bolts !! Two points, you can buy many of the EN series steel as free machining also in the annealed condition. Both will help you achieve a good thread finish. Do you really need "precision" bolts ? I guess there are M20 bolts threaded all the way to the head which you could "nip" the ends off.

Ian S C07/12/2017 11:57:09
6777 forum posts
224 photos

The M20 bolts are probably 3/4" BSW, if they are going in reamed holes, they should be machined to fit, try and make the right size and form of bolt head, ie, were they square or hex, when you have finished the restoration, even you should not be able to see which bolts are the new ones, even if you have to give the heads a bash with a hammer.

Ian S C

Clive Foster07/12/2017 13:46:15
1317 forum posts
29 photos

Any steel in S or T condition will meet the tensile strength requirements of a grade 5 bolt which is the lower end of the high tensile bolt range. Due to potential crack propagation issues if given the choice I'd choose S condition rather than T and a simpler steel composition with moderate heat treatment.

EN19T is fine if it really is EN19T by both analysis and properties. Might be better to order it by the more modern designation 709 M40 T. Unfortunately at the small quantity and economically priced end of the market it's becoming common to be supplied steel sourced by properties only when buying by EN numbers which can give you a nasty shock when you come to machine it. If making bolts ands similar threaded items you need something which machines nicely at low speeds giving a good finish with unsophisticated tooling. Steels optimised for high speed machining under serious coolant flow or for thread rolling and similar forming applications will not behave well on small lathes even though the basic yield et al specifications are the same as a more suitable steel.

605 M 36 T, the old EN16T, will do the deed too. I'm told it can be found inclusion modified for easy machining which sounds like an advantage for home shop folk. Probably what I shall look for when I need to restock bars for general purpose jobs.

Possibly unreasonably I'm prejudiced against EN24T / 817 M 40. Seems a waste to use such a relatively sophisticated steel composition in T tensile range. Especially when the material is known to be sensitive to heat treatment details leading to occasional, inexplicable, brittle failures. Best reserved for when you want a big chunk of metal in the higher tensile ranges as its ruling section is around double that of 709 M 40, 8" - 250 mm diameter as against 5" - 100 mm in T condition, 1 1/4" - 29 mm diameter against 3/4" - 19 mm diameter in W condition. if you need that quality of steel then you pays the price for the right thing complete with certificates.

Whether any ordinary Model Engineer or Home Shop worker should be involved with anything that needs components made from anything above T range being a whole n'other issue.


duncan webster07/12/2017 16:28:54
1495 forum posts
14 photos

It is impossible to suggest a suitable bolt material without knowing what loading it is going to experience. Yes going for EN19 or similar is playing safe, but it could also be needlesly expensive and that EN8M (free cutting) might well be good enough. Bearing in mind the loco was built in 1916, which at least in the UK was the middle of WW1, I doubt the originals were anything exotic. Can you get a hardness check done on one of the originals, this will give you some idea of what the originals were? You could even machine a tensile test specimen and get a friendly university or test house to do a load test, as it's for a restoration job they might do it for nothing.

I can't help feeling the 30mm long must be a typo!

jimmy b07/12/2017 16:47:47
360 forum posts
21 photos

Possibly not much help, but I use bolts to make bolts, either by turning the thread off, or by turning and threading the plain shank.


Peter Bell07/12/2017 17:32:22
228 forum posts
111 photos

Many thanks for all the help and info, didnt think I would so many considered replies! Yes the 30mm is a typo, they are 57mm long. EN 19 modern equivilant looks the favourite.

Perhaps I'd better explain a little. The loco is a 1916 WW1 Henschel which spent all its life after WW1 in Mozambique at the Sena Sugar plantation and was in use on a seasonal basis until around 1984. During its long active life it was extensivley repaired and welded many times but suffered from bolted components "working loose" and the bolted axle box horns are a good example of this.

The bolts were originally 18mm but we have had to ream the original holes to 3/4", 20mm and 7/8" also weld some depending on wear first, to make them suitable for a fitted bolt. As we need 32 bolts we plan getting a friendly cnc shop to machine them for us. The originals had a large size head and nut , rather like old Whitworth and we want to keep to that style. So these requirements rules out anything off the shelf. hence the question.

Difficult to gauge materials used at the time of the build but the horns and axle boxes appear to be cast steel. Another loco I have worked on which is UK built and 120 years old, also has cast steel axle boxes and connecting rods are like glass but have survived well so I can only think quite a lot was understood about using the correct materials in the right place.


We found this works photo of our loco in a book.


Condition when we bought it, complete but worn out!

frames .jpg

Frames under repair showing the hornes and bolt locations. If you look at the frames carefully some of the welding repairs can be seen.

OldMetaller08/12/2017 08:11:09
136 forum posts
14 photos

Wow! What a great project! I really hope you will keep us up-to-date with your progress!



Howard Lewis08/12/2017 11:00:57
1161 forum posts

Stating the obvious, bolts securing horn guides, and cylinders will need to be fitted, (accurate shank diameter in reamed hole) to prevent the problem that you have of "things working loose". In this day and age, anaerobics on the surfaces, (and possibly on the threads) might well be a useful back up, hopefully, to prevent any movement starting.

As an indication of load capacity, a 1/2" bolt in W range, will go into yield at a tensile load of about 9 tons.


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