High Tensile Steel Question

[Les RileyParticipant @lesriley75593]

New thread about my steel question.

I have to make some special bolts to hold the balance weights on my 6" traction engine crankshaft. The drawing says to use "High Tensile Steel". Normally in this situation I machine down some tensile bolts. However, this time the shape of these bolts is outside the scope of modifying an existing bolt. I will have to start with some steel stock.

Photo of crank drawing with bolts bottom right.

Les

[Les RileyParticipant @lesriley75593]

[duncan webster 1Participant @duncanwebster1]

So come on you 3d cad men, save me some tedious sums and work out the mass and cg of the balance weights

[Michael GilliganParticipant @michaelgilligan61133]

Car axles were once the preferred ‘make-from’ material … but scrapyards aren’t what they once were

MichaelG.

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Edit: __ alternatively, here’s an ebay listing with two grades in various sizes:

https://www.ebay.co.uk/itm/222987908510

Edited By Michael Gilligan on 26/12/2022 22:56:55

[duncan webster 1Participant @duncanwebster1]

Posted by duncan webster on 26/12/2022 22:47:00:

So come on you 3d cad men, save me some tedious sums and work out the mass and cg of the balance weights

Don't worry about the holes, they will be full of bolt.

[duncan webster 1Participant @duncanwebster1]

Or just use m12 capheads

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 26/12/2022 23:09:33:

Or just use m12 capheads

.

I presumed that Les wanted/needed the square on the head … I suppose he could make adapters and fix them with Loctite 638 or similar.

MichaelG.

.

Edited By Michael Gilligan on 27/12/2022 00:23:36

[JasonBModerator @jasonb]

Can't you just get a bolt who's shank is large enough to get the biggest diameter out of and cut the whole thing from that, square head and all. If you want a spec then EN19 or 24 should be OK

Though as these bolts usually had the hole filled with lead afterwards you could just use cap heads and fill with soft solder or JBweld for a similar flush finish. Also a lot easier to do up than trying to get to those square heads. 

Edited By JasonB on 27/12/2022 07:08:31

[JasonBModerator @jasonb]

Duncan, us CAD users need a drawing where we can read the dimensions, I don't think any CAD system can second guess it.

Also what to do about the part of the hole not filled with bolt but possibly lead

[David George 1Participant @davidgeorge1]

EN16T is the correct steel for high tensile bolts. You can get a meter length for around £25.00 delivered price. It machines well but use a tool with a small radius so you don't cause sharp corner fracture points.

David

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 27/12/2022 07:03:29:

Can't you just get a bolt who's shank is large enough to get the biggest diameter out of and cut the whole thing from that, square head and all. […]

.

Squinting at the image … I think that would require Qty.8 … 3/4” high-tensile bolts

Starts to look like an expensive little job

MichaelG.

[JasonBModerator @jasonb]

Michael Couple of M20 x 300 bolts should not be too expensive, certainly less than David's EN16

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 27/12/2022 07:55:06:

Michael Couple of M20 x 300 bolts should not be too expensive, certainly less than David's EN16

.

I had no idea they could be so inexpensive, Jason … or that 8.8 qualified as high-tensile

… must admit, I was thinking in terms of 12.9 cap-heads !!

MichaelG.

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https://www.westfieldfasteners.co.uk/BO_ScrewBolt_Unbrako_SHCap_M20.html

Edited By Michael Gilligan on 27/12/2022 08:31:08

[DC31kParticipant @dc31k]

Posted by JasonB on 27/12/2022 07:55:06:

Couple of M20 x 300 bolts should not be too expensive…

I think the smallest single item his required bolts will fit into is M20 x 120 (74mm plain shank, 12.5mm head). In single item quantities from Orbital Fasteners, they are £1.94 each. Box of 10, £12.94. That might be more post-friendly than longer items.

It would be interesting to work out the best combination of standard bolts which would produce what he wants: eight 'blanks' which give one bolt each or fewer blanks which have more than onen bolt inside them.

With shorter blanks, you can chuck on the threaded part of the parent item. With a longer blank, you can only do this once, so some of your stock is wasted. With the 300mm long item, the unthreaded length is 255mm, so with some considerable head scratching you might get four finished items out of one bolt. Orbital list these at over £7 each, so two bolts already exceeds the box cost above.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 27/12/2022 08:12:17:

[…]

… or that 8.8 qualified as high-tensile

.

Let me re-phrase that, for clarity:

… or that 8.8 would qualify as ‘high-tensile’ in an application like this

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, these two scans may be of interest to you, scan 1 scan 2

Regards Nick.

[Les RileyParticipant @lesriley75593]

Thanks for the replies.

Normally I would use cap heads but the square heads are very visible and in this case not easy to fake. Plus I don't want the rivet counters to get me!

I think the 3/4" dimension is an error. I think it should be 3/8" square with 11/16" diameter head.

I am tempted to go for the M20 by 120mm solution.

The square heads are easy for me as I have CNC mills.

Edited By Les Riley on 27/12/2022 09:16:48

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Nick

Not sure if you saw my last post, but I felt the need to clarify what I had written before

… in the context of the job Les is doing, I would feel uncomfortable using the low-end of the “high-tensile” spectrum.

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi MichaelG, I didn't see your post until after I posted mine. When high tensile bolts are specified on drawings, the grade should really be quoted, because as can be seen in my scan 1, there is a fair bit of difference of strength between them.

Regards Nick.

[DC31kParticipant @dc31k]

Posted by Les Riley on 27/12/2022 09:16:04:

I am tempted to go for the M20 by 120mm solution.

It is only the 11/16" part that necessitates M20. If it would work with 5/8", M16 bolts could be used.

You might be able to forge the head of a standard M16 bolt (volume = 24mm af hexagon x 10mm long) to make it smaller but longer to accommodate say 3/4" diameter x 3/4" long.

[JasonBModerator @jasonb]

Well until Duncan can work out the forces we won't really know what strength fixing is required but having seen many a model traction engine balance weight held on with mild steel straps with mild steel threaded extensions welded or silver soldered into place I would think 8.8 is fine.

You can also get those bolts in 400mm lengths which will comfortably give you your 8 parts for about £1 more each

If the thread is given as 7/16" Whit or M12 then the OD of the flange must be more than 11/16"

[Michael GilliganParticipant @michaelgilligan61133]

Thanks again, Nick

Yes, we’re on the same page

In the vibration test facility, we used to consider 8.8 as more of a ‘warning mark’ than a ‘claim to fame’

… it does have better tensile performance than Wensleydale though

MichaelG.

[noel shelleyParticipant @noelshelley55608]

I have a stock of m20 and m24 about 200mm long in 8.8 if that's any help ? Noel.

[Dave HalfordParticipant @davehalford22513]

Perhaps given the scale and unknown tightening torque required might this thread be better posted on the Traction Talk forum where the bigger engines live?

To me high tensile means rolled threads not cut and a requirement for a specific tightening torque.

[Tim StevensParticipant @timstevens64731]

This problem can be boiled down to three questions:

1. What tensile strength is required to resist the radial force from the rotating weight at max rpm, times the relevant safety factor?

2. What shear strength is required in the square heads to resist the required tightening torque? Bearing in mind that an increase in torque (to meet the need in 1) means a reduction in tensile reserve.

3. Does it matter what the bolts look like in detail? ie: would a hex socket serve? Or could the square heads be a bit bigger?

Which all depends on – for 1 – what the max rpm is, and how accurately and how permanently controlled this is, and what is the proper factor? And for 2 – What size spanners are carried with the vehicle, and is there a way to check torque with the size selected?

And a further factor: Off the shelf high tensile bolts tend to be much more reliable than home made fittings.

My guess is that at the rpm at which small steam engines run, the answers are not super-critical. But it also depends on what (if anything) surrounds the rotating crank, and how strong it might be to stop a flying bolt should the worst happen.

Cheers, Tim

 

Edited By Tim Stevens on 27/12/2022 12:14:00

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