Does a particular thread hold better into brass

[Chris TickTockParticipant @christicktock]

on a clock plate sometimes we get a situation where we may need to replace what we call a stud. This (or what I mean) is a round steel arbour screwed into the brass cock plate so only held by one end and usually not under too much stress. However some clocks are old, some made in unknown places and knowing the thread can be very difficult.. So in a hypothetical situation where the existing threads are no good and unknown and with the intent to tap a new thread into the plate the question arising in my mind is:

Does a coarse thread hold in a 1/8 thick brass plate better than a fine one? You get more overlap in a coarse thread but more threads per inch in a finer thread.

Chris

[Chris TickTockParticipant @christicktock]

[Harry WilkesParticipant @harrywilkes58467]

I think I once read that fine threads were stronger than course but more prone to seizing and stripping

H

[not done it yetParticipant @notdoneityet]

Would it not depend on the size of the fixing and the thickness? Also rather depends on what you call a ‘coarse thread’ in a 3.2(?)mm plate. If I were you I would go with what clockmakers have done in the past. No point in trying to re-invent the wheel.

[Chris TickTockParticipant @christicktock]

Posted by not done it yet on 12/01/2020 18:26:45:

Would it not depend on the size of the fixing and the thickness? Also rather depends on what you call a ‘coarse thread’ in a 3.2(?)mm plate. If I were you I would go with what clockmakers have done in the past. No point in trying to re-invent the wheel.

Not always possible as some threads were what they made as there were little if any standards, hence my question if you can't match the thread in a given situation is a finer thread better or worse? a lot of English clockmakers did use BA but again a lot did not.

chris

[Bob StevensonParticipant @bobstevenson13909]

BA was only formulated In 1893 (I think?) so relatively recently in horological terms. It was designed at the behest of the GPO by Mr Lehman who set up it's production by his company Lehman, Archer & lane….horological use came later

 

Before BA, and in the great era of English clockmaking the individual clock makers made up their own 'thread plates' and taps, as did other 'techy' trades such as gunsmiths and silversmiths etc. to make a thread plate you first need to make the taps..one method is to wind wire around a carbon steel pin and then file the outline to give the thread pitch…..then you only need to cut the flutes and harden and temper. This method served the industrial revolution and up to the victorian era.

 

When engineering 'by the seat of your pants' like this you need to be an intuitive worker….in brass one needs to be aware of the softness and keep thread pitch large enough to give strength…..

Edited By Bob Stevenson on 12/01/2020 19:00:42

[Enough!Participant @enough]

Posted by Chris TickTock on 12/01/2020 18:04:01:

Does a coarse thread hold in a 1/8 thick brass plate better than a fine one?

That's pretty much unanswerable, Chris, unless you give the approximate size and pitch of the thread you have in mind.

[SillyOldDufferModerator @sillyoldduffer]

My understanding is that fine threads are always stronger than coarse ones, and that the pitch should increase with diameter (or in imperial tpi should rise with reducing diameter.)

As BA was designed for instrumentation, quite a good guide for clock making. Or if you want to be more modern, the small fine metric threads that replace BA sizes.

Strength isn't the only important characteristic of a thread. In practice fine threads are a pain because they require careful alignment, are more likely to cross-thread, and take longer to tighten and undo. Generally industry prefer to use coarser threads unless there's good reason not too. Clocks are – I think – an example.

At least 3 full turns are needed for a screw to develop full holding power, so fine threads are preferred in plate. (Always exceptions in engineering – self-tapping screws are coarse for another reason – speed.)

Meccano threads are a good example of a very coarse thread (5/32" Whitworth) cleverly used to meet a particular need. Screws in a construction toy needn't be strong and it doesn't matter much if they tend to come loose. At the same time, screws quick and easy for children to assemble and disassemble are advantageous. Otherwise 5/32" BSW is a poor choice for real work, and downright inferior in a clock – the BSW thread is too coarse for that small a diameter.

Dave

[not done it yetParticipant @notdoneityet]

Not always possible as some threads were what they made as there were little if any standards, hence my question if you can't match the thread in a given situation is a finer thread better or worse? a lot of English clockmakers did use BA but again a lot did not.

It has absolutely nothing to do with standards. You can measure what they did. If it has been around for a century, or more, it probably worked!

You could also measure what threads are used in modern clocks – plenty that have been discarded. You could check out clock making books for instructions, even. Clicksprings videos likely hold some very good clues as to types of thread used in different situations.

[vintage engineerParticipant @vintageengineer]

You could use other thread forms, acme, square, buttress or truncated.

[Michael GilliganParticipant @michaelgilligan61133]

Let’s not forget that the BA thread system was ‘inspired by’ [‘though not identical to] the Swiss Thury thread series.

MichaelG.

[roy entwistleParticipant @royentwistle24699]

Vintage engineer On a stud in a 1/8 inch thick brass plate, I doubt it

Roy     

Edited By roy entwistle on 13/01/2020 09:20:18

[Chris TickTockParticipant @christicktock]

Posted by Bob Stevenson on 12/01/2020 18:57:02:

BA was only formulated In 1893 (I think?) so relatively recently in horological terms. It was designed at the behest of the GPO by Mr Lehman who set up it's production by his company Lehman, Archer & lane….horological use came later

Before BA, and in the great era of English clockmaking the individual clock makers made up their own 'thread plates' and taps, as did other 'techy' trades such as gunsmiths and silversmiths etc. to make a thread plate you first need to make the taps..one method is to wind wire around a carbon steel pin and then file the outline to give the thread pitch…..then you only need to cut the flutes and harden and temper. This method served the industrial revolution and up to the victorian era.

When engineering 'by the seat of your pants' like this you need to be an intuitive worker….in brass one needs to be aware of the softness and keep thread pitch large enough to give strength…..

Edited By Bob Stevenson on 12/01/2020 19:00:42

Thanks Bob, you have suggested what i thought might be the case.

Chris

[JAParticipant @ja]

Although this does not really answer the question there is a brass Whitworth thread – Whitworth form and 26 t.p.i. This must not be confused with the much loved British Cycle thread which has a very different thread form. There are also microscope threads (microscopes used to be made of brass) which have Whitworth form with very fine thread pitches.

JA

[Clive HartlandParticipant @clivehartland94829]

Thiis is of interest to me, in my work as an Inst. tech on Theodolites. We had a spate of heads popping off of screws and the investigation found that the materiel was not to spec.

It would seem that the screw thread if subject to high torque will pop off. So, using perhaps a Metric fine thread and not subjecting it to a high closing torque would be fine. I do not see coarse threads in 1/8" brass as stronger than a fine thread. One example is Aluminium used in AFV's where the threads to hold exterior items are drilled to take stainless steel helicoil type fittings locked in placed by driving in pins to stop them unscrewing. I think it depends how often it is intended to overhaul and unscrewing the item, if once in 29,years OK. but if it was once a month then use a helicoil.

[Howard LewisParticipant @howardlewis46836]

A coarse pitch thread in thin material will have minimal thread engagement, (A silly example, but think about 8 tpi in 1/8" plate to get the point )

The British Standard brass is Whit form, and 26 tpi. So this would give 3.25 threads engaged without any chamfers in the plate.

My temptation would be to use ME 40, to get 5 threads engaged, even if they are only 0.016" deep.

For your low stress application this should be adequate without risk of threads stripping bin either part..

Howard

[Chris TickTockParticipant @christicktock]

Thanks Guys,

For what it is worth Cousins sell a replacement stud for longcase clocks. These have a 3BA thread. I am investigating still…and more to the point thinking and reflecting on all the posts.

Chris

[Martin KyteParticipant @martinkyte99762]

Coarse threads for strength fine threads for grip. You have already said it's not under much stress you just dont want it come loose so a fine thread is required.

regards Martin

Edited By Martin Kyte on 13/01/2020 13:28:10

[Chris TickTockParticipant @christicktock]

Update:

My findings with specific use of screwing in a 1inch long stud into a 1/8th thicjk steel plate given a free hand (not trying to keep originality) and baring in mind the stud will be not under a lot of stress / tension:

A finer thread would be better in terms of getting more hold in the thin plate. downside is finer threads may be prone to galling between the steel and brass.

However generally coarse thread should be used on soft materials as the material may not be able to stand the strain. (so don't over tighten a fine thread on brass)

Chris

[Author]

Posts