Treads on 1/8″ rod

[malcolm hollinsParticipant @malcolmhollins96641]

I am making a pair of adjustable conrods so that I can get a pair of wheels to turn freely/

I want to have different threads per inch on either end of the 1/8" rod..

This is so that the conrod length can be adjusted and the end that go onto the conrod pins on the wheels are square on the pins.

I have taps and dies for B.A. , BSF , BSW, Metric, UNC and UNF.

My Engineers Black Book lists all the tap and die sizes but I do not seem to find what size of rod is used for the dies.

Which pair of dies should I use?

[malcolm hollinsParticipant @malcolmhollins96641]

What threads and their size can I thread on a 1/8″ rod

[Mike PooleParticipant @mikepoole82104]

5BA is handy for 1/8” rod, the other thread series should be as sized, a 1/8BSW die should thread a 1/8” rod. There is some value in reducing the rod by a few thou as the thread profiles are either slightly truncated or in case of BSW and BSF and BA a small radius is at the root and crown of the thread.

Mike

[malcolm hollinsParticipant @malcolmhollins96641]

Thanks for your swift reply.

It looks like from the information you provided I need to look at The Basic Major Diameter for the Rod Size in my Engineers Black Book

[malcolm hollinsParticipant @malcolmhollins96641]

With the information I have I now I know the tpi of 3mm coarse, 3mm fine, 3mm special pitches,UNC #5, UNF #5, BA #5 and BSW 1/8".

I now can get on making the conrods.

[Howard LewisParticipant @howardlewis46836]

The easy was would seem to be to put 1/8 threasds on 1/8" rod.

To give an adjustable length, you either need Right and Left had threads on each end, or by putting 1/8 BSW 40 tpi on one end,and something different on the other end to get a differential thread effect, to allow adjustment.

Neither Zeus nor Tubal Cain quote 1/8 BSF, although Tracy Tools offer 1/8 BSF 44 tpi Taps and Dies.

Another approach, if you have the appropriate Taps and Dies available would be 5 BA giving 43.1 tpi with the thread a thou undersize, or 5 – 44 ANF, o r to turn down to 3 mm . The 0.5mm pitch gives 50.8 tpi.

HTH

Howard

[Anonymous]

Posted by Howard Lewis on 24/08/2022 21:45:19:

…… Tracy Tools offer 1/8 BSF 44 tpi Taps and Dies.

…. as well as 1/8 UNC/UNF in RH and LH

[File HandleParticipant @filehandle]

Malcolm you might find this useful:
https://pages.cs.wisc.edu/~bolo/workshop/thread.html

Keith

[Mike PooleParticipant @mikepoole82104]

I think when BSF was standardised is was expected to use BA for sizes below 1/4”, British engineering seem to use this in practice. America use the numbered series for UNF and UNC for sizes below a 1/4” and the British car and motorcycle industry adopted these threads in the 1960s but they had hardly converted and metric was decided on.

Mike

[SillyOldDufferModerator @sillyoldduffer]

BA isn't a good choice for this because it doesn't have fine and coarse thread ranges. 5BA is close enough to 1/8" and 43tpi.

Threading BSW on one end and BSF on the other would work except BSW doesn't go down to 1/8", and if it did I fear the thread would be too coarse. BSF in 1/8" diameter is exotic.

US Threads 5-40 (UNC) and 5-44 (UNF) might do: #5 is 0.125" with 40 coarse and 44 fine threads

Same idea with Metric M3 coarse (pitch 0.5) and M3 fine (p=0.35), but 3mm rod is thinner than 1/8" (3.2mm) if that matters. If fatter than 1/8" is acceptable, M3.5 coarse is p=0.6 and M3.5 fine is p=0.35.

Presumably the idea of using two different threads is to exploit the difference to get an extra fine adjustment? My tired brain remembers the method exists, but not what the rules are. For example would 1 tpi difference (5BA and #5-44) be more or less suitable than the 4 tpi difference between #5-40 and #5-44?

Dave

[Mike PooleParticipant @mikepoole82104]

Whitworth did go down to 1/8”, I have a tap inherited from my father 1/8”BSW x40tpi. BSF stopped at 1/4” but it seems that taps do exist which are either not standard or maybe the standard included them as non preferred sizes. My father gave up toolmaking in 1952 when recalled to the RAF so the tap is rather a vintage item.

Mike

[Graham MeekParticipant @grahammeek88282]

Posted by SillyOldDuffer on 26/08/2022 09:44:26:

Presumably the idea of using two different threads is to exploit the difference to get an extra fine adjustment? My tired brain remembers the method exists, but not what the rules are.

Dave

The idea is called the differential screw thread. If you have two pitches which differ by 0,05 mm ie 0.7 & 0.75 mm then one full turn of the threaded items will advance 0.05 mm. One thread is in a static member and one thread is in the sliding member.

I used this method successfully in a Micrometer Box Turning Tool recently described in Home Sop Machinist. This is used to run down long lengths of small diameter material in the lathe. (I have not listed a photo as I did not want to change the topic).

Regards

Gray,

[DC31kParticipant @dc31k]

Posted by Graham Meek on 26/08/2022 10:42:57:

The idea is called the differential screw thread.

The other useful property of a differential thread is a huge mechanical advantage.

Chinese windlass and differential hoist are closely related items.

[Howard LewisParticipant @howardlewis46836]

S O D,

Sorry but 1/8 BSW does exist. I have a bag almost full, of such screws and nuts.

My suggestion of using different pitch threads on each end (Failing the availability of left hand threading tackle ) was to produce differential threads to provide, effectively, a vernier adjustment for length.

i.e Uscrewing one turn of 1/8 BSW moves the rod 1/40 of an inch Outwards, while the 5BA at the other end moves whatever is attached to it, 1/43 of an inch Inwards.

This will provide a fine adjustment of length. Which is what I imagined the OP wanted..

I don't think that the 5BA thread being 0.001" undersize will matter very much.

Howard

[DC31kParticipant @dc31k]

Posted by Howard Lewis on 26/08/2022 11:58:43:

Unscrewing one turn of 1/8 BSW moves the rod 1/40 of an inch Outwards, while the 5BA at the other end moves whatever is attached to it, 1/43 of an inch inwards.

And if you want even finer control, use the 44tpi UN thread with the 5BA, so you see the difference between 1/44 and 1/43.1

If you work out that thread advance in terms of tpi, it is so fine as to be nearly uncuttable

That is the benefit of the differential system: you could use standard coarse M10 and M12 to get 0.25mm advance per turn but at a diameter that will take considerable load.

[File HandleParticipant @filehandle]

Posted by Mike Poole on 26/08/2022 10:16:54:

Whitworth did go down to 1/8”, I have a tap inherited from my father 1/8”BSW x40tpi. BSF stopped at 1/4” but it seems that taps do exist which are either not standard or maybe the standard included them as non preferred sizes. My father gave up toolmaking in 1952 when recalled to the RAF so the tap is rather a vintage item.

Mike

Mine go down to 1/8", but you can buy them down to 1/16".

[malcolm hollinsParticipant @malcolmhollins96641]

Hi Every body

In stead of tapping the ends of the conrods I drilled them out to 9/64" and drilled and tapped 2 x 3mm grub screw holes. using the original conrods to get the approximate size between the their centers I cut down the 1/8" rod so that the wheels would rotate O.K

Now all 4 wheels rotate without binding

I think I now have Conrods on both wheels that I can made solid conrods that will work.

[Graham MeekParticipant @grahammeek88282]

Posted by DC31k on 26/08/2022 11:22:30:

Posted by Graham Meek on 26/08/2022 10:42:57:

The idea is called the differential screw thread.

The other useful property of a differential thread is a huge mechanical advantage.

Chinese windlass and differential hoist are closely related items.

Now that the post seems to be concluded I thought I would add another use of the differential thread principle that I used on my Squeeze riveter.

I wont bore you with why I chose the screw thread over the more conventional lever, but below is a close up of the working part.

The reader will clearly see the two different sizes of screw thread used. Below is the results on my Clayton Timber Wagon chassis.

If a torque wrench is used the tool gives extremely good and consistent results. There are a couple of more photographs in "My Album".

Regards

Gray,

[Author]

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