History of Model Engineering Threads?

[JasonP]

Does anyone know the history of these thread forms? Why they were introduced? What are the advantages / disadvantages? Why use it over BA threads (for <0.25") or Metric?

Thanks,

Jason

[gerritv]

I think there was an article/document produced by ME that went into some of this, will see if I can find a reference.

I do recall reading that more tpi allows for use on thinner sections such as shafts with holes. This is due to reduced thread depth. And the thread depth is constant regardless of diameter, another bonus for counting dial turns for infeed.

an example of where this works well is on the Eureka relieving device, it allowed using a .5" nut on end of shaft while retaining the .500" section for the cutter. (as in the cutter can slide over the nut). Very sturdy threads at 40 tpi.

gerrit

[Jo]

The ME series of threads (26, 32 and 40 tpi) were established by committee of the SMEE in 1912 as the threads of their day were too coarse for making models the only alternative were Instrument makers threads which are 60tpi. The idea being the very fine pitch of 40 tpi allows things to be lined up square on pressure fittings. The 32 is used on coarser kinds of fittings and 26 TPI is used for tools and accessories.

Geo Thomas discussed metricating ME threads back in 1980 in ME and the possible demise of the BA series and alternatives.


Be careful if you go away from the original threads identified on the drawings for any model as future owners may need to replace them and if they try with the wrong type damage is likely to occur.

Jo

[Jasonb]

ME Series is actually only 40 and 32tpi, the 26tpi although used on models is actually BSB (British Standard Brass) which is a constant 26tpi across it's size range.

I'd also say that all are used on models, 26tpi being used on the larger scales and the very large models would then tend to go to BSP, take a look at these water gauges for example where 32 and 26 tpi are available and are fittings you would want to line up.

http://rabarker.co.uk/index.php?main_page=product_info&products_id=5

As Gerrit said their main advantage is that you can put a thread onto something hollow and still have a reasonable ID as the thread depth is quite shallow, still really need copper washers to line things up even with 40tpi

Mainland Europe and some UK builders go with the constant pitch metric threads which offer the same advantages and will typically be 0.5, 0.75 and 1.0mm pitch

[Alex]

"Mainland Europe and some UK builders go with the constant pitch metric threads which offer the same advantages and will typically be 0.5, 0.75 and 1.0mm pitch"

I'm in that camp. I metricated my model-building when living in Mainland Europe. I've continued that tradition over in Canada. I can purchase metric taps and fasteners here locally if I want; BA and ME and all the other older thread pitches have to be ordered from the UK and shipped. (Thanks JasonB for the Kupfer lead, and Gerritv for the one in Holland).

Of course, there's some name-rebranding; IIRC, JIS M1.7 is 10BA, and some other English threads have been brought in under the metric wing.

So, there's my personal "History of Model Engineering Threads". ;-)