metric thread questions

[fcheslop]

Coffee machines including Italian also have the odd imperial thread
I worked for some of the larger European Coffee houses for many years as a service engineer mainly traditional and bean to cup and still have the fault codes if anyone should need the info although they are mainly Italian Iv a few Swiss and German. Although I always liked the Cimbali the best
cheers

 

[fcheslop]

And I only though Jura made whisky small wonder they got confused to much of the angels share
cheers Norm

 

[rodw]

I'm not looking forward to cutting a M10 x 0.9 to repair a coffee machine at the moment.

Well I stand corrected. I took my problem part to get some ideas from a mate. It turned out to be a 1/4" BSP parallel thread. So all I have to do is to slightly modify a commercial pipe fitting and silver solder it on! Very happy that a $5.50 fitting and 10 minutes on the lathe will do exactly what I want to achieve.

 

[rodw]

And besides being quite expensive, except in some very specific conditions the small increments are not necessary as the strength of the thread can be nearly the same with less engagement. That is, a hole drilled a small amount bigger than optimal may yield nearly the same strength but will be a great amount easier to tap. After breaking a few of my smaller taps using the correct drill size, I've started using a slightly bigger one and quit breaking taps yet get acceptable strength for the application.

If you measure a commercial fastener say M8,M10 or M12 you will find the diameter is around 0.2mm less than the quoted size. I think if you look at the appropriate ISO standard for bolts, this is expected.

So these days, I always make sure something is under or oversiszed, particularly when cutting an external thread.

 

[goldstar31]

Somewhere here Rod quoted an odd 13mm and if you 'crunch' the conversion to 'imperial' it becomes the old 1/2".

I'm one of the Old School with a sliderule( mine was a double logarithmic scale) and I did Trachtenburg maths as a 'kiddie winkie' during the war.

If you think 'war' there were TWO metric scales- one French, one German and of course, France was overrun in 1940.

Of course, I owned French and Spanish property- well, Catalan. The latter is a bit -err fractious at this time.

N

 

[joco-nz]

If you measure a commercial fastener say M8,M10 or M12 you will find the diameter is around 0.2mm less than the quoted size. I think if you look at the appropriate ISO standard for bolts, this is expected.

So these days, I always make sure something is under or oversiszed, particularly when cutting an external thread.

One of the joys of cutting metric threads (same issue for Imperial?) is not being able to start at say 10mm for an M10, single point thread it and end up with something that fits. Cose it won't.

I've been using this site to work out correct major diameter and thread depth to get a threaded part that works: http://www.amesweb.info/Screws/IsoMetricScrewThread.aspx
Or I "cheat" and run a die as a chaser over it once mostly done. :thumbup:

Having made quite a few M10x1 parts recently I'm starting to get vaguely proficient. Of course a metric pitch lead screw on the lathe makes it somewhat easier, well unless you have a dog-clutch linked to your lathe lead screw. Ahh what a bonus that would be.

 

[Wizard69]

One of the joys of cutting metric threads (same issue for Imperial?) is not being able to start at say 10mm for an M10, single point thread it and end up with something that fits. Cose it won't.



I've been using this site to work out correct major diameter and thread depth to get a threaded part that works: http://www.amesweb.info/Screws/IsoMetricScrewThread.aspx

It isn't just metric as most thread forms are specified to have a major diameter slightly less than nominal on the external. You have to make clearances someplace or things wont screw together. So yeah unified threads are the same thing.

By the way i say Unified Threads because almost everything these days, in the USA anyways, is based on this standardization. That would be since WW2 when unified threads came about. The unification was negotiated between the USA, Great Britain and some other countries to deal with supply compatibility issues during the war.

From my standpoint imperial threads would be everything in common use before WW2 and unification.

Or I "cheat" and run a die as a chaser over it once mostly done. :thumbup:

I do this a lot at work. That work is automation maintenance and sometimes getting the machine running is far more important than perfect threads. A die will also clean up the threads a bit in hard to machine materials.

Having made quite a few M10x1 parts recently I'm starting to get vaguely proficient. Of course a metric pitch lead screw on the lathe makes it somewhat easier, well unless you have a dog-clutch linked to your lathe lead screw. Ahh what a bonus that would be.

One interesting comment that i heard years ago is that unified threads and the various pitches appeared to be designed for cutting on a lathe. This might be why unified threads have taken so long to die in the USA.

Another thing people might not know is that unified threads also specified screws for instrumentation and watch making, these have always been specced in metric.

The more that I've researched things like this the more it has become apparent how dramatically WW2 changed the world. For a guy born in 1960 it isn't obvious but the more you look at the past and the world before and after WW2, you realize just how transformative the war was.