Thread Problem and Sizing

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bobte2

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I am in the middle of learning to machine watch parts on a watchmakers lathe. I also have done a little restoration on it since it was old. I am puzzled by one thing I cant seem to figure out. It has some machine plugs in several holes normally used for wire entry. I have been trying to size these things for a while without success. I need both plugs as well as the need to add a wire gland. I have one of the existing plugs only and it measures 15MM in diameter with a thread pitch of 1.5MM. This is very hard to find so I was thinking of just tapping out the holes to a more available size of M16-1.5.
Can you run an M16-1.5 tap through what is probably an M15-1.5 hole and expand it?

One of the reasons I am doing this is to put in a wire gland. You can see it next to the plug in the photo. Funny thing is that gland is an M16-1.5 and it fits fine. But I had purchased some set screws that were M16-1.5 that didnt fit (too tight). So that was weird. The gland wire squeeze side screws in perfectly but that it would be backwards :-(

Any thoughts on this?
 

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I suspect it is an M16 threaded hole that is not to the correct specs since if it was M15, your gland with an OD of 15.6mm would not fit. I think the threads are undersized enough, maybe it was a worn tap, that the undersize gland will fit, but the set screw of the correct size is too large.

What is the ID of the threaded hole? If it is big enough, you might not need to drill it larger and just running a tap in might work.
 
I would really expect these threads to be pipe (conduit) threads since they are being used for wires. We were not told where the lathe was made but if it was made in the USA several years ago I would expect the threads to be imperial.

I do agree that 1.5 mm pitch is not really that close to any standard imperial thread. But I only see about three threads on the part and if you are looking for it to be metric then you could easily pick a metric pitch with just three threads.

By the way, there is a M16 x 1.5 tapered pipe thread.
 

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suitcase said:
I would really expect these threads to be pipe (conduit) threads since they are being used for wires. We were not told where the lathe was made but if it was made in the USA several years ago I would expect the threads to be imperial.

I do agree that 1.5 mm pitch is not really that close to any standard imperial thread. But I only see about three threads on the part and if you are looking for it to be metric then you could easily pick a metric pitch with just three threads.

By the way, there is a M16 x 1.5 tapered pipe thread.
Click to expand...
Understand where you are coming from, but there's quite a bit of daylight between those gauges. Even with 3 threads, there should be practically no daylight. The real world is messier than simple gauges, but the threads are not a match if there's lots of light seen between the teeth.
 
suitcase said:
I would really expect these threads to be pipe (conduit) threads since they are being used for wires.
Click to expand...
Metric cord glands are straight threads, so it is unlikely for these to be tapered if this machine was made overseas in a metric country.

Another option is a PG thread, PG-9 is 15.2 OD and a 1.41mm thread pitch. The thread angle is 80 degrees instead of 60, I have a PG-11 that uses the same thread pitch and it looks to fit closer than the picture above when checked with a 1.5mm gauge.
 
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