ER16 collet nut modification

[old martParticipant @oldmart]

I got an er16 plate for the model club Emco SL1000 lathe and it came with a nut which takes a 25mm spanner. I have investigated the possibilities of getting a UM style nut, but find that the threads are different. The one I bought has M22 X 1.5 and the UM use M19 x 1 threads. I recon there is enough meat in the standard nuts for changing them into UM type even though the thread is larger. The part where the UM spanner fits is not over the threads, but over the collet holding area which is identical. The diameter at the thread end will have to be left larger than a UM nut.

What do you think?

[JasonBModerator @jasonb]

Sounds like you are looking at mini or slimline nuts if they are M19. You can get the UM style nuts for standard ER 16 collet holder threads too

https://www.cutwel.co.uk/catalogsearch/result/?q=er16+collet+nut

[Peter Cook 6Participant @petercook6]

What is the issue with using a 25mm open spanner? Overall nut size is not that much different, and the UM style needs clearance between the face of the nut and the thing being held, while the 25mm open ended doesn’t.

I use ER16 collets to hold wheels and arbours when working  on clocks. With 25mm (A type ) nuts I can position the wheels tight against the face of the collet/nut. With typical UM I would have to leave spanner clearance, although a C spanner* could solve the problem.

*Something else for the workshop gremlins to “borrow”.

[bernard towersParticipant @bernardtowers37738]

Yes Peter the collet nut is handy for that and I made a slim half hex spanner to nip mine up, well worth the effort.

[JasonBModerator @jasonb]

On the odd occasion that I use my ER 32 in my 5C adaptor I have often thought it would be nice to have the nose of the nut as small as possible and move the hex, UM or whatever further back over the thread as you can then get in with things like hand gravers without adding hand grazes as well.

So in this case you could turn off the hex and add something to the outside of the threaded portion to take your spanner/tommy bar of choice. Or make it a bit larger and then you can just tighten by hand rather than play search the spanner

[martin haysomParticipant @martinhaysom48469]

i machined flats on a ER20 nut.

[old martParticipant @oldmart]

I am beginning to have second thoughts about the mod, the main benefit would be the spanner size. I have just found a Rolls Royce spanner exactly the right size made from a flat sheet of 1/8″ stainless steel plate. For er16 collets it is overkill, but could be cut down considerably and I have two nuts with the hexagon end. The 3mm greater thread diameter would still make any castellated nut unavoidably bigger.

The UM castellated nut that Cutwel sells needs a larger spanner than the mini type and is an expensive industrial quality, together they cost more than I am willing to pay.

[Peter Cook 6Participant @petercook6]

My Taig ER headstock came with a spanner like this one from Shop-APT. It’s about 1/8″ thick. It works just fine – especially with ball bearing nuts.

[old martParticipant @oldmart]

The RR spanner which I found looks the same shape as the APT one, the advantage of having a workshop in a museum full of donated goodies, it does look huge beside a tiny lathe. I did not know there were two versions of the er16 collet holders, and have not seen any plate mounted version with the fine threads, the 45mm diameter one that I bought suits the little lathe.

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