Member postings for Nick Edgley

I was considering using my imperial leadscrew and nut but discovered the leadscrew is not the correct one, the length is different. It is most likely a Boxford part but from a different machine.

I have decided to buy a replacement nut from Boxford which is a little irritating having made one but been stymied by my inability to cut the appropriate thread in it and the fact that with postage and VAT it is £83!

What a terrific company Tracy Tools are.

I rang them asking about a tap for my oddball size. They would not commit themselves over the telephone and clearly wanted to measure the item themselves. I sent them both the leadscrew and nut on Thursday last week. I received it back on Tuesday and a telephone call shortly thereafter confirmed the size as 7/16" x 2.5mm ACME. The bad news a tap was going to cost around £300 i.e. a one of specially manufactured tap.

I cannot emphasis how helpful and efficient they have been despite them being unsurprised in not making a sale.

Edited By Nick Edgley on 13/09/2019 00:10:43

I contacted reltub34 via ebay and he quickly replied stating that, as Pete stated, the size is a 7/16" x 2.5mm ACME thread.

My heartfelt thanks for all of the valuable input to help me understand what I had actually got.

Hi Diogenes,

Far from reading as egg sucking instructions I appreciate the detail and the time taken to reply.

Interestingly the measurement of the major diameter is 11mm making the thread 11 x 2.5. Nobody seems to make one of that size!

The replacement part mentioned in the link from Michael Gilligan does appear to be the correct part and I agree it would be cost effective. Having said that I enjoy the challenge and like making things!

Hi Pete,

The size quote in your post above from the ebay seller might just be what I am looking for. I cannot find that seller on ebay, do you have a link I could use?

Mystery is solved!

I carefully read all your very useful suggestions and information.

I drilled and tapped a piece of scrap aluminium and it fitted comfortably on my spare lead screw which confirms that the spare is imperial. I am still a little puzzled that my 7/16" x 10 ACME tap doesn't seem to fit the existing brass nut on this leadscrew.

Using the tip above from Pete Rimmer the measurements he gave confirmed the spare leadscrew as imperial and the one on my lathe with the worn brass nut as metric. This also explains the graduations on the cross slide dial which are numbered 0, 0.5, 1, 1.5, 2.0, 0 with 50 graduations between each number (a total of 250 graduations). Unfortunately I do not have the imperial cross slide dial, only the leadscrew and nut.

What tap do I need to cut a metric thread to match the metric leadscrew? I presume it is a trapezoidal tap but the sizes confuse me and they also seem quite expensive compared with the imperial ACME tap I have already purchased.

Imperial leadscrew (my spare):

Metric leadscrew (in use and worn nut):

Cross slide dial:

Thank you all very much for your rapid and comprehensive replies.

I will need to spend some time investigating all of your suggestions and links. I am away from home until Tuesday but when I get back I will post some comprehensive photographs of the two leadscrews in my possession.

I have a Boxford BUD lathe. I have a considerable amount of wear in the brass nut driven by the crossfeed leadscrew so decided to make a new one.

All went well until it came to identifying the ACME thread size. Bear in mind that I am a complete novice when it comes to threads.

I measured the thread pitch at 10 tpi. I measured the major diameter as 7/16". I ordered a 7/16" x 10 LH ACME tap. In my ignorance thinking this must be correct.

When I tried the new tap in the existing brass nut to check that it was correct it quickly locks up, it is the correct diameter but clearly not the correct tap.

I have a spare cross feed leadscrew, which is similar in diameter but the brass nut that is with it neither fits my original leadscrew nor does the new tap fit that either.

I have spent many hours searching the internet and only learned that threads are an incredibly complex subject!

I have learned that ACME threads have a 29° thread angle but that metric trapezoidal threads have a 30° thread angle. Given the age of my lathe I assumed the cross feed leadscrew would be imperial. My spare leadscrew may be metric. Either way my 7/16" x 10 tap fits neither!

I am throughly confused and at a loss to identify the thread and order the correct tap.

I would be grateful for any advice and suggestions.

Thank you.