Imperial Thread Question

I'm stripping down this drill press for rehabilitation and I want to remake some parts.

I don't know the first thing about Imperial threads as I generally use metric or BA (Yes, I know BA is technically metric).

The thread on the spindle nose seems to be 3/8" x 40tpi which I assume to be a ME thread.

The screws for locking the table are 3/16 x 32tpi. I whipped out my Zeus charts and found a match with BSF.

Looking for taps and dies though, I found the same size/pitch available in UNF and UNS as well as BSF.

I think that UNF and UNS might be the same thing but are they interchangeable with BSF?

Steve

BSF is 55deg while the UN ones are 60deg

Just rechecked my Zeus and realised that!

I'm going to have to try and measure the angle. Maybe compare to a known 60 degree thread?

If they were, why would there be two names for the same thing?

UNF is the standard Unified fine series. UNS is generally Unified special.

Also, it would be unusual to use fractional dimensions below 1/4" in Unified threads. Below 1/4", they are normally referred to by numbers (e.g. 10-24 UNC).

I think it might be unwise to try to fit the spindle nose into any series as such. A spindle nose is a different category of threaded item to a fastener.

Perhaps go through every fastener on the machine and list diameter and thread pitch. Hopefully you will find something that belongs to one series or the other but not both. It would then be reasonable to assume that the others belong to that same series.

UNF and UNS are technically different but many suppliers use them interchagably for fine threads. For example 3/8-32 is a common thread in electrical items. I have seen this quoted as both UNF and UNS by component and tap / die suppliers.

Robert.

I am wondering if that is a typo.? 3/8-32 as a member of UNF just does not make sense.

Steve imperial tap's and die's both BSW & BSF are still easy to obtain

H

I am referring to 3/16" fasteners. The spindle nose is 3/8" 40tpi.

I tried a UNF screw (10-32) and it didn't fit so I'm assuming it BSF.

The original screws mate with threaded brass bushes, loosely fitted in the castings so I'm going to replace them with M5.

Steve

Thank you, DC31k, for making this point. And it's not the only member of that category.

I feel that this could, with great benefit, be expanded into a key paragraph as part of Chapter 1 of the next book anybody writes on screw threads.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 02/07/2023 18:46:54

Oops yes. Should be UNEF (UN Extra Fine)

It’s irrelevant now, Steve, because you’ve decided to Metricate the job … but there’s a good illustration of the Whitworth thread-form on this Wikipedia page: **LINK**

https://en.wikipedia.org/wiki/British_Standard_Whitworth

… it was all rather elegantly contrived.

MichaelG.