Which Thread?

[Chris CrewParticipant @chriscrew66644]

I feel sure someone will have the answer to this simple question, so here goes! I had on my eBay watch list a boxed 2MT boring head kit, nine boring bars, Allen keys etc., which I was not really intending to buy but then the vendor offered it at such a ludicrously low price that I could not resist. Although I will find a use for it (eventually) with its 2MT fixing, I would ideally like to swap the arbour for a 30INT for my Harrison mill's vertical head. Such items are available but my problem is I cannot establish for certain what the arbour thread on the boring head is because I only have a cheap set of thread gauges and the old eyes aren't so good as they used to be. So the thread, as far as I can determine, is either metric 38mm x 1.5mm pitch or 1.5" x 16TPI. Chronos sell such an item but they quote it as being 18TPI which may be correct for the boring head they may be selling but not for mine. So can anyone tell me which thread I might require, please? (I think this must be a fairly standard item across all brands and price ranges for what appears to be exactly the same thing).

[Chris CrewParticipant @chriscrew66644]

[JasonBModerator @jasonb]

The ARC ones are also 18tpi.

Why not measure the overall length and then unscrew the arbor 1 full turn and take another measurement, difference between the two will be the pitch of the thread.

[DC31kParticipant @dc31k]

The unscrew-one-turn-and-measure idea is good. Because the arbor is flanged, a set of feeler gauges might work very well for this pirpose.

A 5/16 BSW bolt could be used if your thread gauge does not have 18tpi on it.

You could also go for a majority decision: try to find an 1 1/2" arbor for sale somewhere in the world by anyone at all that is not 18tpi.

[Howard LewisParticipant @howardlewis46836]

Unless the boring head is an Imperial one, I would expect the thread to be Metric. The 38 mm OD supports this impression.

FWIW, a 1.5 mm pitch will equate to 16.933 tpi., roughly half way between 16 and 18 tpi.

Howard

[JasonBModerator @jasonb]

The metric head I have (50mm dia, 12mm tools) has a 1.5 x 18tpi thread and I can happily swap heads and R8/MT3 arbours with my imperial (2" and 1/2" tools) head

Edited By JasonB on 12/08/2023 18:55:34

[DiogenesIIParticipant @diogenesii]

I think pretty much every generic boring head of that common (? shall we call it 'Criterion-pattern' ) style that I've ever seen uses a 1 1/2 x 18tpi arbor..

I swap three arbors around on mine depending on what I'm using it on.. ..dial and tooling is metric

Edited By DiogenesII on 12/08/2023 19:48:22

Edited By DiogenesII on 12/08/2023 19:48:44

Edited By DiogenesII on 12/08/2023 19:49:25

[Ex contributorParticipant @mgnbuk]

Was that the set in the yellow box from the seller in Pontefract, Chris ?

If so, I took advantage of the attractive offer price as well but, other than a quick check on the box contents on arrival yesterday, I have not looked further. I will have a look later & see if I can measure from my example with any confidence.

Nigel B.

[Ex contributorParticipant @mgnbuk]

I maesured the shank on head I bought & it appears to be 1 1/2" x 18TPI.

The thread on the shank is rather short, but the 16TPI gauge is nowhere near a fit, 1.5mm is closer, but still not a snug fit like 18TPI. O/D is 1.495" with calipers.

Nigel B.

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