large four way toolpost

I bought a 4 way toolpost on ebay the other day, it turned out to be bigger than expected. There was very little information about the toolpost from the seller, and I thought I could tell the size. Fortunately, it went for a very low price and I am deciding if it can be used on the Smart & Brown model A at the museum. It could fit directly to the cross slide in place of the compound slide, to add stiffness, or as a rear toolpost to use with larger boring bars. A 20mm square tool fits easily, and 25mm size would as well. I haven't been able to take it to bits yet, maybe someone will know how to. The eight clamping bolts are 3/8" 16tpi, with 3/8" square tops. The four threads in the base are a bit of a mystery, too big for 1/4" and not big enough for 5/16", the only thread left would be 7mm which is rather rare.

Here are some pics:

Biased, but my choice would be as a rear toolpost.

Howard

Does anybody know which lathe it is from?

Does anybody know which lathe it is from?

Could they be 9/32nd BSF? (A little over 7mm, but imperial like the others.)

Dave

I have solved one part of the puzzle, the threads underneath are 5/16 UNC. I made an impression of the threads and found the pitch to be approximately 16 to 18 tpi. That definitely narrows it down to BSW or UNC. I had tried what was probably a BSW bolt without it screwing in, but today I had another search of the garage and found a bolt with the nuts on it. The nuts were too small for BSW so it is probably UNC. It is a tight fit, but screws right to the bottom of the hole. Not being able to get to the workshop at the museum because of lockdown is a handicap.

I still will need to strip it down before deciding what to do with it, the rear toolpost for larger boring bars is current favourite, it will be much stiffer than any standard one can be, and 25mm left hand bars will fit it.

I will be asking about this toolpost on the Home Shop Machinist to increase the chances of somebody recognising it.

If anybody is interested, I have succeeded in getting the toolpost to bits, pictures of its guts here:

**LINK**

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I would be interested, but every image link there returns:

Invalid File Specified

... So presumably one needs to be a member

MichaelG.

Sorry, I forgot that their new format won't allow viewing unless logged in, I hope it can be remedied.

Here are the pics:

It is a clever design using a hurth coupling to align and spring loaded balls to hold the post while the coupling is being tightened down. I think the post can also be locked in any of the angles allowed by the number of coupling teeth. Differential threads in the central column and at the bottom of the toolpost lock and unlock the post. The internal parts which have to be realigned are marked as such.

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That’s brilliant ... Thank You

It looks a beauty

MichaelG.