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Heavy Duty Boring Toolpost

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Charles Lamont:
About 10 years ago a fellow volunteer at a heritage railway who worked in the pattern shop said that he was planning to make patterns for the George Thomas design Versatile Dividing Head, and would I like a set. I said yes, and agreed to make the pattern for the milling machine adaptor plates. The castings soon arrived and I did some work on them before setting them aside to carry on with projects already in hand. One problem was that in his usual haste he had not actually looked at the drawings for the tailstock and had made its pattern much like the headstock one, so the casting was not really much use. I have recently bought a replacement from Reeves/Hemingway.

Not long after that purchase, and starting to prepare for work on the Quorn spindle, it seemed to me that the trickiest job would be those deep trepanned grooves in the end covers. Trepanning is not a job I enjoy. In this case it is important that the diameters are accurate. It seemed to be a good idea to make a proper cutter for the job, as Prof Chaddock suggests. It would need to be held firmly and dead on centre. I let this question mature for a while before it struck me that I already had the answer to hand. By using the redundant casting I could have a massively rigid dedicated toolpost for heavy boring jobs.

I made the cutter from O1 oil hardening steel. While I was at it, I also made the ball handles for the VDH proper. GHT mentions not arriving at a satisfactory design for a stop for the ball handle in the slack position. I could not resist, and had to try out an idea on this job. Although it does the job, I am not sure it is worth the extra work. Another addition that probably will make its way the VDH is the pair of locating buttons on the lower front edge. (In the retracted position these appear to give the front view of the tool the headcode for an express.)

By comparison with the Gibraltar Toolpost, I need a suitable name for this thing. I wondered about Uluru.

Admiral_dk:
By the look of the resulting Cut in the last picture - I would say that this has been a huge success  :praise2:

How often will it be used  :shrug: - but you now have an easy option in the future  :ThumbsUp:

Per            :cheers:

nj111:
Wow, a great idea which worked so well!

petertha:
The tool holder looks great. I like your idea of the finger stops so it self aligns to the cross table face (self parallel to spindle axis).
A question about your cutter. Was it shop made to cut very specific groove OD/ID dimensions? You probably know but just in case, good quality HSS annular cutters are available in a wide range of diameters. I've bought some off AliExpress (typically metric) but they have been just fine. They are decently accurate on the OD but I still consider them as a 'drill'. The ID is just a resultant byproduct of whatever tooth thickness they designed, no control there. These are used more for cutting a big bore vs drilling. Much kinder to low power / rigidity machines. Plus you get a slug of material vs a pile of chips. Even carbide tipped anular cutters are available if you are so inclined.

Charles Lamont:
Yes the groove is 1.065" OD and 0.935" ID, and both inside and outside diameters matter, providing radial clearances in the end caps nominally of 0.0025" from the ring on the revolving parts.

The available space means there is not much scope for variation, especially as I have beefed up the spindle without a significant increase in the housing diameter.

I think I was aware of the annular cutters, and might well use them where the design permitted.   

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