t-bar material advice

I finally got round to making a new locking nut for the toolpost on my S7. Hex nuts obstruct the toolholder on the Multifix QCTP I use, and I am quickly turning an internally-threaded piece of round bar to replace it.

But, rather than using a permanent ball-end handle to tighten it, I intend to cross-drill it (twice) and use something like a simple 6mm t-bar through the closed top.

The question is nonetheless a general one. What is the best material for little cross-bars to tighten threaded objects, that might be able to take a gentle tap without turning into a worm, or shearing? Simple EN3 bright bar? Silver steel? Something more technical that should be tempered?

All thoughts, please?

Cheers, Colin

To save having too many spanners hanging about on the lathe I cross drilled mine to take the lathe chuck key tommy bar so just slip that into the hole rather than have a separate bar.

Experience says if you think 6mm will do, go up to 8mm.

The increase in stiffness is huge, and the hole will be less likely to bell mouth as well.

Neil

Colin, Niels suggestion is a wise one but I would suggest either EN19 or EN24T as a material for your Tommy bar

John

Advice taken, and noted.

Neil, I'm going to x-drill this thing just once, but 5/16. Jason, and use the tommy bar conveniently fixed in my trusty chuck key to work it. John, that's sound advice for the smaller t-bar I'm missing for my small vice.

Thanks to all.

Cheers, Colin

All my tommy bars for,toolmakers clamps,tailstock die holders,box spanners, etc are made from silver steel,just as it comes no further heat treatment. just cut to length and face off and then turn a small rad,each end,to save your hands, Currently restorng a Ruston Hornsby stationary engine and doing the water cooling plumbing in 3/4 in bsp steel pipe, threading with a 3/4 bsp die in a large tail stock dieholder ,tommy bar for that is 12 mm silver steel.One curious thing I found with tommy bars was the pair of M&W toolmakers clamps I bought during my apprenticeshiop would not take 1/8 in dia silver in the tommy bar hole,and we only used imperial silver steel in those days,later on I found that the holes took 3mm s/steel, and metric steel was in stock a couple of job later, why in those imperial days were M&W making tools that had metric tommy bar holes, 3/32 ins the readily available size down bent easily so 1/8 dia was reduced in dia to fit.

It seems a good notion (to me, anyway) to relate the sizes of new fittings added to a machine to the 'standard' thread system used in the manufacture. In other words, a new bolt added to a Myford should be a Whitworth size, or a BSF thread, for a mod to a post war Colchester use A/F Unified sizes, for modern stuff Metric. Then you have a better chance that the tools you keep handy anyway will serve, and if you always put such spanners away immediately in the slot on the wall where they fit, then you will know which set of slots to look in.

Cheers, Tim

I made a ball handle to lock the Dickson tool post on my Myford the nut is very tall and clears all the tool holders, the thick washer was sized to lock the handle to the right and I cannot ever remember it being a problem. My Rapidor saw vice had lost its Tommy bar and having a spare sliding tee for a half inch socket set it was sacrificed and is excellent and unlikely to bend unless abused with an outrageous extender. An extension bar for a 1/4 drive socket set is not too much money and unless it is so cheap it’s junk it will most likely be chrome vanadium and unlikely to bend. If you start bending Tommy bars on a Myford tool post then it might be overdoing things a bit.

Mike

+1 for Tim's idea, I have done this for some time and it works well.

Rod