WORKSHOP – FITTING A QUICK-CHANGE HOLDER
A find at the back of the workshop causes some head scratching for our Technical Editor...
During the big tidy up of the workshop at the Fairbourne Railway that followed my appointment last Autumn as the 12¼-inch gauge mid-wales line’s engineer, I discovered tucked away at the back of a shelf, a quick-change tool post – complete with its central pivot pin and holding down bolt.
Handily it is a Colchester model, so assuming it would be a nice quick swap for the tool post on the smaller of the two Colchester lathes we have in the workshop, I took the existing one off.
At this point I discovered a completely different attachment method on the lathe, with sprung ball indents for locating the toolpost parallel and a couple of pegs too, along with a much wider base and a quarter-turn locking mechanism that absolutely would not fit the quick-change toolpost.
So having sat back for a while and compared the two, I eventually decided that the advantages of the quick-change toolpost outweighed the niceties of the old one, and figured out a way of attaching it.
The first thing I did was to strip the cross slide off the lathe – this gave me access to the underside and thus allowed me to remove the mechanism for the quarter-turn lock and the sprung-loaded indents.
Tough customer
This operation also released the vertical pin that the handle attached to. My original intention was to modify this setup to accept the vertical pin of the replacement tool post, however it turned out to be extremely hard material.
There are a few ways around such problems, and the way I went was to heat the pin to cherry red and then to let it cool down very slowly, wrapped up in heatproof blankets. This tempered it enough for me to machine and tap a hole down the centre, this hole matching the threaded end of the new toolpost’s centre pin.
I then mounted the cross slide into the mill and used a face cutter to take the height to the centre boss down to match the recess in the new toolpost’s base. The next step was to clock up on the boss to centre it, and using a boring head, to machine the outer diameter to match.
All that remained was a simple assembly job, with some Loctite being used to secure the threaded adapter in the base.
As a result of a little work I now have available a quick-change tool post on a very nice lathe, which has already proved its worth in the many varied operations we carry out while maintaining the 6-inch scale stock on the line.
■ For Harry’s latest Fairbourne challenges see page 32