Copyright © 2019 Burnham-
This was a first time at our club for John Aitken and he did not disappoint.
John’s theme was “Putting threads in wood” but specifically the demonstration was about using thread chasers. Starting with a bit of history John showed us that woodturners were probably the inventors of the screw thread when it was noticed (as we all unintentionally have!) that when using a skew chisel on a spindle and it catches, a spiral screw thread is created. He further demonstrated that if on a plain spindle a pencil is run along its length whilst the spindle is rotating, and then a carving “V” chisel is used to follow the pencil lines, a screw thread is created.
John showed us a large selection of his thread cutting tools, most of which he has made himself or acquired from various sources e.g taps from Beall Tools Co and cheap chasers from the now defunct Pennyfarthing Tools Co from a stall at Devizes market.
Top Tip 1 -
Top Tip 2 -
Top Tip 3 -
Practicing thread chasing …
With a piece of dowel in the lathe and the toolrest at centre height, draw the chaser tool along and slightly under the dowel. Note that starting from the opposite end of the dowel will create a left hand thread.
Top Tip 4 -
Practical demonstration of a threaded lidded box…
Starting with the square section spindle (Castello Boxwood) turned to round, designate the lid section as being closest to the chuck as it is easier to cut the male thread in the base. (I assume that this would not necessarily be required if a spigot had been created on each end of the spindle in the first place) Having cut off the lid section leaving a “witness mark” for aligning the lid and base screw threads, hollow out the lid and then cut the female thread.
Instead of having the chaser tool supported on the toolrest at right angles to the lathe bed John had the toolrest parallel to the lathe bed and supported the chaser tool on an “Armrest” support tool which itself rested on the toolrest.
The diagram below shows the various features of the process including the important groove and chamfer on the leading edge.
Top Tip 5 -
The thread chasing on the base is completed in a similar fashion with the toolrest about 20mm away and the tool just below centre. Keep cutting and retrying the lid until the threads match. Knock off any thread tops if necessary and then finally turn a tiny bead on the join if desired.
Top Tip 6 -
This was one of the most interesting, informative, useful and enjoyable demonstrations that I have seen at our club and hopefully we will be able to benefit again from John’s vast experience in the near future. I’m looking forward to having a go at thread chasing asap, whilst wearing my new personalised smock from John Hamilton Donovan!