Thread Chasing

From the Archives:  (June 2002 Newsletter)

Most of you will recall, I am sure, the very informative visit we received from John Berkeley who showed us just how easy it was to do some thread chasing.

John gave us a lively talk and for any novices like me, showed a new way of working. He is obviously a skilled turner but rather than churning out bowls, he specialises in producing Victorian screw puzzles of a very high quality.

Whilst I cannot for one minute pretend to reproduce here a distillation of John’s wisdom, I think it worth recapping the main points., gleaned from a number of different sources.

Lathe speed, the position of the tool rest, the tool itself and the method of striking the thread will vary from turner to turner. The only unbreakable rule is that for every complete revolution of the work-piece, the chaser must move to the left a distance equal to the interval between two adjacent teeth. That’s the theory, anyhow!

Each of the chasers will require some preparation. Smooth off any sharp edges and any roughness. Sharpening is done by hollow grinding the top face. The first or leading tooth in particular must be sharp as this is the one that does most of the work.
Smooth and lubricate the tee-rest. A rub with the stump of a candle works wonders.

To practice, try on a piece about an inch in diameter with a slightly rounded end. The wood needs to be fairly hard and dense. Box is particularly good.

Use a medium chaser around 20 to 24 teeth per inch. The rest should be slightly above centre (as chasing is done at the trail, not as a cut with a gouge.) and slightly away from the wood. Hold the chaser at the far end and wrap the fingers of your left hand around the rest or its  pedestal. The thumb of the left hand goes on top of the tool and acts as the fulcrum.

Practice a few clockwise circles with your right hand, the tool just out of contact with the wood. Turn on the lathe at around 200 to 500 r.p.m. and after a few more circles, try to strike the thread when the tool is moving to the left at the bottom of the circular movement. Use the middle of the chaser to strike on the rounded corner. The second and subsequent strikes should become easier as the thread will take the tool along. Here lies the danger, for if there no shallow groove at the end of the thread area, the tool will suddenly stop and hence ruin the thread.

For internal threads, an arm rest is a must, unless you want to spend a lot of time adjusting your tool rest. This is a piece of mild steel about 7 inches long with a right angle bend about a half inch from the end, the whole mounted into a foot long handle which for convenience is hung via a cord around your neck, rather like a ladies handbag!

Thread Chasing Tools

The hollowed work piece must be slightly rounded at the front and have a relief at the end of the thread area. The movement this time is a horizontal oval into and out of the opening.

So much for the theory. Now go and try it!
Good luck.

Our thanks once again go to John for a very lively and enjoyable day.