North Shore Woodturning Guild

Spinning a Thread by Dick Veitch

For some time now I have wanted to put a thread on a small wooden “travelmate” sewing kit I make. That dream remains but I have made some progress on thread making.

Fred Holder’s visit last year was a real boost. When Fred said thread chasing would be one of his demonstrations, I set out to get him suitable native timbers – there was no way he could tour the country and not show us how to do it on our own woods. My initial inquiries revealed that few people were trying any form of thread cutting and all who knew a little referred me to the greater knowledge of Fred Irvine, a highly skilled woodturner just down the road in Hamilton.

His advice was clear – black maire (Gymnelaea cunninghamii) is the only New Zealand timber that will consistently take a chased thread but maybe sometimes you can have success with puriri (Vitex lucens) or pohutukawa (Metrocideros excelsa). So Fred Holder put these timbers to the test and proved that Fred Irvine was right – use black maire only.

Fred Holder went off around NZ demonstrating thread chasing on black maire and left me to study my stack of “unthreadable” kauri (Agathis australis), puriri and pohutukawa.

But all was not lost. Fred had given me a copy of his book on threading. I had seen a jig in the Craft Supplies catalogue, and I had seen that the Teknatool ornamental turner could be used for threads. I would just have to try a jig, as spinning a cutter is hugely different to hand chasing.

My first jig was a cross between a wooden construction I had seen, ideas from Fred’s book, and the all-enclosed Craft Supplies steel model. In simple terms, I obtained some threaded rod the same diameter and thread as my lathe spindle, two nuts to fit and some bits of steel to mount it on the banjo. My chuck, with the work in it, could then be moved from the headstock to the threaded rod mounted on the banjo, and a four-toothed ornamental cutter from Teknatool could be mounted on the spindle.

With the cutter spinning at 3000 revs the wood was advanced towards it and rotated by turning the threaded rod. A thread was cut.

Wonderful, but……..I had already worked out that I would need two or three fine cuts to thread swamp kauri……..there was no way that I could adjust the banjo by the fractions of a millimetre needed. Mounting the jig on the banjo was a waste of time.

There was also a lesson about threaded rods. Just getting some rod and cutting it to length is unlikely to make a successful mount for the chuck. Either the end of the rod needs to be perfectly flat or the threaded rod needs to be made with a flange for the chuck to bed up to.

I needed to be able to move the work with some precision at right angles to the lathe bed. Carba-Tec had made a special jig for just such movements but that was for a totally different sized lathe. The Teknatool ornamental system could do the same but there were none in stock. I hunted further and was pleasantly surprised to find that double cross slides were very cheap. The one I got had a vice on top so is also useful on the drill press.

The common movement sought from the cross slide is across the lathe bed so that thread cut depth can be adjusted. Having a second slide to move longitudinally adds an ability to move the work well away from the cutter for test fits and it also makes multiple threading possible.

With the mechanical bits in place, further improvements were necessary to ensure a good thread and a good finished job every time.

The first, and possibly most important, is to work so that the cutter does its cutting as it goes into the wood, not as it comes out. So the male thread is cut as you would expect – from the edge of the work towards the body of the work. The thread in the female part needs to be cut from the inside to the outside.

As always, sharp tools are important. A cutter spinning a 3000 revs may appear to be doing a good job but a little touch with a diamond hone will make a huge difference. The shape of the cutter is also important. There may now be no woodturning cutters manufactured so you may have to put up with a metal turning cutter or modify one for improved wood cutting. A typical cutter has one to a dozen pointed teeth which have a scraper action on the wood. For the best cutting of wood these teeth should have a slight backward rake.

For a finished job that looks good, make sure that the two faces that screw up to one another are flat and clean. The two parts of the thread also need to be the same length and position in the work and there needs to be a “run off” space so that there is no sideways push to the tail of the thread. The points of the thread need to be a little flat to reduce later damage.