I saw this question and don’t know an answer. Anybody have an answer?
@Emiliano Achaval ?
@Emiliano Achaval ?
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Thread chasing.
- Thread starter Glenn Lefley
- Start date
Well, others know better than I, but when using the Klein threading jig, Bonnie said that male threads could be cut to sharp points, but you didn't want the female threads sharp, or was it the other way around. I would also suspect that one last pass would allow just a little extra room for the threads so they are not tight to start with. I did wax my threads too, both for finishing, and for finish cuts.
robo hippy
robo hippy
If the threads are tapered like pipe threads that would definitely be your problem, if not then another pass on either the male or female thread should give you enough tolerance for a looser fit that won't jam.
The reason you do not want your male threads sharp is that with use and time they could crumble. So once you have them chased all the way, just take the sharp tip off. If this lady is having a problem is because she is making the fit too tight. Takes practice to know how loose or how tight you want your lids.
john lucas
AAW Forum Expert
I a sword that on the original post. Either the threads are too snug of a fit or simply the friction of the wood jammed.together when you turn both pieces. I wax the threads and the mating surface and rarely have a problem with unscrewing the lid. Before I started waxing the threads I had several.lock up on me.
Another thing that will help is to coat the threads with thin CA then take a light pass with the chaser on the female thread and a three corner file on the male thread. The CA will also prevent the sharp points from crumbling and will allow looser tolerance to counter seasonal changes.
Thread chasing implies hand making threads as opposed to using a threading jig.
Some metal working terminology..... the sharp tip of a thread is known as the crest. Crests are never sharp, either a small flat or a radius. Likewise with the root, the bottom between the 60 degree flanks.
The closest thing in metal working to hand chasing is single point threading. For precision thread making a different cutter would be used for a bolt (male) than for a nut (female). The different cutters would be shaped so as to create the correct crests and roots. The typical cutter used with threading jigs is not designed for cutting threads, it's just a 60 degree included angle cutter which is fine for threading, but does not account for the needed crest flat.
The recommendation of making a looser fit between male and female should solve the locking problem in unstable wood where the joint may not have been tight when screwed together. But, not sure why it would happen in Corian which is a much more stable material.
And, what does "nipped up" mean?
Some metal working terminology..... the sharp tip of a thread is known as the crest. Crests are never sharp, either a small flat or a radius. Likewise with the root, the bottom between the 60 degree flanks.
The closest thing in metal working to hand chasing is single point threading. For precision thread making a different cutter would be used for a bolt (male) than for a nut (female). The different cutters would be shaped so as to create the correct crests and roots. The typical cutter used with threading jigs is not designed for cutting threads, it's just a 60 degree included angle cutter which is fine for threading, but does not account for the needed crest flat.
The recommendation of making a looser fit between male and female should solve the locking problem in unstable wood where the joint may not have been tight when screwed together. But, not sure why it would happen in Corian which is a much more stable material.
And, what does "nipped up" mean?
I guess a slightly out of line, as in dead on parallel, could also be causing the problem. A trick I learned from Bonnie Klein, was to use a 6 inch steel ruler and hold it on the threads, both lid and box, then eyeball along the ways to see how close to perfect it is. It doesn't take much to have problems with the lid fitting. I did have one turner tell me that with the threading jigs that this didn't matter, but his boxes, most of them, seemed to push down and slip over the threads until the taper finally engaged the threads. I would expect the same with hand chased threads. Start with both tenon and mortice dead on parallel, cut the threads, then check again for parallel.
robo hippy
robo hippy
Waxing the threads or sealing the threads with CA adhesive will prevent the threads from absorbing humidity from the room which can change over time and location. If you use a threading system that allows for easily re-cutting and fine tuning the thread and fit of the box lid to the box thread you will usually get a good mating up of male & female threads. Another issue can be the wood you turn the lid and box out of needs to be cured and dry, any excess moisture in the wood can allow both pieces to deform from their perfectly round turned form if they lose or gain moisture over time. Wood is constantly moving as it gains and loses moisture, you need to allow for these slight changes with a loose enough fit to provide for these humidity changes in the environment. A coarser thread will provide more room between the threads to allow for these movements over time, a metal thread set can provide stability for the lid and box and allow for using a finer thread if desired. You can glue Corian rings into the lid and box and turn threads into the Corian polymer which can also allow for finer threads to be cut and used., depending on the thickness of the Corian ring they can also provide some stability to the mating fit of the box and lid. The larger the diameter of the box and lid the more movement you will encounter.
The CA on the threads will not stop the wood from distorting with seasonal changes since the underlying wood that the threads are cut from will still change size and shape. The CA's main advantage is strengthening and providing a smoother finish on the thread. Note: When cutting the thread especially in softer woods the fibers bend slightly as they are cut giving a rough surface that can cause chatter or jamming when the male & female are screwed together. The CA may not completely absorb into the wood so it is always a good idea to make a pass with whatever is used to cut the the thread or use a single point scarper or 3 corner file or sand paper at slow speed then apply wax.