Ok guys I need some help here. I’ve decided to try threading and I cannot find any info on how much larger to make the two pieces in order to cut the threads, I’m guessing that about an 1/8” but that’s a guess.
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Ok guys I need some help here. I’ve decided to try threading and I cannot find any info on how much larger to make the two pieces in order to cut the threads, I’m guessing that about an 1/8” but that’s a guess.
Are you going to use a threading jig or chase them by hand? I don't have experience with hand chasing but do cut them with a home made jig. The thread cutter will gradually form a sharp edge at the apex of the thread, therefore I typically don't allow much if any extra material to mill away for threads. I'll typically cut the male threads on a turned box first, then cut the female threads on the lid and creep up on the fit. As long as I stay with typical threads, it is pretty easy to find thread dimensions for the root diameters, etc on line so I just adjust as needed. It seems like 1/8" would be excessive, although it can be easily milled as desired.
Attachment 400049
Thanks Dick, I’ll be using a jig. I looked at building a jig but by the time I gathered the pieces up and drove the 60 miles to get them I could order a refurbished jig for quite a bit less. So what you’re saying is cut the pieces larger and cut the threads to make the pieces fit right?
Depending on the species and things like wild grain, chippiness, I'll allow a little extra and let the fit determine the final sizing by feel. I don't have an exact number as it varies from piece to piece but it is probably not much more than .030 - .040" per side, I have also turned pieces that achieved a nice fit when turned, but have changed or gone out of round with seasonal changes, changes to dryness and other naturally occurring issues with wood.Quote:
Originally Posted by Ken Schleman
I started experimenting on less expensive woods and different species to learn how they behaved. One thing I quickly learned is that on woods and grains that are easily chipped, I apply thin CA glue to the partially turned threads, and that has helped greatly help the process.
It is all fun and rewarding so enjoy.
Rough turn them first, leaving them about 1/4 inch thick. Turn the threads on the lid first. Biggest problem I had was in figuring out how thick to leave the walls. First couple I made, I just cut the threads on the inside of the lid without narrowing down the inside much first. What happened there was when I cut the threads on the bottom, there was almost no wall left to support the threads. So with a 1/4 inch thick wall, on the lid, I pencil mark in at about 1/8 inch. Turn down almost to that line, then cut the threads. Then when you cut the outside threads, you will have some meat behind them.... I don't turn them more than about 1 1/4 inch diameter any more. Wood always moves, and beyond 1 1/4 inch diameter, they can warp to the point where you have trouble getting the lid off. I will be making a threading video eventually. Sam Angelo, the Wyoming Woodturner has some videos up about threading boxes. I think he hand chases though, but he has dome good points.
robo hippy
A 16 tpi thread is normally .040 deep, so you'd add .080 to the total diameter. I come across an old Bonnie Klein handout a few years ago and she recommended 3/64", and it seems to give a little bit of clearance to allow for wood movement. I've made dozens of boxes in the 2 1/2" range and never had an issue. But as with any box wood acclimation plays a big part. After I rough turn a box it gets stored in the house to acclimate (even mild dried wood) from anywhere from a couple weeks to months. And if for some reason I can't finish it while I'm turning it, it comes back in the house with me.
If you do the female thread first make the Males size .070 bigger, female hole without threads 1" Male size without threads 1.070. I use the Baxter Treading Jig and cut the threads .035 on a side,
Thanks a lot for the help guys, I’ll try my first set tomorrow.
Jeff,
I had a show in Davis, CA years ago on Mother's Day Weekend. Bunch of Mountain Mahogany boxes ready. Went down there from here in cool Western Oregon. Only the larger ones moved enough to feel the threads get tight when I turned the tops off. Had another one at a show locally that fell off onto the ground behind the table. Found it when I was tearing down the booth. It was maybe 1 1/2 inch diameter. I could get the lid off, but it was tight, and it never went back to perfect fit. It was myrtle wood. With friction fit lids, I have gone to 6 inch diameter. As long as I make the whole box from one piece, it seems to work even though I can't rotate them all the way around some times...
robo hippy
Ken, you probably have plenty of advice by now. I didn't get to read all the messages.Quote:
Originally Posted by Ken Schleman
I checked my notes and it looks like for 16tpi I cut the threads .043" deep. This left plenty of flat on the top of each thread, important in wood compared to metals.
I cut the lid first then the base but I don't think it matters if the calculations are correct - I made careful drawings before turning anything. The tenon for the base was then the inside diameter of the lid threads to the flats plus 2 times the depth of the cut minus 2 times the desired clearance. (I used .01)
As per Raffan, I shaped the box to nearly the finial dimensions then let it sit at least overnight to relieve any stresses that were in the wood. (This was, of course, after the box blank is completely dry.) I had good success with no chipping threading hard, fine grained woods - ebony is my favorite so far. Given the choice, I'd pick a blank from a part of the tree far from the pith since it is likely to be more stable with seasonal changes.
I was fortunate to have the luxury to set the jig up on a second lathe so it wasn't in my way and I didn't have to touch anything if I wanted to put the piece back on the first lathe for a minor tweak. (Which I did several times on my first little box!)
BTW, these are my first, third, and second attempts at threading using the Baxter jig, Black & White Ebony, no finish. Just for fun I made the one on the right a little "backwards" from usual with the outside threads on the lid and internal threads on the base. This lets the lid look smaller.
Attachment 400351
A funny thing - when showing these to non-turners I was asked twice where I found plastic lids like that. :)
If you are interested, I found some good resources in books on my shop shelf including at least one book entirely on threading. I think one of Darlow's books was helpful too - I can look if you want. When I started threading I wanted to understand what was going on so I read everything I could find, made diagrams, and did the math.
JKJ
Ken,Quote:
Originally Posted by Ken Schleman
As I mentioned here I have some books that were helpful so I checked just now. You, or other book readers, might be interested.
I have two books specifically on cutting threads.
"Making Screw Threads in Wood" by Fred Holder is excellent and covers every aspect of different ways to cut threads including threading jigs.
https://www.amazon.com/Making-Screw-.../dp/1861081952
He answers your question on page 34, describing: "...there is a problem determining exactly how deep to make the threads and how to size the two pieces. I struggled with this problem for several years and came up with a few methods... Then one day I had a brilliant idea and..." etc. Worth reading. He has good diagrams and shows how to calculate, how he prepares a box blank, and exactly how to position the cutter. A book worth getting, IMO. The math might go over the head of the person who can only learn from youtube videos but is perfect for someone who wants to know both the why and the how for any thread pitch.
"All Screwed Up! Turned puzzles and boxes featuring chased threads" by John Berkeley.
https://www.amazon.com/All-Screwed-U.../dp/0941936937
Although about chased threads, the methods also apply to jigs. He shows an entirely different way of sizing using wax on the female threads to transfer the ID to a tapered tenon for the male threads, very similar to sizing the tenon for an unthreaded box. He shows no math but has good pictures - more like a youtube video than a technical instruction. He also has a nice list and descriptions of various woods good for thread cutting. (One thing he doesn't emphasize is the drying and stress relief of the partially turned box.) He includes lots of projects, boxes and other, including a few non-threaded turned puzzles. I consider this one also good to have on hand.
"Woodturning Techniques" by Mike Darlow (one of my favorite woodturning authors) Has an excellent chapter on threading, including some history. On the "how to" side he includes everything from cutting threads by hand carving to using jigs.
https://www.amazon.com/Woodturning-T.../dp/1565231481
I'm undeniably biased, but if I were King this book and a couple of his others (including Woodturning Fundamentals) would be required reading for all turners, at least those who wanted to excel instead of just get by.
JKJ
Not to hijack the thread, but Mike Darlow's book mentioned above was one of the first books that I read early on and got me off to a quick start threading. Although he is very technical in some areas, it was so full of great information on turning techniques that I quickly acquired several of his others. They remain in my go to books whenever I need a refresher :)Quote:
Originally Posted by John K Jordan
Same here - I learned woodturning from two books, the "Fundamentals of" from Darlow and "Turning Wood" from Raffan. I soon bought all that both had ever written and now keep some spare copies to lend to students and others. Those are the books I get out when trying to explain some concept to a beginner.Quote:
Originally Posted by Dick Mahany
I think learning the different perspectives of the first two books gave me a leg up over what I would have had starting with a beginners turning course or watching videos. By in-depth reading, re-reading, comparing to the other book, following the instructions and exercises of both, and experimenting on my own woodturning soon became one of the easiest things I've ever set my mind to. A book contains SO much more information than a video or a class - I'm guessing it would take 100s of hours of video to transfer the knowledge of one book into the brain, and even then you can't put a postit note on a page, highlight a passage, or make a note in the margin!
JKJ