machining custom wood screws

I got a an engine lathe, anybody has any ideas? At least the thread pitch doesn't have to be perfect. But how do I get that angle without a taper bar and that thread form without pulling the work piece out of the chuck?

For short work like 10 or 12" you can fab-up a taper bar PDQ (pretty darn quick)

I've often thought that chase threading would be the way to go for woodscrew. But I've never really needed any that were not available in some form, or able to be modified. The actual threading carriage would have to be sort of spring loaded to the leadscrew follower, but after that it could follow a pretty radical form. Most wood screws have a more or less long section of parallel thread and then a sort of rounded/taper transition to a point that is also the end of the thread.

I have occasionally made hardware with machine threads that threaded into machine tapped holes in hardwood.

smt

I'd make a bar that runs parallel to the bed, maybe attaches to head and tailstock with a contour that has the taper you want where you want it. Use a follower in the toolpost that rides the bar, if you found a way to get a double acting cross-slide to move with the carriager you could just hold it against the bar and setup some feed stops, almost like a hydraulic follower but manual.

me said:

I'd make a bar that runs parallel to the bed, maybe attaches to head and tailstock with a contour that has the taper you want where you want it. Use a follower in the toolpost that rides the bar, if you found a way to get a double acting cross-slide to move with the carriager you could just hold it against the bar and setup some feed stops, almost like a hydraulic follower but manual.

Click to expand...

Unfortunately, I have yet to actually try this but I have been thinking about it on and off for a while: Since the actual force to push a sharp threading tool into a cut seems to be not very great, I suspect that using a setup as described with the addition of mounting the cutter in a block on spring-loaded parallel pins would do the job. A hardened finger following the bar that defines the degree of taper because of the spring loading would make the job easier. The spring would need to be fairly robust but nothing crazy. (Is this what the old timers meant by taking a "spring cut?" )

Since the travel of the taper in and out is really pretty small, instead of the complexity of two parallel pins to act as ways, one might get by with just pivoting a bar holding the cutter on one end and spring-loading the other. Yes, this would result in the cutter moving in a slight arc, but we are making a woodscrew here. The error introduced would be so small that it would be negligible. That is probably true even for a machine screw for most practical purposes.

Denis

Apologies for dragging up an old post, but I was perusing this board and I could not pass it up.

I once made a one-of-a-kind wood screw with a left hand thread. My employer wanted a left hand wood screw to demonstrate on video the power of a motor employed in a product and they figured showing that it could drive screws into wood would be a good way. Trouble was the shaft was only on one end and it turned CCW. I had a very short fuse on the project: literally just hours.

I took a regular, round head, wood screw, mounted it in my metal lathe, and filed the threads off. I grabbed it by the head in a three jaw chuck and supported the point with a improvised hollow ended "center". Then I took a small spring that was wound in a left handed helix and stretched it over the thread-less screw. I bent the end down to the tapered point and cut it off. Then soft soldered it together.

It did not have any proper thread form, but unless you looked close, no one could tell. And it worked just great in soft woods. We screwed it into and out of many holes and it was still as good as new. You really could not tell that it was any different than a "real" wood screw. It took less than an hour to make and I could easily make then in moderate numbers in about 20 minutes each.

I don't know what happened to it, but I like to think it is the only left handed wood screw in the world. I searched and there seems to be little or no reason for making a left handed wood screw.