How should I make this longish screw?

[WobblyHand]

One thought - you really don’t need much adjustment range on the screw-block interface, because it’s for fine motion only. The yoke can slide on the diamond-tool shaft for coarse adjustment. I’d think 1/4” is about all you will ever turn the adjuster. Really much less than that. So there’s no need for the threads to be more than say 3/4” deep in the block (though make the hole through) and about 1/2” on the end of the adjuster. That will make it a lot easier to make.

Also - Composite construction, where you would put a piece of threaded rod in a custom nut, is often a very useful way of making things, to eliminate the need to remove a lot of material.

The screw is a bit too long, I think. Don't have a feeling for this yet, and rather trim it afterwards. Hard to make it longer. The threads in the block can't be longer than 7/8" or so, due to my tap. Honestly still a bit worried about adjustment range still. Version 2 would look a bit different, I'd imagine, but I'm not quite good enough at this visualization stuff to see that far ahead. So plodding ahead with more adjustment than is probably justified. When I get better at this design stuff, I'll learn to make those ranges smaller with a higher degree of confidence.

The good thing about the design is it has both coarse and fine adjustments, which makes it tolerant to screw ups!

 

[rabler]

The screw is a bit too long, I think. Don't have a feeling for this yet, and rather trim it afterwards. Hard to make it longer. The threads in the block can't be longer than 7/8" or so, due to my tap. Honestly still a bit worried about adjustment range still. Version 2 would look a bit different, I'd imagine, but I'm not quite good enough at this visualization stuff to see that far ahead. So plodding ahead with more adjustment than is probably justified. When I get better at this design stuff, I'll learn to make those ranges smaller with a higher degree of confidence.

Yeah, there is a lot to be learned going from design to build. A fun challenge in my mind.

 

[Bi11Hudson]

It seems to me the details(?) of the original question have been lost. Were I to need a long screw with a special head, I would make 2 parts. The actual screw, 1/4-40, could be cut with a die. Or single pointed, since the length of the thread isn't that great. Using drill rod, silver steel, for the screw, thread both ends. Both ends could be the same, or one end at 1/4-20 or 28. Depends on what taps are available. . . The head is machined separately and internally threaded for whatever thread is used on the screw shaft. Once mounted, with LocTite or pinned or using a plug tap and overtorqued, the head would be relatively solid. The overall intent is to reduce the pile of chips and/or waste from cutting down a long piece of stock where it isn't required.

The head could be of steel or possibly brass for a decorative touch. It would be knurled before cutting off. But I think you can see that. . . An advantage to this type of construction is that the 'blind' end could be threaded a little long and a nut, and possibly a washer, added before mounting the head. this to allow adjustment for backlash.

I'm a little fuzzy today, I think better at night. Hence my apologies if I am seeing something that isn't there in the sketch.

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[RJSakowski]

I also would make the knurled knob separate a fix to the screw shaft. If it uses a threaded mounting and a set screw, you have an adjustment for end play.

 

[pdentrem]

I would use a tap to make the nut and then use the same tap to make a die to cut the threads on the adjusting screw. The reason being is the likelihood that the error in tap will be slightly different to the error in the lathe. The error in the leadscrew over the length of the nut may cause fitting issues. A simple piece of hardening steel with a tapped hole and a couple to a few slots can do a good job for a one time use.
Pierre

My First Homemade Threading Die

I have never made a threading die before. A tap, yes years ago, but never a die. I was trying to thread a 3/8” diameter rod to make collimation bolts for my telescope build. I need about a 2” threaded section to make things work. I purchased a 3/8” X 32 TPI tap to give me a smoother and smaller...

www.hobby-machinist.com

 

[WobblyHand]

The overall intent is to reduce the pile of chips and/or waste from cutting down a long piece of stock where it isn't required.

Good point. Hadn't originally thought of that.

 

[WobblyHand]

I would use a tap to make the nut and then use the same tap to make a die to cut the threads on the adjusting screw. The reason being is the likelihood that the error in tap will be slightly different to the error in the lathe. The error in the leadscrew over the length of the nut may cause fitting issues. A simple piece of hardening steel with a tapped hole and a couple to a few slots can do a good job for a one time use.
Pierre

My First Homemade Threading Die

I have never made a threading die before. A tap, yes years ago, but never a die. I was trying to thread a 3/8” diameter rod to make collimation bolts for my telescope build. I need about a 2” threaded section to make things work. I purchased a 3/8” X 32 TPI tap to give me a smoother and smaller...

www.hobby-machinist.com

Interesting. I do have a tap and die at 1/4-40. I used the die on some rod, and tested the fit into a tapped hole. It was a blind hole, and the screw did go in all the way until it hit the tapered portion of the threads. Was a decent fit, not loose, nor super tight. Not sure if I will run into a problem or not. Your tip is a good one and I will keep it in mind as I plow through this build.

 

[WobblyHand]

I also would make the knurled knob separate a fix to the screw shaft. If it uses a threaded mounting and a set screw, you have an adjustment for end play.

Can you explain the end play that you are mentioning? I'm not understanding where that might be.

There will be some play between the knob and the flange of the screw, since the rod clamp has to fit in there. Can't be a perfect fit. Wasn't sure if I would just make a shim or spacer or not. Edit: Is this the backlash you are talking about?

The play I'd also want to control would be the backlash of the screw in the big block nut. Not sure if I could fit in a slot in the nut without blowing up the whole design. I'd be happy if I could adjust this thing to make moderately controllable depths of cut.

 

[RJSakowski]

Can you explain the end play that you are mentioning? I'm not understanding where that might be.

There will be some play between the knob and the flange of the screw, since the rod clamp has to fit in there. Can't be a perfect fit. Wasn't sure if I would just make a shim or spacer or not. Edit: Is this the backlash you are talking about?

The play I'd also want to control would be the backlash of the screw in the big block nut. Not sure if I could fit in a slot in the nut without blowing up the whole design. I'd be happy if I could adjust this thing to make moderately controllable depths of cut.

Yes, I was thinking about the clearance between the flange and the knob. Having the knob screw on and locking with a set screw would provide a means of adjusting that clearance easily. As to play in the lead screw and nut, you could use a compression spring to bias the screw, smilar to the bias springs that used to be used on carburetor adjustment screws.

 

[pdentrem]

I would use a Belleville washer or a spring to remove any looseness.
Pierre