The Stubby Gets a Thread Cutting Jig
Recently I got back to it and solved a long standing problem I had with the chuck not turning concentric to its threading shaft.
The jig consists of a HF multi-axis vice, a few 3/4-16 nuts and a shaft all mounted on a removable platform on the lathe.
I use a 60 degree cutter mounted in the head-stock to cut the threads. The cutter is held in place with a collet and draw-bar.
The object to be threaded is mounted in a chuck which is then screwed to the threading shaft. A hand-wheel manually rotates the object as the cutter cuts the threads.
If you want to thread boxes you have three options:
The object to be threaded is mounted in a chuck which is then screwed to the threading shaft. A hand-wheel manually rotates the object as the cutter cuts the threads.
If you want to thread boxes you have three options:
- Build your own, like this
- Buy a professionally made jig
- Learn to cut the threads by hand
Note: an advantage of a jig like this is that you can easily cut threads in common woods. Hand thread cutting is best done with woods that suited for that purpose.
Later I will post on operating this jig.
The Vice
The vice is a 5" milling vise that cost $70 at Harbor Freight. I took it all apart and cleaned and adjusted it. Its not the best cross-slide but if you insure that you lock the axis after each move, it works just fine. Your cross slide does not need as many axis as mine but I did not find the other options to be any cheaper, perhaps it is better quality? If I had to do it over I probably would have gotten the 6" vice with fewer axis.
The Threading Shaft
The main part of the jig is a shaft that has the same pitch as the threads you want to cut. This one is 3/4-16 but the bar can be replaced with whatever pitch you want. You have to get an adapter to screw the chuck on the threading shaft. I have only found adapters for 16 tpi and 10 tpi threads to fit 1-8 spindle threads.
Cutter & Collet
Any 60 degree double angle cutter should work. I do not know where I got mine, perhaps MSC.
I used a 3/8 collet and draw-bar to hold the cutter in the head-stock:
Assembly
Once you have the parts the assembly is straightforward.
- Make a base that can be clamped to the bed and holds the vice such that the threading shaft puts the chuck on center.
- Clamp the shaft and three nuts into the cross vices upper jaws. The multiple nuts help reduce backlash.
- Screw the adapter on the shaft with a backing nut. If your lucky the face of the backing nut will be share enough to get acceptable run-out of the chuck while threading. If not you will need to make your own nut from wood.
Wood Backing Nut
The problem that caused me to put the jig on the shelf is that the metal backing nut did not insure the chuck seated perpendicular to the threading shaft. So the chuck wobbled and that is not good for threads this fine.
I got a hint from a YouTube Mike Pierce posted and decided to try and make a wood backing nut so that I could get the face of the nut perpendicular with the shaft. Most nut faces are not that precise.
I got a hint from a YouTube Mike Pierce posted and decided to try and make a wood backing nut so that I could get the face of the nut perpendicular with the shaft. Most nut faces are not that precise.
- To make this nut I drilled a 11/16 hole with a forsner bit in a peice of hardwood and threaded it with a 3/4-16 tap. I held the tap between centers to keep it straight. Use CA on the hole to help stabilize the thread cutting.
- Then mount the tap into a collet and put it in the head-stock. Screw the wooden nut back onto the tap and with light cuts surface the face of the nut.
- Now screw the wooden nut onto the threading shaft followed by the adapter.
The Jig
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| Vice, shaft, nuts and adapter |
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| Chuck attached, this backing nut created to much runnout. |
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| Attached to bed with adjustable height bolts for legs |
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| Tapping the wooden backing nut |
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| Holding the wooden backing nut and facing it off. |
The jig with the wooden backing nut installed
The First Successful Threads Cut
The threads in this box were a bit tight. I put the entire jig and assy back on the lathe wondering if it was repeatable and cut the base's threads deeper. That loosened up the threads, apparently the jig is repeatable :)!
Parts for the Jig
- 5" milling vise that cost $70 at Harbor Freight.
- 6 inch cross slide vice $74.99 from Harbor Freight
- Adapter for 3/4-16 tpi to 1-8 tpi" from Penn State. You can also get one for 3/4-10 tpi
Some other threading builds
Donate
If this post helped you solve a problem, saved you time or was otherwise useful consider donating. Use the link in the upper right of the site.
Donations fund some of the expense of tools and materials for my shop and lab so I can bring you more content like this.
Donations fund some of the expense of tools and materials for my shop and lab so I can bring you more content like this.
Also let me know if there is other content you would like to see me explore!
Enjoy and Comment,
Don
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