South bend lathe thread dial

Mark_f

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I have been needing a thread dial for my South Bend 9 inch lathe. There are reproduction units of high quality available to buy for around $120 with shipping. This is a reasonable amount but right now I just can't afford it , so I decided to make one to do until I can purchase one.
The big problem was the gear. I could not find one anywhere, so I tried to make one using some redneck hobbing method I saw on the internet. Well, it didn't work. After screwing up three gear blanks I gave up. Then while surfing eBay, I found a nylon gear real close to the correct diameter and it had 32 teeth. They came from China and cost $5 for five gears. I figured it was worth a shot. they arrived a few days ago and are a regular spur gear. The teeth meshed with the lead screw but not as well as I wanted. I ground a piece of 1/4" square tool steel to fit the acme thread on the lead screw and held it in my hand and scraped the nylon gear teeth by hand. It only took about 15 minutes and it fit a whole bunch better.
I started with a piece of aluminum 1 1/2" in diameter and 3 1/2" long. I milled and drilled till I had the body made.

body gear and shaft assembled.jpgthread dial parts.jpg
A piece of 1/4" drill rod made the shaft.

A small piece of brass made the number dial. I cut a strip of paper equal to the circumference of my chuck and folded it 4 times to divide it into 8 equal divisions. I put it around the chuck and used a pointer and this allowed me to index to position and scribe the lines on the brass number dial I made.

Paper strip divided.jpgpaper on chuck .jpg

setup to scribe dial.jpg

I drilled a 5/16" hole through the dial body at a 3 to 4 degree angle to tilt the dial when mounted. This let the gear mesh much better. the mounting rod was machined to .314" for a press fit into the body. It won't move, in fact it would mess up the body if I tried to get it back out. You can see this angle in the photos. It is slight so it presents no problem.
This was a simple project that took about 3 hours to make and works so well, I don't have to hurry to buy an expensive rpro unit. I am putting all the photos at the end here along with the print. (there are two copies because the picture quality is kind of poor.)


body gear and shaft assembled.jpgthread dial print.jpgthread dial print 2.jpgthread dial parts.jpgthread dial on lathe2.jpgthread dial on lathe 3.jpgthread dial completed.jpgThreaa dial on lathe.jpgsetup to scribe dial.jpgPaper strip divided.jpgpaper on chuck .jpgcompleted number dial.jpgthread dial showing gear.jpg

body gear and shaft assembled.jpg completed number dial.jpg paper on chuck .jpg Paper strip divided.jpg setup to scribe dial.jpg Threaa dial on lathe.jpg thread dial completed.jpg thread dial on lathe 3.jpg thread dial on lathe2.jpg thread dial parts.jpg thread dial print 2.jpg thread dial print.jpg thread dial showing gear.jpg
 
Nice job on the threading dial set up. If the gear gives you a problem you may want to check at Boston Gear for a replacement. Since it is only used while threading I bet your will last a long time. Good job and good luck.

Paul
 
These always go for crazy money here in the UK when they pop up on ebay. I love the simple design and use of paper for indexing .. would machining the gear teeth concave help with meshing?

Have you seen this cheap and easy method of cutting worm gears: https://www.youtube.com/watch?v=J0o3W4_LRBw
 
It is not needed because I ground a tool the shape of the lead screw teeth and used it to hand scrape the plastic gear for a better fit and when it is tilted on the 3 degree angle the mesh is pretty good

Mark


These always go for crazy money here in the UK when they pop up on ebay. I love the simple design and use of paper for indexing .. would machining the gear teeth concave help with meshing?

Have you seen this cheap and easy method of cutting worm gears: https://www.youtube.com/watch?v=J0o3W4_LRBw
 
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