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Thread dial gear

red rose armory

red rose armory

Member
Hello people , I need to cut some big threads on my lathe I restored last year but its missing its thread dial . It's a old rockford lathe over 100 years old , I've looked on the internet for years and can barly find any info on it , It says it can cut up to 56 threads, the lead screw is a 1,1/8 - 6 . I would like to know what size of gear I would need , number of teeth , presher angel and pitch
 

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Using the phone with one hand so rather than posting a bunch of links, try searching “cutting threads without a thread dial” on YouTube. It will bring up a bunch of videos on how to do this (basically the same way to cut metric threads with an inch lead screw: leave the half-nuts engaged), plus how to make a new thread dial.
 
red rose armory said:
Hello people , I need to cut some big threads on my lathe I restored last year but its missing its thread dial . It's a old rockford lathe over 100 years old , I've looked on the internet for years and can barly find any info on it , It says it can cut up to 56 threads, the lead screw is a 1,1/8 - 6 . I would like to know what size of gear I would need , number of teeth , presher angel and pitch
Click to expand...

How do you know it ever had one? My old 1800's Reed lathe, which was also an old line drive unit, never did have one. I cut all kinds of threads on it by leaving the half nut engaged. I still do that today on my newer gear head lathe with metric threads and also very fine threads where I don't trust the thread dial 100%. Assuming you have the correct gears, you can never go wrong just leaving the half nut engaged.
 
YotaBota said:
Anyone know the gear tooth count for the 6tpi leadscrew?
Click to expand...
From what I found online it looks like most people go for 24 teeth but no one specifys the gear pitch or out side diameter. Do I need a 24 Tooth 1.5 dia gear or a 24 tooth .875 dia gear or maby a 24tooth 1.625 diameter? For that I can't find a awser anywhere
 
So need the dial to advance 1 full turn every inch of travel. 6 tpi x 4 is 24 as you posted. You need to figure out the gear size from the diameter and the pitch of the thread. On the practical machinist site there are couple threads on it. But no one working on the variables you have. If you have a 3d printer you can print off different gear blanks and try them until you get a good fit.
 
I know the lead screw is 1.125 diameter and 6 threads per inch acme threads, that's all the info I have on it , is there a math formula I can throw My two brain cells at and see what maths pops out
 
That should be enough info. Just have to find an online calculator.
I found a couple builds if you did not see them.
https://www.hobby-machinist.com/threads/south-bend-thread-dial.27289/
www.hobby-machinist.com

Make Your Own Thread Dial

I did this with plans from an article in Popular Science from November 1940 on page 184. Check it out in Popular Science Archives. I used my lathe with the little fixture shown in the article. I made a mandrel to hold a small saw cutter and turned it with my chuck and held by a live center...
www.hobby-machinist.com www.hobby-machinist.com
That last one has a reference to popular science 1940 issue that i have now been completely sucked in to. Wow what a magazine and 15c at the time. The US knew war was coming. Everyone was getting ready for it. Page 184 has the build for the thread indicator including how to cut the gears.
 
It works with 6 tpi lead screws to from what I understand, 36÷6 is 6 . One full rotation of the gear should be 6 inches of travel on the lead screw
 
Nm , found a thread dial calculator online , it dosnt have all the info like gear diameter but it does have most of the info and it looks like if I went with 36 tooth gear with 4 decisions on the dial I'll get all my threads on the thread chart exspt for one the 5.75 thread , idk if it will affect the other threads and my chart says I should be able to do them all , with a 24 tooth gear it looks like I can thow , I'm going to have to play around with it . This question has been driving me nuts for 4 days and it feels like im going around in circles and it's driving me nuts , maby I need to take a weekend break at this
 
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