PM-1440GT Change Gear Thread Pitch Calculator

jbolt

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For the PM-1440GT owners.

I created an Excel spreadsheet calculator for the change gears for threading. It can show the thread pitch for both inch and metric threads for any change gear and lever/knob combination.

When the change gears are set for inch threads the Metric Pitch table shows the metric equivalent. Visa versa when the change gears are set for metric threads the Thread per Inch table shows the inch equivalent.

I currently have it setup to select the gears with drop down boxes in the upper left. Click on the cell to change and a selector box will show. Click on the box to make a gear selection. The table updates automatically.

The rest of the sheet is protected to keep from accidentally changing a cell with a formula. It is not password protected so if someone wants to experiment with different gear sizes you can turn the protection off and edit the drop down lists.

I am also working on a feed calculator. As soon as I can figure out the apron gearbox ratios I will post it.

I hope you find it useful.

FYI on the name plate on the head stock there is a typo for one of the lever selections. On the TPI chart for the 5.75, 11.5, 23 & 46 threads using the 69T lower gear the shift lever setting should be R-X. It is currently listed as P-X. The manual is also wrong.
 

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  • PM-1440GT Change Gear Thread Calculator.xls
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In my opinion, Jay, the most useful chart for the user machinist is one that shows all the raw carriage feeds in decimal inches, decimal millimeters, and decimal threads per inch -- per each spindle revolution, displayed in order from smallest to largest carriage travel per spindle revolution, and showing the change gears and controls combinations to achieve them, showing all possibilities when using all the control positions and change gears included with the lathe from the factory. That is a universal chart, quick and easy to use, and often shows multiple options that are right on or "close enough."

Your idea of choosing from the myriad possible combinations to see what the result is gives good information, but gives no guidance in what a working machinist really needs, which is "How can I make a thread (or feed) of "X" TPI, MM/rev, or inches per revolution?" This is not intended to be a put down of your gracious volunteer work, which is greatly appreciated by all of us.

A shameless personal aside: I do not have the computer savvy to do that work myself, but would sure appreciate it if someone compiled that chart for my Kent KLS-1340A... :)
 
I like your idea Bob but your making my head spin. LOL. I do like a challenge though.......

Do you know or have a way to figure out the gear ratios for the control positions on your lathe? Once the ratios are known it's not that difficult to create the tables. I could put something together if you like.
 
I don't know the ratios of the various gearing levers, but I am sure I could deduce them with some effort. They would need to be deduced because the gearbox is sealed and underneath the headstock, no exposed gear train. The controls are coaxial and rotating types, and gear tooth counts are not included in the parts catalogue.

I was going to post a link to the Kent website parts catalog for my lathe, but IT IS NO LONGER THERE! Manuals did not come with my lathe, and I had downloaded it earlier, and now I am printing it out as I type this. DAMN! It appears they are dropping support for the line, or at least making it more difficult for us to figure out what we have. I will print out the operation catalog as well.

Edit: Posted below, none of the gears are labeled with tooth counts, and the gear selection protocol is indecipherable in the pics as well. It would take a tear down to figure it by observation. It still could be done by deducing the gear trains from the threading and feed charts. Maybe this project is not worth the effort...

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I was able to figure out mine from the assembly drawings and parts list but mine did include the tooth counts for each gear. I just had to figure out the order in which they are place on the cluster gears and which gears engaged each other.

Your gearbox looks almost identical to mine. Post a picture of the thread/feed charts. Might be enough similarity to figure it out.

Also need to know the gear ratios in the apron to calculate the feed rates. Do you have an assembly drawing of that?

I think I have apron gearing ratios worked out I just need to figure out the formula.
 
Jbolt, like your spreadsheet, my wife can do wonders with them (and make them look nice), I just plug and chug the formulas. Not pretty but works.

You can just back extrapolate the ratios without counting teeth. You know the TPI/mm output, the gear selection and the the open gear ratios side, The open gear is a 1:1 for the 1340GT, the 1440GT is 2:1. Once you have that I just pulled the new open gear ratios x the TPI or mm thread. You get a matrix of ratios that are of interest and then you can use the ones of interest in a simple to easily follow table.

The interesting option on the 1440GT, would be to flip the 30 and 60 gears, this would give one TPI's up to 112. The machine does have a wide selection of both TPI and metric threads, but a number of gear changes if you were doing a lot of threading.

On the Kent KLS1340A the gear combination charts are on Page 12 of the machine manual. Seems like there are variants based on the lead screw. I guess the question is what threads are you interested in that are not covered in the charts?
 

Attachments

  • Kent KLS1340A Part A.pdf
    1.7 MB · Views: 107
  • Kent KLS1340A Part B.pdf
    1.6 MB · Views: 115
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Those are the same manuals I have. The threading charts on page 12 are for a metric lead screw and for an imperial lead screw, both posted twice for some unknown reason. The only threat pitch I have looked for so far that is not there is 27 TPI, which I was able to do with a 1/8" straight thread pipe tap.

Note that at the beginning of the operator manual, the lathe models are not Kent model numbers, but for C0632A and C0636A, which are probably the actual lathe builder's model numbers. I downloaded those manuals from Kent about 5 years ago when I got the lathe. Heaven knows who the actual builder is...
https://www.alibaba.com/showroom/lathe-c0632a.html
 
I was able to figure out mine from the assembly drawings and parts list but mine did include the tooth counts for each gear. I just had to figure out the order in which they are place on the cluster gears and which gears engaged each other.

Your gearbox looks almost identical to mine. Post a picture of the thread/feed charts. Might be enough similarity to figure it out.

Also need to know the gear ratios in the apron to calculate the feed rates. Do you have an assembly drawing of that?

I think I have apron gearing ratios worked out I just need to figure out the formula.
Here ya go!
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I was able to figure out mine from the assembly drawings and parts list but mine did include the tooth counts for each gear. I just had to figure out the order in which they are place on the cluster gears and which gears engaged each other.

Your gearbox looks almost identical to mine. Post a picture of the thread/feed charts. Might be enough similarity to figure it out.

Also need to know the gear ratios in the apron to calculate the feed rates. Do you have an assembly drawing of that?

I think I have apron gearing ratios worked out I just need to figure out the formula.
The metric and imperial lead screw charts are in manual A that Mark posted, page 12. They were double posted in the manual, charts 1 and 3 are duplicate metric lead screw charts, charts 2 and 4 are duplicate imperial lead screw charts. Don't get confused like I did the first time I saw them...
 
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