# PM-1440GT Change Gear Thread Pitch Calculator



## jbolt (Jun 23, 2017)

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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## Bob Korves (Jun 23, 2017)

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...


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## jbolt (Jun 23, 2017)

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.


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## Bob Korves (Jun 23, 2017)

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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## jbolt (Jun 23, 2017)

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.


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## jbolt (Jun 23, 2017)

Bob, How close is the G9036 to your lathe? http://cdn0.grizzly.com/manuals/g9036_m.pdf


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## mksj (Jun 23, 2017)

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?


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## Bob Korves (Jun 23, 2017)

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


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## Bob Korves (Jun 23, 2017)

jbolt said:


> 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.
> 
> ...


Here ya go!


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## Bob Korves (Jun 23, 2017)

jbolt said:


> 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.
> 
> ...


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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## Bob Korves (Jun 23, 2017)

jbolt said:


> Bob, How close is the G9036 to your lathe? http://cdn0.grizzly.com/manuals/g9036_m.pdf


Jay, the G9036 appears to be a perfect match with my Kent KLS-1340A.  Spindle speeds, feeds, and threading ranges are the same.  It does have a different color paint, and no doubt one of them is much higher quality than the other...  8^)  I won't say which one.


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## jbolt (Jun 25, 2017)

Bob, after digging into this, while it might be possible to make a "universal" chart with the numbers displayed in order from smallest to largest I don't see a way to do it easily. 

For just threading with the lead screw, your lathe has 25 gearbox lever combinations of which 21 are usable.(Five have duplicate ratios, so four are not used.) For each lever combination there are 64 possible change gear combinations for each idler gear setting (127/127 $ 120/127) with the stock change gears. Times that by four for each control knob setting (A-D, B-D, A-C & B-C). You get, 21 lever combos * 65 change gear combos * 2 idler gear combos * 4 control knob settings =  10,920 possible combinations. 

That does not take into account the 100 tooth gears used for the feed. If that gear could be used in combination with the 120 or 127 idlers then you would double the number of combinations. 

Double all that for metric equivalents.

I'm not sure how or if all of that could be graphically presented with the numbers displayed in order from smallest to largest in a useful manner. 

The feed rates are slightly easier as there are only 5 usable lever positions.

Making a chart for each change gear combination is quite doable but it would not be sequential smallest to largest. However in a spreadsheet or pdf file you could use the search function to find a near equivalent.


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## ronboult (Jun 25, 2017)

Jay
As Bob has pointed out the presentation of the feedrate and pitch on the printed tables on most lathes are based on what is easiest for the manufacturer to present in a compact form.
However they are not in a form that is very useful. My way of thinking is to first decide what pitch/ feed rate I require and then work out how to get there. I dont find my machine tables easy to do this!
Despite that most of the required data is actually present in the tables.
A spreadsheet in ascending feed rate or pitch which only includes what is already in the machine tables is what most of us would require. On some machines, some extra ( a few) combinations for missing commonly used pitch/feed rate could easily be added. I dont think most of us would require every possible combination.
Ron


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## jbolt (Jun 25, 2017)

Hi Ron,

If I understand what your saying is you would prefer if the published table was just reorganized in ascending order?

In Bob's example he was looking to cut a 27 TPI thread which is not published for his lathe. Based on his description of wanting the raw data represented in decimal form was to be able to find the decimal equivalent or near equivalent that could be used, 1.e.  27/1 = .03707. As far as I know the only way to find if that exists within the available gears/settings is to calculate all the available combinations. 

Maybe I've misunderstood?


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## MikeWi (Jun 25, 2017)

Sounds to me like a spreadsheet will do what you want still.  Instead of a chart with over 10K possibilities, let the user set the parameters they want, and calculate what's available for that info.  That way all 10K are available, but you only see what's relevant to your needs at the time.  I can help out if you want.


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## Bob Korves (Jun 25, 2017)

MikeWi said:


> Sounds to me like a spreadsheet will do what you want still.  Instead of a chart with over 10K possibilities, let the user set the parameters they want, and calculate what's available for that info.  That way all 10K are available, but you only see what's relevant to your needs at the time.  I can help out if you want.


MikeWi has my intentions correctly.  A physical chart of all possible combinations is not needed or wanted, it would be huge and not user friendly.  'All' that is really needed is a spreadsheet that shows all the possible rates of carriage travel per revolution, feed/speeds, in order from low to high, along with listing the required gear train components and settings for each.  The columns would show the travel in decimal inch and decimal metric feed per revolution, as well as in revolutions per inch (TPI), that would make it quick and easy to use.  Others have done this work for other lathes, it is by no means a new concept, and is highly useful when we need to make a "bastard" feed or thread (or for other uses.)  I have the skills to use such a spreadsheet for my lathe, but sadly do not have the skills and knowledge to create one...

Programs like Jay posted above and others like http://www.lathes.co.uk/threading/nthreadp.zip have created let you learn the thread pitch any gearing combination will result in.  I want the reverse of that.  I know the 'answer' and want the spreadsheet to show me the possible combinations to get there, or close to it...

Edit:  I know this is not at all easy to do, and I am not really asking for someone to do it for me. It is an awful lot of work to ask of someone.  But if this information was out there, both I and many others as well with similar lathes would certainly use it, and it would be a truly useful tool.


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## mksj (Jun 25, 2017)

Kent KLS-1340A gear charts, although this would also apply to similar machines like the Grizzly G9036 and quite a few others that seem to have the same gearbox.

I believe that people are over thinking all the combinations, as opposed to looking at the available gear ratios and working backwards to what ratios you need to get a particular thread pitch. I have attached gear tables for both imperial and metric, basically just about every pitch is available using the gear selectors setup as either imperial (direct drive X:127 and 127:Y) or metric (X:127 and 120:Y). So if you wanted a 27 TPI, you would use any two X and Y gear combination that had the same gear number of teeth (i.e. the set used for metric 42 to 42 but both driving the 127 tooth gear) OR 48 tooth X input and a 32 tooth Y output on the 127 tooth gear, the gear selectors are set per the chart. The PDF is searchable, so just put in the pitch number you want to 3 decimal places "27.000" and search the table. This also applies to the metric, so say you want a 0.700mm pitch, there is only one combination which would be a 44 X input to the 127 tooth gear with a 55 Y output to the 120 tooth gear. This assumes one has a full set of gears per the gear charts shown.

You can fiddle with the tables to look at other gear combinations, but the easiest thing is to first figure out what you need and then make a simple table that works for you. I just use the spread sheets to look at the raw data and if additional combinations are needed. Like I said if you know the factory pitch, and you want a new pitch not listed, just figure the ratio relative to the factory setting and what gear combination ratio gives the same ratio.


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## Bob Korves (Jun 25, 2017)

mksj said:


> Kent KLS-1340A gear charts, although this would also apply to similar machines like the Grizzly G9036 and quite a few others that seem to have the same gearbox.
> 
> I believe that people are over thinking all the combinations, as opposed to looking at the available gear ratios and working backwards to what ratios you need to get a particular thread pitch. I have attached gear tables for both imperial and metric, basically just about every pitch is available using the gear selectors setup as either imperial (direct drive X:127 and 127:Y) or metric (X:127 and 120:Y). So if you wanted a 27 TPI, you would use any two X and Y gear combination that had the same gear number of teeth (i.e. the set used for metric 42 to 42 but both driving the 127 tooth gear) OR 48 tooth X input and a 32 tooth Y output on the 127 tooth gear, the gear selectors are set per the chart. The PDF is searchable, so just put in the pitch number you want to 3 decimal places "27.000" and search the table. This also applies to the metric.
> 
> You can fiddle with the tables to look at other gear combinations, but the easiest thing is to first figure out what you need and then make a simple table that works for you. I just use the spread sheets to look at the raw data and if additional combinations are needed. Like I said if you know the factory pitch, and you want a new pitch no listed, just figure the ratio relative to the factory setting and what gear combination ratio gives the same ratio.


Wow, just wow!  Thanks!  Totally understandable, and if I can say that, you have a winner.  There are lots of ways to my 27 TPI, and lots more as well.  I am in your debt...


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## jbolt (Jun 25, 2017)

mksj said:


> Kent KLS-1340A gear charts, although this would also apply to similar machines like the Grizzly G9036 and quite a few others that seem to have the same gearbox.
> 
> I believe that people are over thinking all the combinations, as opposed to looking at the available gear ratios and working backwards to what ratios you need to get a particular thread pitch. I have attached gear tables for both imperial and metric, basically just about every pitch is available using the gear selectors setup as either imperial (direct drive X:127 and 127:Y) or metric (X:127 and 120:Y). So if you wanted a 27 TPI, you would use any two X and Y gear combination that had the same gear number of teeth (i.e. the set used for metric 42 to 42 but both driving the 127 tooth gear) OR 48 tooth X input and a 32 tooth Y output on the 127 tooth gear, the gear selectors are set per the chart. The PDF is searchable, so just put in the pitch number you want to 3 decimal places "27.000" and search the table. This also applies to the metric, so say you want a 0.700mm pitch, there is only one combination which would be a 44 X input to the 127 tooth gear with a 55 Y output to the 120 tooth gear. This assumes one has a full set of gears per the gear charts shown.
> 
> You can fiddle with the tables to look at other gear combinations, but the easiest thing is to first figure out what you need and then make a simple table that works for you. I just use the spread sheets to look at the raw data and if additional combinations are needed. Like I said if you know the factory pitch, and you want a new pitch not listed, just figure the ratio relative to the factory setting and what gear combination ratio gives the same ratio.



I like the layout Mark.

What I was getting at is there are more combinations than just those that can be extrapolated from the machine chart. On Bob's machine there are 14 more lever combinations.


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## jbolt (Jun 27, 2017)

Bob, Attached is a comprehensive thread chart with TPI, decimal TPI and decimal MM. Doesn't fit on one sheet. LOL

It's a bit cumbersome and only really useful using the search function.

FYI the the data driving cells are hidden but the visible cells are not protected.


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## Bob Korves (Jun 27, 2017)

jbolt said:


> Bob, Attached is a comprehensive thread chart with TPI, decimal TPI and decimal MM. Doesn't fit on one sheet. LOL
> 
> It's a bit cumbersome and only really useful using the search function.
> 
> FYI the the data driving cells are hidden but the visible cells are not protected.


Wow!  Thanks yet again, Jay.  Great and useful stuff!


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## jer (Jun 27, 2017)

Once again friends. We are blessed here with a wealth of knowledgeable members willing to help when the occasion arises.  I personally will/have abuse(d) Jay and Mark myself. I am glad Jay and I have the same lathe. LOL


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## jbolt (Jun 27, 2017)

jer said:


> Once again friends. We are blessed here with a wealth of knowledgeable members willing to help when the occasion arises.  I personally will/have abuse(d) Jay and Mark myself. I am glad Jay and I have the same lathe. LOL


Wait until you get my bill......


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## ronboult (Jun 27, 2017)

jbolt said:


> Hi Ron,
> 
> If I understand what your saying is you would prefer if the published table was just reorganized in ascending order?
> 
> ...



Hi Jay
I have had a look at your latest table and it is quite impressive. You must have put an enormous amount of work to produce it. It will clearly be very useful to some members.

From my point of view it is really overkill. There would only be a very few times if any in my lifetime where it would be used. I really only use a limited # of feed rates and thread pitches. These are actually presented in the tables attached to the headstock of my lathe- but in a form that is not so easy to use.

How do we actually use thread and lead lathe tables?

Take a typical scenario trying to cut a std pitch thread.
We first decide on the thread pitch required then,
Choose the appropriate change gears
Then set each to the Gearbox levers /dials in logical  sequence to achieve the desired result.

From my point of view this is the complete reverse of what is presented on the headstock tables.
When I looked at your spreadsheet with its myriad of options I was immediately confused by how I would find the option that was closest to the pitch /lead that I required. (There are many many options presented on many rows)

For my needs I am merely going to translate what is on my headstock into two tables sorted initially on increasing pitch and lead then listing in logical order as to how it would be achieved. Clearly this is not what everyone wants but I think the logic behind the suggestion would improve the presentation in your table. Perhaps just eliminating options that are not the closest option would improve the usability. 
Cheers
Ron


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## jbolt (Jun 27, 2017)

Hi Ron,

As I pointed out to Bob. That kind of table is only useful by using a search function but it does provide all the raw data which could in turn be further manipulated if one wanted to take on that task. . The KLS-1340A table is only good for that model or equivalent so only useful for a few.The table itself not all that complicated to do once you know all the gears and gear ratios. 

My purpose of going down this road in the first place was to figure out all of the combinations that could be used on my lathe that are not published on the factory tables. Can I cut "X" thread on my lathe even tough it is not on the factory table? Even if the pitch does not come up as a whole number there may be a combination that is close enough.

The kind of table you're looking for I think is what I have seen on some lathes with universal gear boxes where the first column lists the pitch in ascending order and the second column list the lever positions. These lathes usually don't have change gears so it simplifies things.


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## ronboult (Jun 27, 2017)

Thanks Jay
I will photograph my lathe labels for pitch & feed and reorganise the existing data. I don't think I even need a spreadsheet. I think a simple table will provide all the organisation I require. 
My lathe is metric, these days I only cut metric threads and my lathe only has two change gears,  30 teeth and 60 teeth. Quite simple I hope. Hopefully each table will fit on A4 sheet at font size that I can read. Will laminate them and stick them to the outside of the change gear cover. 

Thanks to all who have contributed to this thread as it has got me motivated to fix a problem that has been bugging me for a while.
Ron


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## jer (Sep 14, 2017)

Hi Jay, did you come up with a full set of possibilities for the PM1440GT? I can't open the attachment in the first post.



jbolt said:


> My purpose of going down this road in the first place was to figure out all of the combinations that could be used on my lathe that are not published on the factory tables. Can I cut "X" thread on my lathe even tough it is not on the factory table? Even if the pitch does not come up as a whole number there may be a combination that is close enough.



TIA


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## Bob Korves (Sep 14, 2017)

ronboult said:


> Hi Jay
> I have had a look at your latest table and it is quite impressive. You must have put an enormous amount of work to produce it. It will clearly be very useful to some members.
> 
> From my point of view it is really overkill. There would only be a very few times if any in my lifetime where it would be used. I really only use a limited # of feed rates and thread pitches. These are actually presented in the tables attached to the headstock of my lathe- but in a form that is not so easy to use.
> ...


The charts on the lathe panels only cover the common threads that people use, otherwise the tables would be as huge as the spreadsheet is.  When you need a thread and it is not on the chart, what do you do?  Go buy a different lathe?  Consider yourself limited and give up?  The great help Jay gave me opened up MANY more possibilities for other threads, using only the change gears that came with the lathe.  On a lathe with simple change gears only, no quick change box, it is not too difficult to check for the possibility of a given ratio with pencil and paper, but it still takes a lot of time.  Before there were computers everywhere, what Jay did in an hour or so would be more like a life's work.  I cannot thank Jay enough for what he did for me.  He made sense out of FM (f'ing magic.)  The aha! moment was when Jay found the tooth counts of the change gears, which are not in my manual, and figured out the actual ratios of each thread/feed box position (the feed/thread box is fully enclosed and in an oil bath, and has no cover like the headstock does so you cannot easily count teeth.)  He then added way more computer skills than I have, and shazam, a chart with all the possibilities.  The sum of those skills is beyond f'ing magic, it is brains, knowledge, and willingness to take on the task.  Wow, just wow!


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## jbolt (Sep 15, 2017)

jer said:


> Hi Jay, did you come up with a full set of possibilities for the PM1440GT? I can't open the attachment in the first post.
> 
> 
> 
> TIA


I have not done a full chart for the PM-1440GT like I did for Bob. The calculator I posted above works enough for what I need. If you don't have Excel I can convert it to another open source format. I will eventually get around to making a full chart. It won't be nearly as large as Bob's since we have less gears. Not high on my list right now.


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## jer (Sep 15, 2017)

Not a problem, I was just curious. Thanks.


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