# New Lathe Change Wheels Calculator



## jdm23 (Dec 1, 2021)

Time ago I needed to cut a non standard thread on my Chinese 250mm lathe, finding the solution was not difficult, but I remained a bit unsatisfied with the available calculators, both online or Windows executables, so I started working on an existing one and made a bunch of improvements to it. Screenshot of  the compact version, it has four buttons that can be used to show additional information.







*Brief feature list*

Written in JavaScript, runs within the browser on any device. A specific goal is the *widest possible compatibility*, to run even on old devices.
*It's not dependent on the Internet*. Copy it as a single .HTML file on your device then open it with the browser. That will require enabling "local file access" which varies from a device and browser to another.
*Supports metric and English* (in TPI or thou) units, including inch leadscrews, with internal conversions reduced to the minimum to preserve accuracy.
Has an *embedded list of few popular* lathe models, new ones can be added editing the source file
Supports entering or *changing lathe parameters* in a simple form, so you can test for a different lathe before adding it to the as described above.
Calculate the* most important "physical constrains"*, to exclude combinations which cannot be fitted for a reason or another
Supports lathes with one (still untested) or two axles on the quadrant. At this time only a straight quadrant arm pattern is supported.
Immediately presents the *full list of possible threads* that can be cut, in  either units that you can switch, as well a* list of standard ones*
The lists on the point above are presented as links so you can just *click on them to get the solutions*
Shows approximate solutions (within 0.01mm, or 4 tenths) also, just because it can
*Includes the gearbox speeds* (if any) in the calculation.
Shows all the setups (as in number of gears used and position of the cluster) which have solutions as separate boxes
Collapses common solutions using idler gears on a single line. Idlers are represented as a range from the smallest to the largest possible.
*Solution format*
To avoid cluttering the screen with diagrams, the solutions are compact and given as a single line.
If the solution is exact for a given thread, only the list of gears (and gearbox reduction if any) transmitting motion is given. Gears / cluster physical position is fixed for a same box and is illustrated if you expand "show wheels config".
If the solution is approximate il would be slightly greyed, and show first it actual resulting pitch.

*For example* in the screenshot above the first 3 gears solution is 20…85 20…85 60 1
The first two gears (on top and bottom axle) are idlers. You can use anything from 20 to 85 teeth - as long these two are matched to fit!
The lowest gears (on the leadscrew, or gearbox input if present) must be 60 teeth.
The gearbox reduction for this solution must be 1. It can be identified with a letter on the lathe itself.
However, 3 gears solution are little used. If we go to use a 4 gears solution there will be no guessing on the idler gear. Of course, 5 gears solution have no idlers.

That's all about the present version, goes without saying it may have bugs and for sure new features can be added. I will try to address both requests as my time permits.

*Link to the online version* which I'm hosting for the time being: http://pab.fastmail.com/ChangeWheelsCalc/index.html
Remember, as with evertyhing 'JavaScript open source', once opened you can context click on the page, do "view source" and save it locally. It should be identical to the one I'm attaching here.

Questions and issues, *please post here, do not PM*. That to be more useful to others.


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## jdm23 (Dec 20, 2021)

I've just fixed a silly bug about presenting a default lathe when running the page for the first time. If you had tried and could not get it to work, it should now, my apologies.

What I want to do next is to calculate the physical fitment of the quadrant cover, so not to induce working without it.

Any feedback is welcome.


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## ScottGunSmith (Mar 23, 2022)

Awesome! Thank you!


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## Hard_ware (Mar 23, 2022)

Nice!

Only problem I am seeing is with a 5 gear combination the 2nd gear must be smaller then the 1st gear as they are on the same axle. The 1st gear contacts the spindle, so the second gear on that axle must be smaller to not contact the spindle. Not sure if I have a setting wrong allowing this to happen. But any  combo with a smaller 2nd gear can be found by looking down the list.


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## jdm23 (Mar 24, 2022)

Hard_ware said:


> Only problem I am seeing is with a 5 gear combination the 2nd gear must be smaller then the 1st gear as they are on the same axle.


Correct. That is the case not only when using 5 gears, but also 4 gears with the compound on top. Furthermore, the 2nd gear needs to be not just smaller than the 1st, but small enough to clear the spindle, which diameter in that exact segment may vary depending on how it the spindle is realized. The program takes all that into account, and as you can see in the example screenshot above, all 4 and 5 gears solutions have the 2nd gears smaller than the 1st.



Hard_ware said:


> Not sure if I have a setting wrong allowing this to happen.


Possibly you have entered new parameters but not filled the field 'Spindle Dia. above 2nd gear'? I was initially reluctant to do that, but based on your feedback now I think I will change the program so that a default is presented for this value, that is the root diameter of the 1st gear,
Also, if you have a lathe that is not listed among the ones I had inserted, would you please post it's full parameters here, so I can add them to the embedded list.


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## ScottGunSmith (Mar 24, 2022)

I ran into the smaller/larger wheel thing last night. I am curious. Why do none of the calculators match what is on my chart when I input those threads? Mine is a MX-210V, 56T Spindle, 2mm lead with 20 30 33 40 50 52 60 66 72 80 84 gears (Which I need to address soon, they will not align correctly). It threaded 1mm nicely.


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## jdm23 (Mar 24, 2022)

ScottGunSmith said:


> Why do none of the calculators match what is on my chart when I input those threads?



Well, I don't know about the others, but mine does. It is listed last, because normally with a quadrant cover that is smaller at the top, you need to fit the largest gears on the bottom.



If you can post the rest of the parameters I will add to the program.

BTW, looks to me that the design of the belt is good on your lathe, with a reducing countershaft and multi-v belts. Without these, there would have been not enough grip for sure on the small pulleys.


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## ScottGunSmith (Mar 24, 2022)

Man, that is awesome. What parameters do you need me to get and I will get them. Also, I am also a web host, I am happy to host the site at no charge if you need it anytime since you are doing this out of the kindness of your heart.


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## jdm23 (Mar 24, 2022)

ScottGunSmith said:


> What parameters do you need me to get and I will get them.







Basic parameters should be easily understood.
Module:_ for a gear of dia D and Z teeth, M = D / (Z - 2)_
Spindle and spacer dia, spindle-leadscrew center distance_, these should be clear enough?_
Maximum Center distance between top axle and leadscrew:_ push the top gear all the way up in the arm slot, measure its distance to leadscrew between centers_
Biggest possible gear on leadscrew: _so that the cover still closes. most likely, the biggest gear in the factory set_
Gearbox ratios:_ 1 for no gearbox_




> Also, I am also a web host, I am happy to host the site at no charge if you need it anytime since you are doing this out of the kindness of your heart.



Thank you for the offer, what I'm using isn't that great. Let's iron out the last details and then you're welcome to host it permanenty.


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## ScottGunSmith (Mar 24, 2022)

jdm23 said:


> View attachment 401575
> 
> 
> Basic parameters should be easily understood.
> ...


Ok, I will measure it all. Only thing I am unsure of is module. I assume from others it is 1.5. Sounds good on hosting, my dedi server has been online for almost 20 years so we can communicate via email when you are ready. It costs me nothing to add it on and moving is simple, you would just need to maintain your domain.


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## jdm23 (Mar 24, 2022)

ScottGunSmith said:


> Only thing I am unsure of is module. I assume from others it is 1.5.


I put above a general formula to get the module of any (metric) gear that one can measure.
In general, the bigger the gears, the larger the module. 1.5 is reasonable for ours, small one would use 1 or 1.25



ScottGunSmith said:


> you would just need to maintain your domain.


I don't care about under which domain is hosted, it's in the public domain, and can be used on PC/mac/mobiles etc even without servers or the internet at all.


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## Hard_ware (Mar 24, 2022)

ScottGunSmith said:


> I ran into the smaller/larger wheel thing last night. I am curious. Why do none of the calculators match what is on my chart when I input those threads? Mine is a MX-210V, 56T Spindle, 2mm lead with 20 30 33 40 50 52 60 66 72 80 84 gears (Which I need to address soon, they will not align correctly). It threaded 1mm nicely.


The factory chart is good for some and way off for others. The 28tpi is like 30 tpi on the chart. 56/50 x 30/80=.042 x 2mm =.84 travel per chuck rotation.  25.4mm/.84=30.24tpi not even close to 28tpi. With a 56 tooth gear you could use 84:66 top  30:56 middle 52:spacer on lead screw.
56/84x66/56x30/52= .4532967 x 2mm=.90659341 travel per chuck rotation. 25.4/.90659341=28.016TPI


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## jdm23 (Mar 24, 2022)

Hard_ware said:


> With a 56 tooth gear you could use 84:66 top  30:56 middle 52:spacer on lead screw.


But SGS doesn't have a 66T gear. So entering what he has we get the following for a 250mm lathe. Without knowing the full parameters it could be that some solutions don't fit, or aren't shown.


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## Hard_ware (Mar 24, 2022)

jdm23 said:


> But SGS doesn't have a 66T gear. So entering what he has we get the following for a 250mm lathe. Without knowing the full parameters it could be that some solutions don't fit, or aren't shown.
> 
> View attachment 401635


He has 66, needs a 56. One can be 3d printed. Adding a 34T and 56T will cover most standard Imperial threads. Just don't disengage the leadscrew when cutting imperial. Stop back out and reverse.


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## jdm23 (Mar 24, 2022)

Hard_ware said:


> He has 66, needs a 56. One can be 3d printed. Adding a 34T and 56T will cover most standard Imperial threads.


Right. What I was trying to convey with the calculator screenshot above is that SGS can accurately cut 20 TPI with gearset he already has. When the solution is printed in full black that means it is accurate to better that 0.01mm.
I have found the the factory gearset on this class of lathes is chosen so to cover perfectly the measure system to which the leadscrew belongs, and well enough the other one. The calculator shows the standard, and all the possible threads clicking on the buttons at the bottom of the page.


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## Hard_ware (Mar 24, 2022)

jdm23 said:


> Right. What I was trying to convey with the calculator screenshot above is that SGS can accurately cut 20 TPI with gearset he already has. When the solution is printed in full black that means it is accurate to better that 0.01mm.
> I have found the the factory gearset on this class of lathes is chosen so to cover perfectly the measure system to which the leadscrew belongs, and well enough the other one. The calculator shows the standard, and all the possible threads clicking on the buttons at the bottom of the page.


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## StevSmar (Mar 24, 2022)

Wow, thats great!!! It will be fun to put the gears in for my PM-1236T lathe and see what other combinations it has!


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## ScottGunSmith (Mar 28, 2022)

Good morning. Sorry for the delay, I have been pretty swamped lately. I setup the page on a sub-domain for you. If you want to use your own personal domain, I am happy to set that up. I can get you FTP login info if you shoot me an email.

The page is:

https://jdm23.180v.com

Non SSL Link until I fix the cert: http://jdm23.180v.com/

I tried doing some threading but none of the options seemed to line up for me. I may be an idiot and doing them wrong lol....strong emphasis on may be. Using the chart below I assumed the First row are the outside gears so 66 on left and 80 on the right for the top shaft then the lower shaft has 33 on the left side and 40 on the right side and 40 is connected to 52.

Did I do that correctly?

I forgot to take any more measurements while I was at home but my specs are below in my attempt. What I did do in trial and error that miraculously did work was take my info from the side panel and use the metric 3mm and change the lead screw gear from 33 to 30. So upper left was 72 and right 60 middle left spacer and right 80 and lowest gear 30.


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## jdm23 (Mar 28, 2022)

ScottGunSmith said:


> The page is:
> 
> https://jdm23.180v.com


Thanks for that, but the one you posted an https (secure) link. Since your web server does not have a valid public certificate, any browser will present a warning and require extra steps to open the page, something which is not user friendly, so I suggest that you only post http (no s) links.




ScottGunSmith said:


> Using the chart below I assumed the First row are the outside gears so 66 on left and 80 on the right for the top shaft then the lower shaft has 33 on the left side and 40 on the right side and 40 is connected to 52. Did I do that correctly?



It depend on how the lathe is build. The solutions, as explained in my opening post, are given in a compact form, going in *sequence of motion from the gear meshing to the spindle*, to the one on the leadscrew. There is not left or right, or spacer information, that allows to support multiple types of lathes, but is different from the format used on the cover.
If you click on 'show wheels config' at the bottom of the calculator you should understand what I mean with the above.




ScottGunSmith said:


> I forgot to take any more measurements while I was at home


Without all the correct measurements entered the calculator will give solutions that can't be fitted, and hide others that would work fine, so it becomes of limited usefulness, and I don't recommend using it that way.


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## ScottGunSmith (Mar 28, 2022)

I will get the cert updated in a bit and put the non ssl link also. I will digest the above. I really appreciate it.


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