Compound gear train estimates from decimal target

[MRA]

hi Folks

I have been thinking about compound gear trains, and trying to get close to a decimal target value (eg, 1:1.2104114 etc etc). I used to know enough to program this into something like Matlab and rank order the estimates based on error magnitude...but that was in a former life when I was clever! I found a site which will do something like this, here:

http://ninoslavp.users.sbb.rs/WRI_en.html
...but this prioritises minimising the error, and so suggests all kinds of gears which I could cut, but would perhaps rather not! It would be handy to use something which lets you select from a given selection of gears one happens to already have, obviously at the cost of larger error. Has anyone seen anything online, or know of a paper method?
Thanks
Mark

 

[Charles Lamont]

Any Myford lathe owner should have Duncan Munro's ML7 gear calculator program. It is brilliant. It knows what will fit. It allows you to add non-standard gears.

http://metal.duncanamps.com/software.php

 

[MRA]

That's fantastic Charles. The second program, under the heading 'Hobber Gear Calculator', is exactly what I need, and allows one to select from a list of gears one already happens to have and see how far off the 'best case' is. Thank you very much - that's saved me a lot of head-scratching.
cheers
Mark

 

[Drawfiler]

Go to scientific601,this will enable you to pick any pitch from your set of gears

 

[awake]

FWIW, I wrote a little program some years ago to use with my 7x12 mini-lathe:

It lets you input the list of the change gears you have available and set the leadscrew pitch; these parameters are saved, so only have to be set up once. (Note that if you have two of any gear size, you put it in the list twice.)

Then you can select to solve for imperial (SAE), metric, module, or DP, and input the desired thread pitch based on that measurement. Click the "Calculate" button and it will give you the best combinations from the gears you have available, and show the amount of error. Note that the one thing it doesn't do is to determine whether the gears will actually fit in the selected places, but I've never had a problem using this to find a combination that works easily and conveniently with minimum or no error.

The program is written in C++ using the wxWidgets UI; I can compile it for Linux or Windows. You can download the .zip file with the Windows version here: www.wakefieldphd.com/hobbies/ChangeGears.zip - just unzip it into a folder and run it from there. Using wxWidgets to write this means that it can also be compiled for the Mac, but I've not had a Mac to try that on - would love it if anyone wants to do that to see if / how it works. Just let me know and I'll send you the source code.

I never bothered to put a copyright or anything on this - consider it free and open source; feel free to use any way you'd like.

 

[methuselah1]

There is another one, NthreadP, which is free to download from lathes.co.uk, written by Geoff Carter. My changwheel set rises by fives, but a similar model rises by fours, so I have supplemental gears too, and there really isn't much I can't cut within 0.5%, and usually far better. I seem to cut more than my share of DP, in multiple starts!

 

[nealeb]

There's also a variation of NthreadP for use with a thread-cutting gearbox which is very useful - you enter the range of ratios that the gearbox gives, plus list of changewheels, and it sorts it all out. What has always puzzled me is why the standard set of changewheels usually seems to be in 5s, sometimes 4s. I have a Smart and Brown 1024VSL; I get the impression that they changed the set of changewheels supplied as standard over the lifetim of the machine and they seem to be all sorts of odd sizes - but when you look at the thread-cutting table and the NthreadP results, you see that you can get a wide range of threads with fewer gears that way. Maybe it just needed someone to sit down and do the sums in the days before computers - or even programmable calculators.

 

[L98fiero]

There's also a variation of NthreadP for use with a thread-cutting gearbox which is very useful - you enter the range of ratios that the gearbox gives, plus list of changewheels, and it sorts it all out.

That's handy, thanks for pointing that out, I downloaded BoxfthreadP from the lathes.co.uk site. I found that my lathe won't thread 1.75mm pitch, this will involve a little work calculating/measuring the gearbox ratios but then, even if I have to make a gear or two I can cut pretty much any thread within the capability of the lathe, now I just have to build a taper attachment so I can do NPT.

 

[terryd]

That's handy, thanks for pointing that out, I downloaded BoxfthreadP from the lathes.co.uk site. I found that my lathe won't thread 1.75mm pitch, this will involve a little work calculating/measuring the gearbox ratios but then, even if I have to make a gear or two I can cut pretty much any thread within the capability of the lathe, now I just have to build a taper attachment so I can do NPT.

Hi,

there's an interesting app here, it has been developed by a Boxford (UK) / Southbend (US) user but suits most lathes, metric and Imperial with or without Norton gearbox. It's worth a look even just for comparison of your results,

http://www.herosteamengine.com/RideTheGearTrain/
Stay safe

TerryD