How necessary is having modular / Diametric pitch capability on your lathe...

[ArmyDoc]

If you don't have it on your lathe, can you still make a worm gear, gear hob etc?

 

[Jim F]

Isn't that a cutting tool parameter ?

 

[ArmyDoc]

I don't know. I'm trying to decide on a lathe, the ones with universal gear boxes have inch, metric and Modular and diametric pitch settings. I'd never heard of the latter two, and when I looked it up it said it was used with making worm gears. I'd seen a video on making gears, but it was on a horizontal milling machine. I found another that was making a worm gear on a lathe, but he used a tap as the gear hob. Final video I saw made a hob on a lathe, but didn't say what the settings were. It's a case of not even knowing what I don't know, and not knowing where to start...

Lathes with universal gear boxes cost 50% to 100% more... hard to know if that's worth it, since I don't know how/when you use the modular/DP settings, other than apparently they are used when making gears.

 

[Jim F]

My understanding is Modular are metric gears tooth shapes and DP are Imperial.

 

[ArmyDoc]

My understanding is Modular are metric gears tooth shapes and DP are Imperial.

Not so much shape as pich. Modular are measured in milimeters and Diametrical are measured in inches. Both are related to pi... But I don't know how they are used, or if there are alternatives if your machine doesn have those settings.

 

[benmychree]

Module and diametral pitches can be accomplished on ordinary lathes that can accomodate change gears (there are lathes that cannot mount change gears) I made a set of change gears for my 19" Regal LeBlond lathe that creates the capability of cutting metric pitches and diametral pitch leads, I have not cut any DP leads so far, but do occasionally use the metric pitches. The necessary tables of change gears came from a LeBlond manual.

 

[savarin]

This would make an awesome "How to" video for someone who knows "How to" make these along with easy descriptions of all the terminology.

 

[Lo-Fi]

Module and diametral pitch are terms to describe the size and spacing of gear teeth, with dp usually describing gears of imperial measurement and module metric, though is entirely possible to express a module as dp or dp as module.

Pitches for threads, which is what you're going to be using a lathe for, are described using the number of teeth per inch - similar to diametral pitch for gear teeth - for imperial threads, with metric being specified by how much one turn advances the thread, or "lead".

With a change gear lathe, it's possible to make any thread you can imagine regardless of the leadscrew pitch, providing you have or are prepared to make the required gears. With a thread cutting gearbox, you often have some options for cutting threads of the type that your leadscrew isn't, though metrics on a lathe with an imperial leadscrew are often approximations only, and vice versa. The smallest gear that can correctly convert inches to mm is 127 teeth - quite a thing to fit in a small lathe. There are some smaller gear combinations that result in a ratio close to 1.27:1, and these are often used, but 127 being a prime, nothing spot on. Mostly the inaccuracy is academic for hobby purposes.

We're in odd positions either side of the pond with standards and what equipment is available. Here, most work is metric, though most old machines available are imperial. I'm so glad my mill is metric - I'm no great fan of the (sorry) imperial system - but my lathe is imperial and that needs to change as I work in metric. In the US, you're still using inches in a largely metric world, but most machinery is still set up for inches. I guess it depends what you want to do?

 

[benmychree]

I also have a change gear device for my B&S milling machine that can divide table movements in diametral pitch and circular pitch, it was made mainly for spacing gear rack teeth, but I have also used it to space graduations on several brass blacksmith's rules that I have made. this can also be done with a universal dividing head geared to the table screw, but it takes a lot of cranking; 10 turns of the crank for 1/16". B&S in their book on milling and milling machines has a table on various spacing movements using combinations of change gears and crank movements.

 

[Jim F]

Module and diametral pitch are terms to describe the size and spacing of gear teeth, with dp usually describing gears of imperial measurement and module metric, though is entirely possible to express a module as dp or dp as module.

Pitches for threads, which is what you're going to be using a lathe for, are described using the number of teeth per inch - similar to diametral pitch for gear teeth - for imperial threads, with metric being specified by how much one turn advances the thread, or "lead".

With a change gear lathe, it's possible to make any thread you can imagine regardless of the leadscrew pitch, providing you have or are prepared to make the required gears. With a thread cutting gearbox, you often have some options for cutting threads of the type that your leadscrew isn't, though metrics on a lathe with an imperial leadscrew are often approximations only, and vice versa. The smallest gear that can correctly convert inches to mm is 127 teeth - quite a thing to fit in a small lathe. There are some smaller gear combinations that result in a ratio close to 1.27:1, and these are often used, but 127 being a prime, nothing spot on. Mostly the inaccuracy is academic for hobby purposes.

We're in odd positions either side of the pond with standards and what equipment is available. Here, most work is metric, though most old machines available are imperial. I'm so glad my mill is metric - I'm no great fan of the (sorry) imperial system - but my lathe is imperial and that needs to change as I work in metric. In the US, you're still using inches in a largely metric world, but most machinery is still set up for inches. I guess it depends what you want to do?

To add a bit to your post, a 127/100 transposing gear for a SB9 and 10k, and probably the Atlas/Craftsman is 7" dia.
You have to remove the gear cover to use.
This is mine that I had 3D printed.