need some help on a machine mod.

[MCRIPPPer]

hey everyone. i have a little mini lathe that i enjoy modifying. i want to make a quick change gearbox for it at some point to make it more user friendly, and just because!

im wondering if any of you guys have pictures and explanation of how the nicer quick change gearboxes work on big lathes. i have seen pics of the simple ones with two levers and tumbler gears with the sloped detent holes. what i want to make is the type with two knobs that turn into different positions to select the gear. but i have not been able to find out how these kinds work. the reason i want this kind is simply that i like it more than the old school ones like on little atlas machines.

so what is the mechanism that allows a rotating knob to mesh different diameter gears?


here is the kind i am wondering about.

 

[Swifty]

I think that it may be far cheaper to go and buy a new lathe with a quick change gearbox. Or alternately,
change to a variable speed motor and controller.
Paul.

 

[MCRIPPPer]

even if i dont end up making one, i still want to know how they work.

a variable speed motor wont do threading.

i want to do this as a hobby project.

 

[techonehundred]

http://swarfrat.com/MiniLatheGearbox.htm

Like this one?

 

[MCRIPPPer]

kind of like that. but i want to make one that will fit in the normal spot where gear boxes go (will relocate the motor controller)
but i want to know how the type with knobs works. i dont really want to make the kind with two levers that slide along.

 

[Cogsy]

but i want to know how the type with knobs works.

Let me stress that I don't know, I'm just guessing. I assume each knob is connected to a 'shift drum' of sorts, like the gear shift on a motorcycle. That's the only straightforward way I can see it being done, barring electronic shifting.

I'd be interested in what you find out, just for fun.

 

[Noitoen]

You could adapt a small motorcycle's gearbox.

I'm adapting a variable speed motor to my Belflex and I don't see no reason for it not to thread.

 

[Tin Falcon]

The first thing to do is dowload a manual for lathe with such a grearbox.

Most decent manuals have an illustrated parts breakdown.

you will need to set up quite a few gears ranges to get a full set of thread choices.

Do not thinks A mc gearbox will have enough or the correct gear ratios.

Tin

 

[MachineTom]

Forget a MC gearbox if you want threading, the ratios would be useless. Be ready for some $$$, gears while relatively cheap you need a bunch of them, a 32DP gear would be as small as I'd go for pitch, and you should use .5 width, if larger pitch is used like a 20 DP 3/8 would work. $200 in gears fit in one hand. and you will need a least two hand fulls if not three.

Before you get to the shifting, think of how the bugger is going to work. For threading you need half nuts , how to mount them, is the apron large enough, how to mount the leadscrew, Then the drive from the spindle, how would that work, is there enough spindle to mount a gear to it.

As Tin suggested, better to buy another lathe with the capabilities you need, this project is not a good idea.

Many of the knob shifters use drive dogs to engage various constant mesh gearsets, a cam or drum moves the levers to position the dogs.This adds another level of complexity and great expense for custom cut gears, an dogs.

 

[tjwal]

This may end up a double post! I downloaded the manual to the grizzly G0750G lathe. It shows a parts breakdown of the gearbox. The shifter knobs have a gear on the inner end that mates with a rack. This allows the shifters to be moved left and right. After that its just a matter of gear ratios and how they are mounted on the various shafts. There is enough info in the drawing that it good be figured out. A 3D model would work better though.

 

[MCRIPPPer]

the mini lathe already has half nuts and lead screw, and tumbler, change gears, ect. i can buy a whole set of change gears for this lathe for about 30 bucks (but plastic gears). i just want to put all the change gears in a box, like the swarfrat one.

the problem with the mini lathe is that it takes a while to change gears out, and feeding and threading are shared by the lead screw.

im thinking if i had enough gear ratios to make some common course threads, and had a 1/2 ratio or 2X ratio on the output, it would cut alot of different pitches, such as 16, and 32 tpi using the same gear set.

 

[tjwal]

Have you thought about an electronic lead screw?

 

[Tin Falcon]

you can buy metal change gears for $ 50.

changing out gears is not that hard. And unless you do a lot of threading not a big deal .

electronic lead screw could be an option.
Tin

 

[MCRIPPPer]

i mostly like doing these things for the same reason we build engines. "why dont you go to the hobby store and buy an engine".

instead of only making engines i like also making tooling and modifications on my machines.

 

[kf2qd]

Here's how someone else did it. Probably the most practical way to do it.

http://swarfrat.com/MiniLatheGearbox.htm

 

[Tin Falcon]

This guy has all the metal gears and change gears for a mini lathe .
https://thehobbyistmachinestore.com/store/Mini-Gears/
full set of gears $115
change gears only $56. but you may need a couple hundred $$ worth of gears.
Tin

 

[goldstar31]

Might I suggest that you get a copy of Cleeve's Screwcutting in the Lathe?

Somewhere in what is laughingly called my library, I have probably the various articles on making a box with 20DP cutters. OK, I have a whole set but apart from lending the set to a colleague, I have replaced broken gears and made a few the odd rack and so on.

If Professor Dennis Chaddock was right, 20 gears loose equates to 750,000 pitches. Shoving them into a box gets a lower- much lower result. I'll take his word for that.

Write me- if you must

Norman

As an addendum, I don't have MEW165-166 but I have articles by Abigail and a series on 6" American lathes.

So far the Sparey stuff has failed to surface as with the stuff by Machin