Making gears in the lathe

My lathe arrived without a full set of changewheels, so one of the projects I'd like to do is to replace the missing items. According to John P's manual for the Warco equivalent, the gears should be:

26 27 28 29 30 33 34 35 36 38 41 43 45 (ones I have in bold)

They are mod 2.5, p/a 20 degrees, 6mm thick, and rotate on a splined hub.

However, the front panel of the lathe:

also has 20 and 40 tooth gears listed (and it occurs to me I should check the imperial and DP charts as well!)

Either the Warco lathe has a slightly different internal gear train or there are more ways of achieving the same thing than what is listed - quite possible with the slightly unusual setup.

So the actual list of needed gears is pending, but in the meantime I'm thinking about the making process. I've already acquired the necessary M2.5 cutters - fortunately, two cutters covers the 26-54 tooth range. I don't have the next one down, but I suppose instead of making a 20/40 pair I could make a 52 to go with the 26.

Although the lathe has steel gears, I was thinking about delrin, for a couple of reasons: cheaper, less likely to damage the cutters, less likely to damage the lathe, and easier to make. There is already a sacrificial plastic gear so I don't think there's any reason to worry about strength.

To make the splines, I was thinking of mounting the blank in the headstock and using the carriage as a shaper. Not the quickest but should be easy enough in delrin.

It's cutting the teeth (on the lathe, as I have no mill) that has me a little puzzled. I've got an HV6 rotary table with dividing plate set on the way, but I'm scratching my head a little on how to set it up. I have a fixture plate I can attach to my cross-slide, but the centre height over this is a little under 75mm. The HV6 centre height is 100mm but more to the point I don't fancy packing it up for each different blank (the largest blank, the 46 tooth, will be 120mm dia)

The other way of doing it is to mount a vertical slide (not yet acquired, alas) and have the HV6 hanging off the side of it, which I think would be safe but hardly conducive to rigidity. Everything else I can think of seems worse by comparison. Maybe having the vertical slide facing the back of the lathe rather than the headstock and mount the table vertically on it?

Edited By Calum Galleitch on 11/04/2022 14:34:16

you need a copy of Ivan Law's book on Gears and Gear cutting.

Ketan will provide, or even your local library book

Chapter 9 in Gear and Gear Cutting Workshop Practice Series No 17. Show how it is done. This might help

Hi Calum,

To me it seems using a vertial slide is the best way if you don't have access to a milling machine. Any model engineers near you that could assist you? A horizontal milling machine would do those gears nicely. Module 2.5 are bigger than any gears I have cut, so I wonder if the lathe setup you describe would be rigid enough for that size of gear teeth.

Thor

Hi Calum

Here is the change wheel list from the Warco GH1000
lathe ,i expect the internal gears will be the same but they
have replaced some of the changewheels.

The third list down has the same result as your listing
but the gears in the first rows are altered.

John

Callum,.

I don't know your machine, and so, risk raining, / pouring on your parade.

The hobby lathes that i have come,across, admittedly few, all seem to use gears with Modules of 1, 1.25, or 1.5.

2.5 Mod is pretty coarse. Your 45T gear would have an OD of 117.5 mm ! Has it?

In Imperial, terms Myford 7 Series use 20 DP gears, whereas other machines use gears as coarse as 14DP.

In this case a 45T gear would be 3.351" ( 85.271 mm ) OD The 127T Myford Imperial to Metric translation gear has an OD of 6.45" (163.83 mm) The equivalent 45T gear would be 2.35" (59.69 mm ) OD

So your 2.5 Mod gears are pretty coarse!

Before trying to cut any gears, buy and study Ivan Law's "Gears and Gear Cutting"

It is No 17 in the Workshop {Practice Series.

It will ,be a help to you, and possibly prevent some costly mistakes.

May i suggest that you check your gears, before investing in cutters?

Take a gear and measure the OD in mm.

Count the teeth.

then use the formula

Module = OD / (Tooth Count +2 )

A 1.5 Mod 45Tgear would have an OD of 70.5 mm

A 1.25 Mod 45T gear would have an OD of 58.75 mm

My ETR BL12-24 which is 150 mm centre height (So not a small machine by hobby standards ) uses 1.25 Mod change gears, so the 120/127 compound has an OD of is 158.75 mm.

The 40T gears driving and driven to the gearbox are 52.5 mm OD.

The pinion engaging the rack to traverse the saddle is 13T, 1.5 Mod so is 22.5 mm OD,

Mini lathes use 1 Mod changegears, so the 80T gears have an OD of 82 mm

HTH

Howard

I tend to only cut about three different thread pitches. So you don't waste any effort, do you need these gears?

Just reread your thread on installing the lathe and the gears do look coarse.

Maybe this is why they stop at 45T

But you will still find Ivan Law's book a tremendous help. It gave me the data and courage to start cutting gears, not that I am good at it.

To cut gears in the lathe, you will need to find a way to mount a Dividing Head or Rotary table , with the axis horizontal so that the blank can be indexed.

Hopefully, the tooth counts that you need will be available with the division plates, (Not all are, sadly )

Howard

Howard

If D is driving E you don't need the specific values - just something to give you a 1:2 ratio. Since you have a 36 you could make an 18 to give you that with less effort unless they are needed elsewhere.

Posted by Bazyle 11/04/2022 19:02:00

If D is driving E you don't need the specific values - just something to give
you a 1:2 ratio. Since you have a 36 you could make an 18 to give you that with less
effort unless they are needed elsewhere.

-------------------------------------------------------

The problem with doing this is if you would wish to keep the original
splined hub ,the od of the splined hub on this machine is 34mm,
the OD of an 18 tooth  gear would be 50mm and the the root diameter
is 38.5mm which means that there would be only 2.2mm from the bottom
of the tooth to the od of the spline.
The maximum that the gear could be profile shifted is about .9 then the
tip diameter becomes 54.5mm and the root diameter would be 43.1mm
and would be about 4.6 mm from the root of the tooth to the spline ,the
tooth height is about 5.5 mm.
This would almost certainly need to be a generated gear ,solving these
sort of problems are not always that easy.

You can see the sort of problems that this can cause here with this
gear to fit on this type of lathe at 1.0 mod and 40 tooth even when
it is cut oversize there is not much left below the tooth roots.
As when it is used the lathe spindle is revolving below 2 rpm
so it is transmitting little power and is safe to use.

John

Edited By John P on 11/04/2022 21:53:17

I once replaced all my POM lathe gears for (self made) aluminium gears. They where to loud so I put the original POM gears back. Until now, I haven't broken a POM gear despite my abuse of the lathe.

I have made a post and video of how I make my gear cutters and gears. Maybe it is helpful.

Making gear cutters and gears

Thank you all. Yes, I have Ivan Law's excellent little book, and I had forgotten it went into a fair amount of detail on setup; when I read it, I was more interested in the theory side as I knew nothing about it. I see from a quick scan that my notion of mounting it on the vertical slide facing backwards isn't completely ridiculous.

The change gears are definitely Mod 2.5 - the measurements are correct, the manual says they are, and the tooth profiles match the module 2.5 cutters I bought!

On making threads, no, I don't intend to produce vast numbers, but the ones I can do are fairly constrained and I do want to be able to do some very specific ones - for example, at some point I want to make an ER collet holder to fit in the MT5 spindle, as commercial items are £££-y, and I can't pick my own thread for that! But cutting just a 33 tooth gear would open up a lot of useful sizes.

John, thanks very much for that photograph - it makes me wonder if my cover plate is 100% correct - I've still to find time to sit down and work through the rest of the calculations, but it does seem a bit strange that it calls for a 20/40 pair there and nowhere else. Also the labelling of the ABCDE gears is different from my machine which I think matches the manual.

In which case I'd be inclined to buy one! £28.48 from this firm for example. Still a fair amount of fitting work to do, but far easier and faster than making a gear from scratch, and it will work. (I think Delrin will be OK, but...)

Making the other missing gears potentially saves money, but shaping them on a lathe is a challenging beginner project that will take a long time. Educational of course, yet burning time that might be spent better on other projects.

Same problem with making your ER collet holder to fit in the MT5 spindle. By the time metal has been bought and machined correctly, it's hard to compete with a commercial item, which will probably be better made. (Precision ground rather than turned on a lathe.)

Even though I enjoy making tools and accessories, I avoid getting sucked into producing them. There isn't enough time in my day...

Just a thought: our circumstances may be completely different!

Dave

No need to look for ER collet chucks with 5 MT shanks.

Get a 5 -3 MT sleeve and use the available 3 MT tooling.

My lathe, and many others like it came with a 5 - 3 MT sleeve.

Howard

You'd be better off with a backplate mounted ER32 chuck, then you maintain full bore of the spindle. This one is already machined to fit D1-4 nose, but plain ones are available **LINK**