Headstock measurement - What module are the spindle gears?

[RotarySMP]

Hi guys,

I am currently running my spindle with a 3:1 reduction belt from a 3Ph motor.

With the VFD I get about 250-2500RPM which is not bad, but could do with a bit more low speed torque. I'm considering putting the headstock two speed gears back in (replacing them with steel ones).

I have also been thinking about using a second set of these gears in the space under the bed where the original motor sat. With the two gear sets, I could have three ranges of about:
70-540
165-1250
380-2900.

To design that second box, I need to know the distance between the spindle axis, and the lay shaft axis. Does anyone have a mini lathe head casting sitting around and could measure this for me please?

Anyone know what module these gears are? The 20 tooth on the lay shaft has an OD of 50mm, which would put it between Module 2 and module 2.5 in the metric system. Is there an imperial standard 20 tooth gear which would have pitch diameter just below 2", and therefore an OD of about 2"?

[Vogavt]

I was wondering the same thing. I also have plans to implement a swappable banjo with a gear set that has higher tooth count to enable a smoother finish.

I've been playing around with some gear creation software and have printed out drawings for various sized toothed gears that came with my lathe. I'm getting very accurate modeling using a module of 1, Addendum multiplier of 1 and a Dedendum multiplier of 1.

Will have to look at your calcs to see if I can improve.

[HuFlungDung]

RotarySMP
Your thumbnail does not show the gears you are referring to, so I am assuming that there is an actual transmission elsewhere.

IF the gears are straight cut spur gears, then the closest standard module appears to be 2.25 from the measurements you provided. Such things are available in the Travers Tool catalogue.

From your chosen set of 3 ranges, I suspect that you've got unnecessary overlap, which means you'll use the low one and the high one, and not likely bother with the middle one, unless you've got an easily shiftable transmission. That is just my experience, running a cnc lathe with a two speed gearbox.

Assuming you are running your motor up to 120hz:
70-540 has full and constant hp from 300 rpm, which gives you more torque than running the motor at the bottom hz end of the second range, so you probably wouldn't.

And chances are probably good that on a mini lathe you're going to value speed over torque unless you are turning stuff that is typically too big for that lathe. So you'd want the high range as it is proposed (or higher) and probably you'd be using it anywhere from half to full speed in high range anyway. This puts the motor in a good operating range.

Upsizing the motor and VFD is common practice to improve the low torque range, to be able to skip one gear range in a gearbox.

[RotarySMP]

Hi HuFlungDung,

I was referring to the main drive train gears in the head stock, which transfer the power from the motor to the spindle.

I didn't realise module 2.25 existed. Thanks.

I already have the motor (3/4HP) and VFD, so I will not be upsizing it . I have only been running it to 75Hz, as it is a 2pole motor. At that frequency is it running at 4072rpm Running up to 120Hz on it would be about 5500rpm, which may, (or may not) kill it.

As you can see from the photo in the first posting, I have currently got the main drive train gears in the headstock removed, and am running with a 3:1 reduction belt directly between the motor and the spindle.

I value torque over top speed. I have had this lathe for about 6 years. It is really not the right machine form me (a DS&G 13x30 would be more like it), but am limited to what will fit on the inner city balcony. I use my lathe for relatively big stuff, and have not had a need for more speed than the 2500 I currently have. I would like a lot more torque low down.

You will always have some overlap in gear ratios, especially given the 7.5:1 turn down ratio from the VFD, and then with two separate two speed boxes, unless the ratios are extremely widely spaced. Such wide spacing is not practical in terms of space, or lay shaft speed for this application.

I looked at putting 15:45 and 45:15 pairs in the second gearbox, but the 3:1 step up pair would end up with crazy lay shaft speeds and an over speed intermediate belt drive.

The physical size of the additional gearbox is limited by the space under the bed where the original motor was located.

I have attached a block diagram of the concept I have been planning. Obviously doing the job with two gearboxes is not a great solution, but:

1/ the head stock gearbox is already there,
2/ there is not enough space under the bed to install a single wide range gearbox
3/ I want to remove the pulley from the spindle, so I can fit an indexing plate
4/ I want to remove the pulley from the spindle so I can more easily add a guard.

Maybe I should do an intermediate step in just reinstalling the main drive train gears in the headstock and running that set up. Maybe it would turn out to be enough of a solution.

[RotarySMP]

Hi Vogavt,

I don't mean the leadscrew change gears. My Lathe is CNC'd so the change gears have long be retired to a box under my bed.

[blades]

My Lathe is CNC'd so the change gears have long be retired to a box under my bed.

Only a lathe nut would assume you mean your lathe bed, right?

[RotarySMP]

I sleep better with gears, motors, electronics junk, wires, tools etc under my bed. It improves my aura

[HuFlungDung]

Let me see if I understand correctly: you are going to buy 4 gear cutters to cover the range of teeth you want to cut, @$92 a pop. Build a gearbox. Make shafts. Make some sort of quickchange shift. Live with the noise of straight cut gearing.

But you won't spring for a 1.5hp 4 pole motor (better torque at half the rpm of your two pole) and a VFD that will do away with all the above nonsense? Motors cost nothing on Ebay. Small VFD's are cheap on Ebay.

[RotarySMP]

Hi HuFlung Dung,

Ouch that was a good call.

Actually I was not going to buy four cutters and make the gears myself, I was going to buy the four gears from maedler.de at about €10 a pop.

Although buying GEAROTIC (GEAROTIC.com) at $75, and then making up a CNC mill axis to mount on the cross slide, and putting a stepper on the main spindle to drive it as an A axis so I could machine gears out with a 1mm end mill is also weirdly attractive.