Presto 14-B (similar to 8DG) Variable Pitch motor

[MrMegaEli]

Hey guys, I have a Presto 14-B. Does anyone have any suggestions on how to figure out the RPM, torque, and horsepower of a variable pitch motor? This will just be manually controlled for very basic pitch adjustment.

I also need the motor to turn the lead screw slower so I can cut at higher pitches (in the 250LPI range) than the original 136 max LPI

Thanks!

Eli

[dubcutter89]

I've once done this to a Presto-8D
Back then I used a little precision-DC-Motor (low noise) and some tooth belts to get the rpm in the needed range...

If I had to this again I would still take the same little DC-Motor, but I wouldn't use the tooth belts again (too much bearings that need exact
manufacturing to get rid of noise etc...)
Instead I would make disc that has a rubbber o-ring on its edge and a pulley for the rim that goes to the overhead pulley...
The motor shaft is driving the disc on its rubber edge, and the disc is driving the original pulley of the lathe via a rim...
So you would only need a motor and this disc (+ something to mount...) and a dc regulator for variable pitch control.

AFAIK the pulley of the feed mechanics is driven by the turntable
so the rpm is in the range between 10-80 ??
If your motor has a 5mm shaft and something like 1000rpm
and you want 50rpm of the disc then the diameter would be about:

D2 = n1/n2 * D1 = 1000/50*5 = 100mm

D2...Diameter of the disc
D1...Diameter of motor shaft
n1...rpm motor
n2...rpm disc

Hope this helps...

Lukas

[MrMegaEli]

Thanks Lukas!

I’m wondering why you would put an O-Ring around the motor shaft and lead screw pulley, instead of hooking up the motor shaft to the lead screw pulley via a longer shaft and shaft couplers?

Eli

[dubcutter89]

Hmm,
as i said your motor will probably do about 1000 rpm, you need ~50rpm on the lead screw pulley
-> you need a gear!
gearwheels, toothbelts etc. make noise + must be precise machined

so an easier solution would be mine where the little motor shaft is driving a bigger disc on its edge (making a gear). Only one rubber O-ring to get more friction.
same principle as on tt-drives with idler wheels...

an alternative would be to find a motor that already has a gear on it.
long shaft + 2 couplers (and maybe some rubber damper)
but be aware that most small motors with gears make lots of noise...
maybe a car wiper motor works...

hope this helps
Lukas

[MrMegaEli]

I have an old Bodine gear reduction motor. After the gear is 45 RPM. I am going to put a DC volt meter (150VDC) across this, and draw a 33.3 and 45RPM scale on it.

[MrMegaEli]

OK, so I don’t think this bodine motor will be the best option. First of all, it uses a $50 set of bearings, plus the time it will take to replace them, and isolate the BIG motor! It would be great to find a smaller motor that will be quiet and easy to isolate

[symatic]

I just found this thread, and I'm looking into the same thing.

My 14-B needs some sort of motor control for the LPI.

It looks like the original system would have been a belt between the Platter's drive shaft, and a 2nd drive shaft that is hanging below the Pitch Gearbox.

I'm guessing the belt would have turned the Pitch drive shaft at the same rate as the Platter was turning, and the gears turn it into the right LPI.... but the old specs make the LPI's pretty lame by today's standards.

So one idea is to hook up a separate motor, with a pulley turning the Pitch drive shaft, and this way I could work out the speed i'd need to turn it so the original LPI settings would translate to more modern equivalents.... this way I could also keep the ability to manually wind on the lead screw for track markers etc.

But my dream setup is to have total computerised control of the lead screw... and to do this I tihnk I'd need a motor and pulley connected to the manual winding wheel, which could offer much finer tuning I hope. then with some sort of Arduino controller I'm hoping I could draw midi automation alongside my audio programme in my DAW, and basically automate the process.
This could potentially lead to the ability to do clever lock groove stuff, inspired by sillitoe's precision head-dropping mechanism.

if anyone's got any advice it'll be greatly appreciated, there's no info I can find on 14-B's so I'm going in extra blind!

[symatic]

i managed to fing imperial measurement pulleys to reinstate the original mechanism for LPI. so far so good, i thik with different sized pulleys i could get differnt LPI's