Inside the LeBlond headstock you see this:
A full gear train with selector levers and gearing and shafts and an oil bath and and and..... It doesn't have syncros so you have to stop it to shift it into gear. If you don't you can clash the gears and break off teeth. If you crash the compound or tooling into the work or the chuck you can break off teeth and damage it. My old one had a few teeth worn down from shifting while running and crashing. To be expected from a military asset and then working in commercial production. It was a bit ragged out when I got it, but still useful.
The Sheldon is a different breed of goat.
Glen asked a good question about speeds, so here is the visual for the answer.
So, it's an eight speed belt drive. The belts directly drive the spindle, no gearing in the head.... Well, it does have gears for the quick change gear box.
This isn't the exact model I have, but the theory is the same.
My under drive looks like this:
Note that there aren't any cone pulleys in this drive. It's a single speed. Using the VFD to vary the speed of the motor is the way forward. I do have the cone pulleys, but that is the option if the VFD doesn't work like I want.
The two belts on the left run the spindle. They come up into the rear of the headstock where the QC gear train lives.
Of interest is the way Sheldon addressed a crash in the QC gear train. That small gear to the left of the tan one is a composite. Not steel. It's sacrificial. If there is an overload, its teeth will shear and save the rest of the gear train.
Here is the QC box and feed plate.
This is driven by the small gear on the lower right of the photo above this one.
Here is a cool gif of motor control wiring.
Yeah, Cluster Gear No Bueno Amigo.
ReplyDeleteThat damn Sprite has one in it with a Non Synchro 1sr gear.
That's why every MG Midget and Austin Healey Sprite built before 1975 always sounds like the transmission is full of gravel when they are in 1st gear.
People try to downshift into 1st and grind the teeth off.
You could always still go with cone pulleys if you really wanted to, if you wanted a lower or higher torque and /or speed.
Mighty nice of them to put a composite gear in there as a fuse, I'll bet you can just run down to the nearest drug store and pick up as many as you want, right?
Amazingly, someone is 3d printing replacements. My mentor kindly included one in there for it. Ya know, I should get a picture of it.
DeleteThe LeBlond 13 inch Roundhead Regal was also known as a trainer. I've heard tell the old machinist instructors could hear an attempt gear change whilst rotating across a huge building and be chewing on the student before they even began to scurry over really start the browbeating....
One cool thing I like about the LeBlond is the handwheel on the left of the headstock. That was your brake. It was shiny and smooth. Worked perfectly.
STxAR, it looks very cool - also, I have no idea what I am looking at. What does one do with this beast?
ReplyDeleteWell, your question will be a springboard for the next post. Thanks for asking!
DeleteThat VFD could be a stroke of genius, STxAR - if you can direct drive the lathe with it? Or do you need a gearbox reduction? What is it? 1800 RPM? What does a metal lathe typically run at? It’d be nice if you can dispense with the belts, sheaves and gears…
ReplyDeleteVFD stands for Variable Frequency Drive. It takes 230 V 60 Hz and can put out 230V from about 0 Hz to about 400 Hz. It's a way of driving an industrial three phase motor. You can use single phase (house wiring) or, like I plan, use the industrial electrical service (generated by my rotary phase convert) to vary the frequency which will adjust the motor rpm. It's a trade off though. When you are not feeding 60 Hz to the motor it will heat up more and lose torque. Limiting the frequency range from about 20 Hz to 100 Hz will probably give me all the adjustments I need. And also keep the heat and torque issues to a minimum.
DeleteAnother plus is you can soft start the motor. That is to say, have the motor spin up to speed over a few seconds and also spin down over a few seconds. Adding an external load resistor will allow you to brake the motor quickly, dumping the generated electricity into that load. Like an emergency stop.
The VFD is programmable and has so many options it'll overwhelm you. Most folks don't even scratch the surface of what they are capable of. I'm pretty sure I won't either.
I am familiar with them. They can be a handful - we often sold them as a pre-engineered unit that included the motor. Our design guys came up with a way of using the VFD to catch downhole PC pumps that unloaded torsional loads on their drive shafts. The VFD would catch the runaway load as the shaft unloaded - and slowly unwind it instead of letting it go in a fashion that would demolish the top drive. Back in the 90's those things were user UNfriendly as hell and you could pull your hair out by the roots trying to configure them. They were expensive as all get out too.
DeleteI hope your experiment works. There's actually a lot going on there...
My guess is they had a resistor bank to take that motors output as it unspooled and dumped it into heat via the resistors. Like dynamic braking in a locomotive, or the big LeTourneau dump trucks I used to build.... ehhehehehe..... But I'm just spitballing.
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DeleteMr. STxAR,
ReplyDeleteYour mentor here. I didn't tell you there is another one of those micarta made disposable gears located in the quick-change gear box. I didn't know that until about ten years ago. I had a conversation with someone out there that had one of these lathes and asked me about it. Of course, I've never had a need to take apart the gear box either. I'm working on restoring my third lathe like this one you have. Learn something new every now and then.
And there you go! More good info. I can 3d print with PLA filament. I wonder if that is stout enough to make a decent sacrificial gear?
Delete