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Machine Shop and Tool Talk

Slowing Down a Lathe


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  #1  
Old 07-14-2019, 01:40:38 PM
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Scott Kocher Scott Kocher is offline
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Default Slowing Down a Lathe

ok guys can you use a rheostat to make a single drive lathe into a variable speed or must I do a step pully set up for it
the lathe is a SOUTH BEND 9 BUY 3 1/2
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  #2  
Old 07-14-2019, 01:49:59 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: slowing down a lathe

How slow do you want it to go? Does it have back gears? Back gears will give you the slowest speeds. What rpm motor does it have? Should be 1725 rpm, has someone installed a 3450 rpm motor? I don't think you can use a rheostat to slow down a single phase motor, if you use a 3 phase motor you can use a vfd to control speed, or use a DC motor and you can control speed, but either way low speed = low torque.

Answer above questions and explain the problem you are having in detail. And show me a pic of your motor/pulley arrangement.
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Old 07-14-2019, 04:01:30 PM
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Default Re: slowing down a lathe

thanks for the reply. please be patient with me. this is all new for me.
#1 i dont know how slow I guess it depends on what you are doing correct #2 i dont think it has back gears
it is 1/2 hp motor 1725 rpm. the motor has a 3" pully driveing a 6 1/2" pully wich is belted to what says is a vary speed box with a handle to shange your speed but i dont know if it dose anything .the handle dose not move . comming out of the box on the other side is a 4" pully that drives the lathe wich has a 4" pully as well . even if the vary speed box dose work i would like to eliminate it because i have minimal space to put the lathe . it sticks out the back way to far for me to put it where I want it. that is why i thought of useing something like a dimmer switch to lower the speed if possible
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Old 07-14-2019, 04:11:38 PM
PLCtech PLCtech is offline
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Default Re: slowing down a lathe

You won't be able to slow down that motor. Your speed will depend on the gears.
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Old 07-14-2019, 04:29:29 PM
Vanman Vanman is offline
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Default Re: Slowing Down a Lathe

No, you cannot vary the speed of that type of motor, unfortunately.

As Dgirl says, a three phase motor and variable frequency drive is probably your best option if going that route. But, hp will not be constant, rather torque is, so slow speed won't give you extra torque the way a gear reduction will.

If the vari-drive can be made to work, my vote would be for keeping it and accommodating it, if possible. Some of those must have the motor running when changing speed, by the way.

I'm pretty sure I see back gears in your first photo, those gears in the headstock.

Keith
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Old 07-14-2019, 04:34:32 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Slowing Down a Lathe

Not sure if that is original, or someones modification, either way you are going to need that varidrive, cleanup the shop and make room for it. Varidrive probably needs a good cleaning, you've either got gummy oil or some rust keeping things from moving. My guess is that it originally had a 3 or 4 groove pulley on the spindle, then behind it would have been the countershaft with a matching pulley and the motor would have been belted to that with a 2 groove pulley, long story short there was always something back there. You might be able to shorten up that space by mounting motor above the varidrive.

As Vanman stated, the motor most likely needs to be running in order for varispeed to work, most have a tag on them explicitly stating NOT to move lever unless motor is running.
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Old 07-14-2019, 05:11:12 PM
Russell Walker Russell Walker is offline
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Default Re: slowing down a lathe

The vary speed needs to be running to adjust.
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Old 07-14-2019, 05:47:39 PM
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Default Re: slowing down a lathe

ok another piece to the puzzle
I was looking in a box that came with it & found these gears .
is this what I need to do the different jobs
will this do what I want to do (change my speed ) by using the different gears ? . if that dose then can I eliminate the vary speed box ? & hook the motor up direct
1 what gear dose what
1 has 48 teeth
1 has 39 teeth
1 has 36 teeth
I believe there is one on it already that has 45 teeth
also what gear gets used for what job .
like I said this is new to me & I'm trying to learn
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Old 07-14-2019, 06:05:59 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Slowing Down a Lathe

You cannot eliminate the varispeed. The gears are for changing the speed of the drive rod that runs across the front of lathe, that rod determines rate of autofeed, and if you have the proper chart may allow you to do threading, but you might also need more gears. From my limited experience with a changegear lathe, use taps and dies for threading, its easier than fiddling with the gears. Good first projects for you might be a spring loaded tap center and a die holder, both are used in the tailstock.

Basic instructionals are available from mrpete222 on youtube
https://www.youtube.com/watch?v=olC9xyHheDU


Spring loaded tap guide build by mrpete
https://www.youtube.com/watch?v=y79op3DM4uo

Lathe die holder (have not watched this one, search "lathe die holder" on YT for other ideas)
https://www.youtube.com/watch?v=bq2NtnbViF4

Oh yeah, welcome to owning a lathe! How much tooling did you get? Ahh does not matter, you will always need more :-)
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Old 07-14-2019, 06:54:23 PM
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Default Re: Slowing Down a Lathe

Speed control need not be that complicated. Just mount a jackshaft with a couple of stepped pullys on it.
Doc
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Old 07-14-2019, 07:46:35 PM
cornbinder89 cornbinder89 is offline
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Default Re: Slowing Down a Lathe

Unless my eyes are playing tricks, it does have back gears, exposed in the 1st pic, but under covers in the later pic's.
Back gears are like deep reduction in a transmission. If you engage them without disconnecting the chuck from the main shaft it will lock the spindle for removeing the chuck. there should be a pin or some sort of lock that can release the spindle from the main shaft so it can be driven thru the back gears. There should be a lever behind the main shaft to the left that move the back gears into mesh with the gears on the main shaft (to either side of the belt pulleys.
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Old 07-14-2019, 07:47:10 PM
Jake Jacobs Jake Jacobs is offline
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Default Re: Slowing Down a Lathe

Lots of South Bend Lathe books on ebay. You would find them helpful. https://www.ebay.com/sch/i.html?_fro...D+9+By+3+1%2F2
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Old 07-14-2019, 08:43:17 PM
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Default Re: Slowing Down a Lathe

corn binder I think you are right . yes there is a lever to the left behind the main shaft with a set of gears. like you said when I pull or engage that lever it locks the main shaft for removal of the jaw chuck. so when this is engaged it will run at a slower speed?
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Old 07-14-2019, 10:22:50 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Slowing Down a Lathe

Quote:
Originally Posted by Scott Kocher View Post
corn binder I think you are right . yes there is a lever to the left behind the main shaft with a set of gears. like you said when I pull or engage that lever it locks the main shaft for removal of the jaw chuck. so when this is engaged it will run at a slower speed?
Yes, but you have to figure out how to disengage another gear. 3rd post, 3rd pic, to the right of spindle pulley what is under that cover? Should be a gear, look at face of it for a knob to pull.
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Old 07-14-2019, 11:17:20 PM
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Default Re: Slowing Down a Lathe

Your lathe appears to be a South Bend 9 inch Model C Workshop lathe. You can see it in the South Bend catalog at this link. http://vintagemachinery.org/pubs/1617/16868.pdf

There is a lot of information on how to use your lathe at this link.
http://vintagemachinery.org/pubs/1617/17260.pdf

There are many more South Bend publications at this link. http://vintagemachinery.org/mfgIndex...?id=1617&tab=3

The files are free to download. I hope this helps you figure out your lathe. It looks like a nice one.

Mark S.
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Old 07-15-2019, 12:25:43 AM
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Default Re: Slowing Down a Lathe

Looks like someone made a vee groove in that large flat belt pulley
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Old 07-15-2019, 04:41:37 AM
M.Canute M.Canute is offline
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Default Re: Slowing Down a Lathe

Quote:
Originally Posted by Motormowers View Post
Looks like someone made a vee groove in that large flat belt pulley
Agreed. It looks like somebody swapped out the jackshaft arrangement for the variable speed drive.

Scott Kocher, if you can get the varispeed to work and it's still too fast, changing the pulleys on the motor and on the varispeed will slow it down but if the range of speeds isn't sufficient a step pulley setup should give you a very workable range. For facing work a varispeed would be very nice to have and for just regular turning it would be nice too for a quick and easy way to fine adjust your SFM. A VFD would be great too but since you already have the varispeed I would recommend you get it to work first if possible.
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Old 07-15-2019, 06:35:38 AM
Rbruner45 Rbruner45 is offline
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Default Re: Slowing Down a Lathe

the back gear is designed to provide another set of low range speeds. When engaged the main spindle gear needs to ge disngaged so itos free floating on the spinde. This is generally accomplished by pulling a small knob on the right side of the spindle gearing. While folks do use the back gear to 'lock' the spindle for chuck removal - that is not the purpose and it not recommended - the are many spindle vear/back gear sets with chipped and missing teeth because of this usage.

Rick
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Old 07-15-2019, 06:56:39 AM
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Default Re: Slowing Down a Lathe

Here is a picture of my 9" South Bend lathe, with the jack shaft you are missing

To use the back gears you lift the cover by the chuck and pull a pin, then move the lever you use to remove the chuck and you will be in the low gear.

I believe those extra gears are for changing the speeds of the drive, they go on the left side of the lathe, moving the lever with the 2 gears will change the direction of the feed
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Old 07-15-2019, 09:45:07 AM
Pete Spaco Pete Spaco is offline
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Default Re: Slowing Down a Lathe

Lots of good advice already.

I only add this:
Do NOT apply power to this lathe until you have studied at least one of the good books already recommended!!!

You might even check to see if there are any evening classes in basic lathe/machine tool training at local high schools or vo-techs.

Or, even look for a related club in your area.

Pete Stanaitis
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