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Machine Shop and Tool Talk Shop Equipment, fabrication, repairs, how to fix it, which tool to use for the job. Machinist shop talk, straight to the point.

Machine Shop and Tool Talk

Slowing Down a Lathe

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Old 08-13-2019, 08:58:21 PM
dkamp dkamp is offline
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Default Re: Slowing Down a Lathe

Pete- the shock usually does a whole lot more to break free a stuck chuck than the torque.

I had a faceplate stuck in a machine I did an 'operational' rebuild on. After exhuasting all other options, I tried something silly, that actually worked.

I had to drill the bolts out of the chuck to get it to release the faceplate. once the chuck was clear of the faceplate, I used a 4" disc grinder to cut three flat spots in the outer edge of the faceplate. Then I started the machine, and placed a MAPP torch on the compound, pointed at the faceplate, at the same radius as the spindle threading (I had to approximate here). After a few minutes of spinning, it was starting to show warming signs.

I removed the torch, stopped the spindle, and (with the belt still engaged)... I put a stout chisel in one of the notches and gave it a firm whack with a deadblow.

I would've repeated it with the other three notches, but it came loose on the first whack.

And the faceplate was still perfectly useable. I was expecting the heat to distort it enough so that a chuck wouldn't run true, but I cleaned the spindle nose threads lightly with a hand-brush, and rubbed a candle (wax) against 'em, same for the faceplate (after it cooled), threaded it back on, and gave it a visit with the dial indicator, and it was just fine.

Now, for speed control... for anyone learning to use a lathe, having variable speed is the FAST way to learn the importance of feeds and speeds, and for facing (going from large outside diameter, in to the center of the workpiece) it's the ONLY way to get it 'right'.

For the SB 9, a 1/2hp 120-single in/240 3ph out VFD, belted direct to your spindle with a sheave about half the spindle sheave size, is the perfect solution. A TECO or Minarik drive will do that on the relative cheap. A low-horsepower 3-phase motor is easy to find used, and you won't need anything fancy to make it work.

If you were me, you'd set it up on your workbench with VFD control inputs to include a variable-speed control knob on the left side, and a forward/stop switch by speed knob, and an emergency stop mushroom button on left side, with an actuating bail on the front edge of your workbench, so that if something goes wrong, a bump from your hip, elbow, or hand will shut it down. A control contactor to power the whole thing up, as well as a pair of LED lamps on flexible necks to put light where you need it.

As far as height, on a 9" machine, you'd likely be more comfortable setting it so that the work axis is about level with your shoulders... because you'll be spinning smaller workpieces, you don't want to be hunched over while trying to make cuts.

When mounting the lathe, look at the feet. Notice that there's mounting holes in some places, but not others. On precision machines, it's counterproductive to mount them TIGHT to a surface, and typically, you will not mount them down with more than 3 points, because doing so will tend to distort the geometry of the ways. If your SB9 is like mine was, there's only three mounting holes... don't add more, and don't bolt it to a bench that's subject to twisting itself in such a way that it'd carry that twist to the machine. You'll find all the mounting instructions in the SB manual- follow it closely and it'll stay true.
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Old 08-14-2019, 01:48:52 PM
Pete Spaco Pete Spaco is offline
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Default Re: Slowing Down a Lathe

Pete- the shock usually does a whole lot more to break free a stuck chuck than the torque.
I totally agree on that.
But then, why would you use a deadblow hammer?
(maybe I am missing something).

Pete Stanaitis
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Old 08-14-2019, 11:01:46 PM
dkamp dkamp is offline
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Default Re: Slowing Down a Lathe

I used a deadblow because I presumed that a little thermal expansion would have been sufficient to incite release of the bind, and I really didn't want to shock the chisel enough to bounce it loose and have it visit my leg.

once warm, it surrendered peacefully, so I had no need to escalate. I was really hoping that I wouldn't have had to go to any more heat, because that can cause more, and worse problems with a machine tool.

next challenge for me, is a tapered arbor and drawbar on a Cinci #2 horizontal. It's been in there TIGHT for many years, since long before I acquired the mill, and last time I tried to free it, it laughed at me... and promptly handed me back my arse.
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