my chuck got minor damage today :(

[precisionworks]

There are only two types of machinist - those that have crashed & those that will:D

A useful chuck mod is to bore the end of the jaws to hold thin parts, like washers or spacers. My South Bend has only one-piece hard jaws, so there's no soft jaw option. Mine are bored for a small OD part (a short piece of 1/2" drill rod was clamped in the jaws for a spacer), so anything larger than that has 6 point contact, which isn't perfect but still works OK. When this was posted on the PM forum, many members gave me Holy Hell for mucking up a "pristine" chuck. But, it works well.


3 jaw chuck tip after boring

Holding a thin spacer with 6-point contact

 

[Anglepoise]

Will,
We all have our 'pet' procedures and as you get to know your new machine, you will adapt yours.

If the design specs allow it, I always try to machine a run out groove for the threading insert. Then the sound changes as the cutting tip arrives at the groove. You will probably notice that to disengage the half nuts, it take more pressure on the lever when actual cutting is going on. When it enters the groove,and cutting stops, disengagement is instant with no resistance.

Also IMHO,DRO is useless when threading. Of course it works, but most people find that watching a digital readout is not easy as the digits rapidly change.

I set up a 1" dial indicator, and watch the swing of its needle aproach Zero, to let me know when action on my part is required ( open half nuts, rewind cross slide, or whatever system you use to disengage )

Good luck, and thanks for sharing all this. Takes me back a few years...<g>

 

[precisionworks]

I set up a 1" dial indicator

+1

The best $10 you can spend is for a pair of mag-backs for two of your indicators:

(Little Machine Shop, P/N 2531)

If you want an indicator with mag back already attached, J&L often has them on sale for around $30:

Stick one where it will contact the carriage when it gets within range of the end-of-thread. Stick the other on the cross slide ... when the threading tip is retracted, you lose zero, and this indicator allows return to zero + your next depth of cut.

Useful for lots of other lathe work in addition to threading, like boring to a shoulder, or drilling to a desired depth.

FWIW, these indicators get beat to death. Hot chips, cutting oils, etc., are tough for them to handle. Mine look like they've been through World War III, with cracked lenses, melted spots, you name it. When one stops working (or starts to get sluggish), it goes in the trash. This is not the place for a nice Starrett or Mitu indicator:eek:

 

[cmacclel]

Wow Will bigtime BUMMER!

Once I engage the threading lever my hand never leaves it. I crashed my Grizzly once as I tried cutting threads at the slowest speed and the threads looked somewhat torn as yours do. I then with the same piece chucked bumped the speed up to 200 rpm and when I engaged the threading lever to take another finish pass the threads did not line up in the same spot so I essentially was cutting threads in one pass. With that much load on the cutter I could not disengage the lever. I immediatlely hit the panic button and luckily I just broke the carbide tool.

Mac

 

[kromeke]

I prefer to use the half nuts when I can, my hand also never leaves it while threading. However, on the lathe I use, which is a new lathe, the nuts don't seem to engage cleanly. So I've frequently use it with the half nuts always engaged, using the foot brake to stop it, and reversing the carriage. This is a little slower and not ideal, but you also have to use this technique when metric threading, which I've done on occasion. (I think there are a couple of lathes out there that use a dog-clutch to disengage the leadscrew and can metric thread with inch lead screws without reversing the carriage, Hardinge and Monarch come to mind)

I still plan to fully diagnose the issues I have with the half-nuts on this lathe here, but I haven't dived into it yet.

Know the proper direction with the control lever. This is where I like having forward and reverse buttons, but the lathe here has a control lever that rides with the apron. For mine, down is forward, up reverse. Don't forget, hammer it into your brain. Engage brain before lever.

On this new lathe, I've run the post into the workpiece (it was aluminum so just some grinding sound, no permanent scar. I've also power fed into the limits of the machine, once against a stop in the Z, once at the end of the cross slide throw. This lathe has a slip clutch on the feed rod, so it doesn't break anything. The post against the work was because I didn't look carefully at the job before applying power to the spindle. I was then looking at the cutting edge, not the toolpost an inch and a half behind it.:oops:


I usually spin the chuck by hand while in neutral to make sure my jaws clear everything when my carriage is all the way to the left, for a given cut. I've got a DRO on this one, it helps with a lot of things, but I don't pay attention to the Z while threading. I'm focused on the cutting edge while the half nuts are engaged. And the sound.

 

[Alan B]

Ouch! :eek: :poof::mecry::broke:

Variable speed also can be helpful, crawling the chuck around to check clearances or approach the end of the cut is really nice. Little momentum at crawling speed.

-- Alan

 

[will]

I use a reverse cutting tool for inside threads. Put the lathe in reverse and cut on the way out. I cut a clearance groove inside, position the tool in that spot and go from there.

I generally spin the chuck by hand on the last 2 threads on outside threads. I also put a clearance groove in the back.

 

[Mirage_Man]

I generally spin the chuck by hand on the last 2 threads on outside threads. I also put a clearance groove in the back.

Hard to do on a geared head. Especially if you're cutting the threads at like 80rpm. On my lathe it takes quite a bit of muscle to get it to turn by hand at that gearing.

 

[kromeke]

Hard to do on a geared head. Especially if you're cutting the threads at like 80rpm. On my lathe it takes quite a bit of muscle to get it to turn by hand at that gearing.

Just put it in neutral and turn by hand. The leadscrew should be geared separately from the spindle drive. I can turn mine easily in neutral and the leadscrew turns with the spindle.

 

[Mirage_Man]

Just put it in neutral and turn by hand. The leadscrew should be geared separately from the spindle drive. I can turn mine easily in neutral and the leadscrew turns with the spindle.

But wouldn't doing that loose the exact gear point you're threading at? IOW when you re-engage the gears the position of the threading be off? Maybe not much but not exactly the same spot? Did that make sense?

 

[will]

Hard to do on a geared head. Especially if you're cutting the threads at like 80rpm. On my lathe it takes quite a bit of muscle to get it to turn by hand at that gearing.

Mine is a belt driven mini lathe, easy to turn by hand.

 

[kromeke]

But wouldn't doing that loose the exact gear point you're threading at? IOW when you re-engage the gears the position of the threading be off? Maybe not much but not exactly the same spot? Did that make sense?

On a properly designed gear head, it shouldn't matter. I would think that most are "properly designed".

On my lathe, I have a spindle gearbox, up top. Down lower, the feed/threading gearbox. On the back of the headstock, there is usually a removable cover to get at the changegears. Mine has 4 small change gears to get all inch and metric combinations. Under the cover, you can see that the leadscrew gearbox is tied to the spindle exterior to the spindle gearbox. It is a separate gear train.

You can change to any spindle speed in the middle of a theading job and not loose the synchronization. If you change the threading gearbox settings, then you might well loose your sync.

 

[cmacclel]

But wouldn't doing that loose the exact gear point you're threading at? IOW when you re-engage the gears the position of the threading be off? Maybe not much but not exactly the same spot? Did that make sense?

Post 24 :)


Mac

 

[modamag]

Major bummer, will.
FYI: I saw a set of 6x jaws for ~$150. You might have to grind though.

I don't do much threading (or anything these days), but when I do I try to leave 0.060"-0.100" clearance. The HLV thread stop also helps out alot.

 

[wquiles]

+1

The best $10 you can spend is for a pair of mag-backs for two of your indicators:

(Little Machine Shop, P/N 2531)

If you want an indicator with mag back already attached, J&L often has them on sale for around $30:

Stick one where it will contact the carriage when it gets within range of the end-of-thread. Stick the other on the cross slide ... when the threading tip is retracted, you lose zero, and this indicator allows return to zero + your next depth of cut.

Useful for lots of other lathe work in addition to threading, like boring to a shoulder, or drilling to a desired depth.

FWIW, these indicators get beat to death. Hot chips, cutting oils, etc., are tough for them to handle. Mine look like they've been through World War III, with cracked lenses, melted spots, you name it. When one stops working (or starts to get sluggish), it goes in the trash. This is not the place for a nice Starrett or Mitu indicator:eek:

Yup, I have those already - really useful:

Will

 

[wquiles]

Major bummer, will.
FYI: I saw a set of 6x jaws for ~$150. You might have to grind though.

Linkie? :D

Will

 

[SafetyBob]

Neighbor uses those dial indicators on his mini-lathe all the time...and now that I see them here I can't believe I didn't get the clue earlier.

At least I know what to do at home tomorrow since everything will be closed due to the ice. Any particular place a favorite for those magnets?

Bob E.

 

[wquiles]

Got mine from CDCO Tools:
http://www.cdcotools.com

Will

 

[SafetyBob]

Thanks Will, I will order a couple tonight, I cannot believe the rediculously low price on them.

Still trying to figure out why I haven't done this before.......

Bob E.

 

[wquiles]

Will,
We all have our 'pet' procedures and as you get to know your new machine, you will adapt yours ...

Well, I finally have done just that. I now have a nice, safe, and repeatable process in the new machine. I am using a combination of the DRO "and" the dial on the carriage - it is working great :D

and the resulting threads work perfect - in fact, I like these threads better in this heavier/stiffer machine than in my 8x machine:

Will