Pm-1340gt Crash -- Now What?

Coug67

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Hi all.

I'm a little sick to my stomach writing this. I just got my 1340GT a couple of weeks ago and have really been enjoying it. This afternoon I was parting off some aluminum (with lots of oil) close to the chuck, when the tool stuck and ripped the piece right out of the jaws, which cause the parting tool to kick sideways into the chuck and quickly stop the works. The idea that I may have severely damaged my brand new toy felt like a kick in the...well, you know.

I hit the e-stop as quick as I could, but by that time the damage is pretty much done. I was running extremely slow (maybe 60-70 RPM), so I think I managed to avoid any major damage. I disassembled the work, spun the chuck by hand, then jogged it for a few rounds. When I started the motor back up, there was a noticeable tick. I stopped again, pulled the cover off the gearbox, and slowly rotated everything by hand to take a look at the gear teeth. Nothing looks perceptibly damaged, and to be honest the tick may have been there before but I had just ignored it. There were no chipped or bent teeth (that I could tell). The spline shafts don't appear damaged. The shift palls look good. Everything moves smoothly. The tick only happens in low gear. It doesn't matter if it is L1, L2, or L3, the sound is the same. The tick doesn't exist at all in high gear. That lead me to believe I may have damaged the final low input gear that drives the main spindle. When I jog the machine with the cover off, I can just barely hear it, and it seems to correspond to the rotation of the low input gear.

What would you guys do? I'm tempted to just run it for a while without a load and let the gears wear back together. It's not a grinding sound, just a light tick. I could try to disassemble the gear train and do a deep inspection, but that proposition scares me a little. I would expect a person needs a pretty decent machine shop to tackle a job like that. Thoughts?

-- Jason
 
The good news is you didn't get bashed in the face. Personally I'd start with the spindle and a test indicator to make sure its still turning true and not knocked out of whack. If it turns true, smooth, no binding and nothing is broken via a visual inspection I'd run it a while and keep an eye on it.
 
Hi Jason,

5h!T happens. It wasn't intentional. So let yourself off the hook.
Parting-off is always one of my most nervous times.
It sounds like no major damage (to you or the equipment!) occurred; so chalk it up to a great learning experience.
Take this time to figure out why it occurred and how to stop it happening again.

My lathe is flat-belt driven and I tend to loosen the belt just a little for parting, if anything jams it slips and provides a "fuse" in the circuit.

There are some great general suggestions for parting here:
http://www.hobby-machinist.com/threads/parting-for-idiots.32938/

Yep check the lathe all over, the spindle, the chuck, the tool post, all gears, etc.

Is it possible the tick could be from a sheared-off key under one of the gears (I'm not familiar with your machine). I have just seen one in the gear-box of a horizontal band saw.
There it looked like the gear had enough friction on the shaft/sheared key to transmit some power and turn the output shaft until the blade touched the work, then it would just spin.
Although in this case the clicking happened only under load as the key way in the gear slid over the rough sheared key.

Pick up, dust off, and back in the saddle.;)

-brino
 
When it bound the motor belt most likely started to slip. I always make sure everything is locked down when parting things can get ugly fast. I be inclined to agree with the above posts, if it checks out OK id run it the tick will most likely quite down with some time. Nice looking cougar in your avatar
 
I haven't put a dial on it yet. I'm headed back out to the garage to do that now. I'm also going to change out the headstock oil. It still has the original oil, and there is a lot of break-in particulate (floaties) making it difficult to see everything. I hadn't thought about sheared keys, but I don't think that's a player here. The gears ride on large splined shafts. Good idea though. Turning it by hand, I can feel a very slight rough spot as it passes one or two of the input teeth. I've shined a bright light on the suspect teeth, and I can't see any gouges or rough spots. I think I'm going to do like you guys said, keep an eye on it for a while and hope that it quiets down. I need to talk to Matt at PM this week anyway. Might ask him his thoughts on it. Thanks for the replies.
 
Nice looking cougar in your avatar

Thanks Steve! I wish I could claim that one's mine. I have one that looks nearly identical, but it's in pieces right now. I've had it since high school. I had to choose between spending the money on the lathe or finishing the restore on my car. Guess we know how that turned out! Someday..... ;)
 
A picture inside the gearbox. The cluster in the top right is the final high/low input to the spindle. You can see some wear/pressure marks on the smaller (low) gear, but the teeth are smooth. I checked the spindle runout, and it seems to be within a few tenths. I think I'm safe, just got a good scare. Like Brino said, "5h!T happens.... so chalk it up to a great learning experience."

Gears2.jpg
 
Feel for a notch worn in the drive belts. If the spindle stopped and the motor was going it takes very little time for the motor drive pulley to make a divot in the sides of the belts. Might be visible but might be hard to see. Rotating till you feel the spot and then checking that spot on the drive belts (part that is then on the motor drive pulley) you might find a wear spot in the sides of the belts that makes the belt jump once per revolution when it passes the drive pulley.

Parting can be intimidating, but to slow sfpm can be a bigger problem than to fast as far as the grabbing.
 
Sorry for your trouble with lathe. Reading the start of your post, you mentioned aluminum , parting and real slow. Assuming you are likely parting something under 2" in diameter, your speed is way too slow. I part 6011 T6 at 400 rpms + for one inch stock. Parting blade has some side relief, dead nuts square and on center. Too slow gives it a chance to bite in and grab, also power feed and make that feed a little quick as opposed to slow.

michael
 
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