lathe crash

D

dmcmd

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All,

I was working on a project a few days ago and I was too slow disengaging the half nut on my G0602. I don't know if I hit the stop button fast enough or if the lathe stopped on its own due to the carriage being unable to advance and stopping the feed screw. I hate to say it, but I did this twice - once when the carriage hit my carriage stop and once when it hit the steady rest. Yes I know I need practice. That's why I have a small lathe to start with before I get a nice gunsmithing lathe.

All the gears are ok as far as I can tell. I am concerned about the lead screw and half nut. It seems like there's more slop when I engage the half nut than there used to be.

Any advice as to what I should do/look for?

Thanks,
Darren
 
Practice not crashing!!!!:)

A little more play will not hurt you since the lathe takes up the slack every time before it allows the carriage to advance. However,you should avoid crashes since on many Asian lathes or old lathes as it may be impossible to get parts. Or,if you CAN,they will be really too expensive. I think Jet makes a lot of money that way.

So many things can account for the extra play. The half nut may have gotten its teeth damaged. The half nuts might have gotten deformed or loosened where they are attached to the carriage. You'll have to take the carriage apart to check for play in the half nut mechanism. The bracket at the rear end of the leadscrew might have gotten pushed sideways a bit. The leadscrew at the front end may have gotten jerked forward some. There is usually a SOFT steel shear pin at the front of the leadscrew(Though I have no idea which model you may have. It may not have a shear pin) If a shear pin is there,it is soft steel,and could have gotten deformed some,allowing the leadscrew to move a little to the operator's right hand end of the lathe(and possibly moving the bracket as I mentioned,where he leadscrew is held at the tail end of the lathe.
 
You need to physically check all the functions and insure that you have not damaged the plastic gears in the outer gearbox on the end of the lathe. Those gears are plastic just because of guys crashing into stuff. If it all checks out good the just practice avoiding the crash in the future. You can do this by turning up to a shoulder on a piece of scrap stock I would only take off .001 to avoid damaging the machine. Good luck and practice makes perfect really applies here.

Bob
 
I would start on page 62 of your owner's manual, Half Nut Adjustment and Leadscrew Shear Pin Replacement. Neither of those may fix your problem, but they're easy fixes if one of them turns out to be the problem.

Edit to correct page #.
 
My G0602 doesn't have any plastic gears in the end case but I can't say about the enclosed gear case, never had it apart. There is an adjustment (allen screw) for the lead screw half-nut engagement lever just around the corner under the carriage if you look. Mine got tight and I had to loosen it a bit.
 
Thank you! Exactly what I needed. I should go re-read that manual...
 
You mentioned you had a crash when your carriage under power feed hit the carriage stop. You should NEVER use the carriage stop when using power feed UNLESS your lathe has a stop that disengages power feed when hit (Hardinge HLV series for instance.)
If you hit the stop under power feed, you risk damaging or destroying gears, leadscrew/halfnuts, etc.
 
As you may have already discovered by now, don't hold your breath on the shear pins doing their intended job (shearing off) when you have a crash.
I have crashed my Jet 1340 lathe twice which resulted in a trashed bronze gear and a bent shaft both times instead of the shear pins doing their intended job.
 
Pat,If I were you,I'd make a new shear pin out of brass,if nothing else. Those shear pins are SUPPOSED to be made of VERY soft steel,like old fashioned rivets are made of. Apparently your Jet did not have a shear pin made of the proper material.

I know of an instance,in the machine shop of a local college,where someone sheared off the pin,and made a replacement pin from STAINLESS STEEL. The next time a student crashed that lathe,it tore the face of the quick change gearbox off. It was a 9" South Bend lathe.

Correct metal in the shear pin is VERY important.
 
When I started at the place that I currently work at, They had a crashed Jet Lathe. To get it going again, I made & installed brass shear pins for the end of the spindle and adjusted the gear set at the end of the gear box (the gears were designed to be pushed out of the way in the event of a crash). It took a few hours to fix a machine that had been down a couple of years.
I hope this helps.
 
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