# lathe crash



## dmcmd (Oct 14, 2014)

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


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## george wilson (Oct 14, 2014)

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.


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## Rbeckett (Oct 14, 2014)

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


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## higgite (Oct 14, 2014)

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 #.


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## Fabrickator (Oct 14, 2014)

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.


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## dmcmd (Oct 14, 2014)

Thank you!  Exactly what I needed.  I should go re-read that manual...


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## Andre (Oct 14, 2014)

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.


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## PatMiles (Oct 17, 2014)

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.


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## george wilson (Oct 17, 2014)

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.


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## Mark in Indiana (Oct 17, 2014)

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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## PatMiles (Oct 19, 2014)

george wilson said:


> 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.


George,
The pins are brass.


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## NightWing (Oct 19, 2014)

My G0602 jammed in the cut which stopped everything except the motor, which was still trying to drive the slipping belt.  The cut wasn't excessive, the spindle speed wasn't excessive and the material was mild steel.  I have had this happen several times.  That wimpy belt is a piece of crap and (in my opinion) too narrow for the job.  I have to adjust the idler so tight that I am concerned that the bearings will fail.


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## Shadowdog500 (Oct 19, 2014)

Thanks for the tip on soft shear pins.   My Taiwanese lathe has roll pins.  I may turn some pins out of brass this week.

chris


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## GarageGuy (Oct 20, 2014)

NightWing said:


> My G0602 jammed in the cut which stopped everything except the motor, which was still trying to drive the slipping belt.  The cut wasn't excessive, the spindle speed wasn't excessive and the material was mild steel.  I have had this happen several times.  That wimpy belt is a piece of crap and (in my opinion) too narrow for the job.  I have to adjust the idler so tight that I am concerned that the bearings will fail.



When you are learning, a belt that slips is a good safety valve.  My first lathe had a flat belt that could slip, and although I only crashed it once, nothing bad happened because the belt slipped.

GG


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## GarageGuy (Oct 20, 2014)

dmcmd said:


> I hate to say it, but I did this twice



Especially while learning, be sure to slow down your spindle and feed speeds.  Also eliminate anything that could distract you.  I silence my phone when working with machines so I'm not tempted to look away, even for a second.  Just a couple of observations from my own learning process.

GG


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## spaceman_spiff (Oct 21, 2014)

My strategy at dealing with this sort of thing is to learn to accept that you will break stuff learning to machine..end mills, tools, machinery, workpieces..its going to happen. If you never break anything while learning then you are not learning aggressively enough and are playing it too safe to really push your skill acquisition and confidence. Thats why its good to learn on cheap machinery that you can afford to hurt and repair. I've known machinists with years of experience but not very well developed skills and a low confidence level, and they were always the most timid about trying new things, and, ironically, the ones who seemed to always be hurting themselves. 

I'm not saying to be reckless or just wing everything and cross your fingers, but at the same time, you should be willing to go into "the unknown" and experiment. As others have suggested, putting in "safety valves" like slipping belts or other things can be a great way to allow you to be aggressive about learning but reduce the casualty count of your poor equipment. I think thats the path to follow.


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## NightWing (Oct 22, 2014)

GarageGuy said:


> When you are learning, a belt that slips is a good safety valve.  My first lathe had a flat belt that could slip, and although I only crashed it once, nothing bad happened because the belt slipped.
> 
> GG



I'm not a learner.  I have been running lathes since the 60's  I have been in metalworking since then and owned a machine shop for 22 years.  The belt drive on the G0602 is trash.


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## GarageGuy (Oct 22, 2014)

NightWing said:


> I'm not a learner.  I have been running lathes since the 60's  I have been in metalworking since then and owned a machine shop for 22 years.  The belt drive on the G0602 is trash.



I apologize.  I didn't mean to imply that you were.  There are lots of people here who are, though.  Myself included.

GG


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## NightWing (Oct 22, 2014)

I'm cool.:allgood:


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