JET 12 X 40 threading problem

eugene13

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Here's where I'm so far, and every job needs a fluster-cluck. To get to the gearbox I have to remove the lead screw, feed shaft, and control shaft. My plan is to leave everything hanging on the carriage and to move it aside enough to attack the gearbox. Bad news; the work bench is in the way, good news it's easy moved.
 

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eugene13

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Finally, down to the nitty gritty, tomorrow I tackle the gearbox, Experience is what don't have when you need it, if any one has ever done this before, I will appreciate your input. During my big cleanup prior to this job I found this rusty adjustable wrench, the other part is a 95 year old Model-t chassis part, I'm going to see what Evaporust can do for them.
 

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eugene13

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Here's where I am so far, this is the lead screw shaft, the small gear on the right is loose on the shaft, all I have to do now is get the shaft out of the gearbox. Looks pretty straight forward on the exploded diagram but I can't get it to move, tomorrow's another day.
 

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eugene13

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I need to remove the upper shaft in the photo. I can turn the flange but I can't get it to pull out of the gearbox, am I doing something wrong?
The alternative is to remove the two nuts that set the pre-load on the thrust bearings. (115 in exploded view) Building it that way doesn't make any sense from a manufacturing point of view, but we all know inscrutable Japanese reverse engineering. Need help please, thanks
 

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Jim F

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I need to remove the upper shaft in the photo. I can turn the flange but I can't get it to pull out of the gearbox, am I doing something wrong?
The alternative is to remove the two nuts that set the pre-load on the thrust bearings. (115 in exploded view) Building it that way doesn't make any sense from a manufacturing point of view, but we all know inscrutable Japanese reverse engineering. Need help please, thanks
I am not seeing the part you need to remove in the parts breakdown.
 

eugene13

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I am not seeing the part you need to remove in the parts breakdown.
I need to remove the entire lead screw shaft to replace the small gear (#118), this is the bottom shaft in the exploded diagram, thanks.
 

ericc

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Dec 24, 2013
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We had a similar problem at the local makerspace with a Jet 1440. I don't know what the exact problem was, but the gearbox had to be fully disassembled, and it took weeks to get it fixed. Every time I came in, I noticed a few more gears sitting on the work table, so progress was being made. Eventually, the lathe got put back together and it worked. They did not bother fixing the other lathe. They just said only use the one lathe for threading.

After seeing this, I swore that I would never get a lathe with a gearbox for my shop. The change gears are slightly more inconvenient, but no mysterious slipping problems. If the key is there and the teeth mesh, it is going to work. Just a little messy every time you need to swap gears.
 

Jim F

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Sep 24, 2020
Messages
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We had a similar problem at the local makerspace with a Jet 1440. I don't know what the exact problem was, but the gearbox had to be fully disassembled, and it took weeks to get it fixed. Every time I came in, I noticed a few more gears sitting on the work table, so progress was being made. Eventually, the lathe got put back together and it worked. They did not bother fixing the other lathe. They just said only use the one lathe for threading.

After seeing this, I swore that I would never get a lathe with a gearbox for my shop. The change gears are slightly more inconvenient, but no mysterious slipping problems. If the key is there and the teeth mesh, it is going to work. Just a little messy every time you need to swap gears.
And most home/hobby guys are not pressed for time to thread something.
 

eugene13

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This has turned into an adventure but I am making headway, good thing the mill works, I may have to build a wrench.
 
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