Broken Keyway???

boostin53

boostin53

Registered
Registered
Joined
Sep 11, 2015
Messages
293
To make this short, I think my keyway in my gearbox is broken on my Jet BD920N. But figured I would ask here before ripping it all apart.

I went to change the gearbox to the number 1 gear for a slightly faster feed. Made a light test cut. Turned the lathe off then backed the carriage towards the tailstock. I was happy with the results, so I went to make another pass. Turned lathe on, lead screw not spinning. Turned lathe off. Confused, I engaged the second gear to see if it even worked. Turned lathe on and the lead screw was spinning. Switched back to gear 1 and same thing, lead screw not turning. Gears 2-9 work, but number 1 does not.

Is it possible that the end on the keyway under the first gear somehow broke? And to be clear, I have never crashed the lathe to possibly cause damage/stress. The previous owner may have, but thats a mystery to me.
 
boostin53,
sometimes the gears don't quite line up even though they appear to be when looking a the numbers on the lathe. I had a Jet GHB1340A that did the same thing on one particular gear. Don't remember which one, but I would work the lever back and forth and it would finally engage. Don 't know if that is your problem or not.
Hope you get it figured out, last resort pull the cover off the headstock and have a look inside, should be easy to see whats going on. Of course you will have to drain the oil first.
 
I took the front cover off, the one that has the holes to line up the gears. They engaged, but the first gear just spins around the shaft. I should be safe to assume that's not correct. The others dont spin around the shaft, they turn the lead screw. I dont really know where to begin taking everything apart. It seems like i need to take the shaft with all the gears out so i can check for a damaged keyway.
 
Well, I just finish taking the gear box a part. The key way is fine and so is the gear. Then I found the problem. The shear pin that connects the lead screw to the gear box shaft. This isnt the original pin. The original owner must have broken the original and replaced it with wire. I failed to notice that before hand.

Since the wire is a smaller diameter that the hole, it causes slop. The first gear rides so close to the end of the keyway. The slop is enough for the shaft to slide to the right, removing the gear from the keyway. Tomorrow i will fashion a new shear pin of proper diameter and reassemble. What could i use as a shear pin? I would think aluminum wont break if i crashed the lathe. But idk.
 
Brass ,bronze ,aluminum , copper, & hardwood could all be made to work to varying degrees of success.

if i had aluminum or brass on hand-(and i always do!) those would be my first 2 choices
the pin would have relative strength, and still shear should there be a catastrophic crash.
 
Good to know the materials! I have some aluminum and brass on hand. I will make a few tomorrow. Thank you Ulma!
 
Does the lathe have plastic or pot metal gears? You want a shear pin that will be the weakest part of the assembly. So hopefully when it needs to shear nothing else will break…Dave.
 
after further examination of the manual, the 80T change gear appears to be a safety gear and is composed of plastic,

but i'd still make the pin from aluminum or brass :grin:
 
Last edited:
Ulma Doctor said:
after further examination of the manual, the 80T change gear appears to be a safety gear and is composed of plastic,

but i'd still make the pin from aluminum or brass :grin:
Click to expand...

This is correct. All the gears are steel, except for the 80T. It's made to give out instead of the other gears, and so is the shear pin. I already set aside a nice little scrap aluminum rod to make a few shear pins tomorrow.
 
You must log in or register to reply here.
Back
Top