Jet 1236p rebuild and help

[millturnman]

Hi there! I purchased a Jet 1236P second hand a while ago. it has been converted to run off of 110 power and it seemed to cut nicely on the piece of aluminum I brought with me to test on. I ran the lathe through the gears for auto feed as well as threading and it all seemed to work............ When I brought the lathe home, I had to make a few parts from 1018 and 4140 steel and holy ****ocky mushrooms this thing managed to cut with the worst surface finish I have ever seen a lathe produce. (I've worked in machine shops for years with many different lathes) I didn't have time to dive into this at the moment so I got handy with a file and pushed forward. That is until I needed to cut a thread. I've cut threads on manual lathes many times before and proceeded with confidence as I made my first pass. Everything looked good until I made my second pass. Then my 3rd, fourth and so on until I had successfully turned the stock all the way down to the thread minor diameter. THE THING DOESN'T TURN AND NOW IT DOESN'T EVEN THREAD.

At this point I realized I had a lathe that could only turn aluminum (and brass) and couldn't thread.

Anyway, I am now rebuilding in hopes of finding the source of it's garbage. I noticed the rear of the spindle got very hot after just a minute or two of running so I have taken out the spindle and put the new bearings and seals on order. The rear bearing shows clear signs of wear, the chuck side bearing shows some wear but not nearly as much as the rear. The transmission appears to be in good shape. I can't seem to find any trouble there... If anyone can offer me some advice as to what the error is in it's turning abilities and threading, that would be greatly appreciated.

Just to bring you all up to speed, here's what I've tried so far for improving surface finish:
-I've tried every possible shape of grind, rake angle, back rake angle I can think off in HSS (the lathe doesn't turn fast enough to use most carbide tooling)
-I've tightened up all the gibs and made sure nothing is absurdly loose
-Yes my tools are on centerline

For threading I have made sure that i am clamping down the half nut on the same number on the thread indexer (that is how it has worked on every other machine I have used, perhaps this one is different and no one told me? lol) I have also used "Z axis" hand wheel to put pressure backwards as it threads to ensure that backlash is not coming into play

Here is a picture of the rear bearing:


Here's a few pictures of the lathe in its current state:






Here's a picture of the chuck side bearing and the spindle:




Here is an example of the surface I've come to know and love because of this lathe (just the OD turning on the stem, the ID work was done on a cnc when I gave up lol):
Lots of galling present (I use plenty of oil so i don't suspect that is the issue). Also random grooves that take .001-.002 of material removal to sand out. the finish looks like this with a diametrical .01 finishing pass, .002 finishing pass, .005 finishing pass etc. etc...

 

[Ulma Doctor]

Chuck side bearing is toast
The original motor is anemic at best
Inspection of the gearbox would be next

I have 2, 1236 lathes-no issues with surface finish when the feed rate , doc and spindle speeds are in the correct range

 

[millturnman]

Chuck side bearing is toast
The original motor is anemic at best
Inspection of the gearbox would be next

I have 2, 1236 lathes-no issues with surface finish when the feed rate , doc and spindle speeds are in the correct range

Perhaps my eye is not calibrated to bearing wear lol. The gears and keys and shafts under the spindle end cover are all fine. I took the cover off the gearbox and couldn't see any obvious issues, although I should tear that down as well. Not exactly sure how as of yet.

 

[benmychree]

Were you trying to thread with the compound in the position pictured? It looks like 45 degrees instead of 30 degrees; that would not be helpful.
So far as the thread dial goes, you should be able to cut even numbers of threads on any line or number, and odd numbered threads on any numbered line, half threads on opposite numbered lines and 1/4 threads in a single numbered line.

 

[markba633csi]

If the motor seemed to be bogging down you should run it on 240 volts- especially if it's 1 HP or more
-Mark

 

[Ulma Doctor]

1018 usually machines like crap, as far as surface finish
Small radii tooling can improve on this

As an example, 303 stainless on either of my machines can easily take .050” cuts with a roughing tool
Finish tools cut best .005” and less, I’ll keep these very sharp

 

[matthewsx]

Hello and welcome

Looks like the same machine I have, mine is labeled Samson although I think they're all Tida Lathes.

Hopefully I won't have the troubles you're having but if I did I think I'd be looking to replace the spindle with a D-1 type.

Looking forward to watching your progress....

John

 

[millturnman]

Were you trying to thread with the compound in the position pictured? It looks like 45 degrees instead of 30 degrees; that would not be helpful.
So far as the thread dial goes, you should be able to cut even numbers of threads on any line or number, and odd numbered threads on any numbered line, half threads on opposite numbered lines and 1/4 threads in a single numbered line.

I tried to thread over a year ago. So the compound has changed positions many times since then haha. Interesting about the lines, i've never had a lathe work that way before. Thanks for the info

 

[millturnman]

1018 usually machines like crap, as far as surface finish
Small radii tooling can improve on this

As an example, 303 stainless on either of my machines can easily take .050” cuts with a roughing tool
Finish tools cut best .005” and less, I’ll keep these very sharp

I agree, 1018 can be tricky. But on the lathes i have used at work they do a much better job. I've also turned chrome moly, 303ss, 410ss etc all with terrible results. it only likes aluminum. After a lot of thought, i'm thinking there wasn't enough torque on the bearings (the nut and jam nut on the back of the spindle). i've received all the new seals as well as new NTN bearings so we'll see as it goes back together.