Jet Lathe Wet Apron Conversion

Wednesday, February 20, 2013

Last week I posted my progress cleaning the apron on my “new” Jet 1024P lathe. As I said, I am very pleased with the overall condition and build quality. As I was putting the apron back together I realized that there are no provisions to oil the insides once it's coupled with the saddle. The only way to get any lubricant into the apron is through the opening around the cross slide screw, but it is normally covered with a piece of sheep metal bolted to the saddle. Getting to it isn't very convenient, but even once the cover is removed only some of the gears are accessible.

My initial instinct was to drill some oiling holes and deliver oil to each gear and spindle via thin tubes. I was already underway researching the best way to do it when it hit me that my apron is basically a bucket with a few holes drilled in it. After close inspection it became obvious that the apron can be safely filled all the way to the bottom of the lead screw. With that much oil the hand-wheel’s spindle and the small gear at the end would be almost completely submerged in oil, and two of the large gears will have at least some teeth breaking the surface. Finally, there should be enough oil touching the power feed worm gear to keep it well lubricated.

It looked like there would be three spots that can potentially leak:

  • The worm gear bracket is simply bolted to the apron body, and there will likely be leaks in the thin gap.
  • The hand wheel spindle fits fairly loosely into a sleeve. There is at least a thousandth or more for the oil to sip out.
  • Although the sleeve mentioned above fits pretty snugly against the apron, the surface is pretty rough, and there are two bolt holes.

Getting rid of the small gaps between the worm gear bracket and the hand wheel spindle sleeve is fairly easy. Pretty much any automotive RTV designed for the engine application would do the trick. I happened to have a tube of “Ultra Copper” silicone gasket maker. A thin bead applied the to one of the mating surface should do the job nicely. Once the silicone dries, any excess that gets squeezed out cn be cut with a utility knife.

Worm gear bracket sealed using automotive RTV to prevent oil leaks

Sealing the spindle is a bit more problematic, though. The proper way would be to cut a groove in the sleeve and install an O-ring, but the shaft isn't polished, so it will destroy that O-ring in no time flat. I might need to do it after all, but first I decided to try using a Teflon washer first. There should be enough pressure between the sleeve and the hand wheel to create a good seal. Cutting the washer took a minute, so not a big loss if it doesn't work.

Finally, to ensure that the oil level inside the apron is correct I decided to add an oil sight window. An oil sight window from a commercial machine was the closest thing available on eBay. It looked promising and was promptly ordered. Once the part came, I bored a 1” hole with a small step to make the acrylic lip flush with the apron body. The top of the windows is at the same level as the bottom of the lead screw hole in the worm gear bracket. This way as long as the oil level is somewhere near the top of the window, things are good. Once the hole was bored, it was a matter of RTV-ing the window in place.

Oil sigh opening was first drilled with a series of drill bits (1/4" - 7/8" in 1/8 steps)
and broed to the final dimension with a micrometer boring bar.
The top of the hole was then enlarged to provide flush fit.
The gap between the handwheel sleeve and the casting was sealed with the same
automotive RVT that was used to glue the sewing machine oil sight window into the opening.
Addition of the Teflon (PTFE) washer should minimize leaking between from the spindle

The whole “upgrade” took no more than an hour and was pretty easy to do, as the apron on my lathe was cast as one piece bucket. The only tense moment was drilling the hole, since putting a crack into that apron meant almost certain death for the lathe. I probably spent more time building up intestinal fortitude to bore the hole than on boring itself. I haven't had a chance to test the apron yet, as the rest of the lathe is at different stages of cleaning. (And the bucket of Mobil Vactra 2 hasn't arrived from McMaster Carr either). I don't expect major leaks, but honestly, even if it leaks a bit, having good lubrication is worth it. After all I'm a strong believer that a the best environment for a lathe is inside an oil bath, so a few leaks here and there simply prevent rust.

Sewing macine oil sight window installed into Jet 1024P apron
Oil sight window is readily accessible on the fron of the apron


  1. Hi Yuriy,

    Nice clean. I just picked up the same lathe. My original worm gear has 19 teeth (or what's left of it!) and a steel worm. You just can't buy one from the factory any more. I'd be interested in replacing the worm assembly with a standard replaceable size. Any idea where the previous owner picked up the worm gear and worm. If I have counted correctly you've got a 25 tooth worm gear. I have an owners manual that's close to the original if you want a copy.

    Great Post


  2. Andrew,
    The gear on my lathe looks custom made (it has very nice profile and finish and I haven't seen this kind of workmanship on any Grizzly or Jet parts).
    With that said, some of the Jet 1024/1236 lathes (and there appears to be more than a few variations) are similar to Grizzly G9249. ( That lathe has been discontinued but parts are still readily available from grizzly. On mine
    the lead screw and change gears were different but the internal apron gears were the same (I messed up the dog clutch gear and grizzly part was a perfect match.)
    Also, there appears to be at least 5-6 different spindles, so watch out for that. I talked to a guy at Jet and he said that the spindle thread changed every few years and different suppliers had different thread/bore combinations.

    Thank you

    P.S. Yes, I'd like a copy of the manual.

  3. Hi Yuriy, I like your work!

    I have a Jet 1024P, here's the manual PDF: