Missing and Broken Gears for Lathe

[bbourdon]

My lathe has a broken worm-wheel gear for the power feed, and is also missing a gear and a shaft inside the apron.

It's a Jet 1024P (10") lathe, made in Taiwan in the 1980s (I think). I got it used from a factory that was closing, no information is available from the source. The manufacturer does not have any information, but I did find a couple of PDFs for the manual searching online - neither is exactly my machine, but close in most areas except the apron.

I'm not terribly worried about the brass worm wheel gear; fixing or replacing / making a replacement isn't too bad when you have the original part in hand. But the missing parts have been a show stopper. Best I can tell, it was some kind of idler gear and shaft (mounted between the lower shaft that's connected to the worm, and the clutch power feed gears - notice the space and hole in this area in the attached photos).

The parts diagrams from the manuals I've looked at don't show this assembly. It appears that the worm wheel gear shaft on mine is mounted much lower than others, resulting in a large gap - where an idler probably existed.

One thing that's really confused me here is that all of the other shafts have substantial support on both ends, yet the idler is supported on one end only without any shoulder from the casting (the casting wall is at its thinnest in this area). It appears like a design flaw on my model, that the other manuals show corrected (by moving all the worm parts up so the drive gear contacts the clutch gear).

I'd appreciate hearing anything helpful that you may think of.
Bruce.

 

[Entropy455]

Those look like straight-cut spur gears. Being a 1980s vintage lathe, they are most likely 20-degree involute spur gears. You’ll need to verify the diametrical pitch, and also the pressure angle - to ensure they are not some weird metric gears.


If you can’t find the correct replacement gear, you can replace the gears in sets. Simply choose an appropriate diametrical pitch family of gears, and select the required gear diameters to fit your application. You can purchase blank gears, and machine a custom hole and keyway to fit your existing shafts.

Boston gear has an excellent technical publication for identifying and sizing spur gears (linked below). Boston Gear is also one of many sources to purchase replacement spur gears - both in 14.5 degree, and 20 degree pressure angles.

http://www.bostongear.com/litportal/pdfs/P-1482BG_pg133-153.pdf

 

[Entropy455]

Boston Gear will also make custom replacement gears. If you send them your broken gears, they will template and fabricate new ones. But be prepared to pay ($$$). Custom gears can be expensive. . .

 

[Philjoe5]

The 10 x 22 Grizzly lathe I have (2007 vintage) has module 1 (metric) gears with a 20 degree Pressure Angle.

Phil

 

[chipenter]

That hole is probably part of a safety device to stop the power feeds and the half nuts being engaged at the same time , and the idler gear was probably on a fork , that's all guess work on my part .

 

[bbourdon]

Entropy455, thank you very much for the reference to Boston Gear, and the related info! I'll look into that, and reply when I have something worthwhile. I can't justify the expense of having custom gears made, but if they stock something that will mesh OK, I can make a shaft...

Philjoe5, thanks for the info on your lathe. I wonder if the gears will be similar? Either way, good to have more info, thank you.

Chipenter, the lever that's just above the hole is the lockout to prevent the half nuts and power feed from being both engaged at the same time. You may be right about the idler being on a fork - I have nothing more than the remaining assembly to go on, none of the manuals I've seen so far show anything like my arrangement.

Bruce.

 

[Wizard69]

My lathe has a broken worm-wheel gear for the power feed, and is also missing a gear and a shaft inside the apron.

Thinking outside the box here, how difficult would it be to modify the apron with a small gear motor supplying your drive feeds? Sort of like a Hardinge HLV. Just a thought.

It's a Jet 1024P (10") lathe, made in Taiwan in the 1980s (I think). I got it used from a factory that was closing, no information is available from the source. The manufacturer does not have any information, but I did find a couple of PDFs for the manual searching online - neither is exactly my machine, but close in most areas except the apron.

Keep searching over the years a bunch of these Jets have been sold.

I'm not terribly worried about the brass worm wheel gear; fixing or replacing / making a replacement isn't too bad when you have the original part in hand. But the missing parts have been a show stopper. Best I can tell, it was some kind of idler gear and shaft (mounted between the lower shaft that's connected to the worm, and the clutch power feed gears - notice the space and hole in this area in the attached photos).

First a qualification: looking at pictures can be misleading, so I could be way off base here.

Looking at the photos I see to much interference to believe there was ever an idler in there. It looks like any idler shaft would interfere with existing gears. This makes me wonder if the gear on the shaft driven by the worm gear is just there as a keeper. That is the machine was disassembled once and some problem gear removed to facilitate repair and a spare gear inserted to keep the shaft in place. I've seen stranger things. It would not be unheard of to carve out an idlers shaft to gain clearance for another gear in the gear train, but looking at the pic we are talking an excessive amount of carving here. I don't think the camera angles are that bad that I'm being mislead here.

The idea of an idler makes sense, the problem is how did it ever fit in there. One way to tell for sure is to walk through the motions. In other words will the cross slide or saddle go in the right direction with an idler in there. There is a bit of mental game involved here but you should be able to determine the need for an idler by walking through all of the direction changes.

It probably wouldn't hurt to do a bit of reverse engineering. That is see if ratios provided with the currently installed gears give you the right feed rates at the saddle this means a lot of teeth counting as you have no documentation for the machine. This will be a bit of a pain and hopefully all the settings at the head stock make sense and are legible. In the end you will want to know anyways when it comes to buying new gears.

The parts diagrams from the manuals I've looked at don't show this assembly. It appears that the worm wheel gear shaft on mine is mounted much lower than others, resulting in a large gap - where an idler probably existed.

Are there any plugged holes that might have been used to support an idler shaft?

One thing that's really confused me here is that all of the other shafts have substantial support on both ends, yet the idler is supported on one end only without any shoulder from the casting (the casting wall is at its thinnest in this area). It appears like a design flaw on my model, that the other manuals show corrected (by moving all the worm parts up so the drive gear contacts the clutch gear).

The idler shaft most likely had the idler turning on a bearing of some sort with the idler shaft fixed. In such a case the walls would be plenty thick enough.

I'd appreciate hearing anything helpful that you may think of.
Bruce.

Well you have my out of the box thinking above. The feasibility of such a mod would have to looked into, and frankly it has its advantage and disadvantages. I really like that approach on a Hardinge though.

Otherwise it is just hard to say much more by looking at the pictures.

 

[Wizard69]

Entropy455, thank you very much for the reference to Boston Gear, and the related info! I'll look into that, and reply when I have something worthwhile. I can't justify the expense of having custom gears made, but if they stock something that will mesh OK, I can make a shaft...

Before jumping to conclusions here make sure a simple idler is what is needed. We are assuming an idler goes in there.

Philjoe5, thanks for the info on your lathe. I wonder if the gears will be similar? Either way, good to have more info, thank you.

Chipenter, the lever that's just above the hole is the lockout to prevent the half nuts and power feed from being both engaged at the same time. You may be right about the idler being on a fork - I have nothing more than the remaining assembly to go on, none of the manuals I've seen so far show anything like my arrangement.

Bruce.

My biggest problem with the idea of an idler is the obstructions the shaft for the idler would have. Pictures of course can distort things so maybe in real life it just doesn't look that bad.

As to stripping out the worm drive, a harmonic drive can be pretty compact these days

 

[bbourdon]

Wizard, thanks for the posts. Please see the image below:

If you look at this image, through the idler mounting hole you can see the lower gear that drives the idler. The gear that seems to be just above that is actually the crossfeed gear - it is up against the front of the apron, it is not lined up vertically with the driving gear on the worm wheel shaft seen at the bottom. If you look hard, you can just see the tips of the gear on the upper shaft that is lined up vertically with the bottom gear - this is the clutch gear that needs to be driven. So the idler is just a little bit smaller than the hole.

 

[Wizard69]

Wizard, thanks for the posts. Please see the image below:

If you look at this image, through the idler mounting hole you can see the lower gear that drives the idler. The gear that seems to be just above that is actually the crossfeed gear - it is up against the front of the apron, it is not lined up vertically with the driving gear on the worm wheel shaft seen at the bottom. If you look hard, you can just see the tips of the gear on the upper shaft that is lined up vertically with the bottom gear - this is the clutch gear that needs to be driven. So the idler is just a little bit smaller than the hole.

That is the thing, how would a support shaft for the idler pass through both sides of the castings? I just don't see how the idler shaft would be supported. One could imagine that the idler sat on a cantilevered shaft to avoid the interference with the obvious (cross feed) gears in the way. Honestly though I've never seen such done. Further a cantilevered shaft like that would require a boss built into the casting for better support.

I still think your best bet here is to verify the hard way that the ratios and directions would be right with an idler in there. Yes a bit of pain but it would convince you one way or the other.

Looking at the previous pictures the the clutch assembly and related gears all look pretty new compared to the lower drive wheel. Makes me wonder why.

I understand why you want to believe an idler gear goes in there. The problem is how, that is what I'm stuck on. The normal practice (at least on the few units I've worked on) is that any installed shafts pass through both casting walls. I have to wonder does that cross slide drive gear line up properly with the driven gear on the cross slide? Something is strange about this gear box, I'm not sure what yet.

 

[Tin Falcon]

Here is the manualJet 10 24 p manual for your machine I think,
thise machines ofen sold with differnt labels and paint colors so you may be able to get parts from grizzle. Jet is supposed to be top of the line so they may mbe able to help if you push the right buttons.
Tin

 

[Philjoe5]

[FONT=&quot]I’m a bit puzzled by your drawing. You have two 32T gears with different OD’s. That would make their diametrical pitches different and they won’t mesh, nor would an idler gear placed between them.[/FONT]


[FONT=&quot]Phil
[/FONT]

 

[bbourdon]

Correction: The OD of the lower gear shown is incorrect; it was actually 2.00", just like the top gear.

Thanks Phil!

I think I measured the OD of the adjacent gear, as it is very close to the value listed, while the clutch gear I should've measured is no where near the 1.88" no matter how many ways I try to get that value...
Bruce.

 

[bbourdon]

Tin Falcon, thank you for the effort I do appreciate it.

Unfortunately, though the lathe in that manual is very similar to mine, the apron assembly is very different; notice how the worm wheel is mounted in the upper half, on mine it is near the bottom - hence the gap between the driving gear and the clutch gear, requiring the idler.

I am convinced that mine has a design flaw that was later corrected - as shown in that manual. The idler, especially as it must've been installed on my machine, is a mistake. :wall:

A friend took the measurements and determined that there's an 18 tooth, 1.5 mod, 1.18" OD gear that belongs there. I'm going to attempt to make one and see how it works out. Will update this thread when I have more to report.

Thank you all for your help, it means a lot.
Bruce.

 

[Tin Falcon]

well was not sure if it was an exact match but worth a try at least you did no pay $10 for a hard copy only to find it different.

Tin

 

[bbourdon]

well was not sure if it was an exact match but worth a try at least you did no pay $10 for a hard copy only to find it different.

Tin

Absolutely!
Thank you!
Bruce.