While we are on gears

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Chewy

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We have had several recent posts about gears, so I thought I would add this one. I have a PM 1228 lathe and the thread indicator gear is toast. I did some work on the carriage and noticed the thread indicator was not turning. After taking it off I found that the shaft was seized and the gear chewed up. It is steel upon steel and no lubrication. Took a hammer to drive shaft from housing. Polished everything and drilled and installed a button oiler so I can get some lube there in the future. People reading this might want to check their lathes and see if they are starting to get the same problem. OK. Gear is $20 bucks and shipping another $35 to $40 when Chine gets out of lock-down. Supplies build back up. Delivery services speed up again. Meanwhile the only way to single point is Metric method. Lock in and stay in until done.

Thought I would find a replacement and that isn't working out. Here are the gear spec's. 32 teeth. OD is 31mm. Max tooth depth diameter is 27.20mm Gear is 10mm thick, 5mm is gear and 5mm is hub. 18mm diameter hub which is not critical. 10mm shaft with 4mm key way. I just started going through all the gear books and reference stuff. I came up with a .91 module, which is probably right. .8 module gears are too small and 1 module gears are too big. The gear dos not really engage in the leadscrew but enters on around a 45 degree angle. Only tips of gear to a width of 1/2 the tooth engages the lead screw. The gear that I have has 1/2 of the tooth width ground away. Thought I would make a trial gear out of delrin, but I really don't want to try to make the involute cutter too. Can I use a module 1 cutter to cut gears a little smaller? Suggestions?? Gear part number is PM # ZZ7495. Anybody know from the spec's if another make gear will fit?

Thanks Chewy
 
Do you have a way to index 32 teeth? The gear is relatively acritical since all it has to do is slowly turn the indicator. Is the gear
chewed up on only a few teeth? If so one could repair it. The only critical factor would be that the gear would have to engage
without a lot of slop so it will perform it's intended function.
 
Would slop really matter? It only has to turn in one direction so backlash isn’t an issue.
 
I can do 32 teeth with the rotary table and an index plate. Grizzly Book says 16 holes and 2 & 13/16 each time. Teeth are chewed up badly all the way around and really bad in one spot. I was able to jam it in a little further and it turns but not a long term solution, or one I want to use on a couple of hour part. I'm figuring a delrin gear and prussion blue to check fit and then make an aluminum gear for longer term solution. If it fits really good then do steel. My main concern is to "do no harm" to the leadscrew.
 
Chewy said:
We have had several recent posts about gears, so I thought I would add this one. I have a PM 1228 lathe and the thread indicator gear is toast. I did some work on the carriage and noticed the thread indicator was not turning. After taking it off I found that the shaft was seized and the gear chewed up. It is steel upon steel and no lubrication. Took a hammer to drive shaft from housing. Polished everything and drilled and installed a button oiler so I can get some lube there in the future. People reading this might want to check their lathes and see if they are starting to get the same problem. OK. Gear is $20 bucks and shipping another $35 to $40 when Chine gets out of lock-down. Supplies build back up. Delivery services speed up again. Meanwhile the only way to single point is Metric method. Lock in and stay in until done.

Thought I would find a replacement and that isn't working out. Here are the gear spec's. 32 teeth. OD is 31mm. Max tooth depth diameter is 27.20mm Gear is 10mm thick, 5mm is gear and 5mm is hub. 18mm diameter hub which is not critical. 10mm shaft with 4mm key way. I just started going through all the gear books and reference stuff. I came up with a .91 module, which is probably right. .8 module gears are too small and 1 module gears are too big. The gear dos not really engage in the leadscrew but enters on around a 45 degree angle. Only tips of gear to a width of 1/2 the tooth engages the lead screw. The gear that I have has 1/2 of the tooth width ground away. Thought I would make a trial gear out of delrin, but I really don't want to try to make the involute cutter too. Can I use a module 1 cutter to cut gears a little smaller? Suggestions?? Gear part number is PM # ZZ7495. Anybody know from the spec's if another make gear will fit?

Thanks Chewy
Click to expand...
Precision matthews cant get you a new gear?
 
Sure can. Sometime in the future. Around $50-60 when China goes off lockdown or around $20 added to their next order, sometime this year.
 
If you have a fly cutter, you can actually grind your own tool and single-point it instead. YOu have to slow down the RPMs (because 1 tooth isntad of 10!) but I hear it ends up being pretty easy, AND you can grind it to match the teeth perfectly.
 
That will be the absolute dead last option. I need Opti-Visors just to look at the teeth. I have angled flycutters, so I would probably make a mandrel that holds the cutter at 90 degrees and use a 3/16" square bit. Problem as I see it is to make both sides of the cutter even. I would have to get a sharp edged dish wheel. Wheels I use for grinding have a radius bigger then the cutting edge required. Don't know if I can pull this off with a Dremal tool.
 
I'll see if I can model one in CAD for you.

You could 3d print a half dozen and be good 2 go for a long time. Or, at least until PM ships you one.

I'm assuming a 20° pressure angle?
 
I'm going to guess that it is 20 degrees. I don't have a 3d printer yet. It's on the list for the future.
 
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