# 9X20 Lathe, replacing the plastic 80T gear with a Grizzly metal one (p4000119A).



## MetalPlane (Jan 23, 2021)

Just ordered the Metal 80T gear from Grizzly to replace the 80T Plastic gear on my JET 9X20 Lathe. Are there any reviews by others that have tried the same?

Concerned that I will remove a layer of safety by replacing the sacrificial Plastic gear.


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## Bi11Hudson (Jan 23, 2021)

I use a G-1550 lathe, an older version of the 9X20s. The plastic gear got set aside when I built a reversing mechanism for the lead screw. To maintain the "weak link" in a gear train is important in that if something jams up, a piece of plastic will "give" before something metal. I do generally light machining with the 1550, often on synthetics such as plastic. For the most part, jamming something is not likely. I also use a 12X36 Craftsman (Atlas), which has no provision for a sacrifical link. 

As a general overview, if the plastic gear is intact, leave it. If it's damaged, replace it with plastic. It's there for a reason. You must make the final call based on what you do. The plastic gear can possibly save some more costly part of the machine. If you are making a change to the train, such as mine, there may be no other option. Just do it. If the appropriate plastic gear had been available when I built the reversing toggle, I would have used it. Call it a "judgement" call.

.


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## markba633csi (Jan 23, 2021)

My observation is that instead of being a sacrificial part, and doing it's thing maybe once every 3-5 years, it's just a part that wears out too fast. 
But then, I don't expect the lathe to protect itself from my clumsiness. 
-Mark


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## MetalPlane (Jan 25, 2021)

Bi11Hudson said:


> I use a G-1550 lathe, an older version of the 9X20s. The plastic gear got set aside when I built a reversing mechanism for the lead screw. To maintain the "weak link" in a gear train is important in that if something jams up, a piece of plastic will "give" before something metal. I do generally light machining with the 1550, often on synthetics such as plastic. For the most part, jamming something is not likely. I also use a 12X36 Craftsman (Atlas), which has no provision for a sacrifical link.
> 
> As a general overview, if the plastic gear is intact, leave it. If it's damaged, replace it with plastic. It's there for a reason. You must make the final call based on what you do. The plastic gear can possibly save some more costly part of the machine. If you are making a change to the train, such as mine, there may be no other option. Just do it. If the appropriate plastic gear had been available when I built the reversing toggle, I would have used it. Call it a "judgement" call.
> 
> .


Thanks for the sound advice. I may still go with the metal. I'm just a hobby machinist. I am considering replacing some of the metal woodruff keys with plastic ones I will make. Cheaper, and I can make them myself. I'm on my third plastic gear after facing a square plate. the tool post slipped and destroyed the gear. Grizzley changed to a metal gear for a reason. Figure its just a "Pot Metal" replacement or aluminum. 

I'll post the results.


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## markba633csi (Jan 25, 2021)

Watch it there- "pot metal" is fightin' words around here to an Atlas lathe owner.  Their zinc metal alloy is called zamak and is actually quite a strong, long wearing material which helped to reduce the price of those lathes considerably so that more folks could afford them. In fact, the large number of zamak parts and gears that were produced is one of the reasons those lathes are still around today, and still popular
-Mark


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## MetalPlane (Jan 25, 2021)

markba633csi said:


> Watch it there- "pot metal" is fightin' words around here to an Atlas lathe owner.  Their zinc metal alloy is called zamak and is actually quite a strong, long wearing material which helped to reduce the price of those lathes considerably so that more folks could afford them. In fact, the large number of zamak parts and gears that were produced is one of the reasons those lathes are still around today, and still popular
> -Mark


Thanks for the advice. The gear was ordered, but I haven't seen it yet. Was hoping that someone that has made the switch to the Grizzly metal replacement could shed some light on just how well they work and if they encountered any problems.


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## Stockyj (Jan 26, 2021)

You have already broken 2 bit risky taking the plastic one out. I am running a 3D printed Nylon gear and no problems yet still got the original.


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## Bi11Hudson (Jan 26, 2021)

For what it's worth, the "pot metal" gear is actually "ZAMAK", _as noted above_. ZAMAK is an alloy of Zinc and Aluminium, and is considered *almost* as strong as cast iron. On most (all?) of the Asian lathes, the change gears are (I think) iron. Even the very low end HF machines are iron. They, all that I have crossed, are Modulus 1, 20 degree gears. I have made a few, to learn the process, out of aluminium. Eventually making a 127 tooth out of plastic for the Atlas/Craftsman at 16 DP, 14 degree. 

Aluminium works well for the change gears. Actually, plastic works almost as well. My experiments with plastic were machined, not printed. I may get  into printing later, but the process doesn't "speak" to me. A  while back, I acquired both a set of 16 DP, 14 Deg and a set of Mod 1,(25.4DP) 20 Deg gear cutters. They were Asian, hence of questionable quality. They worked fine for Aluminium, I would question my skills to make any gears out of steel. I also acquired several sets of very small (<Mod1) cutters, to make gears for my models. That is more where my interest, hence skill, lies.

.


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## markba633csi (Jan 26, 2021)

3D printing speaks to me, but so far my wallet hasn't heard it


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## MetalPlane (Jan 31, 2021)

3D printed gear sounds great, but I don't have a 3D printer. JET sells a plastic replacement for an outrageous $70. Grizzly sells a "metal" replacement for just over $18.00. My Jet BD-920N and the Grizzly G4000 are the same. 

I just received the Grizzly metal gear in the mail and it is Cast Iron just like the change gears. I replaced the stripped Plastic gear with a new plastic spare I have been saving, so there is still a sacrificial gear in place (for now). I plan to use the metal gear as an emergency spare.

Since many companies sold this lathe, does anyone sell the plastic 80T gear at a more reasonable price? I assume that Grizzly went to the metal version due to cost or ease of manufacture.


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## Diaric (Dec 21, 2021)

New member, old topic. First post.
I just ran into this dilemma yesterday, the plastic gear snapped after years of use on my new to me lathe.
I popped in the metal one that came with mine.  Apparently poor die casting, the centre crumbled out of it. Partially my fault, I tight fit on the shaft, I should have filed it rather than tap.
Apparently no one has stock, except Jet, at their gouging price, but I found this on my search. The plans for 3D printing the replacement gear. I will be back in business when my Son in Law, with a printer visits. I hope this helps someone else.





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						Printables
					






					www.prusaprinters.org


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## Stockyj (Dec 21, 2021)

Hi there I printed and designed my own gear has been running for a while. If you get one printed it needs to be printed in nylon at about 260deg C using an enclosure to reduce shrinkage, warpage and get better layer strength.


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## addertooth (Dec 21, 2021)

Keep in mind that if "the center crumbles", you may have the option of chucking it up and cutting a fresh I.D. and then brass sleeving it.


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## markba633csi (Dec 21, 2021)

If the center falls out the whole gear would follow soon enough- impurities in the alloy
-M


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## Diaric (Dec 21, 2021)

I don’t have the skill set to do that sort of business yet.  It’s actually a cast iron gear, and the centre broke out in an ugly manner. Son in law has one gear printed, is printing a few more and be up on the weekend


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