Replacement Gear Materials

cdhknives

cdhknives

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Our old Atlas machines use Zamak gears (threading or QCGB drive) which are not readily available except as used gears...or very expensive factory units. The ones generally for sale that fit are steel, cast iron, brass, etc. Not Zamak. How are these materials going to treat our existing Zamak gears? Is excessive wear going to be an issue?
 
"Excessive" is a tough term to define.
All gears wear. Even super-duper tough and hardened ones wear. And when they need replaced, they're often accused of 'excessive wear'. Indeed, that's exactly the reason they get replaced! So it's a matter of how much and how long.
They will wear *differently*. That much is true. And you'll have to examine relative sizes and therefore loads. For instance, a small pinion meshed with a large gear will have a likelihood of tearing up teeth if the gears are of dissimilar hardness and toughness. But QCGB gears don't see high loads in the first place (hence, the Zamak). Even Nylon would work (and run a lot quieter ;-). But once you switch materials, all you really get is a different wear pattern. Whether that's up to your standard or not is another issue.
That bit of trivia aside, surely someone has done this and has a success/failure story to share.

Wrat
 
I can just see the harder steel or brass gear eating the Zamak...especially during break in when the surfaces are a bit rough. Similar hardness on both would mean equal wear, but a steel gear against Zamak...??? Seems like a possible problem. The gears in my drive train are already showing significant wear, worse the closer you get to the spindle gear...the 2 tumbler gears are pointed, but the QCGB looks near new. Low RPM vs. high RPM I'd wager. Still, I'd rather not replace more of them than necessary.
 
The gears in the QCGB are steel and are driven by 2 48T Zamak gears. They don't seem to wear differently than the other Zamak gears that mesh with just Zamak gears. I know that Spiral Chips is using the Boston Gears on his lathe. Not sure if he is running all of them or just some. Also you might be supprised at the price on new gears. Some times new parts for the Atlas are cheaper than what people charge for used parts on EBay. Half nuts are one example, new ones from Clausing are around $34. A couple of the resellers are asking 2X that. I do understand a profit but I think that is excessive.
 
Gear wear is also inversely proportional to how well they are lubricated.
 
Of the several gear making books I've read in the last year. Maybe a dozen. Some chapters with selective second reads.
Gear materials are specific to the task.
The composite and zamac gears may suffer a poor reputation for longevity.
I recall a chapter wherein the author mentioned that composite gears were actually fairly durable albeit softer than the gears they meshed with.
The selection was usually intentional as they were the least expensive of the assembly and functioned as sacrificial shearing gears which were intended to suffer the most wear preserving their more expensive or more difficult to find/replace brothers.
Zamac is supposedly pretty hardy stuff. I've been told that the bad reputation of pot metal comes from bad quality control and or making the items so thin/light that durability suffers.

Have you considered making one?

Daryl
MN
 
I do not have the equipment (mill, dividing head) to make gears. All I have is a lathe and time. Since this drives the leadscrew and any irregularities would show up in threading, I'll probably be best served by leaving it to the experts.
 
Ah,....
I've seen lathes used like shapers.
Gears were often made on shapers in the 1900s.
Especially possible if you are using a softer metal.
Wild thinking here: I'm wondering if a jig could be made to copy a the gear with a finger set to toggle on the gear you are modeling.
Certainly easier to purchase one, especially as you may end up making a couple before all is done.

Daryl
MN
 
Clausing sells the plans to make a gear cutting attachment for the lathe. PN is BP-102. I order a copy of it a couple of years ago and it cost something like $5 plus shipping. It uses the milling attachment along with a arbor you make for your lathe to use gear cutters. It also uses gears for doing the dividing. You will see a picture of it in some of the older Atlas catalogs.
 
Uglydog said:
Ah,....
I've seen lathes used like shapers.
Gears were often made on shapers in the 1900s.
Especially possible if you are using a softer metal.
Wild thinking here: I'm wondering if a jig could be made to copy a the gear with a finger set to toggle on the gear you are modeling.
Certainly easier to purchase one, especially as you may end up making a couple before all is done.

Daryl
MN
Click to expand...

I've looked into this, actually, but I wanted to use the bull gear holes for my dividing head. That would require a separate cutter and motor, or using the handwheel crank to drive the carriage. I couldn't see that working on a gear slot sized cut. All attempts to figure out how to drive the leadscrew under power with the spindle decoupled got too complex in a hurry. Maybe with polymer gears...but probably not metal. The saddle traverse and split nuts might not be strong enough to take that much force...to drive the cutter. I don't have a good feel for the strains and strengths involved in that kind of operation...definitely not how the lathe was designed to cut.
 
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