Pinon gear for Famco arbor press

rke[pler · Apr 13, 2021

I picked up a well used Famco 31-C arbor press at an auction, and just completed disassembly (it was frozen and needed much high-impact love). After pulling the arbor I found that the teeth were pretty well smushed, so I figured that I'd draw it up in case I wanted to make another after getting this one pack together. In measuring the gear part of the pinion (the whole this is 13.5" long and the gear is integral in the middle) I came up with a 12 tooth gear with a outside diameter of 1.675. This would be a DP of 8.35. An OD of 1.750 would be a DP of 8. Slipping a gear gage into a relatively unworn part of the pinon it sure seems to fit at the bottom. Did Famco use a stub tooth design or something here? Given the pressures on the pinion it might be a good idea...

David_M · Apr 13, 2021

Measure distance between x (more is better) number of teeth divided by x on the rack to get the circular pitch. Depth of teeth to find out if you are looking at a stub tooth and pressure angle since it is easier there.

kjones95206 · Apr 13, 2021

If you aren't aware, Famco sells parts for your press, and their catalog has a parts breakdown for your press.
High Speed Mechanical Shear Manufacturer | Famco Machine : Famco Machine

Dan from Oakland · Apr 13, 2021

Probably a small number of teeth. If so, good chance its a long addendum gear with a non-standard OD. One of the tricks of the trade- essentially a gear cut to full depth on an oversize blank, which will eliminate undercut at the root that weakens the gear tooth. If the teeth look kinda pointy at the tips, this is most likely what you have.

1yesca · Apr 13, 2021

years ago there was a used machinery sales that a pal of mine from city collage worked at and on Saturday i would go there and he would let me dig in the scrap bin i learned a lot and i got a lot of projects to play with at school and one was an arbor press that had a broken pinon gear well god bless them navy machinist mate instructors there they could tell you , help you or show you how to make or machine any thing well my prof was on the Dixon sub tinder [mike b.] and he helped me make the gear for that press

rke[pler · Apr 14, 2021

David_M said:
Measure distance between x (more is better) number of teeth divided by x on the rack to get the circular pitch. Depth of teeth to find out if you are looking at a stub tooth and pressure angle since it is easier there.

The problem is that the teeth on the pinion are really mangled from applied pressure. The diameter measurement is from an area that is the original pinion diameter, you can't measure over the teeth for the raised area. The same goes for measuring tooth form - the teeth are so bent up that you can't get a good read, and the small area that didn't ride on the arbor and bend the tooth is too short to get a read using pin gages.

But in the end I'm pretty sure that it's an 8DP with a reduced diameter. I'll look for an 8DP pinion gear that I can mount on a shaft to check things but really it might just be easier to whack one out on the mill and see if it works as expected.

I did reassemble the press to make sure I hadn't lost anything and it all works OKish, so I might just leave this on the back burner.

rke[pler · Apr 14, 2021

kjones95206 said:
If you aren't aware, Famco sells parts for your press, and their catalog has a parts breakdown for your press.
High Speed Mechanical Shear Manufacturer | Famco Machine : Famco Machine

Yeah, I called them and they want near $600 for the pinion. It's a nice part and seems well made but that almost twice what I paid for the press so I'm motivated to spend a day or so to make a replacement myself. I'm retired and it's not a commercial shop so I don't put a big value on my time when it's my projects (else nothing would ever get made, really).

rke[pler · Apr 14, 2021

Dan from Oakland said:
Probably a small number of teeth. If so, good chance its a long addendum gear with a non-standard OD. One of the tricks of the trade- essentially a gear cut to full depth on an oversize blank, which will eliminate undercut at the root that weakens the gear tooth. If the teeth look kinda pointy at the tips, this is most likely what you have.

I've seen something like that on the Hardinge gears made for the HLVH and also used in the helical milling attachment on the UM mill. This seems to be the other way - a gear cut in a smaller diameter blank. Since an 8DP 12 tooth gear would have a 1.500" CP and a 1.750" diameter I think they might have just cut the diameter down to the 1.675" I'm seeing and lost the engagement above that - it's an arbor press after all.

rke[pler · Apr 14, 2021

Just checked the teeth on the arbor as they're in better shape. The whole depth is .219 instead of the expected .269 for a .060 difference, so it's definitely not a clean 8DP gear. Setting a gear vernier to a tooth thickness of .196 and measuring the height above that I'm seeing .090, so .035 less that the expected addendum of .125. On the pinion that'd show double on the diameter so .070, so pretty close to the .1675 measured below the expected 1.750. So the arbor matches the pinion in tooth form and it's something of a 8DP stub.

gustafson · Apr 14, 2021

big teeth on a small diameter are usually some bastardized gear. YOu could make that gear with a hatchet and it would work fine since you are not concerned with geartrain noise and the like

wunner if any of any of the imports copied them accurately enough that a trip to harbor freight would be worthwhile....

EmGo · Apr 14, 2021

gustafson said:
big teeth on a small diameter are usually some bastardized gear.

Not really bastardized at all ... the involute curve came to be the most common way to make teeth because it's so flexible. You can manipulate it all over to get the results you want. "Standard" teeth are just a convenience ...

You could make that gear with a hatchet and it would work fine since you are not concerned with geartrain noise and the like

Except if you're trying to press something together with some control ... you'd like it to move smoothly. Problem with this for o.p. is that he's not going to find a space cutter that matches these dims so easily. If you're generating, no problem, just pull the cutter in or out but for a space cutter that won't work.

He could draw it up big, then shrink to the correct size, then try to grind a one-off to match the profile. Buncha work but hey, save $600

Occasionally time is more available than money ... (been there before, for sure)

edit: you know what ? Along these lines, you could do a tooth layout really big, then reduce it to actual size and have a laser shop knock you out a template. Or do it on the computer and make a dxf, but that's going to be a rabbit hole. Rough the teeth with whatever, then use a single tooth finish cutter ground to fit your template to get the proper shape.

David_M · Apr 15, 2021

11-tooth stub on a 12-tooth-stub blank:

12-tooth standard stub:

gustafson · Apr 15, 2021

EmanuelGoldstein said:
Not really bastardized at all ... the involute curve came to be the most common way to make teeth because it's so flexible. You can manipulate it all over to get the results you want. "Standard" teeth are just a convenience ...

NOt really a convenience, as the large teeth start moving in an ever diminishing circle, they start doing more sliding and less pushing. When you have 9 teeth on a 1 inch diameter there is a lot of sliding compared to pushing. Those gear teeth look like inbred baby teeth compared to a nice fully formed gear tooth that would be the same pitch on say 4 inch diameter.

My point was that with a dividing head and enough of the original pinion left to serve as a pattern one could make a serviceable pinion with a hand ground tool, it would just take longer than I would ever have patience for.

gustafson · Apr 15, 2021

Also occurs to me that if I were ever to somehow wear out my 30 year old Phase II 3 tonner, I could probably mod the pinion shaft to back it out and give it fresh purchase on a new section of gear. Or push it in further

rke[pler · Apr 18, 2021

gustafson said:
Also occurs to me that if I were ever to somehow wear out my 30 year old Phase II 3 tonner, I could probably mod the pinion shaft to back it out and give it fresh purchase on a new section of gear. Or push it in further

If it was like my Famco there's not a lot of the pinion not in engagement with the arbor. On mine there was maybe 1/8" on one side and maybe double that on the other (where the cuts for the teeth run out).

After all the discussion and whatnot I'm pretty sure that Famco went with a 'standard' 8DP stub tooth, so if I make a replacement I'll go with that.

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