Thread: Gear off of a Howard Roto-Tiller Model K, need to make or buy one

Originally Posted by laminar-flow

Well, a search for a standard gear shows this from Amazon. Yes, Amazon. Boston Gear NJ20-1 1/4 Spur Gear, 14.5 Pressure Angle, Steel, Inch, 6 Pitch, 1.250" Bore, 3.666" OD, 1.500" Face Width, 20 Teeth

For 92.00, but with no spline.

I have a slotting head on my Deckel. How hard would that be?

I don't know anything about a Deckel, perhaps you could check with Milacron or Deckeldoctor to use a slotter for broaching. I would consider mounting the gear blank on a rotab, grinding a cutter to match the spline and broach the spline one tooth at a time. Like gear cutting with a form cutter.

Tom

Originally Posted by laminar-flow

Well, a search for a standard gear shows this from Amazon. Yes, Amazon. Boston Gear NJ20-1 1/4 Spur Gear, 14.5 Pressure Angle, Steel, Inch, 6 Pitch, 1.250" Bore, 3.666" OD, 1.500" Face Width, 20 Teeth

For 92.00, but with no spline.

I have a slotting head on my Deckel. How hard would that be?

Totally doable. ... in softer material...
Your best bet is to buy the gear and WEDM the splines in.

That was the plan, but the tooth form of the spline looks like involute. So forming the cutter may be tricky. I do have a J&L and a T&C grinder, so we'll see. Wire would work if I could model it accurately. Checked and it would be about 350 to cut the spline. But If I do it, I can get the shaft out and check fit. Plan is to mount the gear on a plate with index pins in the teeth so I can remove and replace. That way I can check fit and re-cut.

Originally Posted by Zahnrad Kopf

Totally doable. ... in softer material...
Your best bet is to buy the gear and WEDM the splines in.

Might get a price on wireing the whole gear from a hardened blank

I should read the whole thread before answering , but, I'd be trying all the Ag. wrecking yards for parts still useable around the country also.

Originally Posted by laminar-flow

Checked and it would be about 350 to cut the spline.

Originally Posted by Heavey Metal

Might get a price on wireing the whole gear from a hardened blank

No, I would not wire the gear when one can buy it already done for $92. But I would WEDM the spline for him for less than $350 more.

What would you need to wire the splines? CAD file? Existing Gear? How much? I would imagine that the spline is a standard and was probably initially cut with a broach? The machine is 50 or 60 years old. If I can get a decent tooth profile ground, it should be fairly easy. Also, checking fit in the shop is so nice. The shaft is about 3 feet long.

Most farm machinery like this will use a hardened gear. Most of these gears are made from 8620 then carburized to get the surface hardness. Off the shelf gears are generally made from one of the freer machining steels that do not take well to case hardening though the spline would be easy to cut. Did a bearing go out and cause the shafts to get out of align? Check the mating gear for cracks near the bottoms of the teeth.

Ed.

So my thoughts are having the spline teeth hardened are more important than having the gear hardened, just due to smaller dia and all the torque flowing thru that interface. Gear teeth much larger contact area, larger running dia from the shaft center.

Just from a home shop/farm shop perspective, I would think if you can source a professional case hardening, then the Boston Gear would be good. Probably need consultation about any "growth" of the part relative to the spline fit. Ideally a medium carbon steel 4140, 4340 would be nicer but then you are into the teeth AND the spline.

As far as cutting splines/indexing, I think I'd practice on a piece of CRS before you mount up the $92 blank to make sure you can get the fit correct. Not the most time efficient but could potentially save some money.

Is there anything else complicated or difficult on the shaft apart from the spline?
If not maybe easier to make a whole new shaft with an equivalent modern spline on it and have the gear blank broached to fit with a standard broach. Might even be able to find a gear ready done. Likely to cost nigh on as much as fix-it but more straightforward and less gremlin room.

Clive

May I suggest NOT to over think this, it's a rotavator g/boxbuilt to a price - AKA low! and Howards were notable for their ''fit where it touches'' standards.....just because the gears hardened doesn't mean it's super precise.

So that was easy. Bought the gear, cut the hub to length, and bored it to the correct diameter. Then, using the existing gear, sketched a profile on the screen of the comparator, and using a tool and cutter grinder, and started the rough angle of the cutter. Then finished it by hand while comparing it with the profile in the comparator. The gear was mounted as shown and after a few times around, the shaft was a good fit. No word yet whether the teeth are holding up, but I guess that is good news. Pics attached.

Thank you for keeping us informed.

Thanks everyone. I put a bit of back relief on the cutter but not sure how much is correct. It did seem to cut just fine, as the cutter was made with a piece of .250 carbide from a boring bar. It had the flat which was utilized to keep it in rotation and it also provided a start for the flat of the cutter. It sure looks dangerous when cutting though. Used about 120 strokes per minute.

Originally Posted by matt_isserstedt

So my thoughts are having the spline teeth hardened are more important than having the gear hardened, just due to smaller dia and all the torque flowing thru that interface. Gear teeth much larger contact area, larger running dia from the shaft center.

Matt,

Yeah but....it is the gear teeth that have failed.....so perhaps the splines are not as fragile as they look....I guess because they are all sharing the load (in theory) whereas all the load goes onto one of the gear teeth?

laminar flow, thanks for the update.