Helical gear cutting setup

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L98fiero

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I'd better point out that spur gears -can- transmit more power because the area of contact as they roll across each other is across the entire
I'll defer to a mechanical engineer on this but helical gears always have multiple teeth in mesh which means less load on each individual tooth so that at any given time their load is distributed over several teeth resulting in higher load capability. Not being an engineer I can't prove that but my experience in the mining industry is that most of the high load gearboxes, 1500+ horsepower had helical gears. That said, because of the sliding friction and the axial loads they are less efficient.
 

methuselah1

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All gears have multiple teeth in mesh, otherwise the constant velocity condition cannot be met. Helical gears do have more room for movement, I suppose, before becoming "notchy", but as long as the design is sufficiently robust to cope with the power transmission requirement (plus safety factor) there is no reason not to use either. In addition, whilst in the past really big spur gears were cast, or produced with a "sunderland rack" machine (that -could- produce helicals to an extent), modern hobbing technology can produce large scale, precise wheels in either form with comparative ease.
 

TSutrina

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What is the advantage of a helical gear over a spur gear? Correct me if I'm wrong. I thought helical gears in vehicles ran quieter than spur gears. But spur gears are stronger than helical, that's why racing engines use spur gears. They don't care about noise, just strength.
Grasshopper
Spur gear and helix gear tolerance can result in lose of contact for some range of travel. Bending load of a spur gear not making contact is zero. Helix gear load is carried by both the portion of the tooth making contact and that not making contact since they are part of a single helix. Big reason for noise.
Helix gears have an additional force due to trigonometry at right angle to the force created by torque. Total stress on a tooth also follows trigonometry, and the same trigonometry effect the amount of metal. Small angles the helix gear can be stronger but the face needs to be long so that tooth contact is a constant. For large helix angle the application is normally to change the direction of the axis. Weaker helix gear is not driving the design.
Finally for custom one off gears that racing cars use, cost sometimes favors spur gear ground to tighter tolerances over helix gears.
 

SmithDoor

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If have horizontal mill it simply as data is in machinery's hand book.

The easy way is on Follow gear shaper you buy the shaper with 30 degrees dies and buy cutter too. But do need both L/H and R/H.

Or just to Auto salvage yard and feel close match for projects they hard and done ready to go lower cost than a set of cutters..

Dave

Since Chuck Fellows published the drawings for making and using the helical gear fixture I have made quite a few of them. The problem with the whole setup is the indexing/cutting fixture is always at some angle to cut the required gears. At the cutting end of the mandrel is an arbor to hold whatever blank you're going to be cutting. I have posed the question to machinist friends and thought about it myself but couldn't come up with a reasonably accurate way of centering the cutter both vertically and transversely relative to the centerline of the gear blank.

I'm in the process of starting a new project with the completion of the Galion road grader and thought I would like to make another transmission, this one for my flathead engine. My son knows a fellow that has several of them and he offered one to me so that I could take the necessary dimensions. When I built the Borg-Warner T-5 transmission I used spur gears instead of the normal helicals because of the large amount of gear cutting templates required to make all the gears. With this one which has fewer gears I thought I would make the helicals.

Now back to the problem at hand. The gears will all be .250 wide so I made a setup gauge, if you will, that mounts onto the end of the holding arbor. I started by turning a piece of stock that fits the arbor and is .25 wide, the same as the gears. I cross drilled it .093 diameter and inserted a pin in each side, one with a point and one flat ended. I moved the shaft of the fixture to approximately halfway of it's travel and locked it with the locking screw. The next step is to secure the gauge to the arbor and align it horizontally by eye. I then used the dial indicator to get it completely flat. Step three was to use the edge finder to get to the center of the pin. This was done and -0- set on the readout. (X travel)
 

L98fiero

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What is the advantage of a helical gear over a spur gear? Correct me if I'm wrong. I thought helical gears in vehicles ran quieter than spur gears. But spur gears are stronger than helical, that's why racing engines use spur gears. They don't care about noise, just strength.
Grasshopper
I did a few searches to verify my assumptions and found that in general, all of the manufactures of gearing state, in one way or another that "Helical gears are stronger than other spur gears and are used in high power and load applications." Yes, you can design with bigger spur gears but a helical gearbox of a given size will be able to handle more power than a comparable gearbox with spur gears and as a bonus it's quieter.
 
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