Need to make variable shaft angle bevel gears

Rich L · Jul 26, 2017

I have a machine with some badly worn ... ummm, ... bevel gears ... that I would like to replace by making them myself. Does anyone have experience with these kinds of gears that engage under a variable shaft angle? The picture shows the engagement, just for illustration purposes, at about 15º from parallel. Machine constraints only allow a max of about 70º of shaft angle (from parallel) so they engage pretty much on the corner at that setting. The big messed up screw head shown between the gears is the pivot axis for setting shaft angle. The gears are roughly 2.5 inches diameter. It seems to me that backlash would vary as well since the variable angle engagement is not spherical but some variation (don't know how much yet) would be tolerable.

Would it be as simple as:

determine pitch angle for the bevel
determine pressure angle
cut the blank with a standard gear cutter paying attention to the cone angles on the beveled face.

??

Maybe somehow chamfer or radius the edge between the spur and the bevel?

I'm throwing out gear terms and I hope I'm not too far off base with them.

These are brass and there is little load on them and they operate at less then 20 -30 RPM.

Thanks for any thoughts!

Rich

johnoder · Jul 26, 2017

Seems like a better result would be teeth curved on a radius that was 1/2 of pitch diameter

Easy on CNC

Problem of doing it any way with formed type cutter is accommodating the ever smaller teeth on the "bevel" portion - that is the reason for the existence of bevel gear form cutters - which are thinner than spur gear cutters

On edit...chapter in here on bevel gears

Internet Archive: Error

Rich L · Jul 26, 2017

johnoder said:
Seems like a better result would be teeth curved on a radius that was 1/2 of pitch diameter

Easy on CNC

Problem of doing it any way with formed type cutter is accommodating the ever smaller teeth on the "bevel" portion - that is the reason for the existence of bevel gear form cutters - which are thinner than spur gear cutters

Thanks for that tip on the bevel gear cutter - I'll be looking for sources.

Rich

moonlight machine · Jul 26, 2017

Rich L said:
I have a machine with some badly worn ... ummm, ... bevel gears ... that I would like to replace by making them myself. Does anyone have experience with these kinds of gears that engage under a variable shaft angle? The picture shows the engagement, just for illustration purposes, at about 15º from parallel. Machine constraints only allow a max of about 70º of shaft angle (from parallel) so they engage pretty much on the corner at that setting. The big messed up screw head shown between the gears is the pivot axis for setting shaft angle. The gears are roughly 2.5 inches diameter. It seems to me that backlash would vary as well since the variable angle engagement is not spherical but some variation (don't know how much yet) would be tolerable.

Would it be as simple as:

determine pitch angle for the bevel
determine pressure angle
cut the blank with a standard gear cutter paying attention to the cone angles on the beveled face.

??

Maybe somehow chamfer or radius the edge between the spur and the bevel?

I'm throwing out gear terms and I hope I'm not too far off base with them.

These are brass and there is little load on them and they operate at less then 20 -30 RPM.

Thanks for any thoughts!

Rich

View attachment 204079

What is that machine????

Rich L · Jul 26, 2017

moonlight machine said:
What is that machine????

It's a metal engraving machine called a brocading machine. For folks that don't know, it copies and can scale a pattern onto metal plates, cylinders, cones, other "round" shapes by following a pattern die in a spiral manner. The engraving is physically done by a "bright cut" engraving cutter the same way rose engines and straight line engines do their thing. In fact, this is a variety of rose engine.

If you Google "brocading" you will get tons of hits with respect to textiles - this machine has nothing to do with textiles.

Back to the thread - I have not been able to find any outfit on line that sells bevel gear cutters. Anyone got a hint of a source. I can find the spur gear cutters but not bevel.

johnoder · Jul 26, 2017

Say Diametral Pitch and I'll see what I have

Diametral pitch can be determined in this way:

Measure OD with mic and record

Count teeth - add TWO to that count

Divide OD in to the sum

Example:

2.125" OD

32 teeth

34 divided by 2.125 = 16 DP

I have not been able to find any outfit on line that sells bevel gear cutters. Anyone got a hint of a source. I can find the spur gear cutters but not bevel.

David_M · Jul 26, 2017

Try calling Ash Gear if Mr. Oder can't help you with a cutter.

Rich L · Jul 26, 2017

johnoder said:
Say Diametral Pitch and I'll see what I have

Diametral pitch can be determined in this way:
Measure OD with mic and record
Count teeth - add TWO to that count
Divide OD in to the sum

Example:

2.125" OD
32 teeth
34 divided by 2.125 = 16 DP

OK, the OD is 2.36"
tooth count is 49
add 2 = 51
Diametral pitch ( P ) 51/2.36 = 21.61

I'm also waiting for pitch cone angle (or edge angle) to factor in somewhere since the above calculation is independent of it.

I'm reading ... lot to learn about cutting bevel gears ...

Cheers,
Rich

Monarchist · Jul 27, 2017

Rich L said:
I have a machine with some badly worn ... ummm, ... bevel gears ... that I would like to replace by making them myself. Does anyone have experience with these kinds of gears that engage under a variable shaft angle? The picture shows the engagement, just for illustration purposes, at about 15º from parallel. Machine constraints only allow a max of about 70º of shaft angle (from parallel) so they engage pretty much on the corner at that setting. The big messed up screw head shown between the gears is the pivot axis for setting shaft angle. The gears are roughly 2.5 inches diameter. It seems to me that backlash would vary as well since the variable angle engagement is not spherical but some variation (don't know how much yet) would be tolerable.

Would it be as simple as:

determine pitch angle for the bevel
determine pressure angle
cut the blank with a standard gear cutter paying attention to the cone angles on the beveled face.

??

Maybe somehow chamfer or radius the edge between the spur and the bevel?

I'm throwing out gear terms and I hope I'm not too far off base with them.

These are brass and there is little load on them and they operate at less then 20 -30 RPM.

Thanks for any thoughts!

Rich

View attachment 204079

Probably a Bronze, not a brass, a very strong one, and a rather "special" cut you may play Merry Hell replicating..and..

whomever made that rig actually WORK should be given a medal for creativity.

Then locked in a padded cell to reflect on the grief he visited on his fellow man as to maintaining it!

The "usual" approach is to fix the gears and provide for angular shaft movement at their hubs, or even within their hubs. Think "Rzeppa" CV joint inside a ring gear, etc.

EPAIII · Jul 27, 2017

From the photo it seems that they are standard spur gears on the OD and those teeth meet with some fairly standard bevel teeth on the face. The pivot point is somewhere close to where the two pitch diameters and two pitch cones meet. So at in-between angles the entire load is taken by the corner where the two types of teeth meet.

I would cut the spur type teeth first and then see if I could cut the bevel teeth to match/meet with them.

Good luck and please post photos of the product. I am very curious as to how it comes out.

The idea seems to be a 1:1 gear ratio. I wonder if something could be done with a timing belt, a couple of smaller, toothed pulleys for it and a couple of idler pulleys to turn the angle. But the axis for the idler pulleys would not coincide with the center of rotation between the shafts. It would have to be determined to allow the belt to not go slack at some positions. It may even have to be spring loaded.

johnoder · Jul 27, 2017

No such cutters here. Sounds like a grind to suit fly cutter job

Rich L said:
OK, the OD is 2.36"
tooth count is 49
add 2 = 51
Diametral pitch ( P ) 51/2.36 = 21.61

I'm also waiting for pitch cone angle (or edge angle) to factor in somewhere since the above calculation is independent of it.

I'm reading ... lot to learn about cutting bevel gears ...

Cheers,
Rich

Rich L · Jul 27, 2017

David_M said:
Try calling Ash Gear if Mr. Oder can't help you with a cutter.

I called them but they have no milling cutters for bevel gears - they scrapped them all some time ago. All they have are generating cutters for special machines (Gleason). They said they could order a milling cutter but I'd have to send them the actual part because the cutter manufacturer would not work with my specs. $200-$300

I hope I can find or get directed to some outfit that can work with specs or can sell me a cutter.

Is it sacrilegious to use an "appropriately sized" spur gear cutter to make the beveled teeth? The result has got to be better than what I have operating now. The pitch angle is 60º. I also think that since the ID area of the bevel never really gets engaged, the length of the teeth on the bevel could be minimized (OD - ID = half what there is now). I realize that having this variable shaft angle work with a non-spherical engagement that the bevel/spur design that this gear set has doesn't engage optimally anyway.

Cheers,
Rich

johnoder · Jul 27, 2017

That is just it, there are no "appropriate" sized cutters made. Your choice will be 24 DP, which will make too small tooth spaces and 20 DP which will make too large tooth spaces. May get a little closer with module gear cutters for metric gears

Union Twist Drill Co. listed 22 DP in their catalog, but that was in 1910. In this same catalog, the only near bevel gear cutters were 20 and 24 DP

Rich L said:
Is it sacrilegious to use an "appropriately sized" spur gear cutter to make the beveled teeth? The result has got to be better than what I have operating now. The pitch angle is 60º. I also think that since the ID area of the bevel never really gets engaged, the length of the teeth on the bevel could be minimized (OD - ID = half what there is now). I realize that having this variable shaft angle work with a non-spherical engagement that the bevel/spur design that this gear set has doesn't engage optimally anyway.

Cheers,
Rich

SeaMoss · Jul 27, 2017

Rich L said:
Is it sacrilegious to use an "appropriately sized" spur gear cutter to make the beveled teeth?

Glorp. Who designed that thing ? They should be shot.

Do you expect to use it, or is it mostly for looks ?

You could cut the bevel teeth, then line them up with spur teeth, then do some judicious hand filing.

Or you could make a solid model using teeth on a sphere and make it work correctly. They couldn't have done that in the old days and it would take hours on a three axis machine with an indexer. Or a four-axis machine. Or you could even justify five ...

What an awful part.

MAYBE machine one tooth on both sides, oversize, use it to plaster cast a whole bunch of wax or styrene teeth, make a spherical kinda blank, put slots in it, glue the individual teeth into the slots, then use the whole shlemeer to cast a one-piece replacement ?

No, bad idea. Surface machine the damn thing with tiny little end mills. 6800 hours later you'll have two working parts ...

Ugh.

Or just do the bevel-cum-spur, but then you're right back where you started, a crappy design that wears out fast and doesn't work well in the meantime.

You could try using a skinny bevel cutter, tip the axis of the part, profile the top half then tip down to profile the bottom half, leave the teeth fat then finish them by hand.

Ugh.

Put a spur gear on one shaft and a spur gear on the other shaft with a cv bearing inside it ? That might work the best. Better than the abortion that thing came with stock :eek:

Rich L · Jul 27, 2017

johnoder said:
That is just it, there are no "appropriate" sized cutters made. Your choice will be 24 DP, which will make too small tooth spaces and 20 DP which will make too large tooth spaces. May get a little closer with module gear cutters for metric gears

Union Twist Drill Co. listed 22 DP in their catalog, but that was in 1910. In this same catalog, the only near bevel gear cutters were 20 and 24 DP

Right. Understand. What I meant by "appropriate" was a compromise probably being an undersized spur gear cutter so I'd make at least two passes per tooth on the bevel. Possibly the 24 or something metric, as you say. Travers shows a 14 1/2º 22 DP spur gear cutter but only 20 and 24 DP for 20º. I don't know what pressure angle I have. Have I got my compromise understood?

Cheers,
Rich

Rich L · Jul 27, 2017

SeaMoss said:
Glorp. Who designed that thing ? They should be shot.

Do you expect to use it, or is it mostly for looks ? ...

Yep! It's a very old design evidently well before advances in non-linear drive technology. Yes, I will be using this machine. At the rate I'd be using it, a re-done crappy design will still last me a long time. I appreciate your thoughts on the matter (I had many of the same) and the potential solutions

The undersized involute cutter approach seems most doable at the moment.

Oh, by the way, I'm sure the designer is dead by now.

Cheers,
Rich

Clive603 · Jul 27, 2017

If you plan to make your own maybe its worth looking into doing parallel depth bevels with curved teeth.

Curved teeth spur gears are usually associated with floating sleeve internal - external gear type couplings where the teeth on the external gears are curved along an axis parallel to the shaft to give a small amount of angular error tolerance between the input and output shafts. Typically a couple of degrees.

However similar methods have been (are?) used to make spur gears able to handle considerable angular error tolerance between co-planar shafts. Low powers and moderate speeds only I think. One of the UK gear suppliers used to list such things. Probably plastic. As I recall it angle error capability was said to be up to around ± 20°. Whether per pair or for one gear working against a standard gear I know not. Conceptually at least the pitch lines are two spheres, or rather part spherical slices, rolling against each other with tooth addendum and dedendum imposed in the usual manner. Basic tooth shape remains correct but the engagement length will be very narrow so clearly power transmission capability will be limited.

At first sight it would seem that if you applied the idea to parallel depth bevels, which can be cut with ordinary involute cutters, it might be possible to get enough angular variation for your job without silly levels of backlash.

Clive

David_M · Jul 27, 2017

How important is verisimilitude?

Edit: I see you already said you don't mind changing things some.

I agree with John Oder that this is a self-ground fly cutter job.

http://www.pbase.com/image/165911659/large

Rich L · Jul 27, 2017

That's a very important 50¢ word

I've seen those in my research on this subject. They are real. The gears, that is.

David_M · Jul 27, 2017

Rich L said:
That's a very important 50¢ word

My inner Norm Crosby and our malapropism :Ithankyou:

I've seen those in my research on this subject. They are real. The gears, that is.

How is the pivot point located compared to the gear that swings? Maybe one of us could sketch you a preliminary model unless you are setup to do it.

Need to make variable shaft angle bevel gears

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