Spur Gear Selection Advice Needed

[Rex]

Before I spend a few hundred dollars on gears for my pump, I'd like confirmation of my selections. I've used a couple on-line calculators and the Martin Gear catalog to arrive at the following pair.
Crankshaft speed won't be more than 30RPM, and pressure developed will only be enough to circulate water in and out of a bucket for display at engine shows.

Shaft Center Distance: 9.95"

Pinion
Martin S1038
Material: Steel
Diametral Pitch: 10
Pressure Angle: 14.5
Teeth: 38
Pitch Diameter: 3.8"
Outside Diameter: 4.0"
Face Width: 1.0"
Bore: 0.75"
Hub OD: 2.25"
Hub Projection: 0.875"
Bore Through Length: 1.875"

Driven Gear
Martin C10160
Material: Cast Iron
Diametral Pitch: 10
Pressure Angle: 14.5
Teeth: 160
Pitch Diameter: 16.0"
Outside Diameter: 16.2"
Face Width: 1.0"
Bore: 1.0"
Hub OD: 2.75"
Hub Projection: 1.0"
Bore Through Length: 2.0"

 

[johnoder]

Before I spend a few hundred dollars on gears for my pump, I'd like confirmation of my selections. I've used a couple on-line calculators and the Martin Gear catalog to arrive at the following pair.
Crankshaft speed won't be more than 30RPM, and pressure developed will only be enough to circulate water in and out of a bucket for display at engine shows.

Shaft Center Distance: 9.95"

Pinion
Martin S1038
Material: Steel
Diametral Pitch: 10
Pressure Angle: 14.5
Teeth: 38
Pitch Diameter: 3.8"
Outside Diameter: 4.0"
Face Width: 1.0"
Bore: 0.75"
Hub OD: 2.25"
Hub Projection: 0.875"
Bore Through Length: 1.875"

Driven Gear
Martin C10160
Material: Cast Iron
Diametral Pitch: 10
Pressure Angle: 14.5
Teeth: 160
Pitch Diameter: 16.0"
Outside Diameter: 16.2"
Face Width: 1.0"
Bore: 1.0"
Hub OD: 2.75"
Hub Projection: 1.0"
Bore Through Length: 2.0"

View attachment 406374

Ratio is 4.21 to 1, and I'll suppose this is in relation to the 30 RPM crankshaft which means 7.25 RPM pump speed - assuming the gear set is used to REDUCE crank shaft speed. If arranged to SPEED UP pump, its speed would be 126 RPM

 

[john.k]

Have you considered a flywheel ring gear for the large gear ?........Might save a lot of dollars.

 

[EmGo]

Before I spend a few hundred dollars on gears for my pump, I'd like confirmation of my selections.

That's a honkin' big thing you're going to be dragging around. Any reason to not use a couple of aluminum pulleys and a belt ?

 

[Dan from Oakland]

If your input RPM is only 30, have you considered using some roller chain and two sprockets? Might look kinda cool and probably less expensive

 

[Rex]

Ratio is 4.21 to 1, and I'll suppose this is in relation to the 30 RPM crankshaft which means 7.25 RPM pump speed - assuming the gear set is used to REDUCE crank shaft speed. If arranged to SPEED UP pump, its speed would be 126 RPM

John, good to hear from you , it's been a while and I always look forward to your responses. When I referred to 30 RPM "crankshaft speed" I meant the shaft with the eccentrics that drive the pistons which I believe you're calling the "pump speed".

Actually my only question is this: "Will the two gears I described mesh properly given the center distance of the shafts?"

One of the online calculators indicated they will, but I'd like confirmation from those who have actually done this.

 

[Rex]

Have you considered a flywheel ring gear for the large gear ?........Might save a lot of dollars.

Thanks for the suggestion, but I'd like to maintain a period correct appearance.

 

[Rex]

That's a honkin' big thing you're going to be dragging around. Any reason to not use a couple of aluminum pulleys and a belt ?

Honkin' big thing is actually the point of this sort of display, and I'd like to keep it looking as it did in original form.

 

[Rex]

If your input RPM is only 30, have you considered using some roller chain and two sprockets? Might look kinda cool and probably less expensive

Pump eccentric shaft speed is 30 RPM. I actually bought sprockets and chain, but it required an awkward looking idler pully to take up the slack in the chain. I also prefer the original look of the gears.

 

[Homeshopblob]

My experience with Martin gears is that they are cut to nominal size with no backlash built in. I'd buy the gears and set them up on a stub shaft in your mill and on the table to measure actual c-c dimension needed before making the case for the shafts.

 

[Rex]

My experience with Martin gears is that they are cut to nominal size with no backlash built in. I'd buy the gears and set them up on a stub shaft in your mill and on the table to measure actual c-c dimension needed before making the case for the shafts.

I understand the concept and concern, but the shaft distance is fixed as shown in the photo of the pump.

 

[Homeshopblob]

I understand the concept and concern, but the shaft distance is fixed as shown in the photo of the pump.

Then you should get the measurements of the gears over wires as delivered and calculate whether or not you'll have adequate clearance between them.

 

[Rex]

Sounds like a reasonable plan.

 

[johnoder]

John, good to hear from you , it's been a while and I always look forward to your responses. When I referred to 30 RPM "crankshaft speed" I meant the shaft with the eccentrics that drive the pistons which I believe you're calling the "pump speed".

Actually my only question is this: "Will the two gears I described mesh properly given the center distance of the shafts?"

One of the online calculators indicated they will, but I'd like confirmation from those who have actually done this.

Your CD is .005 more than the two gears "advertised" combined half pitch dias - so maybe so. You could alyays MEASURE the pitch dias and see just exactly what they are. See some good pubs like those written by Earle Buckingham. I like the idea of something far less capability as suggested.

 

[Mud]

The Van Keuren manuals are very handy for these calcs and easy to find the info in. They are always available cheap on Ebay

 

[Rex]

Your CD is .005 more than the two gears "advertised" combined half pitch dias - so maybe so. You could alyays MEASURE the pitch dias and see just exactly what they are. See some good pubs like those written by Earle Buckingham. I like the idea of something far less capability as suggested.

More CD is better than less in a case like this I suppose, I'll assess them upon arrival.

 

[Rex]

The Van Keuren manuals are very handy for these calcs and easy to find the info in. They are always available cheap on Ebay

Martin's site has a lot of good reference sources also.

 

[EmGo]

Actually my only question is this: "Will the two gears I described mesh properly given the center distance of the shafts?"

If they are made on-size then your center distance will give about 20-25 thousandths backlash which might be a little sloppy. I'd probably squeeze them in about twenty ... but then, I like to live dangerous

John : He's fifty big, not five. 138/10/2 = 9.9

 

[EPAIII]

My calculations agree:

0.050" loose in C-C distance
and
About 0.026" backlash.
(Backlash = 2 * 0.050" * tan(14.5°) )

The involute curve is highly tolerant of spacing errors so for low speed, low load, and probably not being reversed often, this will probably work just fine. And with a face width of 1", I don't think they will break in the next thousand years of operation.

The other consideration would be appearance. With a tooth height of a bit over 0.2", the difference in C-C spacing will be around 20% of that tooth height. So a careful eye with experience with gears may see that as excessive. Of course this will be hidden to a great extent while the engine is running. So, the problem really is can you stand the comments that may be made?

If they are made on-size then your center distance will give about 20-25 thousandths backlash which might be a little sloppy. I'd probably squeeze them in about twenty ... but then, I like to live dangerous

John : He's fifty big, not five. 138/10/2 = 9.9

 

[Rex]

Yes, .050 too much according to the calculator I found shown below. That's what led me to come here for advice, I didn't know how much variation would be acceptable for this sort of thing but hoped someone here would.

This pump is over 100 years old and will be driven by a 103 year old engine that has gear backlash at some points over .100" as does most everything at an antique power show. These gears will be beadblasted and chemically rusted to look the part, and .020" slop will fit right in.