So I'm Looking for some Gears...... ?

[Doug4d3s]

I have a project idea that will require six identical gears, basically used paired as gear-style pumps. I don't wish to even attempt making them myself.

I'd prefer carbon steel, but stainless could work. Plastic or brass will not (high temps). Cast iron might work, but it would need to be really cheap for me to bother trying with it.
The OD needs to be from ~4 to ~6 inches, with the bores at least 1/2" or so.
The tooth size isn't critical, but for the pump reason I'd prefer it larger, ~40 T for a 6" OD, for example.

I would strongly prefer angled teeth. If the teeth are straight, the thickness needs to be maybe .5"... If the teeth are angled, the thickness could be as wide as .75" or so.

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I know that the pressure angle of gears needs to match, and I also know that the angle of teeth must match also.... but I would have figured finding some surplus parts for this would be pretty easy, since all six wheels need to be identical,,,,,, And yet I have found almost no examples of surplus angled-tooth gear wheels at all. Pretty much all of what I have found is too small, made of brass or plastic, or both. Usually with 1/4" bores, and topping out at 3" or so diameters.

One gear manufacturer wants nearly $40 for a single 4-inch diameter .25" thick gear, and that's with straight-cut teeth. All the helical-tooth gears in their online catalog seem to say "out of stock".

I have seen several custom gear shops online; is this basically the only way to get helical-cut gears? And is there a great deal of difference in price for helicals, as opposed to straight-cut teeth?

[dly31]

You might find something suitable in automotive timing gears. Some are very inexpensive and a rebuild shop would have lots of good used ones in the scrap as they are routinely replaced. I think a pair of identical helical tooth gears will not mesh when the gears are parallel as the teeth will be crosswise to each other. It may be possible to find different timing gears that have opposite angles and thus will mesh. Of course if you can use a 2-1 size ratio, you could use a regular set.

[hammermill]

look at the gears/sprocket on a 350 chev or any salvage yard but you may find pump gears are built a little differient while there look at a engines oil pump

[Dave_C]

Doug,

Not too sure how the timing gear thing will work but if you examine an oil pump gear in a car motor or small engine, most are just straight cut envolute gears. There is a good reason for this I think and as you study the pumping action of the gear you will see that it is a positive displacement pump. Meaning that as the gear turns, the cavity between the teeth have oil in them. As the approacing teeth mesh it forces the oil out and since it can't escape past the rotating tooth it creates pressure.

Needless to say, if the clearance around the gear ends is large enough you won't make much pressure if any at all. That's the tricky part to get right if you're making a pump. I have seen angle cut gears in some pumps but I've seen more straight cut gears than angle cut.

$40.00 a gear for a steel 6" gear is pretty reasonable. If you have ever made your own you will find it takes a lot of time to cut each gear. Granted, if it is being done with CNC the time will be 1/10 of or less of what it takes me by hand to make a gear. Still, hobbs and tooling is quite expensive to make gears.

You are correct: Pitch angle and Diametral Pitch have to match for two gears to run together.

Here is as close as I can calc for a 6" OD Gear
Number of Teeth 46
Diametrical Pitch 8
Pressure Angle 14.5

Dave C.

[Doug4d3s]

The timing gears may well work and some are only $40 or so for both. Tooth size is smaller than I'd prefer, but oh well. I'll have to buy at least one to see how well they mesh.
If I build the thing and it doesn't work well with the timing gears, then I'll have to go pay for custom gears anyway.

I figured that there had to be something commonly made out there that already used suitable gears, but didn't know anything.
I had seen timing gears on engines before, but just the larger-engine ones that use two intermediate gears between the crankshaft and cam. And most of those are straight-cut besides.

Thanks much.

[wsippola]

If you are making gear pumps, that's kind of an odd dimension for your gears. The 1/2" shaft is very small for that size of gear, and even 4" gears would make a for a large hydraulic pump. Now you may very well be doing something different which requires these sizes. As far as where, maybe a tranny shop?

For Dave, I read your post as the pressure is built by the oil being squeezed between the teeth in the center of the pump. If that's what you meant, it's not what's happening. The oil is pumped along the outside edges of the gear pair, with the left gear rotating CCW and the right gear turning CW. It can't return through the center because the teeth mesh and block that route.

Wayne

[dly31]

Also look at timing gears for small engines such as mower and generator engines. Some of these have straight teeth so you could use a pair of the same size. They are also usally plentiful in the repair shops salvage bins.

[Dave_C]

Wayne,

I may not have explained it the way you did but since the oil is pulled around the gear teeth it would continue on around unless the "messing teeth" stopped it or forced it out of the gear teeth pockets.

Edited: 03/24/11 From Wikilinks: As the gears rotate they separate on the intake side of the pump, creating a void and suction which is filled by fluid. The fluid is carried by the gears to the discharge side of the pump, where the meshing of the gears displaces the fluid.

Now that we are totally "Off Topic" I forgot what the man was trying to accomplish with his need for gears.


My appologoies to the original poster.

Dave C.

[Doug4d3s]

.... I think a pair of identical helical tooth gears will not mesh when the gears are parallel as the teeth will be crosswise to each other. ....

Yea I see that, looking closely at the photos now.
Did not ever need to use angled ones for anything before. Its a good thing I didn't find any, I might have gone and bought them.

The timing gears may work, if they can mesh close enough. I don't need both of each pair to be the same diameter, I just figured that if I could use the same diameters then it would have been easiest to find six gears all the same size.
About $50 for all-steel gears. No car parts store has them on hand, but any can order them.

The part is Cloyes 2764s, fits a few of the Ford I-4's and I-6's.
http://www.autopartsnetwork.com/catalog ... _year:1966_
...I'm guessing the big gear will be around 5-6 inches dia? I'm assuming that the camshaft end wouldn't be much smaller than 3/4-inch.


...A couple other things need to go well before I'll get to needing these, but I knew I couldn't possibly make these myself.

[hammermill]

lots of engines have gon from builts to gears for cams and stuff a quick walk behind a repair shop shows all kinds of posibilities for cheep hondas seem to love em

here is a link to some photos/drawings of various gear pump designs

http://en.wikipedia.org/wiki/Gear_pump

[gregvasale]

since no one has asked, whats wrong with buying an oil pump instead of looking for gears to make an oil pump?

[Doug4d3s]

since no one has asked, whats wrong with buying an oil pump instead of looking for gears to make an oil pump?

In this instance a the same gears need to do both. Which they could easily do, if they were just made the right way (for this).

I got a pair of the timing gears and they could work for a first version, but another two pairs will bring the total cost up to $150.
The 2:1 sizes aren't ideal, 1:1's would be easier to handle, as would smaller OD sizes, maybe even down to 4 inches,,, which was what the $40 straight-cut one cost.
So I'm wondering,,, if I can get custom smaller ones cut for $240 or so, then I'd rather do that than pay $150 for the timing gears that I know would have issues.

Guess I'll need to bother someplace.....