Author Topic: Galloway Castings  (Read 22219 times)

PatJ

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Re: Galloway Castings
« Reply #15 on: December 09, 2013, 09:31:18 PM »
The gears were drawn from an old engraving, and so while the relative size of them is correct as far as the proportions to the other engine parts, there has to be a conversion to a standard tooth/gear size, which is what I can't remember how to do.

I guess I could look up some typical gear/tooth sizes for approximately the same size gears online at McMaster-Carr, and then go from there.

Offline Jasonb

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Re: Galloway Castings
« Reply #16 on: December 09, 2013, 09:54:06 PM »
The basic rule is if you half the size of the gear the DP double, third the size the DP goes up 3 times.

for example if your full size had 4" gear with 48 teeth at 12DP, a half scale model would have a 2" dia gear with the same number of teeth but they would need to be 24DP

So if you can say what the diameters scaled or what the distance between the two gear centres scaled it will allow us to suggest some likely candidates. As you are not scaling to an easy ratio it my be you need to adjust the tooth number to allow a standard DP  cutter to be used rather than sticking to 48:24 which may result in say 26DP profile which would need custom cutters.

J

PatJ

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Re: Galloway Castings
« Reply #17 on: December 09, 2013, 10:07:47 PM »
Thanks Jason, it seems to be a knotty problem, but definitely solvable.

I dug out some of the notes I made a few years ago, just before I stopped working on this engine design.
They are as follows:
(Note, I have no idea if the following information is correct or not, these are just my best understanding of it a few years ago.  Worse yet, I don't even recall the source of this info).

And I seem to recall a gear blank chart in the Machinists Handbook, I will look for that.

For an internal combustion engine, the gear ratio needs to be 1:2, ie: the smaller gear on the crankshaft turns twice for every revolution of the larger gear which contains the cam, unless you have a pivoting cam like the Wright Brother's engine, in which case the cam rotates at crankshaft speed.

Obviously, as the gear gets larger, then in general, the teeth get proportionally larger.

Spur Gears: Spur gears are cylindrical and have teeth which are parallel with the axis of the gear. The are designed for use on shafts whose axes are parallel with each other. A spur rack has teeth at right angles to the axis of motion. Spur gears are the most commonly used used type of gear, and are normally used with moderate speed and moderate tooth load. Spur gears can be used on pairs of shafts requiring varitations in speed ratios.

Diametral pitch defines the size of the gear tooth.

The defiinition of Diametral pitch (P) is:  A ratio equal to the number of teeth on the gear per inch of pitch diameter.  P=N / D

where: N = The number of teeth on a gear or pinion, and D = the Pitch Diameter, which is the diameter of the pitch circle of a gear or pinion.

The Pitch Circle is an imaginary circle that rolls without slipping with a pitch circle of a mating gear.  (In rough terms, it is a circle with a radius located about half the way up the height of the gear tooth.)

The term "Involute profile" refers to the shape of the gear tooth.  There are a number of gear tooth shapes with varying functions, but the involute profile is in common use for many general purpose gears today.  The idea behind the gear profile is to be able to transfer power from one gear to another with a minimum of slippage and friction.

Below is a chart of "Involute Gear Teeth", and the "P" number refers to the teeth per inch.

So for a given tooth size, and a given number of teeth, you generally know the size of the gear.

Gears have to transmit power, so the size of the teeth used and the strength of the material used to make the gear, as well as the velocity of the gear determine which pitch to use.  Generally, the more power that is required to be transmitted, the larger the teeth need to be, and probably the wider the teeth need to be.

To mesh two gears together, they have to have the same tooth size.

Standard gear cutters will cut a range of gear teeth quantities, with the lower number meshing more efficiently that a higher number.

Cutter No.   Cutting Capacity (Quan. of teeth)
1      135
2      55 to 134
3      35 to 54
4      26 to 34
5      21 to 35
6      17 to 20
7      14 to 16
8      12 to 13


Ok, like I said, don't assume any of the above infomation is correct.
I have no gear experience, but rather I am trying to learn how to make some gears.

PatJ

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Re: Galloway Castings
« Reply #18 on: December 09, 2013, 10:50:31 PM »
I found a spreadsheet for gears.
That seems like the way to go.

Gear design can be a can of worms I guess, there is a lot too it.

I just need some simple straight cut gears though using standard gear cutters, so I guess I will go the spreadsheet route.

I don't want to re-invent gear theory, I just want to make a couple.

It looks like the rough diameters of the gears I need are 2.27" and 1.135".
It woud be nice to keep the 48:24 tooth ratio to match the original engine, if that is feasable.

I will try and figure out blank sizes and tool bit feed-ins, and tooth size.

And I found the chart below, that will be helpful (if it is the rigth chart for the cutters I have).
« Last Edit: December 09, 2013, 10:53:41 PM by PatJ »

PatJ

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Re: Galloway Castings
« Reply #19 on: December 09, 2013, 10:58:07 PM »
From McMaster-Carr:

To work together, gears must have the same pitch and pressure angle (the angle between contact points of meshing teeth). A gear's pitch is its number of teeth divided by its pitch diameter. For example, a gear with 16 teeth and a pitch diameter of 1/2" will have a pitch of 32. For higher load capacities, choose 20° pressure angle gears over 14 1/2° gears.

Use gauges to measure gear pitch and pressure angle.

Offline swilliams

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Re: Galloway Castings
« Reply #20 on: December 10, 2013, 07:19:10 AM »
The calculation you need is pretty straight forward Pat

If you take the distance between the two gears, lets call it x
Then you want a 48 and 24 tooth gear

so take (48 + 24) / 2 / x = 36 / x
This will give you the DP of the gear

The diameters you gave are 2.27" and 1.135", I assume they are the outside diameters of the gears??
To get the outside diameter you add 2 teeth. So (48 + 2) / 2.27 = 22.02DP

On the other hand if it's the pitch circle diameter (that corresponds to x above), then 48 / 2.27 = 21.14DP

We can convert this to metric which gives more options 25.4 / 21.14 = M1.201
The nearest standard metric size is M1.25 which corresponds to 20.32DP

Obviously you've got some playing around to do. Anyway hope that makes sense

Steve

Offline Jasonb

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Re: Galloway Castings
« Reply #21 on: December 10, 2013, 07:51:06 AM »
As your large dia is exactly twice the small dia I have to assume this is the PCD of the gears as the OD will not be exactly twice.

As I mentioned above by using a odd scale you are unlikely to be able to use standard cutters and keep the same number of teeth so unless you want to get into making your own 21.14DP cutters you would be best to choose the nearest standard DP and adjust the tooth count.

24DP would be close with 54T @ 2.250PCD and 27T @ 1.125PCD which only moves your centre to centre distance 0.012"

I don't know if the 7.5HP used a a larger gear but the 5HP had a 6" PCD 8DP 48T large gear and 24T small and I doubt they used an odd DP which means the next size up 6DP would put the gear at 8"PCD (8.333" OD ) which would scale to approx 2.4PCD which is too large for what you want

Online Jo

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Re: Galloway Castings
« Reply #22 on: December 10, 2013, 07:58:08 AM »
Personally with designing spur gears I cheat and use Shopcalc: http://home.scarlet.be/mini-draaien-frezen/engels/program-01.html It is so quick and easy to have a fiddle with the numbers and find what numbers of teeth/DP will give you what you need.

Sadly I couldn't find a similair dodge for spur gears and had to create my own spread sheet.

Jo
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PatJ

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Re: Galloway Castings
« Reply #23 on: December 10, 2013, 08:38:04 AM »
Thanks for the info Steve, Jason & Jo.

I am going to have to study gears a bit more to get more familiar with the terms.

I am a bit slow when it comes to learning, so I try and make up for it with extra effort.

Offline swilliams

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Re: Galloway Castings
« Reply #24 on: December 10, 2013, 08:58:44 AM »
I am a bit slow when it comes to learning, so I try and make up for it with extra effort.

Sounds good Pat. Don't matter how you get there, so long as you arrive  ;)

Steve

PatJ

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Re: Galloway Castings
« Reply #25 on: December 22, 2013, 08:47:22 AM »
I started working on the valve gear for this engine, and traced the shape of the cam from a photo that was found online.

I modeled the various parts; cam, pushrod, pushrod end, and rocker arm and support, and then assembled everything for a simulation.

The factory cam was symmetrical so that the engine could run either forward or backward depending on where the timing gears were set.

My cam shape was off, and so I did not get the factory settings of exhaust valve opening at 35 degrees before BDC and opening at 5 degrees after TDC.

I reshaped the cam to the the correct valve timing, and then raised the top of the lobe to get slightly more lift.

I noticed from the brochures that the older engines used a single flyball, and the later models used twin flyballs.
I will go with the single flyball with the forked arm that hinges from the front.

The most recent effort on this design is to determine the surfaces that require machining allowances, draft, etc. so that pattern drawings can be generated.  I am marking the machined surfaces in red, and will extend those bosses probably about 0.1" outward.

PatJ

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Re: Galloway Castings
« Reply #26 on: December 22, 2013, 08:53:47 AM »
I have tried to accurately model the flywheel spokes for this engine from the very beginning, and I think I finally have a layout I can live with on the 4th attempt.

I used a lofted ellipse that tapers in both directions, but not linearly; there is a slight break about 1/3 of the way out from the hub.

Lofted shapes wreak havoc on fillets, and so the fillets I had to use are fudged in place, but they can be hand sanded on the pattern.


PatJ

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Re: Galloway Castings
« Reply #27 on: December 22, 2013, 08:57:40 AM »
Here are the beginnings of some core prints that I will need to add to the patterns.

The cylinder and frame will be cast as one piece, but so far it has been easier to model these two parts separately.

PatJ

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Re: Galloway Castings
« Reply #28 on: December 22, 2013, 09:00:38 AM »
And the non-draft-angle machining allowances on the flywheel (in blue), and machining allowances with draft angle at the outside of the rim (in orange).

Online Jo

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Re: Galloway Castings
« Reply #29 on: December 22, 2013, 09:05:15 AM »
Welcome back Pat  :ThumbsUp: you have been busy.

What wood are you planning to use to make the patterns?

Jo
Enjoyment is more important than achievement.

 

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