Author Topic: Gears for Pacific Model Design's Mogul side shaft  (Read 559 times)

Offline Hcrotalus

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Gears for Pacific Model Design's Mogul side shaft
« on: July 05, 2021, 08:57:00 PM »
I am looking for the mate for the helix gear on this model.  I do not have this gear but I do have the smaller cam shaft gear that mates to it.  The drawings of the engine are of no help.  I cant find the gears called out anywhere.

Pinion specs:
16 tooth
.75" OD
Left hand
That makes it a dp 24?

So am I looking for a 32 tooth (2:1), left hand, 24dp gear?  Since the cam shaft gear is steel should the other gear be from brass?

Does anyone have this model and can look for me?

Thanks
Todd

Offline gbritnell

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #1 on: July 06, 2021, 12:04:59 AM »
Usually the helical gears for a sideshaft engine don't have a 45degree helix. The reason being that it makes the side shaft gear way too big. By making the 2 gears with (approximation) 30 and 60 degree angles it keeps them about the same size (diameter). The problem is you can only buy gears with a 45 degree helix.
To what you asked, yes you need a gear with 32 teeth but you also need to know the helix angle of the crankshaft gear you have.
gbritnell
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Offline Jasonb

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #2 on: July 06, 2021, 07:06:47 AM »
If the drawing shows the centre distance between crankshaft and the side shaft you will then know the PCD and that should allow you to work out the diameter of the other gear and from that the angle of the two gears teeth.

All the open crank engines I have made have both gears in steel.

Offline Alyn Foundry

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #3 on: July 06, 2021, 12:17:48 PM »
Surely, if Todd has the sideshaft pinion with 16 teeth he needs an 8 tooth crankshaft wheel?

Many early British small power engines used a variety of materials for the gears but most often they were paired ( material wise ) to each other.

I have a " shout " out on the Small power engine and models group, we have many members worldwide.

Cheers Graham.

Offline Jasonb

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #4 on: July 06, 2021, 01:16:57 PM »
That sounds right Graham, the Crankshaft gear will have the shallower angle gears that wrap a lot further around the gear so you can't fit as many teeth onto itand it may well be the same diameter which can be confirmed from the Ctr to ctr distance.

This is the best photo I could find of the model

I think Gil who runs the "office of Steam" forum has one of these models, you could ask him to have a measure up. he is Reddrryder on Youtube where you could also ask.

https://www.officeofsteamforum.com/index.php
« Last Edit: July 06, 2021, 01:24:00 PM by Jasonb »

Offline gbritnell

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #5 on: July 06, 2021, 06:39:24 PM »
Using your number requirements here are some calculations:

16T, helix angle 60 degrees, 24DP, OD 1.4167
32T, helix angle 30 degrees, 24DP, OD 1.5934 You see by having the different helix angles the OD's are close. Which you want.

16T, helix angle 60 degrees, 32DP, OD 1.0625
32T, helix angle 30 degrees, 32DP, OD 1.2172

45 degree helix angles are pretty much what commercial gears are made with so here's some numbers for this type.

16T, helix angle 45 degrees, 24DP, OD 1.0261
32T, helix angle 45 degrees, 24DP, OD 1.4767 When you use 2 gears with a 45 degree helix the larger gear gains almost .50 in diameter
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Offline Hcrotalus

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #6 on: July 06, 2021, 06:44:32 PM »
Thanks to everyone.  I realized that I was running my dp calculation off of straight tooth formulas.  Thanks gbritnell for bringing up the helix angles.  Your examples helped.  I expected a 60-30 but when I measured the cam shaft gears helix angle I got 70deg.  I also found the distance of the shaft centers from the drawing,

So here is all I know for sure from the cam gear and the drawings:
OD  = .75"
Teeth = 16
Left hand
HA = 70deg
Shaft distances = .812"

BUT the fact that you can not get helix gears in other than 45deg makes most of this moot as I am not yet building this model.  I know I needed this gear so I thought that I would purchase it along with the gears for the Topsy-Turvy that I plan to start this fall.

I'll try and talk with Gill to get the specs. 

Thanks to everyone!
Todd

Offline gbritnell

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #7 on: July 06, 2021, 07:28:19 PM »
Since I learned to cut helical gears it's not that big of a deal. You do have to make the fixture but other than that it's about the only way to go if you want specific helical gears.
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Offline Jasonb

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #8 on: July 06, 2021, 07:42:12 PM »
The gear you have is more like a 20degree one than 70.

I'm not that familiar with drawing in F360 as I mostly use it for CAM but punching in 24DP and 20degrees gives a gear approx 20mm dia so angle may be slightly different. I then put in the crankshaft 8T gear with the complimentry 70degrees and ctr to ctr is close to what you say (10 thou out) so a bit more work on the angles and the spec can be found.

Diameter of the larger 8T Crankshaft gear works out at 1.132" with the 70/20 angle
« Last Edit: July 06, 2021, 07:49:56 PM by Jasonb »

Offline Jasonb

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Re: Gears for Pacific Model Design's Mogul side shaft
« Reply #9 on: July 07, 2021, 01:31:41 PM »
You could also ask on SmokStak forum, several there look to have the Sam Harmen built engines as well as a couple with the Pacific one.

https://www.smokstak.com/forum/forums/scale-model-engineering.54/



George, if you are still following what OD and pcd do you get for a 16T, 24DP 20deg helix gear. I get larger than the 0.75" Todd's gear measures (works out about right for 1MOD though)

This is the cam gear which has more teeth so the mating one would be 8T, 24DP 70deg helix which I get at about
« Last Edit: July 07, 2021, 01:36:05 PM by Jasonb »