Well as long as we are on the subject of gears......

[JorgensenSteam]

I have followed the gear posts for some time, but unfortunately not mastered the art of the gear.

 

[Jasonb]

One other factor that will determine the size of gears you use is the centre to centre distance, this will be determined by adding the PCD of the two gears and dividing by 2

Size of tooth/diameter will also depend on the loading the gear will take, a 48dp gear will not trandmit the same as an 8dp

Taking your 1 1/2" gear, lets say thats the PCD not the OD of the blank then

1.5 = 18T / DP so DP = 18 / 1.5 your gear would be 12DP

J

PS your Gallaway gear will need to be a lot smaller probably not much over 7/8" diameter.

Edit scaling up my 1/6 drawings to suit your 8" flywheel gives a center distance of 1.250, to get this you will want 24DP but have to alter the tooth count to 20 & 40. 0.833 & 1.667 PCD respectively

J

 

[tel]

My limited gear cutting experience is confined to DP type gears, and for those you can usually crunch the numbers for the blank diameters in your head (even me, who is about a numerically challenged as it's possible to be).

The rule is this: For outside diameter add 2 to the required number of teeth and divide by the dp number.

F'rinstance you want a 40 tooth wheel at 40dp. 42/40 = 1.050", that's all there is to it.

Go again? a 40 tooth gear of 20dp. 42/20 = 2.100", get the idea?

A 20 tooth wheel of 40dp? 22/40 = 0.550"

 

[shred]

You can also run idler gears and such if the sizes of just two gears doesn't work well.

Since I've not seen John Stevenson about lately (I think he's dinking around with CNC-milled gears), I'll throw in his usual plug for "Gears and Gear Cutting" by Ivan Laws-- it does a pretty good job of explaining a very complex subject down to the ME level.

 

[compspecial]

Tel. once again you have taken a difficult subject and made it "SOUND" easy. I wouldn't have the nerve to tackle gear cutting as i always have the vision of the last tooth ending up twice as thick as the others (or half as thick) thanks for all your great hints.
Stew

 

[Cedge]

Pat
I stumbled onto a small utility that took the pain out of the subject. It even gives cutter tip width for single tooth cutting and making hobs.
http://www.leatherwoodplayground.com/GearCodeit.zip

A similar Utility for metric gear calculations is offered at
http://www.leatherwoodplayground.com/GearCuttingCodeGenerator.zip

Steve

 

[cfellows]

It looks like in order to maintain scale, the crankshaft diameter has to be rather limited in order to fit the smaller gear on the crankshaft.

I was hoping to use a 0.625" dia. crankshaft, but that throws the gears way out of whack, with the larger gear being approx. 2.7" dia.

Any way around this limitation?

Pat J

You could cut the primary gear directly into the crankshaft like is done on the Plunket Jr. Look at reply #120 here:

http://www.homemodelenginemachinist.com/index.php?topic=10818.0

You could cut 13 teeth with a diametral pitch of 24 into the .625 crankshaft and be just about right. This would make the secondary gear 1.166" OD ((26 teeth / 24 DP) + .083).

You can also use a hubless pinion and pin it to the crankshaft. A 24 diametral pitch gear has a tooth depth of ~.173. So, a 20 tooth primary pinion would have a pitch diameter of .833 (20 / 24), an OD of .916" (.833 + .083) and the diameter to the root of the gears would be .743" (.833 - .083 - .006 for clearance). If you bored a .625" hole through it, you would still have almost 1/16" material to pin through.

This would make the OD of your secondary gear 1.75" ((40 teeth / 24 DP) + .083")

Chuck

 

[Jasonb]

Pat can you confirm if these gears are for your NTS Galloway? or are you also working on another hit & miss thats twice the size.

If it is the Galloway then based on your 8" flywheels and scaling up the 1/6th crank which is 0.312 your comes out at 0.489" so 1/2" crank will be fine. Also look at the pics of the full size, there is no hub on the crank gear, its no larger than the bearings and the centres will be as I said above. A 2.7" gear on the cam would touch the crank!!!

Jason

 

[tel]

A 24 diametral pitch gear has a tooth depth of ~.173.

Are you sure Chuck? My calculations say 0.0899"

 

[Jasonb]

Chuck came up with the same sizes I suggested in my earlier post

"Edit scaling up my 1/6 drawings to suit your 8" flywheel gives a center distance of 1.250, to get this you will want 24DP but have to alter the tooth count to 20 & 40. 0.833 & 1.667 PCD respectively"

As I said look at the parts pictures on the bottom of this page, you can see the small gear is almost a "ring gear", there is a shallow keyway in the gear.

Jason

 

[Jasonb]

Are you sure Chuck? My calculations say 0.0899"

I make it 0.100"

Addendum 0.042 plus dedendum 0.058 = 0.100 whole depth ( using 1.4 / DP for 24-100 teeth)

Tels depth of 0.090 would be OK for working depth but wee need to use the whole depth to work out the metal between the bore and tooth gullet

 

[cfellows]

Tel / JasonB, you guys are right. The difference between the overall diameter and the root diameter is ~.173. The tooth depth would be half that.

To get the addendum, I divide 1 by the DP. For a 24 DP, the addendum would be 1 / 24 = .0417. To get the dedendum, I add about .006 to the addendum (.0417 + .006 = .0477. The sum of those two equal the tooth depth (.0417 + .0477 = .0894).

And was trying so hard not to confuse anyone (mostly myself!). :-[

Chuck

 

[precisionmetal]

Typically in standard gears -- if pitch is finer than 20DP, then whole depth is (2.2/DP + .002)

.... so a 24DP gear would be .0937".

Ultimately, what counts is how the gears mesh (i.e. having the desired backlash). The best method is typically to cut to a specific dimension over wires, which nails down the tooth thickness.

PM

 

[mklotz]

My program agrees with Tel - 0.0899. In agreement with what precisionmetal wrote, it uses the following calculation...

if (P <= 20) W=2.2/P+.002; else W=2.157/P;

Regardless of who among us is right, do you understand why it's worth putting all these calculations into a program after the correct formula is determined?

Bugger all the approximations and forgotten formulae. Code it up once and it's remembered perfectly with no computational errors for all time.

 

[swilliams]

Pat, if you decide to go the gears straight into the 5/8th shaft root, here's another option.

16mm = 0.63"
You can get a #7 and #4, module 1 (M1) cutter from here

http://www.ctctools.biz/servlet/the-Cutting-Tools-cln-HSS-Involute-Gear-Cutters-cln-Individual-Gear-Cutters/Categories

which will cost about $32 bucks including shipping for the pair.

Make the pair of gears 14 and 28 teeth, having nominal OD's of

(14 + 2) * 1 = 16mm = 0.63"
(28 + 2) * 1 = 30mm = 1.181"

the * 1 is because you're using module 1

So your pinion will be 5 thou undersize, just cut the teeth 2.5 thou less deep than you would otherwise.

The distance between your gears should be
(28 + 14) / 2 * 1 = 21mm = 0.827"

Cheers
Steve

 

[Jasonb]

Distance between gears needs to be approx 1.25" as I said above so that won't work

J