Determining Gear Parameters 2

[makary]

Need help in determining spur gear parameters. I believe the manufacturer used correction P but that's over my head (I can analyze gears with correction P-0 only).
Gears come from the valve train of a tiny engine used in a Try-Bilt leaf blower which I am converting to a model plane engine.
So here we go:
T1 = 17 teeth streight
D_major1= 23.02 mm
D_minor1 = 18.12 mm

T2 = 34 teeth
D_major2 = 41.22 mm
D_minor2 = 36.31 mm

Distance between Axis A = 30.1 to 30.2 mm (it's difficult to measure accurately because shafts are on a different casting each).

I need to have the larger gear T2 (34 teeth) custom made so I need to provide the shop with gear parameters. Any help will be greatly appreciated. Accuracy doesn't have to be great - close enough is all I need.

I expected it to be metric gears but from the tooth height it looks to me Troy-Bilt went with 22 DP. Other dimensions however don't check out.
Thanks!

 

[lbmakem]

hi
if you take it that these gears are 22dp then your first gear (pinion) has a profile shift of .0454" (1.154mm), which would give a OD of .909"(23.1mm)and a PCD of .8182(20.78mm).The depth of your second gear would be shallow for 22dp by .006"(.15mm),if you take this to be so, then the OD would be 1.636"(41.56mm)which is a standard gear, therefore the Centre's would be 1.1818(30.02mm)

 

[makary]

Thanks Ibmakem,
I see that you are shifting gear profile in one gear only as oppose to shifting profile in both gears. I did no know that this is acceptable. Will gears mesh correctly? Any major adverse effects?
Thanks again for your help.

 

[dinjin]

as to the amount of gear shift, it depends on the application and also if the pinion is always driving the gear. The pinion is normally the weaker part and it usually
has the most profile shift not only to strengthen the pinion but also give it better approach action. The manufacturer of your part was probably trying do strengthen bost parts and made profile shifts on both. It does seem strange that he had more profile shift on the gear rather than the pinion. Assuming 30.15mm is the normal center distance, there appears to be a total profile shift of
.61417/Dp which equals .0279 inches or .7091mm. If your pinion is your driver, I would recommend a .50/Dp shift for the pinion and a .115/Dp shift on the gear if you think it too needs strengthening. Otherwise, put all of the profile shift in the pinion.

 

[lbmakem]

hi makary
there would be no adverse effects to the running of these gears you would infact get a better contact ratio.take note of dinjin's answer it gives a good understanding of profile shifting.running this set of gears at your centre's would give approx .005" backlash (.13mm)if they were cut with no backlash.

 

[tbuelna]

makary,

If you're not sure of the existing spur gear pair's geometry, and you intend to make a replacement gear for one of the pair, then you might wish to consider making both gears so that you get exactly what you want. If the gears are not high PLV or high precision (and made of metal), you can have the gears wire EDM cut for a fairly reasonable amount of money. All you need to do is create an accurate 2D CAD profile in .dwg format.

Just a suggestion. Good luck.

Terry

 

[makary]

Thank you everyone. I knew I could count on you!
Thanks to you, it is all clear to me now. My main problem was not knowing that I can shift profile of each gear independently. I thought that shifting profile of one gear requires a very speciffic shifting of profile of the other gear.
And no Buelna - I can not make both gears beacuse there is a cam incorporated into one of the gears. A cam that I can not make.
Thanks again!