Data required to machine 2:1 ratio spur gears

My quest to find an off the shelf set of 2:1 ratio spur gears to supply the timing for my current project has drawn a blank. The problem is of my own making as I've scaled up the engine by 50% which means that the crank and cam shafts are now on 50mm centres instead of the original 1.312'' which is proving a problem with the suppliers I've contacted. This means I'll have to machine up a set, the cost of a suitable cutter should prove a great deal cheaper than getting a bespoke set machined. Trying to figure out the the number of teeth Vs the diameter is getting me no where, as I've no real idea of how or indeed they will work when in mesh Looking at the gearing data charts just leaves me more confused than when I started. My hope is that there's a kind soul out there who spent his (or her) formative years in a drawing or planning office, who could let me know the gear diameters, number of teeth and DP for the two gears I will need.

Thanks.

Mick.

Hi Mick,

Gears are normally made to conform with either Modulus or DP range of tooth dimensions so unless you are very lucky using a standard tooth form is unlikly to give you the spacing you require. You may have to make totaly no standard gears. One possible solution would be to find a pair of gears that did not touch each other and have a third gear as an idler between them. This would mean that the camshaft rotated in the opposite direction so the camshaft would have to be redesigned to take this into account.

Les.

If you have gone up by 50% you just need to increase the number of teeth by 50% if you don't mind keeping the smaller tooth size.

eg 32DP 14/28 has PCDs of 0.438 and 0.875 giving your original 1.313" cts

32DP 21/42 has PCD of 0.656 and 1.313 giving your nes cts as 1.969

1.313x 50% also equals 1.968 also equals 50mm

so give or take 0.001 for various rounding up & down thats what you need, easily available off the shelf from HPC etc.

J

Edit forget that I did't half the PCD, post what the originals are and I'll work it out again

Edited By JasonB on 24/02/2012 18:42:16

Right lets start again

16DP 14/28 has PCDs of 0.875 & 1.750 = 2.625 div 2 gives 1.313 cts

16DP 21/42 has 1.313 and 2.625 = 3.938 div 2 gives 1.968 cts

1.313x 50% also equals 1.968 also equals 50mm

As 16DP is not divisible by 1.5 you can't keep the same number of teeth and change the DP unless you want to start making custom cutters. But say what the original gear spec was just in case it can be worked back from another DP.

Edited By JasonB on 24/02/2012 18:55:00

Hi Mick

Have you looked at metric gears ie Mod gears as well as imperial (DP).

0.9 mod in 74 tooth and 37 tooth should give you a centre to centre distance of 49.95mm (the lubrication will take up the remaining 0.05).

Using 1mod gears in 66 and 33 teeth will give you a centre - centre distance of 49.5 which would allow some backlash but not excessive and a thicker lub. oil should keep them fairly quiet. Depending on the temperature around the gears you could go for plastic ones in which case they'd be pretty quiet without the oil.

Keith

Plenty of ratio's will give 49.5 mm but as Keith says 0.9 mod in 74/37 gives 49.95 centres.

16 DP in 42/21 gives 49.98 [ thanks to Jason ] as does

32 DP in 84/42 you might want to choose to make the teeth look scale.

Another close one is the Myford change wheels at 20 DP and 52/26 gives 49.53

John S.

With 1 module gears two gears at 50mm centres will have atotal of 100 / 1 - 4 teeth = 96 teeth.

Divide by 3 = 32, so you can have a 32 tooth gear meshed with a 64 to give 2:1.

1 mod is very close to 25 dp and easy to source.

Neil

Stub I think you are getting OD mixed up with PCD

1.0mod 32t = 32mm pcd, 64t = 64pcd.

64 + 32 = 96 div 2 = 48mm cts

1.0mod 32t = 34mm OD, 64t = 66OD

34 + 66 = 100 total dia

As John S says there are plenty that give 49.5 cts, 1.0MOd is one of them

Edited By JasonB on 24/02/2012 20:40:59

Jason,

As they say on the street... You is right, man!

I have made the complicated simple.

But if he wants 2:1 he'd better use 33 and 66 not 34 and 66 or he'll end up with an engine like the one that took ETW a long while to troubleshoot - the maker had subsituted his own gears with something like a 21:40 ratio.

Neil

I used the 34/66 as an example of how your 100mm could be achieved not what ration was needed.

33/66 gives the 49.5cts that I mentioned

J

Edited By JasonB on 25/02/2012 08:00:19

Scaling the engine up should measnt you have a bit of latitude and don't have to stick slavishly to the 50mm centre distance - alter that to fit an easily obtainable/makeable pair of gears.

Hi. Tel.

I'm at a stage where the cam and crank shaft centres have been bored and bushed. I tried to scale up the gears by 50% but the originals spec are 40DP which worked out at a half tooth spacing.

I'll try the stockists again armed with the information kindly supplied.

Thanks to all.

Mick

So the original was 70/35 40DP in which case I would go 84/42 32DP keeps the tooth size as near as possible in proportion and gives the 1.968" Cts.

J

Hi. All.

Not having an awful lot of luck with your useful ideas. There's no 84 32DP or 21 16 DP in any stock list. Like wise there's no 74 0.9 mod either. The only set I can find is the 52 and 26 20 DP but i'm not at all sure about the 0.47 difference in the centres, I don't know of any oil that thick to take up the play! All suggestions welcomed.

Regards.

Mick

HPC list both 21 and 42 in 16DP

http://www.hpcgears.com/newpdf/spurgears_16dp.pdf

If you want to keep the smaller teeth then a 32DP cutter is not that expensive if you can index 84T.

If you do go with a ratio that has a bit of play in it and cut them yourself then slightly reducing the depth of cut will be better than thick oil.

J

Bugger! Tel's Rule of engagement #5247 - Never mark out centres for gears without the gears on hand. You could make an offset bush for the camshaft hole..

Hi. Jason.

So they do, I did look yesterday, but I must have been going DP blind by that stage, think I'll stick with these, although the pitch is a bit course as I don't feel the choice will get any better.

Thanks for every ones help.

Mick