Correct they are called skew gears which are just helicals with the same hand.

Normally helicals operating in the same plane need to be opposite hand but if mounted in the a 90 degree plane they need to be same hand.

Normal plane.

Opposite plane.

Hi David

There was in the Model engineer some time ago an interesting
method of producing these type of skew gears .
The author was Jock Smith and can be found from 1995
Me Vol 174 issue 3989 page 336 and 3991 page 468.

Seen in album " gears " 3 photos 2 are from article MEW 193
Gear hobbing in the mill and shows a skew gear being hobbed
and the other some completed gears .The hobs were from Arc Euro
I think these are now all sold out and they now don't seem to sell
them anymore which is a shame as they were a very good cutting tool.
Obviously there is quite a lot to make to be able to produce these
type of gears in this way and to some extent depends on how many
gears you need ,i seem to make more and more of these as time
goes by the third photo some gears and some toothed belt pullies
made recently.

John

One aspect of skew gears to remember – especially on drives like camshafts where the load is high and variable – is to ensure copious lubrication. Another is to ensure that end float of either gear is eliminated (so far as poss).

On my 1928 car with a skew gear to drive the magneto (a light load) the gears are trapped between thrust bearings, and the pressure relief from the oil pump blows all the 'spare' oil onto the gear just ahead of engagement.

Cheers, Tim

David,

It depends on the helix angle. For helical gears, if you want a right angle drive then the helix angles just have to add up to 90 degrees. The pitch diameter of a helical gear is given by N divided by (DP x Cos(A)) where N is the number of teeth, DP is the Diametrical Pitch and A is the helix angle. For 45 degree helix angles Cos (A) =1 so the relative diameters depend soley on the number of teeth – 36 teeth will be twice the diameter of an 18 tooth. If you choose 26.6 degrees and 63.4 degrees for the 2 helix angles then you end up with 2:1 gears that have the same OD – which is what the Wyvern uses:

HTH,

Rod

Edited By Roderick Jenkins on 18/02/2016 13:20:47  To correct the error MichaelG pointed out below

Edited By Roderick Jenkins on 18/02/2016 13:33:04

You can see the angle on this Domestic that I made, the shallow angle on the crank gear lets it be larger than the cam gear where you would normally find the opposite with spur gears. This allows the larger dia crank to pass through without such a thin wall as in Rod's photo

Better shot where you can see the helix of both gears

Edited By JasonB on 18/02/2016 13:28:57

Edited By JasonB on 18/02/2016 13:30:56

Further to this 2:1 ratio in similar sized diameters for skew gears:

The angles in the example above are found from the inverse tan of 0.5 and 2 (half the speed one way and double the speed the other).

Tan(63.435)=2

Tan(26.565)=0.5

The angles have been rounded to 3 significant decimals. If they are rounded to 1 decimal you get the angles stated earlier.

Hope this helps anyone considering other possible ratios.

Martin

Well if we are picking holes then sq root of 2 is 1.414 in my book