Constant Depth Bevel Gears

I’m looking at making a set of mitre gears, 20 tooth 48 DP using the two button method of making the cutter. I have done this for small spur gears before and they have come out satisfactory.

I have Ivan Law’s book and the ME articles by Dave Lammas ( Jul. 91) and D. A . G. Brown (Sep. 94) and looking at the tables for the dimensions of the button diameter, spacing, in feed, and cutter blank width, those of both Lammas and Brown agree very closely but the ones by Law are very different. Only Brown gives the formulas for their derivation.

Out of curiosity I ran through the formulas and found that while the one for button diameter gives values that agree with the table, the ones for button spacing and infeed do not. The values from the formula for spacing give figures consistently higher than in the table. But when plugging the numbers into the one for infeed I get a negative value under the root sign (which is impossible). So either I’m reading the formula wrong or there is a mistake in the formula. Anyone else tried to use these formulas and can shed some light on this??

( The way I read the infeed formula is, Cutter infeed F= 1.25 + sqr root of the quantity “ { (D/2)sqr’d - [ D/2 x cos bravo - T/2 + pi/4]sqr’d} - d/2 x sin bravo ".

John

Hi John,

I recently made 3 gear cutters (pictures in my album).

I started with Ivan Laws book but also dug around on the net. I came across articles by the late John Stephenson and D J Unwing (Making milling cutters for cutting gear wheels. ME Oct 71) Both have tables for 20 deg PA cutter proportions and both are identical but differ from Ivan Laws table.

From memory the reason they differ is that you initially touch off from a different point.

Take a look at mikesworkshop site. Just to confuse you more his figures differ again. This is also due to the point of touch off. He delves into the math too.

Mike will also send you a very handy spreadsheet if you email him direct.

http://mikesworkshop.weebly.com/designing-gear-cutters.html

**LINK**

Good luck.

Steve.

Edited By fishy-steve on 19/06/2018 23:28:25

Steve

Thanks for the link. I'll have a look at that and probably get more confused!

John

Whilst I haven't actually got around to making my cutters I did look at the link steve gave (amogst others) and then drew up all the sizes in 2D CAD for the gears i wanted and used the measuring tool to check figures and pick the infeed starting point and depth from my choice of diameter material.

pgk