Gear Noise

[rdean]

I have been making gears for my projects for many years and in several different DP sizes. I started out by grinding a steel fly cutter by eye and it did work but it left much to be desired. I had a project that required a 16DP cutter so I bought a set of involute cutters from China. They were actually a good set and I finished that project. Later there was a project that required M1 cutters so again I bought a set from China and surprise they were of good quality.

A couple of years back I started building model internal combustion engines. At first I was cutting the gears for them with the M1 but the teeth were just too large and they didn't look right. I decided on a set of cutters from India that are M.7 in size and matched the models size better.

When running my engines I have noticed that they are very noisy and most of that noise is coming from the gears and not from the rest of the engine. The gear noise does drop down with each each step down in DP and tooth size but it is still very annoying. I know that helicol gears do run quieter than straight cut gears so I will have a go at making some helicol involute gears.

I choose my Royal Blue hit miss engine for the test as the gears are eisiely accessible.
I used my M.7 cutters and tilted the rotary table back 20 degrees as that looked about right. I thought 30 degrees was a little too much.


After figuring out the tooth count that would the closest to the outside diameter of the original set I made the gears. I should have done some closer research as I found out that there is a left and right side to helicol gears. Well I made two right hand gears and they do not mesh in a straight line. They fit together with the shafts at a 40 degree angle to each other which is not what I wanted. (I do need to remember that as it may come in handy on another project)
I made a new driven gear with the cutter on the left hand side of the center and here are the results.
M1 gears on top and M.7 on the bottom.




There were several things that had to be corrected and moved and this shows them installed.


The gear noise level was dropped by at least 50% and now you can hear the engine.
I was hoping for some improvement and am happy to say they are quieter than expected.
Now I have 4 other engines that might get this upgrade.

Thanks for looking
Ray

 

[benmychree]

Helical gears are cut in a helical path, not an angular path, if you were to use a marking medium on the meshed gears you would find that they do not make contact all the way across the teeth, they would wear quickly under load and make much more noise than they should and also not mount on their correct center distance. A universal milling machine or hobber is necessary to generate a helical gear or any other helical work. there are videos out there of helical attachments for ordinary milling machines that folks have made.

 

[Lo-Fi]

As said above, helical gears are cut with the gear blank itself being rotated as the table moves to cut a helical path:

Properly cut helicals will be much quieter again if meshed correctly. Note that there's a formula for which cutter to use for a given helix angle which is not the same as a spur gear of the same module and tooth count.

 

[woodchucker]

here's one from another utuber... evolvent .. he is hobbing them.

 

[markba633csi]

Helical gears should be quieter than straight cut gears if they are cut correctly.
There's an British fellow on youtube who makes them on modified British lathes
-Mark