Gear Making - Fly Cutter

[ctwo]

I wanted to make a metric transposing gear set for my Logan. I read that a 47T/37T compound will be close enough, and that would allow the gear train cover to be closed as opposed to the 127T/100T compound.

I found this site that describes the angles and circles and other items one would need to know about making gears and cutters, but I had difficulty applying the information. Specifically, I saw on youtube a fly cutter ground on the lathe with a grinding stone (mounted point) in the chuck, and the cutter in the usual place on the tool post. I was trying to use the calculated button diameter for the gear I wanted to cut and the button (mounted point) diameter just seemed way too small. I've spent most of the day just trying to get the HSS bit ground properly, and have only been comparing to a standard 48T gear.

Anyway, I think my Logan has 16 diametric pitch gears and the button diameter should be 0.463" but that seemed way too small. I ended up fiddling with an ~1" stone and have something very close. The radius on the 48T is just a tiny bit shy, and that might be a good compromise for the 47T/37T combination. The gears will be plastic anyway, so probably not too critical.

I just wanted to verify that my understanding was correct as at some point I will want to make the rest of gear train and quick change gears.

Here is some data:

gear DP Dia. depth Button dia.
127 16 8.063 0.135 1.252
100 16 6.375 0.135 0.986
60 16 3.875 0.135 0.591
47 16 3.063 0.135 0.463
37 16 2.438 0.135 0.365

[ken572]

ctwo,

Are you going to share the URL for the site you
found and speak of

Ken.

[ctwo]

That blasted keyboard...

http://mikesworkshop.weebly.com/designi ... tters.html

[ken572]

That blasted keyboard...

http://mikesworkshop.weebly.com/designi ... tters.html

Thanks ctwo,

Mike is a most creative hobbyist.

I like the way he keeps it all plain, and to the point.

Ken.

[ctwo]

I've attached a photo of what happens when I tried interpolating Mike's formulas, using a 48T, 16DP gear as a close enough sample, to the 47T gear that I want to make.

Using the table's he's provided, interpolating a 48T gear results in a crest diameter of 50 mm (shown as the number of teeth plus 2 mm). Well, that does not work out because my 48T gear is 3.127" (79.4 mm). Of course there is a Module multiplier, which he conveniently has as 1, but he does not explain how to calculate that.

Now, after some thought, I realize I can infer the Module by using my sample gear, and I get 1.5875! Now I'm off to fix my spreadsheet.

Note that I also suspect that my cutter has a too shallow radius for the smaller gears I want to cut...

[ctwo]

Still not even close. It looks like the button diameter is more like the gear diameter.

[Russ Hanscom]

The button sizing process can also be found in Gears and Gear Cutting by Ivan Law, #17 of the Workshop Practice Series.

[drmico60]

I've attached a photo of what happens when I tried interpolating Mike's formulas, using a 48T, 16DP gear as a close enough sample, to the 47T gear that I want to make.

Using the table's he's provided, interpolating a 48T gear results in a crest diameter of 50 mm (shown as the number of teeth plus 2 mm). Well, that does not work out because my 48T gear is 3.127" (79.4 mm). Of course there is a Module multiplier, which he conveniently has as 1, but he does not explain how to calculate that.

Now, after some thought, I realize I can infer the Module by using my sample gear, and I get 1.5875! Now I'm off to fix my spreadsheet.

Note that I also suspect that my cutter has a too shallow radius for the smaller gears I want to cut...

Hi ctwo,

I have never applied my formulae/spreadsheet to inch DP gears but I think if you enter the mod = 1/DP then the answers in the table will be in inches. I do not have time right now to look at this in more detail but I think this should work.

Mike (of mikesworkshop)

[epanzella]

I've attached a photo of what happens when I tried interpolating Mike's formulas, using a 48T, 16DP gear as a close enough sample, to the 47T gear that I want to make.

Using the table's he's provided, interpolating a 48T gear results in a crest diameter of 50 mm (shown as the number of teeth plus 2 mm). Well, that does not work out because my 48T gear is 3.127" (79.4 mm). Of course there is a Module multiplier, which he conveniently has as 1, but he does not explain how to calculate that.

Now, after some thought, I realize I can infer the Module by using my sample gear, and I get 1.5875! Now I'm off to fix my spreadsheet.

Note that I also suspect that my cutter has a too shallow radius for the smaller gears I want to cut...

I never cut gears but I did visit Mike's website. Your picture shows your two button circles touching each other but on Mike's website he shows the button circles separated by a dimension he represents as "E". I think that's the width of the flat on the end of the cutter.

[ctwo]

Hi Folks. Wow, I'm impressed. Thank you, Mike, for stopping in, joining, and for the assistance. The tip gives me a bit of a "Doh!" moment. I came to the same result in a much less elegant manner, but only because the formulae are all linearly related due to the trig functions being constants, and of your fine examples to manipulate. It was really enlightening realizing the intellect behind that.

epanzella, thanks for pointing that out as it is certainly something I neglected. Mike's formulae for the distance is given as bs = NM (Cos p){ Sin (p + 90/N)}, and represents as the distance between the button centers. In his first example, the distance is less than the button diameter so there would be overlap of the two buttons; yet in the second example, the distance is greater so there would be a space. I think this space is not the same as the width of the flat, however.

I still have some study to do on this, but what I can share now is my first practice run on some mystery plastic...

[RCW]

ctwo:

Keep posting! {Please?}

[Grantham]

It's not my intention to take you off in another direction, have you considered buying an individual involute cutter. And since you have the equipment to make the tooling for a fly cutter, another option is a milling cutter.

If you're interested in using an involute cutter, my video "Machining a Spur Gear", http://www.youtube.com/watch?v=VHTXaU7GZC0



may give you some insight about what's involved.

A milling cutter is demonstrated in my video, "Simple & Cheap Dividing Head - Part Two", http://www.youtube.com/watch?v=wTinL_fFGv4 .


A milling cutter is easier to make than the button method for a fly cutter bit. A big advantage to a milling cutter is the entire range of tooth profiles for that diametral pitch is made with one cutter. A milling cutter does not produce a true involute tooth shape, but a fly cutter doesn't either.

Many of my projects require gears, and as you are finding out, the cost of commercial gears is completely nuts. Making your own fly cutter or milling cutter is going to require heat treating if you are planning to make your gear in brass or steel. You might get by with a material like stressproof 1144 steel. It machines quite easily and is tough enough to stand up to plastics and will last a little while in aluminum. Stressproof is one of my favorite steels and is what is used as the cutter in my modified rotary machine for cutting circles used in my metal spinning video. So this post doesn't look like an advertisement for my YouTube channel, you will have to explore to find that video on my channel<g>.

Good luck with whatever approach you decide to try.

Rod