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A quick and dirty way to get very close is to simply measure the base pitch. Pick 2 "numbers of teeth" where it's clear you can get the jaws of a vernier onto the *profiles* of the teeth (don't touch the tip or the root). e.g. 3 teeth and 4 teeth, or 6 teeth and 7 teeth, etc. Span one "set"...

Todd, Hopefully every gear you check has the same number of teeth as it has spaces! :-) Are you referring to "pressure angle" when you ask about angles? PM

As an FYI -- the point where undercut happens on an external gear is... 2 / (sine of PA)^2 ≤ = number of teeth where undercut happens (Two, divided by the sine of the pressure angle squared) 17 teeth on 20° 32 teeth on 14.5° PM

The problem with machining TI is "dwell" will kill you -- and it's difficult NOT to dwell if doing this on a manual lathe. It only takes a second (or a split second) of dwell to work harden TI, and the tool AND the surface finish on the part both go in the crapper almost instantly. I too would...

Great information! Thank you!

Holy MACKEREL that cabinet is nice! :bow:

Antman, Your information is correct: parting is a common (maybe the most common) procedure leading to tool breakage in a lathe. I've been running an engine lathe for over 40 years, and while I break very, very few tools, I'd have to say that I've had more mishaps during cutoff operations than...

As I recall it took half a day or so. One skim pass after the drop was out.

Here you go -- toward the other end of the spectrum: A rear end spool out of a Trophy Truck. Customer was stepping up in axle size, but wanted to continue using an existing spool. Part was fully heat treated. The spool, the axle and the drop in the first photo, and just a photo of the drop in...

I'd echo what others have said: probably not ideal for shafts, but excellent for other applications. When machining, the most important thing is to NEVER NEVER dwell with the tool -- it will work harden almost instantly. I've cut lots of it, but I cheat: I cut it in my wire edm machine where...

Typically in standard gears -- if pitch is finer than 20DP, then whole depth is (2.2/DP + .002) .... so a 24DP gear would be .0937". Ultimately, what counts is how the gears mesh (i.e. having the desired backlash). The best method is typically to cut to a specific dimension over wires, which...

Calculating the rule of thumb ;) Anything under.... 30° PA - 8 teeth 25° PA - 11 teeth 20° PA - 17 teeth 14.5° PA - 32 teeth ... will have undercut. Yes... that is cutting to standard addendum/dedendum numbers whether generated via rack (Maag method) or shaper cutter (Fellows style). --...

fwiw: Undercut happens any time the number of teeth goes below: 2 / (sine PA)^2 (2 divided by ... the sine of the pressure angle squared). e.g for 20° PA -- 2 / .34202^2 = 17.097 So anything under 17 teeth with a 20° pressure angle will have undercut.

If the situation allows it, I will often enter/exit the cut dead center in the bottom of the gullet. Then just stop the machine a tiny bit before the profile is finished and apply a clamp to hold the gear in position (and give conductivity to the drop) and finish the cut. More often than not...

I suppose that's theoretically possible, however I'd think it would be far more efficient to optically inspect your current part and then create a CAD model from that inspection data.

I'm sorry, but I don't understand what you mean by "use a wire edm machine as a measure thing". As far as cutting -- if the shape can be defined in a computer, I can cut it (within limits of course -- too large it won't fit in the machine, and if the part is so small it can't be seen, that...

Cut this gear over the weekend -- a sample for someone building a very tiny scale racecar model. 254 DP - 20° PA - 42 teeth. This was done on an Agie wire edm machine using .0028" diameter wire. Material was a piece of .025" Starrett shimstock.

Brian, The key word is: experience Unfortunately, there really aren't many shortcuts to that. It just comes from an awareness of all the variables, and a feel for what the machine and the cutting tool are doing. Does size wander with temperature? (yes... it does on any machine). Do you know...

In modern gear design, 14.5º PA has fallen out of favor many, many years ago. About the only reason to use 14.5º (IMO) is if the goal is to replicate a scale model of an old design that used that PA. (a valid reason of course) Using standard numbers, the undercut limit on 14.5º PA gears is 32...

kcmillin, A hob IS the way to go, unfortunately a hobbing machine is required to use one as DaveB mentioned. When cutting gears (regardless of method used) it's always best to measure them "over wires" rather than simply relying on a "depth of cut" from touching off on the OD (at least if...