Can I substitute different DP gear cutters?

[jeff10049]

Hello A question for those who know gear cutting. I rarely cut gears. I need to make one gear that is 12 tooth 8DP 20degree PA.
That cutter is a little hard to come by and expensive when I do find it. Even then two places emailed back to inform me they don't actually have it.
This gear is for reverse only in a 1911 hupmobile transmission and is only engaged to other gears when in reverse so there is probably some room for error.

I have a #8 12DP 20 degree cutter it seems to match the gear quite well with the exception of being slightly narrower profile. Can I use this cutter and make an additional pass to widen the profile and produce an acceptable gear for
the application or is this a total hack idea?

I also think a 3module metric #1 cutter may be close enough and is much easier to obtain but I'm not sure how close is close enough.

As I have been reading and trying to learn a lot about gears the last few weeks I'm starting to understand how it all works a lot better but I still lack the practical experience to know what can and can't be made to work.

Thank you for any input or if someone has an #8 8dp 20-degree cutter you want to sell let me know.

Jeff

 

[HappyWyo]

I have done like you when I couldn't find the exact cutter I needed, I used the closest one I could find and then made a high speed steel cutter to clean it up. High speed won't work on hardened steel of course. If you use cutting oil with your high speed you can get away with a lot though. I have cut gears in 4140 with high speed steel cutters using oil.

 

[jeff10049]

I have done like you when I couldn't find the exact cutter I needed, I used the closest one I could find and then made a high speed steel cutter to clean it up. High speed won't work on hardened steel of course. If you use cutting oil with your high speed you can get away with a lot though. I have cut gears in 4140 with high speed steel cutters using oil.

This could be an option as the blank is 4140. I may be overthinking this and worried about nothing I just need to cut the thing and see what I can make happen it's a small blank so if it goes south it's not a big cost. We have more 4140.
Gears are just one of those things that I'm never sure of myself like, the first time I cut threads years ago it seemed like such a big deal now I don't even think about it. I've even made quite a few taps for special sizes too small to get a tool into. Maybe someday I'll have that confidence with gears.

 

[Dan from Oakland]

If you want to send me a PM, we can discuss your gear. I have a 1910 Hupp myself and have been cutting gears for over 40 years, so I kinda know both worlds pretty well. I would be very surprised if your gear is actually 20 deg. PA, but I may be mistaken.

 

[wood2steel]

Jeff,
I agree with Dan on the pressure angle considering the age factor. Of course, he's the Specialist here, so just ignore me. Ha
I have a collection of 200++ gear cutters here; re-check your specs and send me a PM this weekend and I'll see if I can cover the size needed. Johnny

 

[jeff10049]

Thanks Guys, Dan your pm box is full.

A 20degree gear gage seems to fit well compared to a 14.5 but maybe other factors influence that? I have a copy of an original document that seems to suggest 20 but I may not be deciphering that correctly I will post it here. I can't seem to get the pic to post so I put a link to the document in the next post its page 221 that mentions the gears.

 

[jeff10049]

The New Model 20 "B" for 1910 - Hupmobile - Antique Automobile Club of America - Discussion Forums

 

[Dan from Oakland]

PM box cleaned out- sorry. So from the AACA link, they are probably Fellows combination pitch: 8-10. this means they have a dimetral pitch of 8DP but a tooth depth of a 10 DP gear. The depth will most likely be in the ballpark of .225". Not sure how to decipher to "20% involute", and all Fellows combination pitch tooth forms are 20 degree PA.

 

[jeff10049]

Yes, the depth is very near.225" so I assume that an 8dp cutter is still used and depth adjusted to a stub profile? I also assume this was done to prevent tooth interference with the much higher tooth count mating gear. This is all starting to make sense the gear doesn't measure to be as worn in diameter as the stubby teeth make it look.

 

[Peter.]

I thought that I had the cutter you need and would have been willing to loan it to you by post but alas it's the no6 I have not the no8.

 

[jeff10049]

Just wanted to update the thread and thank all that replied for the help. I was able to find a new cutter for less than the $300.00 I had originally found. Cut the gear as Dan suggested and it came out perfect. The next question is should I heat treat it? Keep in mind it is in use only in reverse. It is 4140 I have access to a furnace machinist's handbook suggests 1600f oil quench and draw at 400f.
Any other input should I heat it in a stainless foil? Or not even worry about heat treating?
Jeff

 

[Peter.]

Well done Jeff,

I would probably consider case hardening it if it's only working when reverse is selected.

 

[4GSR]

Find someone that can either induction harden, or flame harden the teeth only. They can get the teeth around 45-55 HRC, which would probably last a lifetime for you there.
I'm not familiar with this tranny, but in some the reverse gear setups, the idler will spin way much faster when in forward gear, if it's a gear that stays in mesh to the forward running gear cluster. Ken

 

[jeff10049]

Thanks, Ken this gear is only in mesh for reverse so pretty low use and rpm. I will look into induction I may have a coil that will fit over this gear I just need to read up on induction treating 4140.

 

[jeff10049]

Thanks, Ken this gear is only in mesh for reverse so pretty low use and rpm. I will look into induction I may have a coil that will fit over this gear I just need to read up on induction treating 4140.

So I put the gear on a rod spun it slow in the lathe heated it to nonmagnetic quenched it in 120-degree canola oil and it got harder than a 50 file would cut so I drew it back in the furnace just to where the 50 file would just cut and pulled it. checked distortion with blueing and it's good to go. I know the files aren't the most accurate hardness test and the process was home brew but for what it does I'm happy and confident it will work fine. If it were a more critical gear I would have sent it for professional treatment.
Thanks for all the help.