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Question about calculating change gears for prime tooth gears?

David_M

Hot Rolled
Joined
Sep 30, 2014
Location
Midway, GA, USA
This is the book sample:
170299509.jpg


This is what I am getting:
170299510.jpg


Does the book sample look wrong to you or is it mine or both? :confused:

317 tooth
12/N index constant
0.075 per rev feed constant
5/L differential constant
54 diametral pitch (0.05817764 circular pitch)
1 start on the RH hob
~~0.025 feed rate
 
It turns out to be a rounding error. When taken to the extreme with lots of digits it looks like this:

170300466.jpg


a lot closer to the sample (but still not an exact match).
 
That formula is for checking the setup to cut primes, by setting the machine differential to cut a specific helix angle or lead and then cancelling the lead non- differentially. If done correctly the answer should be very close to zero.- even sin-1 of .oo4 is 0.2 degrees- pretty small. Glad you got it figured out. For everyone else this method allows cutting gears on a gear hobbing machine with prime numbers of teeth without needing an index gear with the same prime number of teeth.
 
This is an attempt with the code that I have so far:

170302433.jpg

R 0.03801652892561983471074380165289

V 0.85036356678147722923842326827401

L 39.62500000000

circ pitch 0.05817764173314431923078969228295

20 x 23
----------- index
110 x 110

101 x 44
---------- diff
78 x 67

Feed is any set of gears that gives an exact feed of 0.025/rev

sine of the angle -0.0000003872120450133567562

tan^-1(-0.0000003872120450133567562) = -0.0000221856159558938866931 (error in decimal degrees)
 
Dan has it correct. I struggled through this with a Koepfer a few times.

The larger, much more interesting question here is where the bloody blazes did you find a 6-10 with a diff?!?!?!?!?!?!?

I want pics.
 
The larger, much more interesting question here is where the bloody blazes did you find a 6-10 with a diff?!?!?!?!?!?!?

I want pics.
I know where one lives, nanner nanner :D

It's actually a late #3 but same difference (heh heh). Came from Lenny Epstein, who always had strange stuff. It's a factory bolt-on but still a bolt-on, goes behind the big feed handwheel on the right, looking from the front.

Speaking of which - David M, do not disengage the feed at the end of the cut when you're doing this. Stop the machine, back the work away, then reverse the spindle to get the hob all the way back to the start point for a second cut. Otherwise you'll lose the helix and that will be sad :(

You probly know that but just in case ....

I struggled through this with a Koepfer a few times.
With a Cleveland with minch, you struggle through it every time just to cut a spur gear. I love those things but the change gears were no fun at all. In practice, with coarse pitch, I found you could be off up to about .0002 on the angle without it being a problem. I'd guess that fine pitch on a Barber you'd want to be closer but sounds like op has it covered.
 
Sounds like an opportunity for someone with connections and lot a money to burn. :cool:
Already did that once (except for the money to burn part.) Too old now or I probably would, but getting old scrappers and retrofitting them would be easier. There's a few places making money hand over fist doing that. Do you know what a retroed 20-4 costs and how much of it is profit ?
 
What is the title and author? Is an errata published?

Joe, this is a reproduced operator's manual for 6-xx and 16-xx Barber-Colman gear hobbing machines.

Dan has it correct. I struggled through this with a Koepfer a few times.

The larger, much more interesting question here is where the bloody blazes did you find a 6-10 with a diff?!?!?!?!?!?!?

I want pics.

Z, I was just copying an example solution that happened to use that little critter. I wish I had one, but age keeps me from spending money on machines these days.
 
Z, I was just copying an example solution that happened to use that little critter.

Well, dang... color me deflated...


I know where one lives, nanner nanner :D

It's actually a late #3 but same difference (heh heh). Came from Lenny Epstein, who always had strange stuff. It's a factory bolt-on but still a bolt-on, goes behind the big feed handwheel on the right, looking from the front.

EG, I'd love to see pics if you find any. I've never seen a 6 with a diff. Heck, I've never even see a layout page for one. I've heard mentions of them over the years, but they're more rare than hen's teeth. Let me know if you have any pics.
 
For sure ! You gotta watch those guys like a hawk or they'll go through your blanks like Sherman through Georgia ! :D

One regret is I never had an 1886. Even the 188 was a terror for production .... a cnc 1886 would be killer. Too bad the US doesn't make anything any more :(


Send me a e-mail or clear your PM in box...can't send ya anything...
Cheers Ross
 
I see change gears referred to by letters.

Is there an industry standard for referring to change gears by letter designations? Would the index gears be A through D? Would the feed gears be E through H and the differential I through L?

Would B be the second drive gear or would it be A's driven gear? And, does this pattern repeat for the others?

I want to get my variables and constants to have more proper names on my new prime-gear software.

Thanks very much!

David
 
This is the first version of a program to find change-gears for hobbing a prime tooth gear using Barber-Colman 6xx through 16xx hobbers (among others).

download link: https://1drv.ms/u/s!AjRYB9hC1AwChvp4qkUX3m8rNgHYew?e=dmnEzp

Use only after double checking. The 'print' menu item hasn't been worked on yet.

At this point it is for win 7 and newer.
64 bit.
Lots of ram.
The more logical processors your cpu has, the faster it runs.

Don't hold back on your criticism.
 
Dan has it correct. I struggled through this with a Koepfer a few times.

The larger, much more interesting question here is where the bloody blazes did you find a 6-10 with a diff?!?!?!?!?!?!?

I want pics.

Well, dang... color me deflated...

EG, I'd love to see pics if you find any. I've never seen a 6 with a diff. Heck, I've never even see a layout page for one. I've heard mentions of them over the years, but they're more rare than hen's teeth. Let me know if you have any pics.

Hey Z,

I just saw a Barber Colman 6-16 with a differential and remembered this post.

5560 barber colman 6-16 | lsmachines
 








 
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