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View Full Version : Gear cutting Hercus or SB 9"



The Fixer
01-02-2009, 11:47 AM
I have posted this same request on the Third hand forum.....

I wonder if anyone can help me out with finding the correct gear cutter size to make some back gears for my Hercus 9". They are straight spur gears so the cutters can't be too complicated. I know a little about gear cutting but not much about selecting the right cutters, they are 20 deg PA is all I know. I need to make a new 56t gear.
al

LES A W HARRIS
01-02-2009, 02:35 PM
A # 2,

14.5° PA chart. #'s Same for 20°PA.
http://i37.photobucket.com/albums/e97/CURVIC9/GEARS06/FORMCUTTERS01.jpg

Cheers,

.RC.
01-02-2009, 05:15 PM
Depending on how much of a clone the lathe of the South Bend, the change gears could be built using british standard gear involute profiles...

John Stevenson
01-02-2009, 06:28 PM
If they are a SB clone then they are 18 DO but I'm certain they are 14 - 1/2 Pa and not 20 but I don't own a Boxford or SB so perhaps someone who has one can comment.

Most lathes are 14 -1/2 on change gears to factor in older models, even the brand new Myford's are still 14.5 because of the spares issue.

Some of the later Colchester's [ don't know about Clausing ] and Harrison's are 20 PA as they made a lot of changes when they went onto the square head pattern

.

franco
01-02-2009, 09:08 PM
John S,

FWIW here is a quote from a Hercus forum. No idea whether or not it is true, but given the quoted source, it probably is.

http://www.woodworkforums.ubeaut.com.au/showthread.php?t=85885 post #6

"I should point out that the biggest difference between the Hercus and the Southbend is the gears. All Hercus gears have a pressure angle of 20degs. Southbends, except for the very late model ones, have 14.5deg. I found this out at a talk given by one of F. Hercus' sons in the 80s. Apparently Fred had lot's of experience with manafacturing gears before building the 9" and was the firm opinion that 20degs was better. He also said that Fred turned up at the Southbend factory to have a look at some point and was promptly shown the door."

franco

John Stevenson
01-02-2009, 09:19 PM
Thank you much appreciated, at least someone had some sense.

.

The Fixer
01-02-2009, 10:20 PM
I had read that on the aussie forum Franco, thanks.
Les, thanks for that. I was kinda hoping that I could cut of the smaller gears too with the same cutter but I guess not.
Any ideas where to but these gear cutters? I have a name of a place on the east USA coast that seems to have lots of cutters but the name escapes for the moment.
I have written down at work tho.

Any thoughts on selecting an appropriate metal, I have access to heat treating forge/oven.


al

The Fixer
01-02-2009, 10:24 PM
Just remembered, here's the link if anyone else ever needs gear stuff.

http://www.ashgear.com/

.RC.
01-02-2009, 11:38 PM
So noext question is what 20 degree profile is it cut to...One would assume the british profile

http://img.photobucket.com/albums/v606/OzRinger/gear001.jpg

The Fixer
01-03-2009, 11:42 AM
I'm guessing that with all the fasteners on the machine in imperial sizes the gears will be too. Your thoughts on the pics?
http://photoshare.shaw.ca/view/5965310276-1230997064-27100/

The Fixer
01-07-2009, 04:40 PM
Great info so far, thanks to all.
I have ordered my gear cutters and now I'm wondering about what material to use. The original gear looks like a cast iron gear given the way the tooth broke off. should I be trying to find some cast billet for material or a carbon steel, or mild steel? I am also considering some nylarod material and make this a true sacrificial gear, anyone have any experience with the nylon material for gears?

al

garyphansen
01-07-2009, 04:59 PM
Most of the original gears were cast iron. I would go with cast iron, Bronze or steel no problem. Gary P. Hansen

oldtiffie
01-07-2009, 06:07 PM
Good pic Ringer.

If I recall correctly, I read recently in my Machinery's Handbook that many/most/all?? of the cutters in the "sets" have an involute curve where the tooth side/flank intersects with the pitch circle and a epicycloid curve above that point (in the addendum) and a hypo-cycloid curve on the dedendum - irrespective of the pressure angle (14 1/2 deg and 20 deg pressure angle).

(I may have transposed the cycloid curves but the explanation will still stand - irrespective of the curves ands pressure angle/s).

Ringers's pic shows the pressure angle quite well at the pitch circle.

OK - now for the suggested "rough as guts" or "belt and braces" way of approximation of the pressure angle.

Take a good high resolution pic of at least one half - a quarter will do - of any gear in the set from vertically above the gear - ie normal to it.

Print the gear or import it as a *.jpg file into your CAD system.

Draw a circle (centred on the gear) on the pitch circle such that it is just under half the tooth depth (from the outside diameter) and passes through several gear teeth.

Draw a line tangent to the curve on the tooth side/flank, say 2 to 4" long (line "A").

Draw a radial line 2 - 4" long from the gear centre (line "B") passing through the intersection of line "A" with the pitch circle.

Using a protractor (a cheap "school" one will do) - or any other method - measure the angle between line "A" and "B".

That angle will be the pressure angle. It may not be exact for several reasons but it will be sufficiently accurate to tell whether it is 14 1/2 or 20 degree.

I can post a pic or a sketch if needed.

oddball racing
01-07-2009, 06:32 PM
Good explaination Oltiffe, I've done similar tricks with CAD as well. However, by me allowing the program to do it's stuff, I'm left with a solved problem without a clear vision of how I got there. I'm trig. challenged :confused: ,I know. So, YES, I know I would appreciate a sketch to shake my brain cells toward a more proper alignment. :)

Thanks, Mike

oldtiffie
01-07-2009, 08:18 PM
Mike.

I will do it later today. I have grass to cut today.

dockrat
01-07-2009, 09:39 PM
Mike.

I will do it later today. I have grass to cut today.

Hey Torker!!! didja hear that???? He has GRASS to cut today!!!! We should send him some snow:D

oldtiffie
01-08-2009, 03:59 AM
Its better 'n' that. Wife and I were both mowing but had to get down to short sleeves and wear hats and transitional lens in the glasses due to the warmth and glare in the sun. We will finish it off tomorrow - another similar day.

Its tough - but I guess it might as well be us doing it this hard. It just wouldn't be fair to swap with those that are freezing and snow-bound as I guess we'd only get a refusal anyhow.

This also serves as a "bump" until I get the geometry for the gear/s done.

.RC.
01-08-2009, 05:16 AM
snow:D

snow?????? never seen snow before....

oldtiffie
01-08-2009, 05:26 AM
Snow?

Its the difference between snow men and snow women.

's'no balls.

Or so I am led to believe.

oldtiffie
01-09-2009, 06:59 AM
Good pic Ringer.

If I recall correctly, I read recently in my Machinery's Handbook that many/most/all?? of the cutters in the "sets" have an involute curve where the tooth side/flank intersects with the pitch circle and a epicycloid curve above that point (in the addendum) and a hypo-cycloid curve on the dedendum - irrespective of the pressure angle (14 1/2 deg and 20 deg pressure angle).

(I may have transposed the cycloid curves but the explanation will still stand - irrespective of the curves ands pressure angle/s).

Ringer's pic shows the pressure angle quite well at the pitch circle.

OK - now for the suggested "rough as guts" or "belt and braces" way of approximation of the pressure angle.

Take a good high resolution pic of at least one half - a quarter will do - of any gear in the set from vertically above the gear - ie normal to it.

Print the gear or import it as a *.jpg file into your CAD system.

Draw a circle (centred on the gear) on the pitch circle such that it is just under half the tooth depth (from the outside diameter) and passes through several gear teeth.

Draw a line tangent to the curve on the tooth side/flank, say 2 to 4" long (line "A").

Draw a radial line 2 - 4" long from the gear centre (line "B") passing through the intersection of line "A" with the pitch circle.

Using a protractor (a cheap "school" one will do) - or any other method - measure the angle between line "A" and "B".

That angle will be the pressure angle. It may not be exact for several reasons but it will be sufficiently accurate to tell whether it is 14 1/2 or 20 degree.

I can post a pic or a sketch if needed.


Good explaination Oltiffe, I've done similar tricks with CAD as well. However, by me allowing the program to do it's stuff, I'm left with a solved problem without a clear vision of how I got there. I'm trig. challenged :confused: ,I know. So, YES, I know I would appreciate a sketch to shake my brain cells toward a more proper alignment. :)

Thanks, Mike

My apologies for the delay Mike - sincerely.

Here is the sketch - I hope it helps.

http://i200.photobucket.com/albums/aa294/oldtiffie/Sketches/PA_sketch1.jpg