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riceone
05-04-2008, 10:29 PM
I have a small gear 1.100" dia. .193" thick with 16 teeth. Came out of a Japanese mortar. How do I determine what gear cutter to buy. Thanks. Riceone

HSS
05-04-2008, 11:31 PM
a number 7 involute gear cutter would be required for 16 teeth

Mcruff
05-05-2008, 11:26 AM
This post will tell you how to calculate what the pitch is.
http://bbs.homeshopmachinist.net/showthread.php?t=17870
And then you will need a number 7 cutter in the pitch you determine.

lazlo
05-05-2008, 12:42 PM
Outside Diameter = Number of Teeth + 2
___________________
Pitch Diameter

riceone
05-05-2008, 06:41 PM
OD is 1.100" - 16 teeth plus 2 = 18. 18 divided by 1.100 = 16.3636.
MSC list 14 1/2 and 20 degree pressure angle. What do I order? Is there a difference in this gear made in Japan in the 30's and an American gear made today? Are there different cutters for Metric and would there be a different way to calculate the pressure angle? riceone

riceone
05-05-2008, 06:44 PM
I'm looking in the MSC catalogue; would I order a dimetrical pitch of 18 in a No. 7 Cutter? riceone

oldtiffie
05-05-2008, 07:08 PM
The original post was:

I have a small gear 1.100" dia. .193" thick with 16 teeth. Came out of a Japanese mortar. How do I determine what gear cutter to buy. Thanks. Riceone

Why is everyone going "inch" when the item is Japanese which is probably "metric"?

A re-work for metric is:

OD = 1.100 x 25.4 = 27.940mm (say 28.00mm)

For Modular (metric) gears:
Mod 2

OD = PCD + (2 x 2) =28

PCD = 28 - 4 = 24

(or for DP equivalent) DP = 24/16 = 1.5

Width of gear = 0.193" x 25.4 = 4.9022 mm (say 5.00mm nominal).

It is quite possible and perhaps probable or a certainty that I am wrong, but as it is Japanese I would at least consider that the gear might be:
- 28mm OD;
- 24mm PCD;
- 16 teeth;
- Mod(ular) 1.5;
- 5.00 mm (nominal) wide; and
- 1.5 DP (equivalent).

The pressure angle is yet to be determined whether it be "inch" (DP) or "metric" (Modular).

So if it were me, I wouldn't order that gear cutter yet.

John Stevenson
05-05-2008, 07:09 PM
With these specs and being Japanese chances are it's 1.5 mod and 20 degree pressure angle.

.

oldtiffie
05-05-2008, 07:19 PM
With these specs and being Japanese chances are it's 1.5 mod and 20 degree pressure angle.

.

Thanks John.

That has "closed the loop" and so I'd support what you say:
(sizes in mm):
1.5 Mod.
20 deg PA
28 OD
24 PCD
16 teeth
5mm wide

It is possible - as John says- that the Pressure Angle (PA) is 14.5 degree.

riceone
05-05-2008, 09:52 PM
Oldtiffie, your measurements are correct, just used a metric caliper - should have done that first. Now could anyone tell me what to order, I have found several suppliers of metric cutters on the net. But it all Greek to me. Thanks,

riceone

oldtiffie
05-06-2008, 12:12 AM
Oldtiffie, your measurements are correct, just used a metric caliper - should have done that first. Now could anyone tell me what to order, I have found several suppliers of metric cutters on the net. But it all Greek to me. Thanks,

riceone

Hi riceone.

I guess you have the original gear.

I'd also guess that it is on a static (ie non-moving and non-critical) model or original Mortar weapon and perhaps not the "bomb"/projectile.

If this is the case, why not use what you have to grind the profile on a fly-cutting tool and make the part/gear from brass or "free-cutting" steel (for "show" and ease of milling). Use what ever you have of the existing gear to grind the tooth/cutter profile from. Its not too hard and not all that "fussy" either.

It will cost next to nothing to make the fly-cutter and you will get huge satisfaction and "bragging rights" if you do the whole job.

A fly-cut job should work very well in a "dynamic" situation.

Just take your time!!! "Hasten slowly".

You will always have the "fall-back" option of buying a milling cutter.

If buying a milling cutter (MacMaster Carr (Sp?) in the USA?), just quote the details in my previous post and they will identify the cutter you need.

If you have any problems - just start a new thread or continue to post on this one.

I am sure that you will get all the help you need.

Best of luck - enjoy the experience and the satisfaction of "doing it".

riceone
05-06-2008, 08:00 AM
Thanks for all your help. I will call someone and give them what you have posted. I have made a few of these using a fly cutter every one has a flaw that I can see, however they fit and work and have had no complaints. I just would like to be able to make one exactly like the original on the right. Here is a photo of the last one I made.

http://img.photobucket.com/albums/v283/riceone/DSC03891.jpg

vmil3
05-06-2008, 09:14 AM
There is a problem with the numbers here,
For a 1.5 module pitch gear, the addendum is equal to the module or 1.5mm. If going by the formula in Machinery's Handbook for O.D. of the gear.

Rule; for O.D. = "Add 2 to the number of teeth and multiply sum by the module".

or (2 + 16teeth) x 1.5 module = 27mm (1.063") not 28mm (1.100")

What accounts for the extra .9398mm (.037") increase in the gear's original O.D.of 1.100"?

PS; Whole depth of a 1.5 module tooth is 3.250mm (.1279")

lazlo
05-06-2008, 10:35 AM
Rice, those are 1.5 Module, which are very close to 16 DP -- the roots of the teeth look like they might be 14 1/2° pressure angle. On a 16 DP gear, the 20° PA teeth have a thicker base, and look more like an isosceles triangle. 14 1/2° teeth have more of an undercut below the pitch diameter.

The easiest way to tell would be to scan the actual gear, and then superimpose a CAD drawing of a 1.5 Mod, 14.5 & 20 PA gear on top of it in your favorite Photoshop-type program.

You can get the CAD models from Boston Gear, Small Parts, etc...

This is from the Boston Gear catalog, 20° PA on the left, 14.5° pitch angle on the right:
http://i164.photobucket.com/albums/u15/rtgeorge_album/Gearteeth.gif

oldtiffie
05-06-2008, 08:03 PM
I incorrectly inserted a Mod value of 1.5 (instead of 2.0) in my original text as I suspect that I confused or transposed it with the equivalent "DP" value:


OD = 1.100 x 25.4 = 27.940mm (say 28.00mm)

For Modular (metric) gears:
Mod 2

OD = PCD + (2 x 2) =28

PCD = 28 - 4 = 24

(or for DP equivalent) DP = 24/16 = 1.5

Width of gear = 0.193" x 25.4 = 4.9022 mm (say 5.00mm nominal).

It is quite possible and perhaps probable or a certainty that I am wrong, but as it is Japanese I would at least consider that the gear might be:
- 28mm OD;
- 24mm PCD;
- 16 teeth;
- Mod(ular) 1.5;
- 5.00 mm (nominal) wide; and
- 1.5 DP (equivalent).

The pressure angle is yet to be determined whether it be "inch" (DP) or "metric" (Modular).

So if it were me, I wouldn't order that gear cutter yet.


The corrected and Mod value is 2.0:


OD = 1.100 x 25.4 = 27.940mm (say 28.00mm)

For Modular (metric) gears:
Mod 2

OD = PCD + (2 x 2) =28

PCD = 28 - 4 = 24

(or for DP equivalent) DP = 24/16 = 1.5

Width of gear = 0.193" x 25.4 = 4.9022 mm (say 5.00mm nominal).

It is quite possible and perhaps probable or a certainty that I am wrong, but as it is Japanese I would at least consider that the gear might be:
- 28mm OD;
- 24mm PCD;
- 16 teeth;
- Mod(ular) 2.0;
- 5.00 mm (nominal) wide.


The pressure angle - as advised by John Stevenson is probably 20 degree with a chance that it is 14 1/2 degree.

Sorry about the silly mistake on my part.

riceone
05-06-2008, 09:36 PM
Oldtiffie, I will use that information tomorrow to try to find a cutter. This is a very helpful forum. I will let you know if I find the correct cutter.

lazlo
05-06-2008, 09:41 PM
I incorrectly inserted a Mod value of 1.5 (instead of 2.0) in my original text

The corrected and Mod value is 2.0:

The pressure angle - as advised by John Stevenson is probably 20 degree with a chance that it is 14 1/2 degree.

It's still 16 + 2 / 1.1" = 16.3636 DP, and if you look at the Boston Gear chart I posted, those look like 14 1/2° Pressure Angle teeth.

riceone
05-06-2008, 10:31 PM
I went to Boston Gear and printed the picture out and layed the gear on it and it seems to match the 14 1/2 the best. riceone

oldtiffie
05-06-2008, 10:40 PM
It's still 16 + 2 / 1.1" = 16.3636 DP, and if you look at the Boston Gear chart I posted, those look like 14 1/2° Pressure Angle teeth.

Your are pretty right again lazlo - I FUBAR-ed again!!.

The pitch circle diameter is 28 - (2 x 2) - 28 - 4 = 24mm/25.4 = 0.9449"

Number of teeth = 16

Diametral pitch (inch) = 16/0.9449 = 16.933 say 17

The best "rough" way of measuring the pressure angle is to measure the angle of the tangent on the face of the gear at the pitch circle.

If the OP could post a pic of a vertical view it would help - other than that its more guess-work than is necessary.

http://i200.photobucket.com/albums/aa294/oldtiffie/Involute_wheel1.gif

http://i200.photobucket.com/albums/aa294/oldtiffie/Gear_theory/Gear_theory7.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Gear_theory/Gear_theory8.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Gear_theory/Gear_theory9.jpg

LES A W HARRIS
05-07-2008, 12:52 AM
It may be an enlarged gear!
http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES06052008_215823.jpg



single radius tool.
http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES06052008_222703.jpg


full sceen.
http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES06052008_222806.jpg

Above is 20deg PA. I can run for 14.5PA if your interested.

Cheers,

dp
05-07-2008, 01:55 AM
I would think that by using a very good image of the original gear imported into even a simple drawing package it would take just minutes to draw a basic rack at both 14.5 and 20 degrees to see which is the best fit. It may actually be neither and that will be revealed too.

A very good image can be had by placing the gear on a scanner.

http://thevirtualbarandgrill.com/machinery/newgearinmesh.jpg

oldtiffie
05-07-2008, 02:53 AM
It may be an enlarged gear!
http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES06052008_215823.jpg

single radius tool.
http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES06052008_222703.jpg

full screen
http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES06052008_222806.jpg

Above is 20deg PA. I can run for 14.5PA if your interested.

Cheers,

Thanks Les.

Yes please - 14 1/2 degree.

The OP can scan his gear in (nah - not THAT gear - that's for the office party on the photocopier!!!) and then re-scale it and print it out and over-lay his mortar gear on the print from your post - and re-scale that too I suppose.

riceone
05-07-2008, 12:32 PM
I went to MSC and MacMasters with 28mm OD, 24mm PCD, 16 teeth, Mod 2 and neither had that gear. MSC said they could have it made.

Then I printed out the gear picture, reduced it almost to the size of my gear it seems to be perfect match. What do you suggest now? riceone

lazlo
05-07-2008, 12:39 PM
It may be an enlarged gear!

Les, do you mean a stub tooth form?

LES A W HARRIS
05-07-2008, 06:03 PM
Les, do you mean a stub tooth form?

No, the gear data for 16tooth, 1.5 Metric Module, would be 24 mm pitch dia, 27mm [1.0630"] major dia, it appears that as the major dia in question is 28mm [1.1024"] [Basic]. The 16 teeth were cut on an enlarged blank, [1mm Oversized] this was a quite common proceedure to reduce undercut in gears with low numbers of teeth, the gear is cut to standard depth on the oversized blank. Not saying that this is for certain the case here but the data strongly sugests it.



OldTiffie,

4:00 PM here have to head of to town I'll run the 14.5 PA this evening,

Cheers,

oldtiffie
05-07-2008, 09:31 PM
Thanks Les.

You really are a top resource and a well of information - great!!

Can you please "run" an image of a 28mm OD, 24mm PCD, Mod 2, 16 teeth, 14 1/2 degree PA profile as well?

This is now a very good thread as regards analysis and form-finding thanks to your info and expertise.

oldtiffie
05-07-2008, 09:35 PM
I would think that by using a very good image of the original gear imported into even a simple drawing package it would take just minutes to draw a basic rack at both 14.5 and 20 degrees to see which is the best fit. It may actually be neither and that will be revealed too.

A very good image can be had by placing the gear on a scanner.

http://thevirtualbarandgrill.com/machinery/newgearinmesh.jpg

Thanks Dennis.

Great advice and use of a generally available resource (scanner) - and in retrospect - all too obvious now that you have pointed it out!! Good example of thinking "laterally" and "outside the square"!!

LES A W HARRIS
05-07-2008, 11:45 PM
Thanks Les.

You really are a top resource and a well of information - great!!

Can you please "run" an image of a 28mm OD, 24mm PCD, Mod 2, 16 teeth, 14 1/2 degree PA profile as well?

This is now a very good thread as regards analysis and form-finding thanks to your info and expertise.

Now Young Man, Pay attention to details,:D .

Where D = Pitch Dia, N = Number of teeth, & P = Pitch expressed in Metric Module, we have the following:

D = N*P, so 16 teeth times 2MMod[pitch] = 32mm pitch dia.

From this we have N = D/P, 24/2 = 12 teeth.

So if we have 16 teeth & 24mm pitch dia? [P = D/N] giving 24/16 = 1.5mmodule Pitch.

So how about 16 teeth, 24mm Pitch dia, enlarged OD of 28mm instead of standard 27mm for 1.5mmodule Pitch, with 14.50 Pressure Angle?

If the OD is enlarged and standard tooth thickness is cut for 1.5 mmodule it will probably point out and not be possible to have a 28mm OD. That i'll check.

Cheers,

oldtiffie
05-08-2008, 12:39 AM
Thanks Les.

You really are a top resource and a well of information - great!!

Can you please "run" an image of a 28mm OD, 24mm PCD, Mod 2, 16 teeth, 14 1/2 degree PA profile as well?

This is now a very good thread as regards analysis and form-finding thanks to your info and expertise.




Now Young Man, Pay attention to details:

Where D = Pitch Dia, N = Number of teeth, & P = Pitch expressed in Metric Module, we have the following:

D = N*P, so 16 teeth times 2MMod[pitch] = 32mm pitch dia.

From this we have N = D/P, 24/2 = 12 teeth.

So if we have 16 teeth & 24mm pitch dia? giving 24/16 = 1.5mmodule Pitch.[/COLOR][/SIZE][/FONT]

So how about 16 teeth, 24mm Pitch dia, enlarged OD of 28mm instead of standard 27mm for 1.5mmodule Pitch, with 14.50 Pressure Angle?

If the OD is enlarged and standard tooth thickness is cut for 1.5 mmodule it will probably point out and not be possible to have a 28mm OD. That i'll check.

Cheers,



Thanks Les.

Touché.

I sure have dug myself into some hole - I'd better stop digging!!

I needed that "kick in the ar*e"/"whack in the ear"/"wake-up call" as its just been one cock-up after another with/by me on this thread.

Just as I was telling myself that it was the end of cock-ups; that I've made a big enough dick-head of myself; and that it won't get any worse; - sure enough - you prove me wrong on all counts!!!

Can you "run" and post the result so that we can see where we are with this.

LES A W HARRIS
05-08-2008, 10:17 AM
Thanks Les.

Touché.

I sure have dug myself into some hole - I'd better stop digging!!

I needed that "kick in the ar*e"/"whack in the ear"/"wake-up call" as its just been one cock-up after another with/by me on this thread.

Just as I was telling myself that it was the end of cock-ups; that I've made a big enough dick-head of myself; and that it won't get any worse; - sure enough - you prove me wrong on all counts!!!

Can you "run" and post the result so that we can see where we are with this.

"By dicussion do we learn".

I've added two & three tooth span measurements, for reference, maybe this may shed additional light on the subject gear?

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_074140.jpg

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_072523.jpg

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_074643.jpg


20deg enlarged version.

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_081109.jpg


Cheers,

oldtiffie
05-08-2008, 07:55 PM
"By dicussion do we learn".

I've added two & three tooth span measurements, for reference, maybe this may shed additional light on the subject gear?

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_074140.jpg

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_072523.jpg

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_074643.jpg

20deg enlarged version.

http://i37.photobucket.com/albums/e97/CURVIC9/08%20GEARS/LES08052008_081109.jpg

Cheers,


Touché 2 Les.

Many thanks.

"By discussion do we learn".
I can relate to that!!

This has been a very religious and educational experience for me.

There have been at least 3 occasions in this thread where I've said - and meant: "J---- C-----, that's taught me a bl**dy good lesson".

riceone
05-08-2008, 08:05 PM
I have been measuring my original gear and come up with some wierd measurements. I have gone around the gear several times and the three teeth measurements range from .453" to .468" and the measurement over the two teeth go from .269" to .280." Apparently Japanese quality control was not watching to close. Maybe I am chasing a ghost. I have measured OL Diameter on several original gears and they too differ. riceone

JCHannum
05-08-2008, 08:50 PM
Just because it is a gear does not mean that it has to conform to the standard formulas for involute gears. The standard gears are used in many instances due to convenience and availability.

A manufacturer can play as fast and loose with gear design as he can with threads to make it fit his particular application. While those gears may appear close to a modular gear, it does not necessarily follow that they are. I am guessing they are for a low speed application such as elevation, where perfect form is not a requirement. That being the case, your original approach of making a single tooth flycutter ground to match the existing gear form is probably as good as any.

riceone
05-08-2008, 09:30 PM
JC your assumptions is correct. A knob turned by your thumb and index finger rotates this gear against another like it, to raise and lower the firing pin in a mortar. That probably accounts for the ones I make with a fly cutter working as well as the original. Guess I'll just keep on doing it that way. You guys are a most helpful bunch and I thank you. riceone