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
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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.
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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
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Whoa!!
The original post was:
Originally posted by riceoneI 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
A rework 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.
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Is this it??
Originally posted by John StevensonWith these specs and being Japanese chances are it's 1.5 mod and 20 degree pressure angle.
.
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.
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Make it
Originally posted by riceoneOldtiffie, 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
I guess you have the original gear.
I'd also guess that it is on a static (ie nonmoving and noncritical) 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 flycutting tool and make the part/gear from brass or "freecutting" 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 flycutter and you will get huge satisfaction and "bragging rights" if you do the whole job.
A flycut job should work very well in a "dynamic" situation.
Just take your time!!! "Hasten slowly".
You will always have the "fallback" 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".
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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.
Last edited by riceone; 05062008, 09:05 AM.
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problem with the numbers
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")Last edited by vmil3; 05062008, 10:18 AM.Doug
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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 Photoshoptype 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:
"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."
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Error in Mod gear value
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:
Originally posted by oldtiffieOD = 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.
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.
Sorry about the silly mistake on my part.
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