Author Topic: Making replacement gear  (Read 850 times)

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woodone

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Making replacement gear
« on: January 03, 2022, 10:04:41 AM »
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Any one able to help me on this? I need a gear made that I have not been able-to find a replacement for.
Very small about 1/4 inch O.D  0.040 THICK 17 tooth. Very small center hole.
I have tried to get local but most will will not give me the time of day or wants to charge a large sum of $$.
I only have a sample to go by. Small P.D. Tooth. Guessing 42 or smaller.
Thanks
Contact jwoodone@cox.net
Jerry Rowley. AKA. woodone.

JeffB

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Re: Making replacement gear
« Reply #1 on: January 03, 2022, 11:08:44 AM »
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Any one able to help me on this? I need a gear made that I have not been able-to find a replacement for.
Very small about 1/4 inch O.D  0.040 THICK 17 tooth. Very small center hole.
I have tried to get local but most will will not give me the time of day or wants to charge a large sum of $$.
I only have a sample to go by. Small P.D. Tooth. Guessing 42 or smaller.
Thanks
Contact jwoodone@cox.net
Jerry Rowley. AKA. woodone.

You'll have to get a pretty accurate measurement on the gear OD (over the top of the teeth).  If you have that, plus the # of teeth, you can derrive the Pitch of the teeth. 

I purchase gears from a company in Poland that sells a large variety of gears.  They are pretty reasonable pricewise, definitely cheaper than NWSL.  Based on what you've given so far, it might be either a 0.3Mod gear, or a 72DP/0.35Mod gear.  But you need to measure the OD with calipers or a micrometer. 

I wouldn't recommend a 3D printed gear, at least not for a drive application (static application is fine though).

Jeff

woodone

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Re: Making replacement gear
« Reply #2 on: January 03, 2022, 02:22:08 PM »
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Measuring the O.D. Will be no problem. Has for fear of gear failure , I do not think there is that much torque  on it that it would cause any problems. Plus there are two gears that are the same Being  driven  This is an N scale loco gear.

peteski

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Re: Making replacement gear
« Reply #3 on: January 03, 2022, 03:57:21 PM »
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Measuring the O.D. Will be no problem. Has for fear of gear failure , I do not think there is that much torque  on it that it would cause any problems. Plus there are two gears that are the same Being  driven  This is an N scale loco gear.

Why not give us more detail about the model itself?

And to answer your question, yes gears can be 3D printed.  As an example, when I was servicing Lee's old Bachmann 2-8-2 loco, I discovered that the prone-to-cracking Bachmann driver gears have all been replaced with what looks like FUD-printed gears (which unfortunately also cracked).  In this photo you csan see the telltale artifacts of 3D-printing (2 smaller gears on the bottom of the photo).



I would still prefer to have a replacement gear machined (not printed). The gear you need can likely be produced that way (by NWSL or that Polish company).
« Last Edit: January 03, 2022, 04:02:41 PM by peteski »
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woodone

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Re: Making replacement gear
« Reply #4 on: January 06, 2022, 11:43:21 AM »
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The Model is a French  Le monde en "N" powered rail car. Also on the box is the name ArTrain, no other ID that I see.
Unit got stalled on a turn out and melted the trucks and a gear on both ends.
I could maybe make one myself with my lathe and mill.
I have no idea has what Pitch diameter is.  I am guessing Mod 3.5 but have no way to check.
I would go out and buy a pitch tooth gauge but at over $100 per set I do not think that will happen
Seems like every job requires a new tool.

Chris333

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Re: Making replacement gear
« Reply #5 on: January 06, 2022, 03:17:54 PM »
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Probably an Atlas truck gear that will fit. You could take a photo of the gear next to a measuring device.

woodone

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Re: Making replacement gear
« Reply #6 on: January 06, 2022, 04:39:42 PM »
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I have several Atlas diesels and none of the gears match. I also have som Kato steam & diesel units and none of theos match eather.
When I buy a loco I usually buy some spares, gears being one of the spares.
I have drawers that have spares, marked Atlas, Kato & Bachmann .  So far no luck in a match.
Was hoping someone with a 3D printer might be able to help.

Chris333

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Re: Making replacement gear
« Reply #7 on: January 06, 2022, 04:56:32 PM »
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Well 3D print or not you still need to measure the gear.

peteski

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Re: Making replacement gear
« Reply #8 on: January 06, 2022, 05:21:29 PM »
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If you know the number of teeth and the diameter you can calculate the pitch. We had a lengthy discussion about this some time ago.  I know that @GaryHinshaw  was involved.  :)
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JeffB

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Re: Making replacement gear
« Reply #9 on: January 06, 2022, 05:42:07 PM »
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If you know the number of teeth and the diameter you can calculate the pitch. We had a lengthy discussion about this some time ago.  I know that @GaryHinshaw  was involved.  :)

Diameter of the gear/# of teeth + 2 = tooth pitch (for metric)

Example: a gear with a diameter of 5.1mm / 15 + 2 (for a 15 tooth gear) = 0.3(mod)

For Imperial/DP gears:  1/(Diameter (in inches)/# teeth + 2) = tooth pitch (DP)

Example: 1/(a gear with a diameter of 0.3055"/20 + 2 (for a 20 tooth gear) ) = 72(DP)

Basic math...  Getting the correct pitch is dependent on how accurately you measure the OD of the gear (as well as how accurately it was manufactured).

Jeff

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woodone

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Re: Making replacement gear
« Reply #11 on: January 06, 2022, 06:55:36 PM »
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I understand the gear data. This happens to be a 17 tooth spur gear. So when you measure the OD you are going to be a bit small in diameter be cause you are not measuring exactly 180 degrees from one tooth to the other. One side of the miic will be setting in a valley. Do not know how far off that could be.
Pete- the gear discussion we had earlier was about gear ratio using a planetary set up not quite the same here?
I can not even measure the root diameter because my indicator hits the sides of the teeth before it contacts the bottom.
Not going to grind on a $100.00 indicator so the tip would fit between the teeth.
Thanks Ron I will see if they can help.

SkipGear

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Re: Making replacement gear
« Reply #12 on: January 06, 2022, 09:00:55 PM »
+1
I think you may be making this more difficult than it needs to be. Measure the outside diameter, count the teeth. You can assume that if it ends up very close to a common module/pitch, it probably is.

The gear below although slightly simpler was done by measuring the diameter, counting the teeth, then eyeballing it to see if it looked right. Worked right on the first try, although I did make 3, one 5% smaller, measured size, and one 5% bigger just in case.




« Last Edit: January 06, 2022, 09:03:55 PM by SkipGear »
Tony Hines

peteski

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Re: Making replacement gear
« Reply #13 on: January 06, 2022, 11:16:30 PM »
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I understand the gear data. This happens to be a 17 tooth spur gear. So when you measure the OD you are going to be a bit small in diameter be cause you are not measuring exactly 180 degrees from one tooth to the other. One side of the miic will be setting in a valley. Do not know how far off that could be.
Pete- the gear discussion we had earlier was about gear ratio using a planetary set up not quite the same here?
I can not even measure the root diameter because my indicator hits the sides of the teeth before it contacts the bottom.
Not going to grind on a $100.00 indicator so the tip would fit between the teeth.
Thanks Ron I will see if they can help.

I thought we had a discussion about how to calculate the gear module.  Maye it is buried in that planetary thread? Either way you have been provided with the formula to calculate the module earlier in this thread.  The accuracy is not vital when you measure the OD of the gear.  Why? Because most gears use standard module, so if the calculation resulting from your measurements result in some "oddball" module value, you should be to round it of the the closest standard value.

As for measuring the gear, can't you remove one of the gears out of the gear case? Or are the gears melted so badly that there is not enough undamaged outside diameter to get a measurement?  Can you at least get a tooth count?  If yes, then measure one of the other gears the damaged gear meshed with -- it will have the same module as the damaged gear.  And if you have module and tooth count, you can get a replacement gear made.
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Lemosteam

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Re: Making replacement gear
« Reply #14 on: January 07, 2022, 09:36:55 AM »
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Without knowing the pressure angle and the pitch circle diameter, I'm afraid one is still guessing.  The pressure angle is what determines to tooth tangent to pitch resulting in tooth curvature; OD and number of teeth is simply not enough to know the true mesh.  As the pressure angle decreases the contact face of the tooth becomes more pitched.

Also one cannot measure the diameter of an ODD number of teeth.  Liken it this way, if you measure a three legged stool, you will measure from the tangent of one leg to a line between two tangents of the other two legs, I.e, a flat spot, which will skew the measurement.

Not saying you can't come close, but you really are just guessing, and there really is no way to determine if the mesh is English or Metric without an optical comparator, or measuring across pins of a very specific diameter.

Yes, I used to design Ford Tractor (now New Holland) transmissions many moons ago.

See the image below to truly understand all the the dimensions that are necessary to 3D model a properly meshed (teeth actually touching at the pitch circle) spur gear.