Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Default Fixing oversized gear issues?

I am assembling some complex drive gearboxes for a 150 lb competition
robot. The gearboxes use 24 DP gears from Martin Sprocket, Boston
Gear, and Stock Drive, all high quality components. The one part that
I did not supply myself is the drive pinion from the 12 volt motor,
which is an 8mm shaft with a 2mm keyway. Prior to this year, I have
always used supplied pinions from Martin Sprocket (reamed and broached
by a third party supplier), which have been the same high quality as
the rest of the gears . However, this year, due to availability, I am
using pinions from a different supplier, which are of much lower
quality, most likely machined from gear bar stock.

The main problem is manifesting itself in that the low quality pinions
seem to be slightly over the correct pitch diameter, making proper
meshing difficult. Furthermore, the pitch diameter seems to vary
along their length, which makes it difficult to be consistent across
the 8 different gearbox parts.

My question is what is the best way to reduce the size of just one
gear. If the poor meshing was due to an undersize center-to-center
distance, I would simply apply some fine abrasive compound and run in
the gearbox, dissasemble, clean, and lubricate. However, in this
situation, I want to target only the low quality gear, and not the
high quality gear with which it meshes. Additionally, two pinions
actually drive this gear (two motors feed into a single gearbox), and
I need to target them individually to get the least binding with as
little backlash and slop as possible. I could individually locate the
high spots on each gear and attend to them with needle files and
scrapers, but this is extremely labor intensive for all 8 pinions, not
to mention the time and labor to disassemble and reassemble the
gearboxes several times.

Any suggestions would be much appreciated
Thanks
ww88
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Default Fixing oversized gear issues?

In article
,
woodworker88 wrote:

The main problem is manifesting itself in that the low quality pinions
seem to be slightly over the correct pitch diameter, making proper
meshing difficult. Furthermore, the pitch diameter seems to vary
along their length, which makes it difficult to be consistent across
the 8 different gearbox parts.


First option - bite the bullet and order some good ones, even if it
means boring them out yourself.

Second - set up a sacrificial good gear and the 8 pinions in a dedicated
grinding setup, apply abrasive, and run for a while - but this requires
disassembly, reassembly, "cut and try" and building a new fixture, and
getting another good gear. If I understand grinding theory correctly, a
softer "good gear" material should embed the abrasive and grind the "bad
gears".

--
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Default Fixing oversized gear issues?

On Feb 11, 5:10 am, Ecnerwal
wrote:
In article
,

woodworker88 wrote:
The main problem is manifesting itself in that the low quality pinions
seem to be slightly over the correct pitch diameter, making proper
meshing difficult. Furthermore, the pitch diameter seems to vary
along their length, which makes it difficult to be consistent across
the 8 different gearbox parts.


First option - bite the bullet and order some good ones, even if it
means boring them out yourself.

Second - set up a sacrificial good gear and the 8 pinions in a dedicated
grinding setup, apply abrasive, and run for a while - but this requires
disassembly, reassembly, "cut and try" and building a new fixture, and
getting another good gear. If I understand grinding theory correctly, a
softer "good gear" material should embed the abrasive and grind the "bad
gears".

--
Cats, coffee, chocolate...vices to live by


Alright, I was thinking about doing that. I can bore out new ones,
but what would you suggest doing about the 2mm keyway? The new
pinions are a press fit onto the motor shafts (the old ones had
setscrews) and they seem to be holding, although those are still also
keyed as well.
Thanks, ww88
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Default Fixing oversized gear issues?

In article
,
woodworker88 wrote:

Alright, I was thinking about doing that. I can bore out new ones,
but what would you suggest doing about the 2mm keyway? The new
pinions are a press fit onto the motor shafts (the old ones had
setscrews) and they seem to be holding, although those are still also
keyed as well.
Thanks, ww88


Enco has a 2mm broach for $38.63
McMaster wants $40.93
MSC wants $43.34

Bushing looks to be another $10 or so. Add another couple of bucks worth
of stuff and use the February free shipping code from Enco.

Members of the crude expedient club have been known to file a keyway, in
a pinch. Not that anyone else in this high-falutin' newsgroup would
admit to stooping so low...

--
Cats, coffee, chocolate...vices to live by
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Default Fixing oversized gear issues?

On Feb 11, 9:45 am, woodworker88 wrote:
On Feb 11, 5:10 am, Ecnerwal
wrote:



In article
,


woodworker88 wrote:
The main problem is manifesting itself in that the low quality pinions
seem to be slightly over the correct pitch diameter, making proper
meshing difficult. Furthermore, the pitch diameter seems to vary
along their length, which makes it difficult to be consistent across
the 8 different gearbox parts.


First option - bite the bullet and order some good ones, even if it
means boring them out yourself.


Second - set up a sacrificial good gear and the 8 pinions in a dedicated
grinding setup, apply abrasive, and run for a while - but this requires
disassembly, reassembly, "cut and try" and building a new fixture, and
getting another good gear. If I understand grinding theory correctly, a
softer "good gear" material should embed the abrasive and grind the "bad
gears".


--
Cats, coffee, chocolate...vices to live by


Alright, I was thinking about doing that. I can bore out new ones,
but what would you suggest doing about the 2mm keyway? The new
pinions are a press fit onto the motor shafts (the old ones had
setscrews) and they seem to be holding, although those are still also
keyed as well.
Thanks, ww88


Depending on the torque being transmitted, you could file off the
keyway and produce a flat on the motor shaft. The pinion set screw
would press on the flat.

I have bought good quality gears from QTC in New Jersey; price was
quite reasonable: For M 1 module pinions (just a little smaller teeth
than 24 DP) the price was less than $10. Enlarging the pinion bore
without affecting the concentricity between PD and bore took some
thought but can be done if you have a lathe and face plate.

I bolted a piece of aluminum plate to the face plate and drilled/
bored a counterbore for a light press fit on the gear OD. Pressed the
pinion into the bore using the tailstock. Added 2 small finger clamps
to hold the pinion tight in the bore... Since I was curious about the
concentricity between the gear OD and its bore I checked with a dial
indicator: The indicator needle did not move perceptively and I was
happy. Then drilled to 7/16" and bored to 12 mm. Had to buy a 3 mm
broach for the keyway. Since these were change gears for a hobbing
machine the keyway was necessary.

You can lap the gears for improved running smoothness. But you should
use an appropriate non-embedding abrasive that breaks down after a
short period of use. Powdered turkey bone is one such material,
another is the old domestic cleaning powder named "BON AMI". I found
some at a flea market.

Trust this helps.

Wolfgang


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Default Fixing oversized gear issues?


"woodworker88" wrote: (clip) the low quality pinions
seem to be slightly over the correct pitch diameter, making proper
meshing difficult. (clip)

^^^^^^^^^^^^^^^^^^^^^^
The pitch diameter of a gear is not a fixed number. It is determined by the
center-to-center distance of the gears and the gear ratio. IOW, the two
pitch circles adjust so they roll on each other. If the pinion is slightly
too large, you might be able to solve the problem by just moving the drive
motor out a little. This will work, but it will depend on how the motor is
mounted whether it is practical.


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Default Fixing oversized gear issues?

On Feb 11, 10:39 am, Anthony wrote:
Members of the crude expedient club have been known to file a keyway, in
a pinch. Not that anyone else in this high-falutin' newsgroup would
admit to stooping so low...


I've file one or three in my years of working with mechanical things, in a
pinch. If you have good files, and patience, you can actually get a very
good keyway with this method, getting it started straight is the worst
part.


Alright, I may do that. Lots of good suggestions, I'll try them out
and see what works the best.
Thanks again,
ww88
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Default Fixing oversized gear issues?

On Feb 11, 9:35 pm, Bruce Spainhower
wrote:

Timesaver lapping compound is a commercial product with the properties you
describe:

http://www.newmantools.com/lapping/time.htm

No affiliation. It was just the result of a search I did about a month ago
when I needed to deal with some tight gears for a project.


Looks like good stuff to me. Did you buy it directly from them or
through someone else?


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Default Fixing oversized gear issues?

woodworker88 wrote:

On Feb 11, 9:35 pm, Bruce Spainhower
wrote:

Timesaver lapping compound is a commercial product with the properties you
describe:

http://www.newmantools.com/lapping/time.htm

No affiliation. It was just the result of a search I did about a month ago
when I needed to deal with some tight gears for a project.



Looks like good stuff to me. Did you buy it directly from them or
through someone else?


Auto parts stores. Another brand to ask for is Clover. Ask for valve
grinding paste or valve grinding compound.

Cheers
Trevor Jones

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Default Fixing oversized gear issues?

In article tmCsj.21444$w57.15734@edtnps90,
Trevor Jones wrote:

woodworker88 wrote:

On Feb 11, 9:35 pm, Bruce Spainhower
wrote:

Timesaver lapping compound is a commercial product with the properties you
describe:

http://www.newmantools.com/lapping/time.htm

No affiliation. It was just the result of a search I did about a month ago
when I needed to deal with some tight gears for a project.



Looks like good stuff to me. Did you buy it directly from them or
through someone else?


Auto parts stores. Another brand to ask for is Clover. Ask for valve
grinding paste or valve grinding compound.


Be careful. The "valve grinding compound" one gets in auto parts stores
is carborundum grit in some kind of water-based gel, and does not break
down into harmless stuff. The standard maker is Permatex. One must
carefully wash all traces of the grit away.

Joe Gwinn
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Default Fixing oversized gear issues?

woodworker88 wrote in news:58ca7768-f27a-4064-80f0-
:

On Feb 11, 9:35 pm, Bruce Spainhower
wrote:

Timesaver lapping compound is a commercial product with the properties you
describe:

http://www.newmantools.com/lapping/time.htm

No affiliation. It was just the result of a search I did about a month ago
when I needed to deal with some tight gears for a project.


Looks like good stuff to me. Did you buy it directly from them or
through someone else?


Got it through a Model T parts house, the yellow stuff, for lapping softer
metals. Pretty common for fitting babbit bearings in old engines. I needed it
for both the cam bearings and the cam gear.
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