German Involute Spline or Gear?? 3

[wratchet]

Hello all,
I've come to you guys, because I don't know where else to turn. Hopefully someone can steer me right?

I have a small DC Motor driveshaft that has, what I'd call a spline, machined into the steel shaft. It drives a set of planetary gears in a wheel gearbox. For the life of me, I can't seem to figure out what it is. Of course, I haven't dealt with gears that much anyways. Mostly the diametral pitch gears.

The dimensions that I find are as follows; the outside diameter is 17mm. The minor diameter at the base of the (gear) is about 12.5mm. I'd estimate the distance tooth to tooth to be about 3.75mm and the overall depth to be about 2.25mm, measured with a flat rule. I'm told there is a DIN standard called 5480 and that may apply here I don't know.I know it has an involute shaped tooth because I can see the curve of it. The module (pitch) appears to fall between 1 and 1.25, using a profile print that I got from Maryland Metrics site. I can place a 60 degree thread gage right in between the teeth, so I believe it is a 30 degree pressure angle.

Right now I'm considering making a flycutter to mount in a Bridgeport and grinding a cutter to match the tooth shape from a 1/4" lathe knife and trying to cut it this way with an indexer. May work, I don't know.

Does anyone here have any experience with this sort of thing? If you can help me out, you'll have my undying gratitude.

Best regards, wratchet.

 

[israelkk]

If it drives planetary gear set it is probably standard 1mm module 20 degrees involute pinion and not a spline. I assume it has 15 teeth? You can use AGMA metric 1mm module 20 degrees involute to hob such a pinion. It is best done on gear cutting (hobbing machine) and not a milling machine if you need accuracy. I believe you need accuracy if it drives a planetary set.

 

[dinjin]

It could be either a long addendum 14 tooth pinion or a standard 15 tooth pinion and probably cut with 20 degree pressure angle hobs. Like Israelkk, I thinkg too it would be a 1 module design.

 

[mfgenggear]

wratchet

how many teeth?
does it roll in the planetary or is there an internal spline
it mates with that is in a gear that rolls with the planetary? I think a better discription is required.

can you measure span over 3 & 4 teeth with caliphers.
report the # of teeth in the span & the distance of the span.
the diffrence between the 2 span checks is the base pitch.

base pitch=Pi/P*(cosPA)
then P= (pi*(CosPA))/base pitch

PA=pressure angle of gear
p=diametral pitch

can you make a dentist mold of the tooth space
an try to measure the angle in an optical comparator.
it will not be exact but will give a close idea.
try to measure at the midway point of the tooth diameter.
the best place to measure is at the pitch diameter.
here at my shop the gear would be measured in an involute
machine to verify the correct Diametral pitch & Pressure angle.
You need to roll against the mating part. It should roll smooth with no interference.

for ref only
OD = #T+2/p if standard.
so for a std gear the #T+2/od =DP

#T= # of teeth
OD= outside diameter of gear
p= diametral pitch

for modual = mod = 25.4/p

 

[wratchet]

Hey thanks guys for your input. Yes, I'm sorry I forgot to put that down, had my stupid hat on I guess.

It is a 14 tooth gear. It does turn in between 2 gears which then are coupled to other gears within this geartrain. The measurements over tooth to tooth is about .190". Between 2 teeth is about .307". Between 3 teeth is about .420". We do not have an optical comparator on site, so that option is out. I have been told it works out closely to a 24 diametral pitch/20 degree pressure angle and I do have a gage from Boston Gear and it does fit pretty closely, although you can tell it is a little off.

If you need more info. don't hesitate to ask.

Best regards, wratchet.

 

[mfgenggear]

wratchet

your measure base pitch = .113

looking at ash gear catolog #96 page I-156
base pitch charts, according to your measurements
the closes base pitch standard is .1136
which = 26 DP 20 deg PA

now what Israelkk & dinjin have said it could be a 1 mod
which is 25.4 DP. but the base pitch for 1 mod =.11622565.
to have your gear roll correctly it must be a straight involoute.

there was a good discussion at meshing with gears
on how to flycut a gear. but I do not recommend it.
I would recommend EDM the gear use dummy parts to
fab & roll check against the mating parts if you can.
check the span measurement against the sample part.
then make good gear.
request .0005 max recast layer,bead blast & buff the recast layer off. for 1 part that should be acceptable.

 

[wratchet]

Well I could be off slightly on my measurements. .003" would not be out of the question here. I simply placed my calipers across the teeth and rolled the shaft like it was turning and that's what I got.

I'm sorry I don't have the means to do the above mentioned process. I'll only be able to weld in a new stub shaft and work from that. We have limited tools available at our disposal at this shop. Bear in mind that this gear is machined directly into the motor shaft and is not a stand alone gear, so to speak.

I'm basically just trying to make a decent repair and really need to determine what the module is. It just wasn't working out using the available tables that I have access to. I figured maybe someone on this site has dealt with this type of thing before.

Regards, wratchet.

 

[mfgenggear]

then it will be trial and error.
cut some gear samples before cutting the gear on the shaft.

most shops don't have EDM facilities, I recommend to
subcontract it out, better yet sub contract the
gear out to gear shop.

 

[dinjin]

What is the name of the manufacturer and model number
of this machine. If it is made in Germany, you can be almost be certain it is a module design. If it is made in the States, it is more than like a dp design. Do you have
access to any 1 module pinions with teeth either 11, 12, or 13 teeth? If so, will they roll ok in the internal gear?

 

[wratchet]

It is a German made machine and I would assume that the gearing would be a module system. The only gears I have available are the ones that mesh together with the existing gears.
Isn't there any formulae for making a determination as to exactly what this gear is? Or is the standard different for this type of gear?
I printed off a profile of the module rack gears from a Maryland Metrics site and cut out the profile with scissors and the M1 seems to be the best fit, although the measurements that they show don't coincide with the gear that I have, but this is for a "rack" tooth and not an involute, so I would expect some deviation from that.
I believe this to be an M1 module tooth. As far as the diametral pitch, the 24 seems to be the best fit with the 20 degree pressure angle.For that I do have a gage.That's the best I can do.

Regards, wratchet.

 

[dinjin]

The fact that it is a 14 tooth cut on a 15 tooth blank
shows that it is special as to center distances. The other parts may be standard but no guarantee. If you can find a rack of 1 module and run it across the external gear, it should roll without interference with it. You could call the manufacturer for the information. Almost anyone with any gear knowledge could draw you the 14 tooth pinion or provide you with the information that you need. Racks are by nature straight and not involute but roll across external gears without interference.

 

[mfgenggear]

wratchet

I tried the best way to help you.
but because you are limited on tools,
that really limits your capabilities.
like dinjin said if you could some how roll test
against some known gear this will help you.

can you check the span measurement over 3 & 4 teeth
on the other gear that meshes with the pinion gear on the shaft.
try to take span (cord measurement) carefully
try a few times until it repeats.

recheck the base pith of the pinion carefully.

the base pitch has to be exact for Modual & pressure angle.
the base pitch must be the same as your for new part.

If i had your gear I would check it on an involute inspection machine to verify the correct pitch & pressure angle. &/or roll with an other known gear.
Unless you have a known gear or rack, the base pith is your best bet.

 

[juergenwt]

m = module. A m1 is not a 1mm. m1 means that 3.14 goes 1x into
the pitch measured along the pitch circle.
So set your caliper to 3.14 and hold it over the teeth. If it reaches from tooth center to tooth center (I know this is not 100% accurate because the pitch dia curves but it will give you a pretty good idea where you are), you have a metric m1 gear.
Get out your MH and with the knowledge of the number of teeth and the OD you can than figure out everything else.
One more thing: If it is metric don't try to mix it with inches.
m = P/3.14 (in mm)
P = m x 3.14 (in mm)
P/m = 3.14
Outer dia = (number of teeth + 2) x m.

 

[israelkk]

juergenwt

This gear is not standard it has a profilr/rack shift. Your formula for Outer dia. is incorrect for gears with rack shift.

 

[juergenwt]

israelkk-you seem to know so much more than any one of us and I appreciate your input. This does not seem to me like a big project, but could you explain profilr/rack shift?
And why?
I don't think it matters to "wratchet", but I would be inrested. Does rack shift have anyhing to do with "tooth width"? Thanks.
Why is my formular for the OD wrong? What would be the correct formular?

 

[mfgenggear]

actually Buckingham & Vogul
both have nice books on the subject
enlarged pinions & recessed gears.
It is true that non standard gears will deviate from the standard calculation.
The major diameter is generally larger.


It would be great to start an other post just on this
subject alone.
know the fit form & function would help to help us know
how to make you better gears.

I am at the manufacturing end.
and I have to calculate the whole depth of the Hobs or cutters to properly cut long addendum gears.
and in addition calculate to cut gears when I have to leave grind stock on the profiles. I am an expert in this scenario
I have to be . no other choice.

but I trolled here picking up the design guys info on the subject. I am like a sponge soaking it up.

 

[israelkk]

juergenwt

As a starting point see:

Profile Shift in External Parallel-Axis Cylindrical involute Gears, Phillips D. Rockwell. GEAR TECHNOLOGY • NOVEMBER/DECEMBER 2001.

As to wratchet's problem, to my opinion the correct way is:
1. To measure the actual/designed center distance from the pinion to the mating planets of the gearbox.
2. To measure the planet gears to figure if the are standard or have a positive of negative profile/rack shift too.
3. To re-design the pinion with the correct profile/rack and AGMA/ISO/DIN accuracy to achieve the desired backlash.

 

[israelkk]

juergenwt

Profile Shift in External Parallel-Axis Cylindrical involute Gears, Phillips D. Rockwell. GEAR TECHNOLOGY • NOVEMBER/DECEMBER 2001 is downloadable here:

http://dim.usal.es/eps/im/roberto/inves/conversions0306.pdf

 

[juergenwt]

Israelkk - Thank you.

 

[israelkk]

juergenwt

The downloadable file is not the Profile Shift in External Parallel-Axis Cylindrical involute Gears, Phillips D. Rockwell. GEAR TECHNOLOGY • NOVEMBER/DECEMBER 2001 article, but it deals with the rack/profile shift calculations too.