Internal Gears, Practical Applications

[Anthony]

Went to BAEM monthly meeting yesterday . One member was asking for sources for internal gears for radial engine cam drive internal gears. For a number of existing model engine designs there appears to be interest in 64 and 65 tooth internal gears. I asked the individua l for the rest of the requireme nts. In each case he specified:
32 DP, 20 PA, approxima tely 2-3/4" OD, approxima tely 3/16" thickness, hardened steel preferred .

Even though these gears have been specified by the designers there appears not to be an available commercia l source for either gear. So the obvious question is are there any known sources for such gears? Regarding making the gears if not already available, usual practice I presume would be manufactu re with a gear shaper. Alternati vely a possibili ty is CNC milling, however, because the width of the space at the dedendum is very narrow, would an end mill small enough to fit into the space be up to the job without snapping off?

Finally, anybody here up for the job? Any idea of prices? The individua l who broached the subject and I are located in the San Francisco Bay Area, Californi a, USA, but I expect there are other persons in other parts of the USA and in the UK who might be intereste d in such gears. Being small component s, shipping anywhere should not be a problem so manufactu re anywhere should be acceptabl e.

Hoping for offers, will try to pass the informati on on to appropria te parties and fora.
Anthony

[ArtF]

It woudl take a .5mm or .02" milling bit.. Im no expert on materials or how they cut though, but it sounds liek a rough thing to mill to me.. Easy enough to make if you cut an involute cutter for it I guess..

   GM wont have involute cutter code for a few months yet I dont think..

Art

[Anthony]

How would you use an involute cutter to cut an internal gear?

[ArtF]

Anthony:

 Sorry, missed the fact it was internal. I guess that leave milling it or EDMing it out. If milling your stuck with .5mm bit.. Not a gear Id like to try cutting.. .but then Im no expert, Im just a number cruncher. .

Art

[alenz]

Could you use a CNC mill as a shaper? I’m thinking in terms of a Sherline 5400 mill. Never tried it but have heard of it being done. Mount the rotary table/blank flat on the mill table, i.e., R/T axis parallel with mill Z-axis. (That makes it the C-axis). Lock the spindle and X-axis. Use the rotary to advance to the next tooth, the Y-axis to control depth of cut and the Z as the ram. Concern I think  would be the stiffness of the mill column. By doing the cutting at the 12:00 position or as close to the mill column as possible the bending loads would be minimized . The cutter shape would be a single tooth of a spur gear which GM will already do. Maybe lots and lots of very light cuts? Thank goodness for CNC, that would be impossibl y tedious to do manually. 
Al (just thinking out loud) Lenz

[Anthony]

Looking through other threads on this forum there is http://gearotic.com/ESW/FavIcons/index.php?topic=36.0 , about half way down the page. The attachmen t is copied from the page cited above, per the posters descripti on:
"Gear is 0.1 module (254 DP) 20° PA, 42 teeth.  Cut from a piece of .025" thick Starrett shimstock ."
He also said:
"Made on an Agie wire edm machine, using 70 micron wire (.0028")."
As far as I can see it could just as easily have been made as an internal gear.

The obvious question is could this method be used for the gears I've asked about. And if so, at what cost. The market for these gears is admittedl y quite small so if somebody could do short runs, maybe less than 10, at a not outlandis h price I think the people building model radial engines would be quite appreciat ive.

So again, anybody capable and intereste d in the job?

[John S]

HPC Gears in the UK, www.hpcge ars.com do 60,63, 66, and 69 as off the shelf internal gears.
Can the design be altered to take these into account?

John S

[Anthony]

HPC Gears in the UK, www.hpcge ars.com do 60,63, 66, and 69 as off the shelf internal gears.
Can the design be altered to take these into account?

John S

No. They are part of a coaxial 1:8 reduction drive to a cam ring that runs in reverse direction relative to the crankshaf t. These are standard setups. I've forgotten all the details of the gear trains but I have a vague recollect ion that the 65 internal is used with a 13 sun and an additiona l 1.6 reduction between. Likewise, the 64 internal would have a 20 sun with an additiona l 2.5 reduction between. These are very compact gear trains and difficult to fit into the space as they are. Any starting gears can be used if you have enough space to assemble a train to alter the results but trains with no space for modifying elements pretty much need to be respected as "best solutions". Additiona lly, these are working scale models of existing prototype s and are supposed to be scaled in all elements of design.

[John S]

Rush gears do a 64 tooth internal.

http://www.rushgears.com/Tech_Tools/PartSearch5/partSearch.php?gearType=INTERNAL

[Anthony]

John,

I've posted your link to the R_and_R_e ngines Yahoo group and told the intereste d parties to make contact on their own. Thank you for your assistanc e.

[precisionmetal]

Anthony,

I'm the guy that cut the 0.1 module external gear in the photo above.

I've cut many internal gears and splines.. . from very tiny, up to very large.  All via wire edm, and often from pre-heat treated material.  I also have a #7 Fellows gear shaper, so that would be another option if I have a cutter of the correct DP/PA.

If it's something that could lead to even a short run, I'd be happy to cut a sample.

PM

[Anthony]

PM,

Please send me an email to anthrhode s at aol dot com. I'll post your message to the R&R Engine group and see if something comes of it.

Anthony