Seeking geared plastic axle

[mmagliaro]

Awesome photo and very helpful old Atlas thread! Thank you!

Yes, that is the truck.  So it looks like I'll also be getting an extra stash of 0.2 module gears.  Always nice to have.

[Sokramiketes]

Why not mill your own gears? I thought you were making everything yourself? Get an index table and do it right!

 

[mmagliaro]

Why not mill your own gears? I thought you were making everything yourself? Get an index table and do it right!

 

Um... no.  LOL!   
There are a few things I admit I am not mentally prepared to try to build.  The gears, the motor, and the headlight LED,
alas, I am going to have to buy.  I throw myself on the mercy of the forum.

[nkalanaga]

In old articles I have heard of people making their own gears fairly often, and their own motors a few times, but I defy anyone to make their own LED at home.

[Sokramiketes]

In old articles I have heard of people making their own gears fairly often, and their own motors a few times, but I defy anyone to make their own LED at home.

Yeah, the motor and LED thing is beyond reasonable scope.  But gears?  Much easier than those drivers!!  Nstars can probably advise.

[mmagliaro]

Yeah, the motor and LED thing is beyond reasonable scope.  But gears?  Much easier than those drivers!!  Nstars can probably advise.

It is possible with a rotary table and dividing plate, so I'm told.  But these are awfully small gears.
Motorman makes some of his by slicing off pieces from "gear wire" (a long stick that is basically just a long gear that you
slice like a pound cake into separate gears, but that wouldn't really be "making" it, now would it.)

No.  It is not worth it to my sense of accomplishment or my sanity to do such a thing.

[Sokramiketes]

It is possible with a rotary table and dividing plate, so I'm told.  But these are awfully small gears.
Motorman makes some of his by slicing off pieces from "gear wire" (a long stick that is basically just a long gear that you
slice like a pound cake into separate gears, but that wouldn't really be "making" it, now would it.)

No.  It is not worth it to my sense of accomplishment or my sanity to do such a thing.

[Chris333]

Yeah, but that dividing head is probably $500.

[narrowminded]

As far as making your own gears goes, here's just a little background on what's involved.  It could help with a decision and could broaden our understanding of these machine elements that we use every day. 

As referenced above, there is a product in the smaller sizes that's akin to buying all thread.  It's called pinion wire.  It is typically drawn through dies putting the tooth profile on the wire, therefore the name pinion WIRE.  As such it is most typically made in brass or also mild steel.  While it's usually in the smaller gear sizes, relative to the gear industry, to my awares it's not readily available in the extremely small sizes that we use. Numbers like 48DP and down is what's typical and we are operating closer to 100DP and up.  In the sizes available it comes with the tooth form/ pitch on the OD and solid center to be finish machined as we like.

Then there are gear hobs and gear cutters.  They are two different methods of cutting gear teeth.  The gear cutter might be described as a fancy looking, heavy duty circular saw blade and cuts one tooth at a time while a gear hob very much resembles a threading tap and cuts the teeth in a continual motion by rotating both the blank and the cutter (hob) in sync with each other, set to the ratio of the gear being produced.

In a mill with a dividing head or rotary table you would use a gear CUTTER.  It has the involute tooth profile ground in to the cutter profile and the teeth are cut by advancing the blank one tooth at a time and then cutting that tooth lengthwise.  This is how a gear can be made with basic machine shop tools, a mill, lathe, and rotary table (or dividing head).  Two problems with this are 1) cutter cost as the tooth profile must be ground involute, with a radius calculated to match the infinite angles encountered as the gear smoothly enters and exits its mating tooth in rotation, and 2) Each cutter is only good for a gear in a specific range of teeth, usually 3 to 4 teeth difference.  As can be imagined, a larger diameter gear with more teeth, even though it's of a particular pitch, meshes at a different arc than a smaller gear of that same pitch but with fewer teeth.  Even though the pitches and therefore the basic profile remains the same, the rotational meshing angles (arc) change, become more gradual with more teeth, sharper with fewer teeth.  Therefore there is only one optimal profile for any given number of teeth.   In practice, because the profile changes caused by just one tooth more or less are slight, there is a range where they can accept the profile error +/- a few teeth and the cutter will be identified with what its acceptable range is.  The fewer the teeth, the sharper the change.  So if you were to want to make 2 different gears with a measurable gear ratio change you would need two different, expensive cutters. Three gears, another expensive cutter.  Also, as can be imagined, this process is slow, takes a long time.

Then there's the gear hob.  It resembles a thread tap and is constructed very similarly.  It is run in a purpose built machine that rotates the hob and the blank at right angles to each other (basically, more later) and precisely in sync with each other at the ratio of the gear being cut.  The hob advances one tooth per revolution and has straight sided vee shaped teeth cut into it at the pressure angle of the gear teeth you'll be making.  There is no involute (radiused) form required in the cutter profile as that form will be generated in the cutting action.  The correct involute tooth form is being generated continously, by default, as the cut is performed, because the rotation of both the cutter and the blank are meshing those two faces in the exact same fashion as the gear will be required to mesh in service, cutting that form as both parts rotate.  By default that makes for a very nice and precise involute tooth profile without having to create that in the cutter's machined profile.  It is self correcting for the involute form so one cutter correctly covers any number of teeth we can physically fit in the components' dimensions. 

Now lets add one more function to the hobbing machine's functions and that's the ability to address the cutter and blank angle relationship.  Because the hob looks like a tap, that means it cuts like a tap, and if we are to have a spur gear with the teeth running parallel to its rotational center, we need to be able to set that hob at the angle that cancels out that advancing angle of the cutter (or set an angle if it were to be a helical gear we were cutting).  That angle will be dictated by the hob diameter.  These are the basic elements of a gear hobbing machine. It's purpose built so very costly initially and really only good for one thing so not a common shop tool but, if you're making a lot of gears it can easily be justified.  Once set up it'll spit 'em out like popcorn!

Now to add one more thing to this and that's how I am making the gears for my loco.  I'm hobbing them.  Because they are small and made from easily cut materials I don't need the big hogging capabilities of a serious gear hobber but I DO need those basic functions just outlined.  That's where a sweet live tool lathe comes in.  I had to make some tooling (not all done yet, more this week) to accomplish this but the hard to get functions, a spindle and separate programmable, synchronizable, live tool are already features of the machine I have access to.  I've had to make the hob and a vertical spindle holder with adjustable angles but the basic functions were there and the rigidity needed for small gears is plenty adequate, so I have proceeded.  I only made one hob for a 120DP as it's an appropriate  tooth size for all of my foreseeable needs and also my worm diameter and pressure angle is fixed based on that hob.  That means that without making another hob, I can make any (appropriate) combination of 120DP gears, spur gear or worm gear, and one diameter worm.  The setup is involved but once the basic setup is there, diameter changes are easy.  That's how I was able to make the offer I did to mmagliaro, figuring I could throw it in with a run that will be coming soon.  No, in general, I won't be and don't want to be in the custom, one-off gear business.   But when I can, I'll happily help out.

[mmagliaro]

You guys are all helping me make the case for not making gears.

Perhaps I should clarify my personal philosophy and goals of this project, and then we can just drop this.

Yes, I want to make "the whole thing myself", but what does that really mean?  It means I want to
make every part that I can, as long as I can make it with the tools I have, and end up with parts
that are as good as I could get commercially, or at least (and this is the subjective part), close enough
to the best commercial quality that it won't matter to the appearance or performance.

That concept does not include buying thousands of dollars' worth of additional machine tools in order to
make a part.  I have what I have.  As John so eloquently put it, I have sandpaper and files.
And yes, I have a small vertical mill, a Dremel, and a bunch of other hand tools.    But that's it.

[Sokramiketes]

Yeah, but that dividing head is probably $500.

The one shown, yes.  But the Sherline one is only $210 list!



Ok, I'll stop now.   

[rodsup9000]

 Max,

 If I had any extra time, I would make them for you. It's not that hard. The time consuming part would be making the cutter as they are not available. I've made a lot gear stock in .5 mod, 1 mod 40DP and 48DP.  These are 40 DP.










 

[mmagliaro]

Darn cool gear wire, man!

Yes, I looked around, and nobody makes any in finer than 0.4 mod, so I assume it's not easy and there are no readily available
cutters for it.

Thanks anyway.

[Chris333]

You can buy whole sticks like that from NWSL and cut them if you want.

[mmagliaro]

You can buy whole sticks like that from NWSL and cut them if you want.

You can?  In 0.3 module?