A new product?

Ideas

A lot of folks in the large scale crowd (yes, they have cracked gears to deal with as well) wrap a few turns of fishing line around a cracked gear, then secure it with super glue.  It seems to work well for them, and has the advantage of needing no measurements at all.  I don't know how well it would work in the smaller scales, though - would there be enough material to bind the crack properly?

If you cast collars, how will you deal with the problems of different diameters?  I see two possibilities - either cast the collar with internal teeth capable of biting into a variety of diameters (don't know how well that would work) or include/sell a tool to shave the outside diameter down to a pre-determined diameter.  You know more about tooling than I do, but I'm thinking it could be as simple as a tube with a bore of the correct diameter, a tapered opening, and one or more slits in the side to form a cutter.  Ideally it would have a shank which a modeler could chuck into a pin vise or Dremel tool - 1/8" diameter, I believe.

3d printer

Would the output of a 3d printer be accurate, smooth, and robust enough to work for this application?

Charlie

Good ideas coming in

@Rick,

I've got some ideas about casting. I'll keep you posted as to progress.

@Ken,

That fishing line sounds like an interesting solution. It would be interesting to see if it would work on HO scale models. I'd be afraid the glue would seep through the crack and plug the hole or getting glue on the gear. Again remember it's a smaller scale. Also not knowing the make of plastic used, ACC glue might not stick to it.

I have some ideas on the casting part. Need to pursue that idea.

You can use a tapered reamer of the proper size.

Your idea of a collar with teeth gives me an idea of using something similar used in wood working. It's called a plug cutter. Question is could one be built small enough to work properly.

@Charlie,

Another idea that could possibly work. But, like I said, the diameters are different size. As much as .012" difference. You'd still need to correct that diameter.

Well the brain is working on some ideas. Give me some time and I'll see what I can come up with. I'm trying to keep it as simple as possible for the guy that doesn't have the tooling.

The ideal setup would be a tool that takes the hub to a definite diameter and then provide collars that fit that. Something to contemplate.

Bernd

Hopefully as simple as possible would include...

not having to remove drivers/wheels from the axle to get the reinforcing device in place.  This would be particularly welcome if the loco is a steam engine.  Also, what are the odds any such device will be compatible with the variety of frame designs out there?

I just thought od something else that might work.

I've noticed new cars are using a large shrink tubing instead of clamps on all of the coolant hoses.  I'm wondering how it would work to put small pieces of heat shrink tubing around the axle mounts, and shrink it with a soldering iron or gun to control exactly where the heat is applied so that a flame doesn't melt the gears.

Fishing line

As I understand it, the fishing line does the work.  The ACC is only there to keep it from slipping off or unraveling.  A small drop ought to do the job, and prevent the glue going where it's not wanted.  I expect that the only way to know would be to test the method.  I know it works well in the larger scales, but I've never seen it done in HO.

Other models

The trouble is that the axle forces the cracked gear open.  Removing the axle allows the crack to close, and then you need to find a way to clamp it in that position.  That's why a collar works so well, and why something as simple as fishing line can do the job.  All you need is something which will not stretch.  Then the gear can properly grip the axle again.

Also, I've never seen this problem on a steam loco.  If it did occur, it would presumably be on a flat gear which has no place to put a collar.  In that case, replacement is probably the best option - but even if the gear could be repaired it would still require removing the gear from the axle.

As far as I know, this seems to be a problem specific to all the Athearn-style trucks out there.  It should work in any of them, as they're pretty much identical internally.  It's not likely that other completely different truck designs would use gears with the same diameter collars, so they would need different parts to repair them.

Miniature plug cutters and insurance

That's exactly the tool I was thinking of.  I have no doubt that it could be made - but how difficult would it be, and would it be worthwhile?  It seems to me that being able to make all the gears the same size would allow a single accurately machined collar, which would be the strongest, simplest, and most efficient arrangement.

Also, a thought.  If you can come up with a simple DIY kit, you might be able to market it as a preventative measure.  A gear with a metal collar is not very likely ever to crack, and if the parts are less than $10-20, you could probably have a large group of people interested in buying them as insurance.

Great ideas

We've got some great ideas flowing in. That's great.

@ Russ,

I've got some heat shrink tubing. I'll give it a try and see what happens. If that works it would be the easiest and simplest solution to the problem. I'll give it a try tomorrow.

@ Ken,

I discovered that the plastic used on the axles must be a delerin or nylon. Plastic weld glue will not touch it. ACC didn't fare much better. Interesting that the ACC holds the fish line. I think it's made of nylon, isn't it?

The collar I'm using in the picture is a piece of turned aluminum. I was in the process of making up a simple mold that would let you make a tube out of a fiber glass resin. When cured you can then cut off slices to put on the stub. Not as tough material as aluminum but might work. I figure if the bore of the cast tube is a bit tight one could use a piece of sand paper and open the hole until the collar fits.

Ok time for my Wednesday night shows. More on this tomorrow.

Bernd

How about a snap ring?

Could you make one of these that fits around the cracked axle?

Just put the split opposite the crack.  It should be able to handle a slight variation in diameters, and I doubt the slight imbalance would matter.

Lots of effort.

   The P2K cracked axle gear was a wake up call to Walthers. They used to just send you the gears and wheels as replacement sets for the 2 axle trucks. Then Athearn, Bachmann, and even some Atlas wheelsets started cracking gears. I bought a package of 24 from Athearn for under $10 years ago. I still have a few left. None of the replaced gears have cracked.

   I have had to replace 2 of my Bowser steam loco gears and one of my BLI steam loco gears. They seem to have gotten brittle and just split. The replacements are a softer nylon instead of a hard delrin. My theory is the plastic compatible lube is not as compatible over time and some sort of chemical reaction takes place and makes the gear brittle. My 52 year old brass locos axle gear still looks new even though the plating and side rod screws wore out and needed replacing. That gear is some sort of fiber almost like Masonite. 

         Pete

Seems they all get there eventually

I have had cracked gears in almost every manufacturer that uses them. I bought a couple Kato gp 35s off ebay that had all axles cracked in both. Bad lube, age, climate? I have found the Athearn replacements are not even all the way through, there is a smaller inside dia on the side with the notch. which is generally the side the crack will start on. I run a .092 reamer through before I install them. I've seen someone use a piece of brass tube to hold these things together. 

Good Theory

I believe that is a sound theory. It is a known fact that petroleum distillates affect plastic over time. It is also a fact that plastic becomes more brittle as it ages.

We supply paint to most of the major athletic helmet manufacturers. In fact, when you watched the Super Bowl you were seeing our paint on the players helmets. Safety testing pre and post painted helmets shows amazing changes to an otherwise virtually indestructible plastic. Painting changes the plastic's properties so much that we had to develop a special product specifically for helmets to ensure they would pass impact testing for a long period of time after being painted. I am sure petroleum lubricates have a similar effect.

EVOO?

Is it just petroleum?  If so, seems a simple matter to start lubricating our models with vegetable oil and prevent the problem.

Not Sealed

Vegetable oil as a lubricant is only suitable in applications that prevent or at least minimize oxygen contact, i.e. sealed systems. Synthetic lubricants are probably the answer but doubtful you will find those used in a China made toy. Ummm... sorry, imported model railroad locomotive.

Full synthetic

I've heard once or twice that full synthetic motor oil is plastic compatible.  Wherever I read it, it made enough sense that I've tried it, and so far I haven't had any gear boxes turn into piles of goop.  What's your take on the subject?  It's certainly a LOT cheaper than the stuff we usually buy for our models.

Synthetics

I really don't know enough about the subject to speak to it but it seems to me synthetics should be a better choice because they don't contain all the different reactive moieties that organic substances do. Organics tend to react with their environment.

Nano-Oil

is ideal for our applications. They make several different grades and they are a MRH sponsor. Lots of testimonials and discussion on several threads here at MRH. The oil I won on the first contest is definitely helping the engines I've changed over to run quieter and I think smoother. I don't have an ultrasonic cleaner so I use toothpaste to clean my gears before I use the Nan-Oil. I'm sold and plan on purchasing additional weights when the Department of Finance is looking the other way.

Roy

Nano-Oil

Yes, very impressed so far with Nano-Oil, and will be ordering additional weights also.

The heat shrink idea is interesting but watch the heat around those plastic gears.

In another thread someone mentioned a glue made for delrin.  That might be something to look into?

And Another Glue

Another glue for Acetal plastics from Microscale (another MRH sponser).

-Jack

External Retaining Rings

Ken,

I think you've come up with the universal fix that anybody can do. I looked at McMaster Carr and they sell a ring with the size needed, plus the tool to put them on a shaft.

Plan on stopping at the local hardware store today and see if they have something that small. I'll try it out and if it works I'll order from McMaster Carr. Details within the next week or so.

We may be on the way to a simple fix and one that any body can do without machine tools.

Bernd

Heat Shrink Tubing

Russ,

Tried some heat shrink tubing. Not very successful. The tubing still stretches after heating it and shrinking it around the axle.

Bernd

Snap rigns - off the shelf parts?

I never thought there would be a commercial product that would be a perfect fit!  I'm impressed, and I'm looking forward to hearing how well it works.  I wonder if the axle can exert enough force to spread the ring and open the crack?  I suppose it would depend on the exact diameter of the bore, so running a reamer thought it might still be required in that case.