Diameter?

...

That's going to be a challenge in plastic, I don't think 3D will give you the strength you need that Delrin would provide.

Maybe a metal sintering 3D print would do.

Brass

A brass 3D print from Shapeways would certainly outlast anything plastic or resin.

Laser Cut

Possibly laser cut from acrylic?

Cut the gear and hole, then added the boss as a separate piece.

I have move gears for my turntables this way.

Howard Garner

Got Gear?

Hi Bernd,

Have fun! 

Answer to the gear problem

I appreciate all the answers to the gear problem. I've solved it by doing a casting using the original gear. Here's how I did it.

Using clay I made a small holder for the silicone rubber. Note that I filled in the missing teeth with clay.

I then mixed up a batch of Smooth-On OOMGOO 30 (tm) Tin-Cure Silicone Rubber.

Once the rubber had cured (the next day) I removed the clay. Note the extra portion of clay that left a cavity where the two teeth are missing.

The gear was removed and turned 180 degrees so the missing teeth could be added to the mold.

Next a dam was built up to contain the liquid rubber. Enough rubber was poured to cover the top of the gear.

The rubber was shaved off the top of the gear using a razor blade. Just enough was removed to uncover the top of the teeth.

I was a bit sloppy on this mold. The result was one tooth cavity was blocked. I discovered this after I poured the resin and pulled the mold.

In my hast to cast a gear I made a mess. I should learn to be more patient.

So here's the first cast gear using the original as a master with that one tooth missing, plus a large lump of resin on the other side of the gear. Haste makes waste.

Second try. Made a new smaller mold using the clay.

Poured the silicone rubber.

Pulled the mold from the clay.

Trimmed the excess rubber from around the gear.

Note that the bore does not have any silicone rubber in it. The mold looks like it'll work. No filled in tooth cavities.

Gear gets turned 180 degrees for the second pour to fill in the missing teeth.

The cavity is filled carefully with the liquid rubber and the bore is filled also.

Once the rubber is cured the excess is shaved away exposing the side of the gear.

And a much better mold has been created.

This time I made a small dam to contain the resin. Really didn't need it. The resin used is Smooth-Case 320 fast-setting - off-white resin from Smooth-On.

And the first good gear. Note that the bore has a D-section in it. How many missed that from the first picture?

I made a fixture to hold the gear so I could remove the excess resin on the back of the gear.

Two gears and the original ready for a try out.

I hope I've shown that sometimes a simple solution to a problem is staring you right in the face. All the suggestions made would probably have been cost prohibitive or to time consuming. I've tried Sketchup several times and find it a very hard program to master. So 3D printing was out from the start. The gear is a very coarse tooth type that I don't think NWSL would have in stock or even be able to cut. Sometimes the best method is to try and use the original to make a master mold and then make copies. So would this come under craftsmanship, skill, or just years of experience from being inquisitive of how things are done and a bit of critical thinking?

I hope some will take this idea and apply it to a solution to a problem they have run in to.

Bernd

Strength?

How strong is that resin compared to the original gear?

How Strong?

I'll find out once the resin has cured to it's full strength and it gets installed in the item the broken gear came from. All I wanted to show was how something can be made if other options take more time or are not cost effective. This may not work at all in the application. It could be a solution for other items that need replacement. I'll post the results once the gear is installed. Right now I question of how true the gear will run. This is just the beginning of solving a problem.

Bernd

Creative thinking - kudos to you

Sometimes the simplest solution is staring right at us.   Kudos to you for your ingenuity and cleverness.

Kudos +1

Kudos again. I like how you thinked "outside the box" of fixing your problem & the steps you showed us  to make a mold off the original one.

You're Welcome

Bob & sn756krl,

Thanks for the kind words. This method can be used for other things besides gears. It can also be used for non-model railroad fixes.

Bernd

Now to lost-wax it?

Dear Bernd,

Nice work as always  

As far as "will the resin one be strong enough?",
you've got 2 resin castings, so if you test one and find it fails,
the other can possibly be used as the master for a "lost-wax" conversion into brass?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS Agreed Sketchup can be agravating, but with AutoCAD Fusion 360 being free,
I found it much more "intuitive" to a geometric and measurement-minded bod...

Dear Prof_Klyzlr

I haven't mastered brass casting yet. I've been wondering if aluminum casting would be possible. Only need 1100 - 1300 degrees F (593 - 704 degrees C) to melt. I've done that before. If only there would be some model casting shops in the area like in England. I'd be all set. Thing is this is just a one time fix from what I gather from my friend.

Am looking into table top plastic injection. Cost for a machine isn't that bad. Uses epoxy molds.

BTW, thanks for the kind words. Much appreciated.

Bernd

Had to give it a try in

Had to give it a try in SketchUp.

I am off on the tooth thickness and depth. (Guessed the dimensions)

For myself, I find SketchUp works better with larger objects, so I usually enlarge the subject, in this case by a factor of 100, and then scale it back.

It would be interesting to see how long PLA would last as a gear.

Great solution for a gear replacement.

Eugene

@ Eugene

Looks pretty good for no dimensions. I use a program called DesignSpark Mechanical 2.0. The program uses real inches/mm for dimensions. I've used it to draw a TT scale caboose body. I'm better at just putting something together as my mind sees it.

Thanks for the kind words.

BTW I tried the gear out on the subject project. It's a round circle of plastic about 3 feet in diameter with a painted track. The mechanism uses a magnet underneath to pull a train around. Think of a Christmas Tree layout. All toy like. The gear wobbled just a bit but it worked. So the project is a success as far as making a gear. Now the time test. How long will it last. I'll keep the mold around just incase it needs another gear.

Bernd

Bernd..........your ingenuity always

.........makes me smile.  "Necessity truly is the mother of invention" isn't it.  I love it and hope it works.  Hmm, why not melt down some old Delrin trucks and try your mold.  It has to melt at less than 1100 degrees!

Peter

@ Peter

Hi Peter,

Thanks for the come back. Yes, necessity does make you look for ways. It's working. Placed the gear on the shaft, not quite a perfect fit and a bit of wobble but it worked. I had expected to see teeth coming off. Now for the "how long will it run" test.

Melting Delrin, Mmmmm, might have to try that.

Bernd

I suspect that if it is an

I suspect that if it is an accurate copy it should be fine. I am saying that as for years American cars were made with large displacement v8 engines that had a nylon timing gear. Those things typically ran for more than 100,000 miles before needing replacement. I suspect the loading by chain and the weight of the cam was much greater than anything that a model locomotive will see. I know there are differences in material but I would be surprised if it did not work out well.

The engineering plastic Delrin also sounds like a good choice to try as well.

Something to look into...

This is something I need to look into.

I recently bought a Bachmann 44 tonner (to use with my Boxcab Diesel... I eventually went with a Bachmann 70 tonner, as it had exactly what I needed)

Anyway, when I broke the plastic off of the box, opened it up, there was a beautiful, shiny, new Spectrum 44 ton diesel! Single motor, DCC (no sound)

I put it on the program track, everything checked out, so i placed it on the layout!

*bump* *bump* *bump* < stop> *grind*

All four gears on each wheel set was cracked. The "Life Like Bump"... on a Bachmann!

So I checked with Bachmann, and surprise, surprise... they don't have replacements. (they have replacements for the new, third gen, but third gen won't work on first, or second gen, and mine is second gen)

So I did some research, and only ONE company makes replacement gears, and that's NWSL.. can't find them on their site, but they are readily available on eBay for... $49.99.

I paid $30 for this diesel, and to be honest, as it stands, it's really only worth about $25 to me... it isn't my era, but, i would like to run it... but $50 for four stupid gears!?!?! I don't need the wheels that come with it, just the stupid gears!

So I may have to figure out a way to make my own gears from the old... or... find someone with replacements more in the $10 range (and even then, $10 is steep for such small things, but, reasonable, as I would suppose there wouldn't be a huge demand)

After Typing...

I did a search a few minutes ago, right after posting my last missive, and I found hem on NWSL... for $39.95...

So, yeah... never mind on those. Shapeways has them for the two motor, so... maybe... the price is low enough I suppose... but it does warn that a lot of tuning will be needed. In the box this loco stays, probably.

Call it a someday project

Call it a someday project warflight. If you can get the gears you can build the thing. NWSL gears will be much better than anything from the oem guys. Tuning it should be no issue after those tiny steamers you just did. Besides with your movie set theme and the period pieces you are working on would you not need something different as the movie set mule?

Cracked gears

@Warflight, Bernd did a thread on those cracked gears, his was an Athearn blue-box, but the ideas should be applicable, check it out here: https://forum.mrhmag.com/post/cracked-gears-12192527

EDIT: removed errant word from my statement.

@ Jim

I also mentioned in that thread that it wasn't a 100% fix. There still was a slight bump in the gearing.

Bernd

@Bernd

Didn't remeber that it wasn't 100%, thanks for noting that here as well.