Micro Machining Question

[hwp]

I dabble in model railroading and I currently have two engines that have the same problem (same manufacturer, same wheel configuration [4-8-4], different road names), the drive wheels are loose from the drive axle. This is a common problem with these models. These are fairly good quality older plastic models, admittedly not brass, but worth restoring. To put this in perspective, I would be willing to pay up to $100 per engine to have them fixed properly.

The models work in a similar way as the prototypes, with one major difference. The real ones were driven by steam pistons whereas the models have electric motors. On both, power is initially transfered to one axle and then side irons are used to transmit power to the other drive whels on the same side of the engine. In order to have a reasonably smooth running locomotive, the driving wheels have to be quartered, meaning that the drive wheels have to be oriented so that the dowels for connecting the side irons are exactly ninety degrees apart from each other. In the models there is a drive gear in the middle of the axle between the two drive wheels. All driver axles are rigid, so power applied to a drive wheel on one side also provides power to the other drive wheel on that axle. As a result the axles are always getting power from one side or the other. So you end up with a sequence such as: push left, push right, pull left, pull right. This only works if the drive wheels properly quartered, otherwise the mechanism works against itself.

I have tried gluing the drivers to the axles with ACC but that didn't work, possibly due to faulty quartering on my part. I also tried making a flat spot on the axle before gluing but that didn't work either, possibly for the same reason. My current thoughts are to cross drill the hubs and axles and insert pins though the hubs and axles to have positive connections. between the hubs and the axles. The question is whether or not this is viable. The axles are 2mm (0.078") in diameter. I am thinking of using 1mm (0.039") cross pins. Can this be done on a micro lathe? Or is there a better type of machine for doing this? Drilling the 1mm holes though the hubs and axles shouldn't be too hard with the proper equipment, but obviously it can't be done by hand, at least not by me. But what about the indexing to ensure that the drivers are properly quartered? There are quartering marks scribed on the inside surfaces of the drive wheels. Any thoughts on how I might find someone who could do this for me? Thanks. /forums/images/graemlins/smile.gif

 

[MadReferee]

Try asking on one of the Home Shop Machinist Magazine forums. Almost everybody there works with smaller things in their "home" shop. There are plenty of people there who would be willing to help you out. It's the right place to go and ask.

Home Shop Machinist Forums

 

[MossRoad]

Start at your local hobby shop and see if there are any model train clubs in your area. They are a good source of information and someone there will know who does that kind of repair work.

If that doesn't work, the start searching the internet for model train repair. You will get thouseands of hits. Good luck.

Also, you didn't mention what gauge your engines are. Just curious.

 

[Spiffy]

If you they have a "4th axis" in a VMC, even a standard machine shop could likely do it. They could index the shaft 90 degrees with a very high degree of acuracy; probably want to rest the far end on something unless they have a tailstock for their rotating axis. They could then mount the wheels with the drive feature in the same spot [or locate and index from it] and drill them. Also probably mill flats on the shaft and likely the wheel hubs first so the bit doesn't walk.

Not sure if many places want to deal with that small of item, but since you're willing to pay what I'm guessing is actually better than normal shop rates, they'd probably be cooperative.

1mm cross-wise through a 2mm shaft will weaken it significantly [though maybe not an issue for you]. They should be able to get you something around .020 round stock. Even a .0313 hole would be a bit better than .039. Are you adding permanent glue in addition to the pins? Then I guess shaft strength wouldn't matter as much.

 

[hwp]

I've been through the local hobby shop and model clubs, which quite large and very active locally, but no one knows of anyone with the right equipment. Several of the people I contacted want me to let them know if I find a solution. I'll follow up on various suggestions. Thanks.

P.S. My layout is HO gauge. /forums/images/graemlins/smile.gif

 

[GaryM]

Just wondering of Locktite Stud and Bearing mount might be a better choice than your ACC adhesive?

 

[timb]

For quartering, get the NWSL jig, solves the problem. I assume you've got steel axles and metal (zinc? brass?) driver hubs? You might just try knurling the end of the axle with the edge of a file. Depending on how the electrical pickup path works - the locktite may be a great additional step.

 

[scott_vt]

hwp,
But what about the indexing to ensure that the drivers are properly quartered? There are quartering marks scribed on the inside surfaces of the drive wheels. Any thoughts on how I might find someone who could do this for me? Thanks.

If I understand you correctly, you are performing two operations here. First you are trying to pin the axles to the hubs. I wouldnt recomend going much larger than a 1/32 pin. Might I suggest a dowel pin, I think that would work fine, I use them at work all the time.

As far as the drivers go, any machine shop with a bridgeport and a square collet block could accurately position your drive pins. I daily use a CNC bridgeport with the Anilam control retrofit and it is accurate to .0001. Also you can buy permanent stud luck to aid in your project. Any machining questions just ask, been doin it for 34 years.

scotty

 

[Kyle_in_Tex]

If I read correctly, there are 4 axles, each needing a way to time the wheel at both ends 90 degrees apart. I'm guessing the wheels were originally pressed on. What do you plan to keep the wheels on if you put a pin thru at each end? I would recommend no bigger than a 1/32 dowel, smaller if possible. Drill and ream it to size for about a .0003" press fit. Any shop with a bridgeport mill can do it. There is another possibility but a bit more difficult. Slot the end and use a key to drive the wheel and glue everything to hold. The key could be square or round depending on what tools you have. What are the wheels made of? Are they metal too?
A picture of the wheels could be worth a thousand words.

 

[hwp]

There are four drive axles on each engine but the probem only exists with one axle on each, the powered ones. The other three driven axles on each engine are in place and are properly quartered. The issue is to get a solid connection between the drive gears and the drive axles, properly quartered. The plastic gears were originally pressed onto the axle stubs but with use over the years, the axle stubs have came loose from the gears. I am attaching a picture of a dissassembled axle. I should have included this picture in the original post. The quarter is to show the realtive size. As I indicated earlier, the axle is 2mm in diameter. My intention is to cross drill the hubs and axles to fit a 0.5mm (not 1mm as I stated earlier) pin through the hubs and axles to lock them together. A spring pin or roll pin would be great but I don't think they are made in such a small size. At the time of final assembly, I will glue them as well. The suggestion of Locktite instead of ACC is one I hadn't thought of but will try. If you look closely at the driver on the left, you can see a quartering mark at approximately the 6 o'clock position. There are four quartering marks on the inside face of each driver. Close to the hub on that quartering mark is a small hole. That hole is opposite the dowel for the side irons on the outer face of the drivers as seen on the driver on the right. When assembled the dowels on the drivers must be offset from each other by 90 degrees.

To date I have contacted numerous machine shops and watchmakers and only one machinist said that he could do what I want. But he wants a $280 set-up fee, plus run-time. So I will keep searching.

Thanks for the many helpful suggestions. /forums/images/graemlins/smile.gif