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Handaid Track

Past Articles

Converting a Sunset SP P-8 Pacific to Proto48

Gene Deimling Constructing an ATSF Bx-27 boxcar

Tom Mix Another Method to Make Rivets

Tom Mix Scratch Building Some Drivers

Robert Lerners's Tank Car Conversion

Dan Ellis's South West Industrial Railroad

Part 2 of
Tom Mix's Locomotives

Tom Mix's Locomotives

 

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Working Coupler Pocket for the San Juan Type-E Coupler

Improving San Juan Type-E Coupler

Bottom Operating Cut Levers

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Proto48 Article:
Scratch Building Some Drivers..

The art of scratch building is alive and well in Colorado

by Tom Mix

Drivers in "O" scale are almost impossible to find. And when a set is found it must be machined to Proto 48 standards. This means new tires and the wheel casting must be thinned to be more prototype. Or, build your own.

Many years ago Precision Scale had extra 63" drivers that were for their SP cab forward import. I bought enough for a Burlington 2-8-2 and a 2-10-4. That was the learning process for working with redoing drivers to P48 standards and reassemble with the proper 90-degree quarter between left and right sides. I built a quartering tool to do this. Often, to be prototype, new counter weights and even centers have to be fabricated and soldered on before assembling as I did with the 2-10-4.

I have several projects going at the present time, two of which are a 4-8-2 with 74" drivers and a 2-6-2 needing 69". These are not available on the market�that I know of anyway. Through the years I have admired the work of Louis Bartig and with some of his later models he handmade the drivers.

Wonder if I could do that?

So a new project was started. I have just finished a set of the 74" for a CB&Q B1 mountain and it was a real learning process! I have many component drawings of this engine, including the drivers. So first I machined the outside wheel rims from brass bar stock and then the counter weights, to exact scale. The hub cranks were made with the hub for the heavy counter weight wheels slightly larger as per prototype.

These drivers had 17 spokes that were not divisible with my Emco dividing tool. I had one old 81" 17 spoke driver that I used as a pattern to mark off spoke positions on the end of a piece of aluminum bar. This bar was then machined to the inside diameter of the wheel rims. Then slots were cut with a slitting saw to hold the spokes for soldering

 

 

These two photos show the wheel rims with attached counter weights and the aluminum jig for holding everything together for heating with a torch.

 

 

The next two images show a sheet of 0.040" brass for the spokes. I filed and rounded the full edge of the brass sheet, marked it off, then used a slitting saw to cut strips. Another small piece of .32 brass sheet had a cut out pattern to match the length and taper of each spoke.

 


 

This photo shows a close up of the aluminum soldering jig with some spokes in place and more cut to length ready to insert in the slots. Note that some of the spokes must be cut to progressively shorter lengths on the bottom of the crank hub and to the counter weights. After spokes are filed to length and fitted in the slots, the jig is positioned in a vice and a torch is used to heat up the complete aluminum jig. Then solder is touched to each spoke where it touches the rim, counter weight, and hub. Just enough solder to give a little filet to give the appearance of a prototype wheel casting.

 

 

The next two images show a section of a brass bar holding jig in the lathe that is used for both trimming the insides of the steel tires to fit the wheel, and as you can see, to bore the center axle hole to the proper size, and most importantly, to true the tire with the axle hole. This is one of the critical points in assembling the drivers. I used 6MM axle stock. The fit must be enough to need pressure to push the wheel onto the axle…but only a little! I learned a long time ago that trying to make a real tight fit usually caused the axle hole to distort and the wheel to go on crooked. I use LocTite and it works! (LocTite is also used to attach the steel tires to the wheels. The insulated wheels use .10 x .100 strips of styrene). You have to move right along or it will begin to cure before you have the wheel set ready to assemble in the quartering tool. I press a driver, one each axle, then after some cure time for the LocTite, get the second driver ready to go on. Using pins in the cranks, positioning the 90 degrees required, then using a vice with the quartering tool, press on the second wheel on the axle.

 


 

The completed set for the Mountain engine. The steel tires on this set are from Pat Mitchell. All the other tires on my engines were machined on my Emco lathe from stainless steel.

 


 

A close up showing that filet of solder to make it look like a casting.

Right away you may be asking, "why not send one of the wheels as a pattern to a professional casting service?" Saves a lot of work. Actually I did that. The first model railroad parts caster said the spokes were too narrow and may not fill. So I sent the same pattern to another casting service. No response. Sent a letter asking "what about my pattern?" No response. That ended that.

This experience has shown that it is possible to build drivers so my next task will be to make those 69" drivers for that CB&Q Prairie. The frame and cylinders have already been built.

I should let readers know that I am NOT a professional machinist. I learned this stuff when I bought a small Unimat SL back in about 1958 when I was a young sergeant of Marines. From that start it progressed to a Unimat 3, and now I have an Emco Compact 5 lathe. Also I have a milling machine. The point is, anyone can learn to machine, you just have to try. I have made a lot of mistakes over the years�and still do!

This was more of a demonstration than a complete instruction on building drivers. If you have specific questions I would be more than happy to try and explain in more detail. Please e-mail me with questions you may have.

Tom Mix