# Cast resin steam loco driver centers - Possible?



## dwalker (May 14, 2011)

I want to try to make G scale 79" steam locomotive drivers by casting the spoked wheel centers in resin, then pressing on a steel tire. 


I can use my mill and rotary table to make an aluminum master, then a rubber mold, then cast in resin.

Has anyone done this, and if so, which resin did you use? It needs to be able to handle the stress as well as not shink over time.


Thanks!


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## Mr Ron (Sep 23, 2009)

You have come to the right place. I've been doing some research on the subject of epoxy casting resins to cast centers for 1-1/2" scale wheels. The main thing I looked for was strength and hardness of the resin. I need to finish machine the wheels after the casting has cured, so I was looking for a hardness > 75 shore D of the durometer scale. That hardness is about the hardness of a hard hat. Another thing I was looking for was the resin had to be rigid without being brittle and shrinkage was to be minimal. I finally came up with the following products: 20-3652 epoxy resin (epoxies.com); Smooth-Cast 385 (Smooth-on.com); Plastic Steel liquid(B) (devcon.com). They all exceed the 75 durometer hardness (80-88D). I have some resin samples, but have not tried them yet. I hope this helps. Let me know how your project turns out.


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## dwalker (May 14, 2011)

Posted By Mr Ron on 31 May 2011 12:09 PM 
You have come to the right place. I've been doing some research on the subject of epoxy casting resins to cast centers for 1-1/2" scale wheels. The main thing I looked for was strength and hardness of the resin. I need to finish machine the wheels after the casting has cured, so I was looking for a hardness > 75 shore D of the durometer scale. That hardness is about the hardness of a hard hat. Another thing I was looking for was the resin had to be rigid without being brittle and shrinkage was to be minimal. I finally came up with the following products: 20-3652 epoxy resin (epoxies.com); Smooth-Cast 385 (Smooth-on.com); Plastic Steel liquid(B) (devcon.com). They all exceed the 75 durometer hardness (80-88D). I have some resin samples, but have not tried them yet. I hope this helps. Let me know how your project turns out. 
Great! Looks like you already did the research for me!

I'm planning a scratchbuilt model of a Santa Fe 4-4-6-2 Mallet, and I didn't want to machine all those spoked wheels...

I think I will machine the blank from styrene so I don't break so many mill cutters.


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## Pete Thornton (Jan 2, 2008)

I can use my mill and rotary table to make an aluminum master, then a rubber mold, then cast in resin. 
If you can do that, you can have the wheels cast for you in anything from resin to brass. I hope your resin idea works out. If not, Valley Brass, the new owners of Trackside Details, are making brass parts for a friend of mine. 

If you have the CAD files,Hartford Large Scale can have a master made from a plastic 'printing' (3D modelling) shop and then they make moulds and cast you a white-metal part (or 20). Alternatively, Hartford will take your master, make a mould and cast as many copies as you want in white metal. 

But, isn't that loco standard gauge? So you are making a 1/32nd scale model, or 1/29th? Or are you really going to make a 1:22.5 G scale model running on 64mm track?


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## dwalker (May 14, 2011)

Posted By Pete Thornton on 31 May 2011 02:31 PM 
I can use my mill and rotary table to make an aluminum master, then a rubber mold, then cast in resin. 
If you can do that, you can have the wheels cast for you in anything from resin to brass. I hope your resin idea works out. If not, Valley Brass, the new owners of Trackside Details, are making brass parts for a friend of mine. 

If you have the CAD files,Hartford Large Scale can have a master made from a plastic 'printing' (3D modelling) shop and then they make moulds and cast you a white-metal part (or 20). Alternatively, Hartford will take your master, make a mould and cast as many copies as you want in white metal. 

But, isn't that loco standard gauge? So you are making a 1/32nd scale model, or 1/29th? Or are you really going to make a 1:22.5 G scale model running on 64mm track? 
I'm still researching the idea right now. Probably either 1/32 or 1/29. 
I have Fn3 equipment now.


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## Torby (Jan 2, 2008)

How about making your metal tires and flanges, then fitting them into the mold and casting the inner detail right into them?


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## jonathanj (Jan 24, 2008)

Posted By Torby on 31 May 2011 06:24 PM 
How about making your metal tires and flanges, then fitting them into the mold and casting the inner detail right into them? 
I've also been thinking about doing this - I 'need' drivers for a 1/29 5011 class ATSF texan that I want to build one day - and I'd wonderer about doing it this way round instead. Or casting the centres so that they were a comparatively slack fit inside the tyre, notching the facing edges of both, and then gap-filling with a final resin cast to lock them together. BUt I haven't tried any of them, so I'll be watching your experiments with interest

Jonathan


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## dwalker (May 14, 2011)

Posted By Torby on 31 May 2011 06:24 PM 
How about making your metal tires and flanges, then fitting them into the mold and casting the inner detail right into them? 
Good idea! Hadn't thought of that...


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## dwalker (May 14, 2011)

Posted By Mr Ron on 31 May 2011 12:09 PM 
You have come to the right place. I've been doing some research on the subject of epoxy casting resins to cast centers for 1-1/2" scale wheels. The main thing I looked for was strength and hardness of the resin. I need to finish machine the wheels after the casting has cured, so I was looking for a hardness > 75 shore D of the durometer scale. That hardness is about the hardness of a hard hat. Another thing I was looking for was the resin had to be rigid without being brittle and shrinkage was to be minimal. I finally came up with the following products: 20-3652 epoxy resin (epoxies.com); Smooth-Cast 385 (Smooth-on.com); Plastic Steel liquid(B) (devcon.com). They all exceed the 75 durometer hardness (80-88D). I have some resin samples, but have not tried them yet. I hope this helps. Let me know how your project turns out. 
Do you know if it makes any difference which type of rubber molding compound you use with these resins? 

I've used Alumilite with their resin only.


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## Mr Ron (Sep 23, 2009)

I believe you want to use a silicon compound for your mold. Check out the Smooth-On web site. They have lots of good information www.smoothon.com .BTW, I'm using an aluminum rim and core and pouring the resin directly around the rim and core. once cured, I will finish turn it on a lathe.


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## wchasr (Jan 2, 2008)

Remember either way of assembly that you will want to make a final pass on the outside to ensure concentricity with the axle once it is assembled. 

Chas


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## Phippsburg Eric (Jan 10, 2008)

I agree that the casting should be machined for final fit and finish to ensure the wheels roll true. a metal hub as well as a metal tire are probalby a good idea. I would knurl the hub and cast it into the mold, I think i would roughly machine the tires and possibly sand the inner surface to give teeth for the resin to grab.

If you are building for live steam than I would use cast metal...ideally investment cast brass or bronze. There are outfits that will cast to your pattern fairly reasonably. For electric models resin is the way to go...gives you great detail and is insullated to boot!


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## Mr Ron (Sep 23, 2009)

Posted By Phippsburg Eric on 01 Jun 2011 01:53 PM
I agree that the casting should be machined for final fit and finish to ensure the wheels roll true. a metal hub as well as a metal tire are probalby a good idea. I would knurl the hub and cast it into the mold, I think i would roughly machine the tires and possibly sand the inner surface to give teeth for the resin to grab.

I was thinking of doing the same thing except I was going to machine a groove around the inside of the tire. Is there any way to knurl the inside diameter of the tire? My wheels will be 4.5" in diameter x 3/4" thick, no ribs; just a plain wheel as used on railroad cars and diesel locomotives. If I need to make spoked driving wheels, I will have to make a mold first; then make the casting from the mold.


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## dwalker (May 14, 2011)

This is a great discussion! I wish I could get this level of collaboration where I work.... 

Here is what I'm planning to do: 

1. Turn a steel tire to the correct inside diameter, but don't cut the flange yet 

2. Make a wheel center master out of styrene that has an outside rim about .1" oversize and a dimple in the center for drilling the axle hole. 

3. Make a silicone rubber mold from the master 

4. Cast the master in a resin similar to Smooth Cast 385 

5. Clean up the casting. 

6. Drill and ream the axle hole 

7. Mount the center on an arbor in a lathe 

8. Turn the outside for a tight fit on the tire 

9. Epoxy the tire to the center. 

10. Turn the tire and flange to a final diameter on the arbor. 

This assumes that the resin is strong enough for the axles. If not, I'll have to epoxy in a metal center.


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## jonathanj (Jan 24, 2008)

Posted By dwalker on 02 Jun 2011 01:40 PM 
This is a great discussion! I wish I could get this level of collaboration where I work.... 

Here is what I'm planning to do: 

1. Turn a steel tire to the correct inside diameter, but don't cut the flange yet 

2. Make a wheel center master out of styrene that has an outside rim about .1" oversize and a dimple in the center for drilling the axle hole. 

3. Make a silicone rubber mold from the master 

4. Cast the master in a resin similar to Smooth Cast 385 

5. Clean up the casting. 

6. Drill and ream the axle hole 

7. Mount the center on an arbor in a lathe 

8. Turn the outside for a tight fit on the tire 

9. Epoxy the tire to the center. 

10. Turn the tire and flange to a final diameter on the arbor. 

This assumes that the resin is strong enough for the axles. If not, I'll have to epoxy in a metal center. 


If it works out OK this should give you a nice concentric wheel, but I'd be seriously worried about the sheering load on the epoxy (from stage 9) when you came to turn the tyre (stage 10), which won't be helped if the workpiece gets at all warm.

Couple of ideas for ways round if the epoxy can't take the strain, neither of which I've tried in practice..

There's a guy in the UK sells wheel castings for various prototypes with scale size and profile spokes - beautiful, but it's not unknown for people to buckle the spokes when turning up the treads and flanges. His suggested method is to make a lathe spindle fixture which clamps the wheel front and rear (with the clamping screw through the axle hole), and has its contact with the wheel rim, so that the torque from the spindle is transmitted through the clamp directly to the rim, and not through the spokes. You could do something similar if the tyre was deep enough to give the clamps somewhere to land on and and not get in the way of the cutting tool.


Or - Turn the tyre up to a finished standard, then drop in the fitted resin centre (having underbored its axlehole) and epoxy. When set use some suitably cunning fixture to centre the wheel on the lathe from perspective of the flange/tread and then bore the axle hole true relative to that.


Jonathan


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## Mr Ron (Sep 23, 2009)

I was going to do pretty much the same, except I was going to cast the flange and hub in the mold with the resin. I was going to machine a groove all around the inside of the flange and the hub to lock the resin in place. Machine the whole thing at once in the lathe. This will insure everything is concentric. Hold the wheel on the outer diameter in the lathe chuck and bore for the axle. Fit the wheel now to an arbor, chuck in the lathe and turn the flange to final size and profile. In place of styrene, I will use machinable wax, since in my case, the spokes will be 5/8" thick, so I don't think styrene will work. Don't forget, everything is possible. It just depends on ingenious you are.


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## dwalker (May 14, 2011)

Posted By jonathanj on 02 Jun 2011 02:51 PM 

Or - Turn the tyre up to a finished standard, then drop in the fitted resin centre (having underbored its axlehole) and epoxy. When set use some suitably cunning fixture to centre the wheel on the lathe from perspective of the flange/tread and then bore the axle hole true relative to that.


Jonathan 


Good point, I'll do some experimenting. I'll probably turn the tire and flange very close to actual size before fitting.
Final turning after epoxying the center will then be very slight, so it shouldn't heat up too much.


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## Andre Anderson (Jan 3, 2008)

My one sugestion to the whole project is to solder music wire between the hub and the wheel, the music wire would take the strain and the resin would be there for looks, but one way or another I would have some sort of reinforcing in the spokes so that the epoxy or resin would only be for looks not for strength.


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## Pete Thornton (Jan 2, 2008)

If it works out OK this should give you a nice concentric wheel, but I'd be seriously worried about the sheering load on the epoxy (from stage 9) when you came to turn the tyre (stage 10), which won't be helped if the workpiece gets at all warm. 
As an aside, it is an old trick in the UK to insulate wheels by epoxying the rim to the spokes. They usually cut the spokes after machining though. 

I would suggest joining G1MRA and posting some questions for the UK guys. They have quite a lot of experience making wheels for obscure locos.


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## Phippsburg Eric (Jan 10, 2008)

I like the idea of machining the tire first, then molding the wheel into the tire along with a metal hub. grip the tire on the lathe accuratly then machine the hub (and crank pin hole) which also has to be very accurately placed. 

I have made brass wheels. I machined the shape including spokes, counterweight and crank boss using a CNC sherline mill. getting the proper "cast" profile of the spokes was beyond my ability with the CNC but they looked good. I rounded the edge with a file by hand to give the correct impression. I drilled the axle and crank on the CNC which is plenty accurate, then chucked it in the lathe to machine the tire and flange profile. 

here is a video of making the wheels and some other parts: http://www.youtube.com/watch?v=Hb7vfhee020


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## Bill Martinsen (Mar 4, 2008)

How about making your metal tires and flanges, then fitting them into the mold and casting the inner detail right into them?


I used this technique back when I was modeling in Sn3. I used an aluminum-filled epoxy for the casting. It had good hardness and could be drilled and tapped, but was hard on the silicone molds (short mold life). Unfortunately, the epoxy I was using became unavailable and I've not located a substitute (but I haven't really tried too hard).

Bill Martinsen


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## Mr Ron (Sep 23, 2009)

An idea came to me. If you are casting wheels in a small scale like< 1:19, you might want to experiment in using JB Weld. It could be pressed into a mold and it hardens up to be machinable. I understand it has an open time of 20 minutes and a hard time of 4-6 hours. According to their spec sheet, it can be thinned with denatured alcohol (not rubbing alcohol). This might extend the pouring time. This way, a small amount of epoxy could be experimented with without committing to expensive resins. I would recommend downloading the specs on JB Weld and follow them carefully. I've also looked into using Bondo, but I think the JB Weld might work better; our UK readers might take note.


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## jonathanj (Jan 24, 2008)

What's JB Weld? (I'm in the UK, so we probably call it something else) 

I'm guessing the loads riselt rapidly (and out of proportion with) the scale - somewhere (probably the back inside cover of an old MR) I've seen a picture of a loco - a forney I think - that's said to have plaster drivers with steel tyres. I've got a feeling the late John Ahern was said to be involved in it somehowbut wouldn't be 100% sure on that. 

J.


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## SteveC (Jan 2, 2008)

Johnathan

Here you go.

J.B. Weld Co. - Products[/b]


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## old john (Dec 29, 2008)

This has nothing to do with casting drivers, but I was out in my boat, 200 miles from Seward, Alaska, when I developed a crack in the thermostat houising on the engine, used JB Stik and 14 years later its still holding, so I think JB Weld would work for Drivers.


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## dwalker (May 14, 2011)

Posted By Phippsburg Eric on 03 Jun 2011 03:31 PM 
I like the idea of machining the tire first, then molding the wheel into the tire along with a metal hub. grip the tire on the lathe accuratly then machine the hub (and crank pin hole) which also has to be very accurately placed. 

I have made brass wheels. I machined the shape including spokes, counterweight and crank boss using a CNC sherline mill. getting the proper "cast" profile of the spokes was beyond my ability with the CNC but they looked good. I rounded the edge with a file by hand to give the correct impression. I drilled the axle and crank on the CNC which is plenty accurate, then chucked it in the lathe to machine the tire and flange profile. 

here is a video of making the wheels and some other parts: http://www.youtube.com/watch?v=Hb7vfhee020 


Great video! I have a sherline mill, and I'm thinking about upgrading it to CNC.


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