areibel
Joined: 09 Jun 2006
Posts: 5
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| Turning Drivers? |
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Does anyone have experience turning driver castings? I have several nickel silver castings and found someone to turn them. The only scary part is while the machinist is experienced, he's never done model RR work before. I've sent him a sample and a copy of the NMRA's RP25 specs, but is there anything I should warn him about?
Thanks!
Al |
Fri Jun 09, 2006 8:48 pm |
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toolmaker
Brakeman
Joined: 17 Apr 2006
Posts: 21
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As long as he has a blueprint. I would also provide him with the appropriate sets of tires, as these are press-fit.
I have seen the insulated side done two ways. Either an insulator ring between the wheel center and tire, or pressed into the wheel axel hole.
In any case, do provide him with a set of tires so he can machine an accurate press-fit. |
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Tue Jun 13, 2006 12:23 am |
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drhanna
Joined: 04 Apr 2006
Posts: 8
Location: Ohio |
| Turning Drivers? |
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I have a little experience from long ago. If the driver casting is placed in a chuck it will probably be distorted by the jaws, perhaps beyond hope. The problem with a collet, or a chuck, is that one needs to machine where the collet or chuck grabs. My solution was to make a custom face plate out of brass (or your favorite metal) with clearances for the axle hole and crankpin machining operations. Four holes were drilled and tapped in this face plate for screws that pass through two spanner bars and then through the driver spokes to hold the work piece to the face plate. The spanner bars span a nominal two spokes each. The insulation needs to be between the driver center and the tire unless you are sure that the main rods and valve gear are fully insulated from the chassis. Then hub insulation may be considered. The tire to driver center mating surfaces need to have a matching taper of 2 or 3 degrees after allowing for the insulation material thickness. Without the taper it is unlikely that the insulation will tolerate the pressing operation without bunching and/or tearing. LockTite is appropriate. Tires can be machined from brass, nickel silver or stainless stock. A custom cutter bit with the RP25 NMRA contours is highly desireable. A friend used to have one that he loaned me at the time, but he is mostly unavailable these days. Tires from brass should be nickel plated.
Hope these thoughts help,
Dave Hanna |
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Tue Jun 13, 2006 5:52 pm |
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camtrains
Joined: 06 Aug 2006
Posts: 2
Location: Rochester NY |
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I am sorry for the late reply to this topic - I just joined the Brass Backshop.
I have turned driver tires and wheel castings for six O scale steam engines. The smallest wheels I have done are 3/4 inches in diameter. I use the following technique:
If the wheel casting is new and unmachined, I carefully hand file the rough casting to remove all sprue or moulding marks. The casting is then held in a premachined step collet, rod side of casting facing out, and I check the runout of the casting and axle hole. If the axle hole is not centered I boring the hole until it cleans up. This will set the final axle diameter - If the cast hole was for an 1/8 inch axle I bore to 5/32's, etc. The tolerance for this bored hole will be about .ooo1 to.0002 of an inch smaller to make a tight press fit onto the axle. I also use stainless rod for axles. All axle bearings must be bored to fit the new axles. Half of the drivers will be bored 1/16 inches larger for the electrical insulators. The insulators I use, nylon, is tightly pressed into the wheel centers. The insulated wheels are again placed into the step collet and bored to accept a tight press fit onto the axle. Next the wheels are pressed on to a premade arbor held in the appropriate size collet. I use the lathe tail stock to allign and press the wheels onto this arbor. At this time the outside diameter of the wheel castings are turned to the intended size. Once the tool is set and cuts the correct dimater I keep the same tool setting for all wheel castings. This step is important to make all wheels the same outside diameter. The wheels are removed from the arbor and set aside.
Next I cut tires from stainless steel round stock. After boring the inside diameter of a piece of round stock, enought to make all tires from one continuous piece of stock, I use a form tool to shape the flange and tire width. The form tool for P-48 wheels was supplied by Jim Harper back when he ran the High Sierra shop in Nevada. A form tool can be tricky to use because of the way the cutting edge is loaded and chip clearances. I found that the last .001 inches of diameter was best done by turning the lathe slow by hand. This gave a mirror finish to the tires.
The last step is to make up tooling to hold the wheels and tires in proper alignment so as to set wheel spacing and quartering when assembling.
I think quartering is overlooked to often. I have heard some folks say 90 degrees is not important as long as all wheel sets have the same error! Don't you believe it. If you expect good performance on curves and/or grades you had better get it right.
I also make insulator bushings for the main rods.
Sory again about this late message. Thank you. Dave Thompson |
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Mon Aug 07, 2006 5:47 pm |
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rocko59
Brakeman
Joined: 08 May 2006
Posts: 56
Location: Vernon BC Canada |
Hi Dave Welcome to the forum!! No need to apologise for a late reply, I see you just joined. Really looking forward to learning more from you & big Thank You for sharing your techniques. I have to manufacture a tire for a loco I have, one tire had split when the original builder was working on it. It is a Winton 2-6-6-6 from the late 50's, one of the second design with many great lost wax castings, seems to be the only thing wrong with it, other than having some kind of liquid on some of the brass parts which left blue powdery deposits on it. Regards, Russell |
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Wed Aug 09, 2006 1:31 am |
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rocko59
Brakeman
Joined: 08 May 2006
Posts: 56
Location: Vernon BC Canada |
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The next few posts are PM's we sent,I am posting them so everyone can learn & enjoy, Regards, Russell
Russell,
If a tire split it is quite possible it was expanded with heat and allowed to shrink as it cooled onto the wheel center when assembled. I have heard of tires being assembled this way. It make a very tight fit to the casting - soo much that the tire can actually split or the casting can be crushed. However, this method is okay if things are machined for this kind of assembly.
Personally I would remake all new driver tires. My reason would be that maybe, with time, other tires could split for the same reason, what ever that might be. It would give peace of mind knowing the splitting issue is resolved.
I prefer to maching parts with light press fits. If the fit seems it might not hold tight enough then I would center cut a groove about .003 inches deep 1/4 to 1/3 of the tire width into the OD of the wheel casting. This groove would then be filled with Loctite at assembly. Loctite needs some volume in order to set up right - that's what the groove is for. And the remaining stock on both sides of the groove will hold the casting and wheel center in allignment while the Locite cures as well as make an electrical path for power pickup. I don't think Loctite by itself is a good electrical conductor.
Dave Thompson |
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Thu Aug 10, 2006 12:28 pm |
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rocko59
Brakeman
Joined: 08 May 2006
Posts: 56
Location: Vernon BC Canada |
From: rocko59
To: camtrains
Posted: Wed Aug 09, 2006 5:13 pm
Subject: Re: Turning Drivers
Hi Dave Thank You very much for the info. If it's OK I would like to post it to the board so others can learn as well. I am considering making all new ones as they are brass & I would prefer nickel silver. It will be a learning curve in making these on the lathe, not sure if it's precise enough, a good machine but a little on the large side. The only way is by trying though, so I'll let everyone know how the progress is. We also got a pretty well built vertical milling machine, I will have to buy the tooling for any of this type work though, looking forward to milling the frame & rods for a CPR T1 2-10-4 I plan on building in the future. I'm just starting out with this area of modelling & really looking forward to developing my skills with help from guys like you. Thanks Again, Regards, Russell |
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Thu Aug 10, 2006 12:30 pm |
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rocko59
Brakeman
Joined: 08 May 2006
Posts: 56
Location: Vernon BC Canada |
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Hello again, Russell,
I thought the message I returned to you would be posted directly to the board. I must have pressed the wrong buttons. So go ahead and share it with anyone. It is ok by me.
You said you are thinking about making tires from nickel silver. Two thoughts come to mind here. 1) I found NS to be very expensive and it was hard to find the right round stock or tubing. 2) Nickel silver tires runing on NS rail might not the best way to go. For example: similar materials for rails and wheels like NS tires/NS rail or aluminum to aluminum, steel to steel, stainless to stainless and brass to brass will tend to gall. This, in time could leave a rough surface on the rail and tires. Dirt now has a place to attach to the wheels or rail causing bad electrical contact. Cleaning could be a major chore.
I know some guys that claim steel tires cut from iron pipe and run on the old brass or steel rails worked great and gave plenty of traction. Keep in mind those old engines weighed 10 to 15 pounds and the current often exceeded 6 or more amps per engine! With that weight and power dirt rarely gets in the way. DCC does not like dirty rails and high current loads. Ho scale engines don't have the weight to cut through dirt.
Nickel plating on brass tires should be good on nickel silver rails because NS is about 30% copper. The copper makes the NS a different enough material that it works well with nickel wheels. Nickel is noted for its corrosion resistance and good electrical conductivity. This combination probably won't give the beter traction the old guys claimed - who cares?
What this all comes down to is this; Brass tires will be easier to turn on a lathe than nickel silver or stainless. But, you will be faced with the cost of quality platting the tires. That is why I make tires from free machining stainless steel.
(From Dave Thompson) |
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Thu Aug 10, 2006 12:32 pm |
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ShopMaster
Site Admin
Joined: 18 Mar 2006
Posts: 227
Location: Royal Oak, MI |
| Turning Drivers |
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Big thanks to Daves Hanna and Thompson for some great info on driver turning. That what I want this forum to be about - great brass craftsmen sharing ideas and experiences !!
Thanks,
Dave |
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Thu Aug 10, 2006 5:42 pm |
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rocko59
Brakeman
Joined: 08 May 2006
Posts: 56
Location: Vernon BC Canada |
Hi Dave T What kind of material do you use for stainless tires? I went to the machine shop on Wednesday & there is a lot of different kinds of stainless. I'll dig out my books & look but wondered what you use. Thks, Russell |
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Fri Aug 18, 2006 2:06 am |
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Jay Criswell
Joined: 03 Jan 2009
Posts: 1
Location: Cetral California |
I just came across this site and immediately joined. The interest in turning drivers is what really got my attention.
I 've been building drivers in O Scale (2R) for some time now and the best material I've found for making tires is Ledloy or 12L14. The beauty of this steel alloy is it's small lead content (something like .15 to .35%). The when the cutter is working the lead acts as a lubricant. This steel alloy machines almost as easily as brass but make no mistake it's steel. I know this because I've been careless a few times and had the tires rust on me.
Anyway, 12L14 is readily available in rod form and really isn't all that expensive.
It's getting late. I'll add more tomorrow.
Jay |
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Sat Jan 03, 2009 3:27 am |
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