Just sitting here thinking theoretically about the old sintered wheel sets of BB locos and their reputation for collecting crud and scum. I've read a lot about replacing them with either plated sets or the turned sets available from NWSL and others. But apart from the wheel maintenance differences and related electrical pickup issues, I'd like to address the issue of their inherent differences in coefficients of friction. I would suppose that it has a major bearing on the resulting drawbar pull of any particular powered loco whose wheelsets are subject to being swapped out.
I'm presupposing that, under a given amount of torque, the original sintered wheels would have a tad more "grab" than plated or turned ones. Is there a general figure of merit that is applied to this issue for each type of wheel? And to throw in a related posibility, do any modelers out there ever so slightly dress or "rough up" their plated or turned wheelsets for more pull? The issue is not just theoretical: I have a half dozen powered BB F units for which I've secured Athearn's plated wheelsets as replacements. Just wondering what to expect.
No doubt these matters have been discussed here many times before. I'll confess at the outset to begging off on a forum search - previous attemps on other subjects generally were efforts in futility for me.
John
Coefficient of adhesion (or coefficient of just about anything) is a phrase not often used in these here parts, pardner.
I do know this - that a buddy who bought his first ever brass locomotive (a rather small CB&Q 4-6-0) was dismayed that his new acquisition - the most expensive thing on the layout - could hardly pull itself around and even his modet grades were too much for the thing. Reason? - the drivers were highly polished. But he ran the thing anyway "pretending" it was a pusher engine - it was quiet and smooth and that could not be said of all brass steam of that era.
Eventually he wore away enough of the polished nickle silver on the drivers - evidently they were plated -- that it started to pull better and better and eventually when you could see hints of brass on the driver treads, it pulled rather well. Perhaps it gathered more dirt on the drivers but otherwise it was going to sit on a shelf and gather dust instead. This was natural wear however, not the result of him trying to "rough up" the treads. That just sounds like an invitation to gather dirt.
I never had complaints about the pulling power of my Athearn diesels. Even the rubber band drive Hi-F drive engines pulled pretty well with those sintered metal wheels. I seem to recall Model Railroader testing and finding that the rubber band drive F7 pulled better than the geared version (until Athearn beefed up the drive on their geared versions that is). I can't say that was my experience but my rubber band drive F7 (which cost $3.99 from America's Hobby Center!) pulled plenty of cars at a time when trucks did not roll all that well.
I am not sure this is even responsive to your question. Oh well not the first time.
Dave Nelson
This is not a worry with Athearn Blue Box diesels.
The upgraded wheels are better, and they will pull fine. Athearn locomotives are reliable good pullers.
If they lose a little, it is doubtlful it will matter or be noticed.
-Kevin
Living the dream.
I too would like to see some actual science-based reports on this, or investigation if the science was not correctly done. That would specifically include the propensity (or lack thereof) of certain wheel types to be adversely affected by dirt and scurf buildup, or to have greater or less compatibility with a given railhead profile, state of cleanliness, quality of line and surface, etc.
"Roughening" the tread for better pickup on something using DC pickup through the contact patch is just silly. Look at the discussion a few days ago about 'micro-arcing' and think for a moment -- it won't take more than a moment. After that we can get into the relative lack of enough weight to 'conform' surface asperities on driven wheels with the metal in the railhead, but even absent careful study I wouldn't expect this to be meaningful in most modeling contexts.
I have always been a proponent of wheels that have appropriate rust and grease in prototypical places, and appropriate shine in other prototypical places. I got the shine by using one of those jewelry-plating rigs with a fine-cut tip, so my treads were only shiny where the prototype's would be, and my rims were only shiny where hump retarders would have 'gotten' them. (Chuck the wheelsets in a collet in a variable-speed motor tool or handpiece, and clamp the tool in a vise for easy alignment; I used a small precise lathe with multiple-axis slide but that's overkill for most people...)
Theoretically you could modify the metal in the 'plating' to reflect rustier treads or the usual kind of rust that starts in a few days. You could start with a chemical blackener although you have to watch conductivity across insulated wheelsets with some chemistries, then apply appropriate 'weatherants' -- you can leave tread 'shining' for last, or use plating that 'cleans up' well.
My personal preference was to 'dress' the treads for smoothness before plating them -- when I got the Unimat with watchmaker spindle I'd carefully chuck with a reverse-cone center and true the flange profile at the same time. If you have the patience that's what I'd recommend for 'general' best treads.
A separate discussion -- which is appropriate here but might be confusing if not kept fairly strictly separate -- is what you can do to increase locomotive adhesion, overcome the effects of contaminants on the track, etc. This was traditionally the place where stuff like Bullfrog Snot would come into play, the traction-tire approach being something strictly for the toy-train folks. Here I think the recent developments of magnetically-enhanced adhesion are the place to go -- the world has gotten a lot more interesting since the age of Magnetraction. (We've had some good threads on this, but until Kalmbach gets the lead out they will be hard to find unless someone more patient than I finds and links them.)
Hi John,
I replaced all of my BB wheel sets with NWSL plated wheelsets many years ago and there was some slipperyness when compared to the original sintered wheels but nothing that would have made me go back to the original wheels. The slipping has gotten better as the years and miles have accumulated.
The biggest improvement was electrical contact. Fewer stops and less gunk accumulation. This became even more importance when I started installing decoders.
Just got done giving my remaining BB locomotives a good cleaning and they continue to run well. Most of them run better now than they did when they were new.
I wouldn't worry about the slipping much.
Scott Sonntag
Attuvian,Yes, sintered metal wheels do have a higher coefficient of friction than nickel-silver or brass. Using them will improve pulling power. To what degree, I'm not sure. You'd have to set up a static test with a scale for the same engine with sintered wheels vs. nickel-silver wheels to find out.The problem is electrical. Sintered wheels from Athearn have porous surfaces, which means they collect non-electrical contaniments and are difficult to clean and to keep clean. They are also not shiny, so they don't look like what we're modeling. So yes, they will pull more, but they won't pull anything if they don't pick up power. The trade off is always worth it.As for roughing up the surface of wheel for more grip? I wouldn't think that would work. I can't help but think of how running across pavement wearing hard plastic soccer cleats is a bad idea due to reduced friction. The contact area between an HO rail and an HO wheel is so tiny, I would think that adding a rough surface to only one of them would not improve things. You might have to rough up both wheels and track to get better grip, but then keeping that clean might be an issue.
Thanks, guys. I will admit to a fair level of idealism in this matter and recognize that there are a lot of other factors and variables that apply. And I'm certainly not anticipating doing an extended series of pull tests that generate tables of comparative figures. I just want to ensure that freight hauls of 20 or so cars behind a dual-powered A-B lead will make it up a grade approaching 3%. The F units will certainly be subject to decoders in the future so the Athearn replacement sets are in order for that reason alone. Add to that the fistful of superweights that I've collected here and there. I suppose that I should be good to go.
OTOH, I'm certainly not urgent to put this thread to rest just yet.
Mel: Thank you for that well executed experiment. I enjoyed your write-up.
I don't recall ever having the problem of the sintered wheels collecting crud. When those diesels were brought almost to their knees trying to move heavy trains up my twisting 2.8% grades, they quickly shed any minor amounts of accumulated crud.
Wayne
Thanks from me, too, Mel. Wow, a whopping 5ma difference at wheel-slip? Why that could be accounted for by far more things than just the surface of the treads!
doctorwayne I don't recall ever having the problem of the sintered wheels collecting crud. When those diesels were brought almost to their knees trying to move heavy trains up my twisting 2.8% grades, they quickly shed any minor amounts of accumulated crud. Wayne
Attuvian Thanks from me, too, Mel. Wow, a whopping 5ma difference at wheel-slip? Why that could be accounted for by far more things than just the surface of the treads! John