Unc's Cheap Tips, Tricks & Gimmicks

Yep, a place where slot car drag racing's premier cheapskate cuts those corners, pinches those pennies, and then tells you to make the very same mistake. Or not. Your current menu:   Semi-Jerkproof Pinion Spacing & Soldering   Inexpensive (or Less Expensive) Lead Ballast O.k., so it's not the longest list in the world. Trust me, it'll get longer - my reservoir of misinformation is almost limitless, and what kind of guy would I be if I didn't share it with my friends?
Semi-Jerkproof Pinion Spacing & Soldering 19 September 2000 Here's a little deal I use when soldering pinions on armature shafts. It spaces gears a fixed, constant distance from bearings and bushings, as well as offering them some protection from flux "splatter" or spread when the shaft is being tinned. Since I run the absolute minimum amount of protruding shaft possible (unlike mass, arm weight is still arm weight, no matter where it's located), use of this spacing system permits me to run some awfully tight bushing-to-gear clearances, on the order of .010-.015". This is accomplished without fear of the gear ever actually touching the bearing/bushing, with the accompanying friction and Bad Juju that condition, or the use of a permanently-installed "barrier" spacer/washer, might entail. The following probably takes fifty times longer to read than it does to do, so bear with me here.
	Making the Spacer. This is a no-brainer. Find a new or used phenolic spacer somewhere in your box. The ones I use start out about .013-.015" thick by .210" in diameter. Using something like a #11 X-Acto blade in your knife, cut part of its diameter as shown in Figure 1.0, at left. Make the notch ever so slightly smaller than the I.D. of the spacer. This, in effect, turns it into a crude "c-clip." Make certain it will slip sideways over and armature shaft while being held with a pair of tweezers. If it won't, keep making them until one does. This, by the way, is the only use I ever make of these sleazy spacers; if you want to put one of these relatively heavy,
oversized, oil and com drop-absorbing and slinging deals immediately behind your commutator, be my guest. While you're at it, once you determine how to cut one so that it slips on and off and arm shaft to your satisfaction, make two or three more while you're at it. I keep a few in my go-to-races pinion and spur gear container, and a few more in a relatively safe place on my workbench. They're relatively small, and like anything else small regarding slot car drag racing, they have an inordinate ability to dive to the floor in both my shop and at the track when I most need them. As crawling around on my hands and knees at the track does not, shall we say, present my, ah, "best side" to the world, this saves some grief for all involved. Shortening the Armature Shaft. Any work on the arm shaft is best done during construction of the motor, with the arm removed from the motor/setup. Editorial comment: this is a polite way of saying that anyone who cuts the shaft after the motor is built, with the sucker completely set up, gets what he deserves. Which, when you think about it, is a spray of carbides, oxides, and steel bits aimed in the general direction of two relatively strong magnets with, what? Maybe .004" clearance max per side between them and an expensive bit that's 'gonna be turning nine gajillion rpm in a minute or two? And it's so much easier to clean when it's assembled, too, right? No thanks. I usually do the arm shortening just after setting the endplay/"float" and spacer "package." Occasionally, I do it after the first brief break-in period for the motor. As it turns out, despite meters and checking, one occasionally encounters an arm that simply hates a given setup. It might, however, love another one. If you wait until after that first break-in (what I call the "arm audition," it will still have original-length shafts for some other setup. Not a necessity, just something to consider.
	Marking the Armature for Shortening. Once you've decided on an arm, have the can and endbell assembled with screws tightened to their normal torque, and have the appropriate spacers installed to get the endplay you want, mark the arm for cutting. Use a new (or cleared-out) gear that slips firmly over the shaft all the way to the bearing/bushing, either the one you intend to install or one of the same length - you have noted that all pinions aren't the same length, right? - and a fine-point, permanent magic marker. After taking the endplay of the armature out toward the endbell end, slip the gear over the shaft until it touches the bearing/bushing. Make a positive
line as close to the gear as the tip of the marker will permit, and as far around the shaft as you can manage. Figure 1.1, above. shows what's happening at this point. You'll note that the normal offset of a fine-point marker tip from the end of the gear is just about the same spacing as the thickness of our spacer. Now remove the gear, putting a slight side load on it to avoid wiping off all of the cut mark you've just made. Cutting the Shaft. Now that your armature shaft length dimension is set at the gear end, it's probably a good idea to also mark the other end at this time for the same purpose. Keep a few things in mind before you start whacking at the arm, however. One area of concern is (or should be) making sure that you don't shorten an arm to a degree where you (or whomever) have to change the spacing dimensions on your com lathe before the arm can be trued. If you've done it, you know that getting it all back in exact alignment after moving the "ways" can occasionally be a career opportunity rather than a simple task. Another caution would be to not get carried away with shortening and finishing the shaft end(s) at the expense of forgetting a) the gear has to go on it at one end, and b) it would be nice if the shaft didn't fall out of the bushing/bearing at the endbell end. You think I make this stuff up right? Uh uh.
	Installing the Spacer. Presuming that you have shortened the shaft appropriately and reassembled the motor, including brushes and springs, start by preloading the armature back against the endbell spacers. Take all the play out - the brush pressure on the com should hold it there. Now apply a very small drop of oil with the smallest-tip oiler you own to the junction between the arm shaft and the bushing/bearing only. With some tweezers, slide the spacer over the shaft while pressing it against the bushing/bearing. The point is to keep the oil at/in the bushing, and not spread it out along the shaft. You might add another small drop to the slot
in the spacer if you're nervous. Figure 1.2, above, illustrates what it should look like at this point; the arrow notes that the slot is oriented to the top of the motor. Apply a light coating of your normal flux to the shaft, tin it with the high-strength solder of your choice, and install the gear as you normally would. Make sure to seat the gear all the way against the spacer.
	Removing the Spacer & Inspecting the Gap. Once you've soldered the gear to your satisfaction, and it looks like everything is positioned about right, let it cool a bit, then remove the spacer. I find this is most easily accomplished by checking to make sure that the opening in the spacer is still where it was originally positioned, then using the back of an X-Acto blade to slide it off the shaft. Figure 1.3, left, shows what we're talking about here. Since the back of the blade will stop when it hits the arm shaft, the spacer probably won't pop completely clear of the shaft. Not a problem. Invert the motor, and use a pair of tweezers to pull the spacer out, as illustrated by Figure 1.4. Clean it off with some naptha or similar solvent to make sure there's no soldering flux or residue left on it before putting it away. Now inspect the resultant gap between the gear and the bushing or bearing, making sure you haven't push an excess of solder out behind the gear. This takes some close inspection with decent lighting, so take your time. Figure 1.5, below left, shows you what the gear-to-bushing relationship should look like at this point.
	In the event there is a bit of excess solder, you can trim it off by taking that same X-Acto blade and scraping the back of the gear in towards the shaft until you feel satisfied that whatever remains, if anything, won't contact the bearing or bushing. Use the tweezers or the tip of the knife blade to remove the residue so it doesn't contaminate the bushing, or, of greater danger, a ball bearing. Should this make you nervous, my personal experience in more than a few years of using this system has been zero damaged bushings/bearings. Pay attention, be a bit patient, and your experience will probably be similar. Once you're satisfied with the relationship, clean the gear, the shaft, the bushing/bearing, and the front (including the inside) of the can with your choice of cleaners or solvents to remove any remaining
flux splatter and the protective oil. Those handy little eyeliner brushes - the "mini-bore-brush" variety -  are particularly useful in this application. Without eyeliner on them, of course. If you have the option, blow it dry; if not, make sure that whatever you use has evaporated and reoil the bushing/bearing as you normally would. I once actually timed the difference between soldering on a pinion with and without the spacer system: it took 20 seconds more time, including searching the container for the spacer. I figure uniform and consistent pinion spacing and soldering, even when in a hurry at the track, are worth 20 seconds a motor. You might, too Some Additional Observations. Unless it's a real pain or the gear just won't move for some reason, I use the X-Acto blade to remove gears as well as install them. A little heat and a twist of the widest part of the blade against the can and the back of the gear usually does the trick in a vast majority of cases. I figure it this way about gear pullers: First, they were originally useful for 48-pitch gears which were designed to be pressed on and pulled off. Neat, but I haven't used 48-pitch gears since the late '60s, and hopefully never will again. Second, most of the ones I've seen are, to be polite, imprecise at best. The puller and companion gear press I own are jewels by comparison, and they weren't cheap by any means. If you must rip gears off shafts, spring for a quality piece to do the ripping with. Third, a quality puller will feature a strong, thin web that will fit behind the gear and pull it off without having to be hammered into place between the gear and the bushing/bearing. You think I'm kidding? I get to see and rebuild a fair number of motors, and you wouldn't believe the number of bushings with jaw-shaped gouge marks on them or bearings with distorted outer races I come across. Which, by my reckoning, means that the person who built/rebuilt or changed the gear on the motor before I worked on it either didn't know what he was doing, or, perhaps worse, didn't really care. None of this stuff is free, and messing it up can meaningfully affect performance, so I figure a little care goes a long way here.
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Inexpensive (or Less Expensive) Lead Ballast (This article originally appeared on the DRS Drag Board in September, 1999.) If you sometimes get annoyed at spending what amounts to serious money over the course of a racing season for simple ballast, as in stick-on 7 gram “wheel weights” or adhesive-backed sheet lead, here are some lead ballast alternatives you might explore. 7 gram "nugget" weights. Check out a local tire/wheel service store, and politely inquire (usually with the manager) whether they recycle the wheel weights they remove before rebalancing a tire. If they don’t, ask him to save you about a week’s worth. If they do recycle them, ask what he’d take for a pound or two. The last time I pursued this avenue, I got 143 useable 7 gram weight for $5 (not to mention a gajillion smaller stick-ons and clamp-ons. Ignore what the stick-ons look like and dump a handful or two into a sealable glass container with a few inches of lacquer thinner in it, seal it up, and ignore it for a day or so. Then pull them out with a pair of tweezers – or anything else that won’t melt and keeps the lacquer thinner off your hands – and clean the remaining soft, gooey adhesive off them with a lint-free paper towel. Stop by your local hobby shop or a serious RC car dealer and pick up a roll of their most aggressive “servo tape.” Not carpet tape, not picture-hanging tape – servo tape. Yes, there are other available double-sided foam tapes that seem to be as thick and aggressive, but, at least in my experience, the hobby servo tapes have an adhesive that lives through exposure to oil, glue, and occasional impact better than “household” tapes. Commonly ¾” wide, the 7 gram weights will fit across the usual servo tape with only .040-.050” excess tape, easily trimmed off. If you butt them up tight, side-to-side, you can minimize tape waste and easily separate them with a hobby knife. With a 60” roll of servo tape costing about $3, and figuring $5 or so for the used weights, the $8 investment (plus time and tax, of course) can produce 150-160 usable weights per roll. So? So the last time I looked, stick-on wheel weights at my local auto parts stores averaged between $2.39 and $2.79 for a package of between 6 and 8 weights. Even at an average of $2.50 a pack, that’s roughly $47.50 worth of “slug” weights for your $8. And if you can’t figure out what to do with 150 weights, I’ll bet your local track can if the price is right. Since your “manufacturing” costs (including labor) work out to under 7¢ cents each (or appx. 1¢ a gram). Yes, your acquisition costs may vary, but you’ll still come in considerably under 31¢ average for each “new” weight. If you have a recurring need for this kind of weight, it’s worth a look. Not-So-Cheap Tip for adhesive-backed “sheet” lead (for the truly dedicated or truly mercenary). This one’s a little harder to do, as far a sourcing of materials in concerned, but offers a similar degree of savings – at a cost of some complexity and “bulk” buying. First, a source for lead. Find a serious hobby shop with an extensive model train section, or, better, a model train store that caters to HO or O scale builders, rather than a shop that carries just “collector” stuff, Lionel, or LGB. See if they have or can order packages of sheet lead strip (model RR guys may be the only other model builders around who have a common need to make things heavier, rather than lighter, to make them perform better). If they have/can get it, expect to pay $6-$7 for a pack of 6 1½” x 12” lead strips appx. .042” thick. Then have your track order a package of Trik Trax STS double-sided adhesive sheets, ten sheets to a card for $6.90 a card (each sheet is 2” x 6”; 12 sq. in. x 10 sheets = 120 sq. in. $6.90 / 120 = appx. 6¢ per square inch). Other adhesives may work in this application (and probably do), but I’ve used this stuff for a long time with no adhesive failures. Ignore their instructions and keep it refrigerated – it simply makes it easier to deal with come application time. No luck on the hobby/train shop lead? Punt. Get ready to become the “ballast king” of you particular metroplex. Check out a local roofing supply dealer, and inquire about the cost of something they probably call “2½ pound sheet lead flashing.” In this case, the dimensions are (relatively) standard, usually 30” x 30”, and the “2½ pound” reference denotes sheet appx. .042” thick (should you desire, “3 Pound” usually comes in at .051”, and “4 pound” at appx. .067”. In my neck of the woods, the thinner sheet cost me $18.75, which works out to a little over 2¢ a square inch (at 900 square inches total). Combined with the adhesive cost, this gives you sheet ballast at under 8¢ per square inch. Figuring the cost-per-gram is also useful. Some commercially-available lead is available in 2” x 3” sheets, and others in 1” x 3” form. While some is .051” thick, others are .032” thick. Most commercial lead retails for slightly under $2 a sheet. That means the .032” sheet, not only costs appx. 32¢ per square inch, but, because of its thickness, also costs appx. 14½ ¢ per gram. The .051” packaged lead costs appx. 28¢ per square inch, but reduces the “weight” cost to appx. 4¢ per gram. Your “roofing” lead, even assuming adhesive costs, comes in at under 1½ ¢ a gram. Hmm. Makes almost any adhesive cost per gram negligible. Granted, not many of us have an immediate need for this much sheet ballast, even at a reduced unit cost. However, as with the “slug” lead, the total costs are relatively low, can possibly be spread over more than one “consumer,” and, speaking from personal experience, offer the possibility of actually ending up with an honest-to-God “lifetime supply” of a useful slot car drag racing consumable. Note(s): any adhesive mounting system needs a clean surface to function properly. Slimy, gluey, oily, or badly rusted surfaces are not what we’re looking for here. Nor is a piece of sheet lead spanning the gap between two round .062” frame rails. All of this stuff needs flat surfaces to work well. Which means cleaning the surfaces with some none-residual solvent like naptha. It also means cleaning off all the remains of old adhesive. If you must stick sheet lead to curved surfaces, consider using the servo tape, which can conform to more irregularities than the thinner sheet adhesive. And: this being America at the end of the Millennium, some generic cautions: we’re talking antimonial lead here, which, besides lead and antimony, may also contain trace elements of copper, tin, and, uh, arsenic. It is widely and generally regarded as hazardous if absorbed. Don’t saw, sand, grind, or attempt to melt it. Don’t breathe its dust or fumes. Don’t eat it or swallow it (and, it goes without saying, let any one/thing do it either). Don’t bury it or shoot it at anything, whether or not it/they can complain about it or not. And if you do any of that stuff, remember to tell your legal counsel that I specifically told you not to. top
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Contents and illustrations © UFIE 1999, 2000 and may not be reproduced for commercial purposes without specific permission. Which means that you, Joe Guy, can make copies for yourself or to give away, but not to sell. Fair enough?