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Tiny SlotIt Set Screws

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  • Tiny SlotIt Set Screws

    I raced in the second IHSR endurance race this summer. Both races were 4 hours long -- a total of 8 half-hour segments. All the cars were SlotIt brand, and largely stock. The teams were typically two drivers. In both races there was a three-man team, because an odd number of racers showed up.

    The rules for the race required at least one driver change per segment, and at least one change of the rear wheels and tires, done under green. No work could be done on the cars except during green-flag racing.

    The wheel/tire changes turned out to be very challenging. The reason? SlotIt brand cars use 2mm set screws for the rear wheels. In both races I, my teammate, and others who tried to help out, had a devilish time trying to get our tools to fit and turn those set screws.

    We had a selection of quality tools, including the allen wrenches provided by SlotIt with their cars, premium Wiha brand hex drivers, and other industrial quality hex drivers sold by McMaster-Carr. We couldn't get enough purchase to unscrew the little -- danged -- screws. And then we couldn't get them tight again.

    At one point I used a Dremel cutoff wheel to grind a new, sharp end on the SlotIt allen wrench. That helped a little bit, but not for very long.

    I also tried substituting brand new 2mm set screws I had purchased from McMaster-Carr. Again, presumably industrial quality fasteners. Didn't solve the problem.

    During the race today the track owner/race director got out his own tool and tried to help us. He finally allowed my team to finish the race without any more tire changes.

    In both races my team lost so much time in the pits we had no hope of being competitive. We finished last in both races.

    No sour grapes here. Endurance races are notorious for WTF issues scuppering teams. But I am frustrated that both our races were bitten by what can only be quality issues with the equipment.

    My solution will be to drill out and re-tap all of the SlotIt set-screw holes for larger screws, and hope they pass tech. I suppose I'll have to bring along stock hardware just in case they don't.

    Has anyone else run up against this issue? Any better solutions?

    Comments please.

    Ed Bianchi

    PS - I am coming to 1/32nd racing from a long career in HO. I'm used to small parts.
    Last edited by HO RacePro; 08-17-2019, 05:06 PM.

  • #2
    I found the same issue with my Whia tool for slot-it grubs. Over time them seem to not grab. I switched to an NSR driver with the correct size for slot-its. Work better and the tips are replaceable.
    A tip for quick changes. I will sometimes insert the driver in the grub before placing on the axle.



    • #3
      If you are running in an endurance race you need to practice for tire changes in advance. For a start replace the stock set screws with higher quality ones. Never use a regular L shaped wrench, those round off easily and when they do they will also damage the set screw leaving you stuck with a screw that won't come out. I have used many hex drivers over the years. some were not properly heat treated and would easily round off, others were too brittle, so the tip would snap off if you tightened the screw too much. For a long time I used the orange torque limiting wrench that sold. The tip on those was a good compromise between hardness and brittleness, they did round off after a few years however. The orange wrenches have been replaced, but I have not tried the new ones. Right now I use a Scaleauto torque limiting wrench, those have replaceable tips. If you are using hubless wheels you need to use a wrench that does not have a fat shank. Wera and Wiha hex drivers have good tips, but they may not work well with some hubless wheels. If you have damaged the socket of a set screw you may be able to remove it using a slightly oversized 0.95mm driver.


      • #4
        Thanks for weighing in Rich. I know you have a ton of experience in 1/32nd.

        Where would you find 'high quality' set screws? The replacement screws I purchased are M2 18-8 stainless steel from McMaster-Carr. I would have thought they were quality parts, but maybe not. Perhaps stainless was a mistake. Might not be as hard as carbon steel.

        I had noticed that there were torque-limiting hex drivers available. That seems to indicate that over-torquing set screws is an issue. I guess I will invest in same. Ticks me off though, because, again, I thought I was buying quality hex drivers. That money appears to have been wasted.

        Ages ago there were axles and wheels with a tapered fit. The ends of the axles were threaded so a hex nut could hold things together. That tapered setup assured everything was concentric, and the wheels were held on with a death grip. The gears had a two-part tapered setup where a hex nut pulled things together. In my opinion, both methods were superior to set screws, but almost certainly more expensive. Good ideas sometimes don't survive in the open market.

        I still think larger set screws would be a better solution. Some folks would say they'd unbalance the wheel. My solution would be to drill and tap all the way through the hub, so you could install set screws on both sides of the axle. This would not only achieve balance, but would allow redundancy. And nobody says both set screws would need to be tight. You could leave one just a hair loose for quicker wheel changes. Of course you would need to mark the wheels to indicate which set screw is the tight one. Maybe a stripe of Wite-Out would do the trick.

        I had always thought HO cars would be more delicate and touchy than 1/32nd. I'm learning that isn't necessarily the case.

        Ed Bianchi


        • #5
          (Duplicate posting deleted.)


          • #6
            Why is this a problem ? If everyone is racing (proper spelling) cars, everyone has the same problem, so, it's really a moot point.

            Yes, "most" stainless steel fasteners are of a lesser grade than carbon steel fasteners. But in many cases, you can pay more money for higher grade stainless, but not all stainless fasteners are made in high grade material.

            I've never payed any attention, but is the hub on the wheel large enough for the next larger thread size ? Also, would it be legal for your racing ? I know there is a few 1/32 car manufacturers that use the larger set screws.



            • #7
              Don't use silver stainless grub screws, they're soft as sh*te, always use high tensile steel ones.


              • #8
                I must admit to being somewhat perplexed by this thread. Between and Racer cars plus numerous other brands which I have retrofitted with gears and or CB Design wheels, I have probably more than a hundred cars with 2mm hex setscrews. And I have pretty much never had any significant problems with them over many years of racing. OK, maybe once in a blue moon I rounded the head of a setscrew or had to grind the tip of the wrench back to get a nice clean hex shape and I think I once stripped the thread in a wheel. But that is it.

                And as for quick change: last year we had a rather big Western Canada endurance race of similar duration to the one the OP described. Because insufficient ground clearance was a disqualifiable offence, we changed wheels and tyres under green near the end of the race. I believe the car was off the track for less than a minute in total: stopped, picked up the car, we had to take it to the pit area, replaced the two rear wheels, back to the track and off again.

                Over the years I have used the original little simple hex wrenches that come with the cars, a adjustable torque wrench (which has been my least liked wrench), a Hudy wrench, a Slot Car Corner wrench, a Scaleauto wrench and a Wiha wrench. They may differ somewhat in dimensions and in quality but all of them have worked at least OK and lasted some time.

                Ergo: over many years over many cars, my experience has been very different, hence my surprise at the OP's experience. For whatever that is worth and of no use to the OP I am sure.


                • #9
                  Duplicate post.
                  Last edited by SlotsNZ; 08-19-2019, 01:59 AM.


                  • #10
                    I'll have to repeat some of what at least "the Slab", Rich, Glen and Kevan have already said, to summarise what I would always consider in such situations.

                    First, forget the O.D., just think the driver size - You have cars with M2 hex grub screws which screws require a 0.9mm or 0.95mm driver - a very important difference in itself that 0.9 or 0.95. as there is not a universal size of hex for M2 grub screws, and one maker's 0.9mm hex driver tip, may in fact measure larger than another maker's 0.95mm tip.
                    You may find the Wiha are on the smaller side, which could lead to rounding out. - Just surmising, as I vaguely remember reading about this here years ago.
                    I am surprised that a track owner, did not have all this down pat as well.

                    Next up - and I have to be a bit cruel here - you were not bitten by any kind of quality issue of parts, tools or anything else, you were bitten by your own lack of understanding of your parts and tools, and a failure of the team to fully prepare.


                    Depending upon the combination of wheel to tyre, and the amount of gap between the outside of the gimbal bush and the inside of the wheel boss, you may not have a lot of viewing room to check the screw position around the circumference of the wheel with the body still on the car.
                    However one side or the other - usually the non drive side on a sidewinder, will have a larger gap, making viewing of the grub screw easier.
                    So step one: I always align the 3 grub screws - so I can go off the grub on the sidewinder spur, angle-winder spur, or the inline crown gear, to find the approximate position around the circumference of the one on the wheel I wish to remove. - I know some purists will tell me this puts the drive train minutely out of balance, but so does uneven glue, so do marbles on the tyres and other things, I don't really experience a problem.
                    2) If you know the tyre will overhang the wheel boss on the inside, making the grub screw position harder to identify, mark the inside edge of the tyres with a silver paint pen where the grub screw is to be found.
                    3) ALWAYS use a torque driver to set the grub screw tension on the wheel to begin with so it isn't over tight and you cannot round out the grub on the way in. I have both and Scale Auto torque drivers, and the tips should last years. I have worn out 2 drivers, and about 3 tips on the ScaleAuto driver in 12 plus years racing. - and I have a lot of wheels on and off cars, as I build a few, and help out lots of guys in my club and a few other customers.
                    4) Make sure having located the grub screw, you press firmly with the driver against the tyre in order to push it in straight into the hex recess, not at an angle.
                    5) Have a pair of nice strong close up glasses on hand specifically for doing this work. Our older eyes aren't what they were
                    6) Take lights with you, a torch, bench light, or miner style headlamps if you need them for working in racing rooms that aren't as well lit up as your work bench at home
                    7) Prepare, prepare, prepare. For an event like yours, have several sets of wheels and practise wheel changes until you can do them asleep, one handed, while whistling yankee doodle and fighting off a bob cat. - okay, I exaggerate, the bob cat may just be a hungry golden retriever.
                    8) If using anything other than a stock combination of grubs and torque driver, make sure the two items are matched before you choose to set your car up.The driver should feel firm, almost tight when you press it into a grub screw. If it is loose, you have a mismatch, and are asking for trouble.

                    There are probably quite a few more, but that's a good start to avoiding a repeat of the problem.


                    • #11
                      I do repairs and custom builds for a local hobby shop. I have an assortment of Wiha, Align, Thorp, and Bondhus hex tools. They are not dimensionally equal. There are times when one tool fits better than another. It's when manufacturing tolerances stack up against you. The tools I use generally don't round off or twist if properly fitting into the grub screw. Conversely, if the tool properly fits the grub screw, there is little chance of rounding out the inside of the screw.


                      • #12
                        I remain disappointed in the touchiness of the SlotIt set-screw design. Other brands manage to use larger set-screws which are much less prone to failure. I consider SlotIt's setup a design flaw. There is no need for it to be so delicate. When you have to cherry-pick tools to achieve a proper fit, there's a problem. When the tool that SlotIt supplies with their cars isn't useful there is a big problem.

                        Since my last post I have been thinking about ways to improve the whole wheel-mounting business. Not that there is really a need! But I enjoy noodling with alternate ideas.

                        Right now my favorite -- which still needs some work -- is a way to snap-on/snap-off the wheels. No tools needed, quick and simple. Not quite F1 two-second changes, but a whole lot closer.

                        I'm thinking in terms of a spring-element that snaps into a detent on the axle. A small, straight piece of piano wire fit into a hole in the wheel, so the wire is tangential to the axle, would be the spring. The axle would have a straight, close-fit cut across it that the piano wire would snap into, locating the wheel both axially and radially.

                        The end of the axle would have a taper so the piano wire can flex out of the way when mounting the wheel. It would have an opposite taper at the cut to allow the wheel to be pulled. The taper at the cut would have to be steep enough to keep the wheel in place during operation, but shallow enough to allow the wheel to be pulled off by hand.

                        Like I said, the concept needs work. And it might not be practical at all. Could be fun to prototype and test, but it is not anywhere near the top of my To-Do list.

                        Still, there are many other ways to approach the problem. If a good, cheap and reliable solution could be found, tool-less snap-on wheels would be a neat feature.

                        Ed Bianchi


                        • #13
                          Here is an example of an industrial part -- a ball detent -- that is almost small enough for use in a 1/32nd scale slotcar wheel. I'm not presenting it as a solution, but an idea-stimulator.

                          Ed Bianchi

                          Screen Shot 2019-08-21 at 9.11.03 AM.png
                          Attached Files
                          Last edited by HO RacePro; 08-21-2019, 05:17 AM.


                          • #14
                            Ed, still too complicated. A simple "spindle" that could be grub screwed to the axle and then a wheel/tire combo held on by a pair of super magnets.


                            • #15
                              Yeah Gerry! Put a taper on that spindle and let the magnets draw everything tight. Dead simple, inexpensive and a two-second tire change looks realistic!

                              You write up the patent and I'll witness it!

                              Ed Bianchi

                              PS - And you're not far off from having a torque-limiting feature on the rear wheels. Now that might be an interesting tweak!

                              Dang! That would be easy to prototype!

                              Stand clear! Brainstorm in progress!