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Enlarging keel on slot car guides

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  • Enlarging keel on slot car guides

    I'm building a new banked oval with crossovers at each end of the track so a solo car will cycle through all 3 lanes. Most of my oval cars are custom built using the larger Parma or Champion commercial track guides and tests suggest they will negotiate the crossovers just fine. But, a battery powered test vehicle with a small RTR guide (Monogram?) didn't always follow the intended route. When going through a crossover on lane 3 that was intended to divert it to lane 2 it often had it's momentum deflect its guide so it remained in lane 3.

    I think the key to having the crossovers work as intended will be enlarging the keel on smaller guides using glued on thin plastic stock. I know others have done this and am looking for tips on what has worked. The slots on this track are 1/8th inch wide & 5/16th inch deep. I want guide keels to be 1/4" deep but not more than that. More importantly, the needed upgrade is increasing the keel's length. Would it be best to extend it forward, backward, or both? And what contour did you use for the extension (rounded, slanted, etc.)?

    The problematic small guide on the test vehicle is around 5/8th inch long. The Parma commercial track guide is 1 inch long. The red Carrera guide keel is 3/4 or 7/8 inch long.

  • #2
    Click image for larger version

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    A strip of kevlar folded and epoxied into place helped this old Scalextric Formula Junior to work on my routed track. Click image for larger version

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    • slothead
      slothead commented
      Editing a comment
      Thanks for the reply. Can you remember the kevlar's thickness and where you can get it?

    • Kevan
      Kevan commented
      Editing a comment
      I thought Kevlar is woven fibre, that isn't woven and doesn't look like Kevlar, more like a nylon or white lexan

    • dinglebery
      dinglebery commented
      Editing a comment
      Yeah, that's not Kevlar. It's probably Delrin.

  • #3
    If the dimensions/profile of the Parma guides work well, I would just replicate them when modifying your smaller "RTR" guides.
    As the Parma guides have their posts towards the rear of the guide, I would add the additional length on the "RTR" guides at the front of the guide...this will most accurately recreate the Parma guide design.

    As for methods,.... John's (Munter) suggestion will work, or you could glue some thin styrene sheet to either side of the guide blade , and trim to match. If you go this route, it is advisable (highly) to insert/glue additional pieces of styrene into the gaps (bottom and front) formed by gluing the side pieces on to either side of your existing guide blade.

    Hope this helps......

    Chris Walker


    • #4
      Thanks for the feedback. I assume the cars with larger Parma guides will negotiate the crossovers as intended because the car I tested did. However, I understand the physics of a car being pushed around a corner are different from one moving under its own power and momentum.

      I just took a closeup picture of the crossover in question and it looks like a guide keel would need to be a minimum of 1" long, possibly as long as 1 1/4" long to totally ensure the front of the keel is steered into the correct slot by the rear of the keel.

      Click image for larger version

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      I'll do some testing to ensure a longer guide keel won't bind anywhere in the inside lane, especially since the inside lane slot on this turn has narrowed a little during banking.


      • #5
        We used to routinely add a strip of styrene to the bottom of the flag to deepen them. Just make sure it's flat before you glue stuff on or it will eventually peel off.
        As far as the transition, you can ease the guide in by filing or sanding the slot slightly wider on the side the car is heading toward (as opposed to leaving). it doesn't take much, but it should run better. As soon as those sharp points crack, you will have round them now to avoid the problem.
        Come Race at The Trace!
        Timberline Trace International Raceway - SW of Mpls, MN


        • slothead
          slothead commented
          Editing a comment
          I almost want to put something like a small finishing nail right at the tip of the 'island' where the lanes diverge after the crossover. I'll try filing one down so the shank is triangular and then test to see how accurately I can place it on a scrap piece of MDF.
          Last edited by slothead; July 25, 2020, 06:06 PM.

      • #6
        and doesn't look like Kevlar
        Thanks for the reply. I was told it was by the guy I got a sheet from and didnt know any better.
        I am just glad my pictures are still showing as I have had a problem with that lately.


        • #7
          Navigating the crossovers in the corner is the same issue I had when I built the crossover oval with Monogram track and Scalextric curved crossovers. I didn't want to have to make special guides for the cars and finally realized it wasn't feasible unless I just used all Scalextric Sport, but that narrow lane spacing wasn't practical for open wheel cars.
          Matt B
          So. In


          • #8
            Looking at the photo of your crossover, I would imagine the guides with rear mounted posts would have less trouble negotiating the crossover than guides with front mounted posts simply because the centrifugal force of the car is pushing outwards at the point of the guide post, and on a rear post guide will steer it inward where a front post guide will steer outward at the crossover. Therefore it would be beneficial to extend the length of the guide at the front, would it not?

            Clear as mud? ..... maybe this'll help?

            Click image for larger version

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            CHCH NZ


            • slothead
              slothead commented
              Editing a comment
              I get your point, it matches with what Chris Walker stated above. I appreciate your thoughts.

              An extension will be added to the front of short guides.

          • #9
            Another picture of the crossover with some finishing nails I found in the tool shed. Think I'll use 2 of the longer shiny ones in front of the crossover tips. Don't really need one on the right side since cars will only be going counterclockwise on this oval, but 2 nails will shorten the gap.

            Plastic from these flossing picks may be used for a guide extension - possibly including part of the pointy end.

            Click image for larger version

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            Attached Files


            • #10
              I would think about taking a mm or two out of the lower point - and rounding that a bit. All your pressure is on the outside of the flag - and bouncing around. If it bounces at the right moment - your going to deflect off that lower point and maybe not make it. If the track is one direction - I'd open up the side that will catch the flag a little.

              I'd try to get the track working with stock setups otherwise every car you get will need a modification


              • #11
                I'd be opening the slots on the far side to give the guide less chance to hit the nail, rather like this if you're driving left to right >---
                Kevan - Isle of Man
                Life is like a box of Slot cars...🚓🚗🚚🚜


                • #12
                  Yes, the oval will be counter clockwise ONLY. I'm certain any car going in the opposite direction would be instantly struck by lightening.

                  I expect the most frequent failure to be when a car in the outer lane fails to exit the crossover in the inner lane (in this case from lane 3 to lane 2). That would be when the guide is pressed against the outside and just follows that path. When this happens for lane 2 crossing over to become lane 3 a car will be following its intended path.

                  Because I've been assured the other corner section I got routed last weekend is going to break when banked (there was a CNC error and it has a crack), I'm already working on a new design that will move the crossovers to the exit of a corner. I hope to have at least 1 lane, if not both, be on straight paths as they cross to minimize the deflection problem. If I can get the crossover gap to be less than the length of even a short guide keel the problem should be eliminated.

                  I greatly appreciate all the comments. I know this is an odd project, but I'm new to this retirement gig and have endless time for my imagination to come up with things.


                  • #13
                    After reading all the comments in this thread, and studying the crossover, it's finally filtered through my somewhat thick cranium that what needs to be redone is the crossover(s), not the guides.

                    I measured the crossover pictured above and did some math - the divergence angle is slightly less than 10 degrees. It looks nice and the CNC routing is crisp, but with such a small angle causing a wide crossover gap it's likely cars will tend to favor exiting the crossover on the outside lane unless ridiculous changes were made to the guide keels.

                    While I'm still playing around with the corner section to see if it can be modified, I'm also also moving forward with the alternate design where that divergence angle will be at least twice the size. This will shorten the crossover gap and make the convergence and divergence tips thicker and less likely to be damaged by the passing guides. After a lot of planning I think I'll even route the new corner(s) myself using a fence to guide the router.

                    Here's my first raw sketch of the newly developing plan. I'd like to get all the crossovers into the lower left corner (section E) so the lane paths on the front straight (F) are straighter.

                    Click image for larger version

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                    Comments welcome.


                    • #14
                      Is this for just one car to run on at a time? If it is, then why don't you change the apex of the E section entirely so that your crossover lane is more like in this pic
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                      This can be massaged in any number of ways


                      • slothead
                        slothead commented
                        Editing a comment
                        Yep, that's just what I would like to do. This is my solo racing oval intended for time trialing my dirt cars and then using the lap times for simulated races. The lap counter & timer dead strip would be halfway down the front straight in lane 3, meaning a lap time would actually be the sum of 3 trips around the track. Lap times on the outside lane of my 2 lane oval are around 2.8 seconds and it would be nice to work with 8 - 10 second lap times.

                        Thanks for augmenting my sketch. Those crossover angles look much better than what I have now.