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Rookie Mistake

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  • Rookie Mistake

    My current track is my first 4x16 routed track so it used 2 4x8 sheets of MDF. When I started I screwed the MDF down to my plywood topped table and used a level to ensure the seem between them was basically flat.

    Sadly, it wasn't perfect. One side of the table is very slightly off. I tried to fix it by using a small amount of Rock Hard over the seem then sanding it down. It helped a little, but I suspect I can't drive a G-Jet over it with out going airborn.

    I only have two ideas to fix it:

    1) More Rock hard and more sanding to try and get it nice and smooth.
    2) Unscrew the MDF from the plywood, Slide the MDF off the plywood and screw a joiner to the to sheets of MDF. If the joiner is tight it might pull the two sheets cleanly together. Odds are doing this it'll pop the rail out in which case I'd cut it loose and patch it by dropping it down the table and re-laying the rail in the space that popped out. One problem here is that the MDF if 1/2" not 3/8" thick. This is going to make it a lot harder to "flex" from the joiner. The good news I guess is it doesn't have to flex that much...

    Any thoughts on this? Any better ideas?

    Thanks
    Dave
    Last edited by daufderh; 08-07-2018, 09:42 PM.

  • #2
    Can you shim the mdf with paper between the mdf and plywood?

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    • #3
      depending on the magnitude of the unevenness, maybe easier(less mess) to level out the track?

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      • #4
        Got a pic of the problem area??? RM

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        • #5
          You are going to have a hard time of it if the two sheets of MDF are not the same thickness. I'd be willing to bet that is your problem.

          The only good solution in that case is to insert a shim between the thinner MDF and the plywood. Sorry if that is going to be very hard to do without screwing up your power rails.

          My solution would be to (carefully!) cut the power rails at the joint, do whatever is necessary to insert the shim, then jumper the gap in the power rails.

          Could you bridge the gap with a bit of solder? Maybe. Might be worth a try. I'd practice on a mock-up first.

          Ed Bianchi

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          • #6
            Tap some set screws along the edges of both sheets MDF where they butt up against each other (harden the threads in the MDF with CA). Loosen the plywood in this area. Adjust the set screws until the surfaces perfectly match.

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            • #7
              shimming!

              Shimming from underneath is the answer. You could build the surface up and sand it down till the end of time and there will still be a bump there.

              Scott (who really dislikes sanding things and making clouds of dust only to do it again.)

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              • #8
                Originally posted by wartnose View Post
                Tap some set screws along the edges of both sheets MDF where they butt up against each other (harden the threads in the MDF with CA). Loosen the plywood in this area. Adjust the set screws until the surfaces perfectly match.

                I thought a picture might clarify things. Tap screw holes. Harden screw holes with thin CA. Retap to clear any globs of hardened glue. Pretend the screws shown are set screws. Adjust up and down. You may just need these in the area of your rails. Problem with this technique is that when you drill the hole the MDF, being soft, bulges out of the other side of the hole and you have to scrape it flat with a chisel. Also since your MDF is already attached to the plywood you would need to separate the MDF from the plywood to drill the holes so might not be the best option for you
                Last edited by wartnose; 08-18-2018, 07:31 AM.

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                • #9
                  I can confirm that trying to smooth the distance out with bondo/rock hard/whatever and then sanding it down does not work that great. The magnet cars now run really well, but the G-Jet at full speed goes flying...

                  I had previous used wooden shims to even out the two boards. Either they moved (I didn't secure them to the MDF) or they didn't fix it 100%. I remember putting a level across the entire table and thinking it was "close enough" but for me that could have meant the bubble was not centered on the level but with mostly in the area.

                  I think the biggest problem is that I used 1/2 inch MDF. The stuff doesn't give much at all. Sadly to get 3/8 inch I have to special order it which was a giant hassle, but I won't be using 1/2 inch on my next track for sure.

                  I bought metal spacers that I can screw on to the underside of the MDF. I think that's basically the same concept as what wartnose is suggesting. The problem is, where they're needed there's essentially 6 lanes of track. So the screws have to be placed carefully not to mess up traction magnets or worse guide pins.

                  Because the track runs really well for magnet cars, I'm probably going to run it for a bit then try to fix it. That way if I destroy it trying to fix it I'll just start a new build sooner than expected.

                  Thanks folks
                  Dave

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