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  • 4x16 Track

    I'm getting ready to rebuild my last failed 4x16 track. In building the 4x16 table, I'm using 2 4x8 sheets of MDF. Of course there's a small gap between the two sheets. The plan is to run either Rock Hard or Bondo over it to make a nice seamless tabletop. So my questions are:

    1) Do I do this before I route anything or do I do it after. As I recall on my last track I did it before I routed, but the router ended up chipping it in places forcing me to have to patch it up and in one place even patch the slot and route

    2) Do I need to get the Rock Hard (it'll most likely be Rock Hard) down into the gap? I can't see me being able to actually fill the gap, and its got to be less than 1/8 of an inch wide.

    3) Any suggestions on this? I can't help but feel like it was a pain point on my last track

    Thanks
    Dave

  • #2
    Will the table be plywood with the MDF on top of that? Even fairly thick MDF will eventually sag if it is not supported. We have never had a problem with the MDF chipping where there is a joint. Possibly the bit that you used was low quality, cheap bits get dull quickly and will make a mess. Go for a good carbide bit. You might do a test before you start to route the actual track. If you do get chipping with a good bit you can use Water Putty on the joints and then do the routing.

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    • #3
      Dave,

      To handle the joint, back cut the two pieces of mdf that are going to be butted together. 3 degrees should give you a good tight joint.

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      • #4
        Sorry, to be clear, its not the MDF that's chipping. Last time I did this I put some Rock Hard over the seam. That made a nice flat surface but when I took the router through it to cut the guide slots and rail pockets a lot of the rock hard chipped away.

        I had to do a lot of patch work to fix it, including in one place I had to fill the guide slot so I could patch the seam, then re-route the guide pocket. Ultimately I think it came out okay, but it seems like it was more work that it should be.

        Oh, and use, my MDF is on top of ply wood. Originally I was going to use the MDF as the table top, but I had the ply wood already and its so convenient having it under there. Good to know it'll also prevent sagging...

        I'm not sure I could put anything in between the two sheets of MDF to fill the gap. If I did something like that, wouldn't I have the same problem on both sides of the filler instead of just in between the two sheets of plywood like I have now?

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        • #5
          I don't understand why you are so concerned about the joint between the two sections of MDF. The whole game is to properly support it. Do that right and you won't have an issue. I've done many such joints, and never felt the need to fill them.

          Since you are going to use plywood to support the MDF, all you need to do is support the joint from underneath with a piece of plywood that spans the gap, at least six inches to either side.. And it helps to fasten down the MDF to the underlying plywood with a number of screws, both close to the joint and a few inches away either side of the joint. Use more screws rather than less. Countersink the screws, so you can fill over top of them later.

          On rare occasion I have had to shim joints because one sheet of MDF was slightly thicker than the other. If the joint is not flat you may have to open the joint and insert metal shims. Don't try to sand the joint flush. It's too much work and the end result will not be satisfactory.

          Once you are satisfied that your joint is level, fill over top of the screws, then sand the fill flush.

          NOTE: It is possible to remove screws that have been filled. I have done it when I had to disassemble a track. Not hard at all, really.

          I strongly recommend that you assemble your table -- plywood, MDF, but not edging -- BEFORE you do any routing. (That's assuming you aren't doing anything fancy like banked turns or overpasses.) I would not bother with any filler at the joint. You should be able to get the joint mechanically tight. If you simply MUST fill the joint, I'd use something made for the purpose, such as 'Plastic Wood'. But honestly, I can't see that being necessary or helpful.

          One last piece of advice -- paint your track BEFORE routing it! The router base will not damage your paint job! On the other hand, if you paint AFTER routing, you are going to get paint down in the slots, and have a fussy old job getting it out again.

          Ed Bianchi

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          • #6
            Hmmmm. Maybe it's a two person job but I could not get the two sheets of MDF completely flush. I did get them nearly perfectly level, but there's a gap that's probably 1/16 of an inch or so. Maybe I'll take another stab at getting them flush. One sheet screwed down, the other forced hard into it...

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            • #7
              The gap shown in the photo below is typical of joints on my tracks. I measured the gap with precision dowel pins -- the largest pin that would fit in the crack was 0.029 inches in diameter (0.74mm). For reference, the slots and the braids are both 1/8 inch wide (3mm).



              There should be no trick to getting two MDF sheets to meet up this close, as long as you are fitting the factory-finished edges, not edges you have cut yourself.

              Okay, maybe one trick...

              Fasten one sheet down to your table. Set the other sheet up next to it, then clamp it to the table with rubber-faced clamps. Don't clamp it too tight, because you are going to use a rubber-faced assembly hammer to tap the second sheet into close contact with the first.

              You might find it best to clamp the second sheet of MDF very close to the joint, or even span the joint with the clamps.

              Work everything into close alignment. When you are satisfied, fasten the second sheet to the table.

              If you want to fill the joint to make it invisible, well, do that. Any old wood filling compound should work. Slightly overfill, because there will be some shrinkage as it cures, then sand flush and paint.

              Ed Bianchi

              PS - I should mention that the joints on this track had to be shimmed to get them level, because the two MDF sheets were not the same thickness. Taking measurements before fitting things up will give you a good shot at deciding if you'll need shims, and how thick they'll need to be.

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              • #8
                Okay I should be good then. Just looking that looks a lot like my table. I will throw something over the seam to hide it but that's it.

                Just wanted to make sure. Thanks
                -Dave

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                • #9
                  Route it first, fill the slot with a piece of plastic BEFORE you Bondo to keep it slot clean.

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                  • #10
                    Originally posted by daufderh View Post
                    Hmmmm. Maybe it's a two person job but I could not get the two sheets of MDF completely flush. I did get them nearly perfectly level, but there's a gap that's probably 1/16 of an inch or so. Maybe I'll take another stab at getting them flush. One sheet screwed down, the other forced hard into it...
                    Dave,
                    Another trick that might work. Lay MDF sheet #2 on top of sheet #1 with a very small overlap (1/4" or so). Place another sheet or something else under sheet #2 so it sits flat. Clamp everything down tight. Using a straight edge and circular saw cut through both sheets at the same time. This will give you a very tight fit even if your not perfectly square. You will lose a bit of board at each joint, but should not be more than 1/2" or so.

                    Charlie

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                    • #11
                      No need to cut the MDF. Edges from the factory are very straight and very square. Just try to avoid banging up the edges during transport.

                      Here is something most people don't know. MDF sheets are intentionally made oversize. A 4 x 8 foot sheet is actually 49 x 97 inches -- one inch oversize both ways. Sometimes I have cut sheets down to 48 x 96, other times I have left them oversize.

                      So if you do want to try Charlie's trick, you have excess material you can cut away and still end up with 4 x 8 sheets.

                      *************

                      And I still say save routing for last. The router base will not damage your paint job. And if you are paranoid about it, buy some self-stick felt at your local Ace Hardware store and cover the underside of the router base (http://www.acehardware.com/product/i...ductId=1296622).

                      'Course I always use a template when routing my tracks, so I almost never have to patch a wayward slot. If you are using a compass and straightedge you can expect to do some patching. (It just happens!) And if you paint first that means touch-up.

                      I've blathered on endlessly about why you want to rout from a template. But everyone is SO much smarter than me! Just remember I said so.

                      Ed Bianchi
                      Last edited by HO RacePro; 06-14-2017, 12:05 PM.

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                      • #12
                        I've always routed from trammels and straightedges, and you're right, Ed. any pix of what your templates look like?
                        thanks!
                        speedy

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                        • #13
                          Patching is my middle name

                          I'm still debating when to paint. Usually I paint after I route the slots but not before I route the pockets. In my experience the router scratches the paint job and you can see trails where the router came through. I could touch that up, but if I were going to do that why not just paint after.

                          I've never really had a problem with paint in the guide slots. I just do 2-3 coats and lay it on super thin so there's no dripping. I can generally go right over the guide slot like this with no problem. Clearly I don't 100% trust that though which is why I paint before doing the power rail pockets.

                          I'm getting closer to routing, but I still have a few decisions to make. The good news (or bad depending my perspective) is that I don't think the track will be ready for the next time my family is in town which means I basically have all the time in the world to finish.

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                          • #14
                            I have added a post about routing with templates on the next page.
                            Ed Bianchi
                            Last edited by HO RacePro; 06-19-2017, 03:26 PM.

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                            • #15
                              Really cool to see the close up.of your braided track Ed. I'm assuming there is a noticeable raised surface on the braid so that it works the same as rails for pick up shoes. Is that right?

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