Roadbed Help Needed!

Screw a rib to the underside of the plywood along the length between the risers to support the entire thing. If your rib has a flat edge (run it through a table saw or planer), then you should pull the bow out of the plywood.

Peter,

 

Your solution is another riser at the 2' point (mid-point), right?

 

That's probably still not enough support.  I second Boilermaker1's solution - a rib. 

Even so, you may need 2-3 risers (one every foot).  The current lowspot in your track is bad news, trust me.  I've had them myself.  It's always a good idea to fix these as soon as possible.  You don't want to tackle low spots after you've ballasted or put scenery down.

 

George

George and Boilermaker 1,

Thanks for the responses.  What is a "rib?"

Thanks.

Novice questions here:

A rib sounds like the best solution to straighten out the warped 1/2" board, but is this one of the dangers of using 1/2" instead of 3/4"? I plan on using 1/2", but risers will be 16" apart and I'm leaning toward cookie-cutter style.

 

I understand wanting the 48" point to be at a certain level, but if it's tightened down and then interim risers are added, couldn't that warp the board? I would think the 48" point should be used for temporary support until the other risers are added one at a time. Wouldn't that help minimize the warping a d low spots?

If you use a rib use plywood ,not dimensional lumber, it will warp. Use 3/4" x 1.25 or 1.5" rip on edge w/white glue, just a touch and screw & clamp…10 minutes later you will feel the rigidness. I built w/3/4" and 12" spacing. My friends and family know in crisis to hide under my train benchwork!! All my benchwork is 4" rips of birch ply!

So, is a "rib" synonymous with just adding additional joists about a foot apart from each other across the four foot expanse or ...? Thanks

Its a reinforcement along the length of the roadbed. Instead of your roadbed having a profile that is flat, it will have a profile like a 'T'.

Does anyone have a diagram or photo so I can better understand how it looks and how to construct? Thanks

Technically, if you search for "rib", that is basically what you'll find, mostly images of aircraft wings, canoes, etc. In this case the best way to describe is this:

Cut a 6"x 96" sheet of 1/2" plywood.

Now add a 2x4 on its edge down the middle.

You've just added a rib to make the 6"x96" plywood sheet rigid.

That's a good image - thanks! One last thing I should have mentioned is the roadbed is already all connected and only the risers are remaining to be put in. And because two sections of roadbed were attached about a foot to one side of this four foot expanse, there is a connecting plywood plate glued underneath that area and it extends about 1.5 feet into this four foot expanse. So the underside of this section of roadbed is not even/flat. Any thoughts on how to improvise affixing a rib? Thanks again

The problem with adding a rib below the roadbed is now you have to deal with it to make your risers the correct heights. You could add a rib on each side of the roadbed and then cut the risers to fit between the ribs. That might be okay if you're only having problems with this one 4' section, but it's a lot of work if it's more than that and then there are the curves to deal with.

 

Of course, I could be all wet too.

 

 

The board indicated by the RED arrow is a rib.  It is placed lengthwise under the subroadbed between two risers and used to stiffen the subroadbed.

 

George

Maybe fill it in with more plywood and then add the rib? If the roadbed is wide, it might be best to add 2 ribs on each side. It's kind of hard to be specific without seeing the section you're talking about. Obviously, putting a rib below where the track will be should flatten the track part.

Excellent example George.

George and DoubleDAZ - thanks to both of you. Was thinking the same thing about how to get underside of roadbed flat. And the photo is great. My roadbed is approx 9 inches wide as it will be a double main with a turnout around that point to a third line. So basically, get a straight 2x4 (or maybeveven a 2x6?) and screw it up into the roadbed from underneath. Screws prolly every couple inches or so, right? I guess the other problem is trying to figure out how to make sure the 2x4 is pressed flat against the roadbed underside. I don't have any clamps broad enough for that width.

George

Like your benchwork construction.

I appreciate the compliment, Charlie, but I've made more than my share of mistakes with benchwork.  That rib and others were necessary because I used 11/32 plywood for the subroadbed instead of 1/2", 5/8", or even 3/4".   Earlier this year, I fixed a number of low spots and uneven trackwork due to benchwork errors.

 

George

I think it's a 1x4 in George's photos, but I could be wrong. Anyway, I believe it should stand on edge and be screwed from the top. If you don't have a planer, you might need to run it through the table saw so one edge will be straight. That edge is the one that would mate to the plywood. Oh, and you can't just tighten it to the Homasote, the screw should go down through the Homasote to the plywood base.

DoubleDAZ - thanks again. Didnt realize why it would need to be planed till your last post. But screwing it in from top down is contrary to Linn Westcott's methods. His book says everything gets screwed from bottom up. Makes it easy to unscrew things without tearing apart scenery, or running into a screw head while scenicking. Gonna investigate screwing options and see how it goes. Peter

George and Boilermaker 1 and DoubleDaz - still curious to know how to secure the rib so that it is perfectly flat on underside of roadbed. I don't own a clamp wide enough to reach the center of the roadbed where the rib would go in order to secure the two together for me to screw them together. Maybe I'll head over to HD and see if they make a clamp with very wide jaws. In the meantime, am thinking maybe to place rib in place under the roadbed. Then place a transverse piece of wood across the bottom of the rib with blocks of wood under transverse piece on each side of rib. Then use clamps from bottom of transverse piece of wood to top of roadbed to sort of sandwich the rib in place - the blocks of wood on each side of rib would prevent roadbed from warping downward from clamp pressure. Put screw in rib / roadbed right next to place being held firmly by the sandwich and then repeat this process down the 4 feet until all screws are in place?

Yes, it is a 1" x 4".  I simply screwed it in from the top (pulled track and roadbed off).  You can also hold it in place with weights (used my wife's nursing text books); support it from the bottom.  I used a number of 1 5/8" drywall screws.

 

George

Good point, but Linn is talking about regular benchwork, not a rib added after the fact. I could be wrong, but you won't be taking this rib out any time soon without replacing that entire section of the layout.

 

In any case, here are my thoughts:

If you use a 1x4 on it's side and screw from the bottom, you'll need 4 1/2" screws or you'll have to drill deep holes in order to use shorter screws. And then you'll only be "grabbing" the 1/2" of plywood.

 

If you screw from the top, you can use shorter screws, you won't have to drill deep holes and you'll be drawing the rib up to the plywood to create a very tight connection. If you use, say,  2 1/2" screws, you be drawing on 2" worth of material below the plywood to create the bond, not just the 1/2" of plywood.

 

Now, if you screw from the bottom and add glue to the mix, you don't need clamps. Simply add temporary screws from the top to hold it all together until the glue dries and then remove the temporary screws. Don't waste time and money trying to come up with a way to use some kind of clamp, the temporary screws will do the job quite nicely.

OK, so the plot thickens. It's actually a 2 foot section where the dip is located. I had some spare L girders (1x4, with 1x2 glued to one side) and they were true and flat. I dry-run clamped them with the lip side pressed to underside of roadbed. Not only did I need to mount two ribs (one to each side of this section) but needed to use two clamps on each end of both ribs (with a 2x4 wedged in the middle, pushing up) to get 95% of the dip out!!! I then took it all apart, put glue on the lips of the L girders and mounted them. I also put a few screws for now. So still have a slight dip, but like 1/16 or less of a dip. Seems okay given it's just straight track over this spot. By the way, your posts made me go back and spot check the entire area where my yard will be with all turnouts. Much to my chagrin, it too had some dips. Amazing, since I had it all perfectly flat a month ago when I did this area. Anyway, added some reinforcement and that area is flat again! Really appreciate all the help. Thank you.

PJB,

 

Glad things are improving.  You've taken the big steps to improve your track performance.  If you are still having problems or need to smooth out those small dips because of scale locomotives, you can insert shims under the low spots.

 

By the way, do you have high humidity in your train room?  That could contribute to warping.

 

George

I don't think 1/16" will be a problem. but there is obviously something going on with the wood. Perhaps it's moisture or just acclimating to the space. Unless the environment is completely controlled, I would think there's bound to be some expansion/contraction with the seasons.