Plywood thickness

[UNIONPACIFIC4018]

Okay got a thickness issue on plywood.
I started building a new layout around the room 2' depth. Ihad some 3/4 inch plywood from a previous project and stared laying that down. I needed 4 more sheets of plywood so I headed off to the lumber store and got what is called 3/4 inch. Well after I started laying it down and reached a joint between the two thickness I noticed they were of different thickness. I have a 1/16"-1/8" difference. I realize due to american greed they can turn out more of a tree if they shave off a 1/16" of an inch on the thickness so now I am at a quandry as what to do. Anyone have any ideas

[Anonymous]

I am wondering if they are both sheets of 3/4" plywood? Sometimes stuff goes in the wrong stack.

I feel your pain. The supply of plywood has gone to the dogs around here in the last few years. Potato chip warping, voids, uneven thickness etc. I always buy cabinet grade 3/4" birch or oak for my subroadbed and I am very picky about the individual sheets. More expensive, less headaches. I have had some thickness issues but less than a 1/16".

My suggestion would be to shim along the joint or get other plywood that does match thickness and use the wrong sized stuff for other projects where the thickness is less critcal. Maybe you can take back the sheets that you haven't cut for some that are in tolerance.

[Eriediamond]

3/4" plywood should be 3/4" period. Are you sure you purchased 3/4" and not plywood measured in mm, as some plywood is meaured in millimeters and some inexperienced stock people will place this millimeter stuff in the wrong shelves cause it looks like 3/4. That would explain the 1/16" difference in the other sheets you already have. The size should be stamped or stenciled on each sheet. Also, if the newly puchased wood is 3/4", are you sure the older stuff is actually 3/4". Did you actually measure it to be sure?? Ken

[claycts]

Sorry folks per my lumber yard, 3/4" plywood is FROM .625 to .725.
There is 5/8" plywood that is .5625 to .625. The ONLY plywood that is true is the cabinet grade period at $38.00 per sheet in my area.
We worked on our car shop and used OSB nominal 1/2" there was a full 1/16" in every sheet from end to end. The next lift was dead on 1/2" for all 50 sheets. Now that is QUALITY CONTROL for you.
I look like a nerd but I take a micrometer to the lumber yard when I am doing a project. This is why spline roadbed was invented. I just wish I could make some that worked.

[dehusman]

Its not greed, its wood quality. The 3/4 in isn't absolute, its a nominal dimension, just like a 2x4 isn't 2 in by 4 in.

If you are using a joist and riser on open grid or L girder benchwork system for your roadbed the plywood thickness is immaterial. You could mix 3/4 and 1/4 if you wanted. I assume you are not doing that.

What benchwork style are you using?

What it will involve is at a joint between the two, put a 1/16 (basswood, balsa wood, aircraft plywood, shims, veneer strip) shim under the new plywood and then use only new beyond that.

Dave H.

[UNIONPACIFIC4018]

I guess I could shim it up it would be the easiest solution.

thanks

[Adelie]

If you are joining the two, cut a piece of the "thicker" 3/4" and attach it to the underside of the "thinner" 3/4" where the joint will be. Then cut a piece of the "thinner" 3/4" and attach it to the underside of the "thicker" 3/4" where the joint will be. Then attach whatever you are going to use to join the two on the underside of the two pieces you have just used, and it should be flat.

You can use this method to attach different thicknesses (like 3/4" to 1/2") as well.

[TBat55]

Plywood is made up of layers and should be specified in 1/32" increments. 15/32" plywood is called 1/2". As dehusman said, it's a nominal description. If you ant to make up the difference, try 1/32" fillers like from a model airplane hobby shop.
I would not recommend good-one-side meaning the not-good side has knot holes or cutouts that have not been filled and sanded smooth. These defects can vary a lot and can be trash-one-side.
It's a good idea to prime at least the edges to prevent de-lamination.

[bogp40]

After shimming the joint, just belt sand any spots where your roadbed will be. If you are glueing foam over the ply, even a 1/8" discrepancy should be no problen at all.
Some info about ply. As mentioned only cabinet grade and specific lumber core plys are full thickness. Underlayment grades of ply, PTS plugged and sanded in fir, and 1/2 or 3/4 luan from a quality lumber yard not Big Box, should be considered. Any ply used should be a min of 5 plys if not 7 for stability and strength. 1/2 luan is more stable than 3/4 CDX in pine.
Check out the differences between the quality from a real lumber supplier(where all us carpenters go) and the crap at the big boxes. I really don't want to get going about the pine from those places.
Good luck and hpoe you get track laying soon.
Bob K.

[Anonymous]

If you're going to overlay the whole thing with foam, just make sure that the foam joints don't match up with the plywood joints.

Mark in Utah

[Anonymous]

[

QUOTE: Originally posted by claycts

Sorry folks per my lumber yard, 3/4" plywood is FROM .625 to .725.
There is 5/8" plywood that is .5625 to .625. The ONLY plywood that is true is the cabinet grade period at $38.00 per sheet in my area.

Gee that great we in australia have to pay $60 a sheet for crapy pine plywood[:(!]

[Medina1128]

If your over laying with foam, don't even worry about the difference. Just sand the foam to get a flat surface.

[olequa]

If you are using foam, you don't need the plywood. At all.

[UNIONPACIFIC4018]

You cannot get 2" thick foam here in Texas without special order. I have put my hobby on hold until I redo our backyard so maybe in a year or so I can get back to model railroading.

[grayfox1119]

Many , many times, I have been picking up plywood at Home Depot, and Lowes, and have found that some lazy cutomers had pulled some 5/8" off the stack, saw something they didn't like, so they slid the sheet onto the adjacent stack. Now some poor soul comes along and things what is in the pile marked 3/4" is 3/4"...nay, nay, you need to check!! This is what happened to you. 3/4" will be 3/4", not 1/8 thinner etc. to save money from the saw mill.