Spent Saturday evening working on building the top for my Norm-ish router table and watching the NCAAs — two cocktails… I swear.
I started by cutting to size, gluing and screwing together a piece of 3/4 MDF and a piece of 1/2 baltic birch plywood for the top. Used 1″ drywall screws and Titebond II glue. When I started, both pieces of material appeared to be dead flat (check this by laying both on the table saw top.
Came down to the basement the next morning with plans to cement the high pressure laminate and voila, the top had a 1/8″ bow in it. Unfortunately, it is concave up on the MDF side – the side I wanted to laminate and insert the plate. If it were the other way, I would have minded less becuase the weight of the motor may have pulled in down – but not this way. I really didn’t want the 1/2 Baltic birch side up.
Three questions: 1) What could have gone wrong? 2) should I have used 1/2 MDF instead of ply (I thought the ply might provide some add’l rigidity – I was unfortunately right) 3) Should I try again or is this top still salvageable?
Replies
1) You applied moisture to two disimilar materials that react differently to moisture.
2) Yes
3) Maybe salvageable. Try drilling a couple of holes where the cutout will go to help the moisture dissipate and clamping flat using cauls top and bottom. Give it a week and check for flatness.
Unless you're in a tearing hurry, it might make sense to just wait a while. It'll take some time for the moisture from the glue to evaporate through the plywood and MDF, and it might very well flatten out again.
Possibly not, though. Besides the dissimilar materials problem, gluing 1/2" and 3/4" material creates an unbalanced contruction, which will be more likely to warp than a balanced one.
Ok. That a reasonable hypothesis. The plywood may have absorbed more water from the glue, swelled and caused a cupping effect. Same night I glued two pieces of the same ply together for a drill press table with no such effects. I will try punching a 4" hole through the center, where the insert will go.
Maybe also try stacking some some weight on it as it dries further or alternatively lay on the TS top with plywood side up and use some quick clamps on each end to bend it as it dries further. Reasonable approach?
Probably work better with stickers between it and the TS top to allow air flow underneath.
Robbie,
The fact that you used two different materials and added a lot of moisture from the glue is the main cause of your problem. However it was probably the MDF that did most of the expanding not the plywood. My guess is that the MDF side is convex shaped, which is what would happen if it expanded more than the plywood.
I wouldn't put a lot of weight on the panel, if it is going to straighten out and be stable it will do so just by drying out. If you force the panel flat it will probably cup again later, which is a good possibility in any case, since the top will gain and lose moisture as the humidity changes in your shop.
John W.
Robbie,
To assist the table top in reaching a moisture equilibrium, place it on a flat surface on top of 4-5 stickers - (scrap sticks of wood approximately 3/4" square x the width of the table top). Make sure they are of equal thickness. This will allow air to circulate around the whole top.
If you have any questions, please feel free to ask!
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
You said that the stickers should be 3/4" thick. Do they have to be that thickness or can they be thiner? I have wood drying but not a lot of room so I cut my stickers down to 1/4" to save space. Does this effect how the wood will dry?
L',
The purpose of stickering wood is to allow air to circulate uniformly around each piece. This helps the wood to dry evenly over its entire length. If the air is not allowed to circulate evenly over the stock, it could lead to possible warping, cupping, or bowing of the boards due to areas having higher or lower moisture contents than others areas.
Your 1/4" stickers will work to an extent - but if at all possible, I would switch to something closed to 3/4". The 1/4" stickers may just thick enough to allow cool air to linger between the boards (thus slowing the drying process in the center of the wood), while the warmer outer edges will dry more quickly. Glue three of your 1/4" stickers together and wrap some masking tape around them until the glue dries.
If you have a freestanding bench, you might consider creating a drying rack between the legs. You'd be surprised how much lumber can fit there, and as an added bonus, you bench will be more stable due to the added weight.
If you have any questions, please feel free to ask!
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Trying to laminate dissimilar materials is always risky. If they expand and contract differently with changes in moisture content, they will always be tending to flex one way or another with changes in humidity, just like a bimetal strip does with changes in temperature.
You can reduce this tendency by securing the top to a stout frame, and by using a yellow glue that allows some creep. The movement of the materials you are using will be miniscule, but since the pieces are glued together, it is still enough to make them want to flex. As an analogy, the coefficients of expansion of the two different metals in a bimetal stip in a thermometer differ only minutely, yet a difference in temperature of only one degree causes perceptible movement.
Personally, when I make router table tops. I laminate two pieces of particle board together because they give the best stiffness and sound deadening, then cover both sides with scrap laminate (formica, etc.). This gives a very slick, stable, long-wearing top, and the surface material can be removed and replaced fairly easily if you so desire.
Michael R.
(Edit: this should have been directed to Robbie.) Or, you might have clamped to an uneven surface, which is what I concluded I did when laminating 2 pieces of mdf and a piece of hardboard. My second top is a single 3/4 mdf with lots of support. Also, instead of a rabbeted space for an insert, which when combined with an uneven top makes it impossible to get a flush fit, I used support pieces as levelers attached to the main supports, and used screws to adjust the height. This is similar to a recent FWW article, and I think it will be fine. I'm not sure about the recommendations to try to adjust, when it seems likely it will become uneven again sometime. The cost of the materials is minor (except for the Baltic birch I suppose), so trying again makes more sense to me. OTH, the other posters have much better qualifications than I do. Todd
Edited 3/31/2004 11:20 am ET by TODDHUNTER
Todd: Thanks for the reply.
I corresponded back and forth with Pat Warner. He would be in favor of your approach Todd - a single piece of MDF with motor directly mounted. Actually, his website was a wealth of information and ideas. A few neat products as well.
Pat did provide a good idea of stressing the top by securing it to the carcass. I plan on doing this. I guess that I could probably stress the bow out of the existing top, but instead I will construct a new one with MDF and secure it to the carcase.
When I was attaching the top, I was careful not to "pull" the top down at the points of contact. I pretty much just wanted to keep the top from moving around, and keep it resting on the supports (basically an mdf box with extra cross pieces). I just used L brackets attached first to the top, then while resting on the supports, I screwed into the supports. I became obsessive about avoiding anything that would stress the top. I probably got the idea from a Pat Warner article. Todd
Todd: Pat Warner advocated that one "does" stress the top.
Robbie, I was concerned about uniformity, figuring I would try not to interfere with the original manufacturer's surface. We'll see. Thanks for sharing. Todd
Todd: He also suggested using four coats of Watco to finish the table top (I don't know if it mattered before or after stressing). Have you used this? Is there just one kind of Watco or multiple?
Robbie, I used several coats of waxed shellac, which was recommended for mdf in a recent FWW. It's a good sealer, dries fast, and the wax makes it slippery. I don't believe I thinned it first. The look is somewhat mottled, but I don't mind the instant "character." I also waxed the surface. For edges I began by "sizing" with a 50/50 mix of water and yellow glue, which is supposed to provide even better seal. I just painted it on with a disposable brush. Todd
Report one week later...
I have left the laminated MDF / Baltic Birch panel to dry for one week. I have let it sit upright without any weight on it. I did, however lean it against a wall at a 30 degree angle so that its own weight, if it had any impact, would be to reverse the "bow" (sorry, I can never remember which to use: convex and concave, only that they are antonyms).
No effect. The 1/8" bow still exists. So tonight's project will be to try again, this time 1/2" and 3/4" MDF only, followed by laminate.
Question... on the router top, I have seen that Jessem and Benchdog both have aluminum track that incorporates both a T-track and a miter track. Unfortunately they do not sell the track alone. Woodpecker does not have such a thing. Have you seen this in a 36" or longer length?
A 1/2"and a 3/4"piece of MDF glued together to create a 1-1/4" thickness will cause you problems too. It's an imbalanced construction and although you are using the same material throughout the end result will probably (almost certainly will be) still out of whack.
If you want to build up a total thickness of 1-1/4" you'll have better success with five pieces of 1/4" MDF or five pieces of 1/4" ply glued together. Or maybe two bits of 5/8" material might do it but you need pieces that balance throughout the structure.
You'd even be better with three bits of the same material at 3/8" thick, or one bit at at 3/4" sandwiched between two bits of 1/4" material.
Whatever you do, it all has to be in balance-- an MDF core with equal thicknesses of ply either side, or ply in the centre and MDF either side.
Whatever goes on one side of the core needs to be matched by whatever goes on the other side of the core. Anything else is a fairly surefire means to experience disappointemnt or failure. Slainte.RJFurniture
Try Lee Valley for the Aluminum T-track and Miter track. They sell 48" lengths
http://www.leevalley.com
Hardware tab then project supplies. Used the same thing for my router table top.Rome wasn't built in a day, take your time and do it right the first time.
Big Rick:
Thanks for the tip. However, I am looking for a piece of track that incorporates both a t-slot and a miter slot in a single extrusion. I did see one that is 32" on a different site, based in Philly, but not 36" or longer. Was surprised Woodpecker hadn't come up with this yet as has Jessem and apparently BenchDog.
BW
Just to second and third, and forth, several of the previous posts...
When you laminate two different materials together like a piece of MDF and Ply wood, my sad experiance has been that is will never remain flat. This one goes in my mistake book right under "don't glue wood cross grain to long grain.
I made a really nice workshop table a couple years ago. I wanted a heavy, thick top, so I laminated a 3/4 thick piece of MDF over two 3/4 thick pieces of plywood. Then covered the top and bottom with laminate. It was great for the rest of the winter, but when summer came the table bowed up so much that a ruler laid across the top had almost an inch of clearance at the ends.
I tried several things to save the top, wedging up the ends and setting my anvil in the center, but that top was more stubborn than I was.
I have a large router table top that is made from two pieces of 3/4 MDF glued together and laminated on both sides, and it is still dead flat after two years. As a further note, make the top so that if you need to you can adjust it. The old saying "if you can't make it perfect, make it adjustable. Justus Koshiol
Running Pug Construction
Justus:
Thanks for the first hand experience.
I will use the two pieces of MDF, laminate on side and seal the ends / other side. To ensure it stays flat, I will take Pat Warner's advise and "stress" the panel. I plan on doing that with 6 screws through the top and into the table base.
BW
Robbie, You're on the right track, but as so many have pointed out, you still have to balance your construction. Put some cheap backer laminate on the underside of the top. No matter how you tie down the edges, the middle will still want to hump up or down with changes in weather. If you have a balanced panel, the problems almost all go away. Sealing the back definitely won't do the job.
I rout an opening through the bottom layer so my router can mount closer to the surface, and this doesn't seem to cause any problems. The extra thickness elsewhere provides good stiffness and helps reduce resonance, which can be a real problem with thinner tops.
Michael R
Woodwiz - Gotcha on the laminate. I have some cheap stuff I can slap on under there. I am using the Woodpecker lift, so I've got to cut completely through the top to mount.
Have a DW625 and a Woodpecker Plung Lift, but the lift is too shallow to allow deep seating of 1/2" panel raising bits. Am sending it back and getting the PRL and with the PC rebate, I am going to bit the bullet and buy a 7518 and just leave it in the table.
Robbie
What a bonehead move...
Woodwiz: I laminated the underside of the table... and forgot to transfer my layout lines. As such, I have no idea where the screw pattern is underneath the formica. Actually, I know what the pattern looks like, I just don't know which side it starts from (clear space for miter track and PRL insert).
Beyond getting it X-ray'd, any other way to figure it out? Need help here please.
Magnet??Tom
Douglasville, GA
I like the magnet idea. Even better, one of the old magnetic stud finders with a swiveling magnet would let you "cross out" each fastener and locate it within less than 1/4". Run your stud finder in a right - left pattern in rows down the piece to locate them on one axis, then run it at right angles (top to bottom) to locate them along the vertical axis. X, or should I say + marks the spot. Should cost about $5.00 and take about 15 minutes.
Don't worry about the mistakes - just learn from them. I've made enough in the past 30 years that I should be a genius by now. Can't imagine what went wrong.....
Michael R
Justus:
Any suggestions for smoothly cutting in the hole for the router lift? I also have an MDF table that is Formica laminated on both sides. Am concerned of laminate chipping and tearout if I make the first cut on the table underside with my jigsaw. I already have a template for cutting out the final "ledge" for the top side - just being a bit anal.
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