The Right Way to Glue up Boards

Published: 16th April 2010
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There are several procedures to ponder in the process of edge-gluing planks including (1) lumber selection, (2) cutting to rough length, (3) ripping, (4) jointing, (5) grain matching, (6) biscuit joining, (7) gluing, (8) clamping and (9) thickness sanding. Just how you go about these steps depends on the condition of the lumber, the capacity of your machinery and the final size of the glue-up.

If at all possible, try to have all planks in the glue-up out of the same tree. If that is not possible, select boards that are of similar color and grain pattern. To my mind, the ideal glue-up looks like one, extremely wide plank with the glue joints invisible to the naked eye. Since this only an objective, I just try to get as close to it as possible.

Another, less-important goal would be to have all lumber in the glue-up of the same approximate width. I am not suggesting ripping the wider boards down to match the narrowest board as this would be a terrible waste of expensive lumber. I do suggest, however, ripping extremely wide boards in two to reduce the possibility of curling due to changes in humidity after delivery.

Straight or ribbon grain makes the best harmonious final appearance while wavy or swirly grain makes for an interesting but more difficult glue-up. Swirly grain will require arrangement of the different planks to minimize the number of places that the grain line suddenly stops at the glue line rather than appearing to continue into another swirl in the adjacent plank. This orientation is highly subjective

I always rough-cut my lumber into lengths an inch longer than the length of the final product. This allows the entire glue-upto be neatly trimmed to size after the glue has adhered. It also makes the ripping and jointing processes a lot easier as I will describe below. The same is true concerning the width of the glue up: Make sure it is at least an inch wider than the final product after trimming.

Kiln or air-dried wood often decides to bow into a curve as it dries and this must be corrected before a glue-up can be accomplished. If my finished glue-up is only 3 feet long and it is coming out of a 14-foot bowed board, it will be far easier and economical to get the curve out of the 3-foot pieces than it would to remove the curve from the entire 14-foot plank before cross cutting. This is one reason that you should always do your rough cross-cutting before ripping and jointing. Another reason is that a 14-foot, 2" thick x 12" wide plank is very difficult to control on a jointer or table saw.

If there is a bow in one or more of your rough-cut pieces, those parts should first have the curved edges ripped off on the table saw. The concave side of the board should always be towards the fence. Measure from the fence out to the outside of the end of the board that is nearest the fence and set the fence to cut this width. Once you have ripped off the convex side of the board, flip it over side-to-side and find the point where the outer edge of the piece of wood is closest to the fence (somewhere near the middle) and rip the plank to that width. When all planks have been ripped straight, take them to the jointer.

The jointing process should now be comparatively simple in that the boards have been ripped straight. Take shallow depth cuts to minimize the possibility of tear-out. In loose-grained lumber with a lot of swirls on the face side, tear-out is sometimes unavoidable. If this happens, try running the board over the jointer head in the reverse direction. If the tear-outs reappear, you will have no other option than to rip the tear-outs away on the table saw. You will then have a sawn glue joint in your glue-up. If you have a clean-cutting table saw blade like a recently sharpened Forrest Woodworker II, this should not be much of a hindrance, especially if you plan on using a biscuit joiner to secure your glue-up. You probably won't be able to tell which glue lines are jointed and which are ripped in the final product.

Lay out all the lumber segments on your work surface and position them for best symmetry. Clearly, if one side of the final product will show more than the other in a piece of furniture, then you will want to have the best-looking sides all on that face of the glue-up. Examples of this would be table tops and cabinet doors. You also must orient the boards so that the glue lines are not highlighted, as discussed in the paragraph on board selection above.

Whenever feasible, make sure that you biscuit-join your glue-ups. I say, "Whenever feasible" because you will not be able to use a biscuit joiner on very thin boards. On the other hand, very thin lumber (3/8", for instance) does not usually have a sufficient amount of strength to pop open a glue line. So, with very thin lumber, you will simply be using glue without biscuits. With regard to lumber 3/4" or thicker, I have seen a number of table tops, cabinet doors and cabinet casings open up along a glue seam after delivery. At this point, repairs are difficult or impossible so the further step of biscuit joining is well worth the slight additional time and expense. Consider it as major headache insurance! If you don't yet own a biscuit joiner, there are a number of great manufacturers out there including Porter Cable, Lamello and Freud. There are also two good alternatives to using a biscuit jointer: Those are the Festool Domino floating tenon joiner and the Freud Doweling Joiner. Different methods, same result.

When you have your planks oriented the way you want them in the glue-up, make sure all the ends are flush and the edge joints are touching. Double-check to make sure the glue-up will be about an inch wider than the final product after trimming. With a builder's square or a straightedge mark a pencil line in 4" in from each end of the rough glue-up across the grain, crossing all glue lines but not continuing over the side edges of the glue-up. Make a similar pencil line across the grain at the mid-point of the boards. Make additional pencil lines half-way between the other pencil lines until all pencil lines are about 6" apart.

Mark the pieces on one end A, B, C or 1, 2,3, etc. so that you can put them back together in the same arrangement when it is time to glue them up. Put the boards aside and nail, screw or clamp a stop board (scrap) to the work surface top, left to right, in front of you and about a foot in from the edge of the bench. As you are applying pressure with the biscuit jointer, while making mortises for the biscuits, this stop board will keep the plank you are mortising from moving away from you. Make a mortise wherever a pencil line touches a board edge on every board.

There are two ways to clamp up a glue-up: Horizontally on the work bench top and vertically with the first board mortised edge-up in a woodworking vise on the end or side of the bench. In the case of the horizontal glue up, place pipe or bar clamps about 2 feet apart on the work surface top with the clamp handles hanging slightly over the edge of the work surface. Pre-adjust the clamps to an inch larger opening than they will be when tightened. Place the first board on edge on top of and across the clamps with the mortises facing up. Do the same with all the pieces, in proper sequence. Make sure you have a supply of biscuits for the job ready.

A small dispensing glue bottle with plenty of glue for the job should be nearby. The kind of glue is important: If the glue adheres too quickly you will have a predicament. If the glue dries too slowly, you will be losing valuable production time. I like to use Franklin Titebond I Glue indoors or Franklin Titebond II for outdoor applications. These are "aliphatic resin" type glues that can be easily cleaned up with water. Ether formula gives a very strong joint and has a reasonable, 45-minute clamping time. Both of these glues are widely on hand in hardware stores, home improvement centers and woodworking stores.

Run about a 1/8"-thick line of glue down the center of one edge of the first board, making sure that the glue drops into every biscuit mortise along the path. Then apply short glue lines on both sides of every mortise. This should result in sufficient glue so that it appears squeezed out of both sides of every glue seam after clamping. Insert a biscuit into each mortise. With 2" lumber, you may need an extra glue line for the full length of the joint. There is no such thing as too much glue because you can wipe up the leftover with a wet rag. There is, however such a thing as too little glue and you will recognize that state when you see that glue is not being excreted from the full length of both sides of the glue joint. That is called "starving the joint" and starved joints often open up later. Glue is cheap! Don't skimp on it!

Situate the first plank with the letter or number up and the mortised edge away from you. Apply glue in the same manner to each succeeding board wherever there are mortises and place biscuits in the far edge of each plank, except, of course, the last board.

The board ends should be flush and the left clamp should be about 6" in from the end. The right clamp should be about 1-foot six inches in from the right end. This is because you will be placing alternately spaced clamps on the top side of the glue-up so that there is a clamp (top or bottom) about every foot. The top, right clamp will be in about 6" from the right end.

Once you have all of this in place, start tightening the clamp handles. Clamp all the bottom clamps finger tight, then the top clamps finger tight. Then, go down the row of clamps tightening them fully, bottom, top, bottom, top, etc. With a wet rag, wipe off most of the excess glue. Turn over the entire glue-up and wash the other side. Look at your watch or clock and add 45 minutes to the time. This will be the minimum clamping time, any time after which you may release the glue-up from the clamps. Mark this future time on the glue-up with a felt pen. If you have multiple glue-ups, you can rest this glue-up against a wall to get it out of the way while it dries.

If you have been reading the above, then you can put together how to do a vertical glue-up in a vise: This procedure is applicable for smaller glue-ups and is easier to manage. The difference is that when it comes time to apply the glue, you will clamp the first plank at its center in the vise with the mortises facing up. Add the glue and biscuits. Apply glue to the mating edge of the second board and place it in correct position on top of the first plank, and so on. Place the first clamp 6" in from the end, in front, the second clamp a foot away from the first clamp, in back and so on.

Once your glue-up is out of the clamps, it is ready to be thickness sanded either in a drum sander or wide-belt sander. If you don't have either of these machines, don't worry. Most professional furniture-manufacturing shops in your area will be happy to thickness sand your glue-ups for an hourly cost. You might want to consider buying your own drum sander or wide-belt sander, if you can justify the price.

It is best to know the maximum width capacity of the sanding machine you will be using: 48"-wide glue-ups will not pass through a 36"-wide sander. If you know that you will have this limitation in advance, simply make two, 24" glue-ups and glue those together with biscuits after the thickness sanding is complete. The glue line won't be completely even and so it will have to be sanded true with a random orbit sander. Your glue-up should be sanded to at least 150 grit. 220 grit is even better. Trim the finished panel on the table saw to its final size, rout the edges, if appropriate, and then random orbit sand the final piece to 220 or 320 grit before adding the finish.

For some woodworkers, gluing up lumber may not be the most appealing part of the craft. It is one of the most crucial, however, because a glue-up done improperly can be a recipe for disaster. Furthermore, the way you place the boards in the panel will have a lasting and irremediable effect of the quality of the finished work piece.



Bob Gillespie

© 2010 Robert M. Gillespie, Jr.

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