The Delta Contractors Saw came with a melamine table top, sized about 27×32”, to support work on the right side of the blade. The Unifence attached to it. This table top has gotten beaten up with use, particularly because I formerly did not have a good workbench and it got misused, so I have replaced it a couple of times, and the current one is in only fair condition.
The Incra fence has provisions for using a fence, though as noted in an earlier blog entry, you add the table top after attaching the fence. As an interim, I put the most recent table top back in place, so I can use the saw to make the new table top.
Requirements for The New Table Top
My IncraDelta saw will also serve as a router table, so that I can use the Incra fence with the router. Router tables need to be very flat, and it needs to stay that way. Ideally they also have very low friction to make it easy to move heavy pieces of wood across the table.
I plan to use a router plate, so the ability to route a lip around the hole that is both hard and smooth is crucial to being able to adjust the plate to be flush and level. This rules out particle board and solid-core doors (which these days are filled with corn husks and glue, according to a guy at Home Depot). The best choices are then plywood or MDF. MDF is both flatter and less expensive for solid construction.
Two layers of MDF glued face-to-face seems to be the best choice for my needs, but it is heavy, and it is a bit of work.
I am also making this top 27×42 before adding hardwood trim on three sides, because I am using the “custom” arrangement of having the fence mounting rails shifted 8 inches to the right, to allow a maximum cutting capacity of 40”.
First Attempt: Learn From My Mistakes
I am embarrassed to report how I made a stupid mistake with my first attempt, but friends, we are here to learn, and we can learn from each others’ mistakes.
I posted a question about the best way to glue two MDF pieces together face-to-face. One method, which I got from reading Bill Hylton’s router book, said to use glue cauls to apply center pressure to the top face as it was glued to the bottom one. Another method suggested by a lumberjock was to screw the faces together, noting that the screws would evenly apply pressure.
I decided to make glue cauls. I visited PurpLev (as reported in an earlier blog entry) and he suggested a sliding board on my table saw, to which ripped 2×4’s could be clamped down and tapered with a pass through the blade. For the length of 4 feet, the taper went from 0 (at 2 inches from center) to 1/4” (at the edge, 2 feet from center), and the same for the other side of center.
I cut two pieces of MDF, a bit oversized for trimming after the glue dried. I had to work quickly, because the Titebond I glue dries and sets quickly. I used a paintbrush to spread the glue over both surfaces – NOT the best way, see below. I flipped one on top of the others, leaving two factory edges offset by about a quarter of an inch, so that they could be used to accurately trim the opposite sides after drying. Then I placed four cauls along the long way – two about 4 inches from the ends, and the rest placed for equidistance. I clamped the cauls to the edges.
I should have gone back to read Bill Hylton’s suggestions before I started gluing. The key sentence I missed was that using caults, you need to clamp them to a flat surface.
An hour later, much too late to do anything about it, it struck me that I had made the fatal mistake: the clamps were squeezing the lower face to the upper face and clamped only to the caul. It occurred to me that if there was any flex to the MDF at all, I was making a bowed surface. The clamps are strong, and indeed, that’s what happened. The real problem is I don’t have a table of a size to which I could clamp the two surfaces plus the caul.
So I ended up with a table top that was bowed 1/4” from the center on both sides, which has no use I can think of. Rats. And I have spoiled my reputation as a smart woodworker with my lumberjocks buddies. But if I can save one of you from making the same mistake, that’s ok.
The Second Attempt
Someone else suggested using sheet rock screws to screw the faces together after gluing. Someone said I did not need to drill pilot holes. But I reasoned (thinking before gluing, this time) that the top face needed holes larger than the threads, but stopping at the lower face, so that tightening the screws would pull the two faces together with no resistance. If I did not pre-drill the holes, the threads in the upper face would prevent this tightening action.
I drew a grid on the surface to become the lower face, so that the screws would be regularly spaced. How far apart? I imagine the clamping effect to be strongest at the screw, and going down as you go away from the screw in all directions, effectively a circular pattern, with overlapping circles from neighboring screws. But that did not answer the question. Eight inches seemed too much distance; four inches seemed overkill. I think I used 5 inches. Here’s a picture of the pre-drilled holes in the MDF:
I vacuumed away the debris, spread some newspaper on the floor below the edges, then began spreading glue. I found a glue spreader I bought for just this kind of task. It’s like a 3 inch scraper with a series of small notches, and it made very short work of spreading the glue thin yet even: at first there were streaks, but in seconds the glue flattened itself out. It worked much faster than the paintbrush, and made the glue thinner. Perfect.
With both faces glued, I sandwiched them face to face, and again offset the one with the factory edges by about 1/4”, to allow it to guide the trimming against the fence after the glue dried. Then I started drilling in the screws, starting in the center and working outwards in both directions, to avoid an arc in the middle. I noticed on finishing that some edges did not quite meet, only one one side; I tried using clamps around the edges, but it did not help much. Here is the glued, screwed, and clamped MDF assembly:
When the glue dried, I noted that the gaps were still present on one end, so I made note that this would be the end farthest from the blade and the router. Since I plan to glue on hardwood edges, it won’t be visible, except perhaps when using a long straight edge.
I removed the screws (they no longer serve a purpose), sanded, filled the holes with filler, and sanded again the next day. Naturally, the side that had the screws will be the bottom face.
My square is only 24” long, but it shows that the top face (the one without screws) is very flat, and the corners are very close to right angles.
I used the factory edges of the face that were offset by a quarter inch as a fence guide, and cut to a very accurate size of 27×42”. I don’t have a tool capable of measuring distances larger than 6 inches within thousandths, but I believe it to be within a few thousandths, thanks to a carefully set up Incra fence. This accuracy is completely unnecessary for this job sense I can trim to fit after adding the hardwood trim.
Some of you are rolling your eyes about the over-engineering – things like screws every five inches, predrilling holes, filling the holes after removing screws, trimming to exact size. I know it is overkill, but for me, accuracy is part of the pleasure of what I’m doing. This kind of extra work would make me unprofitable if I were doing this as a business, but I am doing this for fun.
Next up: laminating the faces.
-- Mark, hack amateur woodworker, Medford (greater Boston) MA