How square is "square"

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Forum topic by xeddog posted 03-21-2016 09:15 PM 1030 views 0 times favorited 7 replies Add to Favorites Watch
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207 posts in 3182 days

03-21-2016 09:15 PM

I am rebuilding the router table fence I built for my homebuilt router table. I had to do this because I found out the hard way that the base platform for the fence had warped just a little and some frame-and-panel doors didn’t come out quite right. When dry fitting all of the pieces and clamping them together, they would not lay flat. I checked the “squareness” of the fence face to the table and it was off by . . . well . . . quite a bit. somewhere in the rage of .025”-.035”. I should have known better than to use a cheap piece of crappy plywood for the base. Lesson Learned.

So this time I am using a new piece of Baltic birch plywood for the base, with a red oak face and maple corner blocks from the old fence to keep them square to each other, and the steel rear rail from an old Delta table saw fence. But there is square and there is square. When using my engineers square to check for square, the fence is back about .002”-.003”, MUCH better than before. Now this would be a fairly easy to shim and get it “perfectly” square, but this IS a wooden fence using three different kinds of wood, so is a couple of thou really worth all the effort to eliminate, and just how long would it last anyway?



P.S. Here are some pictures of what I am working on. Both the fence and the table are still a WIP. The table needs a door on the front, a safety power switch, and dust collection. The fence just needs to be finished. Oh, I didn’t quite leave enough space between each of the drawer fronts so in very humid weather, open one drawer and you are likely to open them all. So they need some finish applied to them to help with that.

7 replies so far

View splintergroup's profile


2341 posts in 1397 days

#1 posted 03-21-2016 09:39 PM

I think you are golden.

My fence (split with sliding faces) was off about .020” across the face. I would never have noticed except when using a bull nose profile bit (no bearing). The workpiece would take a slight ‘dip’ into the bit as it lost support from the infeed face. Basically about 1” of ‘snipe’ at the end of the board.

Square is good! You might pencil in a note of the error you measure somewhere on the fence. In the future you could recheck it and see if things have changed.

View Kazooman's profile


1215 posts in 2127 days

#2 posted 03-21-2016 09:43 PM

Not addressing the question of how many thousands of an inch is “square enough”, but I am curious about the choice of the red oak for the face of the fence. You are trying to build a new fence that will hold good tolerances. In my experience, red oak is a wood that moves quite a bit. Square today, out of square tomorrow is a real possibility. Also, why add a third variety of wood for the supports? Why not use more of the Baltic birch for the face of the fence? I would suggest making ALL of the parts out of good quality 3/4” Baltic birch and rest assured that the fence isn’t going anywhere.

View sawdust703's profile


270 posts in 1594 days

#3 posted 03-22-2016 02:27 AM

I’m with kazoo. Red oak does, & will move constantly, much less maintain a square edge. Use the birch & be done with it. Your headaches will be solved.

-- Sawdust703

View jerryminer's profile


944 posts in 1616 days

#4 posted 03-22-2016 02:52 AM

As I said on SMC, I’m having a hard time understanding why you think your fence kept your doors from being flat. Are you using a standard cope-and-stick set-up? Milling the parts lying flat on the table (or coping sled)? If so, then the fence serves mostly to establish the depth of the cut, not the flatness of the joint.

More likely the stock (or possibly a sled) was not flat, or did not remain flat.

Or the door got pulled out of flat at the clamping stage (did you check for flat at that stage?)

By all means make a nice flat, square fence, but I question whether that will resolve your out-of-flat door issue. My .02

-- Jerry, making sawdust professionally since 1976

View rwe2156's profile


3134 posts in 1655 days

#5 posted 03-22-2016 12:02 PM

As for the .002” that is plenty close enough. Whether it will stay that way is the question. I agree you will face issues with solid wood for the fence face.

My suggestion is scrap the red oak and use a more stable material like MDF or particle board (yes, particle board).
If you laminate both sides of either one you will have an extremely flat, stable material that will never move.

-- Everything is a prototype thats why its one of a kind!!

View JBrow's profile


1366 posts in 1094 days

#6 posted 03-22-2016 03:08 PM


It appears that a lot of work has already gone into the fence and you have achieved fairly close (probably good-enough but dead square is best) “squareness” of the fence face to the table. Over time, given the use of maple squaring blocks and red oak face, this “squareness” you now have may be lost. The steel reinforcing rail may help some, but I would think wood movement could overwhelm the strength the steel.

“Squareness”, if lost over time, would likely be due to wood movement, unless all hardwood components were quarter sawn materials, the squaring blocks were cut from the same plank, the squaring blocks were installed in a consistent orientation, and a film finish is applied and maintained. The quarter sawn material will move but in a way that will help maintain “squareness” – as I understand wood movement.

Nonetheless if you plow ahead with the fence, I would think adding a few more squaring blocks along the length could help. From the photos, it appears that a large distance exists between the end and center squaring blocks. Applying a film finish to the fence could help control moisture and wood movement.

If you were to rebuild the fence, using MDF, Particle Board, or Melamine coated Particle Board, as rwe2156 suggested, would be better choices for the sub fence (base), squaring blocks, and face. These are, in my view, the most stable wood products.

Regarding the raised panels that do not lie flat, I assume the problem could not be attributed to uneven clamping pressure. If clamping pressure was evenly applied, I agree with jerryminer if you were using a cope and stick router bit set. If this was the case, then looking for the source of the problem elsewhere is a good idea. But if these were shaker style raised panel assemblies and the grooves were made with a straight bit on the router table, then squaring the face of the fence to the table could, I would think, go a long way to solving the flat panel problem.

View xeddog's profile


207 posts in 3182 days

#7 posted 03-22-2016 10:08 PM

Thank you all for the replies. To answer some of the questions -

The sliding faces I have made are aligned pretty well. I can run a profile the entire length of a piece with no snipe at the end. I will have to say that I needed to add a strip of painters tape to the back side of the outfeed end. They are scraps of a good quality maple veneer plywood with the 4 edges and the face covered with plastic laminate. One suggestion for everyone, DON”T USE BLACK! You just cannot see pencil marks on them so setting up stop blocks, etc, is a pita.

My material choices for the first iteration of the fence were two-fold. First, simply material at hand. I was very low on wood supply at the time and this is what I had. Second, it wasn’t supposed to be permanent. More like a “proof of concept” that had to work for a while. I had used some red oak for other things and it seemed like it was pretty stable, so I used my one remaining piece for the face of the fence. The Maple came from the scrap bin. I did not have any other decent material of proper size, including plywood. Now that I have some BB plywood I should just start over again. I did use two layers of 3/4” MDF for the table top, but overall I HATE MDF!!!!! Everyone says how stable it is, but my experiences are just the opposite. It is difficult to assemble without splitting it, and it doesn’t hold screws very well either. The one thing it has going for it is that it is flat, and that is why I used it on the table top. Even at that, ALL sides and edges are covered, and it is supported at 4 places along its 4’ width.

As for the doors not being flat, I just found the fence to be off a bit (OK, QUITE a bit) and jumped to a conclusion. If I had taken the time to analyze what was going on I probably would have reached a different conclusion, but . . . Anyway, I was using a bit set that I got from Rockler some time ago. It has worked very well in the past so I don’t think that is the problem. The sled that I used is no longer in existence, but could certainly have been an issue. Another hurried scrap piece that I threw together, but it was perpendicular to the fence horizontally, and held the workpiece well with two lock down clamps. I never thought to check if the workpiece was actually perpendicular to the fence vertically. Clamps were Bessey quick-clamps (the mini K-body style clamps), and were never more than “snugged-up”.

I have come up with a couple of things I want to add to the fence. First, while digging around I found some old 12” extension drawer slides that I want to see if I can incorporate. Don’t ask me why, just because. The second thing I would like to add is a micro adjustment feature. That might actually be useful.

Thanks again for all the replies,


Oh, one more thing. The maximum distance between the two squaring blocks is 25 3/4”

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