I have a Delta Uni saw with a Biesemeyer fence. I often get a concave edge when I rip a board with a straight edge against the fence. If I attach a very long straight edge (longer than the fence) to the board and put the straight edge against the fence, I don’t get this problem. What causes this and what can I do to avoid the problem.
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Replies
I suspect that your Biesemeyer fence is slightly concave. The long straight board bridges that concavity. When you rip without it, the two ends are up against the fence, but the middle is held slightly away.
Thanks. That sounds right to me.
Do you have any suggestion for a more accurate replacement fence?
Sorry, I'll have to let others put in their opinions about more accurate aftermarket fences. My Powermatic 65 has an original style cast iron fence, not perfect. If there is a way to attach a board to the fence, you could then run the combination over the jointer (if you can get the near end of the fence off the body of it.) If you do, make sure the fasteners aren't going to hit the jointer knives!!
First take the fence off and lay it on the saw table, you'll see instantly if the sucker is straight. A straight edge or long enough level should also tell the story. Padding out the fence to create a flat face is an option.
For an aftermarket fence I recco the Vega Professional. I had one on my old saw and bought my Sawstop PCS without a fence so I could install the Vega.
I would not replace a wonderful fence like a Biesemeyer just because the face is a bit out of whack. The original design does not make face replacement easy like a lot of the 'better-than-Bies' fences now available. I would pry the face off, drill and tap some holes and attach a new face. You could add laminate or not, use UHMW plastic, MDO, aluminum extrusion, even MDF with a poly finish; as long as it is flat and true. You threaded attachment method would allow you to shim the face to assure it is true.
First off, check that your fence is perfectly parallel to the blade. If the fence is even slightly farther away at the back of the blade than at the front, a board seems to want to drift into the blade, possibly a pivot effect as you press the feeding end against the fence. After that use a feather board. Hopefully that helps.