Delta DJ 20 question

[Robert Maloney]

I have a DJ20 jointer and when I edge joint I get a convex joint,meaning center is lower than ends. I checked and rechecked knives and tables. I checked the tables for coplanar with a 4foot straight edge and the seem fine. I do have a .004" dip in the center of the out feed table. What might be causing the convex joints. Any help would be appreciated

[Dan Friedrichs]

I believe Delta's spec on this is "flat to within 0.008"", so that dip you noted isn't to be worried about.

If you're getting convex edges, likely the end of your outfeed table is a little low.

How are you checking for coplaner? I've always had a difficult time doing it by referencing a straightedge to the cutterhead. I'd suggest getting a LONG straightedge (Lee Valley sells a nice affordable one), then clamping a cheap dial indicator to one end of it. By moving it around the table, you can easily (and accurately) tell exactly what's going on (much easier than feeler gauges, IMHO).

If you do end up needing to adjust the table, don't fear - these are easy to adjust. I can explain further if you are unfamiliar with the procedure.

[Chip Lindley]

Even if your jointer might be in *perfect* alignment, convex may be caused by excess pressure applied as the stock enters and leaves the cutter head. Check to see if you are bearing down heavy on the ends and light in the middle. Sometimes it's a subconscious thing to try and keep the stock under control. Try for even pressure throughout the cut.

On my DJ-20, once the first half of stock is past the cutter head, I bear down on the outfeed table *only* so that the stock is pulled through the cutter in the same plane. Try it!

[Glen Butler]

A dip in the outfeed would cause the joint to go concave. If you are getting a convex board your tables are sitting in a V. Adjust the stops ever so slightly and try again.

I tried and tried to get my tables coplaner using a straight edge. Straight edge did well, but the boards jointed told the real story. Now I just use the resulting joint to decide how to adjust the table. A straight edge just won't give you that .001 ~ .002 that will make all the difference. Any more questions feel free to PM me.

[Don Morris]

That point about putting excess pressure on the end as it passes over the blade is what got me once. I have a machine shop long straight edge (cost me $$$) to check with and my jointer, while not a DJ-20, is flat and gives me flat pieces. But, once gave me the same problem. I found it was me putting excess pressure on a particular piece of wood at the end as it passed over the cutter blade. I tried to ease up a little as it passed over the blade, not pressing with everything I had, and eliminated that discrepancy. Didn't realize that technique could play such an important role in the result, not just the alignment of the tables.

[Jeff Duncan]

The others have made some good points. Before you start adjusting, try edge jointing a wide piece of stock, say 6"+. Then you'll know you aren't putting enough pressure to bow the board, and will have a better idea whether it's machine or technique.
good luck,
JeffD