37-280 Jointer Knives adjustment

[Greg Magone]

Gentleman:

I was wondering if any of you have ever tried to adjust the jointer knives on the Delta 37-280 6" jointer. I recently purchased one used, replaced the knives with some new ones I bought on Amazon, and adjusted them to the best of my ability.

Unfortunately, my wood that I joint comes out slightly bowed (which defeats the purpose of jointing) and also sometimes has deep ripples perpendicular to the direction I jointed.

I worked for several hours trying to adjust them and make the blades equal height to the outfeed table and was going to try again this weekend. I thought I'd post here first and see if anyone has suggestions before trying again this weekend.

I have checked to see if my tables are coplaner. I don't see a way of adjusting them? I believe they may be out by a little but haven't found a way to readjust the alignment on this jointer.

Thanks,

Greg

[Simon Dupay]

Is this an US made one or an Asian made one? I believe the older ones had springs and newer ones have jack screws to adjust the knives. The video on setting jointer and planer knives by Bob Vaughan would be good one to check out first. I think you can find it on owwm.com.

[Frank Drew]

If by ripples you mean knife marks or machine marks, sometimes called chatter, you might be feeding too fast or one knife is higher than the others (most likely).

The geometry of a correctly set up jointer is subtle and it can take a while to get to know your machine, assuming nothing is essentially wrong with it, but that it's just not yet correctly adjusted (outfeed table height, knife height, ...).

For instance, even if the knives are set perfectly in relation to each other and to the cutterhead, and the cutterhead and tables are parallel, if the outfeed table is either slightly above or slightly below top dead center of the knives' arcs, then you'll either get a belly or a hollow in your jointed edge -- that is, something less than perfectly straight.

A belly (a convex edge) is always wrong, but some people like to set up their jointers to produce a very slight hollow (a concave edge), so that when two boards are put together to make a joint there's just the slightest amount of daylight in the middle of the joint (called a sprung joint) and one clamp in the middle with just a little bit of pressure could make the joint.

[Peter Quinn]

I haven't used that jointer but with straight knives there isn't much difference from one machine to the next as far as I can tell.

A magnetic jig that references off the out feed table (store bought or shop made) is a big help, though not essential. A good dial indicator with a flat foot on the gauge in a jig (again, store bought or shop made) can also speed up the process and help identify any inaccuracies quickly. A long precise machinists straight edge is critical for any adjustments for co-planer. I've seen guys set up jointers beautiful without instruments or jigs of any kind, just running test pieces and making adjustments by knowing which adjustment solves which problem. Takes a lot of experience and patience, but its possible. I'm lazy, I like jigs!

It would take me too many words to explain what is a simple but precise procedure. My first attempt took all night, now it takes about 20 minutes if I'm moving slow. I'd look for one of those articles in FWW with the good pictures and careful editing, or there's a couple of good books out there with different methods. I'd second that Bob V. video suggestion too.

Also, make sure the knives are themselves jointed (flat cutting edge) as I've gotten new knives from Amazon before that were not. Good luck.

[Greg Magone]

Thanks for all of your suggestions. I'll give it a whirl tomorrow and let you know how it goes with my jointer knives. If I get the set once, I should be able to get lots of woodworking enjoyment from them.