How Straight Is Your Jointed Edge?

[Derek Arita]

So I got this new jointer and for the life of me, I can't get a dead flat jointed edge. I can get close enough that a little clamp pressure will bring the edges together. Both my tables are dipped in the center about .007", but I'm told that that's not that critical.
That got me thinking about my old jointer and how well it worked. I really can't remember whether or not I got dead flat edges. So my question is, how straight are your edges? Are your edges dead flat with no light between or is some daylight showing? And, how much does it matter?
I got spanked for asking this question on another forum because, as I was told, any woodworker worth his/her salt should be able to compensate for bad power tools with hand tools. However, I'm of the belief that when you spend a lot for a tool that's supposed to do a job well, you should expect just that or close to it. Thanks for the help.

[Paul Kunkel]

Originally posted by Derek Arita
So I got this new jointer and for the life of me, I can't get a dead flat jointed edge. I can get close enough that a little clamp pressure will bring the edges together. Both my tables are dipped in the center about .007", but I'm told that that's not that critical.
I think .007 is closer than most woodworkers need to think about. I joint 2 edges, slap some glue on 'em and clamp 'em. It's worked for years. If you see a large gap or have to use the extra heavy clamps tightened with a cheater bar, then you have a problem. My .02c

[Todd Burch]

I have an old powermatic 8" jointer that used to live in a high school shop class. I get dead flat edges and faces with it, all day long.

Todd's rules of jointing:

1) Always flip your boards when edge jointing. When you lay out your boards for a glue up, send one through with the "top" or "front" away from the fence, and then send the adjacent board's edge through with the "top" or "front" towards the fence. This procedure eliminates any and all fence deviances from a perfect 90° setup.

2) Don't press hard on the stock when jointing. Not so much an issue for edge jointing, but it could be for face jointing. Push forward more so than down.

3) Press the stock down on the outfeed table more so than the infeed table.

4) Set the outfeed table to the knives (or the knives to the outfeed table) at top-dead-center. Here's how to tell how close you are. Get a short (3"-5") piece of wood that has a good clean edge on it. Unplug the jointer and remove the blade guard. Set the block of wood so it spans the outfeed table and the cutterhead. Spin the cutterhead slowly in normal cutting rotation until it picks up the block of wood and carries it forward. If the knives never hit the block, the knives are too low, or the outfeed is too high. If the block gets carried, say, more then 1/8" or 1/4", the knives may be too high, or outfeed table too low. This is also a great method to tell if all your knives are set the same without an expensive jig or tool.

If your edges are "low" in the center, the knives are too high. If your edges are "high" in the middle, your outfeed table is too high, and you are probably noticing a small "bump" when the leading edge first contacts the outfeed table.

Todd.

[Kirk (KC) Constable]

I kinda feel like if your edges are 'out of flat' enough to cause problems that you're gonna 'feel' it as you joint them. Todd mentions a 'bump' at the leading edge...or a 'bump' at the trailing edge are definite things you can feel.

Some problems you can also 'hear'...you know what it sounds like to get a nice cut the length of the board, and you can hear the subtle changes.

When in doubt, I use the eyeball test. If I sight down the board and it looks straight after it 'felt good' and 'sounded good' coming off the jointer, then it's probably straight enough.

Also agree with Todd about alternating the edges to compensate for teensy out-of-square issues with a fence. I've been doing that for quite some time and it really helps.

KC

[Jim Becker]

It's a shame that you got whacked for asking such a question on whatever other forum you asked it...it's a good question and a common one.

Assuming your jointer is properly adjusted so that the tables are parallel in all dimensions, et al, what you are experiencing is probably just a matter of "feel". Moving the workpiece through the cut requires that you keep the board on the tables, but not use so much pressure that you "bend" the board into submission. That often results in the effects you describe. Additionally shifting your minimum-required pressure from the infeed side to the outfeed side smoothly and at the right moment also contributes.

I suggest you take some scrap boards and make a whole bunch of chips as you practice the movements over and over. Be sure to pick stock that has a variety of "issues" with straightness and also practice your face jointing...that's a very important function with a jointer--making a board flat--and is usually done prior to working on the edge. Use your table saw top to help judge how you are doing.

I also agree with KC about alternating your edges for a panel glue-up. It definitely gets rid of any vagaries in the fence angle adjustment!

[David Rose]

dull blades can contribute to the problems in odd ways. I suspect in my case that I was applying more downward pressure to get the blades to cut. New good blades helped me tremendously.

David

[Mike Evertsen]

mine come as straight as I hold the board if the edge joint is not perfect alittle wood putty hides the gap,,,,,,

[Steven Wilson]

I use a PM60 jointer and then followup with Stanley/Bailey #7 type 11 with a Stanley 386 fence attached. My edges have no light showing when measured with a Starrett 4' straight edge. Glueups are simple and very little clamping pressure is needed.