Jointer Problem: Results in boards concave up along their lengths

[Brett Bobo]

Ian,
Good point and well taken. I shouldn't minimize the setup of the knives and given that I've spent a majority of time on the outfeed and infeed tables, I'll probably revisit the knife heights first before making any other adjustments.

Mel,
Do you mind sharing your magnetic setup jig, maybe a photo of it too? I've looked at the Oneway multi-gauge, jointer pal, etc. but I figured there has to be an inexpensive method that is just as effective. I have some rare earth magnets that are begging to be used.

[Mel Fulks]

Don't know how to do photos.But this is simple. A 16 inch jointer knife cut into 2 pcs.Its 5/32 thick and about 7/8 wide.
Each has 3 rare earth magnets glued on with epoxy. A 1/2 mag is on one end and a 3/4 on the other end.Another 1/2inch
mag is 5/8 inch from the 3/4 inch mag. I make a wood jig to immobilize cutter head .Consists of a block clamped to jointer
and a adjacent pc which is slid into the end of head and clamped to the other pc. Gauges stick to out feed table held by
the 2 small magnets,the 3/4 mags hold up the knives. I cover the 3/4 mags with elec tape. I pry the gauges off with a ppc of plastic. Works much like magna set,but I like to immobilize the head

[jim gossage]

I believe you are wasting your time until you get a true straight edge. The lee valley is excellent, mine was within 0.001 over 48".

[Brett Bobo]

Jim,
No doubt, I agree with you as I've ordered the Veritas 36" steel straight edge so it's on it's way. The 36" was the longest steel straight edge they offer now so did you purchase the 50" anodized aluminum?

Mel,
Thanks for sharing. Considering that we're talking in thousandths of an inch here, should there be a concern about the possible inconsistency in the thickness of the epoxy when gluing the magnets? I'm just thinking in terms of too much epoxy on one, not enough on another, uneven pressure, etc. Shouldn't bar magnets do the trick?

[ian maybury]

Pardon my coming in Mel. It might make sense Brett to eyeball some stuff on the web regarding the design of commercial versions of those units, and how they are used - there's various versions about.

Chances are the epoxy film will be OK provided the bearing surface underneath is flat and at the correct level, and provided the magnets are clamped firmly enough to ensure that the magnet actually bottoms on the bearing surface. i.e. don't let the thickness of the adhesive film to determine the height. It could be worth measuring the magnets to ensure they are all of the same thickness too if the design you adopt relies on this to set the height of the active face of the magnet.

If the knives on your jointer are sprung so they rise when the locking screws are released a sheet of float glass is pretty effective to set them too. If there are jacking screws in addition to those locking the blades in place that allow the knives to be eased up or down then you may not even need the magnets or the glass - go straight to the carry forward test or use a dial gauge.

Either way the carry forward test or a dial gauge will pretty quickly pick up any variation in knife height above the out feed table...

ian

[Mel Fulks]

Brett, I did check the thickness when I made them .Cant remember what glue I used first ,but I remember it threw every
thing off. Started over with the epoxy and micd them and they were fine. Bar mags might be as good or even better .
I just found freezing the head a big step toward accuracy. But I don't mind adjusting table heights,in fact,on the old jointer that had the knife index feature I would routinely drop out feed before I started putting in the knives.That allowed me to hold the knives in a vertical posistion. And obviously up is the direction to want to go to adjust,I do that by jointing and
checking two pcs together.Tastum Soupo! Please look up the info on making a straight edge. The one you are buying would be a great help in making a longer one.

[jim gossage]

Yes, my bad, its the 50" aluminum

[Bill Space]

Brett,

Just to give you a little encouragement...

After replying to your other thread about the tool for turning the bushing, and reading this thread, I got worried about my own setup, on the G0490X that I just received and set up this week. I had to set both tables slightly. I followed the instructions in the manual and video. Then after reading this thread I got worried that I did not check the test board that I face joined to flatness. It looked good BUT I did not check it with a straight edge...it was red oak, 40" by 6".

This morning I did check it and was dead flat against my 48" Starrett straight edge. Whew! Relief!

My experience reflects what has been said by others above: A good straight edge is necessary. This is the first jointer I have set up it went smoothly, probably only because I have a good straight edge.

The spiral cutter head in the G4090X removes the variable of knife position that you have. My longer straight edge probably benefited me in the set up(don't want to ignore the luck aspect). I did not use feeler gauges, rather, I used a bright flashlight behind the straight edge and visually adjusted things until no light passed between the edge of the straight end and table surface.

I wish I would have took a better look upwards from under the jointer before putting it on the stand, as I don't really understand the mechanical working in there. Maybe I can figure out exactly how the thing is put together from looking in the parts diagram. I did come to the conclusion that there is some interaction between the four adjustment points of each table. I mean, the table is not going to change shape, so if you get out of whack, you can end up with three of the support points being tight against the table, and the fourth not touching. So rocking may be possible.

I will bet once you get the good straight edge you will be able to set the tables right and then address the knife issue if it still seems to be an issue.

Your sequence seems to have been: No problem; Change knifes/problem; Adjust the tables/second problem?;

In my mind, logic dictates that your initial problem is related to the knife change, and a second problem was introduced by making table adjustments. The resolution will be restoring the tables to their correct relative positions and then addressing knife-related issues if problems still exist.

Bottom line is that when you get the new straight edge you will be better positioned to what you need to. I am sure you can.

Keep us posted!

[Brett Bobo]

Thanks Bill, I appreciate it. Given that I've had the jointer for about five years, I'm certain now that I didn't do enough an initial setup to ensure coplanarity since I didn't have an adequate straight edge. Of course, I've made knife changes throughout the years so even though it wasn't using a spitfire method with a dial indicator, jointer pal, etc., I haven't had any issues with larger scale furniture projects, including a bed. Therefore, I would have expected any issues in the setup or knives to be magnified and be noticeable.

Also, my sequence was as you mentioned. I think what compounded the problem is that I needed a knife change at the same time I was trying to mill up some very warped material, which added one more variable into the mix. Despite using much better material as a test of the setup, I still got odd results, which lead to starting over from scratch.

The good news is that my straight edge and feeler gauges arrived yesterday, I purchased the Oneway multi gauge here locally, and I went ahead and got my second set of knives resharpened. So, I plan to start again from scratch, even replacing the knives. While I don't expect it to be an easy task, I'm confident that any error will be legitimate, instead of guessing which variable it could be--the tool, me, setup equipment, etc. I'll tackle it tomorrow, snap some photos, and may even shoot some video but I'll re-post the outcome, which is hopefully success...