Replies

1. 
   forrestb | Jul 15, 2010 05:41pm | #1

   banana boards

   When this happened to me I found out by asking a woodworker what was going on.  When you joint one side of the board it exposes new wood cells that are only too happy to give up water to the environment.  As a result of the uneven cellular moisture content on each side of the board it will want to curl - turn into a banana board.

   I found that by removing a small joint (say 1/32 to 1/16) from each side in rapid fashion (less than a minute or two) the tension equalized and allowed me to continue jointing a side flat followed soon by planing the other side to thickness.  The two will not be parallel of course, you are only equalizing open cells on each side.  You still need to plane.

   I do not joint one side and then remove all of the material from the other in the planer.  Once I have planed the non-straight side flat I will alternate removing material from each side to try and maintain an even balance of the tension.

   Forrest

2. 
   DonStephan | Jul 15, 2010 08:06pm | #2

   My understanding of differential moisture content is that the interior of a board generally has a lower moisture content than the exterior, but that's a minor point.  And I don't expect uneven removal of wood and resulting change in differential moisture content will cause a board to change instantly.  If I'm milling a number of pieces, it might be 5 or ten minutes between jointing one face and planing the opposite face parallel.

   For 20 or more years, I always pushed a board being surface jointed down onto the jointer tables, then about 18 months ago a local woodworker said he never pushes down.  After thinking about it, I realized that with wood up to at least 3/4" thickness by pushing down I could alter the shape of the board.  Now when flattening a face I lightly rest my handplane-shaped push stick on the top of the board to keep it from excess movement, but basically only push the board forward and allow gravity to provide the downward push.  (Obviously this doesn't work well with narrow or thin stock because gravity can't provide much of a pull - then I have to allow the push stick to provide enough downward push for safe operation.)

   To try to hone in on the possible cause, try to find a currently flat board surface and run that face through the jointer 3 or 4 times to see if the jointer leaves a flat surface flat or in fact is removing wood unevenly along the length.  It's possible that over the following few days a flat newly milled board bows, and that a jointer is removing wood unevenly. 

1. 
   forrestb | Jul 15, 2010 08:43pm | #3

   how quickly wood moves when cut

   Well, I think that you can depend on fairly quick movement of wood when freshly cut.  A couple of minutes may be too quick depending on the moisture of the wood and the humidity/temperature of the shop, but it will move.

   But if wood doesn't often move quickly when cut we would not need riving knives and kick-back devices for safety when ripping boards.  I think we all have seen for ourselves how wood will bend after the saw blade on a TS.  In my experience, this can be minimized by small rips on one side (choose the correct side, of course) before ripping to rough width.

   As for jointing technique, there are many, but I was taught to press down on the wood on the outfeed table right after it passes over the knives.  If you want a concave edge joint, press down always right over the blades.  Here, you are bending the wood but for a reason.

   Since we have diverse opinions, ZiggywadeM, I suggest you pose this question to one of the experts, Rogowski for instance has published FWW articles on milling wood.

1. 
   DonStephan | Jul 16, 2010 08:11pm | #5

   You're reference to the need for riving knife is excellent.  My understanding has been that when boards went banana during rip saw, it was due to reaction wood or other internal stress (poor kiln drying, for example) rather than moisture content, but it's an interesting question.  Any article writers getting inspired to research and write?

3. 
   SantaFeTom | Jul 16, 2010 03:19pm | #4

   Double check the jointer adjustments

   I generally agree with the other posters comments as to possible causes. Pushing down on a thin cupped board on the infeed side could flatten the board such that the jointing didn't accomplish anything but remove wood, however you say you are pushing on the outfeed side. If the cup was enough that multiple passes were needed to get it removed, then there would still be an area of cup on the outfeed side and pushing down at that point will temporarily flatten the board and cause the rest of the jointing process to be messed up. Be carefull to only push down where the board makes full contact with the outfeed table.As far as distortion do to moisture diferential, the principle is the same but I would atribute it to disturbing the equilibrium that was initially in the board. The cells of the wood go in lots of directions but establish an equilibium. When you cut, or joint, the board, you disturb that equilibium. Resawing a straight, plain sawn board dramatically shows this. The board might be perfectly straight until it is resawn down the middle but if the resultant boards are around 1" thick, you will probably end up with two banana boards. White oak is usually pretty straight grained though and not as likely to do this. This leads me to suggest the jointer adjustments.

   In my experience proper jointer adjustment is challenging. The tables need to be parallel in a straight direction and across both diagonals. Then the blades need to be  parallel to the tables. Then the blades need to be at the exact height of the outfeed table. As I recently discovered, if you are using new blades, be sure to check the  height of the blade and the outfeed table after using the blades for awhile. Just enough of the sharp edge will wear off with use that the adjustment will be off and you can't get a straight board.

1. 
   Chrismitchell | Jul 18, 2010 09:58am | #6

   Cant get a straight Board

   I agree with you a hundred percent. I played with it a little tonight even though it's holding up the progress of this Buffett I just had to stop what I was doing due to I really dont have the extra Lumber for this project to waste so I'm procceding with caution. Ive had this jointer almost two years now and I havn't yet to make any adjustments. I know what I'm getting myself in to and I'm really not looking foward to it. I had a board 3" wide, 7/8" thick and 42" long. It was pretty straight  so when  I tried to flatten one side , just after two swipes at 1/32" deep cut It looked like the golden gate bridge. Let me ask you this,  because I run the A/C during the day and turn it off at night would or could this be part of the problem? Tommorow I will check the moisture content before I turn the A/C on and then maybe a few hours after. When I got the Lumber it was between 9 and 11 percent.  I of course put it on stickers for almost a month until the moisture content  was 6 percent. I have turned the cutter knives around only once since I bought this rascal that was about 8 months ago. I probably have somewhere between 15 to 25 hours of operation on this jointer. I took all the knives off tonight and cleand them up real good. In the morning I will check the outfeed table to the roller first before I put the knives back on, then I'll make sure that the outfeed table is set flush with the top of the arc of the cutter knives. When I begin my cut If ther is a bow I try to be real careful not to push down in the center of the board. Just as soon as the leading edge of my board passes over the cutter head I put my left hand on top of the board and push moderately. Im sometimes or most of the time feel awkard because I dont know what to do with my right hand so i will place the push block with my right hand just about 4 to 5 inches past the cutter head on the table and I use the side of the push block as a fetherboard. Sometime I will use my pointer finger and let it ride on top of the board as I'm pushing it through just in case a little pressure is needed. I watch a video where Gary Rogwoski had a push block that hooked the rear of the board . Ive tried this but I have a hard time pushing it from the rear without putting downard pressure thus causing the cutter to take too much out in the middle. Another Problem. Ive had this problem  " with Jointing " , for a good while now. Sometimes I seem to get it to work right and Then I have it happen all over again. This is why I asked about  running the A/C while I'm working. My Mortiser seems to burn up every bit I put in despite the fact that I do exactly what the directions say on how to use it. My Table saw  cuts a concave in every board I rip. It crosscuts like a champ. And This is just the begining. And yet I still love and want so badly to learn this craft. I think My biggest problem is that I dont know anybody that does this type of art so I'm trying to learn all this on my own with nothing more than a bunch of books. Today for example, I looked in over a hundred books and not once did I  find a piece of furniture that was even remotely close to what I'm trying to build. The funny part Is I  charged the customer $2000.00 for a buffet That I dont even know how to build. Thanks for the advise any more would be greatly appreciated. On a positive note. My planer does not snipe, I repeat does NOT Snipe at all.Ha HA    Peace , Christopher Wade

1. 
   DonStephan | Jul 18, 2010 02:14pm | #7

   A book I've found very helpful on more than one occasion isa Taunton book called Care and Repair of Shop Machines by John White.  Set up and adjustment guides and jigs described pretty darn well.  Sounds like something has gotten out of alignment with the jointer.My two cents.

1. 
   Chrismitchell | Jul 18, 2010 02:37pm | #8

   This morning I went and bought a moisture meter from HD. Ryobi brand just to see where I was. Most of the lumber was between 8 and 11 percent. Why just a month ago it was 6 percent, Ofcourse right after I checked it we got a pretty good rain? I turned on the A/C so I will check it here in a little while again. I do need that book though I checked the jointers outfeed fence to the arc of the cutter assembly " Not the Knives" I have them off and just finished cleaning them. The outfeed table was dead on with the cutter assembly using a dial caliper . The infeed table was 5 thou out on thr fence side. Is this enough to make a difference in the cut? thanks chris

2. 
   SantaFeTom | Jul 18, 2010 06:10pm | #9

   Don't think it is the A/C

   My shop has A/C that runs all season. Here in Austin, that is  basically May through October! Although I have always meant to get a moisture meter, I haven't yet and I don't really worry much about moisture content. I have never encountered the degree of problems you have run into. Wood that has been the shop for a long time tends to stay straighter but I frequently bring wood into the shop and just start using it. For wood recently brought into the shop I rough cut a little over sized to expose the interior of the wood, let it acclimate for a day or two and then bring it to final dimensions. So I just don't think the use of A/C is the problem.

   As far as jointer adjustment, I follow the basic procedures but have some refinements. Once you think you have it adjusted, take two 3" or 4" wide boards, 3' or 4' long, of equal length. Joint an edge of each and then put the two jointed edges together. This will double any adjustment error. If you see a gap in the middle or if they pivot in the middle then the adjustment isn't right. Keep working the adjustment and tests until you get it right. To double check the cutter height with respect to the outfeed table, I take a 12" or so length of wood, 3" or so wide, jointed on one side. I then darken the end of one of the jointed edge with a pencil. With the jointer running, I then slowly and CAREFULLY pull the cutter guard out just far enough to slide that piece of wood, darkened edge down, from the outfeed table to the spinning blades and examine the point of contace. If none of the darkened material is removed then the outfeed bed is too high. If it creates a snipe, it is too low.

   As far as mortiser bits burning, I have burnt a few myself. I find I need more of a gap between the bit and the chisel than the procedures call for. The smaller the mortise width, the more true this is. I use a small piece of standard formica as a spacer to get started and them may lower the bit a little more if the chips clog and start burning.

   The concave rips on the table saw are a mystery to me since I am willing to bet you have already checked that the fence is parallel to the blade. Anyone else have any ideas?

   I am self taught too and to the whatever extent I am competent, it has been through reading books, Fine Woodworking, watching Norm and trial and error. Hang in there.

   ...tom