Getting slightly concave results when jointing (surface planing) boards

[Gabriel]

Hi.
I'm a hobbyist woodworker. I've just set up my workshop in Madrid, and besides Festool machines (TS55 + guide rails + MFT3, CT22, RO150, etc.), I prepare the stock with a European style jointer-planer Metabo HC260 (260 mm wide x 1000 mm long - 11''x40'' - extruded aluminium tables).
The "mystery" I don't find answer for is the following: the machine is new, well calibrated (outfeed table with cutters) and the tables seem to be flat. However, planing 50'' long white oak boards I get concave results (1 mm-1,5/32'') in the middle of the board. I've looked in many books and woodworking magazines, but until now couldn't find an answer to what could be the cause of that. Any ideas?
Thanks in advance for the answers!

 

[romlee]

My experience is limited to US style joiners so I'm not familiar with the Metabo combination machine.  Although the machine is new and "well calibrated", I suggest you use an accurate steel or aluminum machinist straightedge, perhaps 100cm long and check the following (Be certain to disconnect the power to the machine) after removing the blade guard.

1.  With both outfeed and infeed tables at the same height, use the straightedge to make sure the tables are flat relative to each other.  If they are not flat (i.e., high or low at the cutterhead), adjust to level the tables if your machine allows this adjustment.
2.  Lower the infeed table perhaps 5mm.  Place the straightedge on the outfeed table, rotate the cutterhead so that a blade is at its highest point:  the edge must be level with the straightedge.  If not, raise or lower the outfeed table so that all blades are level with the straightedge.

Nearly all of my problems of this type with joining are due to out-of-level tables.  That is, if the joiner functioned properly previously and then began to joint inaccurately, I would adjust the tables to level and the cutterhead level to the outfeed table.  Then the joiner would function as it should.  However, if your machine is new, is not accurately calibrated and does not respond to adjustment, then you should contact the company you purchased it from.

Good luck!

 

[fidelfs]

I have a Jet JJP-12 European style and had some issues until I corrected my form.  First I was getting tapered cuts and some time I had some bow (concave cuts).

The problem is those tables are short in the European style.  At the beginning when I was building a bed, the wood hanged in the outfeed table and created a bow.  Later I tried to avoid the wood to hang on either bed (infeed/outfeed) pressing hard the wood against the beds.  That was causing the taper.
I decided to trust more the jointer tables and apply normal pressure to the wood and the problem went away.  Also wood eventually  develop a bow (concave) after planed.  I was finishing some drawers over the weekend ( I made those doors quite some time ago) and I like to hand plane before I use sandpaper.  I notice there was a little bow in all faces of the door because when I was hand planning I notice that I was not hitting the middle with my low angle jointer hand plane.

So my advise is not let the wood hang but do not make more pressure than needed.

I am also a hobbyist so take my advise with a grain of salt.

 

[romlee]

Good points about feeding material through the joiner.  I would add that downward pressure on the board should shift from the infeed table to the outfeed table as soon as practical.

My jointer is a basic Jet 6" capacity model.  Table length is 46".  I routinely join short (12" minimum) and longer (6' plus) through the machine.  So it is possible to get good results with an entry level machine (with auxiliary infeed and outfeed stands) even in a commercial shop (I design and build custom furniture).

If you have access to Popular Woodworking Magazine (internet or library), Marc Adams (Marc Adams School of Woodworking) wrote a series of articles in 2008 that discussed best practices on the use of woodworking shop machinery.  Specifically, you might want to read the article on jointers.

 

[Gabriel]

Thanks so much for your suggestions! I'll be trying them today in the workshop.

 

[Notorious T.O.D.]

Make sure the infeed and outfeed tables are in the same plane from end to end, and not tilted down at the ends away from the cutterhead.  When you are sure the tables are in the same plane they must remain in planes that are parallel to each other when the infeed table is lowered to your cutting depth.  Make sure the top of the knives at the peak of their rotation are even with the surface of the outfeed table.
Once these things are set the machine should be capable of producing the proper result.  After that it can come down to you as the operator using the proper technique and learning how and where to apply pressure to get the good straight jointed edge.

Often the cupped joint you are experiencing is a result of the cutterhead knife being just slightly higher than the outfeed qne it is easy to see when edge jointing several wider boards.

Best,
Notorious

 

[porqui]

I prefer to use a circular tablesaw with a sharp blade and a long straight-edge as a guide te prepare the edges of boards for joining. It is difficult to get a straight edge that is also square on even a well set up jointer no matter how good you are. On a saw I can get near perfect edges nearly all of the time with minimum waste. -- Good luck!

 

[fidelfs]

I always get a straight and square edges.  If you have good technique you need just a little practice. If I don't use a jointer then I use my hand plane but I will never use a circular saw for that.  You always get a almost perfect but never a perfect joint.

 

[nickao]

I use my table saw all the time for jointing with my tapering/jointing sled, perfect every time. If you can not get it done with a table saw the saw is out of adjustment somehow.. I also have used the TS 75 many, many times to edge joint hardwoods. Of course a jointer is my choice if the wood I am working woth allows for it.

A jointer is one tool where you really see that this is a craft, the user makes it work. Like the Festool sanders some people just think turn it on and it will work, no I do not think so. An experienced user can use that Rotex one handed and get a flawless finish. Others return it because they do not want to take the time to learn how to run the sander or simply can not master it. Same with a jointer, you have to run the machine and technique is everything.

Here are some pics using my table saw as a jointer. Usually these pieces are for the center stars in my inlays. They tend to be to thin and small for a jointer and there is no place for error so the table saw is the way I guarantee I do not lose an exotic piece of wood.

The second picture show the pieces for the center star on the inlay pictured. I cut the light and dark pieces together in groups of two tips per cut, then edge glue and clamp them, just like jointing and glue up for a large panel.. Perfectly tight every time.