Thread: Uneven jointing/planing on combo unit

assuming the machine is setup correctly with the knives set properly etc etc...

I find I get these problems too with dull knives in my JET combo when I only buzz off a light pass less than 1mm. it has a helical head. i find that there is substantially more resistance from helical heads than conventional heads, and with a light pass it seems to want to just rub over the surface, pushing the timber away from the tables, instead of cutting through the timber and pulling it down hard on the tables. I work around the issue just by very rarely changing the infeed setting of about 2.5mm deep. if i need to do a light pass, i just put alot of downwards pressure on the board forcing it hard down on the table surface.

Sounds like a setup issue. Make sure that your infeed and outfeed tables are coplanar, and that your outfeed table is at exactly the same height as your knives when they are at Top Dead Center.

At a guess I would say that your outfeed table has sagged at the far end? Try using a long straightedge (or a long spirit level if you don't have a straightedge), to see if the infeed and outfeed are coplanar.

Sounds to me to be that the outfeed table is low at the far end.



Pete

They appear to be coplanar, no sag, all looks good.

Think you may have a point Kuffy. I have a helical head and tend to take very light passes. Will try taking heavier passes next time around.

Any other feedback/suggestions?

Thanks,

Gareth

Constant downward pressure close to the head on the outfeed table. If you move your pressure away from the head it may be allowing the back end of the board to rise very slightly

I'm starting to think that Kuffy might be on the money. I have the same machine as Gareth, and get the same issue and I'm pretty damn sure the tables are coplaner (but will check them again). HOWEVER, my cutters are due for rotation and I've been getting this problem more and more. When I first got the machine I jointed about a tonne of timber and everything was good, but lately everything is not so good - I've become the master of the taper (broad faces and narrow edges).

Another common and probable reason will be that the knives are set to close to the height of the outfeed table. As the knives wear and dull, this height becomes closer to equal, or even start cutting below the outfeed in heavy wear situations. I currently set my knives using the 2 lines marked on a stick method, using 3-4mm spacing to roughly match the distance of the cuttermarks. The pros that right books about this stuff suggest a 5mm spacing, but I always found I got trailing snipe at 5mm. I need to rotate my cutters, I might play around and mess up all my settings and reproduce the problem, and then I can fix it. Ill screw around with it until I can shave 0.4mm off a 130mm wide board dead flat, no snipe.

Having the cutters set perfectly level to the outfeed should, in my opinion, be theoretically correct. But given vibration, inconsistant pressure applied, and the difference between the high and low of each cuttermark. it just doesnt work.