Troubleshooting Crown in Ripped Boards
Advice for diagnosing the problem when boards ripped on the sliding table saw come out not quite straight. November 28, 2014
Question (WOODWEB Member) :
I have a Felder k500s. I seem to be getting a very slight spring joint when I'm ripping wood on the fence or SLR on the table. Why is this happening?
(Solid Wood Machining Forum)
From Contributor E:
I have the same saw. Not sure what you mean by spring joint?
From contributor M:
I think he is describing the ripped edge as being slightly concave, rather than straight. There are a number of possibilities. Is this a significant error or are we talking only a few thousandths of an inch? The reason I say this is that even my jointer will produce a slight spring joint (.003) over an 8' board.
From Contributor L
If your table is straight and didn't get dropped the common cause of your "spring joint" is tension in the wood is causing the wood to move. We had a Giben beam saw and occasionally the particle board was crowned after a cut. It was releasing tension and moving. They were cutting a 4x8 sheet in half. Cutting a small trim edge will not cause the wood to crown.
From the original questioner:
Here is the scenario: I am ripping hard maple that has been face jointed and planed to approximately 20 mm. I am using my slider to SLR the rough edge off the board taking as little as necessary to get a straight edge - so less than 5mm typically. After doing so I have a concave edge that over 8-9' is probably 1/16". I have put a dial gauge on the blade since the original post and have noticed that it was slightly out by about .007". It may be the cause but I haven't checked the new blade yet. I have been having this issue for quite a while and with several blades though. I also get similar results when ripping with the fence. I'm stumped.
From contributor K:
Try this; straightline two pieces of material like MDF or ply a foot or more wide, taking off a minimal amount and clamping the pieces to the slider table. Put them together edge to edge. If they fit tight, the problem is not in the saw but in the solid wood releasing tension or slipping on the table as the rip cut is made. If the sliding carriage is not tracking straight, you are out of luck. If your carriage is out by 1/16" over 8', you must be seeing problems in squaring cabinet panels and subsequent assembly. Are your problems strictly with solid wood rips? Sheet goods, especially MDF, are far from immune to crooking due to tension release when breaking down a sheet, but once roughed out usually have less reaction to edge trimming than solid wood.