jointing long boards - advice needed


Hi...I'm trying to edge joint some 7 foot boards so I can glue up a slab for a bartop i'm making for my garage. The boards are 1 1/4 thick and are douglas fir (i used 2x6s from the local lumberyard). I'm having trouble getting a straight edge, it seems the more i joint the same edge, the more concave it gets. It's very slight but it seems the jointer is taking more off the middle of the board than the ends. I'm using a Yorkcraft jointer, 6", 22" infeed table, 22 1/2" outfeed table. I haven't had this problem with smaller boards, and i'm not sure if it's my technique, or a machine setup thing.
Any advice would be appreciated... Thanks, Ken
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ken blais wrote:

One thing that I thought of was are you pushing down on the boards as they go through or just making sure they're against the fence....at 1.25 I wouldn't think you could bow them down....But you might be a mighty strappin lad....
When you push in the middle there might be just enough flex to cause the extra bite out of the middle section...
Just my 2 pennies worth...
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That flex that Bremen68 talks about could work to your advantage. These are long pieces that'll probably clamp together just fine, as long as you've got a nice square edge to glue up. If you really want/need a good edge jointing, you'll have to "extend" your tables with roller supports or somesuch. And their height must be set _very_ well. Tom
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ken blais wrote:

Is your outfeed table maybe slightly too low?
Also a little bit of this is okay, as it gives you a "spring joint". For more information, see about a third down this page:
http://www.taunton.com/finewoodworking/pages/bw0002.asp
Chris
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Chris Friesen wrote:

Too low shows up w/ some snipe at the ends...

Don't disagree here too much as long as it's not excessive...
A 22" exit table is pretty short for a 7' long piece. I suspect a lot of it has to do w/ not being able to hold the ends down as firmly when entering/exiting the cutting area as compared to the middle section.
It is virtually impossible to add and extra infeed/outfeed table to a jointer a _precisely enough_ the right height to be useful.
I'd suggest the expedient of taking one of two paths although the jointer set up should be carefully checked for accuracy first by jointing a 4-ft or so piece and testing that you get a good fit there--if not, tune until you do. After that preliminary step, I do one (or both) of the following for pieces longer than I can handle easily (altho w/ an 8" longbed it's relatively easy to do 7' as long as they pieces are _too_ heavy)...
1. Set the jointer for a whisker-thin cut and start in the middle and go each way to take the concavity out. If the setting is thin enough, the will be no ridge/hollow in the middle
2. Use the jointer for the first rough pass then a sharp hand plane to fine tune the fit. About two or three strokes should do the trick.
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Not making a comment on technique, but if you are using plain old dimensional from your lumberyard, a proper jointing is the lease of your problems. When those boards properly dry out, it is unlikely that they will remain very strainght very long.
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ken blais wrote:

Long boards need long table. Make it simple...use the factory edge off a sheet of ply as a guide and rout the edges.
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jointing 7 foot boards on a 22" table is going to be interesting to say the least.
I would either fasten a temporary table at least the length of your board to the infeed table so the entire length is supported
or
I make glue joints with the table saw using an extension fence.
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44-1/2" total length, ain't enuff tho...
--
Alex - "newbie_neander" woodworker
cravdraa_at-yahoo_dot-com
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ken blais wrote:

Ken,
I had a similar problem. For me, it was that I couldn't control well enough the board when it was only supported by just the infeed (when starting) or outfeed (when finishing) tables. Depending on how precise your work needs to be, there are a number of ways you can do this. First, get one of those 8' metal straight edges and clamp it to the bottom of the board. Clamp it in the middle (if possible) and at both ends. If that sort of straight edge isn't good enough, then ignore everything else after this :).
If you have a router, you can use a spiral bit to do a fair job, as has already been mentioned. But if you have a radial arm saw whose front table edege is square to the fence, put the saw into the rip position and run the straight edge along the front edge of the table. Not only is this faster than the router, but I've had better results over long cuts.
--
Michael White "To protect people from the effects of folly is to
fill the world with fools." -Herbert Spencer
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wrote:

This may be asking an obvious question but are the boards straight to start with? If not you may be accenting a problem that already exists with a crooked board. Be sure you have straightened the board before you put the final edge on it. Once your pieces are ripped from the 2x6, sight down the edge. If you see that they are already concave, take a little off of each end until it's straight then make a final pass. While your jointer not have the longest bed, I'm confident that if it's set up correctly you can get a straight 7' board with it.
Mike O.
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