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Forum topic by nschafer posted 05-15-2018 10:25 PM 741 views 0 times favorited 14 replies Add to Favorites Watch
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nschafer

4 posts in 63 days


05-15-2018 10:25 PM

Topic tags/keywords: question jig tablesaw finishing

I am trying to rip a 9’ board on a table saw. I am using a Dewalt 7491. Every board I rip has a significant bow to it. The center is wider than the ends. I have used the factory edge of a sheet of plywood and an eight foot piece of metal angle bolted to the board to try and straighten the edge. For my last attempt I took another piece of 8’ metal angle and replaced the factory fence. The board still came out bowed. What am I doing wrong?


14 replies so far

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BFamous

143 posts in 173 days


#1 posted 05-15-2018 10:34 PM

Can you upload a pic of your setup?
I’m assuming you’re running your plywood straight edge along your fence, and have your board secured to the plywood, cutting the far side of the board (the side away from the fence).

-- Brian Famous :: Charlotte, NC :: http://www.FamousArtisan.com

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nschafer

4 posts in 63 days


#2 posted 05-15-2018 10:55 PM

I do not have a pic but can get one. Yes I’m running the straight edge along the fence and am cutting the far side.

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Loren

10476 posts in 3700 days


#3 posted 05-15-2018 11:55 PM

The fence has to be twice as long to do that trick
on a table saw.

Another way to do it is nail or otherwise attach
the board to a straight board to the top and cut
opposite edge off. You take the nails out, flip
the board around and rip a parallel edge.

These things do the same thing without putting
holes in the work.

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waho6o9

8238 posts in 2629 days


#4 posted 05-16-2018 12:01 AM

Public Domain

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RobS888

2452 posts in 1897 days


#5 posted 05-16-2018 12:43 AM

I use an 8 foot x 6 inch strip of mdf with a inch strip of mdf around 1 side and 1 end. So it makes an “L” shape. I place the board to be cut on the table between the blade and fence. With the concavety to the fence ( it bows towards the blade) then I place the guide on top of the board with the long strip to the fence side and the short strip on the infeed side. Push the board as far as it will go into the L and then measure smallest amount from strip side of guide to edge of board toward blade. Meaning the point of board closest to guide. That is the setting of the fence. Slide the board and guide back and over in front of blade and move fence to measured amount and make the cut pushing board against guide against fence. The cut I made becomes the reference for cutting the other side without the guide.

It took far longer to write than it does to do it.

-- I always suspected many gun nuts were afraid of something, just never thought popcorn was on the list.

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nschafer

4 posts in 63 days


#6 posted 05-16-2018 01:07 AM

Do you think something along the lines of robs888 idea would work. Would I not need a longer fence?

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GrantA

196 posts in 1460 days


#7 posted 05-16-2018 01:19 AM

If you did what I think you did with the plywood and metal you mentioned, then no I don’t think Robs idea will do anything different. Post up some pictures of what you’re working with so we can try to help

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nschafer

4 posts in 63 days


#8 posted 05-16-2018 11:09 AM

Along with the metal bolted to the board I also tried a factory edge of plywood with the factory fence.

I took the factory fence off after several attempts and put the metal angle to see if that would help. The cut was a bit better but not by much.

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GrantA

196 posts in 1460 days


#9 posted 05-16-2018 11:57 AM

I suggest putting the fence back on, verify it’s locking down parallel to the blade and then turn your attention to infeed & outfeed support. That whole arrangement looks like it would get sketchy without support. I’m sure you’re getting some deflection on your “extended fence” especially since the angle (aluminum) on the board is only riding against a thin edge of the “fence”
Then use either the ply or angle attached to your board and you should be good to go. Maybe practice just running ply through and see how it goes

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rwe2156

2999 posts in 1533 days


#10 posted 05-16-2018 02:04 PM

^^ What he said!!

I usually handle this with a straight edge + circular saw to get it straight, then do a final rip on table saw.

Keep in mind if there is stress in the board it will bow after ripping.

-- Everything is a prototype thats why its one of a kind!!

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JCamp

715 posts in 603 days


#11 posted 05-16-2018 06:17 PM

What grant said or use a circular saw and cut it while it’s laying on the ground with a sheet of foam insulation under it

-- Whatsoever thy hand findeth to do, do it with all thy might

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woodbutcherbynight

5240 posts in 2461 days


#12 posted 05-16-2018 06:53 PM

The table saw probably has 27 inches or less of flat top and fence, of which you are trying to shoot a 9 foot board. A difficult task for the saw with this set up. Other have mentioned a few ideas here is yet another suggestion. Rip it rough with a skilsaw. Then clamp it to a board or angle that is flat and straight. Use a router to achieve a square 9 ft long board

-- Live to tell the stories, they sound better that way.

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BFamous

143 posts in 173 days


#13 posted 05-17-2018 12:08 AM

Straight edge and circular saw get my vote as well, given the table saw setup you have.

-- Brian Famous :: Charlotte, NC :: http://www.FamousArtisan.com

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enazle

53 posts in 60 days


#14 posted 05-21-2018 05:53 PM

That being a contractor saw means the blade may not be true to the table. Check that first, make sure all the bolts underneath are tight. Crank the blade all the way up and measure the distance between a tooth and the table slot at the back and front of the blade. Measure the same tooth by rotating the blade. A 1/100th” is acceptable. Now Mount the fence and clamp it down and do the same for the distance between the fence and the blade. I think you will find your fence and or table top are not parallel to the blade. If all are true then you need to make a catch table you can mount behind the saw to support your boards. A spring board will also help.

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