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bow down the length of pine when ripping on my tablesaw

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Forum topic by Carol posted 12-30-2016 08:21 PM 1354 views 0 times favorited 18 replies Add to Favorites Watch
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Carol

57 posts in 150 days


12-30-2016 08:21 PM

Topic tags/keywords: rip stock ripping pine ripping leaves a bow pine tablesaw

i’ve seen this issue online, have had friends say the same thing happens, but no one has told me why, or how to correct.

when i rip a piece of wood on my tablesaw (it’s just an inexpensive skil from lowes), if it’s solid wood, i get a small bow down the length of the wood, as if the middle of the wood has wandered away from the fence. each end is perfect. if i rip a piece of 3/4 birch plywood, it’s perfect. the bow in solid wood is very, very small, maybe 1/64” but definitely enough to notice.

this happens each time i rip solid wood that’s longer than about 3’. is this maybe a moisture issue? i don’t have a jointer or planer; when this happens, it takes me forever to use a cabinet scraper and sander to fix the problem.

is there something (well, obviously there is) i’m doing wrong? maybe change the way i hold the wood against the fence, push the stock thru the blade slower maybe? get a new blade? different blade? i’ve aligned the blade with the riving knife, the splitter works fine, and the fence is parallel to the blade since plywood rips square to the blade and fence.

i always use a blade guard, measure the distance from the blade to the fence front and rear, and use a push stick.

any clues to help me rip my stock cleanly?

-- Carol


18 replies so far

View Aj2's profile

Aj2

896 posts in 1435 days


#1 posted 12-30-2016 08:56 PM

Table saw tune up align blade to miter slot.Then miter slot to fence.I don’t know if that saw is even adjustable it might be as good as it gets.
It also helps to have a flat fence and flat square wood.

Aj

-- Aj

View Carol's profile

Carol

57 posts in 150 days


#2 posted 12-30-2016 09:07 PM

i wouldn’t doubt that the saw could use a tuneup, but since i can rip plywood true, is there some technique having to do with solid wood that i’m not doing, or doing wrong?

i’ve put my combination square’s ruler against the steel fence, and it looks flat; again, it MUST be flat since plywood rips straight. this is driving me nuts, causing extra work…

when i use my mitre slot with a sled, i can cross cut a square edge.

-- Carol

View wichman3's profile

wichman3

39 posts in 258 days


#3 posted 12-30-2016 09:34 PM

I would say that the issue is the natural warp of the board. Have you tried ripping quartersawn boards? Are you using feather boards?
Try ripping a quartersawn board or two and see if you still get the bow; if you do not get the bow then try using a feather board that is tight to the start of the cut (this will keep the board against the fence) and should minimize any bow.

View MrUnix's profile (online now)

MrUnix

5213 posts in 1836 days


#4 posted 12-30-2016 09:37 PM

If nothing else, make your rip slightly wider than needed, and then make a second pass to final size. Verify the flat edge (against the fence) is still flat after the first rip.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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clin

670 posts in 633 days


#5 posted 12-30-2016 09:45 PM

Keep in mind that your rip cut will only be as straight as the board is where it contacts the fence. Obviously small imperfections (significantly smaller than the fence is long) will be bridged by the fence and not “copied” to the cut. But if the edge of the board riding against the fence isn’t straight, your cut won’t be either.

This of course is where jointing comes in.

Another possibility is that the wood itself is changing shape when cut. This is very common. If this is the case, both sides of the board will be crooked. One side curved out and the other in. Plywood tends to be very stable in this regard. So maybe this is why you don’t have an issue cutting plywood.

While woods vary greatly in this regard, if I ripped a longish 6” wide board down the center, I would be surprised if it didn’t develop a bit of a crook. Wood commonly has internal stresses. When you cut these, the two halves relax into a different position because they can no longer pull on each other.

If you want a really really straight edge, it’s common to make a series of cuts. Generally rough cutting to near final size. Jointing one side to make it straight, then making a trim cut on the other side. The idea is your last cut removes so little material, the remaining wood won’t be affected.

And to be picky, what you are describing is actually a crook not a bow.

-- Clin

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tonycap

1 post in 149 days


#6 posted 12-30-2016 09:50 PM

I had the same issue with my grizzly cabinet saw. The issue was the fence had a bow in it. So as you feed the material into the blade it bows with the bow in the fence. try a mdf sub fence clamped at the ends. That solved my issue

View Ted78's profile

Ted78

293 posts in 1637 days


#7 posted 12-30-2016 10:29 PM

I don’t have anything to add that wasn’t already mentioned, except that instead a scraper, a jointer plane would be a much more efficient tool for correcting the problem.

-- Ted

View Carol's profile

Carol

57 posts in 150 days


#8 posted 12-30-2016 11:43 PM

wow, thx so much for all the replies!

featherboard: usually use one where there’s only a small piece of wood to the outside of the blade, but i can certainly try using it for all rip cuts. i try to keep the biggest part of the stock between the blade and fence.

also, i’ll try using the factory edge of a piece of mdf as a fence, clamped to the work surface.

can also pick up a piece of quartersawn at my lumber mill, although if i could afford beautifully quartersawn wood, i wouldn’t make everything out of pine ;-)

starting this console table in 2 days; i’ll let you know how the ripping goes.

-- Carol

View paratrooper34's profile

paratrooper34

903 posts in 2588 days


#9 posted 12-31-2016 03:38 AM

It could be your technique as to how you keep the board against the fence during the entire rip cut. I found this out for myself when I was at a woodworking school, the instructor watched me rip some boards and he pointed out a small glitch in my technique the was causing the same problem you are having. He had me shift my hand over a little when applying pressure on the fence. It worked, problem solved.

-- Mike

View eflanders's profile

eflanders

167 posts in 1487 days


#10 posted 12-31-2016 05:29 PM

Another possible issue is that your blade is heating up and thus wandrring a bit during the cut in the hardwood. This would explain why the cuts in ply are fine but not thicker stock. HOW high is your blade set above the stock when ripping? Blade height if set too high adds to the friction. Are you using a splitter of some sort? Without a splitter, wood can close up on the cut adding friction as well as causing you to drift off of the fence as you try to force the blade to keep cutting. How sharp is the blade? Dull blades are just trouble waiting to happen in so many ways… As others have mentioned, start by squaring things up and getting a new blade.

View Carol's profile

Carol

57 posts in 150 days


#11 posted 12-31-2016 06:05 PM

i’ve never removed the riving knife/splitter, so it’s always used. i set the blade just high enough to clear the stock but no higher. even though the blade could probably be replaced, it’s much more difficult to cut through the ply than the pine. just about every tool i own runs thru pine like warm butter. i’ve only cut true hardwood using the tablesaw once; ripped some red oak stock and i don’t remember having the same issue. certainly all that soft wood could easily have dulled the blade.

could this “drift” have anything to do with pine being a soft wood i wonder? bet my lumber yard aces will know.

-- Carol

View Aj2's profile

Aj2

896 posts in 1435 days


#12 posted 12-31-2016 06:34 PM

“Even though the blade could probably be replaced”
A good sharp clean blade goes hand and hand with everything mentioned above.
Good luck keep us posted
Aj

-- Aj

View clin's profile

clin

670 posts in 633 days


#13 posted 12-31-2016 06:48 PM


“Even though the blade could probably be replaced”
A good sharp clean blade goes hand and hand with everything mentioned above.
Good luck keep us posted
Aj

- Aj2

I’ll emphasize the “clean” part of this. It’s something easy to do. I find 409 works just fine for cleaning saw blades. As they say, the blade isn’t dull until it is clean and dull.

-- Clin

View Carol's profile

Carol

57 posts in 150 days


#14 posted 12-31-2016 08:10 PM

lol clin, yet another truism to add to my collection

ok, having a idea as to how expensive blades are, thought i’d research how to tell if my blade should be replaced.

does it leave burn marks? no
does it leave clean edges? yes
does it seem to take more effort to cut the wood? hm…that’s a tough one, as i don’t use it very often but i’d say no, no more effort is required than normal
does it bind, chip or tear? no
worn or chipped teeth? no
hit a screw? no (geez, even i know better!!)
hit hard knots? no

however…
after raising the blade all the way, i can that it’s full of pitch from the pine and the teeth are dirty. i’ll clean it well (some recommend simple green, which i use on my boat and works great) and a gentle, soft toothbrush. after proper cleaning and drying, i’ll try ripping again and see what happens.

-- Carol

View MrUnix's profile (online now)

MrUnix

5213 posts in 1836 days


#15 posted 12-31-2016 08:22 PM

i set the blade just high enough to clear the stock but no higher.

Might not be part of your problem, but your blade should probably be set a bit higher. Here is what Freud recommends:

• The sawblade’s projection (t) with respect to the work piece must be greater than the height of the blade’s tooth (fig. 18). Increase or decrease the projection of the saw blade to improve finish quality.

• The number of teeth cutting the wood simultaneously must be between 3 or 4 for ripping and ideally 5 to 7 for crosscutting. With less than 3 teeth cutting the sawblade begins to vibrate leading to an uneven cut. If you want to cut work pieces with increased thicknesses, but wish to maintain the same diameter saw blade, then use a blade with less teeth. If instead you want to cut work pieces with a reduced thickness, but also maintain the same diameter saw blade, then use a blade with more teeth.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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