# How to prevent concave edges on my table saw



## imhotep531 (Oct 5, 2011)

I have a Porter Cable jobsite table saw and I'm using a Freud Diablo ripping blade, although this problem I'm having occurs regardless of the blade I use, and regardless of whether I'm ripping solid lumber or plywood (I have another Freud Diablo plywood blade that I use).

My fence isn't the best but it does slide well and locks well. When I put a known straight edge against the fence and rip, I always get a slight concave or bow along the cut edge. The plywood I use is from a local cabinet shop and the factory edge on those sheets is near perfectly straight. Putting a factory edge against my fence does not get me a straight cut edge. Neither does putting the edge of solid wood worked on my Ridgid Jointer against the fence, which definitely is perfectly straight. I've checked all my edges using a machined aluminum 48" level.

Once I rip that first piece, every edge after that is bowed. I tried using a feather board ahead of the blade and that did minimize the bow somewhat but it's still there.

I need to rip a lot of solid wood to plate join a desk top and I'm hoping someone can help me solve this mystery bowing problem because otherwise that project is simply not possible. I cannot afford a $2,000 table saw upgrade right now.

Any suggestions?


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## bauerbach (Mar 25, 2012)

is the fence aligned with the blade?


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## Wendel17 (Apr 20, 2009)

+1. Check your fence. If you're not getting a sraight cut, it's off. Check to see if both front and back of the blade are the same from the fence.


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## epicfail48 (Mar 27, 2014)

Check technique too. If the straight edge isn't up firmly against the fence it can cause issues


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## woodnthings (Jan 24, 2009)

*If ....*

IF your blade is parallel to the factory fence AND the fence is straight, THEN I would extend the plane of the fence by attaching one of the rips from the factory edge of the plywood. Even though it's only 3/4 thick, laying flat that is enough to form a good edge guide.. for ripping. The Delta Unifence is only 1/2" tall in the low position for example. 

How long should the fence extension be?
Make if around 40" for best results., 36" will work also.

How do you attach it to the factory fence? Butt another piece of 3/4" about 2" tall on top of it and glue it down such that the vertical face and the straight edge you will guide against are parallel. Your factory rip may have the curve and that will have to be eliminated by proper placement of the vertical. You can then clamp the vertical face to the factory fence. 

You are essentially making a straight edge guide in the shape of an "L" . The longer the fence the straighter the rips will be. I once had to make a 28 foot long fence to straight line rip some 14 foot long boards.
Check out this fence:

 Attached Images











Evil Machine


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## GeorgeC (Jul 30, 2008)

i think that you are saying that the wood is bowed after you make a rip cut. Or is it that the part next to the fence is remaining straight and only the cut edge is concave? It makes a big difference in determining the cause as to which statement is true.d

The blade not being parallel to the fence will not cause this unless the wood is rocking on the fence. As long as the wood stays tight against the fence the cut will be parallel to the fence and as wide as the point at which the blade is closest to the fence.

George


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## Eugene Shin (Aug 27, 2014)

Danno said:


> +1. Check your fence. If you're not getting a sraight cut, it's off. Check to see if both front and back of the blade are the same from the fence.


I agree with that... will you check the fence again?


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## Leo G (Oct 16, 2006)

Could just be operator error. If you pull away from the fence a little it will affect the cut. A short fence makes for a low stability cut. Could be the wood itself. When you cut wood and plywood you relieve tension. This will affect the wood in different ways. Usually it will curve in or out. Sometimes it will go up or down too. Usually that will only happen with solid wood and not plywood.

If you have some particle board or MDF try that. It should be stable enough to stay nearly perfectly straight.


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## rr1963 (Jun 10, 2014)

M a newbie. Could the blade be too high and flexing? Just curious. 

Thanks


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## tinstar (Mar 5, 2014)

I had the same saw and the same problem. I found the fence had a very slight bend so that the cut would look straight until it got to the back of the fence where it would push the leading edge of the cut towards the blade making a slight curve. It was really noticeable when edge gluing the ripped boards. I screwed a piece of plywood to the fence that extended past the table. Not perfect but it definitely improved the situation. If you're going to keep the saw, I would replace or build a new fence.


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## imhotep531 (Oct 5, 2011)

GeorgeC said:


> i think that you are saying that the wood is bowed after you make a rip cut. Or is it that the part next to the fence is remaining straight and only the cut edge is concave? It makes a big difference in determining the cause as to which statement is true.d
> 
> The blade not being parallel to the fence will not cause this unless the wood is rocking on the fence. As long as the wood stays tight against the fence the cut will be parallel to the fence and as wide as the point at which the blade is closest to the fence.
> 
> George


Only the cut edge is bowed after the rip cut. It's not that the board is bowing, it's that the saw is cutting a concave edge.

Despite all the recommendations to align my blade to the fence (which I believe it is), like George is saying, I don't see how this would cause a bow. All it would do is give me a different width than I want if I measure of the widest point by accident. It wouldn't cause a bow.


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## GeorgeC (Jul 30, 2008)

I am stumped. I admit it. As long as the board is tight against the fence when being cut and nothing is moving I do not see how the bow could happen.

How much bow is there? With the subject board against a straight edge, how much space is between the center of the board and the straight edge? (I do not know how this information is going to help me, but it is nice to know)

George

George


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## bauerbach (Mar 25, 2012)

I agree, fence, board, blade, if they are lined up, its impossible to not get a straight cut.

The fact that you say a featherboard helps suggests the board is NOT remaining tight to the fence. Or the fence is flexing somehow

If the blade and fence were out of line, it would pull away or push into the fence as it tracks along and that would make a straight cut very difficult to maintain.


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## Zircon (Aug 1, 2009)

Make sure that the splitter is lined up directly behind the blade and is in the same line of the blade. If the front of the splitter is behind the blade but the back of it is toward the fence, the work piece will bind up but if the front of the splitter is behind the blade but the back of the splitter is further out from the fence it will cause bowing as the back of the work piece is pulled away from the fence.


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## woodnthings (Jan 24, 2009)

*good advice*

No one else had mentioned the splitter, so that's another link in the chain that could be the issue. The splitter could be "steering" the board after the cut.
I find the splitter helps keep the work against the fence just as a featherboard would when properly set up. Featherboards should only be used ahead of the blade however, never behind it. :no:

I'm still in the camp that says a longer, straight fence is always a good idea. The goofy British guy on You Tube likes the shorter ones for "safety" reasons, but I like the increased accuracy I get with the longer fences. My Unifence is 43" long, the Biesemeyer is 41" long.


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## BigJim (Sep 2, 2008)

rr1963 said:


> M a newbie. Could the blade be too high and flexing? Just curious.
> 
> Thanks


This was my thoughts also, some of the thin blades will get hot and start to wobble, try a thicker blade and keep the blade just about 1/4 or so through the material and see if that helps.


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## Sorrowful Jones (Nov 28, 2010)

I would like to see some pics of the saw.
Are you using a feather board?


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## GeorgeC (Jul 30, 2008)

BigJim said:


> This was my thoughts also, some of the thin blades will get hot and start to wobble, try a thicker blade and keep the blade just about 1/4 or so through the material and see if that helps.


It would have to heat up and then cool down uniformly from one end of the board to the other.

George


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## woodnthings (Jan 24, 2009)

*here's an idea*

Take a board with a factory straight edge and make pass with the blade only 1/2 way into or through the wood. See if that kerf is parallel to the factory edge. 

If not, then the fence is probably the issue.
I doubt if it's the blade...unless it is dull on one side and favors the sharp side much like a bandsaw will "drift". A new or different blade will determine if that's the issue. 
You can make multiple kerfs in the same board, just slide the fence over until you get a kerf that is parallel, Label each kerf as to what was done differently for the "record" so you will know what the solution was. :yes:


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## Steve Neul (Sep 2, 2011)

I'm wondering if you have had this problem with any other saw. If the problem is with the saw then something is causing the wood to be pulled slightly away from the fence while making the cut. As others have said this happens sometimes if the back side of the fence is farther away from the blade than the front side. In rare cases the arbor on the saw could be out of square with the table and you think you have the fence parallel with the blade by checking it against the table when it needs to be parallel with the blade. In that event the saw blade needs to be adjusted parallel with the saw top. Then as Zircon mentioned the wood could be hanging on the splitter causing it to pull away from the fence.


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## TimPa (Jan 27, 2010)

i may have the answer for you, because i experience the same problem with my unisaw. the fence is bowed. after 30+ years of use, my stock aluminum jet fence has a bow in the center. place a known straightedge against the fence, or remove it and place it on a flat surface and check it. you can make and attach an auxillary fence, or send yours to a machine shop and they can flatten it for you.

you can clamp a straight edge down to your saw (aka fence) and try a test cut to verify.


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## GeorgeC (Jul 30, 2008)

Steve Neul said:


> I'm wondering if you have had this problem with any other saw. If the problem is with the saw then something is causing the wood to be pulled slightly away from the fence while making the cut. As others have said this happens sometimes if the back side of the fence is farther away from the blade than the front side. In rare cases the arbor on the saw could be out of square with the table and you think you have the fence parallel with the blade by checking it against the table when it needs to be parallel with the blade. In that event the saw blade needs to be adjusted parallel with the saw top. Then as Zircon mentioned the wood could be hanging on the splitter causing it to pull away from the fence.


"As others have said this happens sometimes if the back side of the fence is farther away from the blade than the front side."

That normally would not cause this problem without other problems. If the front side of the blade is closest to the fence then the whole board will be this dimension.

George


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## GeorgeC (Jul 30, 2008)

TimPa said:


> i may have the answer for you, because i experience the same problem with my unisaw. the fence is bowed. after 30+ years of use, my stock aluminum jet fence has a bow in the center. place a known straightedge against the fence, or remove it and place it on a flat surface and check it. you can make and attach an auxillary fence, or send yours to a machine shop and they can flatten it for you.
> 
> you can clamp a straight edge down to your saw (aka fence) and try a test cut to verify.


I think you may have hit the answer. So far this is the only explanation that I have read that seems to answer the problem.

George


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## woodnthings (Jan 24, 2009)

*it's the first rule of ripping ....*



TimPa said:


> i may have the answer for you, because i experience the same problem with my unisaw. the fence is bowed. after 30+ years of use, my stock aluminum jet fence has a bow in the center. place a known straightedge against the fence, or remove it and place it on a flat surface and check it. you can make and attach an auxillary fence, or send yours to a machine shop and they can flatten it for you.
> 
> you can clamp a straight edge down to your saw (aka fence) and try a test cut to verify.



You must start with a straight edge against the fence AND your fence must be not bowed, or curved, it must also be straight.
Curved edges in = curved edges out. 
Straight edges in = straight edges out.


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## Steve Neul (Sep 2, 2011)

GeorgeC said:


> "As others have said this happens sometimes if the back side of the fence is farther away from the blade than the front side."
> 
> That normally would not cause this problem without other problems. If the front side of the blade is closest to the fence then the whole board will be this dimension.
> 
> George


Well when the fence is running away from the blade it more difficult to keep the wood against the fence and most folks let the board go completely away from the fence altering the cut making the cut crooked.


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## mncamperguy (Jan 30, 2013)

TimPa said:


> i may have the answer for you, because i experience the same problem with my unisaw. the fence is bowed. after 30+ years of use, my stock aluminum jet fence has a bow in the center. place a known straightedge against the fence, or remove it and place it on a flat surface and check it. you can make and attach an auxillary fence, or send yours to a machine shop and they can flatten it for you.
> 
> you can clamp a straight edge down to your saw (aka fence) and try a test cut to verify.


I believe this is probably the culprit as well. I had the same issue a month ago, some boards would be bowed or I would have varying widths from the start to the end of the cuts. Two things were going on that I can tell:
1. The fence was bowed in the middle, i.e. the middle of the fence was further away from the miter slot than the front and back were
2. the fence trailed away from the blade at the rear of the fence. I aligned it best I could, not an easy fence to align and it didn't really help and then shortly it was out of alignment again.

I purchased the Delta T2 fence and put it on and both issues are now gone. Best cuts I have ever had on the saw. Craftsman 10" Table Saw (Model 315.228390)


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## woodnthings (Jan 24, 2009)

*look at it this way*



Steve Neul said:


> Well when the fence is running away from the blade it more difficult to keep the wood against the fence and most folks let the board go completely away from the fence altering the cut making the cut crooked.


The board is first cut at the front of the blade and at what ever distance the fence is from the blade. No further cutting occurs after that. This is the basis for the "short fence" theory. where there is little or no fence beyond the center of the blade. Initial feeding pressure toward the fence is only at the front or near end of the fence.

If you are going to have a long or standard length fence then it had better be straight and not inboard of the initial distance to the blade, only away at the far end, if at all.

If the fence is curved and you continue to keep pressure against the board, as it follows the curve of the fence, it will also be curved.


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## BigJim (Sep 2, 2008)

GeorgeC said:


> It would have to heat up and then cool down uniformly from one end of the board to the other.
> 
> George


You are right, I didn't think of that.


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## Zircon (Aug 1, 2009)

I think what's happening is if the fence and or the splitter is misaligned or the fence is curved, even though you hold the workpiece tight to the fence when feeding it in, on the back end the workpiece is forced sideways and the BACK of the blade instead of riding in the kerf chews away part of the board forming the curved cut.


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## aaronhl (Jun 2, 2011)

My cuts were not straight once- ended up being the cheap aluminum fence on the table saw- had a dent in it. So you were basically pushing the piece through in a V motion. Solved that problem when I bolted a piece of 3/4" plywood to the fence. Also make sure your throat plate is not moving.


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## Geo Mann (Apr 3, 2021)

This is the first solution that mentions the splitter which is often overlooked in table saw adjustments. Good call!


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## Rebelwork (Jan 15, 2012)

We will take an aluminum fence to the edge sander and sand it straight, unless it's the blade..


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## Tool Agnostic (Aug 13, 2017)

This is a zombie thread, exhumed from the dead. By now, they figured it out or gave up on woodworking.


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## Rebelwork (Jan 15, 2012)

Tool Agnostic said:


> This is a zombie thread, exhumed from the dead. By now, they figured it out or gave up on woodworking.


I dont understand why you make this post.

Too much caffeine?


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## Tool Agnostic (Aug 13, 2017)

Rebelwork said:


> I dont understand why you make this post. Too much caffeine?


It was intended mostly for @Geo Mann. New members often resurrect old posts without realizing how old they are. Sometimes it helps to remind new members to consider the dates on posts before responding to them, that's all. 

I assumed that you are smart and experienced enough to notice. 

By the way, thanks for the reminder. I just looked, and my first coffee cup of the morning is near the bottom, so I guess it is time to refill it before the timer on the coffee machine turns the warmer off.


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## Rebelwork (Jan 15, 2012)

Tool Agnostic said:


> It was intended mostly for @Geo Mann. New members often resurrect old posts without realizing how old they are. Sometimes it helps to remind new members to consider the dates on posts before responding to them, that's all.
> 
> I assumed that you are smart and experienced enough to notice.
> 
> By the way, thanks for the reminder. I just looked, and my first coffee cup of the morning is near the bottom, so I guess it is time to refill it before the timer on the coffee machine turns the warmer off.



Why not let moderators moderate?

I can see why new or unregistered woodworkers might have concern about making posts if they are gonna get punished for making them.


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## allpurpose (Mar 24, 2016)

Something every saw user should do from time to time is to check the washers on either side of the blade and make damned sure they're dead on flat. I'll take them out and hone them flat on a stone from time to time. Just paint from a blade can throw it out of alignment over time. I had a HUGE problem with the exact same issues until I read or watch a video about this very issue. Check those washers and even replace if they're too far off, but just a tiny little bump can throw blade alignment off by a LOT..
By the way..I'm a regular thread necromaniac.. and proud of it.. 👹
I might even be just a plain old, run of the mill maniac, but let's not split hairs today..OK?


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## Tool Agnostic (Aug 13, 2017)

Rebelwork said:


> Why not let moderators moderate?
> 
> I can see why new or unregistered woodworkers might have concern about making posts if they are gonna get punished for making them.


I give up. You're right. I'm wrong.


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## Rebelwork (Jan 15, 2012)

allpurpose said:


> Something every saw user should do from time to time is to check the washers on either side of the blade and make damned sure they're dead on flat. I'll take them out and hone them flat on a stone from time to time. Just paint from a blade can throw it out of alignment over time. I had a HUGE problem with the exact same issues until I read or watch a video about this very issue. Check those washers and even replace if they're too far off, but just a tiny little bump can throw blade alignment off by a LOT..
> By the way..I'm a regular thread necromaniac.. and proud of it.. 👹
> I might even be just a plain old, run of the mill maniac, but let's not split hairs today..OK?


I dont think I've ever checked the washers on a tablesaw or ROS...


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## Rebelwork (Jan 15, 2012)

Tool Agnostic said:


> I give up. You're right. I'm wrong.


Not about right or wrong, it's about being respectful to others.


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## epicfail48 (Mar 27, 2014)

"let the moderators moderate"

Good quote, that.


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## woodnthings (Jan 24, 2009)

I have said for years that to get straight edge boards from ripping them on a table saw you need to start with straight edge boards....? 

How is this possible? Your boards should be flat, surfaced from a jointer on the face. The edges should be straight from edge jointing on a jointer OR using a straight line rip jig OR hand planing them straight before using the table saw. WHY?
Assume the fence is 27" long and straight.
Now register a concave curved board against it and push it along until the front end reaches the rear end of the fence.
The curve on the board will follow the far end of the fence, moving a small amount to the right as you continue to push it along.
When you get to the end of that board, it has traced a curved path along the fence AND the blade will do the same, making a curved edge on the "cut" side of the board.
If the fence is bowed or curved it will do the same.
ALWAYS sight down your board before ripping it to see if it's curved, concave or convex.
You can "freehand" remove small amounts from the ends of a board safely because it's not a full kerf that may bind the blade and cause a kickback.
In this manner, you are using the spinning blade like a hand plane, taking off small amounts to eliminate the curve.
The saw doesn't know any better, it's not very smart and just does what physics demands.
To "get straight" you need to "start straight". 

Regarding "old threads" getting revived, good information is timeless. The title of the thread may attract a newbie or anyone who may have the same issue no matter how old the thread is.......


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