concave cuts on table saw

After 15+years of wood working I've started getting concave rip cuts on my tablesaw. The concave is ~.015" in the middle of the board, on boards that are more than 14-16" long. This happens consistently with hardwoods mainly red oak and walnut. The saw is a Delta contractor with a shop fox fence,a Forrest blade, a feather board, and NO splitter. The far end of the fence is less than 1/64 further out of square with the miter slot to avoid pinching. The blade seems square with the slot - as best I could tell using a combination squate. I've experimented with the amount of pressure by the feather board, hand position, speed of the feed... and nothing seems to make a consistent differnece. Any ideas on what the cause could be? Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/10/13 5:13 PM, ts wrote:

"The far end of the fence is less than 1/64 further out of square with the miter slot to avoid pinching." That's the first thing I wonder about. I've heard people prescribe this notions of the fence tail being slightly "out" but I think it does more hard than alleged good.
Also, explain why you have no splitter? You may have a good reason.... I've just never heard one. :-)
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/10/2013 6:13 PM, ts wrote:

Why would you adjust it out of square. keep it square...
--
Jeff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That is the first of your problems. You want as close to dead on parallel as possible.
The blade

It needs to be in the neighborhood of .001~.005 to produce good cross cuts. This will not help rips however.
I've experimented with the amount of pressure by the feather board,

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/10/2013 5:13 PM, ts wrote:

One thing to check - is your fence straight? Use an accurate straight edge to check.
--


___________________________________

Keep the whole world singing . . .
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It might be worth getting the wrenches out and checking for loose bolts. Even if it doesn't fix the problem, you'll be secure in the knowledge that nothing's moving. (I probably ought to do the same.)
Have you tried a different blade?
Puckdropper
--
Make it to fit, don't make it fit.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, February 10, 2013 3:13:53 PM UTC-8, ts wrote:

Is this immediate, or does the concavity come about in the hours or days after the cut is made?
Oak in particular has a lot of internal stress; a ripped board almost always curls as it 'relaxes'.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/12/2013 10:51 AM, whit3rd wrote:

While not impossible, I doubt seriously that the OP's problem, in two different species of wood, is attributable to anything but the table saw and it's setup 'in toto'; and would venture that "internal stress" in the wood is not even a contributing factor to his problem.
--
eWoodShop: www.eWoodShop.com
Wood Shop: www.e-WoodShop.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The concave is ~.015" in the middle of the board, on boards that

How sharp is your blade? Is it thin kerf? How hard are you feeding. It could be blade flex. A contractor saw trunnion setup is not very solid and can be flexing so it would actually be motor flex.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

y

t

y

4

d,

t

Dull blade. They inevitably dull faster on one side, which forces them to lead toward the sharper side, especially with harder woods.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/10/2013 5:13 PM, ts wrote:

Hopefully you have cured your problem but with the fence set away from the blade it actually either follows the fence which is unlikely as the waste is pulling it back toward the blade or it is not following the fence because of the before mentioned and cutting more narrow the farther it goes, causing you the concave situation.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.