Dana Fujikawa
01-07-2010, 2:47 PM
Help! I've spent the last year trying to get consistant 90 degree cross cuts on my table saw with my large crosscut sled and it's driving me insane. The problem I'm running into is that I can get my smaller test peices to cut at 90 degrees - smaller being about 20"x20", but when I goto cut large panels around 3 by 2 feet, the cut is off by a hair.
My sled is a single runner design with the fence mounted on the back and the sled base is around 4x3 feet of 1/2" mdf. After test cutting a large panel, the end where the edge that was against the fence tends to be a hair longer than at the other edge which was the last to pass by the blade. Heres the test I'm doing: I cut one end, flip the peice over end for end keeping the same side against the fence, and then cut the other end. I then repeat this process on a second test peice. After I'm done cutting I take the second peice, flip it side for side, lay it on top of the first peice and then align the peices. Finally, I run my fingers along the ends checking for any differences between the lengths of the two peices which effectively doubles any errors - and more importantly - exposes any tiny errors that can't be seen visually. During each test pass I take off about 1/8" of an inch or so at each end.
Originally I suspected a problem with either my plywood fence or the UHMW runner. So in desperation I bought an Incra Miter 5000, rippped off the fence/protractor system as well as their adjustable steel runner and integrated them into my sled. I also added metal re-enforcements to each side of the slot in my 3 foot outfeed table to ensure that the sled remains straight after fully travelling off the back off the saw. The sled is therefore rock solid in the slot throughout the whole length of the travel. Even with all of these changes I still have the exact same problem. I then suspected it might be blade flex, so I also tried switching from a thin kerf to a regular kerf blade. Again same problem. The blade is parallel with the miter slot and I see no signs of the test peice shifting as I'm cutting. Off square end cuts appear to be straight which seems to rule out any sort of blade flex or runnout problems.
This is extremely frustrating, because as far as I know I've covered all of the variables and in theory all reasonably sized panels should cut exactly the same way with this configuration. At this point I"m not sure what else I can try. I could tune the fence to square up large panels, but then smaller panels would be out. Now that I think about it, it's entirely possible that correcting for the large panels could be the right way to go, and that maybe it's the smaller panels that are wrong.....
Any suggestions on what else I can try?
My sled is a single runner design with the fence mounted on the back and the sled base is around 4x3 feet of 1/2" mdf. After test cutting a large panel, the end where the edge that was against the fence tends to be a hair longer than at the other edge which was the last to pass by the blade. Heres the test I'm doing: I cut one end, flip the peice over end for end keeping the same side against the fence, and then cut the other end. I then repeat this process on a second test peice. After I'm done cutting I take the second peice, flip it side for side, lay it on top of the first peice and then align the peices. Finally, I run my fingers along the ends checking for any differences between the lengths of the two peices which effectively doubles any errors - and more importantly - exposes any tiny errors that can't be seen visually. During each test pass I take off about 1/8" of an inch or so at each end.
Originally I suspected a problem with either my plywood fence or the UHMW runner. So in desperation I bought an Incra Miter 5000, rippped off the fence/protractor system as well as their adjustable steel runner and integrated them into my sled. I also added metal re-enforcements to each side of the slot in my 3 foot outfeed table to ensure that the sled remains straight after fully travelling off the back off the saw. The sled is therefore rock solid in the slot throughout the whole length of the travel. Even with all of these changes I still have the exact same problem. I then suspected it might be blade flex, so I also tried switching from a thin kerf to a regular kerf blade. Again same problem. The blade is parallel with the miter slot and I see no signs of the test peice shifting as I'm cutting. Off square end cuts appear to be straight which seems to rule out any sort of blade flex or runnout problems.
This is extremely frustrating, because as far as I know I've covered all of the variables and in theory all reasonably sized panels should cut exactly the same way with this configuration. At this point I"m not sure what else I can try. I could tune the fence to square up large panels, but then smaller panels would be out. Now that I think about it, it's entirely possible that correcting for the large panels could be the right way to go, and that maybe it's the smaller panels that are wrong.....
Any suggestions on what else I can try?