My powermatic tablesaw is giving tapered kerfs. The kerf opening nearest to the table is narrower than the upper/outside area, so if i cut a board in half, then push the cut back together, i get a “bend” at the joint, a lift up from the table saw table.. On a 12 inch board, crosscut at midpoint, this is about a 1/16 inch lift at the end of the board when pushed back together. It would be similar to when you make an alignment test cut at 90 deg, then flip one piece over so you can see how far from 90 deg you really are, but this is happening without flipping the board. If after the cut i push the two boards together, but keep them flat on the table, i can clearly see that the kerf is an upward sloping V cut.
I have tried 2 different carbide blades and one steel blade and all do the same thing. If i make the cut with the blade 1/8 above the work, it is very bad, but if i raise the blade full height (a little dangerous) then the cut gets much better, but still not perfect.
I do not know if this just started, or if it is the reason for some of the “issues” i have had with the saw.
I checked out blade-to-track alignment and my dial indicator says things are about 1/1000, which is pretty good.
Any ideas? This makes the saw pretty useless for anything but very course cuts.
Replies
Your lumber is reacting to being cut. This is particularly common when ripping a wider board down the center. Boards can move in a number of directions when this happens, either pinching on the blade or opening up. It may have nothing to do with the saw.
happens on crosscuts
this is happening on crosscuts, and in plywood, too. I've seen all sorts of odd things on ripping, and would agree there, but never anything on crosscuts, and it is always the same. If, after a cut on 3/4 inch stock, i push the two pieces together, they meet at the bottom edge, but there is a gap at the top edge that is almost as thick as a business card. It's always that way -- together at the bottom, gapping at the top.
Really odd.
arbor?
If I understand you correctly, when you crosscut a piece and put them together you are seeing a gap in the center or a little cup and it amounts to a 1/16" in the center. If so that's a tough one. You mention two blades but not the brand? If they are good and this is a new development, I'd also take a look at your arbor bearings as well. Do you have a dial indicator and a mag base(grizzly has a set cheap if not) and check to see if you have any issues. Just a thought.
A saw blade will only cut an even width kerf. The stock would have to move to get the issue you speak of. Even if the blade wobbled, it would still make an even through kerf. Things that come to mind may be things you already know. Stock should be flat and straight, throat plate has to be flush. Don't back up after a cross cut. Saw must be properly tuned. Work pieces can't slip on crosscutting, work can't react and push against the blade when ripping. Rip fence either must be exactly the same distance from the blade or slightly more on the outfeed end, about -1/64" over the length of the miter way/saw top. This will prevent the work from rubbing on the back of the blade as it exits. Obviously, rip fences and miter bars don't go together. The miter bar should be fit to the ways so there is no slop. A non slip surface on the miter gauge face or an added fence helps keep the work from moving during the cut. Waste piece should be free, no hands on it. I often see folks operate the saw with hands on each side of the blade pushing both the keeper and the waste. This can cause rubbing on the back of the blade, maybe a wood lunch.
If there aren't any problems with the saw, bearings, tuning, fresh blade, correct blade, splitters or riving knife properly aligned and the ccorrect size, etc. you should simply be able to set the blade 90 to the table. You need a good square, not on the throat plate. Stretched out combo squares are questionable. You check the cut on the stock by holding the square on the edge that went against the miter head and from the face in contact with the saw. It should be automatic.
I use a straight edge against the blade to check alignment. This stretches out any discrepancy compared to just measuring to the blade tips. You want this alignment to be exact. The rip fence is another place where being too tight at the outfeed will force the work to rub on the back of the blade. If these aren't set correctly, the work can rub on the blade as the work progresses and cause what you describe, even if there is no operator error. Alignment can change, so you need to check frequently. I think I'd spend some time double checking these.
flubbery blade?
Try adding a blade stabilizer - a heavy metal disc between the blade and the nut.
Who Sharpens YOUR Blades??
I dug up a new blade from the extra's box and tried it. Everything is fine. Interesting, since it is the same make and model as one of the offending blades. The common denominator of all three bad blades is that they had been resharpened: two by a local shop, and one by me. The steel one that i sharpened is really sharp, and cuts 2 inch oak or maple like butter, but apparently it wobbles. The other two must have had something "interesting" added in the sharpening process.
Then i took an old set of stablaizers that i have not used in a while and tried them on the 3 bad blades -- in each case it was much much better, or gone.
Thanks for all the inputs. My taper sided saw kerfs are not parallel again. Now, if i could just get that jointer working....... :-)
Blade sharpening
I like Forrest blades and plan to use their sharpening service, since I don't have the equipment to achieve the required precision. While I could do a decent job on a tooth-by-tooth basis, even minute variations can affect the performance of the blade.
I followed what you did to detect the tapered kerf. It is a sensitive test, but so far as it was described it doesn't tell you everything. If you turn one half over, do the end cuts now match up so that the two pieces sit flat on the table with the kerf tight from top to bottom or is there still a gap high or low in the joint?
It is possible that the cut is not wavering "back and forth" but only one way or the other so that the V is not symmetric but slopes more on one side than the other. If that is the case, one side may be square with all the taper in the other side of the cut.
That is the behavior of an improperly set saw--more common in the old days of steel saws and less common now with carbide tips. If the clearance grinds on the two sides of the saw are enough out of balance, the saw can be pushed to just one side or the other. With the blade set low, lots of tips can be rubbing (pushing) on one side of the cut while just one leading tip is cutting on the other to create a force to oppose them. Uneven saw set in a steel saw or relief grinding in a carbide saw can only push a saw, not pull it.
The fact that the problem occurs with resharpened tools suggests this to me.
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