I have been struggling to get my Powermatic 2000 table saw completely accurate. My fence and the blade are parallel to the mitre slots but one problem persists.
Rip cuts on long boards seem to be slightly concave. In order to have accurate glue-ups I have to joint the edge once I rip it.
Could the plastic material covering the fence be slightly concave and thus causing this problem, or are perfectly ripped boards simply something I should not be expecting from my tablesaw. In other words, should I be able to make wide-board glue ups with table saw edges, or is jointing the table saw edge a fact of life?
I am using a WoodworkerII blade. And I have been working mostly with Poplar on my current project.
Looking forward to some insight on this one.
Thanks
David
Replies
I strongly doubt it's the fence. But you can check the fence by either putting a straightedge against it (I use a 48" level which is pretty much dead nuts straight) or check it as part of my alignment process. Here's some info on how to align a tablesaw.
Here is the low tech, low cost way to align a tablesaw that I learned maybe forty years ago and teach to my students now.
Make 3/4 x 3/4 x 12" hardwood stick. Drill a hole somewhat centered in one end and insert a brass #8 x 1" round head fine thread machine screw about half way. UNPLUG THE SAW. Raise the blade completely up. Clamp this board in your miter gauge (if you determine that there is some slop in your slot to miter gauge, use a playing card to take up the slop) so the screw head just about touches the blade at the front. Now rotate the blade by hand and determine which tooth is the closest. Adjust the screw in or out until it just touches this tooth. Mark this tooth. Rotate the blade so the tooth is now at the back of the table and move the miter gauge/stick assembly to the back and see if it touches the marked tooth to the same extent. If it doesn't, adjust the trunnion (if a contractor saw) or the tabletop (if a cabinet saw) until it does.
For a contractor saw, first use a small c-clamp on the rear trunnion and cradle to keep the assembly from moving. Then loosen the two rear trunnion bolts and one front trunnion bolt. Slightly loosen the other front trunnion bolt and use a stick to tap the trunnion until the blade and screw lightly touch. The blade does not move directly around the center so you will need to repeatedly go back to the front of the blade, readjust the screw, and then again measure the back. Be sure to check after tightening the trunnion as the trunnion frequently moves when being tightened.
For cabinet saws, loosen the bolts that hold the tabletop and tap one corner until things come into alignment.
The same adjustment gauge can be used to set the fence parallel to the miter slot. Slide the miter gauge to the front of the table and move the fence over to the screw head and insert a playing card between the screw head and the fence just so you can move the card as it touches both the fence and the screw head. Now move the miter gauge to the back of the table and see if you have the same feel when you insert the card. I like my fence absolutely parallel--if you want to have a slight opening to the fence, you can easily estimate the opening by adding a thickness of paper to the card. Once you have it parallel, check the fence for straightness by check the distance every couple of inches.
I always show my students with a dial gauge that their adjustments are within .001 - .002.
You can also use the same gauge to measure blade runout by using a $5.00 feeler gauge.
Finally, after you are satisfied with the above adjustments, check the position of the splitter to make sure it is exactly in line with the blade.
Bottom line, there is no need to spend more than the $0.05 for the brass screw.
Thanks so much for the reply....I will try what you suggest....
David
What Howard says works great. I have also just used a combination square with the head of the square against the edge of the miter slot & checked with the blade tooth just brushing the tip end of the rule & mark the tooth so you can check at the front & back of the throat plate with the same tooth.Good, better, best never let it rest until your good is better & your better best.
Edited 3/16/2008 7:07 pm by OB
Several of you asked me to respond when I fixed the problem.
It turns out that it was a combination of two things. The face bolted on the fence and the riving knife.
The riving knife on the PM 2000 is easy to remove, but is not at all well engineered when it comes to ease of getting it in alignment with the saw blade. Not only was it not aligned with the left side of the blade but it was not at a right angle to the table top. After a lot of tedious adjustment of 4 screws it is in alignment as well as at a right angle to the table top.
The facing on the fence was slightly concave in the middle. I took the facing completely off and rebolted it back on being careful not to over tighten the bolts.
I did decide to leave my fence parallel to the mitre slots versus having a slight toe-out at the end. I am contemplaing get the rollers (through Rockler) that not only hold the board flat to the table but also hold the edge tight to the fence.
I appreciate all of the helpful comments from everyone.
David
David,
contemplaing get the rollers
If you're talking about Board Buddies be aware that if your fence does not lock down on both ends these have a tendency to lift the fence when passing a board thru them and they can get in the way of push sticks, etc.
I have them on my Bies fence and I simply clamp down the far end and that works ok, just a PITA sometimes.
Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
"In order to have accurate glue-ups I have to joint the edge once I rip it."
The first thing that comes to to mind, daft as it may seem, is do you straighten an edge before you rip?
If everything is lined up correctly, ie, a straight fence set parallel to the blade, and you run a straightened board edge against the fence you shouldn't get a concave sawn edge, unless, perhaps, the wood is warping after the cut due to stress relief.
A classic cause of concave ripped edges is significant fence toe-out at the back end. It's probably worth double checking to make sure that's not the case. Slainte.
Richard Jones Furniture
Thanks so much for your reply....I will look at the toe-out. I am making sure I start with a jointed edge, I have noticed that there is a small gap between the edge of the board and the toe of the fence as the board goes through.......I bet its too much toe-out.
Thanks.
David
Is the riving knife true to the edge of the kerf?
If it is a little off to the left, it could cause the cut to drift that way, leaving a concave surface.
Freud makes a calibration/sanding disc for table saws. It is 1/8-inch thick, and dead flat. They cost less than $30.
The PM2000 is a left tilt saw, which means the arbor which the blade indexes off of is on the left side, and you will need to align the riving knife to the left side of the blade.
I will say that aligning the riving knife has been difficult....I was trying to align it sort of in the middle....obviously not the right way......When you say align it to the left of the blade (just so I don' keep screwing up) you mean the edge of the blade furthest from the fence.........I bet that could be it.
David
If the riving knife is offset to the left, it will try to pull the wood ever so slightly to the left, which if you use your fence on the right side, will cause a concave cut.
As and experiment, rip a piece with the fence to the left, instead of the right and see if the problem goes away. Be careful though because if you have a lot of left offset in the riving knife, the wood may try to bind between it and the fence.
Since your saw is a left tilt, the left side of the blade is against the arbor, and the left side is relatively constant, while the right side will move left and right depending on the kerf of your blade. Thus, when you align the riving knife or splitter, you need to adjust it to align with the left side of the blade. If you tried it on the right side, you would be chasing a moving target.
Also, with you left tilt saw, the fence offset will change if you change kerf widths.
OK my friend it seems your first paragraph and the last sentence in the third paragraph are contradicting......I will align the riving knife to the left side of the blade, and I will have my fence on the right side of the blade........hopefully this will cure it.
David
David, I guess I shouldn't try to explain things when I'm tired.
You need to align the edge of the riving knife with the left edge of the blade.
On all saws one edge of the blade is some what fixed in position, by the flange on the arbor, it may vary a few thousandths depending on the grind of the blade. The other edge moves, depending on the kerf of the the blade.
On your left tilt saw, the arbor flange is on the left, and the left side of the blade will not vary much, if at all, when you change to a saw blade with a different kerf. The right side will vary depending on the difference in kerf width.
If you change the blade from say one with a 1/8-inch kerf, to a narrow 3/32 kerf, the right side of the blade will move to the left 1/32. Which means that if you had very carefully aligned the right edge of the blade and the riving knife, it would now be out of alignment with the edge of the blade, and proud by 1/32 of an inch. So, you need to align the riving knife to the left edge of the blade, since that side doesn't move.
And, since the fence is typically used on the right side of the blade, it also would be off by the difference in the kerf width. And, if you use a dado set to cut a 23/32 dado for a piece of plywood, the fence is now 19/32 off. Which is why, I am not a big fan of left tilt saws.
Hopefully this clears up the confusion.
Thanks....that clears it up.......
I have a suggestion if I may. Using a left tilt saw usually with fence on the right I align the right side of the splitter with the right side of the blade. This holds the wood against the fence after the cut. In mounting the splitter I use flat washers ground to the just right thickness. I rarely change blades but by keeping a collection of ground washers on the splitter/riving knife mounting bolt(s) one could dial-in the right spacing by the right combination of washers. "Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!" -Goethe
Good fix. Have you thought about silver soldering the washers to the blades?
I had not but expect that would work pretty well? if I understand correctly these would be large washers to match the arbor washer dimension. My splitter mounting hole is open so washers stay on the splitter bolt, the trick is to drop the splitter down between the correct washers."Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!" -Goethe
Do you use feather boards? Your own hands can push the material around when feeding the board. I swear by them, even bought a new magnet type so it is quick and easy to set up. Ripping panel stock requires an infeed table so you can just control the pressure to the fence, or maybe I am just old enough that I can't control the lift weight and pressure against the fence.
Let us know what's up.
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Thanks for your reply.......I do not use feather boards, but I will let you all know when I get it fixed...
David
Daviddevine,
I've been chasing that problem for years and it's especially true with poplar...the wood expands after it's cut. That is one of the reasons Norm always jointed the edge after the rip. Also, I suspect its a good reason for using a splitter/riving knife too.
D,
I'm interested in your results. Would you please post what you determine your problem to be?
No one has mentioned these issues that I have discovered with my own saws. The face on the accu-fence on my Powermatic saw is not planar. It's been so long since I checked it, I've forgotten how much out it was. It not only had some waves in it, it also had some twist. At least on the Powermatic fences, you can loosen the face & shim it. I tried doing that, but ran out of patience long before I got it completely trued. On my Biesmeyer (sp?), there is some waviness also. In this case, just a few thousandths, but, there's no way to remove the face on the Biesmeyer to shim it, that I know of. At least, it doesn't have any twist in it.
BD
David,
I would first check to make sure the blade is nuts on 90° to the table.
Regards,
Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
I do not think that your problem is mechanical, if I have understood you correctly. I don't mean to tell you something you probably already know, but here goes:
Cutting a board in two releases "internal pressures" within that often make the pieces crook toward the former center of the board. Also the middle of the board may have a different moisture content than the edges (and I suspect gets immediately altered by the heat from the blade). For these reasons, if your really want a straight edge and are removing more than a fraction of the width of a board, what you need to do is rip, then WAIT 1-7 days, then joint. I think I first learned this in an article by Rogowski. Haven't we all seen the kerf wanting to dive together right behind the blade? One reason why riving knives are so important; it's not only chance that makes the material hug the back of the blade.
Maybe you should see if you have the same problem cutting a piece of acrylic or something.
Brian
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