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View Sark's profile

Scratches on cut driving me crazy, could it be the fence?

by Sark
posted 08-25-2019 02:54 AM


26 replies so far

View Lazyman's profile

Lazyman

3983 posts in 1900 days


#1 posted 08-25-2019 03:57 AM

Are those burn marks or did you do something to darken the wood so it was easier to see? Is this the side of the cut that was between the blade and the fence? If so, it is the back of the blade making the marks. You could try adjusting your fence so that it angles ever so slightly way from the blade (be careful). You might also want to check every tooth with your dial indicator and make sure that one or more of them are not misaligned or sticking out farther than the others.

What about your riving knife? Does it match the thickness of the blades and is it perfectly aligned? If you feel comfortable and safe doing it, you could try making a cut with the riving knife removed and see if it is still there.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Sark's profile

Sark

200 posts in 873 days


#2 posted 08-25-2019 05:17 AM

Not burn marks. I rubbed some pencil on the wood to make the scratch lines show up. The fence I’m using is a 3rd party upgrade to a Unifence. You’ll notice that screws hold a high density face on the fence, and I think that’s where the some of the non-flatness is coming in. I have the old unifence, and will give it a try tomorrow.

View Ocelot's profile

Ocelot

2356 posts in 3151 days


#3 posted 08-25-2019 08:31 AM

Are you using a feather board?

View Peteybadboy's profile

Peteybadboy

1178 posts in 2462 days


#4 posted 08-25-2019 09:54 AM

I put a blade stiffener from Forest on my WW2. Might help some.

-- Petey

View Sark's profile

Sark

200 posts in 873 days


#5 posted 08-25-2019 03:20 PM

Lazyman, I haven’t check the individual teeth on the blade for misalignment. But this actually is the second Forrest blade that I tried. The first one was so bad, and sent it back (via Amazon) for a replacement blade, and then went through more tune-up steps, with pretty much the same result. Good idea, though, and I’ll take a look.

I am using a feather board. And I do use a blade stiffener, and the runout was so small, I don’t that the flange/arbor is the problem.

The mystery is why the scratches are only at the bottom of the cut…perfectly smooth at the top of the cut. I put a lot of weight on the board to make sure there was no vibration. The cuts are perfectly square, too. Could it be saw vibration?

View PaulDoug's profile

PaulDoug

2171 posts in 2216 days


#6 posted 08-25-2019 03:36 PM

I get that occasionally when I cut soft wood. Never worried about t much. Could the blade be not be perfectly 90°? Making better contact with the blade at the top half of the board and less at the bottom….. just trying to think here, only 2 cups of coffee so far.

-- “We all die. The goal isn't to live forever; the goal is to create something that will.” - Chuck Palahniuk

View GrantA's profile (online now)

GrantA

1828 posts in 1920 days


#7 posted 08-25-2019 04:05 PM



Then I set the fence to about .005 run-out so the wood wouldn t bind.
- Sark

Why?? I know some of the YouTube celebrities said to do that so it must be right huh? Set the fence dead straight, parallel to the miter gauge which should be parallel to the saw blade. If not make adjustments.


Finally I measure the fence and it s not dead straight. It bows away from the blade about .005” then 6” later bows in toward the blade by .002, and then back out to .005” where I had set it. Could this be causing the problem?

- Sark


Yes the fence needs to be straight along its length. I also think your blade may be set at a slight bevel. Check that.
Also, if the tools you have available show the resulting boards to be square, which you mentioned, a quick swipe with a plane, scraper or sandpaper would remove the marks. There is definitely a point of diminishing return here.

View Lazyman's profile

Lazyman

3983 posts in 1900 days


#8 posted 08-25-2019 04:47 PM

The only reason to have the fence angled away is to temporarily see if the marks go away. Otherwise dead straight is best, though err on the side of angled away instead of angled towards the blade for safety sake. I don’t think that a slight bevel to the blade would cause that. I think you should just get a nice beveled cut.

I suppose that if the throat plate isn’t level that could cause a problem like this? If the rear side towards the blade is slightly higher, that might cause something like that, especially if one or two teeth stick out slightly more than the others. Just speculating. Usually when I see something like that it is because I screwed up when finishing the cut.

If nothing mentioned so far helps, I would just call them and see what they say.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Andybb's profile

Andybb

2112 posts in 1116 days


#9 posted 08-25-2019 07:13 PM

If you need it for a project, until you figure it out why not cut it a hair wide then run a plane over the edge or run it over a jointer if you have one?

-- Andy - Seattle USA

View AndyJ1s's profile

AndyJ1s

62 posts in 268 days


#10 posted 08-25-2019 07:47 PM

Having a unifence, I can’t imagine the “upgrade” from Peachtree being better than the original except in a few fairly rare applications, mainly for the t-tracks, not the sacrificial part. The high-low feature of the unifence (with the matching dual cursors on the fence head) is a god-send in many more cases than that.

Andy

View Nubsnstubs's profile

Nubsnstubs

1619 posts in 2243 days


#11 posted 08-25-2019 11:41 PM

Welcome to the world of woodworking. I’ve been at it since ‘76. I’m still trying to figure out why one piece will cut fine, the next 3 will have those itty bitty saw marks you show, then the next several will be fine. Even though it’s a piece of lumber from a once live tree, the lumber is still alive. It will move until it doesn’t exist. Learn to live with those itty bitty scratches. You will probably sand them off or hide them with another piece butted up to that edge. Unless you blade is angled by more than a half degree, no on will know. Stop your frettin’........... Jerry (in Tucson)............

-- Jerry (in Tucson) www.woodturnerstools.com

View Sark's profile

Sark

200 posts in 873 days


#12 posted 08-26-2019 01:43 AM

I agree with several of you to stop fretting. As far as a glue joint is concerned, its perfect. So who cares? But as far as perfection is concerned, there is a disturbance in the force, something’s not right, and I’d like to know what. When I ran a cabinet shop there was no way that we could bother with such refinements, we had to get the cabinets out the door and installed.

Tried my old Unifence, same result. So its not the fence. Rechecked the run-out more carefully, and its a total of about .007” not .002 as I had first reported. So I’m thinking that’s the source of the problem. Waiting for a new magnetic base for the dial indicator so I can do more accurate measurements.

As to why I went to Peachtree upgrade fence? It was to have T-tracks along the top for the hold-downs. Also in the normal position it is stiffer than the Unifence. Finally, I cut a big notch in the Unifence when routing something. The sacrificial fence wasn’t quite thick enough so it’s sacrifice was in vain.

View therealSteveN's profile

therealSteveN

3916 posts in 1087 days


#13 posted 08-26-2019 01:52 AM

Blade tilt? Because the indicator says you are cutting 90, doesn’t mean it is. That little screw on the cursor is to adjust it when you bring it to true 90. Check very carefully to see what the plate on the blade says, with a known good square. Stay off any teeth, they will throw you off.

Finally I measure the fence and it s not dead straight. It bows away from the blade about .005” then 6” later bows in toward the blade by .002, and then back out to .005” where I had set it. Could this be causing the problem?

- Sark

I don’t think that is your burn, however it could be. Check the tilt, if it is dead nutz 90* then make a sacrificial fence to mount, shim it so it is dead true. Your saws ability to cut square requires what you already described, plus a flat table, and flat fence to run against. A wobbly cut is not good, but worst if you are pinching the work against fence, and blade, that is high kickback potential, that isn’t good.

That noting the problem just with a Forrest blade, is something also. Lazyman offered the suggestion to check your blade width, versus your splitter width. Make sure to do that. A Forrest has a pretty robust saw plate. If your splitter width isn’t adequate for it, that could be problematic. If you have calipers measuring both the saw plate, and the splitter could tell you a lot.

Whatever you have isn’t a lot, or the entire side of the cut would be marked.

-- Think safe, be safe

View Andybb's profile

Andybb

2112 posts in 1116 days


#14 posted 08-26-2019 02:11 AM

Isn’t burning usually associated with the speed being too slow when pushing the wood past the blade?

Just saying. Can you push it through a little faster?

Probably a dumb question but I had to ask.

I just don’t think it’s much of an issue. More often than not there is some level of something after the cut. It either gets sanded away or hidden in a joint or trim.

-- Andy - Seattle USA

View LeeRoyMan's profile

LeeRoyMan

288 posts in 240 days


#15 posted 08-26-2019 02:26 AM

I’ve never given it much thought. Most of the time that edge will get sanded or routed after assembly of whatever you’re making. I drum sand edges before making face frames to get rid of the cut marks on the interior. Trying to achieve the perfect cut with so many different woods and thicknesses and types of blades cutting different materials. You will spend more time chasing that goal than reaching it. At least that’s been my experience but then, I’m pretty redneck about it.

View Sark's profile

Sark

200 posts in 873 days


#16 posted 08-26-2019 03:00 AM

I don’t quite see how blade tilt would make a difference. You should be able to cut at an angle and still get the cut nice and smooth, no? And yes, to LeeRoy and others that a little post-processing will totally fix any slightly scratched surface. When I make face frames, I usually run through the planer which gets the edges crisp and very smooth.

I’ve got a bunch of projects pending, so I can’t spend too much more time obsessing on fine points, Just a little more time. A few more things to try.

View BurlyBob's profile

BurlyBob

6516 posts in 2778 days


#17 posted 08-26-2019 05:41 AM

I’m going to agree wit others mentioning blade tilt. It’s an issue I’ve had to deal with on my table saw and chop saw.

View Sylvain's profile

Sylvain

881 posts in 3012 days


#18 posted 08-26-2019 08:58 AM

In fact, isn’t it strange that the top of the cut is smooth?
I would not expect a table saw to make perfectly smooth cuts.
Anyway have a look at Matthias Wandel site here
He has enhanced the cut quality by diminishing blade wobble.

-- Sylvain, Brussels, Belgium, Europe - The more I learn, the more there is to learn

View Karson's profile

Karson

35202 posts in 4913 days


#19 posted 08-26-2019 06:44 PM

When I do cut checking like you are showing, I tend to use MDF because it’s cheap and the cut is easy to be seen.

I couple of things to try. If the cut swirl is going up the piece between the blade and the fence on the right then that shows the back of the blade is doings the scoring. If it’s going down the cut then that shows the front of the blade is doing the scoring.

Two other variables are the height of the blade. If the blade just clears the surface of the material being cut then the entire cut line is being touched by the blade teeth. If the blade is to it’s highest max height, then the blade teeth at the front and back are touching the cut and the middle where the metal blade itself should not be touching the material being cut at all.

So one thing to try is raise the blade to it’s max height and push the material just as far as needed to cut the piece between the fence and the blade. Turn off the saw and now take your piece of material out. The back of the piece has gone through the front and the back portions of the blade. The front of the piece has only gone through the front teeth.

So now determine if you have a front of blade or back of blade problem.

One thing to remember that you stated that the fence seems to have different clearances through it’s length. The piece of wood being cut does not follow the fence fluctuation , It only rides the high spots and doesn’t touch the low spots.

I’ve always tried to align the fence to the blade without having an extra 5 thousands clearance at the back. When you have that the material on the other side of the blade has the problem of burning. A problem with Maple and Sapele and probably many other woods.

One change that I’ve started to do is use 7 1/4” skill saw blades when ever possible. The are usually 24 teeth but 40 teeth and 60 teeth are available. These blades are approx 1/16” thick. Those blades are flexible and tend to follow the cut line very well. On my table saw the max thickness of wood is 1 5/8” which is almost every cut.

I just bought 1 blade 1 free in a pack at Home Depot for $15.00 and they were 40 teeth blades. Those are all we use at the toy workshop. We do a lot of ripping 1/4” slice at 1 1/2 thick and burning is a problem, when every piece you cut needs to sand off the burn. that’s on 2,500 pieces. That’s on 1 toy, 110 being made.

As you research the conditions that you are seeing Look at all the variables. If you cut some wood using your miter slider or your sliding table then you have eliminated the fence all together, you also eliminated the blade plate. Check whats happening to your cut line. Let us know of what you are finding.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

View Jim Finn's profile

Jim Finn

2745 posts in 3435 days


#20 posted 08-26-2019 09:44 PM

I suggest you try a 24 tooth blade. Sometimes called a “PLaner Blade” That change works for me.

-- No PHD just a DD214

View Sark's profile

Sark

200 posts in 873 days


#21 posted 08-27-2019 02:45 PM

Thanks Sylvain for the link to Mathias Wandel site. Especially helpful to determine if the blade or the arbor flange is the cause of wobble. Answer: the arbor flange. Out by more than .001” . Today I’ll try grinding the flange and see if we can improve things.

Thanks for the other suggestions as well. I do have a 24 tooth ripping blade (Freud) which makes the same scratches. Not surprising since we know that the flange is not flat.

Karson, the scratches appear on the upcut. Not sure what this implies. Also, you use an extra thin 7 1/4” blade on a regular tablesaw? Never thought of doing that. I moved to a thicker 1/8” blade when I got a Unisaw because it has the power to drive the wider-kerfed blade trough the wood, and the think kerf blades seem to flex too much under stress.

Years ago I went to a local woodworker show packed with vendors. One demonstration that impressed me was a guy cutting perfectly smooth, scratch-free strips of wood out of 8/4 hardwood on a portable tablesaw. I believe that he was selling Forrest blades, so I bought one. Others warned me, don’t think you can get the same results because the guy at the show was using a specially tuned table saw, and its not the blade, per se, but the tuning of the saw, the quality of the wood, and the skill of the sawyer that produces the really fine results. So true.

View Karson's profile

Karson

35202 posts in 4913 days


#22 posted 08-27-2019 06:01 PM

Sark: The out of plane flange should not cause the marks on the wood. What a wobble on the blade would cause the kerf to be wider than the saw blade. Remember the “Wobble Dado Blades” they were made that way to cut a wide dado cut without having a stack dado set. My old table saw had the arbor being the motor shaft and someone had dropped a big board on the blade and bent the motor/arbor shaft. It cut about 1/32 wider than the actual saw blade, but it didn’t cause the marking on the wood.

Did you try cutting a piece of wood using the miter sled to see if the marks on the wood are still present?

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

View Karson's profile

Karson

35202 posts in 4913 days


#23 posted 08-27-2019 06:11 PM

Sark: If the blade is traveling at 2000 RPM then for every second of cut each tooth is cutting 33 times. So I don’t believe that the wobble is causing your situation. I don’t know how many seconds it took to make your cut and then how many inches were cut in that time frame. So if you know the arbor speed and the time you can calculate how much time and how many teeth are being represented in the marks you are experiencing.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

View Bill_Steele's profile

Bill_Steele

572 posts in 2244 days


#24 posted 08-27-2019 06:59 PM

Maybe this product (FinalCut) will help.

View Sark's profile

Sark

200 posts in 873 days


#25 posted 08-28-2019 12:37 AM

Tried grinding the arbor flange, with two different stones. I was not able to take the wobble out of the flange. So I’m stuck with .007 runout. The kerf width of .132 exactly confirms what I measured with the dial indicator on the blade.

On the plus side, the cut on maple had no scratch marks, or marks that were so faint that only with great difficulty that anything could be seen. So as some of you said, wobble by itself doesn’t cause scratch marks. These cuts were made with the Unisaw fence pulled back so that it didn’t extend past the blade by much (more of a euro style). Maybe that made the difference? Also my last cuts were made with maple instead of poplar. Someone noted that softwoods are more prone to getting scratch marks.

So I’m a bit frustrated that the kerf is wider than it should be. But the cuts are fine, smooth and dead square. And I bought the saw for $600 a few years ago, so I can’t complain too much.

Or in the words of the old Jewish saying: If you can’t get what you want, want what you get.

Thanks for all the ideas. I learned a lot. Think I’ll pass on FinalCut, though I found the idea interesting, but rather expensive for the sanding disks. If I were still running around doing trim work I’d definitely give it a try. Any of you using it?

View theart's profile

theart

132 posts in 1067 days


#26 posted 08-28-2019 12:50 PM


In fact, isn t it strange that the top of the cut is smooth?
I would not expect a table saw to make perfectly smooth cuts.

The teeth of the blade are moving almost horizontally at the top of the cut, but more vertically at the bottom. So it’s like sanding with the grain versus across it. And yes, this is already smoother than I would expect from a table saw.

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