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

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Forum topic by Sark posted 08-25-2019 02:54 AM 2173 views 0 times favorited 26 replies Add to Favorites Watch
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Sark

174 posts in 839 days


08-25-2019 02:54 AM

Topic tags/keywords: table saw saw blade scratches table saw tuneup tuneup forrest cmt

This journey started when I bought a Forrest WWII blade to replace the 50-tooth CMT combo blade I’d been using. Then I tuned up the saw: ground the arbor flange, adjusted the throat plate, etc…and most recently bought a a dial indicator with magnetic mount so I could measure the blade run-out, get the miter slots parallel to the blade, and check the fence setting.

The run-out was about .002, and the blade was also parallel to the miter slot about .002. Better than I had hoped.Then I set the fence to about .005 run-out so the wood wouldn’t bind. And here’s the results:

Scratches on the bottom 1/3 of the cut. Adjusting the fence didn’t help. Tried thicker wood. Didn’t make a difference. Then changed blades to the CMT combo. Much fainter scratches, but the cut was rougher too. The roughness hid the scratches, but the smoother cutting Forrest blade revealed them.

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?


26 replies so far

View Lazyman's profile

Lazyman

3873 posts in 1866 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.

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Sark

174 posts in 839 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.

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Ocelot

2323 posts in 3117 days


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

Are you using a feather board?

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Peteybadboy

1013 posts in 2429 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

174 posts in 839 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?

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PaulDoug

2118 posts in 2183 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

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GrantA

1762 posts in 1887 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.

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Lazyman

3873 posts in 1866 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

2024 posts in 1082 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

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AndyJ1s

57 posts in 234 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

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Nubsnstubs

1611 posts in 2209 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

174 posts in 839 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.

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therealSteveN

3606 posts in 1053 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

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Andybb

2024 posts in 1082 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

248 posts in 206 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.

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