Problem ripping wood on table saw

[ejensen]

I am a relative novice at woodworking. I have a table saw and am fairly confident the blade is parallel to the fence (but maybe you'll tell me otherwise). There are no burn marks on the cut side of the wood and the cuts are very smooth. When I rip a board, as the cut portion of the board moves past the blade, the board tends to want to deflect away from the fence. So what you would see as I am ripping a board is at the front (cutting edge) of the board, the board is against the fence, and 6 inches past the back of the blade, the board is 1 or 2 mm off the fence (kind of bowing against the back of the blade).

When ripping a wider board of 4 inches or more I can use two hands and push diagonally and keep the boards flat against the fence, but for thinner boards, like 2 inches, I end up with a board that has a slight bow along the cut edge ( because it is essentially getting shaved as it turns against the back of the blade). So if you ripped a 12 inch piece of wood 2 inches wide, and then put it on its cut side on my table, it would have a 1 - 2 mm bow in the middle. I do use a featherboard at the leading edge of the blade to push the board against the fence.

Any thoughts on what is causing this and how I can stop it? Is it technique? Blade not parallel to fence?

Thanks for any hints/suggestions

 

[LeftyTom]

I'd check to make sure the the fence is parallel to the blade at the front and back of the blade.

 

[Gotcha6]

If you're not getting any blade burn it sounds like a simple case of blade not being parallel to fence. Two things to check for:
1. Is the blade parallel to the miter slot? This must be correct before you proceed to item 2 or otherwise you can't get true miter cuts either. It can be checked with a dial indicator or a simple jig made to fit in the slot. Measure with the blade raised to maximum height and to the same tooth on the blade front and rear. If it is not parallel here, you'll need to adjust the blade trunnion assembly below the table top to get it in line.
2. Is the blade parallel to the fence? This can be verified in the same way by placing the fence at or near the blade & measuring front & back distances again. Most fences will allow adjustment by loosening a few bolts, aligning, and re tightening.
HTH

 

[Glennbear]

If you're not getting any blade burn it sounds like a simple case of blade not being parallel to fence. Two things to check for:
1. Is the blade parallel to the miter slot? This must be correct before you proceed to item 2 or otherwise you can't get true miter cuts either. It can be checked with a dial indicator or a simple jig made to fit in the slot. Measure with the blade raised to maximum height and to the same tooth on the blade front and rear. If it is not parallel here, you'll need to adjust the blade trunnion assembly below the table top to get it in line.
2. Is the blade parallel to the fence? This can be verified in the same way by placing the fence at or near the blade & measuring front & back distances again. Most fences will allow adjustment by loosening a few bolts, aligning, and re tightening.
HTH

I agree with Dennis but would add that you might consider a featherboard in front of the blade to keep stock tight to fence once you have everything aligned. Depending on saw design, the trunnions might need to be adjusted also which can be checked by aligning blade to miter slot before you do fence alignment. If the blade is not square with miter slot and you adjust fence to the blade you could end up with both blade and fence aligned with each other but not at 90 degrees to miter slot. :wsmile:

 

[Henry W]

Eric:
I am not certain that I can diagnose this - although your description is a good one. Here are my thoughts though.

1. Be sure your feather-board at the front edge of the blade is actually IN FRONT of the first tooth. You don't want lateral forces on the wood anywhere past the start of the cut.
2. If the back of the blade is shaving the piece - this is a recipe for kickback! The rising tooth can lift the entire piece and send it back at you - with potentially catastrophic results.
The reason I am not sure this is what is happening is that you describe the cut faces as very smooth with no burn marks. Have you cut maple or cherry this way? These woods can show TS burn marks for every shift in feed speed or hand repositioning. So I too am puzzled at how you 'achieve' the bowed cut that you do.

If you want I could come see this in person and see if I can help diagnose this (I'm near Cary Crossroads). I am not a setup guru by any means, but maybe another set of eyes can help. Send a PM or e-mail if you want.
Kickback is to be avoided; I had a very minor case once and that scare was enough for me!

Henry

 

[zapdafish]

For stuff where I no longer feel comfortable using a hand, I use the gripper. I can maintain control of the piece as it passes over the blade.

http://www.microjig.com/


If things are aligned, these are some other things than can cause what you are seeing.
Not using a push stick correctly. When I started, I wasn't pushing through straight but at an angle, sorta mimicking the gripper as I thought I had to push the piece forward and against the fence so it sorta deflected away. Other things that can cause it are splinters from the cut, the face may be smooth but splinters above or below it if not removed effect the path of the board. Caked up sawdust on the bottom of the board as it passes through. Stuff trapped between the fence and the board before you cut.

I'd recomend a splitter too minimize the amount of deflection

 

[Ken Massingale]

Sounds like you aren't using a splitter. Properly adjusted and matching the blade thickness, a splitter will keep the stock against the fence.

 

[Bas]

I have a table saw and am fairly confident the blade is parallel to the fence (but maybe you'll tell me otherwise).

I suggest you get yourself a dial indicator and make a copy of Joe Scharle's jig:

Harbor Freight sells a very good dial indicator. It often goes on sale for $10 (with coupon). Mark a tooth with a felt-tipped pen, align with the dial indicator tip and zero the dial. Now rotate the blade 180 degrees, push the jig further down the miter slot, and measure again. This will confirm the blade is parallel to the miter slot. If it's not, you'll need to make some adjustments. This is the not so fun part, where you actually learn what a trunnion is.

Now repeat the process with the fence instead of the blade. If the miter slot is parallel to the blade, and the miter slot is parallel to the fence, then the blade is parallel to the fence.

For stuff where I no longer feel comfortable using a hand, I use the gripper.
[snip]
I'd recomend a splitter too minimize the amount of deflection

+1 on the Grr-Ripper and Microjig splitter. Very, very, very useful tools.

 

[Mike Davis]

All very good suggestions.

One other thing to consider...

There could be internal stress in the wood that is being released when you cut it.

Try cutting a piece of plywood with the same setup and see if it acts the same way. Then you know for sure it is the saw and not the wood.

 

[DWSmith]

I'm not as technical about the fence being parallel to the blade as others here and don't own a dial indicator. I use a good ruler and watch the ripping to make sure the stock rips correctly.

However, I have had that same problem recently. It was caused by a dull blade. When ripping a 24" piece, the end of the stock was 1/8" thinner than the start. A freshly sharpened blade cured the problem INSTANTLY. Try another fresh blade.

 

[ejensen]

Thanks for all the good suggestions. I have tried to align the blade with the fence by adjusting the trunnion, and think it is, but I think I am going to buy a dial and build a jig to put a little more precision into this.

I have splitter, but it is somewhat flexible and really isn't strong enough to keep the wood against the fence. And again, this mainly happens with thinner strips (i.e., 1.5 - 3 inch) that I am feeding through with one hand.

The dull blade is an interesting theory - that would be an easy fix and I will try that.

Henry W I do put the featherboard in front of the blade - I really appreciate your offer to help - I may take you up on it if I can't get this straightened out over the Xmas break - I am in West Cary.

Thanks everyone for the suggestions. If/when I fix this, I'll repost with what the solution was.

 

[Bas]

One more thing to consider - is the face of your fence flat? If it's bowed, you'd see this behavior.

 

[DaveD]

You can even check the blade being parallel to the miter slot without a dial indicator. Just slap together something that will allow a drywall screw to be screwed horizontally up against the blade rather than the dial indicator. Then use a 5$ set of feeler gauges to measure between the screw tip and the tip on the blade.

To repeat something already said...be sure to mesure to the SAME TOOTH of the blade when doing the measurement. That will give you the most accuracy.

Another problem is the blade could be heating up and warping as you do the cut. That typically is the result of either not enough power (blade is slowing down) and/or a dull blade, and/or the feed rate is too high. You could also have the problem if you are feeding way too slow. That will also cause the blade to heat up.

You should also run a thin kirf blade. If the teeth have the right set to them the blade shouldn't even touch the wood. Theoretically only the teeth will touch. Good, typically more expensive blades do a better job.

Something else that helps is if the blade is set real high to do the cuts so it has more of a chance to cool. This is a controversial point because many people only run the blade with minimal excess height penetration.

Giving us the particulars about the saw and blade along with the lumber being cut may provide additional insight.

 

[crokett]

If the fence is closer to the blade at the back than the front, you will get this behaviour. If the fence is slightly further away from the blade at the back, you should get straight rips. I align my fence to be a playing card thickness away from the blade at the back than the front. It doesn't affect the cut any and it minimizes kickback. I also use featherboards.

Here is a simple jig to align the rip fence, and align the blade to the table.

Glue together 2 thickness of 3/4 ply about 2" wide and long enough to reach from the saw arbor to the front and rear of the fence. uOn one face at one end, epoxy 2 magnets spaced so they will stick to the face of the blade and not the teeth. At the opposite end and face, drill a hole, cut the head off a nail and glue it in so the point sticks out. Stick your jig to the blade with the nail end close to you. Slide the fence over so it just touches the nail. Flip the jig end for end and see if the fence still touches the nail in back. If it doesn't, make whatever adjustments you need.

To align the blade to the table, stick the jig on the blade and slide your miter fence up so the side just touches the nail. You might need to clamp an extension to it. Flip the jig end for end, slide the miter fence to the back and check alignment.

 

[bluedawg76]

In addition to the adjustments (blade, miter track and fence alignment) others have suggested, here's my 2 cents from someone also learning these arts:

1) In addtion to a featherboard, I push from the corner of the stock on the side in line with the blade rather than pushing from the center of the board. This really helps ride the fence and helped me get much straighter (jointable) rip cuts. Be careful though and do not apply so much force as to cause the board to pivot off the front of the blade towards the back, causing the effect you're seeing. That may be why you have this issue with narrow stock which is easier to "float" around. Then of course, as you approach the end of the board, switch to a push stick and now push in the center of the board and follow it all the way through just beyond the blade.

2) In my hands, thicker stock (like 6/4 or greater) is more prone to twisting and potentially binding with syp taking the prize as the most prone. I do it in 2 passes.

3) A slight offset (~1/64") of the back of the fence away from the blade is fine and will also help prevent the board from binding. In the case of the euro-style fence, they use a half-fence which runs the length of the blade and then stops. This works b/c only the front teeth of the blade cut. The back teeth just grab the board and throw it at you! That's where a splitter comes in and prevents binding.

Good luck
Sam

 

[Joe Scharle]

Thanks for all the good suggestions. I have tried to align the blade with the fence by adjusting the trunnion, and think it is, but I think I am going to buy a dial and build a jig to put a little more precision into this.

I think you may have mis-spoke, because as you probably know, the order of work is:
Blade to miter slot....adjust the table. On contractor saws, by shifting the trunnions; not a trivial exercise.
Then the fence is made parallel to that miter slot. Result is blade, miter slot and fence parallel.

I have splitter, but it is somewhat flexible and really isn't strong enough to keep the wood against the fence. And again, this mainly happens with thinner strips (i.e., 1.5 - 3 inch) that I am feeding through with one hand.

The function of the splitter is not to hold the work piece against the fence, but to keep the saw kerf open behind the blade. If the kerf should close on the back of the spinning blade, be prepared to witness an amazing kickback!

The dull blade is an interesting theory - that would be an easy fix and I will try that.

I would bet that 95% of all "it just started doing (fill in here)", are caused by dull blades.

Henry W I do put the featherboard in front of the blade - I really appreciate your offer to help - I may take you up on it if I can't get this straightened out over the Xmas break - I am in West Cary.

On site help is worth a thousand pictures.....Good luck and keep us post(ed).

 

[eyekode]

Although it is very useful to have a dial indicator it is not required for this operation. There are a couple ways you could do it. One is to simply drive a brad nail half way into the end of a square piece of scrap. Unplug your TS. Use the miter gauge to push the scrap to the front of the blade and set the brad against the edge of a tooth. If it is an ATB blade choose a tooth that leans toward the miter gauge. Then rotate the blade so that the tooth you chose is now at the back. Move the miter gauge (without letting the scrap move around) to the reference tooth. If the brad doesn't touch then the back of the blade is tilted toward the fence and must be remedied (kickback hazard). Adjust the trunions so the brad at the back _barely_ touches. Then lower the blade and check the fence the same way but this time you want the fence either square or ever so slightly tilted away from the blade.

Another way to check the blade to miter alignment which is really cool is to do it by sound . http://www.sawmillcreek.org/showthread.php?t=77578

Check out his "low-tech" solution to this problem. In my opinion this is much better than any static alignment and it is virtually free.

As for the wood drifting: I find that pushing the wood by the corner too hard into the fence will cause it to pivot and drift back into the blade. If the blade is sharp, the fence and blade are square then a perfectly straight push gives me the best result. I measured my error by using a caliper on the leading and trailing edge of the stock after ripped. And I found that I got the most consistent results when I was NOT trying so hard to hold the stock against the fence. All it should takes is gentle pressure. I do however use a feather board whenever possible (and a push-stick like device).

I also use a roller on the outfeed. But I don't try to set it perfectly square. Instead I tilt it so it draws the wood against the fence. This works remarkably well. And conversely if the roller is out of square the other way it will draw the wood into the back of the blade and you don't want that!

Good luck!
Salem

 

[Howard Acheson]

Let's start at the top.

First, what kind of blade are you using? When was the last time it was sharpened?

Second, have you really checked the alignment of your saw? Here is an inexpensive way to go about it that gives excellent results.

Here is the low tech, low cost way to align a tablesaw that I learned maybe forty years ago and use to teach to my students.

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.

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.

 

[timf67]

All very good suggestions.

One other thing to consider...

There could be internal stress in the wood that is being released when you cut it.

Try cutting a piece of plywood with the same setup and see if it acts the same way. Then you know for sure it is the saw and not the wood.

+1 With your flexible splitter you could have pinching of the blade as stress is relieved, and with a contractor style saw (ie lower horsepower) you are more likely to bog down the motor than get kickback

 

[Mtnman]

One other thing that can cause this is the board you are ripping. If it does not have a straight edge against the fence or is concave to the fence you could get the results that you describe.
Hope this helps, Mtnman