Unisaw suddenly burning wood in odd way
I got a (left tilt) Unisaw about a year ago and put new Forrest woodworker (40 tooth) blade. Life was good until about a week ago when I cut a short strip of 1/2 inch plywood and the right side (towards fence) came out noticeably burned. I then ripped some 1 inch red oak and same thing happened. Obviously something went out of alignment, so….
My first suspicion was the anti-kickback (Biesemeyer) guard but although it seemed to have drifted a miniscule amount to the right I couldn’t believe it would cause such a dramatic change so I popped it out and ripped a new piece of plywood and got same burning.
Next I went through all the usual alignment of blade:
1) Nearly dead vertical blade – the top of blade when fully raised was probably 1/1000″ out of perpendicular with table surface.
2) Front to back the blade was maybe a few thousandths (certainly less than 10/1000 – probably more like 3-6) out of parallel with miter slots.
3) Fence (Biesemeyer) was parallel to right miter slot as best as I could determine by running finger tip along edge of fence when aligned with slot (and also sighting along slot).
Now here comes the head scratcher (at least to me). I ran some 3/4″ plywood through and of course the right side of the cut was burnt. However, the first 8″ or so was clean cut with no evidence of burning but this time I noticed there was a very very slight “grab” when the plywood encountered the far end of the blade. I repeated and got the same result. I should mention that I usually set the top of blade about 1/2-1″ higher than what I’m cutting but on these last two cuts I had set the blade about 3″ high.
Next I slid the cut (piece against the fence) plywood back through the gap between raised blade and (unmoved) fence. As expected it fit snugly and slid smoothly UNTIL IT REACHED TEETH AT FAR END! At that point it literally bumped to a stop.
I lowered blade all the way down and laid this piece of plywood against fence and gradually raised blade. As the blade rose the plywood remained on table until the blade was again about 3″ high at which point the far end of the blade started lifting the plywood.
The table hasn’t been bumped or dropped or otherwise “traumatized” and the fence/blade/etc haven’t been abused in any way prior to this sudden burning business.
What could be the problem? If the tablesaw needs to be better aligned than where it is now maybe I need to get a new hobby.
Replies
EB ,
The fence may be the problem , sounds like you are getting a bit of a heel cut , coming from the fence not exactly in line with the blade .
More important than the slots in the table lining up with the blade is the fence being equal distance from the blade . What ever slight variance you found blade to slots may be magnified from the fence being out the other way , possibly.
The other possibility is your blade may have a tooth or more on that side that has become funky for whatever reason and could be causing the burning.
luck to you dusty
The fence is not true to the blade. The back is pinching in. Before you adjust anything take the fence off the rails and make sure nothing is in between the fence and the guide rail. my first guess is a bit of saw dust is caught up in between the rail, and the fence itself.
If you take it off, clean it and it still isn't quite right, then adjust it. I keep mine parallel to the blade. Some say to put a little skew to the right in it. And, a little right skew would be better than a little left skew, as you have found out.
This reply will not help you much but I'll just tell you I have experienced the same thing (Sort of).
I use a FREUD Industrial combination blade 50 tooth with a 10 degree hook. Buy the way, I like these blades. Just me!.. I'm a bit strange sometimes.
I have had the blade awhile and everything seemed Ok untill!.I usually use Red or White Oak or Ash for my everyday projects. No burning from the blade. (Yes I keep it clean as possible).
I started a new project for my youngest daughter. She is about to have a baby and I thought to myself... Hay.. Baby changing table to keep this old brain active.. SO.. I got some Purpleheart and Jatoba.
Solid purpleheart and solid and 3/4 inch ply Jatoba.
Both are HARD, NASTY woods to work with. Well, at least to cut.. They sand very easy though?.
Anyway, I started cutting some sticks from each type. I ran into some reaction wood in some of the Jatoba and Purpleheart.. They went really crazy when cutting some streachers and trim.
The cut pinched the blade and after that I had burning at the far end of the blade (furtherest away from me) on the fence side of the blade.
My blade is a thin kerf. (Yes I use this blade for everything I do) and it is LASAR cut with some serphentine wiggle waggles to keep vibration down? I think?.. By the way I have used this type of blade for along time.. For what that is worth!
Now the blade will burn sometimes. Not on everything, but when you least expect it.. Even on my normal used Oak and Ash.. Same side of the blade.
Something I noticed after this happened cutting my 'nasty wood'...
My stick cuts were about 1/32 longer using my 'normal' settings. I KNEW I did not change anything from what I usually do. SO.. I cut a stick on my JessEm sliding cross-cut table that I know what to expect from. I had the stick clamped to the crosscut fence.. The cut seemed it was at perfect 90 degrees BUT LONGER than usuall..
I scratched my head a-bit and said "Self.. WHAT?". I stopped the saw and put a new stick just touching the blade teeth. NO I did not deflect the blade...
I sarted the saw. What to my wonder... The blade moved away from the cut end of the stick as it gained speed. I really said something else but cannot type it in here.... Yep the blade moved away from the end of the stick.
Did I over-heat the blade? I do not think so, BUT something changed?
Not the saw (edit) fence! I was not using it!
Edited 9/1/2007 4:35 pm by WillGeorge
Ol' Will , is that you ?
Nice to hear you , man were you like placed in absentia or somewhere like that for behavior er sumthun ?
regards hope you are well
dusty
man were you like placed in absentia or somewhere like that for behavior er sumthun ?That sounds like my Penn Dutch Kin!Hi! Been OK.. Just gettin' olds and forgets thinks these days! LOL..Nice you responded! Huggers OK?
Try another blade , see if the burn continues .
dusty
Feeling the fence along the miter way isn't good enough. You should have the outfeed end of the fence just a hair more than the front, not perfectly parallel with the blade. Unplug the saw, raise the blade, and lay a straight edge against it. This will allow you to make a measurement over a longer reference. Slight differences will show up better. Check two measurements, one to the miter ways so you know that the blade is aligned with those. Second, set the fence and measure the front and the back. Over the length of the table, the outfeed end should be about the width of a line on your tape, more than the front. This is hardly measurable at the blade, but it's enough to prevent tail drag. When operating the saw, try to keep the blade projecting through the material only about 1/4". This is for safety. In some situations, a blade will cut better when raised higher but it's not worth the risk of a hand cut that's deeper than 1/4".
Beat it to fit / Paint it to match
The height of the blade is one of those debated things. I personally think it should be raised to full height. That way the force generated during the cut is down, and not back towards you.
Think about what kick back is. In a kickback situation the piece rises up onto the top of the blade and gets launched. If you keep the blade low, you are just that much closer to the kickback point.
Getting the blade high, using a splitter and a guard, and paying attention to where your hands are, is to me considerably safer than keeping the blade low. I have the Biesemeyer splitter and overhead guard system mounted on my Delta Contractors saw. I spent about $200 on the saw as a close-out / lost inventory at home Desperate. The splitter and guard cost about $1000. Which is more than the saw, the blades, the mobile work station I built for it, and the used Accufence I have on it combined.
If you do elect to keep the blade low, then keep the blade high enough that the bottom of the gullet is at least half the depth of the gullets above the top of the work piece.
And, personally, I keep the fence parallel to the blade. I have a right tilt saw, and don't want to retrue the fence every time I want to use the fence left of the blade to cut bevels.
The easiest way I have found to true the fence to the miter slot is to put a 3/4-inch x 1-1/2-inch board in the slot and use it as the reference to true the fence. A 1X2, (they are actually 13/16-in by 1-19/16-in), from the lumber yard or HomeDesperate work well, just plane a slight bevel on one side, just enough you can drive it into the miter slot with a slight pressure, with the bevel towards the fence. Then use a piece of wood as a feeler gauge and true up the fence to the board in the slot. But remember, you don't rue the fence to the slot unless the blade has been verified to be true to the slot, and then true the fence to the same slot the blade is true to.
I just wanted to let all the folks with advice know that I'm not ignoring them. The family is painting inside of the house this Labor Day weekend so I can't get back to trying out the ideas you've posted. It does seem that the main suspicion is on fence alignment so I'll look at that first as soon as I can (without being accused of shirking on the painting - I'm the trim guy). Maybe I'll place fence to left of blade and see if burning moves to other side of wood. Thanks...
Actually, they should go away. The front will cut cleanly, and the back of the blade should not touch the wood.
But. like I said, check for something that has gotten between the fence and guide rail first. T-Square fences don't just go out of alignment.
I finally solved the problem and eliminated burning.
It turned out the splitter adjustment is much more finicky than I expected. The blade (excluding teeth) is about 20/1000" thinner than splitter and I was tryng to center blade and splitter. When I moved splitter so that inboard side of splitter lined up with inboard side of blade the burning went away.
But that's not the whole story.
Early on while trying to track down the source of the burning, I removed the splitter and the burning still occured so naturally I figured that wasn't the problem. It turns out the fence was also slipping occasionally and it probably had slipped when I did this test and didn't notice it. The way I caught the fence slipping is when I went to rip some red oak for baseboards. I was all happy the burning had disappeared when suddenly the smell of burnt wood hit me as I ripped a 7' board. I was all depressed when I noticed the cutoff piece seemed to have a slight taper! I pushed against the fence and voila; it gave slightly.
Now I think I've got everything under control. One side benefit of all this is the tablesaw is sparkling clean with every surface wiped and waxed. Also, this motivated me to give the bandsaw a new sawblade and tuneup.
To coin a phrase, all's well that ends well.
A 40 tooth blade you purchased a year ago.......Have you had it sharpened in that time? Sounds like a small fence alignment issue magnified exponentially by a dull blade. I my experience a small alignment issue wouldn't cause burning unless you all but stop the work as you run it or your blade is dull. A sharp blade in a saw that is healing won't burn the stock as you describe. Sounds like you need to "tweak" the rip fence outward a bit on the tail end and get that blade sharpened.
-Paul
I vote with Paul. These things tend to be a slow accumulation of small factors.
A dull blade coupled with a miniscule change in fence alignment is probably the cause. I think the problem will be corrected by bringing a number of "small" factors under control.
Rich
Edited 9/4/2007 7:57 am ET by Rich14
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