Resawing Issue: Explanation

[jihhwood]

Did some resawing in the shop this morning, using a 14 inch Powermatic bandsaw with a riser block.  My workpiece was a piece of mahogany, 18” long, 2” thick, and 6” wide.  I was cutting along the grain.  When I wad done, I expected to have two pieces; each was to be 18” long, 1” thick, and 6” wide.   Things did not work out very well, so I’m looking for some explanations.  Let me first describe (in some detail) what I did before starting to cut: (1) tensioned my 1/2" (wood slicer) blade, which I’d recently sharpened, (2) ensured that the table and blade were perpendicular, (3) checked for drift, adjusted, and made a test cut, (4) adjusted bearings above and below the table, (5) squared up my stock (I was cutting walnut) and marked the cut lines carefully on all four edges of the board, (6) installed and adjusted my auxiliary fence.  When cutting, I was careful to follow the pencil line I’d marked on the top of the workpiece. I applied consistent (but not excessive) pressure where the workpiece met the blade, both “up-and-down” and “side-to-side”.   Everything seemed to go well; I had every expectation that my cut would turn out fine.  But when the blade emerged from the workpiece I discovered that the blade had deflected inside the wood as I was cutting.   Since I couldn’t see that happening, I could not correct for it.   Instead of running straight, the blade deviated and slanted, so each halfe wound up looking like a very crooked and sloppy trapezoid (photos available.)   I can’t figure out why the blade deviated.  Can you suggest what may account for what happened?

[jcousins2]

it could be the saw blade you're using - looks to me that the blade is not clearing the sawdust quick enough so it's getting bogged in the wood and heating up - then the blade begins to deflect.
jerry

[jteneyck]

Did some resawing in the shop this morning, using a 14 inch Powermatic bandsaw with a riser block.  My workpiece was a piece of mahogany, 18” long, 2” thick, and 6” wide.  I was cutting along the grain.  When I wad done, I expected to have two pieces; each was to be 18” long, 1” thick, and 6” wide.   Things did not work out very well, so I’m looking for some explanations.  Let me first describe (in some detail) what I did before starting to cut: (1) tensioned my 1/2" (wood slicer) blade, which I’d recently sharpened, (2) ensured that the table and blade were perpendicular, (3) checked for drift, adjusted, and made a test cut, (4) adjusted bearings above and below the table, (5) squared up my stock (I was cutting walnut) and marked the cut lines carefully on all four edges of the board, (6) installed and adjusted my auxiliary fence.  When cutting, I was careful to follow the pencil line I’d marked on the top of the workpiece. I applied consistent (but not excessive) pressure where the workpiece met the blade, both “up-and-down” and “side-to-side”.   Everything seemed to go well; I had every expectation that my cut would turn out fine.  But when the blade emerged from the workpiece I discovered that the blade had deflected inside the wood as I was cutting.   Since I couldn’t see that happening, I could not correct for it.   Instead of running straight, the blade deviated and slanted, so each halfe wound up looking like a very crooked and sloppy trapezoid (photos available.)   I can’t figure out why the blade deviated.  Can you suggest what may account for what happened?

That happens when the blade is dull on one side, or the set is not the same, blade tension is too low, or you are feeding the stock into the blade faster than it can cut and remove the swarf.  (Sorry Steve N, it's swarf in my book and swarf it will be in my post.) 

Since you said you recently sharpened that blade that would be my first thought (no offense intended) where the problem might be, followed by inadequate blade tension, followed by the Woodslicer itself.  Those things have almost no set and any little cupping or bowing of the stock can cause them to do bad things.  I gave up on the one I tried after ruining a couple of pieces of wide stock.  I've had much better results getting straight cuts with almost any other blade.  OK, the cut is not as smooth as the Woodslicer but what good is smooth if it's not true?  None to me.  Nearly any 1/2", 3 or 4 tpi blade with normal set should cut 6" walnut very straight.  I'm using Starrett right now and before that Olson MVP bimetal blades, both with very good results up to at least 10".   I'd start with a new blade of different origin, tension it at least as high as the tension indicator says to, and see how that works.  If you don't have a high tension spring on your saw that might help, too, unless the stock one already is of that type.  

John

[Rob Young]

That happens when the blade is dull on one side, or the set is not the same, blade tension is too low, or you are feeding the stock into the blade faster than it can cut and remove the swarf.  (Sorry Steve N, it's swarf in my book and swarf it will be in my post.) 

Since you said you recently sharpened that blade that would be my first thought (no offense intended) where the problem might be, followed by inadequate blade tension, followed by the Woodslicer itself.  Those things have almost no set and any little cupping or bowing of the stock can cause them to do bad things.  I gave up on the one I tried after ruining a couple of pieces of wide stock.  I've had much better results getting straight cuts with almost any other blade.  OK, the cut is not as smooth as the Woodslicer but what good is smooth if it's not true?  None to me.  Nearly any 1/2", 3 or 4 tpi blade with normal set should cut 6" walnut very straight.  I'm using Starrett right now and before that Olson MVP bimetal blades, both with very good results up to at least 10".   I'd start with a new blade of different origin, tension it at least as high as the tension indicator says to, and see how that works.  If you don't have a high tension spring on your saw that might help, too, unless the stock one already is of that type.  

John

I still have the el-cheapo 1/2", 3tpi hook tooth blade from Griz that I bought when I bought my G0555LX (I have a riser block installed).  I think I've sharpened it three times?  Fourth is probably going to be the last as I'll have removed too much set by now.  But heck, at $18/blade plus some shipping, that's pretty darn good.

I sharpen with some little diamond rotary stones in a Dremel.  Nothing fancy, just found diameters that match more or less the shape of the gullet.  I slide in and roll it out so that the pointy tip of the tooth is re-shaped.  I don't remove the blade from the saw.  Just raise the guide all the way up and get to work.  Takes maybe 10 minutes on a 105" blade.

And I've had no issues resawing.  Mostly cherry, soft maple and some QS white oak.  Good control and if I'm patient with this blade, a surface that only takes a few swipes from the plane to clean up.

I've been using deflection to set my tension lately.  Using the part of the blade moving down inside the guard on the right of the table.  Nice long run and if I can deflect it about 1/4", maybe 3/16" without pressing hard (very scientific) it seems about right.  On my gauge, this is about half way between 1/2" and 5/8" marks.  Seems fine.

I run the bottoms of the gullets right in front of the crown of the wheels.  That's where the blade needs support from twisting.  Likewise I set the guides and bearings according to the instructions that Snodgrass gives at the Wood Show.  So far, its worked just fine.

[ez-duzit]

...Did some resawing... a piece of mahogany, 18” long, 2” thick, and 6” wide.  I was cutting along the grain.  When I wad done, I expected to have two pieces; each was to be 18” long, 1” thick, and 6” wide...

I know of no resaw method that will produce two 1" thicknesses from one 2" thickness.


Not enough tension, a poor blade and no saw kerfs. That 2" workpiece should have been easy without a fence.

[Steve N]

Cuts like yours are actually a combination of all the things you mention, with each of them having little errors, or one big thing being off. I haven't owned one, so I can't comment directly about these "Woodslicers" but enough folks talk about difficulty with them I'm going to go with averages that the blade is mostly the cause. Having been sharpened by you, again like John suggested apologies, but that adds a dimension that even what many consider a bad blade to possibly be worse. John also talks about the "stuff that has been cut away from the wood, but hasn't actually cleared the cut" so no matter what you call it, it can be a HUGE determinant to getting a clean cut. Though in only cutting through 6" of height, add to that the fact you mention a riser block, which at 6" you aren't really using, I have to wonder how close do you have the blade guard pulled down to what is exposed of the blade?

I'm going to assume you have a 3TPI blade on the saw, and if your proper tension is something close to a 1/4" or less of deflection when you push in at the side of the blade, then a wonky cutting edge (maybe your sharpening) or simply too fast a feed rate (not allowing the blade to actually work through the cut) is going to be the likely problem. But if you have your 12" blade guard fully exposed, and therefore the guides being way off, that could also be what you are seeing. That much free blade, not engaged into the wood will allow quite a bit of Hula dancing done above the cut.

My first thought for a fix is go to a place where you can buy a blade made just for you. Using hopefully Starrett blade stock, 1/2" inch wide with a 3 TPI blade count, OR LESS if available. I like 1.3 TPI that really moves John's swarf out of the cut line, and doing everything like you did before, did the cut improve? If not then the list of things you mention needs expansion all the way back to; blade off, and starting with how are the wheels coplaner, does the blade track on the wheel, etc etc and just expand out from there, and sooner or later you will hit on what the problem was/is. The really good thing this is like the accumulation of errors that kept you from riding a bike like a pro the first time out, but once you got the hang of it, away you went for life.

Even using the very best blade, set up exactly as it can be, the feed rate of a resaw BS, is no where as close as the feed rate of a TS, or router. Good results come from patience, and fully allowing the blade to cut true, and remove the "junk" as you are doing so. Attempting to force the saw to cut will leave a wonky cut. You don't have an end of the world cut, you have a slightly wonky cut. I think that means you are close.

[mdhills]

Matthias Wandel has a good video on the factors you should be looking at.  If the blade didn't get messed up, it comes down to gullets, feed rate/pressure, and blade tension:

https://www.youtube.com/watch?v=fK9m5PadmiI

Matt

[jihhwood]

Matthias Wandel has a good video on the factors you should be looking at.  If the blade didn't get messed up, it comes down to gullets, feed rate/pressure, and blade tension:

https://www.youtube.com/watch?v=fK9m5PadmiI

Matt

Thanks, Matt, for the careful review of what likely went wrong.  I'd say blade sharpness and lack of adequate set were major culprits.  I will certainly check out Matthias Wandel's vid.  Thanks again.

[jihhwood]

Having read all of the replies to my post, I can say without equivocation that they are a perfect illustration of why Woodnet membership has got to be among the very best choices any woodworker could make!  Thanks to each of you for the thoroughness, knowledgeability, and sensitivity of your replies.  At this point, I certainly have the information and the guidance I need, along with sources to consult and a good understanding of the variables that contributed to my disappointing resawing.  The rest is up to me!

[Alan S]

Highland woodworking has a series of short articles on setting up and using bandsaws, among other topics.  They are here: https://www.highlandwoodworking.com/wood...brary.aspx