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Happy New Year.

Got a new 1/2" Bladerunner from Iturra Design, for my Delta 14" with riser. After setting up to do some resawing (tensioning blade, adjusting tracking, etc), I started working on back sets from my Woodcraft Bubinga pile (see previous posts by Todd), and on a Padauk board from the same place.

Part way through the second cut on the Padauk I noticed that I was getting a lot of bow in the blade, but also that the blade was not contacting the blade guide bearing. For some reason, the blade tracking had changed, and the blade had moved to the front edge of the top wheel. At rest, it was 1/2 way out of the gap between the cool blocks.

Anybody have a clue of what's happening here, at least in a generic sense? I don't really know what to go back and do differently. I had adjusted for drift, and had the tension cranked up pretty good. (No objective way to measure this, other than the push on the blade test.)

Is there a possibility that the tension had tilted the upper wheel enough that the tracking adjusted from it's less loaded position due to change in wheel angle?

The blade went through the Padauk much more cleanly than my 3/8" Timberwolf had done for the side sets (plus I was resawing 9" here as opposed to 5.5"), so I don't feel like I was overloading the system that way.

Your advice would be appreociated.

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Jim Kirby
kirby@udel.edu

Sounds like a tracking issue to me. When you have more tension on it, you have to get the blade running right at the top of the crown of the tire. If it is running off-center, the blade will work itself off the center under the tension. You're fortunate it didn't come off, or start chewing on the covers.

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Don - Thanks. I'll look more at the tracking. The tracking was really hard to adjust with the blade tensioned fully - I couldn't turn the thumbscrew unassisted. I've seen some
references say to adjust the tracking so that the blade is tracking near the back of the wheel under normal tension. I'm guessing that the extra tension bows the wheel forward and moves the blade forward as well. I'll look at all of this first.

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Jim Kirby
kirby@udel.edu

Although not exactly what you describe, I've noticed changes in tracking as the blade heats up on my bandsaw. If the spring doesn't have enough tension to take up the expanded length, the tracking changes. On my saw, this makes the blade move back on the tire- not what you are describing, but it may be a factor all the same.
John

have you fitted the after market tension spring itturra and others sell?

when resawing wide hardwoods, particularly those with resins in them, the load on the blade, and thus the spring, is very heavy and the standard spring really isn't up to the task.

you may also want to replace that piddly little thumb screw with a lever screw or similar, or use a set of vise grips on it. crazymanmichael39078.7905902778

Michael - Carter replacement spring. I question whether it is able to tension the blade.

I DID use vise grips on the tracking screw, after I figured out what was going on.

I've been back to play with the saw once more. I adjusted the tracking so that the blade stays a little back of center on the tire crest while under tension. In this position it does not creep forward. Now, though, the blade drift is huge - more than I can adjust for using the regular Delta fence.

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Jim Kirby
kirby@udel.edu

when resawing many folks use a tall vertical bar type resaw fence which allows you to move the stock to just about any possible drift angle.

did you have a tall auxillary fence, either of the bar type or a flat variety, attached to your factory fence?

not having a factory fence with my ancient walker turner i made a shop built fence which i clamp to the table using welders clamps at whatever drift angle i need.

assuming that you kept the thrust bearing adjusted when you started, did you get any signs of burning on the blade or the stock you cut? was the cut cupped?

[QUOTE=crazymanmichael] when resawing many folks use a tall vertical bar type resaw fence which allows you to move the stock to just about any possible drift angle.

did you have a tall auxillary fence, either of the bar type or a flat variety, attached to your factory fence?

not having a factory fence with my ancient walker turner i made a shop built fence which i clamp to the table using welders clamps at whatever drift angle i need.

assuming that you kept the thrust bearing adjusted when you started, did you get any signs of burning on the blade or the stock you cut? was the cut cupped?
[/QUOTE]

I have an auxiliary fence attached to the stock fence. 9 inches tall, flat, and basically ends even with the blade. It's from a FWW article about 5 years back, I think. Does not allow for following the drift angle if the fence is not adjusted for it. With the initial blade tracking I had (blade centered on tire), there wasn't much drift. But the blade didn't stay there.

The cut was cupped, but this was after the tracking drifted forward and the blade was not touching the thrust bearing.

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Jim Kirby
kirby@udel.edu

Heat is the enemy. Besides affecting the position of the blade on the tires as the blade expands, the lead direction of the blade is changing, because the inside of the blade, which is under compression at the wheels, heats up a lot more than the outside, which is in tension. The teeth set to the inside start to cut differently from the ones on the outside--then you see that big bow in the cut, even though you set up carefully.

One solution is a bigger saw--the heating of the blade from flexing aorund the wheels is less. Another is one of those blade misting systems that cools it. Another is carbide, but from what I've been told, you can't run a carbide blade on a 14" saw.

I have the same problems with a 16" saw. What I have been doing for resawing is sawing both sides of the cut about 2" deep using a 7-1/4" Freud Diablo blade in my tablesaw (takes a 1/16" kerf). Then I don't bother with the fence (since lead direction will change), and just keep the blade feeding through the kerf by eye. It likes staying in the slot--the work is much less. The 1/16" kerf is more than a really good cut on a bandsaw, but not by much, and it's a lot less than you get anytime the blade starts to bow or wander.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Thanks everyone. I'm going to spend some more time on this today.

I don't think it was heat - but I'll see if the blade is overly hot after another test cut. The cuts themselves are pretty smooth and nice - it doesn't look like the blade is fighting the wood at all, or chattering/vibrating. Much better cut than I have gotten from my Timberwolf blades before. I think its just that
the blade didn't stay on track.

Todd's suggestion: I saw the picture of the bent tension arm in Iturra's catalog. My saw has just not been used enough to have that happen, unless the part was defective to start. I'll take a look at that if other tries don't
point to a solution today, though. Tires are pretty clean, but they may be having trouble with the load being applied.


I will probably go back to the 3/8" Timberwolf, too - I've never had any tracking problems with that, and have resawn 9" Myrtle and Bloodwood with that type of blade (and the original tension spring).

Howard, I will try your trick on one of the test cuts. I have the Diablo at hand so it's an easy test.

If the rest of this week is going to be resaw experiments, I had better pull a walnut or cherry board out of the regular wood pile rather than working on my Bubinga stack!

_________________
Jim Kirby
kirby@udel.edu

Todd - your second post came as I was typing my reply to you and Howard. I'll look at whether the wheels are coplaner, and will probably pull the top wheel and look at the tensioner casting. (If that is the culprit, I may spring for the Iturra high tension kit.

The tires look OK - I'll give them a closer inspection this morning.

I'm using Cool Blocks - have since day 1. I don't think I ever even ran the saw with the original blocks.

Blade drift - that was my problem - blade was adjusted or zero drift but didn't stay there.

I just want to point out again that this saw has successfully resawn up to 9" boards (Bloodwood probably the most severe test so far) with the 3/8" Timberwolf blade, so either something has changed/worn/broken since then, or I'm just not able to get the 1/2" Iturra blade up to tension and in a stable position with the present setup.

_________________
Jim Kirby
kirby@udel.edu

I actually have not had the problem with the blade moving forward from the guides, but I have had lead direction change rapidly while cutting. Regarding differential heating of the inside and outside of the blade, I have never tried to measure directly, but if you ever cut green wood, you will see that the gunk all builds up on the inside of the blade; I inferred that it is because the part of the blade that is in compression on the wheels heats up from that. Does that make sense, Todd? What size saw are you taking measurements on?

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Oops...

Jim...one thing about the Bladerunners...they're designed to work at lower tension than you might think. Call Louis Iturra and ask him for his help on these. You might as well go right to the source!

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Don - Yes, I will go to Louis to try and resolve all this, but I want to check to see if my wheels are co-planar and if they stay that way under tension, and if the tracking arm looks OK.

I didn't get as much time with it yesterday as I had hoped, but I did get the 3/8" Timberwolf back on it and tried sawing with what I would have thought was my usual setup. The blade tried to come off again. I think something is out of whack somewhere. It will probably take me a few days to make more headway, and I'm going to keep quiet until then (unless someone has some specific questions.)

Thanks again.

_________________
Jim Kirby
kirby@udel.edu