A Scientist Explains The Physics of Resawing

[Julie Moriarty]

I don't know he's a scientist...:rolleyes:


http://www.youtube.com/watch?v=fK9m5PadmiI&NR=1&feature=fvwp

[Erik Loza]

That's a great video, Julie. I link customers to it all the time.

Erik Loza
Minimax USA

[George Gyulatyan]

What he says makes sense.

[Doug Ladendorf]

Thanks for posting Julie. He has an incredible range of interesting videos like this.

[Julie Moriarty]

I just found this and really appreciated the perspective. Now it makes sense why Lenox told me I needed a 1" wide blade with 1.3 TPI for the 6-9" sapele resaw.

[Erik Loza]

"Wider is better", is also my experience. Which gets us to the next issue, which is having a machine chassis rigid enough to get enough tension into the blade to get it to cut properly. That seems to be the achilles heel of smaller bandsaws.

Erik Loza
Minimax USA

[Chris Padilla]

I dunno...my experience doesn't bear out his theories but I've only EVER used a 20" bandsaw (MM20). I've never had to "struggle" with a 14" bandsaw.

I've gotten excellent results using a 1/2" wide Lenox bimetal blade with 6 tpi (hook style). It is the Diemaster2. I've gotten equally excellent results using a the Lenox Trimaster 1" 2/3 variable pitch carbide blade. One of these blades is ~5x the cost of the other. :)

I tension all my blades using the < 1/4" deflection test at the throat plate and I can slice off veneers all day long. :)

[johnny means]

Wonder if he'd make me a training video about why forstner bits should never make dust?

[Pat Barry]

Very interesting. Thanks for posting this. It explains all the troubles I have had trying to resaw with my little 1/2 blade on my 14" saw. I don't think I could put enough force on a wider blade though.

[Jeff Duncan]

I also have a 20" bandsaw and you can indeed still have trouble re-sawing. If I try to re-saw 9"+ hard maple with my Re-Saw King carbide blade it is really slow going. Having too many teeth does indeed slow it right down. If I have a 4" piece of oak on the other hand, I can zip it through pretty quickly. So I'd have to say my experience mirrors his explanation.

good luck,
JeffD

[Doug Ladendorf]

Very interesting. Thanks for posting this. It explains all the troubles I have had trying to resaw with my little 1/2 blade on my 14" saw. I don't think I could put enough force on a wider blade though.

Pat, you should be able to resaw with a 1/2" blade. I recently had to resaw 6" walnut on my 14" bandsaw (which is it's capacity) with a 1/2" 3TPI blade. No problem. What TPI does your blade have?

[Julie Moriarty]

I saw a Rikon bandsaw that has a 14" resaw capacity (http://www.rikontools.com/productpage_10-350.htm). Going with the information gleaned from the video, about the widest blade you can put on a 14" wheel is 3/4". He said something about metal fatigue and I'm thinking that would be more related to the thickness of the blade. But as you go wider, the thickness increases.

I went to the Lenox website to their blade selector page (http://www.lenoxtools.com/pages/BladeSelector.aspx). I found what they call their Flex Back blade, a carbon blade with "excellent" fatigue life, thinking this would be the best blade for smaller wheels. These are the Flex Back blade widths and thicknesses:
1/4 x .025
3/8 x .025
1/2 x .025
3/4 x .032
1 x .035
2 x .035

The numbers are the same for their Woodmaster CT but they only have 1" & 2" widths.

From this sampler, it looks like blade thickness is determined by blade width. There's about a 25% increase in thickness between 1/2" & 3/4". From 3/4" to 1" is a little less than 10% increase.

Getting back to the Rikon, if you're going to resaw something upwards of 14" wide, it would seem you would need less than 2 TPI to avoid the problems cited in the video. With the Flex Back blade, 2 TPI is the lowest you can get. With the Tri-Master, it's 3 TPI on the 3/4" blade and 2/3 TPI with the 1" blade. The Woodmaster CT blade I have (on an 18" wheel) is 1" x 1.3 TPI and it seems to clear all the sawdust out. The capacity on my bandsaw is a bit under 10", and I have resawed pieces close to that. I have used the Woodslicer but there was sawdust left on the board and the blades dulled quickly, probably because I was feeding so slowly. I'm thinking if you went to a 14" resaw, you'd have to be less than 2 TPI. But where do you get a blade that falls in line with the physics explained in the video?

So if larger resaw capacity is important to you, it would seem you need to look at wheel size then resaw capacity when in the market for a new bandsaw because you would need a wide blade with less than 2 TPI to clear out the sawdust effectively, for the bigger resaw cuts. Anyone with real-life experience that refutes that, please feel free to pipe in.

[John TenEyck]

I've had a 14" Delta for many years, the last couple with a riser block. I've never had trouble slicing veneers with it. I recently did some 10" maple - nice 0.010" thick slices, using a 1/2" - 3 tpi bi-metal blade. Michael Fortune is a pretty well respected woodworker and he recommends low tension, so clearly different people have different opinions on what works best. A Delta 14" saw is only capable of about 12,000 psi with a 1/2" blade, which is well below the minimum recommended by most blade manufacturers. While high blade tension may be helpful in maximizing cutting rate, I have not found it to be a necessity to get consistently straight cuts, even in thick, dense woods. A blade that is sharp and with consistent set on both sides in a well tuned machine with a good vacuum hookup seems to work fine for me. Until I get a higher level machine, that'll have to do.

John

[Stephen Cherry]

I think that the last few seconds sum it up: for more tension and more power, you just need a bigger saw. And this does not necessarily require big money either; if you are willing to accept a 24" or bigger saw, the deals are out there in the used market.

[Mort Stevens]

It explains all the troubles I have had trying to resaw with my little 1/2 blade on my 14" saw.


I have a Delta 14" bandsaw without a riser block and routinely use 3/4" blades on it, as a matter of fact the *usual* blade I keep on it is 3/4" and have had no problem resawing or with tension. A couple of tips, use a carbide tipped blade and don't need to go nuts with the tensioning of it, a 3/4" is thicker to begin with so there's less flutter in the first place and at the first sign of it getting dull replace it. I think you'll find 3/4" blades work just find on 14" bandsaws.

[Tai Fu]

If you put a 1/8" 14TPI blade on your minimax 20, then you're going to have trouble resawing.... blade sharpness and tooth count matters more, having a bigger bandsaw just gives you more option as far as blade goes.

[Julie Moriarty]

This video opened up a whole new perspective for me. I learned early in my career to let the tool do the work and that has proven to be the most effective use of just about every tool I've ever used. Once I learned about the better quality saw blades and how much easier they make the table saw or miter saw work, I never considered lesser quality blades. When I had a big resaw job to do, I contacted Lenox for advise and they recommended the 1" Woodmaster CT with 1.3 TPI. That seemed HUGE to me and I thought the fewer TPI would mean a rougher cut. I couldn't have been more wrong. Now I see the mechanics at work when resawing.

And then there's feed rate. I never gave that a lot of thought. I would feed at a rate based on feedback from how the blade was cutting, if it was tracking properly and if the motor was being tasked. I saw some videos where the wood seemed to fly through the saw. Others had much slower feed rates, which was more in line with my experience. What I wasn't clear on in the video was if slower feed rates dulled the blade quicker? I do understand the blade dulling if sawdust isn't being fully ejected, causing pressure and heat buildup. But if the sawdust is being fully ejected, would a slower feed rate dull the blade sooner? There's always that point in resawing when the wood puts up more resistance because the wood is harder in that area. At that time I wonder of the blade is dulling. Then it gets easier after I pass that.

I've probably burned through 3-4 Woodslicer blades and that was before I took on the sapele resaw task. But about the widest resaw I did with them was maybe 5". I do remember seeing sawdust buildup on some pieces but I can't remember the species or the width of the cut.

[Stephen Cherry]

What I wasn't clear on in the video was if slower feed rates dulled the blade quicker?


If you think about it, a tooth on a blade may be good for a certain number of cuts. So a thicker wood chip results in more linear feet cut before the blade dulls. Of course this is a simplification, but it seems to me to be the underlying principle.

One thing I have adjusted to on some of my industrial machines is feed rates that seem very fast.

[Richard Coers]

And then there's feed rate. I never gave that a lot of thought. I would feed at a rate based on feedback from how the blade was cutting, if it was tracking properly and if the motor was being tasked. I saw some videos where the wood seemed to fly through the saw. Others had much slower feed rates, which was more in line with my experience. What I wasn't clear on in the video was if slower feed rates dulled the blade quicker? I do understand the blade dulling if sawdust isn't being fully ejected, causing pressure and heat buildup. But if the sawdust is being fully ejected, would a slower feed rate dull the blade sooner? There's always that point in resawing when the wood puts up more resistance because the wood is harder in that area. At that time I wonder of the blade is dulling. Then it gets easier after I pass that.

I've probably burned through 3-4 Woodslicer blades and that was before I took on the sapele resaw task. But about the widest resaw I did with them was maybe 5". I do remember seeing sawdust buildup on some pieces but I can't remember the species or the width of the cut.

CNC users optimize their cutting with a calculation called chip load. It's the size of chip you get with a certain rpm and feed rate. Same thing goes with resawing blades on the bandsaw. Bigger tooth and fewer teeth = faster feed. Small tooth, more teeth=slower feed. You can resaw with just about any blade if you feed it properly. It's the 10 minutes to get through a 4' piece of stock that would be hard to control and hard for people to understand if they used lots of little teeth on the blade. I learned to slow down my feed rate years ago based on work in early Fine Woodworking articles and videos. It has to come around every few years to get hobbyists to slow down. Ever watch Scott Phillips on TV? The guy just about throws his work through the band saw. That doesn't help showing people proper technique one little bit.

[John McClanahan]

What I wasn't clear on in the video was if slower feed rates dulled the blade quicker?

The way I understood it was that the chips carry away heat. If the teeth rub without cutting, the tips of the teeth get hotter. Kind of like burning a router bit by feeding too slow.

John

[Jim Neeley]

One topic I haven't seen mentioned here is the advantage of skip-toothed blades. These blades provide larger gullets for a fixed blade width, so give more room to capture the sawdust.

[Edward P. Surowiec]

Thanks for sharing Julie, this video does an excellent job of explaining the important features of a band saw.
Ed

[Art Mulder]

I don't know he's a scientist...:rolleyes:


Matthias (www.woodgears.ca (http://www.woodgears.ca/)) is an engineer. Personally, I'd put that under the "scientist" umbrella. :D

[David C. Roseman]

Matthias (www.woodgears.ca (http://www.woodgears.ca/)) is an engineer. Personally, I'd put that under the "scientist" umbrella. :D

Yep, and a very resourceful one as well. :) Had not seen his website until this thread.

David

[Jim Rimmer]

Thanks for putting up the link. He does a good job of explaining why we do what we do to make the band saw work properly.

[Chris Padilla]

This video opened up a whole new perspective for me. I learned early in my career to let the tool do the work and that has proven to be the most effective use of just about every tool I've ever used. Once I learned about the better quality saw blades and how much easier they make the table saw or miter saw work, I never considered lesser quality blades. When I had a big resaw job to do, I contacted Lenox for advise and they recommended the 1" Woodmaster CT with 1.3 TPI. That seemed HUGE to me and I thought the fewer TPI would mean a rougher cut. I couldn't have been more wrong. Now I see the mechanics at work when resawing.

Let me know if the Woodmaster CT is all you think it is, Julie. I didn't have a very good experience with it. My 2/3 var. pitch Trimaster and 6 tpi bimetal (both from Lenox), cut cleaner than the CT. Perhaps I fed the stock too slow with the CT? It is a carbide blade and therefore quite expensive...especially on my MM20 that takes a 14' blade!

[Julie Moriarty]

Chris, I can't make the comparison between the CT and the Tri-Master, cuz I don't have the Tri. But compared to the Woodslicer, the CT excels. And if I had tried to reasw all the sapele I did with the Woodslicer, I probably would have gone through 5-10 blades.

[Tai Fu]

I get the feeling that Woodmaster CT is more for aggressive cutting rather than a smooth cut (like the Trimaster). On mines it cuts about as clean as a diemaster which isn't actually that clean for a carbide blade, and sometimes I wonder if it's because I didn't tension it enough. The selling point is probably the fact that it lasts forever.

[Sam Murdoch]

He may not be a scientist but he certainly is a teacher! His graphic examples were clear and concise - well worth watching . I thank you Julie for the excellent post.

[lowell holmes]

I follow Michael Fortune's recomendations as well.

The BC Saw recommendations he makes are good also.

I have a 14" Jet bs.

[Matt Day]

This is one of the better posts/videos that I've seen in a longggg time. Thanks for sharing Julie.

[Gus Dundon]

I watched several of his videos. He even created a band saw made from wood.

[Eddie Darby]

The big enemy on band saws for getting a good cut is vibration in the saw itself.
The top saws have very little vibration.
I once chased all the vibrations away on a Delta 14" saw, using upgrades and dampening, and had a cut that people thought came off a table saw.
A lot of work chasing all the sources, but in the end worth it for what I was using the saw for.

The one thing I would recommend in blades is an irregular tooth pattern, since this eliminates resonant vibrations from building up.

This you had in the WoodSlicer blade: "Our famous Wood Slicer bandsaw blade cuts smoother and quieter than any other resawing blade on the market. Its outstanding performance is due to its 3-4 tpi variable tooth pitch design, in which uneven spacing between the teeth nearly eliminates vibration during a cut. The Wood Slicer's tooth pattern damps harmonic resonance extremely effectively; the result is superlatively smooth cuts and much, much quieter operation than ordinary bandsaw blades." link (http://www.highlandwoodworking.com/woodslicer34resawbandsawblades105to166.aspx)

[Metod Alif]

I am not 'comfortable' with his analogy with a hacksaw. A bandsaw works on the pull 'stroke' while a hacksaw on the push stroke. I get by with 'minimal' tension, and let a sharp blade and good feed rate help.
On the feed rate, I think there is a sweet spot (or maybe just a figment of my imagination): the rate when I 'feel' that the saw is kinda pulling the wood into the blade. Resist the tendency to go faster at that point.
Again, it could be rather subjective, but it takes very little to find if it works for others too.
Best wishes,
Metod