Contradictory sharpening info

[barbender]

     Ok, guys, I need you to help me sort through some info here as I gear up for my spring sawing season.  My understanding on blade grinding has always been- very light grind on the face, down and sweep the gullet, and up the back of the tooth. Two of the primary objectives- 1. Sharpen the tooth face without heating it, which cause it to loose it's temper and hardness. 2.  Removing stress cracks in the gullets to prevent further cracking. As I have been contemplating on these things, and making some other observations, I'm starting to wonder if this thinking is backwards, or at least somewhat misguided. Please bear with me as I explain- first, I read an article by Tim Cook where he was sharing his thoughts on gullet cracking. The gist of his thoughts was, gullet cracks were caused by two things. Running blades past dull, and heavy grinding of gullets that basically got the gullet hot and hardened the metal.  Now I thought to myself, I thought burning the blade caused it to loose temper (remember how careful we must be to not burn that tooth tip). Then a while later I saw the sweet retempering setup @Peter Drouin had made for blades where he had ground all of the hardened portion of the tooth through repeated sharpenings. How can it work, though, without quenching the blade? It would seem most bandsaw blades are air hardening. If that is the case, it shouldn't matter if I grind the face of the tooth fairly heavy and it turns the tooth blue (it could even save me some oxygen/acetylene down the line, right Peter? ;D) and save the light grind for the gullet and back of the tooth.  That's what I'm going to try when I fire up the Catsclaw, I hope these theories pan out because man it is tough using a drag grinder and NOT burning the tooth.

[Ox]

I understand your thoughts, as I've thought this as well.  For me, I sharpen not lightly, not heavy, but kinda medium like.  Cat's Claw as well.  The tooth tips are like little razors and they are blued.  This in my eyes is not "burned".  It's hardened.  It air cools.  I have no troubles.  I don't know what the hubub is about "burned tips".  This works for me and I won't be changing a thing. 

[YellowHammer]

There are many good and bad grain formations in carbon steel that result from heating (grinding), quenching or working.  Some of the grain structures are hard and strong, while others may be very hard and brittle. 

For example, a martensite formation is commonly formed when carbon steel is heated and allowed to cool incorrectly.  It is a needle-like microstructure and leads to the metal being very hard yet brittle.  Improper martensite formation is common in welding, leading to brittle and poor weld strength (bands breaking at the weld).  The molecules in metal will move when heated, and if given the proper time, temperature and exposure to materials the brittleness can be reduced and toughness increased, in the "tempering" process.  This process can form favorable formations, while if the hot metal is not given proper conditions, will form unfavorable formations. 

So when grinding a band, if it gets hot enough to blue or blacken, then the metal is undergoing a grain structure transformation, and if cooled or quenched incorrectly, will form a brittle but hard material, as opposed to a flexible and hard material.  Same thing with grinding the tooth.  If they get hot, and the unfavorable grain structure goes deep enough, the tooth will be very hard, but also, very brittle, while a properly hardened tooth will be hard, yet not so brittle and will last longer. 

The gullet of the band is also susceptible to this, and in my experience very sensitive to proper grinding.  A gullet will develop cracks due to band flex and loading.  If the cracks are not removed, they will act as stress concentration zones, and propagate though the body and the band will break.  So the cracks must be ground out, or otherwise removed.  If this is done properly, the bands will behave normally.  If the gullet grind is too hot (whether it's deep or not), and the not cooled properly, then there is embrittlement, and reduced flex life, and the band will fail due to cracking.  So improperly grinding gullet cracks will actually lead to damaging the grain structure of the gullet, and will ironically result in more gullet crack formation, and failure. 

So, the solution to not improperly cooling a band and causing brittleness is to not heat it up to begin with.  Or in the case of Peter's experiment, to heat up the band correctly and let it cool correctly, to allow favorable grain formation.  Or in the case of Ox's bands, he has enough personal experience and "feel" to not let the brittle formation occur, or go too deep.

[sandsawmill14]

 ??? :P   yh what did you do before you started playing in sawdust work for nasa or something ???   just kidding  :D :D :D very detailed and informative post

[Peter Drouin]

I have been with WM from 1987, and in the day they did not  have double hard blades. And did not want you to blue the tooth tip.  Now with the new blades made with carbon steel you can. With the CBN I have to use oil or the wheel will not last a long time. And that's why I heat treat now, And it helps the blade last longer. If I heat to much the tooth will snap off. :D :D This is an ongoing thing for me, but I think i'm getting better. :P

[YellowHammer]

??? :P   yh what did you do before you started playing in sawdust work for nasa or something ???   just kidding  :D :D :D very detailed and informative post

No, my wife is the engineer is the family who works for NASA  :D. 

[barbender]

     Keep it coming, fellas.  Some of you probably sharpen more bands on a rainy day than I have in my whole sawing career ;) So, I am very interested in your experience with this issue.  The main reason this is on my mind is that with my dry stone Catsclaw sharpener, I have found it to be nigh on impossible to not get any bluing of the tooth tips. When I set the machine up to very lightly "kiss" the face of the tooth, it ends up not even touching some teeth. When I adjust it to get a consistent grind, I start to get some minor tooth bluing. I have driven myself nearly mad trying to find the source of this inconsistency, but as I have in the meantime observed Peter Drouin putting the flame to his blades ;D I couldn't help but wonder if I am overly concerned with a bit of bluing. It seems that common knowledge was that heating the tip would soften it, when in reality it could be making it overly brittle? Bottom line, I strive for a light, consistent grind, and as long as I am not breaking teeth off, some minor bluing of the tooth tip should not be a real concern?

[dgdrls]

barbender, is it possible the teeth are not perfectly spaced to match the stroke of the Cats claw or vise-versa?

@Chuck White or @4X4 I believe have Cats Claw units, perhaps they would have some insight?

Dan

[DMcCoy]

I got frustrated enough with blue tips that I added a water coolant 'system' to my grinder.  A $12 HF fish pond pump and 1/2 a 5 gallon propane bottle for a tank some tubing, etc.  Was concerned about it throwing water everywhere which with a few simple guards made from plastic bottles it isn't a big deal.  Not the prettiest thing I have ever built but the teeth are sharp and the blue-ing is gone.

[YellowHammer]

It's very easy to get an inconsistent grind with a drag sharpener.  Inconsistent tooth contact can be caused by several things, including setup of the machine but one of the common reasons for me is taking too heavy if a face grind, and also, not clamping the band tight enough.  Since the cam follower arm contacts the tooth right at the gullet, but advances and indexes by pushing on the base of the face, if the face is not ground perfectly consistent, and the root/gullet crease is not consistent, then the cam follower arm will push and advance on an inconsistent feature and will cause an inconsistent grind.  If during a face grind the rock pushes the face away, it's actually advancing the tooth a few thousandths, and it will also cause an inconsistent feature for the follower to contact on the next pass.  Unfortunately, as the teeth space changes, the grinding gets more and more erratic.  If set up correctly, you should be able to take a polishing pass and touch every tooth.
I like to set my adjustments and keep them consistent based on the flats of the hex nut on the drop adjustment.  Each flat of the hex is 1/6 turn, and that's about what I drop when I'm normally grinding.  When I do a polishing pass, I drop 1/12 a rotation, and that cleans up an blue in the first or second pass.  Thus way I always reaper and keep my drops consistent.

I do the same of the feed arm adjustment, except I scribed a couple index lines in the know so I know how much to rotate each time to keep it consistent.

Sometimes tooth burning is also due to the wheel loading up, so getting some fresh grit with the dressing wheel fixes the problem.

Metals react differently to uncontrolled heating and cooling based on their composition, heating temperate, rate of heating, quite a few things.  Heat it too much, it gets burned (it will throw off sparks under a flame) and it will get hard and brittle.  Heat it a moderate amount, but let if cool slowly, it will anneal and get softer going to a neutral grain structure, assuming it was heat treated to begin with. Most tempered steel is initially heated to a martensite level, where it is hard hard and brittle, but during the tempering process, is cooled in a controlled fashion, the grain structure changes, and the metal remains somewhat hard, but gets less brittle but tougher.  There is a trade off on the properties of toughness and hardness, you can't have the most of each, so proper tempering provides a good compromise on both.  Miss the tempering process, and the metal will not a good compromise of either.

[barbender]

    YH, I was experiencing this on blades that I was sharpening for the first time. I made sure everything was clean on the blade, and that the blade wasn't binding up on the guides going around. Then I started tightening the blade clamp.  I kept tightening it, without the problem going away. I finally figured out I was overdoing it when the gearmotor spit a seal out off of the output shaft Oops, drive the seal back on and lighten up a bit : Perhaps there was a little pitch in the gullets or something, it wouldn't take much to alter the grind when you are just BARELY touching it in the first place. dgdrls, I guess it could be slight inconsistencies in tooth spacing, but I don't really think that is the case. One other thing I haven't checked is band thickness, if that varied a bit it would cause more/less resistance going through the clamp system. I read of other Catsclaw users on the forum experiencing similar issues, and the concensus seemed to be "don't worry about a little bluing of the tips". My resharpened blades cut great, except I don't get a lot of BF, around 300 typically. I have a Mark 1 debarker on my WM whose primary accomplishment is occasionally hitting me in the face with a loose knot. So perhaps I shouldn't expect any more. My real concern is, am I softening my tooth by heating it, thereby reducing it's resistance to dulling? I guess the only way I can know for sure is to go grind one, and check any blue teeth with a file to see if it will cut them.

    DMcCoy, your water cooled system sounds intriguing- any pictures?
   
     I appreciate all of the input- being that I have never observed anyone else setting up and sharpening blades in person, it takes a lot of trial and error to get things right. A video can't capture all the nuances of something where a variance of .005" can throw things haywire either, so I have to rely on the experiences  of others on here.

[Doug Wis]

    I have been going to post on the same subject. The  article that barbender is referring to  is from  Cooks newsletter issue 1 2015 by Tim Cook giving the history of thin kerf bandsaw blades.  He maintains that  grinding the gullet causes more problems than it solves. Has anyone followed his advice and switched from full profile grinding to just sharpening the tip? When I bought my keenerbuilt mill, Frank keener advocated just grinding the tip, but a lot of that was to make his little handheld 12v sharpen on the mill grinder work. I have a TK grinder now and have the same problem as many have stated. Doing a light grind, it misses some teeth. Set it to get all of them, then some get ground too much. But  YH describes the problems well. When you are dealing with tolerances in the  thousandths,  several tiny inconsistancies  can throw you way off.  Don't know if Cooks newsletter is online , but its an article well worth reading.

[barbender]

    Doug, if memory serves me correctly, Mr. Cook wasn't advocating not grinding the gullet at all, rather, that if you grind the gullet heavily and burn the steel, you would be better off not grinding it at all.  For my part, I grind the whole profile more to maintain the profile of the blade rather than for concern over gullet cracks.  The blades that I have broken, most I can blame on myself for running them dull. They predictably get deep gullet cracks when I do that.

[Chuck White]

YellowHammer listed a lot of issues that can lead to inconsistent blade contact while sharpening bands!

I actually think that one of the major issues with inconsistency is adjusting the feed distance while the blade is being sharpened, in other words, when the blade is going around and you discover that it is grinding the face to hard, so you back the adjustment off a little.  When you adjust the feed while it's sharpening, you ARE changing the distance between the teeth, albeit small.  The next time you sharpen that same band you will have hit-and-miss as the band feeds through the sharpener.

To start with, when you initially set up to start a band, set it for a very light grind, let it go all the way around, then if necessary make an adjustment and let it go around again.

I always start and end at the gullet. The face of the tooth at the weld is the first face sharpened and the back of that same tooth is the last thing to be sharpened on that band!

Barbender mentioned that Tim Cook advocates not grinding the gullet too heavy.  If you grind the gullet too heavy, it will harden and eventually break.  Most times when a band breaks, it happens in the gullet.  Doing a light grind through the gullet will lessen the band breaking!

Hope this helps to explain the WHY in hit-and-miss contact.

[customsawyer]

Keep in mind that most of the blade stock that these blades come from is cut out with a stamp/press machine. It cuts 3 teeth at a time. Most times when you get a inconsistent grind it will be in groups of 3 unless you are adjusting the sharpener during a pass. I have sharpened thousands of blades on my cooks sharpener and also on my WM pro series CBN sharpener. If you are making very light grind you will get some teeth that don't get ground with both machines. I never start at the weld I just put the blade on and start sharpening. I then make 3 light passes, over 90% of the time. Sometimes I don't clean up the gullet until the third pass.

[Peter Drouin]

WM wants their customers to keep the whole tooth profile and tooth height when sharpening. And the back of the tooth is very important to do too.
They make their blades, I think they have it down.  :D :D

[Doug Wis]

     I had saved that Cooks newsletter. Quoting Tim Cook  " We have proved through numerous test that not grinding the gullet and simply sharpening the tooth improves blade life".   Keep in mind I only saw when I'm not farming, so most of you guys do more blades in a week than I do all year. So I'm not advocating any particular method, just asking questions. And like so many things, there are several ways to skin the cat.

[Ga Mtn Man]

Uneven tooth spacing doesn't cause inconsistent grinding.  Each tooth is moved into position under the grind stone by the pusher,  independent of the spacing.   

[Ox]

I think we're gonna find everyone has their little own way of sharpening.  Same thing with different opinions on blade manufacturers and tooth profiles.  Same with car tires, engine oils, penetrating oils, boots, jeans, foods, etc.  All you can really do is take it all in, make a decision and go with it.  See if it works for you.  If not, try something else!

[Ga Mtn Man]

I should have said "doesn't cause inconsistent grinding of the tooth face".  Uneven spacing will definitely effect the grind on the rest of the profile.

[4x4American]

I didn't have time to read through the whole post yet, so if it's been said, that's why...


I don't get much blued tips from my cat claw.  I don't know if it's because of the ruby stone or the .055" thick blades dissipating the heat faster.


What kind of blades are you trying to sharpen?  Is the grinder new or used?


To be successful with your mochine, here's some of the best things that I've learned from experience, forum members here, and people I've met in person.


-Never start in the same place.
-Make sure the clamp is tight.  Really tight.  So tight that it blows a seal then back it off a hair. 
-Go alot faster than you think is right.  (It really seems to grind better that way)
-Make sure the grind rock is square to the blade.
-Take the blue stones it comes with and donate them to your local landfill.  Then call up Suffolk Machinery and have them send you a ruby stone.  Much cooler grind (you can hear and feel it, and it keeps it's shape much much better).
-Get an aftermarket cam.  I got one that is so much better than the stock one, I had to put a halter on my llama to keep it under control.  If you want more details on it I can go check what company makes it.  But that cam was a night and day difference.
-Don't fuss with the adjustments.  Get it set, and then leave it.  Mark a "1" on the blade at what tooth you got it dialed in on.  Then when it comes around again, don't change anything til it passes the "1" then get it dialed in and mark it with "2", etc etc.
-More light passes seem to work better than less heavy passes.  (I'd rather give it 3 light passes at mach 1, than 2 heavy passes at a crawl.)
-Keep hydrated with plenty of beer.  If you are dehydrated, you can't focus, plain and simple. 


Hope this helps.








Check the tightness on the grease zerks at the pillow block bearings.  I read on here somewhere they might not be tightened from the factory.

[ladylake]

  How fast do those ruby stones wear off, seems like the ruby stones on a chain grinder wear real fast.   Steve

[4x4American]

They last much longer than the blue stones.  They grind cooler and hold their shape better.  I know a guy who knows a guy who has a brother and his uncle's nephew conducted a study one day on the blue stones.  He found that by the time you get around from a grinding pass on a blade, the blue stone has changed its shape by a few thousandths.  Which is not good at all.

[ladylake]

  That's the way the gray stones I used at first were, by time I got to the end of the band the teeth were taller and the side that ground the face of the tooth wore off way too fast.  Steve

[Chuck White]

I think I'll just stick with the blue rocks!