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Post-Heat Treatment bevel grinding anxiety!!! HELP, PLEASE!!!


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 I'm a self learning knife maker for just over 2 years and finally invested heavily in a proper, yet essential, well made tool, a ($2k) 2"x72" belt Grinder and a vast variety of substrates, grits, and designs of belts... Yada yada yada, in my first 2 years and dozens of knives to learn from, I had unfortunately, and thorougly abused and destroyed a few 1" x 30" harbor freight Belt "Sanders", I relied more on  a tiny but powerful 1/2" x 18" Band File Belt Sander for my bevels and small curved finishing...Now comes the brand new machine..... But I have "Blued-Out", or Burned, almost every post treatment blade since I've been using the new grinder... I have a couple nice pieces just finished tempering and started handles for, but am intimidated and afraid to ruin these as well...I'm a  very quick study and slowed speeds, tried finer grits, less pressure, and am getting pretty messy with constant bucket dipping, seems I've tried everything aside from a circulated, cold water trickle, belt feeder... Am I leaving the edges too thick  before treatment? Does this make any sense?? Maybe some cool physics trick I am humbled to learn?!? WIP in these photos, obviously... Thanks in advance, friends

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It does look like your edges are a lot thicker than they need to be, but the post HT grinding I do always involves a lot of dipping in the water bucket.  Like, every pass, sometimes.  

 

I harden and temper with the edges nearly sharp, but I also use anti-scale, a reducing atmosphere in a muffle tube, or foil to prevent decarb.

 

What speed are you running, and what grits?  Also, use only new, sharp belts (or Trizact Gators) for post-HT grinding. They don't cause as much heating. If you use the Trizacts, don't get them wet, though. 

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Ty for replying Alan... I started with an order from Combat Abrasives with 2-4each of some ceramics ,(36,60,80,120 in their orange "Shredder" series and some 220, and 320 of a light ceramic) then a whole gambit of AO grits and stiffness up to 600... Ive got a 2hp motor 120v(1.5hp I believe it is, yes) with a VFD that I jumped up to 120hrz from 60hertz... And running on a fragile electricity phase due to construction, so I trip breakers if I get er going passed 60-70% power.. but I'll try to get my edges tighter, was skiddish about warping or burnup, but they are almost 3/16 at the choil

, any other thoughts from this info?...

 

Also, is it common to have some bad belts that give the "Speed bump" effect from joining seem? Or did I choose a not so great consumables company?!? Thanks again

Edited by Jason King
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Ive made a couple blades where the edge was thinner then a dime prior to heat treat and still had little to no warping. Lucky I guess.  But everything Alan said is pretty much exactly what you want to do. 

 

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I have a couple of PSA disks from Combat that came with a disk , but I haven't used them otherwise.  They seem to be rebranding stuff for knifemakers using a deliberately macho-sounding name, a practice I can't stand.  I personally use TruGrit abrasives, https://trugrit.com/ and Klingspor or 3M belts.

 

If I'm reading right, you doubled the speed for the motor?  That's great for heavy stock removal with ceramic belts at high pressure, but for finish grinding you want really slow.   I don't have a VFD on the belt grinder, just three-speed pulleys with a low speed of around 800 feet per minute.  That's too fast, but I've learned to use it.

 

My edges, as I said, are almost sharp before HT, maybe 0.024" or so.  If you do the heat treat right, and quench in the proper medium for the steel, warping isn't a big problem for most things. 3/16" is WAY too thick and is making you work a lot harder than you need to.  If you're really nervous about decarb and warping, you can leave the edges at around 0.040", but there is no advantage to leaving it thicker unless you're making a filet knife or a very wide, very thin kitchen knife.  Those you grind totally after HT anyway.  Same with some folder blades and some sword blades, but I digress.

 

Belt bump is a real issue.  All belts have it to some extent, but there are bad ones that really whack you hard.  I just learned that people who have belt-fed surface grinders use a grinding wheel-dressing abrasive stick to level out the bump at the joint, since a thick joint when surface grinding will remove any pretense of precision.  Of course, if you take it all off you'll have inverse belt bump, so go slow and carefully.

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What tremendous, and well appreciated help  you have been on this matter, Alan. Thanks for taking the time to share your knowledge with all that are eager to listen and learn, myself included... I have always tried to take the more challenging path in life, I guess cause I'll be forced to learn, which is up there in the top 3, for me, of the best things about life.  Even though I rarely panhandle for free wisdom, there are days, when you just get stumped... It's refreshing and humbling to finally peruse this forum of such gifted artists and feel comfortable at being clueless about so much of this craft... I tattooed professionally for 30+ years until 3 years ago with rapidly declining vision, and hip replacement... (2or3 scars, stacked on top of one another, right in the middle of my left cornia, was the explination from the doc... Grinding, welding sparks, smoking cigarettes while riding my bike are the prime suspects... But I have to keep my hands busy, or die... Now I tell people that "I make knives, so that I don't stab you all in the face!" Cheers 

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Combat Abrasives is advertised as a veteran owned company, hence the name.  I bought several belts from them to run on my 2x42.  They work well with no jump.  I did find that I needed to push the platen out at least 1/16"past the belt or I got some chatter when grinding. 1/8" worked the best for me.  I'll be saving for a 2x72 someday, but it isn't an option for me now.

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Ah, I didn't know that.  Thanks!  

And yes, the platen does have to be slightly forward of the plane of the wheels, I forgot to mention that.

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It may just be me or my approach, but I keep coming back to the more expensive belts for precise work. 

 

I've tried a number of the lower cost "Super Steel Eater Extreme Shredding" ceramic belts.  I like some of these for rough work that tends to be hard on the belt.  However, they seem to run hotter, don't last as long, and don't run as smooth as the premium brands.

 

Most of my post heat treat grinding starts with either Norton Blaze or 3M Cubitron belts in 120 grit.  I really like the Cubitron belts, but they are expensive, and don't last as long for me as the Blaze.  With the Cubitrons, I run the belt pretty slowly, and you can see the curls of steel falling from the blade.  It feels more like power filing than grinding.  It is easy to control, and doesn't heat things up very fast.

 

After the 120 grit, I jump to cheap AO belts for 220 and 320 at about $1 each.

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What grit belts are you using for the bulk of the post-heat treat grinding?

I prefer using the low grit belts as long as I can, coarse abrasive grinds cooler than finer grits, just be sure to use sharp high quality belts.

FWIW I use 40 grit ceramics for 95% of material removal, higher grit belts are only for removing the scratches.

 

I often remove a lot of material after heat treat, because the oven I use gives me a lot of decarb, I also tend to be lazy and heat treat directly after forging sometimes.

 

 

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I keep repeating this for myself, perhaps others might benefit, but do not try to use belts on bevels once they are not sharp.

 

Dull belts generate heat. They gall and scratch and mess things up.

 

As some have said here before concerning belts: "use 'em like they're free"... at least on the flats.

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All valuable info, thank you all... And I mistakenly put the wrong thickness measurement before... They're closer to 3/32" thickness at the choil... I really need to do more homework on all the different varieties of belts, I have only heard if a couple of what's been mentioned...  An then comes the platten,  when I looked, I had such a gap behind the wheel depth, that I just used right out if the box, and just positioned it slightly forward of wheels and will hopefully have time today to try it out... Ty again y'all. ;)

Edited by Jason King
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Also, The Combat Abrasives Shredder pack should have come with a tube of semi solid goop which is a belt lubricant. 

Are you using that, I have found that with the low grits ( 36 specifically ) it helps a ton. I bought my shredder pack a year ago, and am still using my first 36g belt with that stuff and it still cuts like it was brand new. But I only use 36g for profiling, the scratches from 36g on a bevel take AGES to hand sand out. 

 

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Yep, Robert D. I do have that, and have dressed the belts a few times, but will stay diligent, sounds like a "Win-Win"... I've misplaced my harbor freight "Belt Cleaner/Dresser" huge tan eraser, that would really help keep my belts a lot sharper and cleaner...I took all shared advice and re-attacked the bevel flats and edges, with more of a confident and relaxed, understanding and respect of this process, and the knowledge of the risks involved with the different substrates... Im afraid that this whole issue of anxiety, that I developed, could have all been avoided or limited, if I had ground the pretreatment bevel-edges, a substantial amount thinner than I had previously believed was ok... Just ended up giving myself a hell of a lot more time and work, grinding on hardened steel... embarrassingly obvious now, but am glad I felt comfortable to ask, I gained a lot from this simple little problem.

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