Grit and Pre-HT edge thickness trouble...

M.FREEZE

M.FREEZE

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When grinding, starting with 60 grit and going all the up to 400 grit (for the finished project) do I rough grind the bevel all the way to desired pre-HT edge thickness with the 60 grit belt?

I was making very good progress when flat grinding O-1 with 60 grit. But eventually, I ground the edge too thin. If I continue to progress to 120 grit, 220 grit, etc... I will only make the problem worse.


Thanks, Mike
 
I grind to a 120 grit belt finish to about .0625" at the edge for carbon steels...sometimes a tad bit thinner (.04-.05). You don't need to go up to 400 because you are going to hit it with a coarse belt post heat treat to grind to your final thickness. Some people recommend at least 220 but but I find that 120 is sufficient.


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I should've clarified. 400 grit will only be used post-HT.
I guess my main issue is knowing when to transitions between grits while being able to maintain my desired edge thickness. If I grind to my final thickness with a coarse belt post-HT, won't the edge thickness continue to get thinner when I work my way up to 400 grit?
 
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I usually stop at 120 pre Ht. I haven't had a problem with that yet. This is in oil quench stuff. If you are a little thin, you will be amazed how little you have to bring the edge back to get the thickness you want. Length of blade makes a difference too in how thick you need it. A 3" blade can be pretty thin, MAYBE as thin as .015 or .020 before HT. If it a longer blade, it's better to have some wiggle room. Plate quench stuff even thinner.

A nother thing. All you have to do clean your scratches form the 60, it don't take as much as you would think.
 
So when you are grinding the bevel,start with a 45-ish degree angle on each side the edge. You want these two angles to meet on the edge at your desired pre-ht thickness. Then use decreasing angles to "walk" the grind up the blade towards the spine.
This will keep your edge from getting too small to heat treat.


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I follow Stacy's standard advice and go to .030 pre ht and .020 or .010 after. I rough with 60 then go to a clean 120 before ht, and start right back at 120 after ht to almost finished thickness.
 
If the edge gets a bit thin in shaping the bevels, just grind it back a tad. It only requires a few thousandths to make it wider.

I like to HT at around .030" and sand to .010" after HT. The final edge thickness can be as thin as .005" for some slicers, but that is a delicate edge. Choppers and swords can stand an edge thickness of .020". I usually convex the thicker edges.

I sand to 220 grit Pre-HT, and go back to 120 grit post HT. If you leave coarser grit marks than 220 grit, it can be a lot of work to get rid of them.
 
I'm going to bump this because it has part of the answer for the question I have. In addition to the belt grits, and some basic tips given here, I'm wondering if you guys take your rough grind at 60grit all the way to the desired grind height? Or do you stop short of full height before switching grits, get it to final height with 120-220 all while cleaning the scratch marks from previous grits?

I'm flat grinding on a 2x72 with ceramic belts.
Thanks for the help!

-TD
 
Material removal really slows down after 120 grit. So I basically go to finished sizes for edge width, grind height, etc at the 120 stage. Dimensional changes really slow down after that and while they do still change, they're quite minor, and I find it easier to knock the edge back, or knock the flat down, if I found I've gone too far, than to leave the edge too thick as I progress up the grits and it becomes a real chore to thin it down without stepping back to a coarser grit again.
 
I go pretty close with 36 grit. Once i have any stray grit scratches approaching my final grind line, I switch to 120. I HT at 120.
 
Yeah once you start going up in the grit things slow down rather quickly. I do things a tad different then some but it works for me. I run a corse belt like a 50 grit blaze and get everything roughed in for heat treat. I get my edge down to the thickness I want and the edge bevels nice and flat (flat grind). I then switch to a A300 gator belt and go over everything. Heat treat comes next and after its hardened and tempered I go at it again with the a300 gator belt. Some times I go straight to heat treat with the 50grit finish but most times I bring it up to a300 gator. Then work my way up through the gator belts and stop around a64 or a45 and start hand sanding at 200 grit.

To answer your question about how much material to leave for the next belt to remove. It is more of a personal thing then a "I leave x thousands of an inch" kinda thing. It also depends on how nice and flat (flat grind) you made things with the previous belt. If your just removing the previous grits scratches then it's hardly anything, measured in thousands of an inch. But rarely do we take just that and stop sanding. Lots of times we might be chasing somthing like a scratch, a mismatch grind or what not. But in my case I don't leave much as it becomes much harder to remove that extra material the further you get away from the roughing belt.
 
When I started I took pretty much the final shape to 300 grit pre-HT. It was a serious mistake.
Now I grind with 40 or 60 and leave lots of meat on the blade. I just get it started in the direction I want it to end up. For me the most important aspect pre-HT is to get the 45 deg edge bevel set even. Other than this I am working down the distal taper. No real blade shaping.
Post-HT I start again at 40 or 60 depending if it's thick or thin stock, and take that pretty close to final. I use 120 to refine the blade. 220 to do any slight thickness adjustments here and there, but 220 is mostly for removing earlier scratch marks.
At 220 and above you should be polishing. You will play hell trying to shape anything at these levels.

If you can't get a good grind to shape at 60 or 80 post-HT then slow down the grinder.
 
Some of this factors in with how thick or thin is the blade stock to begin with.

It's all a matter of learning and experience - of which I'm still very much in the learning phase.
 
Great! That's all very helpful. I kind of stumbled into this hobby and don't know anyone around me that does it to be able to answer the simple questions. So I've been hogging mild steel blanks and burning belts up trying not to do it "wrong". You guys are awesome.

Thanks again.

TD
 
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