powered grinding (not sharpening(?))

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Folks, I'm fed up of spending ages at the bench stones shaping the primary bevel of my chisels & plane irons. However, I'm not in the league of never wanting to sharpen a chisel again (very enjoyable thread that) I'm just looking to speed things up. For context, my approach to sharpening is to keep re-honing the secondary bevel until it's worked its way too far up the blade, then grind the primary back down again - my reasoning is that this makes for quick resharpening, at the expense of less frequent but more tiresome re-creation of the primary bevel. Also every so often I nick a blade and then it takes forever on my "coarse" 250 grit waterstone. So time for some power assistance - and the usual set of dilemmas...
Ideally I'd like it to be quick, run cool with no chance of damaging the steel, but also to cut aggressively enough that I can change the primary angle of a beefy chisel without sellotaping it to the tool rest and going back every hour to check on progress. Oh, and repeatable. And preferably not a hollow grind (though I don’t suppose it really makes a huge difference). For the real edge I'm happy with my waterstones.
When I say quick I'm thinking maybe re-form the primary bevel on a LN plane iron in a minute or so? Maybe create a new bevel on a 1/4 inch thick blade in a few minutes?
Here's my current take on my options, and I'd appreciate knowing where my uninformed, theory-no-practice opinions are off the mark from people who actually use these techniques!
* Tormek - pricey (£280), and I believe it's geared towards creating a keen edge as opposed to removing material quickly; Jet do a cheaper (£190) copy of the tormek, it's got a go-faster knob, but really the same probably applies as to the tormek; * Makita horizontal grinder - I read SteveK's posts from some time ago describing clogging and uneven wear; I'm also wary of uneven grind depending on distance along radius; and anyway, I can't get this grinder in the UK :( Though there are some cheaper imitations with what look like inferior tool rests; * 8 inch dry bench grinder - fills me with dread of overheating the tool steel (though I'm sure it'll be fast!); pretty cheap even though better stones and decent tool rest would ratchet up the price a bit; * belt sander - 4" belt/disc sanders seem to be around £100, or £50 for the cheapest (& flimsiest?), so not expensive. I'd have to make a crude jig as the commercial ones I've seen only fit vertical wheel grinders. Not sure about heating of the blade - I see Sorby make one http://www.robert-sorby.co.uk/proedge.htm for around £240 with a little 2" belt - too pricey but perhaps indicative of a belt sander being the way to go? * Learn how to use those bench stones fool! - maybe it's just me, but recovering from a nicked blade would take several tens of minutes with my 250 waterstone.
Having laid that out I guess I'm edging towards the belt sander. Before I just get on with it anything I've missed?
Rgds all, graham.
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I have a Tormek for edge maintenance and a cheap 6" high speed grinder for hand shaping. I have a pink 120 grit stone for my tools, and coarser grey stones for regular metal grinding. No jigs on the 6", I rough shape it and let the Tormek do the precision work.
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wrote:

SNIP
Why not the Scary Sharp method but only the real low grits. 80 grit sandpaper glued to a flat surface makes pretty quick work of a plane blade. Maybe not 1 minute, but not 10 either. I personally take it down a few more grits on sandpaper (100, 150) and then on to the waterstones and the secondary bevel. I do use a $12 sharpening jig. Someday I will learn to use my 8" 1750 RPM grinder for this though ;-)
Dave Hall
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graham wrote:

I use both. A white aluminum oxide wheel which causes much less heating, and a 1 inch belt sander with a blue zirconia belt. I have a block glued to the tilting table and several angle blocks to set the angle quickly. The belt sander is all I use for sharpening turning tools. For finishing the edge on plane blades and such, I use the scary-sharp method.
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wrote:

Belt sander should work fine for what you're contemplating- If you look around a bit, I know at least the Delta belt/disc combos come with a table that can be angled fairly precisely. While that isn't a "jig" per se, it would work fine to set the angle you need.
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I'm no expert, but here's a summary of some of the methods I've tried recently:
* Veritas Power Sharpening System - search the archives for this if you are interested. As the paper dulls, it becomes difficult to produce a good bevel. At least for me, when the paper is sharp it works pretty well for grinding. However, it is pretty expensive just for grinding.
* 4" belt sander - I bought the Ryobi 4" belt sander/disk combo. It works okay, but I actually think a 1" belt sander would work better. There are finer grits available for the 1". Also, with a 2" blade, I found that the corners of the blade got ground down more quickly than the center. I didn't investigate a lot, but it might be that the paper is curving up at the edges. With a 1", you can correct for this by grinding more in the middle of the blade than the outside, but it is very difficult to correct for that with a 4" belt. With either choice, you have to build your own tool rest, which can be kind of a pain. More details here: http://www3.telus.net/BrentBeach/Sharpen / grinding.html
* 3M 40 micron micro abrasive sheets on glass -- A hand method that is too slow for grinding the primary bevel
* 60 grit Norton 3x on glass -- This is a hand method that is really fast. You can grind the primary bevel in about 60 seconds. However, there are two draw backs. The blade becomes magnetized, which is probably minor, but definitely odd. The other problem is that the edge fractures. It's like chunks of the edge get broken out and it takes quite a while with finer paper to recover from that problem. I didn't notice this problem at first, but have definitely seen the fractures under a 20x microscope. You may be able to alleviate this by not grinding all the way to the edge, but that can be difficult. I tried 80 grit paper and it was slower, but had the same problem with the edge. Anything 100 and below is too slow. If you are going to try this method, try the 60. For more details, see here: http:// www3.telus.net/BrentBeach/Sharpen/norton3x.html Beach and I had basically the same results.
* Norton 80 grit blue zirconia sanding belt on glass -- The belt I got was for a portable sander, so it was pretty short. I couldn't get the paper to glue down flat to the glass. When I held it down with my hand, it seemed to work well, but I didn't do a complete test because I couldn't get it flat on the glass.
* Klingspor 80 grit blue zirconia 8" PSA disk on glass -- I tried a used disk from the Lee Valley Power Sharpening System when I was frustrated with the power system. It worked well, which is why later I tried the sanding belts above. However, the disks are expensive and it is difficult to use the paper efficiently since it is in the form of a disk.
* Course silicon carbide bench stone - Norton makes one of these under the name "Crystolon". It's only $16 from sharpeningsupplies.com. Brent Beach has had some success with that. I haven't tried it. Here's Brent's write up: http://www3.telus.net/BrentBeach/Sharpen / benchstone.html
One thing that I have wanted to try is a good, closed coat, wet dry 60 or 80 grit paper that is designed for sanding metal. The theory goes that the Norton 3x is fast, but is fracturing the edge because it is an open coat paper, which leaves large sections of the edge unsupported as you are grinding. You can buy that at auto paint stores, but I haven't taken the time to go get some. All the places online that I have seen it only sell giant packs.
In my opinion, grinding accurately and quickly without destroying the edge is one of the most difficult parts of sharpening.
Mark
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The edge is not actually fracturing. The large abrasive grains are cutting grooves. With an open coat paper, most of the abrasive grain is exposed. Since there is nothing in the hand grinding process that controls depth of cut, the abrasive is free to cut deeply. A closed coat paper is coated so the abrasive will not cut as deeply. You will get the same effect by going to a finer open coat abrasive.
One thing that I have wanted to try is a good, closed coat, wet dry 60 or 80 grit paper that is designed for sanding metal. The theory goes that the Norton 3x is fast, but is fracturing the edge because it is an open coat paper, which leaves large sections of the edge unsupported as you are grinding. You can buy that at auto paint stores, but I haven't taken the time to go get some. All the places online that I have seen it only sell giant packs.
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The finer open coat abrasives are too slow. Have you tried grinding the primary bevel with a course, closed coat abrasive? Does it work well?
Mark
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The courser closed coat are not going to be any faster. Abrasive grains are pointed. The deeper these points penetrate, the larger the groove it cuts. A closed coating will reduce the depth of penetration thus acting like a finer grain size. With the courser grit closed coat though, due to the wider spacing of the grains, the finish wil be worse. The only advantage to the closed coat is that it holds the grains tighter so your abrasive lasts longer. Everything is a comprimize. If you want speed (with your current system), you are going to get a lousy finish. What time yu saved with the courser grits is going to be cancelled out by the amount of time you spend with finer grits. The fastest way to regrind a bevel (in the home shop) is to get yourself a grinder with goods wheels and learn how to use it. If you realy want quick with a good surface finish, get yourself a surface grinder. A small one should only set you back about $10000.00. It'll do the backs too.

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CW wrote:
<snip - re. open & closed grit trade-offs>

so what would constitute "good wheels" (colours seem to get bandied about, but presumably there could be lots of different wheels that happen to be white, or pink or whatever)? and what do you consider to be the essential techniques one should acquire in learning how to use it?
Also, would anyone care to comment on the low (half) speed grinders? I've read somewhere that they're pointless because the "correct" speed for the abrasive is that provided by the higher rpm. I find that hard to believe because (i) cutting speed is surely a compromise between time and edge heating/damage, and that will vary according to the material being cut; (ii) a slower cutting speed must be cooler - bench stones run very cool!

:)
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*snip*

*snip*
So that's how that happened! I thought it odd that the chisel was magnetized, but wasn't sure how it got that way.
Puckdropper
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On 9 Feb 2007 19:32:20 -0800, " snipped-for-privacy@yahoo.com"

Out of curiousity, does your 4" belt sander tension the paper in the middle, or does it slide over a supporting plate?
I ask because my sander at home has a metal plate under the belt, and I've never had an issue- but the ones at work merely stretch the belt over two wheels (the most common type, from what I've seen), and they behave exactly as you've described.
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My sander stretches the belt between two wheels. I didn't even realize there were other types of tension mechanisms available. What kind of sander do you have?
It's good to hear that somebody else had the same problem and it's not just my technique.
Mark
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wrote:

It's a Delta 4" belt / 6" disc combo. I don't want to mislead you, either- it does stretch the belt with a wheel on either side, it's just that the entire length and width of the belt is pulled taut against a steel plate, and it seems to do a very good job of keeping the paper flat- and also manages to support the edges of the belt, so they tend to die quietly of old age, rather than dramtically flying apart because the edge of the belt got nicked.
This is the one I've got: (Amazon.com product link shortened)
Which I'm a little surprised to see reviewed so poorly, but maybe I just got a really good one. If you need something larger, they have a model Delta 31-695 that has a 6" belt and 9" disc on a stand that looks to be similar in design.

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I've got the same sander. Never a problem.
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snipped-for-privacy@yahoo.com wrote:

<snip>
<snip - lots of useful thoughts and links, thanks>

Interesting. Could it have been that you position your blade in the middle thus wearing the abrasive more there, and then any deviation from this position will expose one edge or the other to relatively fresh grit?
? With a 1", you can correct for this

one of the attractions for me was the ability to do the whole blade in one go and not have to carefully feed it across a narrower grinding edge.

In my price range, for sure!
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I was using a fresh belt and moving the blade back and forth. I don't think this was related to abrasive wear, but it could have certainly been related to lack of technique. The belt is not tight against the platen, so that could have been the problem as Prometheus pointed out. The belt sander is really fast and mine is pretty loud, so I found it a little intimidating. Keep in mind that you can put your own custom platen on the sander if you want a hollow grind or if you want to try to make a slight high spot. I suspect that if I had tried all these things, then my $100 Ryobi sander, which is very similar to the Delta, would have work fine.

My theory here is that with a 1" belt and a 2" blade, you can put the belt in the middle of the blade and grind away more material in the middle of the blade to compensate for not removing material at the edges.

Yes, that was my thinking as well and is why I got a 4" instead of a 1" belt sander. I haven't tried a 1", so I can't compare.
The main thing to keep in mind with the belt sanders (and possibly the grinders) is that using those tools is a pretty "rough" operation. Basically you are just trying to get the bevel close and then clean it up by hand. One reason I have been investigating hand grinding techniques is because you can put the blade in a honing guide and get a more accurate bevel. That seems to be true for me, it is just slower than the power tools. That said, the Robert Sorby belt sander that you provided a link too looks really good. If it were available in the US, I would definitely consider it.
On other thing I forgot to mention is that you could look into a hand crank grinder. There are many pretty many for sale on EBay. There used to be a company called Prairie Tool that made them, but I am pretty sure they are out of business. You might also be able to make a grinder. Lee Valley sells mandrels for this purpose.

If you are really trying to save money, I'd really look into a course silicon carbide bench stone and give that a shot. No matter what you try, I think it is important to just stick with that method until you learn to be proficient at it. (I wish I could follow my own advice.)
Mark
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I have a second-hand Makita, and a budget Woodcraft. The Makita was cheaper (gloat) but I had to replace the bearings. The Woodcraft is still quieter. But you are right - the toolrest and water drip on the Woodcraft is crap.
But the Makita toolrest can use some work as well. It does cut fast, so you do need to spend some time on making repeatable controlled angles.
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You will be amazed how quickly a Tormek will remove metal. I use nothing else for chisels and plane blades.
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Limey Lurker wrote:

Amazement on standby (though I find the cost of the thing pretty amazing:)).... could you give me some idea of how long would it take to, say, reshape the primary bevel from 25 to 30 degrees on a 1/4 inch thick chisel?
rgds, graham.
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