Heat damage to blades when grinding...

[David Weaver]

I just ground the chisel, literally a triangle of hardened steel a quarter inch thick and an inch long. Halfway through the chisel was too hot to touch, so I brought a spray bottle over and sprayed the chisel every 5 seconds or so.

Total grind time was about five minutes, no tempering colors appear anywhere on the chisel.

Ian, large amounts of metal should only be removed as a matter of practice when steel is annealed, and I wouldn't want to use a nickel electroplated wheel on soft metal.

Too much of what I did today would probably result in short wheel life.

[Mike Holbrook]

Thanks for making the mega check on these grinding wheels David. Sounds like the pre press was fairly accurate. I can't even imagine grinding that much hard steel that fast. I had to grind something like 1/8" off a Japanese mortise chisel, with a broken corner. I did it with a 120 grit DMT Dia-Flat Lapping Plate. It took 4-5 much longer sessions over two days to get the job done.

So who has tried a Japanese chisel or plane blade on one of these wheels? I am wondering about the softer steel not the harder steel.

[David Weaver]

I haven't done anything not fully hardened yet.

Here's what the grinder looked like after the buildup of the swarf:

IMG_20141102_151244_908.jpg

I spray water freely around my grinder. There's enough loose metal dust, etc, that comes around after this that the rust is never around very long. The spray is only focused at the wheel, not up at the arbor. If there was every anything more than what's on the rest there, I'd stone it off with an india stone or something, anywah.

That matted bit of stuff between the rest and the wheel, here's what about 2/3rds of it looked like...it feels as though it's stuck together like a piece of foam rubber and you can tear it apart like that. When you're grinding, the top layer of it is spark, I don't know what's holding it together, maybe the heat of the sparks.

IMG_20141102_151412_935.jpg

The finish of the wheel is better now than it was when it was brand new. The deep grooves could've been rogue plated particles, or maybe I'm just getting used to the finish of the wheel.

[Steve Voigt]

It doesn't matter if you burn the tool's edge.

You'll do it once, maybe twice. Then never again.

When you do burn a edge, you just need to sharpen it again a bit sooner. No big deal. If you are really pedantic about these things you could just grind it back a bit, which is only 10 minutes of your life gone.

Exactly. The fears about dry grinding are so overblown, though I am sure they are useful to the purveyors of expensive alternatives to dry grinding.

I have been using a hand-cranked grinder with a very course wheel and Veritas tool rest. It takes slightly more practice than a powered grinder because you can only use one hand but it is still easy to get a nice, even grind. You have precise control over the speed, obviously, so it is really difficult to burn the tool and you can grind right to the edge.

I bet your results are just as good as those spending hundreds or thousands more than you've spent.

I have only been playing with sharpening for a few years. I am still learning and improving. However, the grinding seems like the least difficult and least important part of the process. I don't understand why a special machine is necessary. Buying a Tormek for a home woodshop seems like buying a Lie Nielsen scrub plane (although the comparison is unfair because Lie Nielsens are, at least, pretty).

Agree again, though I don't want to minimize the importance of good grinding technique, because that can save gobs of time.

Great post! This is only your 3rd? Looking forward to more!

[ian maybury]

Thanks for being so brave with your (80 grit/low speed grinder?) wheel David. I won't be able to go at it like that in my trial later this week as it'll be somebody else's grinder.

That's mighty impressive - much more aggressive than presumably most users would try anyway. Especially given the relatively narrow chisel. My tendency would be to seek to form a bevel in passes - out of caution. The chisel bevel looks very decently finished as you say too - tends to suggest that the 80 grit wheel alone might be a reasonable choice for bevel grinding once run in. There's two sides to that: (a) cost saving, but (b) it leaves the other end of the grinder free to put a stone on for more general purpose mild steel and other grinding - presuming you have one grinder.

The other positive is the almost (from this distance) pristine condition of the wheel after what (especially with a narrow workpiece/high pressure) was probably a very decent work out. There's no very obvious change in look/colour around the corner where presumably you didn't grind. A look with a loup would be interesting - did it tear out any grits for example?

I've seen a build up a bit like you got when heavily grinding mild steel fabrication parts on a std carborundum wheel, except that yours looks less tightly bonded together. My impression then was that it was caused by molten or almost molten particles of steel bonding/sintering together - suggesting that a lot of the heat is transmitted into the grinding dust...

[David Weaver]

I think I get edward's sentiment, that grinding is just something you need to do and you need to get on with it sometimes.

i do agree with the other comments, though, that getting precise allows you to sharpen with anything. I can sharpen modern steel with oilstones or japanese natural stones as easily as I ever did with synthetic stones, and with more control. It's worth really getting the results in order and whereas the comments used to be about not waiting to go to the stones (as in never work with a dull tool), I'd say it's critical to me to not wait in going to the grinder. 3 or 4 hones on a grind and back to the grinder again rather than working a large area of steel.

[Mel Fulks]

Good to see them ready for employment!

[ian maybury]

A PS on grinders, especially @ Mike:

It's as you said very difficult to find (especially over here) a decent grinder that doesn't cost an arm and a leg, but which at the same time is good enough to at least be a predictable quantity in terms of runout and balance.

Creusen in Holland do some well regarded models, but they are not I think sold in the US. They don't have a low speed in 8in, but this seems not to matter given David's result. It's unclear whether their 8in model has enough shaft length to handle 1 1/4in wide CBN wheels. The underlying shaft is 15mm dia, which if accurate is inconveniently just smaller than 5/8in. (which might possibly explain why they are not sold in the US) : http://www.brimarc.com/products/Creu...nder-22330.htm

The stand out option coming up for me (in a somewhat higher priced/higher spec/better quality but not daft money grinder) is the 8in Metabo DS 200 bench grinder which is also sold in the US. It's a normal speed (3,570 rpm in the US on 60Hz, 2975 rpm here on 50Hz) grinder. Might be worth putting some time into adapting one (presuming it's practicable) if it's as smooth as in the first video below. (PS added later - both David and Derek are usig low speed grinders - so that probably rules out the Metabo - see below)

It lists 32mm grinding wheel bores, and it isn't clear if it has enough shaft length to handle a 1 1/4in wide wheel. Looks judging by the parts list below like the 32mm bore comes from a wheel mounting and spacing sleeve slid over the actual shaft. Could be that the sleeve can be machined to suit the width WTW CBN wheels - but questions remain. What diameter is the underlying shaft, and is it long enough given that the stock wheels are 1in wide.

I plan to phone Metabo in the UK tomorrow to enquire, but in the meantime it'd be great to hear from anybody who has one....

Some DS 200 Metabo related links:

http://www.youtube.com/watch?v=Ufx6CSm8TSM (hear one running - 0.41 and on)
http://www.youtube.com/watch?v=rBw1QPDqTfY (lousy voice over)
http://www.ereplacementparts.com/metabo-ds200-19200420-8inch-bench-grinder-parts-c-8879_9109_291299.html

ian

[Mike Holbrook]

I found the Metabo DS 200 over here too Ian. The information I found said it ran at 3750 rpm, faster than the average which is why I stopped looking at it. I will probably stick with the Delta 8" Variable Speed Grinder for now. It runs smooth with the new wheels on it. I tried putting a washer on it since I did not have a penny and it stayed pretty much in the same place. It runs fine without being bolted down, although I will probably bolt it to some surface sometime so I can position a tool rest consistently. It seems to have as large a following as anything else and I know people who have used one for many years. The 2000 low speed is a little faster than most low speeds but it is nice to be able to turn the speed up or down. The arbor on the Delta may be a hair short for the 1 1/2" D-way wheel but I believe I can fix that easily with a thinner washer or different bushing that I understand D-Way makes for short arbors.

[ian maybury]

Thanks Mike. I was suffering brain fade. David and Derek are both using slow speed grinders with 8in dia CBN. I've added PS to my posts above so as not to mislead. Pardon me.

For anybody looking in from over this side - another look turned up this low speed 8in/200mm dia x 1 1/4in (32mm) width wheel grinder in the UK from Axminster one of my usual suppliers. Not sure how i missed it: http://www.axminster.co.uk/axminster...unning-grinder May not be the right shaft size, but that's fixable. Trouble is I've seen a very similar example get bad press from Derek for rough running, so it needs checking out.

No sign of any reviews of it - but their house stuff is normally pretty good...

ian

ps another Australian grinding jig: http://www.woodworkersinstitute.com/...ry/IMAGE-2.jpg

[David Weaver]

I'm using a regular speed 6 inch grinder, which isn't much different in wheel speed than an 8 inch slow speed.

I didn't notice any damage or stripped grains on the wheel, but it does seem to be a little more broken in on that spot. Still cuts (and sparks) plenty, though.

My grinding is definitely not any harder on the wheel than the round scrapers, etc, that only have one point of contact on the wheel. I just ground that by holding the chisel against the wheel.

[ian maybury]

Thanks for that David

[David Weaver]

Good to see them ready for employment!

They are very nice chisels, very cleanly finished. I already have a 1/2" timber framer, but it is unmarked and not as nice.

[ian maybury]

Just to report on the brief trial run tonight on a very helpful wood turning contact's CBN wheels fitted on an 8in 1,425 rpm slow speed bench grinder (he's been running the fine one sharpening turning tools for months and reports no signs of wear) - in this case one was a 'fine' Optigrind. Probably the 'fine' 8in listed here http://www.toolpost.co.uk/pages/Grin...ng_wheels.html They don't grade in terms of grit - but it looks like 180 or maybe even finer. The other a very coarse CBN wheel by another unknown maker.

I brought an old bevel down plane blade to play with. Basic observations:

1. CBN removes a lot more material than aluminium oxide for a given grit size - for very little pressure, and very little 'drag' on the wheel. The fine wheel above cut much faster than for example 80 grit AlOx on a belt sander, and with almost no sparks - it cut a new bevel on a 3mm plane iron in minutes. It'd be even faster to re-face a bevel/remove a honing bevel. A CBN wheel reportedly significantly speeds up a Tormek compared to the stock wheel too.

2. Heating as David found is very low. Three or four passes across the wheel formed the bevel, but the blade by this stage was just on the hot side of warm. Still easily handled - which means significantly less than 60 deg C. Very impressive.

3. The price of this free cutting and low heating seems to be (for a given grit size) deeper cuts/scratches in the surface than would be the case with even a much coarser AlOx grit. i.e. AlOx grits seem to break down quickly, and to as much 'wipe' material off the surface as cut it away. This possibly smooths the resulting surface somewhat, but probably also contributes to drag/friction and heating. My guess is that the CBN grits remain intact/function much more clearly as individual cutting points. (?)

4. The coarse wheel (which was new) was much more aggressive. It removed material significantly more quickly, but produced more sparks (still low heat) and left a very obviously grooved surface. i.e. running a thumbnail at right angles over the grooves resulted in obvious bumping/clicking. Rough enough that I think I would (guessing since the option wasn't available to hone the blade) prefer to use something finer before moving to honing on waterstones - for fear that it would require significant honing to get back down to a smooth edge and undisturbed metal.

5. Grinding throws out signfificant amounts of metal dust - enough to 'taste' half an hourafter working. Steel dust/mill scale is not harmless: http://www.gerdauameristeel.com/prod...%202-15-12.pdf CBN dust is likely not good either - there's some cobalt, boron plus all sorts of metals in there. My insincts are to wear a decent dust mask, and to ensure that I have enough extraction in the area so that the air is moving away from me.

It's very hard to draw definite conclusions based on this limited test and since there is reportedly quite a lot of difference between different maker's wheels, but i've decided to invest in a grinder and some wheels. On the basis that presuming it lasts well CBN seems definitely to offer the ability to remove metal fast enough with low enough heat input to efficiently get the heavy bevel forming jobs done that have previously caused me problems - while at the same time remaining controllable on smaller tools.

I'm going to buy an 80 and 180 grit pair because shipping is expensive to here, because for me the ability to remove metal quickly matters (not necessarily everybody) and because there's discount from Mike's source for a pair: http://woodturnerswonders.com/produc...esign-180-grit It's possible however that something like the 180 alone would cover most normal sharpening requirements for many people, and leave the other end of the grinder free for a more traditonal stone for knock about grinding - hard to know.

Separately I got lucky on sourcing a grinder - it turned out that a fairly local supplier (unusually) had a stock of the above 8in low speed 1,425rpm bench grinder. He even helped me by doing most of the work in hand picking a good one - we ran a few with the wheels off to check for a true running shaft and reasonably well balanced motor. I'm sure it's very normal with budget eastern bench grinders, but the test tended to suggest that they vary quite a lot in this regard. Also that any underlying balance and true running issue can easily be greatly worsened by loose fitting and/or imprecise wheels and spacer sleeves. I've a sneaking feeling I'm goingt to end up turning up a set of accurately fitted spacers/sleeves.

The latter is likely to matter quite a bit with CBN wheels - any 'bounce' will reduce control, and tend to wear only one part of the wheel. Bottom line - it's not for nothing that an accurate grinder like a Baldor or a Toycen Tradesman costs lots of money….

ps some more grinding rests: http://www.woodworkersemporium.com/woodworking_tools/Woodworking_Sharpening_Tools?page=2

[Mike Holbrook]

A little more information on the new WTW wheels arrived in my email. Apparently the wheels with the thicker edges were quite heavy so Ken elected to change the metal his wheels are made from. I thought the new wheel I got looked like aluminum and according to the latest info. on WTW that in fact is what it is. According to the information I was recently sent from WTW the old wheels were almost 8lbs each and the new ones would have been even higher so they elected to use 6061 aluminum. Apparently the electroplating process works better on aluminum too. I think the inside corner of the new wheel may be a little different than the standard 1/4" rounded edge if I am understanding the new information:
"There is a 9 mm 90 degree gap (about 1/3 of an inch) space shoulder on the inside edge of the grinding wheel for making relief cuts or tapers on hook type scrapers or box scrapers."