In previous blogs we discussed the need for grinding for a variety of reasons. This final reason is the most unfortunate one: you need to repair a damaged cutting edge. This problem could come about from dropping the chisel (see photo), burning the steel from incorrect grinding, or any number of crises. If we were to grind out the damage by just grinding the bevel like we normally do, we would burn the steel and create more damage. The drawing illustrates the problem. Constant grinding on the bevel heats up the entire bevel. When the damaged tip get heated, the heat has no place to go - especially when the rest of the bevel is heated up too. Even with a cool wheel, this will be a problem.
The solution to this problem is simple. We first level up the tool rest and grind the chisel end square past the damage. As we are only grinding at the tip, not the entire bevel, there is little heat, and the heat has someplace to go (see sketch).
I can free-hand grind pretty square on a crowned wheel, but a scribe line to guide your grinding can be useful. Or after grinding, a few passes on a stone to ensure a straight edge can be helpful. If you are a little off, it doesn't matter. Final honing fixes everything. As you can see in the picture, you want to grind back to an even flat just past the damage on the chisel.
Then we will reset the rest and grind to a wire edge, just like we did before in Part 5. The only difference is that instead of setting the rest to grind in the middle of the bevel, we want to grind a bit towards the back of the bevel to compensate for the blunt edge we just ground. If you are shortening the bevel angle and not really correcting damage, you would also grind a blunt end, but not move the bevel back.
In Part 5, when I ground the chisel I checked to see my bevel disappear, then stopped. In this case, the bevel will disappear fairly quickly, but my work will not be done until I have removed the blunt end. As I grind, I look to see that the flat end starts to disappear. In the first photo, the flat end is about half gone (and uneven). I continue the grinding, with more effort on the thick side, until both sides are even and the edge (seen as a white refection in the light) disappears. Then I am done and ready to hone.
For instructions on honing your freshly ground edges - click here.
Also searching my blog will turn up a lot of sharpening material from past years.
Finally if you are in the NYC area I will be teaching both grinding and honing in two free classes in March. Please see the events menu for the exact schedule, more classes will show up shortly.
In the last section, we prepared our grinding wheel so we are ready to grind our chisel.
Before you grind, you have to make sure that the back of the chisel is flat. Now I don't mean flat for its entire length. I mean, from left to right at the cutting edge only - maybe a 1/16". (For the reasons why you don't want to flatten the entire back, click here.)
We need flatness at the edge so that the back will be an accurate reference for grinding. If the back isn't flat when we hollow grind, we would hit the edge at different points and not have a straight ground edge.
Next, we have to set the rest at the right angle. In general, I don't try to measure the angle; I try to maintain the current primary angle of the tool. Put the tool flat on the rest and rub it back and forth against the wheel of a grinder that is turned off. Rub it a few times to establish where you are making contact. A sharpie applied to the bevel will make the scratches more prominent. If the scratches are in the center of the bevel, then you are simply maintaining the current angle of the chisel. If the scratches are past the center towards the body of the chisel, you are increasing the grind angle. If you find yourself with scratches forward of the center, you will be shortening the bevel angle. This latter condition is bad for two reasons. One: you rarely need to shorten a bevel angle. Two: even worse, when you grind, you will hit the fragile thin tip of the chisel before you touch the back bevel, resulting in an uneven grind. And if you continue grinding at the tip, you will most certainly burn the steel. There is a simple technique for shortening the bevel without danger, but we will save that for next time when we discuss repairing damaged chisels.
To get the rest in the right place, I use a mixture of moving it carefully and tapping with a chisel handle. When I think I am done, I will put on my eye protection, make sure all loose clothing and hair is tied away, lower the shields (although for the purposes of clarity in these pictures the shields are retracted), put a large cup of water within arms-reach and get ready to turn on the grinder.
As with wheel dressing, I stand to one side when I turn on the grinder and let it come up to speed. Then, with the chisel on the rest, I touch the bevel to the wheel and then pick up the chisel to look to see where I actually made contact. If I am grinding where I want to be then I will continue, otherwise I will tap the rest to move it slightly, or possibly loosen the rest a very, very tiny amount so that then I can tap it to the right place. Be very careful here. In theory, you will only need at most a minor adjustment but it is easy to slip, especially if you have loosened the rest too much, or are twisting by hand too hard. The rest could turn into the wheel, jamming it, with disastrous results.
With the rest set correctly, I start grinding.
As you can see from the video, I place the chisel firmly on the rest and just going back and forth on against the wheel. Periodically I check to see how far I have gone, and if I neglect one spot or another, I pay more attention to it. In the beginning I concentrate on the center of the tool; as I get further along, I start grinding towards the sides. As I approach the edge, I am trying to work in a uniform way. My finger rests on the back of the chisel, and if it gets warm, I will instantly dunk the tool in a water bath. However with these CBN wheels (or a well dressed, crowned, 3X wheel) I find myself not needing to dunk frequently if at all. Paying attention to what is actually happening is the key here.
I typically grind to a wire edge, but many people don't, and leave a smidgen at the edge. In either case there isn't much to hone away.
In the last picture, you can see a chisel that was ground freehand against a crowned wheel. It probably isn't perfect, but it's pretty close. Any variance in my grinding will be straightened out instantly when I start honing on any flat stone.
Next week we'll show what do to for a damaged chisel or one for which we want a shorter angle. We need to remove a lot of metal without overheating the tip.
N.B. As you can guess from the video, I am new at video making. I'm still learning, but I hope even in this crude way the information is getting across.
When you first mount a wheel on your grinder, the first thing to do is make sure the wheel makes a nice ringing sound when tapped. Tap the wheel gently with a handy bit of steel; it should ring with a fairly bright sound. If there is a defect in the wheel, you won't get a clear tone. Now to be fair, in general modern wheels are very safe, and it's rare that you will get a dud. I certainly have never had that misfortune. I only use new wheels from a reputable manufacturer. An old wheel from Ebay; a Brand X wheel; or a wheel that comes without protective packaging would all be far more susceptible to failure. If you don't get a clear ring when you tap the wheel, do not use the wheel.
You want make sure that the wheel is the correct bore for your spindle. In the case of these 3X wheels, Norton supplies plastic bushing so that the wheel will fit a variety of spindle diameters. There still is a little slop, but not much - it largely doesn't matter. When you clamp the wheel in the grinder (unplug the grinder first, of course), the wheel is sandwiched between two flanges. On either side of the wheel is a cardboard washer. In this case, the washer is glued to the wheel and contains branding. These washers are very important. Clamping between cardboard takes up any minor irregularities in the flanges or wheel and prevents a minor unevenness in the wheel from causing the wheel to crack when clamped up.
When you first get a new wheel or if you are seeking the best performance from a wheel you already have, dressing the wheel is vital. Inevitably the wheel will not sit perfectly on the spindle. If it's mounted slightly off center, dress the wheel to make it centered. This step is important for the wheel to run smoothly. I know some vendors sell balancing kits, but I have never needed one. I am also going to set the rest approximately square to the wheel and fairly close to the wheel. Square because I want the dresser to approach the wheel square, and fairly close because I want to avoid any chances for the dresser (or anything) to get caught in the gaps between moving wheel and rest. After checking that my rest is clamped solid and the wheel can rotate freely by hand, I will lower the guard, put on my eye protection, and turn on the grinder.
Whenever I turn on a grinder I step aside as it comes up to speed and runs for a few seconds. The reason is that just in case there is a flaw in the wheel, or a chip got knocked out, or something is caught in the guards, I would rather not be in the line of fire if disaster happens.
For a new wheel, I want to hold my dresser firmly against the rest and push it forward to contact the wheel. As long as my dresser is held steady against the rest, any high or low spots on the wheel will get dressed off. Don't clamp it; you need to be able to move it forward, and your hand pressure is more than enough. In a few seconds the wheel will be tracking round and round and run smoothly. You might notice a wobble from left to right as the wheel rotates. There are two possible reasons for this. The first (and more common reason) is that the flanges aren't flat. Baldor and many other makers don't machine their flanges, they just die-cast them. We have seen plenty of wobbly flanges over the years, so one hop-up we do on our custom grinders is to machine the flanges. Cast flanges can result in wheel wobble. (We do not sell cast flanges.) A little left-to-right wobble is no big deal. Don't worry about it. DO NOT under any circumstances try to dress the sides of the wheel. Wheels aren't designed for that. They could explode. In any event you will probably make the matter worse. If you encounter a lot of vibrations, a lot of wobble, it could be caused by a uneven, poorly made wheel. In that case return it. There is no way to fix that.
Once the wheel is dressed round you can lighten up on the pressure on the rest.
We now want to dress the smallest of convexity, or crown, into the wheel. With a convexity we can be assured that every time to touch a tool to the wheel we are making contact somewhere in the center of the tool. If your wheel is straight, and your tool is basically straight, the wheel face will always contact the tool at one side or another -- unless your blade is 100% square to wheel, which is nearly impossible to do freehand. With a convex wheel you don't have to grind the corners of your tool until you have ground the middle, which is safer. In the middle of the tool, heat from grinding can go towards both sides and back into the body of the tool. At a corner, heat can't escape at one side, which will rapidly cause a corner to overheat and burn. With a convex wheel you have a controlled point of contact and as you feed the tool into the wheel, you get more and more contact - you aren't grinding just at that point on the wheel. We will go into this in the next chapter when we actually grind a tool. For now, suffice it to say that we need to is put the smallest convexity we can on the wheel.
My process of dressing the wheel: Turn on the grinder, wait until it comes up to speed, and then touch my dresser to the wheel and move it in a very wide arc across the wheel. While doing this, I eyeball everything. The basic step is contact the wheel in the center with the dresser, and then swing it around to either side. As you can see in the video, the process takes about 10 seconds.
With dressing done, we are now ready to grind. I repeat the dressing process just about every time I grind -- and whenever I think the wheel seems to be heating up too fast. Of course CBN wheels never need to be dressed and the wheels we stock have the crown built in.
Next time we are going to set the rest to the right angle and refresh the hollow on a tool.
Part 1 is here. Part 2 is here.
Up until the late 19th century, grinding wheels were made of natural rock. Sheffield, England - that great center of edge tool manufacture - became the center it did because it had a lot of water power and, right outside the city, mountains of sandstone perfect for making grindstones. To this day, in the mountains of Derbyshire around Sheffield you can see remnants of grinding wheels everywhere. The problem with natural stones is that they are rarely consistent. If you are lucky, the inconsistency is just a hard or soft spot in the stone. If you are unlucky, a hidden flaw could cause the stone to explode. Another problem with natural stones: their grit is whatever their grit is, regardless of your expectations or needs.
In the late 19th century, Norton, an American company, figured out how to make a vitrified stone. The basic concept is simple. You take abrasive powder and mix it with a binder. Then you press it into a wheel shape and bake it in an oven. By varying the grit and binder you can make wheels with all sorts of properties.
To alter the abrasive aspect of the stone, you can vary the grit size. Coarser grits grind cooler but rougher. The space between the larger grits have more air and turbulence and keep the grit cooler. You can also use different abrasive materials for different purposes. Silicon Carbide grinds quickly but shatters under pressure, so your wheel will grind very fast for a short mount of time, then heat up as it rubs more than cuts. Aluminum Oxide crystals fracture slowly and therefore run much cooler - at a slightly slower grinding speed. Newer materials such as "seeded gel" are designed to fracture slowly along a crystal structure so that they still cut fast, but also run cool. Our 3X wheels are a consumer version of seeded gel and are the coolest running vitrified grinding wheels available.
Vitrified wheels can also have variable "friability." Friability means how much force it takes for the abrasive to detach from the wheel. A very friable wheel will constantly be losing particles as you grind. This is very messy, but each time you lose a grain of abrasive you also lose the heat on the grain. More importantly, this particle loss exposes fresh, sharp abrasive.
Finally, just recently, CBN plated wheels have come on the market. These wheels are a totally different technology and need to be looked at separately.
Lower grits run cooler; softer wheels run cooler; Seeded Gel (3X) runs cooler than Aluminum Oxide (AO); and everything runs cooler than Silicon Carbide.
To keep a wheel sharp and cutting cool and fast, you will need to regularly dress the wheel. This is a very critical step. More (lots more) on this later.
If you look at the side of a vitrified wheel, you will see a coding showing the material the wheel is made of, the grit, and a letter indicating hardness. If you are sharpening High Speed Steel (HSS) turning tools, which are very resistant to overheating, you can be less worried about heat than about surface finish. For regular carbon steel, heat avoidance is an important issue.
With a light touch, a properly dressed wheel, and a coarse enough grit, you can grind just about anything without overheating. But softer wheels with cooler abrasives make the job much easier.
For regular grinding of edge tools, I prefer a 3X wheel in either 46 or 60 grit. The slightly finer texture is a personal preference. For aluminum oxide wheels, I would want something even coarser - maybe 36 grit? Because I'm not a woodturner, a softer, more friable wheel ("I" Grade) is my preference. If you are using a 3X wheel also for grinding turning tools, you might want a "K" grade wheel. The stock wheels that come with most grinders are typically very coarse and very hard. While you can make them work for grinding edge tools, this option is far from optimal.
None of these wheels will work properly unless they are regularly dressed. Dressing consists of rubbing a very hard stone or a row of diamonds against the rotating grinding wheel. This encounter rips off the top layer of the stone and exposes fresh, clean, SHARP grit. Sharp grit cuts faster and cooler. One way to make a hard grinding wheel run cooler is to dress is regularly. We also dress wheels to get any eccentricity out of them when we first mount them and when we want to curve the surface to make grinding easier. More on the technique of dressing later.
The typical wheel dresser is a block of rough diamonds, either plated to a stick or part of a matrix. What you need to know is that single point diamond dressers are used in tool post grinders for precisely shaping a grinding wheel. We are hand holding our dresser, so a multipoint dresser is far more effective.
Our final choice is plated wheels. The newest grinding technology uses CBN (Cubic Boron Nitride) abrasive, a synthetic, diamond-like material that is plated onto an aluminum substrate wheel. Diamonds, being carbon-based, have a serious issue when grinding tool steel. The carbon on the tools and diamonds want to bond, and - even worse - diamonds are heat insulators, so like vitrified wheels, they reflect heat back into the tool. CBN, on the other hand, absorbs heat and the aluminum wheel just soaks up more heat. So the single coolest way of grinding these days is on a CBN wheel. And the bonus that you do not have to dress the wheels. The only caveat is that non-ferrous metals will clog the CBN wheel so if you mount a CBN wheel on your grinder, keep one side for a traditional wheel so that you can grind other stuff besides tool edges.
My current favorite grinding wheel is a 60 or 80 grit, crowned CBN wheel. The crowning which I will talk about next time is an important step for dressing and since you don't have to dress a CBN wheel. my CBN wheels have the crown built in. The downside of CBN is that it is more than twice as expensive as my next choice - a 3X wheel. But I really like the lack of maintenance and with no wheel dust flying off every time you dress the wheel I like the less mess.
I forgot to include a picture of a wheel dresser. I'll make up next time in part 4 when we mount our wheel on a grinder and dress it.
Part 1 is here.
These days when shopping for a grinder you have a huge number of choices. From $50 dry grinders from Asia to very expensive slow speed wet grinders with lots of attachments and everything in between. When I was studying woodworking (a long time ago) my teacher, who knew a lot about lots of stuff was scared of grinding. I think this is a common fear. We had a high speed grinder, with who knows what kind of wheel, no wheel dresser, and the fear of burning (overheating) the chisel was real. Burning was way to easy to do and the cure was grinding past the burn - which exposed you to the same issue only with a shorter chisel.
So many people are so scared of burning that they do all their rough work on very coarse diamond stones. This isn't totally off base either. In Japan having a grinding wheel on a jobsite was uncommon and working coarse grits on a stone was very common. In England (and the US I think) up until the invention of the small electric motor in the 1900's most people did not have ready access to a grinder. This especially applied to carpenters and joiners who worked on site. Saturday was the big day for hardware stores when craftsman took their tools to be ground if needed. Hand cranked grinders existed going back centuries but you need an established shop to work in and grinding wheel technology was natural stones which cut slowly - so it made sense to pay someone else to do it.
The revelation for me was when Barry Iles of Ashley Iles visited my shop. He needed to grind something, found my grinder, took all the guards, jigs, and thingies off it. Turned the grinder on, dressed the wheel, then touched the chisel he needed to grind on the wheel and was done 5 seconds later. I said "hey - can you teach me that" And he did, turning my entire fear of grinder away. It's not hard to learn. Actually it's pretty easy to learn.
There are many factors involved in selecting a grinder.
Cost - that's pretty obvious. You can buy something that spins a grinding wheel for fifty bucks and it can work. As you work your way up the cost chain you get better materials, better motors, larger wheels, better bearings and more solid rests. Not to mention better customer service.
Wet or Dry
Professional grinders try to grind wet. This solves the cooling problem and you can grind fast. Until recently wet grinders were big complicated machines that were not designed for a home shop. In the past generation Tormak, a Swedish company, introduced a 10" grinder with a water bath for the wheel. Also available from Tormak are some of the best grinding jigs in the industry. It isn't an inexpensive piece of kit but the Tormak is very well made. My issue with the Tormak and all consumer wet grinders is that they are way too slow. The reason professionals grind on big wheels with a water spray is so that they can grind really really fast. The Tormak has a water bath (good) but it also turns really slowly and grinds really slowly (bad). As you get better at grinding the jigs are less and less useful.
Belt, Flat Grinder, or Wheel
Up until recently professional grinders all used large (4') grinding wheels but increasingly belt sanders of various sizes are also popular. A belt will run cooler, and you have a very large selection of grits. We have knife grinding equipment here and can easily hollow grind on a belt. However most less expensive equipment doesn't have that option and since one requirement of mine is being able to grind hollow, a belt sander isn't really a great choice for general woodworking tool sharpening. I have the same issue with flat grinding systems that use abrasive disks. In general they work slowly, I like a hollow grind, and I don't like having to replace disks. One point that should be mentioned. With some of the flat grinding system that use abrasive disks, and belt sanders (but to a lesser extent) you can not only rough grind but also polish. We power sharpen some carving tools on a Koch machine with uses paper wheels. Flat grinders can also polish but in general with a hollow grind I think hand honing is easier, less fussy, and faster.
How big a wheel
We stock two sizes of grinder: 6" and 8". 7" grinders had a certain vogue but currently there are fewer options for wheel selection. For normal woodworking a 6" grinder is all you need. You get a nice hollow grind, and the grinders aren't huge. Lots of turners however like an 8" grinder because the hollow is less and for some turning geometries a deep hollow is a disadvantage. An 8" grinder weight a lot more than the 6" which is great if you don't have to move it. My suggestion would be that unless you turn go with the 6".
The surface speed of a grinder is what dictates how fast we grind and at what speed. Many people recommend slow speed grinders - a 6" grinder running at 1800 RPM as a great way to avoid burning the steel (and it is). A 6" 3600 RPM runs twice as fast and grinds twice as fast, and by the end of this series you will be able to grind on it with no real risk of burning. We stock 8" 1800 RPM grinders which a surface speed between the 6" 1800 and 3600 machines. While faster (3600) grinders exist I don't recommend them, they grind very fast which can be an issue with heat, but also lots of the better 8" wheels aren't really designed for that speed.
A couple of vendors offer variable speed grinders for sale. In general the top speed is slower than 3600 so what you end up with is a slow speed grinder that can go slower. In addition variable speed electronics are just not as reliable as a fixed speed. And why would you want to grind slower once you learn to grind faster. So I cannot recommend them.
With modern wheels there really isn't much of a risk of a wheel exploding. But an exposed wheel is always a hazard. A spinning wheel can grab a loose thread or hair, and rip off your arm or head. A trip and fall can have you grab out to a spinning wheel or have a tool ripped out of your hand with disastrous results. Baldor grinders, which we stock use heavy cast iron guards. That might be overkill but no matter what grinder you use make sure it has guards.
Eyeshields are also important to prevent flying debris. However even with shields always wear eye protection. Hopefully you will never need it. Over the years I have - more than once.
Grinders spit burnt steel and abrasive dust behind them. Some grinders (like the Baldor) have proper dust ports built it. Unless you have a dust collection system only for metal DO NOT connect your grinder to the dust collector. Metal sparks from burning steel and wood dust on a container are EXPLOSIVE.
My grinder is just far enough away from a wall so that it doesn't make to much of a mess.
We want a rock solid rest that won't move or flex during grinding. Some people clamp the tool in a jib and move the jig on a specially designed rest. If you plan to do the latter I suppose no rest is needed because you are going to replace it. Most rests that come with grinders are either cast iron or aluminum or bent sheet metal. Sheet metal sucks - it just bends under pressure. Cast aluminum is fine although it does get scratched from the abrasive dust. The grinders we stock have rock solid cast iron rests. These are by far my favorite. Solid, heavy, and no flex whatsoever. I think no matter what grinder you get if the rests aren't solid either buy an aftermarket rest or make something solid. It doesn't have to be complicated. I adjust my rest by getting it into the approximate correct position and tightening the clamps and then tapping it to final position. The method looks cludgy but works well.
Unlike a printed magazine which has page limits on a blog you can go on and on and on. Which it seems I have done here. On one side this is far more information that anyone actually needs, but I am trying to cover all the questions that I regularly get. As I have gone on at such length I think I will put "Grinding Wheel Chemistry and Nominclature" in part 3.
Happy New Year! I thought I would start off the new year with some practical woodworking information. I have always thought that a grinder is one of the most important tools in the shop -- and it's also one of the least understood. While I do teach an occasional class on grinding at our shop (and will do so again in the future), most people don't live nearby, so written instruction seems in order. The last time I wrote on this subject, in the June 2008 issue of FWW, the response was overwhelming. But I have learned stuff since then, and technology has evolved.
This series on grinding will be in four parts:
1 Introduction + reasons for grinding
2 Grinding wheel and grinder technology
3 The angle to grind at, wheel dressing, and how to grind to maintain the existing bevel
4 Grinding to repair an edge
Parts three and four are hands-on; the rest is theory and background information.
There are three reasons to grind.
1 - To Maintain a Hollow Grind. Grinding an edge tool against a curved wheel will always result is some sort of curvature on the bevel. The larger the wheel, the less the curvature. We call this "hollow grinding" (see picture). Producing a hollow grind enables easier and faster honing. When you think about it a bit, the only part of the chisel that does any work is the cutting edge at the very tip. The rest of the chisel is just support for the edge. So the steel in the middle of the primary bevel is basically waste. With a hollow grind when you go off to hone the tool after grinding, you get a very stable platform of the tool solidly supported at the front and back edges of the bevel. You won't be wasting energy, stone wear, and time removing the middle of the bevel, you'll also get a simple way to make sure you are always honing at the edge. All the force is applied at the edge, and there is no tendency to wobble or rock the chisel. Hollow grinding GOOD!
2 - To Restore or Change the Geometry of the Primary Bevel Angle. Personally I am not fussy about bevel angles. The lower the angle of the primary bevel, the less force it will take to push the chisel into the wood. With less force comes more control. The trade-off is a thinner, weaker edge. A higher primary angle gives you a stronger edge, but more force is needed to punch it into the wood, and with that comes less control. The traditional angle of a bench chisel is 25° but a little more or less isn't a big deal. Paring chisels should really be lower by at least 5° and mortise chisel higher by the same amount. Every once in awhile I realize that my geometry on a particular chisel or plane blade is off enough to annoy me. This usually happens because after several years of honing I find the bevel angle getting steeper. These days, however, as I am hollow grinding to make honing easier and I don't have this problem at all. I'm also not personally adding new chisels to my toolbox - but certainly someone building a shop will always have "new to them" tools that need a geometry change.
3 - The Unfortunate Reason: To Restore a Damaged Edge. Probably the most frequent reason I end up grinding something. Chisels, plane irons and other display tools in our showroom get handled all the time and get dropped. Repairing a damaged edge is a little more involved than a just maintaining the hollow, but there really is no better way of repairing a damaged edge. Honing past damage, even with a coarse abrasive, just takes a lot of time and elbow grease.
The issue that many woodworkers are scared about when grinding is heat. The basic problem is that (with the exception of turning tools made from High Speed Steel (HSS)) if you heat up a hardened piece of steel past 400 degrees it will get start turning brown and blue and get softer -- and most importantly, it won't keep an edge anymore. HSS is called "High Speed Steel" because it can be heated up way past 400 degrees and yet stiff hold an edge. But in general, HSS won't hold a sharp enough edge for woodworking, and it's very hard to hone. The goal when grinding an edge is to achieve a ground edge without overheating or "burning" the edge. And a more important goal is to be able to consistently grind without burning because otherwise the crap shoot of what will happen is too scary.
There are three (or four) basic approaches to keeping cool when grinding. Use a very slow grinder. Use a grinding wheel that allows speedy steel removal without heat. Use some sort of coolant, such as water for wet grinding. Finally in parentheses: (grind really slowly and gingerly). The goal for me is to grind as fast as possible without any real danger so in Part Two we will talk about wheel and grinder selection, and how to keep a wheel grinding as cool as possible.