Tools for Working Wood

 Joel's Blog at Tools for Working Wood

How To Grind Part 3 - Grinding Wheel Chemistry and Nomenclature  

01/19/2017


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.

Dressing

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.
Tags:Unclassified
Comments: 6

How To Grind Part 2 - The Technology of Grinding -, Grinders, and Grinding Wheels  

01/11/2017



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.

Grinders
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".

How fast
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.

Variable 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.


Guards
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.

Dust collection
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.

Rests
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.
Tags:Unclassified
Comments: 4

How To Grind - Part 1 - When To Grind  

01/04/2017


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.

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Comments: 11

Happy New Year, A Great Experience, Ideas for the New Year, & News   

12/28/2016


Over Christmas I went upstate to the 30th wedding anniversary party of a boyhood friend and his wife. We haven't seen much of each other lately, and it was great catching up with him, his wife, and groups of friends (some of whom I haven't seen in 20 years). The emotional connection with people and the recognition of the passage of time are part of what makes us human.

For my friends' wedding I promised to make them a blanket chest for the foot of their bed. The plans were from an article in a Reader's Digest book written by my woodworking teacher. It wasn't a huge project by any standards. It took me two years!

"Did you see your chest?" my friend asked.

"No," I said, thinking it was in another room.

"There it is," he said, and pointed to it. And there it was. In the living room, not a bedroom. It was, as you might expect, "part of the furniture." Covered with stuff, and inside, they told me, filled with things they don't use much. The cherry has aged well, and while I have build many far more complicated pieces since, this was one of the earliest things I made. I was really touched seeing the piece. One of the great things for an amateur about building furniture is that you can give it away and people treasure it. Every day they get the reminder of a long-ago connection. Somewhere on the chest I signed and dated it and probably wrote that it was a wedding present. And I put the info under the finish so it will stay put.


Back to the present.

We are in discussions about what products should be add to the store in the coming year. How should we extend the Gramercy Tools and BT&C lines? We have some ideas ourselves, but I would sure welcome some ideas. What are some of the products you wished we made or wished we sold? Send me an email with your suggestions joel@toolsforworkingwood.com.

In order to make space for new stuff, we need to get rid of old stuff. You can see our sale items here. We are adding more and more as we clear out some of the old items. Currently there is a lot of clothing on heavy sale, but more and more tools are being added daily.

I also want to give you a heads up about pricing. We will be raising prices of most of the Gramercy Tools Saws on January 1 2017. We haven't raised pricing in a few years, and our rent has doubled, materials have gone up etc. If you order at the current pricing we will of course honor the price even if we are out of stock and have to ship you the saw later. We are spending this week going over each tool and figuring out out current costs. Rasp prices will stay the same. Brush prices might go up a little but not for awhile.

I wish all of you and your family and friends a happy and healthy New Year. May you all find that piece of scrap that is just the right size for your project, and cut on the waste side of the line.



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Comments: 0

Nail  

12/21/2016


I have written previously about TATHS so I won't repeat myself except to say JOIN NOW, but I just got the current issue of their magazine and in it was a link to a free ebook about nailmaking. Called "A Capful o' Nails" it's actually not about nailmaking but about the evils of working in the nailmaking industry. The book, written in 1896 is a fictional memoir about growing up in a family of nailmaker's and how the father became an organizer. So it's not about the nuts and bolts of making nails. But it is a story about the grinding poverty that effected so many industrial workers, tool makers too, just about all the semi-skill trades. In this particular case nailmaking was outsourced to level upon level of middleman until the lower paid people on the ladder were the actual nailmakers who worked out of their homes.

What I don't understand is that the story takes place in the mid-19th century. At this time in the US nailmaking was mechanized and industrial. We stock Tremont nails, which, depending on the model are still make on machines from this era. I don't know how long hand nailmaking lasted in England but you know that if your job can easily be done by machine (or automation, or a robot) at a fraction of the cost of a living wage - it's gonna suck. And it did.
Here is the link to the book.

The picture above is from the 1811 edition of the London Cabinetmaker's Book of Prices. I own an original copy but you can download a PDF here. The book is basically pages and pages of different types of furniture with lots and lots of special cases and tables showing how much the craftsman would get paid for that particular work. It's not the only price book of its kind, all over the UK and US these types of books were pretty common. But this 1811 edition is the most comprehensive and was used, basically unchanged, for at least a half century. The prices were the result of negotiations between the shop master and the union but under the table, and in non-union shops, prices were routinely discounted. The particular chunk I copied (which BTW is printed in beautiful letterpress- all they had at the time - but it is so lovely) is of two versions of knife case both costing far north of a pound wholesale. A huge amount of money for at the time. This is fancy work for rich people.

If you are traveling this week and you are looking for something to distract you, both downloads might be of interest. This season is when we reflect back on the year and the good and the bad. And also our hopes for the future. Both of these book gave me a sense of the past of the woodworking craft. From "A Capful o' Nails" I learned about the struggle of hard working people to survive. From the "Book of Prices" I got a sense of the work involved to make the furniture I see in museums today.


From all of us at Tools for Working Wood we wish you and your family happy and healthy holidays. With peace and prosperity to all.
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Comments: 2

The Gramercy Tools Saw Etch Story  

12/14/2016


At the of the summer of 2006 Timothy Corbett and I had finished up the first Gramercy Tools Saw - the Bowsaw and were embarking on our next project - a dovetail saw. Earlier today I was writing a blog entry on the development of that saw and Tim shared with me some of the original artwork for the saw etch of the dovetail saw. I put aside my original story for now so I can bring you this.

The Statue of Edwin Booth stands in the center of the park and in the background of the final etch


We figured out that there are roughly two ways to brand a saw. Stamp or engrave the brass back, which was the common thing up to the mid 19th century, or etch the blade with acid which was popular in the latter part of the 19th century. Both of us really loved the artwork of the old saw etches and Tim, who had experience in acid etchings loved the idea of doing a proper logo for Gramercy tools, appropriate for a saw blade. Originally the etch was for a line of panel saws made for us by a third party but when we sent the artwork to the maker he could not do the detail we needed and the project was dropped. We finally found a company that could actually do a real acid etch on a piece of steel. Deep enough to withstand wear and analog enough to allow the classic detail that we wanted in a professional saw etch design.

The first drawing to show the real elements of the final composition


Gramercy Tools got its name because at the time we were located on 20th street in Manhattan and every day I walked past Gramercy Park, the last private park in NYC dating back since 1831. It seemed appropriate to do something related to the park.

A later sketch - we can see a sketch of the holdfast in the corner - an alternate view that was rejected


We started with a narrative idea, a joiner on his way to work in one of the fancy townhouse next to the park. I don't remember if Tim and I had conversations about the content of the etch or if he just came up with the design. But I do know on one hot day in the late summer of 2006 I found myself walking back and forth in front of the 20th street gates of Gramercy Park. I also lent Tim a copy of my reprint 1897 Sears Catalog so he would have some reference material on clothing.

Then he disappeared for a week or so. I only made two important contributions to the project. Complaining to Tim about how long it took him to draw the logo. And I suggested that some holdfasts to keep the etch from sliding off the saw would be a good idea. You can see he wrote "holdfasts" on the sketch.

The background isn't drawn yet but we can see where we are going


Days went by but soon we had finished art. The original is very large and done by hand. We use the etch on a lot of tools and at exhibitions. Depending on the size of the saw the etch will have more or less detail.

N.B. If you wish to see some of Tim's other, non-tool artwork his work is currently in an exhibition at The Invisible Dog open until December 30th. Go see it - it's a great show.!!!

Tim did some test photos to see how the banner bunting would look when held by a holdfast

The final etch with all its details





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Comments: 4
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