Sharpening Question

[bluthart]

What is the appropriate grinding wheel to sharpen turning tools? Blue, white or pink Aluminum Oxide? What grit? Thanks!

[WoodWrangler]

Someone might have a more precise answer ... but any of those will work. The colored wheels stay cooler and do a good job. If you already have the shape you want, I'd go between 100-150grit to maintain it. If you need to shape a tool, you might 60 or 80 grit.

[rcflyer23]

Originally Posted by WoodWrangler

Someone might have a more precise answer ... but any of those will work. The colored wheels stay cooler and do a good job. If you already have the shape you want, I'd go between 100-150grit to maintain it. If you need to shape a tool, you might 60 or 80 grit.

Okay so where can I get these at. I forgot to look and see if Lowes had them. Would HF have them.... I need to sharpen my lathe tools and don't honestly know how. Any information would be appreciated.

[Mike Davis]

Would a few folks like to have a free sharpening day at my shop?

I can show you how to sharpen turning tools, chisels, gouges and knives by a few different methods.

We could even make some jigs if you think you need them.

[Mike Davis]

MAybe this will answer some of your questins about grinding wheels.

Grit type and color

Grit type is generally either aluminum oxide (white, pink, ruby red, brown, grey, etc.) silicon carbide (black or green), ceramic (blue and pink) or any combination of these. Aluminum oxide is by far the most popular. It is available in the following colors: White, pink, red, ruby red, brown, and grey. Each color has it's own grinding characteristics. Grey and brown grit are the workhorse grits used in bench grinding and production grinding. Tough and inexpensive they are the most 'general purpose' grit found. Can be used on low to high carbon steels. The pink and white grits are typically used on your harder steels which need a cool, friable cutting action to avoid burns. The ruby red grit is a special tough grit also used on tool steels. These grits are a little bit more expensive than the grey/brown. Ruby red is very expensive. Silicon Carbide grits are commonly either black or green. Black silicon carbide is used to grind non-ferrous metals such as aluminum and brass and also on plastics, rubber, and stone products such as marble and granite. Black silicon carbide is a very sharp grit. Green silicon carbide is an even sharper grit than black and is used primarily for carbides, titanium and plasma sprayed materials. One interesting characteristic of silicon carbides is the effect they have on steels. Due to the sharpness of these grits, one would think that they would be too aggressive and not provide a good finish. In fact, on steels, silicon carbide is used as a sort of polishing/finishing grit. It is used in tumbling processes as a surface finishing product. Also, manufacturers will often blend a small percentage of silicon carbide in with aluminum oxide grit in grinding wheels and honing stones to achieve a better workpiece surface finish on steels. The grit will actually dull and provide a rubbing action on steels which produces a better surface finish.

A newer grit that is available is ceramic (also referred to as SolGel® or SG®). Ceramic grit has the characteristic of not dulling -- It will break down or fracture into sharp corners rather than dull and pull out of the bond. This makes the wheel typically last longer and it will also provide excellent aggressive stock removal without heat build up. This grit is only made by a couple of producers and is very expensive, typically two or three times as expensive as aluminum oxide. You will normally not see a 100% ceramic grit wheel. The grit is typically mixed with aluminum oxide in various percentages from 10% up to 50%. Ceramic is used in tool steels and lower carbon steels equally well. These grinding wheels typically require a good bit of custom engineering for your specific application and process to achieve profitable results.

Grit types are sometimes mixed in combination for achieving certain cutting characteristics. Grits are also called friable (white) or semi-friable (pink, brown and grey, red, etc.). Friable grit breaks down more easily and is useful for cutting harder materials.


Grit size

Grit size typically runs from coarse (16 -24 grit), medium (36 - 60 grit) and fine (80-120 grit). Superfine grits run from 150 and higher. Grinding wheels usually will be between 24 and 100 grit. Honing stones and jointing stones and other polishing abrasives will be 150 grit and higher. Use a coarse grit for fast, aggressive stock removal and finer grits for less stock removal but better surface finish.

Grinding wheel hardness

Hardness is rated from A-Z with 'A' being the weakest bond and 'Z' being the strongest. A weak bond is preferred for grinding harder materials while a stronger bond is desired for softer materials. A typical weak bond for steel would be in the 'F, G or H' range. A medium hardness would be in the 'I, J or K' range. And stronger bonds in the 'L, M, or O' range. Hardness is dependant on the grit type, the material being ground, the amount of stock removed, and a number of other factors.

Hardness grades are typically linear: If you increase the hardness by one letter grade (An H to and I for instance) it could give you double the wheel life. Many people mistakenly believe that such a move (from an H to an I) would only be marginal -- Don't be misled here: A move of just one or two hardness grades could have a dramatic effect on your process!

It is important to note that it is almost impossible to match one grinding wheel manufacturer's wheel hardness to another manufacturer: Differences in factory kilns, measuring instruments and the lack of a standardized hardness system do not allow for direct cross-overs. One company's 'G' hardness would be a 'F' with another and even a 'H' with another. We get calls all the time on this: We simply cannot guarantee one wheel to be the same as another. Even when our manufacturers switch their production to a different factory in another state or country we will see some variance. This can sometimes be considerable.

Structure or grain spacing

Structure is basically the spacing between abrasive grains. An open structure would be 12 or higher while a closer structure would be 6 or so. Here again, the structure depends on a variety of factors not the least of which is how difficult the material is to grind. One would think that a closer spacing would make a tougher wheel but this is only true to a point: With less bond holding the individual abrasive grains, the softer the wheel would be. Also, the same holds true for a very open structure: If the grains are wide spaced you have fewer grains to grind with but a greater amount of bond holding each grain -- This could make the wheel tougher. Grinding wheel engineers will typically adjust the BOND STRENGTH depending on the application.

Bond type

There are various bond types but the most common are vitrified and resin. Vitrified is basically a vitreous glass much like pottery or glassware fired in a kiln. Resin wheels are plastic resins mixed and cured at lower temperatures. Vitrified wheels are commonly used for bench, surface and tool room applications such as surface grinding while resin wheels are commonly seen in cutoff wheels, centerless wheels and superabrasive wheels (diamond & CBN). Newer bonds are Plastic bonded wheels based on high technology from companies such as RESEARCH ABRASIVE.

[rcflyer23]

Originally Posted by Mike Davis

Would a few folks like to have a free sharpening day at my shop?

I can show you how to sharpen turning tools, chisels, gouges and knives by a few different methods.

We could even make some jigs if you think you need them.

That would be awesome. I have never had to sharpen any of these type of tools and want to make sure I know how before I screw up my tools.

[Woodman2k]

One thing I would like to add to a great explanation fron Mike is that like alot of tools,you get what you pay for.I bought a 60 and a 100 grit SG wheels for my slow speed grinder and spent some time getting them as balanced as I could and the performance difference from the white wheels that came with the grinder was measurable.Personally,I would not buy wheels from Lowes or HF.Amazon has them as well as Klingspor and a host of mailorder places.

[rsitzejr]

I would love to know more about balancing them. I've never done that to mine.

[Woodman2k]

Rob,
I will admit that the best way to balance them is with the Oneway system,but it is expensive.I put them on the unit with the bolt snug but not tight and mark a spot and then spin it and see where it comes to a stop on its own.If a certain spot comes to the bottom then I give it a nudge towards center,then spin it again and see if there is a difference. It seems to work but then again with a new bushing and good wheels I just might be trying to fix something that isn't broke.
I know one thing,with the green wheels it puts a razor sharp edge on my bowl gouge.I also know somebody that has a Sheppach slow speed sharpener with the tormek jig and that unit sure does a great job for the money.Was under $100 at Amazon.

[Mike Davis]

A good quality wheel will be balanced from the factory. However, it may not be mounted well or your grinder may be slightly out of concentric on the shaft. Higher quality grinders like Baldor for instance are centerless ground and will not vibrate as it runs.

When you mount the wheels be especially careful to check for any play on the shaft. Sometimes a wrapping of paper or brass shim stock will center the shaft in the hole.

If it still seems off after you tighten the nut then the wheel may be defective or just denser on one side. You can sometimes fix it by dressing the wheel with a diamond dresser. Basically a small industrial diamond mounted on the end of a steel handle.

You hold the diamond steady and slowly bring it closer to the stone until it starts to grind off the high side. Work it back and forth across the stone until it is evenly reduced all around and across the face of the stone. Don't let the dressing stick move with the wheel or it will just grind down evenly all around without correcting the concentricity.

[Glennbear]

Thanks for the very thorough explanation Mike, you certainly removed a lot of the mystery for me