Belt Sander
	Finest abrasives.
	Microbevels front and back.
	Use a jig.
	Copyright (c) 2002-15, Brent Beach

Introduction

A 1" belt sander will let you create primary bevels on most edge tools relatively quickly, once you replace the tool rest. It is easy to grind at any desired angle, with little danger of overheating provided you use sharp abrasive belts.

Powered grinders (belt or wheel) are not the only option for grinding the primary bevel. You can use bench stones. I usually do.

Contents

1. Belt Sander or Belt Grinder
2. Belt Sander or Grinding Wheel
3. Belt Sanders -- There are lots of choices.
4. Belts -- A bit harder to find.
5. Replacement tool rest -- You will need to make a suitable tool rest.
6. Replacement tool rest -- Acrylic version may be even better.
7. Setting the tool rest angle - Make a small cutoff for your usual angles.
8. Edge Shaping -- An occasional need, somewhat different from forming the primary.
9. Forming the Primary -- Shaping the tool without damaging the edge.
10. Heat -- Grinding by machine generates a lot of heat - watch it!
11. Belt direction -- Belt should turn into the edge.
12. Controlling the process -- Easy does it.
13. Grinding Wheels -- A discussion of grinding wheels and setting the tool rest angle has moved to its own page.
14. General belt-sander/grinder Tool rest alert. -- A tool rest that cannot work.
15. Website Navigation -- Where am I?

Belt Sander or Belt Grinder

These small machines were originally used by hobbyist wood workers to finish sand small projects. The rest supplied with these sanders is not a tool rest - it is a wooden object rest. The first one I bought was called a Belt Sander.

In my use, they are belt grinders. Either name is fine, with perhaps a slight preference for belt grinder. A search for "belt grinder" got 306,000 hits, while a search for "belt sander" got 2,860,000 hits.

Belt Sander or Grinding Wheel?

Here are a few of the reasons why I prefer a belt sander:

• Range of abrasives. I have belts in grits from 48 to 15 micron - perhaps 8 different grits. Most people only own wheels in 1 or two grits. At around $2 a belt, owning many grits is no problem.
• Ease of grit change. It takes less than a minute to switch belts. It takes a long time to switch wheels.
• Belts are always flat. You have to regularly true the face of a wheel. Truing produces clouds of abrasive particles.
• Belts are less likely to glaze with filings. The abrasive particles on belts are coated with a slippery compound. The belt flexes as it passes around the wheels. You can use a big eraser to clean the belt of the few filings that do stick.
• There are some fantastic belts. 3M makes a belt using the 15 micron Silicon Carbide micro finishing abrasive. Norton makes belts using "seeded-gel" technology.
• It is easy to set the tool rest angle on a belt sander to any angle you want. Setting the angle accurately on a wheel is a challenge.
• Belts run cooler than wheels. The greater length of the surface area means more time for the belt to cool before it again reaches the tool.
• Belts runs slower than wheels. Typical abrasive speed for a belt is 3,150 fps, for a 6" wheel is 5,400 fps, for an 8" wheel 7,200. Heat generated is directly proportional to abrasive speed.
• Belts produce less airborne dust than wheels. The softer wheels common these days produce a constant cloud of abrasive particles. Belts produce less dust because the binder is tougher. Both produce far must airborne dust than a bench stone.

Belt Sanders

• My 1" vertical belt sander
• Harbor Freight 1" vertical belt sander
• Robert Sorby
• Larry Williams' vertical belt sander
• Derek Cohen's horizontal belt sander

People have even clamped portable belt sanders upside down in a vice and use them. People also race portable belt sanders.

My 1" vertical belt sander

The belt sander came with a large tool rest which could not be set to the angles needed for grinding edge tools - typically in the 20 to 30 degree range. You will have to make a new tool rest - details below.

A 120 grit AlO (Aluminum Oxide) abrasive belt will quickly shape tool steel without over heating. Where a lot of grinding is required though -- when changing the bevel angle on a plane iron -- a grit as low as 60 should be used.

While it works very well as a grinder (rough shaping of the bevels), I don't believe any high speed abrasive should be used for honing (finishing the edge). High speed abrasives heat the edge very quickly, especially at finer grits (finer than 120) and even more if the abrasive is a little worn. I have belts with grits as small as 15 micron, but no longer use them.

A 1" belt sander can replace a grinding wheel for many sharpening applications. I have both, but now only use the grinding wheel when removing lots of metal, and almost never on edge tools.

I happen to own a Delta, but have seen many knock off versions that appear identical. The knock offs are usually in the $60 range.

Harbor Freight

In February 2008 this was here on the Harbor Freight web site. While you are there, get some belts - the price looks good but I have not used the belts so have no idea how well they work. (No affiliation. Some readers have suggested the HF belts are not very good. I use Klingspor belts.)

I did manage to buy one of these belt sanders - thanks Ted - and tested it out. It works just fine. By fine I mean: belt tracks, platen seems solid enough. I was able to use the same tool rest as I had made for my Delta - you will have to replace the tool rest that comes with the sander. I have not used it as much as I have used the Delta. Others report using these belt sanders for years. One extremely heavy user reported burning one out. If you intend to sharpen every day you probably want a more substantial machine. If you will only be sharpening your own edge tools, should be no problem.

Update: Peter Schumacher sent me an email, which said (among other things): "Your Harbor Freight sander is a dead ringer for my Woodtek sander. I have owned and used it for over 10 years. I'm a hobby woodworker, mostly wooden toys and small furniture pieces. I use it mainly it smooth curved toy pieces. I have gone through dozens of belts with no problems. I have sanded with enough pressure to bring the motor to a stall many times. No problems at all." Looks like an good alternative!

Update 2: A reader has told me he was able to rewire this unit to have the belt move in the other direction. While this sounds safer - less chance of a catch - I would not do it for the reasons reasons outlined below.

The Harbor Freight unit is the basis of a knife sharpening setup ("Edgemaster Blade Sharpener"). In a recent email conversation with the developer of the system, I learned that he has sold 400 units based on the Harbor Freight belt sander. He has had no complaints about quality problems. He does advise against the belts that Harbor Freight sells - they use Klingspor belts exclusively. Edgemaster is now a Franchiser of a Knife Sharpening business. As of June 2011, he is again selling his modified version of the Harbor Freight belt sander.

Robert Sorby ProEdge belt sander

The Robert Sorby site has a couple of videos on how to use this belt sander. They show a tool holder that does the finger nail grind on wood turning gouges.

Kalamazoo 1SM belt sander

The belt sander has a 1/3 horsepower Baldor motor - should have no problems with this for anything short of all day everyday heavy grinding.

Even with this machine, I expect you would want to build your own tool rest.

Larry Williams' vertical belt sander

Larry Williams uses a much more substantial belt sander, part of a grinder/sander combination machine.

You can see that his shop made tool rest allows very small grinding angles, and allows him to grind complex tools like this gouge. The wider abrasive would also allow more evenness in grinding wide tools like plane blades.

At first it appears that Larry chose to position his tool rest so that the tool hits the belt below the platen (belt support). In fact, there is a notch in the side of the platen. The platen is continuous from well above to well below the area in use.

A nice design. This is clearly a much more substantial setup than mine. With practice, I think most people could do some pretty good free hand grinding on this machine with a tool rest like this.

Larry's grinder was written up in more detail in a Woodnet discussion in 2007 that has since disappeared.

Derek Cohen's horizontal belt sander

Derek Cohen from Perth Australia uses a much bigger belt sander and has built a tool holder for it. He describes it here.

The bevel angle is determined by the extension of the edge from the front of the tool holder. The jig slides back and forth on the bar, much like a Tormek.

I am not sure why Derek chose to set an extension from a jig which holds the blade rather than use a tool rest (as both Larry and I did). Perhaps it would be hard to use a tool rest with a horizontal belt.

The problem with this method - jig on a rod - is that as you remove metal the angle changes (increases). With a tool rest, the angle does not change as you remove metal.

This setup - with the belt horizontal - puts the tool in an awkward position for good control. With a vertical belt (or a grinding wheel) positioned to have the tool between waist level and eye level, you are most able to see and control the tool edge. With this setup, you can neither see nor control the tool edge well.

I have used Klingspor belts for years and been happy with them. I source mine locally and it turns out I was only able to buy the Economy Belts. I had no idea they sold even better belts.

Klingspor has an online site that sells their belts. They sell Alumina Zirconia in 24, 36, 40, 50, 60, 80 grit, Gold Aluminum Oxide in 120, 150, 180, 220, 320, 400 grit, Economy Aluminum Oxide in 40, 50, 60, 80, 100, 120, 150 grit, and Premium Aluminum Oxide in 36, 40, 50, 60, 80, 100, 120, 150, 180, 220, 320, 400, 600 grit.

Lee Valley has long sold 1 x 30 abrasive belts. I see that Lee Valley now sells a 3M Aluminum Oxide belt that they call a Grinding Belt in grits 180, 320, 500, 1200.

Belt Quality

I tend to use belts away from the edge, to shape a blade back of the edge to prepare for honing. I call this the primary or first bevel. I think of this as a grinding operation because it removes metal but is not part of the honing process since it never involves the tool edge. For grinding you would not need the very high grits unless you were working on knives and want to get a particular finish on the primary bevel.

If you want to try power honing you might try some of the higher grits.

The Economy belts that I have been using are X weight. These are sturdy belts. I have never had a belt failure even with the abrasive moving into the edge. The higher grit belts that you might use for honing an edge have lighter backing. More care would have to be taken when using these belts. I don't think normal use would ever cause a failure, but an inadvertent jamming of a tool into the belt could destroy it.

I intend to get some of these finer belts for my experiments with knife sharpening.

Tool Rest Replacement

I have made replacement tool rests from both galvanized metal framing material and from acrylic. I prefer the acrylic version.

Having done a little wood turning, I favour a tool rest that lets me get close to the work and hold the tool in my left hand while controlling the motion with my right. These tool rests give me that option.

Update 12/01/29: Modify existing tool rest
A website visitor, Marko, pointed out that the tab on the underside with the slot for the tool rest adjustment bolt could be modified to allow shallower angles. It is currently straight. By making it L-shaped you could achieve lower angles. It looks like a couple of cuts in the sides are required as well. In the second picture you can see that the tool rest behind the belt had to be modified as well. Marko can set the tool rest to 23 degrees.
Here is the modified rest at a shallower angle. I think this rest has several problems, but you may find it works for you. The distance between the belt and the rest is a bit large. It might be a little too easy to stick something in there that then gets dragged down into the rest. A second problem is the distance from the belt edge of the rest - as modified the distance is 4 inches. You will be holding the tool where it extends off the tool rest. That puts your hand a long way from the point of contact with the belt, increasing the difficulty in controlling the tool edge. A narrow rest lets you hold the tool near the point of abrasion, increasing your control. Most tool rests use on wood turning lathes are very narrow, allowing a grip very close to the cutting tip. This tool rest must be wide enough that you can easily hold the tool flat - assuring the correct angle. It should also be narrow enough to allow controlled movement of the tool against the belt. Getting a width that is wide enough and also narrow enough is important.

Angle Iron

• removed the short side with a hack saw to get a flat piece of steel,
• drilled a slot for the attachment machine bolt - the lower slot on the short side - three holes then a bit of filing,
• bent it to (very nearly) 90 degrees.

Tools used: hack saw, small metal vice, drill press, high speed steel drill bit, file. Depending on your skill with a hacksaw, this could take 15 minutes. The metal should be fairly stiff but there is not a lot of downward pressure on the tool rest during use.

Here, the tool rest is set at 25 degrees.

Since I do almost all my plane iron grinding at 25 degrees, I use an off-cut with a 25 degree angle on the side to set the tool rest (see below).

For other angles I use an adjustable plastic protractor. You can set a bevel gauge from a protractor and use that.

One of the big advantages of a belt sander is the ease and accuracy of setting the angle. Because the abrasive is flat, not curved, one entire surface of the scrap rests flat on the abrasive and one rests on the tool rest. (With a grinding wheel, the scrap is tangent to the wheel over a very short distance, a more difficult setting.)

This really is all you need. No fancy tool rest because I do all my grinding freehand! A little strange for someone who uses a jig for honing, but I can freehand the grinding step because I almost never grind the edge itself! See more about how much to grind in the grinding overview page, at my From New to Sharp page, and at my Sharpening Radiused Blades page.

Acrylic version

This Sketchup model shows the crucial dimensions, assuming my belt sander. First, the slot for the tool rest bolt must have at least 7/32" clearance from the inside of the tool rest to clear the housing. Second, the slot must be at least 5/16" wide to accommodate the tool rest bolt. These dimensions may not be the same for your sander.

I have updated the former translucent model with this opaque model - hopefully easier to understand. The blue piece is the tool rest - 3" wide, 2" tall. The yellow piece on the end connects to the tightening bolt. It is 1" by 2" and is welded to the end of the blue piece. The green piece forms the second part of the connection to the tightening bolt - it is 3/4" by 2". Welding here means chemically joined - a solvent softens the acrylic briefly, letting the mating parts weld together.

Notice in the model that there are two edges labelled Good edge. These edges must be smooth and square to keep the tool rest square. My piece of acrylic was 5" wide and these are the original outside edges - produced by the big saw at the plastics store. If these edges are good the model will line up and the joints will be strong. The second (outer, yellow) 1" piece was added to increase the strength - I just did not think that the tool rest would be strong enough without this.

I cut the 3/4" piece first - using one good end of the original. Then I cut the 1" piece - no good ends. That left the 3" piece with one good end.

How strong does the tool rest have to be?

You don't press down on the tool rest when grinding. You have your fingers beneath the tool rest and your thumb on top of the tool. You squeeze the tool between the thumb and fingers of your left hand. Your left hand (mainly your thumb) controls tool movement back and forth across the tool rest. Your right hand provides gentle upward pressure - along the tool rest - moving the tool against the abrasive. While the force you exert is mainly squeezing, there will be upward and downward forces on the tool rest while you grind.

If you decide to try plastic, check the flexibility before spending too much time building the tool rest. My metal tool rest (above) is just over 1/16" thick and is very rigid. If you can easily twist a 3" by 2" piece of your plastic, it will not be rigid enough. In my tests, acrylic that was 0.093" thick was too flexible. The final version was 0.236" (about 6mm) thick and plenty stiff.

To add another wrinkle to this type of tool rest design, Richard Butts made an MDF version of this acrylic tool rest. He intends to make a steel version if the MDF version continues to work for him.

Acrylic tool rest installed

I use the same Acrylic tool rest on a General Belt-sander/grinder machine. That machine comes with a tool rest that cannot work. See the failed design and the same machine with the acrylic tool rest installed.

Modification for small angles

I built the 3 1/2 inch tool rest shown on the belt sander in order to grind 15 degree bevels on a machete. It is not exactly like the drawing. Rather it is a scaled up version of the first model. It can be made from a 3 1/2 inch by 5 inch piece of acrylic with just two cuts (as described above). The position of the tool rest bolt and the shape of the shroud in front of the bolt mean that 15 degrees is about the smallest angle that can be handled with this type of tool rest on this machine.

Note - While an acrylic tool rest can be quickly built with hand tools, the resulting tool rest is a poor conductor of heat. Any heat build up in the tool will remain in the tool and not be carried away as it would be with a metal tool rest. Be more careful with tool heat when using an acrylic tool rest.

As you can see, setting the angle is foolproof. What you can't see, so will have to take me word for it, is that setting the angle takes 5 seconds once you find the jig.

The total length does not matter, nor does the thickness.

Edge Shaping

Edge shaping is discussed in detail in the Sharpening Radiused Blades page.

As you can see in this picture, during edge shaping the blade is at 90 degrees to the belt. You can just see the tool rest in front of my fingers - it is parallel to the belt. The plane blade is resting on the edge of the tool rest (it happens I cannot set my tool rest to 90 degrees, so set it a 0 degrees and use the edge).

I usually mark the desired shape on the back of the blade and grind down to that line.

When shaping the edge, I am not trying to form the primary. Once I have the desired edge shape (which can be straight if I am just removing a nick), I switch to the second type of grinding - forming the primary bevel.

Forming the Primary

• Holding the blade
• Primary bevel angles
• Assessing the worn tool
• Controlling the process

Holding the blade

The fingers of my right hand are below the rest and behind the blade. My right thumb is on the front of the blade at about the same level as my left thumb. Most of the control comes from my left thumb, which pushes the blade to the right, then draws it back to the left. The right thumb is a follower, not a leader in this operation.

You should practice moving the blade back and forth, up and down, with the belt sander turned off. You should have a smooth back-and-forth motion which brings the whole blade in contact with the abrasive. You should also be able to move the blade up into the abrasive, or back down away from the abrasive smoothly. When you are confident of the motion, then try it with the sander actually running. The blade should be down, away from the belt when you turn the belt sander on.

Primary bevel angles

Working back from the desired final microbevel angle gives me a primary bevel angle of 25 degrees for most plane blades. In some cases other angles work. For example, if you are only planing along the grain on softwoods without knots, you can reduce the final microbevel angle by from 5 to 10 degrees. You would decrease the primary bevel angle by the same amount. With some tool steels and some woods a larger final angle may be required. You are safe to start with 25 degrees and experiment for unusual situations.

Assessing the worn tool

This drawing represents the ideal case - the old primary is already at the correct angle. With some new blades and almost all used blades that have been ground by people unaware of the importance of the primary angle, the old primary angle will not be correct. You can decide which one of three situations you are facing if you put a relatively fine abrasive belt (600 grit) on the belt sander and do a light pass across the blade. Look at the bevel and decide where the belt is scratching the primary.

Heat

With high enough heat for long enough, the crystal structure of the steel changes. The steel softens (its temper is drawn). With a high speed abrasive the time before the temper is drawn can be quite short. Soft steel is much less durable than hard steel.

• Belt Speed

  Stationary belt sanders spin the abrasive quite quickly. In the case of the Delta (most 1" by 30" belt sanders), the motor runs at about 3,400 rpm. The wheel turned by the motor is 3.5" across which means the belt moves 11" every motor shaft rotation. That works out to 52 feet per second.

  A 60 grit Silicon Carbide belt moving at 2.3 ft/s can generate local temperatures of 650 �C (1,200 �F) in 5 minutes. The time drops quickly with increasing belt speed. At 4.25 ft/s that temperature is reached in only 8 seconds. I cannot find any estimate for time required to reach that temperature when the belt speed is 52 ft per second, but it must be very small.

  While local temperatures will reach a temperature at which loss of temper is almost instant, it takes longer to actually heat the tool enough to affect temper.

  Grinder motors spin at about the same rpm as belt sander motors. Since the wheels are from 1.7 (6" wheel) to 2.3 (8" wheel) times the circumference of the belt sander drive wheel, the abrasive speed is greater by the same amount. Since amount of heat generated is exponential in abrasive speed you need to be even more careful when using grinding wheels.

• Pressure

  More pressure means more heat. With increased pressure each grit scratches a deeper groove. Deeper groves generate more heat since more metal has to be deformed. A light touch when grinding will reduce the chances of over-heating.

• Contact point count

  More grit particles means more heat. A finer grit usually also means more grit particles per square inch on the belt and hence more grit particles in contact with the tool. More grit particles mean more scratches. More scratches mean more heat.

• Abrasive quality

  Fresh abrasive generates less heat than worn abrasive. As the abrasive wears the tips of grits fracture. Fracturing almost always produces a new tip that is flatter (the included angle in the tip in contact with the metal is larger). Flatter abrasive particles remove metal more slowly, creating more heat as they work.

  A worn belt may also have attached metal filings - swarf. This is less of a problem with belts than with grinding wheels. The belt flexes around each wheel (one of which is quite small) each revolution, tending to dislodge swarf. Any swarf retained in the belt will generate a lot of heat as it rubs past the tool.

• Metal removal rate

  When grinding we usually want to work as quickly as possible. Rapid metal removal improves with higher belt speed, larger grit, fresh grit, increased pressure. Two of these increase heat, two decrease heat.

• Bevel Surface Area

  Surface area of the tool in contact with the abrasive also affects heat generated - larger surface area means more grits in contact which means more heat. When you grind a knife - 0.01" thick just back of the honed bevel, 15 degree honed angle - the bevel is only 0.02" wide (assuming the knife is double bevel sharpened). When you grind a plane iron - 0.25" thick plane iron at 25 degrees - the bevel is 0.54" wide. With over 25 times the metal thickness, expect 25 times the heat build up.

• Tool thickness

  Metal tools are good conductors of heat. Heat generated on the grinding surface quickly moves into the nearby steel. The rate at which heat is carried away depends on the temperature difference between the surface and the rest of the tool.

  The thin part of the tool near the edge has almost no steel into which heat can flow. Any heat generated here has to flow diagonally into the thick part of the bevel, a longer path with less ability to draw heat away. The thinner the edge (smaller included angle) the faster heat builds up.

• Belt Direction

  The abrasive can either pass the tool edge first or last (move into or away from the edge). As the abrasive passes across the bevel, the heat rises quickly. The abrasive and any swarf ground off is hottest just before the abrasive moves out of contact with the tool. The abrasive cools down as it moves around its path. It is cool when it arrives back at the tool.

  Having the abrasive move into the edge reduces the danger of over heating the edge and drawing the temper there.

Belt Direction

I prefer the belt-moving-into-the-edge mode of operation. Are there any advantage to the belt-moving-away-from-the-edge mode of operation

The Good

• This setup has the advantage that in the event of a belt failure, the broken belt pushes the knife away from the operator.

The Bad

• Over-heating - This setup increases the heat at the edge - the part of the tool least able to dissipate heat. On knives with their very thin bevels this is not too much of a problem. Still, the edge will be the hottest part of the tool during honing/grinding so there is a danger of drawing the temper if you hesitate at all. With thicker tools, the chances of over-heating the edge increase. As shown above, on a thick plane iron the bevel is over 25 times as wide.
• Hot filings and the edge - Red hot bits of steel removed during grinding remain on the belt as it moves past the edge. These bits can be left on the trailing edge of the tool. This is certainly enough to draw the temper in very small areas of the edge.
• Catch events - While the danger of a catch or an exploding belt exists, it is very low. First, I have never had a catch. If you are reasonably careful and slide the tool up the tool rest into a moving belt chances of a catch are very small. Second, belts get dull long before the backing becomes damaged in any way. Third, with the tool held on the tool rest an exploding belt will fly over the tool. Even if it somehow caught the tool and pushed it down, the spine of the tool is toward the operator.
• Burr creation - With the abrasive moving away from the edge you are more likely to get a burr on the tool (if you grind through the edge), or get a build up of filings on the face just back of the edge (if you don't grind through the edge). Neither is a good result.

Controlling the process

As discussed above, machine grinding can ruin your tool (heat) and perhaps even hurt you (exploding belt). You must be aware of what is happening during the grinding process and react accordingly.

In this picture, you see two bevels. The narrow bevel at the edge (top in this picture) is what is left of the factory grind. For some reason, this blade left the factory with a 32 degree primary bevel. This scan was done part way through regrinding the primary back to 25 degrees. See the whole sequence of images in this discussion of grinding a primary bevel.

Stopping short of the edge

The sparks are hidden under the blade, so you cannot really see where the abrasive belt and the blade meet. If the edge appears to be square to the belt, you are probably pretty close.

After 10 seconds in light contact with the abrasive, dip the tool into water. There should be no steam or bubbling on the surface of the tool. After you dip the blade into the water, wipe off the bevel and look closely at it to check your progress. If you find you are grinding one side more than the other, you can correct the problem by rotating the blade a few degrees on the tool rest. For example, if you need to take more off the left side of the blade (when viewing the bevel), then you want to work the right side a bit more (viewed from the back) so tilt the blade a bit to the left (raise the right corner). A very small tilt should be all that is required.

Grinding pressure is exerted by pushing the blade up along the tool rest into the belt. Remember you are squeezing the blade and tool rest, not pushing the tool against the tool rest. The light upward pressure, from your thumbs, moves the tool into the belt. If metal is not being removed quickly with light pressure, there is a problem with the belt.

A fresh 120 grit belt will take off lots of metal without heating the blade. As the abrasive on the belt dulls, metal removal slows and the blade starts to heat up more. If you notice serious heating, try a fresh belt. I also have a large rubber eraser for cleaning the belts - these belts can fill with grit from grinding and a clean belt grinds cooler.

If the bevel is a mess - someone else did it of course - you might want to start with a larger grit. Remove most of the metal using a 48 grit belt, switching to a 120 grit belt when you near the edge. Again, stop short of the edge.

I check progress regularly, as I dip the tool in the water, stopping before the new scratches reach the edge.

I have another page that includes a number of actual size images of a plane blade bevel during grinding. Scroll about half way down the page.

Grinding Wheel Geometry

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