Belt Sander
	Finest abrasives.
	Microbevels front and back.
	Use a jig.
	Copyright (c) 2002-09, 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 Grinding Wheel
2. Belt Sanders -- There are lots of choices.
3. Replacement tool rest -- You will need to make a suitable tool rest.
4. Setting the tool rest angle - Make a small cutoff for your usual angles.
5. Edge Shaping -- An occasional need, somewhat different from forming the primary.
6. Forming the Primary -- Shaping the tool without damaging the edge.
7. Grinding Wheel Geometry -- A little help for people using grinding wheels.
   1. Actual angles.
   2. Setting the tool rest angle.
   3. General belt-sander/grinder Tool rest alert.
8. Website Navigation -- Where am I?

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
• Larry Williams' vertical belt sander
• Derek Cohen's horizontal belt sander

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

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.)

In fact, I have not used this belt sander - Harbor Freight does not ship to Canada. However, for the limited amount of grinding you will do I would be very surprised if it ever wears out.

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.

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!

Tool Rest Replacement

• 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 vise, 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 offcut 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.

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.

Having trouble seeing this jig? A bit too Escherian? The next picture may be a little easier.

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, he as just taken a notch out of the side of the platen. If you look closely, you can see the platen side below the tool rest, and the platen itself under the belt. So, 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 (according to Derek, I have not seen 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.

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 with the blade 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.

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.

Controlling the process

The sparks are hidden under the blade, so you cannot really see where the belt and 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 on the tool. Each time you dip the blade into the water, check your progress on the bevel side. 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, into the belt should produce rapid metal removal. 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.

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

Actual angles.

This drawing shows the shape of the bevel when you use a 6" grinding wheel on a standard plane blade (0.09" thick). As a general rule, stiffness is related to the cube of the thickness, so any loss of thickness has a serious effect on resistance to flex (vibration). [The actual angle at the edge is a bit more than 4 degrees less than the tool rest angle. For thicker irons, the error is larger. For larger wheels, the error is smaller.]

While the nominal (tool rest) bevel angle is 25 degrees, the dashed line shows the actual bevel angle at the edge is 21 degrees.

Many people follow the hollow grind with a freehand honing on a fine stone, using the front and back edges of the hollow to balance the blade. This allows them to hone without a jig.

[Thanks to Robert Fortier from the Oldtools list for this drawing]

Setting the tool rest angle.

It is of course much harder to set for a wheel than for a flat belt since it is hard to tell where the wheel touches the angled face of the jig. You should be able to come pretty close though.

If you are going to hone using a jig like mine it is important that the primary angle not be much greater than 25 degrees (the width of the first microbevel depends on the difference between the primary angle and the first microbevel angle). If in doubt, make the primary angle a little smaller (adjust the tool rest so contact is closer to the corner).

General belt-sander/grinder Tool rest alert.

If you look at the seat around the locking bolt you see a series of ridges. It turns out there are about 50 of them, arranged radially. There is an identical series of ridges where you attach the tool rest to the cover.

If you were an engineer sitting at a CAD machine you might think this is a really good idea - how better to prevent the tool rest from turning in use?

It turns out this is a horrible idea!

Yes, you can set the tool rest to the angle you want. However, as soon as you start the grinder the vibration causes the tool rest to slip to the nearest rib position. You can see in the picture the bit of metal ground off the inside of the tool rest. This is what happens when the tool rest slips and turns into the belt.

So, with 50 ribs you have 50 possible tool rest positions - or about one every 7 degrees. If you are keen on getting 25 degrees rather than 29 degrees, this is a problem.

The folks at General understood the problem but said they had sold thousands and no one had ever complained before. The man I talked to, Dave, told me that grinding the ribs off would probably solve the problem. I asked him if I should grind them off both the tool rest and the wheel cover. He thought both would be better.

Great customer service.

Looking at their other grinders, it looks like General has standardized on this type of tool rest locking mechanism. If you have any interest in actually setting the tool rest angle you will have to modify it some way first.

Hollow Grind Revisited

In Peter's analysis, he calls the grind pictured above a 21 degree grind, since that is the angle at the edge.

To compare the strength of a flat ground 25 degree bevel to a hollow ground bevel, you would hollow grind at 29 degrees. The resulting bevel is actually thicker on average, and hence possibly stiffer.

If you hone after sharpening by resting the blade so both edges of the hollow are touching, then the angle at the edge increases, returning [approximately] to the angle you thought you had. In the flat ground case, I increase the angle by 4 degrees, putting on a microbevel at 29 degrees. In the hollow grind case, you retain the angle of the arc that crosses the hollow -- by coincidence again 29 degrees.

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