Sandpaper Alignment Guide

This guide is also available as a guest post on Scott Rao’s blog, along with a fantastic introduction from Rao. Check it out!

Introduction

Before we begin I want to give credit and thanks to the community at kaffee-netz.de, and to Jürgen Peter Ohler (Jupe3.0) in particular, for coming up with this idea in the first place. I’d have never been able to put together this guide without their pioneering of the method.

I’d like to introduce you to a simple and straightforward way to align your grinder that uses the inherent properties of the grinder itself, rather than relying on user observations like methods such as marker alignment. This method uses readily available supplies to allow the burrs to alter the grind chamber and the burr carrier so that the burrs are aligned parallel to each other and perpendicular to the drive shaft without shims. To achieve this, we’ll be attaching sandpaper flat to the back of the burrs in two different configurations (see diagram) to sand both mounting surfaces.

This method works easily with any grinder with an EK-like burr pattern. With the inner burr fixed in the grinder chamber and the outer burr on a spinning carrier that goes over the drive shaft. EK43, Bunn G1, etc.

Supplies

Spray adhesive, I used “Loctite General Performance Lightweight Bonding adhesive”, available here or most hardware stores. You want something light since it’ll be coming off frequently.
Oil for the sanding, I used “3-IN-ONE oil”, available here or most hardware stores.
Sandpaper of several grits, I used a bunch of big packs from the hardware store, but a multi-pack would be ideal. We’re only going to need a couple sheets of each grit size. Make sure it’s wide enough for your burrs. 98mm for EKs, 80mm for Bunns, etc.
Adhesive remover, I used Goo Gone, available here and most anywhere you can get cleaners. I do want to note that Goo Gone is not a food safe product, but you can clean it off thoroughly. If you do feel concerned, I find that canola oil does a good job of stripping the adhesive as well. Be sure to clean it thoroughly too, for different reasons.
An X-Acto style knife. Most hobby stores, hardware stores, and office supply stores will have something suitable.
Some rags to wipe up the metal filled cutting oil. Expect to throw them away after, so get something cheap.
Masking tape.
The thinnest tape you can find. It has to fit between the sweepers on the burr carrier and the outer burr.
A screwdriver for the burr chamber and another for the burrs themselves. I highly recommend a torque screwdriver for the burrs to put them in with more even tension. It’s not strictly needed, but if you can get even a cheap one you can be a lot more confident you’re not over tightening one side.

UNPLUG YOUR GRINDER AT THIS POINT. LEAVE IT UNPLUGGED UNTIL FINISHED.

Chamber Sanding

Cut out 6 squares each of about 220 grit, 320 grit, 400 grit, and 800 grit sandpaper that will fit the entire burr on them. If you like shine and don’t mind the time it takes, throw some higher grit in there too.
Take the outer burr carrier out of your grinder, remove the spring from it, and set it aside. Then unscrew the inner burr, you’ll be attaching the sandpaper to this burr first.
Take one of the squares of your 220 grit and spray the back lightly with spray adhesive, then press your inner burr on it. Wait for it to dry. Then cut off the excess sandpaper from the edges and middle leaving only a ring of it.
Tape your inner burr to the outer burr that’s still screwed into the burr carrier. You can work around the sweeper post things with masking tape, or try to get the tape under them with the thin tape.
Apply cutting oil to the sandpaper.
Put the assembly of two burrs in the burr chamber (making sure the spring is out of the carrier) and spin it around with gentle pressure. Take it out from time to time to wipe off the oil and metal. Continue until the sandpaper is worn out.
Repeat 3-6 two more times to use 3 discs. You’ll need the adhesive remover to clean the burr to attach the next disc.
Repeat steps 3-7 for each size of sandpaper. You should use 3 discs for at least 220 and 320, and can probably go down from there. Those sizes do most of the work and the rest polish.

Now your chamber is sanded to be perpendicular with the driveshaft. But your carrier may not perfectly match, not yet.

Carrier Sanding

The big EK43 has a stainless steel carrier. It can be aligned with my method, but it’s a big pain to sand stainless steel. The EK43s uses an aluminum carrier. You can also get a drop in aluminum carrier for the big EK43 that’s already been made to be aligned from Titus if yours is off and you don’t want to do all the work of sanding stainless steel. Before doing any of this, you can also check to see if yours needs it with the marker method that’s used more extensively in Matt Perger’s shimming alignment.

Screw your inner burr back into the grinder. Ideally with a torque screwdriver to keep things even. Unscrew the outer burr from the carrier
Take one of the squares of your 220 grit and spray the back lightly with spray adhesive, then press your outer burr on it. Wait for it to dry. Then cut off the excess sandpaper from the edges and middle leaving only a ring of it.
Tape the outer burr, without carrier, to the inner burr. This can be a pain to pull off depending on the individual grinder, and you’ll need some thin tape. The sweeper posts will need to be able to fit over the tape this time.
Apply cutting oil to the sandpaper.
Put the carrier over the two burrs that are affixed to the chamber, apply gentle pressure and spin it to sand down the carrier. Same way you did with the chamber sanding.
Repeat with multiple grits and multiple discs of each grit the same way you did with the chamber.

Your carrier now has a parallel surface to your chamber. Which is also perpendicular to the driveshaft! Congratulations, your grinder is aligned the best it can be this side of a machine shop!

Final steps and notes

Don’t worry about matching things like my grit numbers exactly. They’re there as guidelines for cutting grits and finishing grits.
Your zero will change significantly. We’ve removed material from both burr mounting surfaces, so they will be physically further apart at the same settings until rezeroed.
Make sure to clean your grinder before using it.
Make sure to clean your burrs thoroughly of both adhesive and adhesive remover before reinstalling them.
Make sure to flush your grinder with at least a few doses of coffee, ideally more, before using it.
When you’re applying spray adhesive, have it in a box or other contained area to not make a mess.
Rubbing alcohol, acetone, dish soap, etc all do nothing on the spray adhesive. You do need an adhesive remover or oil. Trust me, I thought I wouldn’t need it.
If you use any water on your burrs for cleaning, dry it off right away. Especially for standard uncoated tool steel burrs.
You can repeat the chamber sanding once the carrier is done for a theoretically slightly more perfect surface, but it’s not really necessary.
Sanding times are for standard sandpaper, and should last several minutes to 10-20 minutes tops for a sheet. If using any especially long lasting sandpaper and it isn’t wearing out at all over several minutes, you can stop after a few normal sheets would have worn out and move on to the next grit.
When cutting sandpaper around the burrs, make sure not to get it too tight. Remember, the burrs have to fit into the sanded area. If the sandpaper is cut too tight and leaves some of the burr face uncovered, the burr will end up sitting on the unsanded edge around the burr. It’s ok if it goes just slightly beyond as well. So if in doubt, it’s better to have a disc slightly larger than needed, than one slightly too small to work.