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Harmonica Workbench: Size Matters

1 April 2011 99,279 views 5 Comments

 Kinya Pollardby Kinya Pollard

For those of you who are thinking what I think you’re thinking; get your mind out of the gutter! We run a clean operation here.

For the Harp-Tech, one of the most important signature techniques to master is “Sizing,” also known as embossing and burnishing. I prefer “Sizing” because the word does a better job of conjuring up the proper image of what the technique is intended to do.

The purpose of sizing is to shrink the reed plate slot just enough to allow the reed to pass through. “But Harpsmith,” you say, “aren’t the slots already properly sized for the reeds to pass through?”  “Oh sure,” I respond, “if you’re happy with the way your harmonica plays.”

For those of you who feel your harmonica can offer more, read on …

When properly executed, sizing the reed plate slots will improve the tone, volume, and playability of your harmonica. The benefits are immediate to any player who has mastered the fundamentals of bending. I am willing to bet that many of you have struggled with hitting those half step bends on the 2 and 3 draw accurately (relative to a C harmonica, this would be F-sharp and B-flat). And for those of you, who think you are spot on, prove it by taking Rod Piazza’s advice and record yourself. Listen to your play back and verify your recording matches a properly tuned F-sharp and B-flat of a piano, guitar or chromatic tuner.

How it Works 

Decreasing the air gap surrounding the reed as it passes in and out of the slot will increase the compression and enable the player to have greater facility over the reed. The photo shows the light surrounding (gap) the reed before the sizing process.


Common tools used by Harp-Techs for Sizing reed slots include: the handle end of Tweezers, Penny, Ball Bearing and Sockets—essentially anything hard with a small radius.

The limitations of these tools become painfully obvious when you reach the rivet end of the slot—the most important part of the sizing process! Notice how the reed stops the tool from proceeding. If you persist, the reed will dive excessively into the slot, thereby, complicating the reed profiling process.

So what do you do? Well, thank the Harmonica Gods for Dick Sjoeberg of Master Harp (http://harmonicasessions.com/?p=91). Dick invented the UST (Ultimate Sizing Tool) for the harmonica universe. Machined to exacting tolerances, this deceptively simple looking tool with indexed cut-outs for your index finger and thumb can easily tackle the “first 3rd”—and again—the most important segment of the reed slot sizing process.  

The blade that pushes the brass edge into the slot is machined at the optimum angle of 64 degrees.

Another innovation of the blade, which cannot be seen without magnification, is its polished rounded edge. This tool is designed to prevent gouging the soft brass of the reed plate slot.

Further examination also reveals that the leading edge of the tool is absolutely flat, enabling me to keep my strokes straight by using the edge of the reed as my “guiding fence.” Ingenious!


Taken It to the Bench

Working on top of a light box (available at most art supply stores) is a preferred technique for Sizing, as it automatically allows you to check your progress. The less light that shine through the space between the reed and the edge of the slot, indicates that you are heading in the right direction! Check out the photo and notice the middle reed. Compare the right side of the reed to the left side. See the sliver of light?

Begin by dipping the tip of the UST into a cap of mineral oil (easy to wash off when you are done). This will ensure a smooth sizing operation. With some practice you will be able to watch the “capillary” action (the flow) of the mineral oil, which will give you a clue of your sizing progress. If the oil drops too easily through the gap, then you have to “push” more brass into the slot.

Starting at the furthest corner with the UST held straight, pull towards the free end. Support the reed with a feeler gauge (shim) to take advantage of the straight and flat edge the reed provides. Otherwise the UST will slip away from you and dive into the slot.

As you reach the final third of the slot, you can remove the feeler gauge and “eyeball it.” By angling the UST towards the direction you are pulling towards will enable you to control the amount of pressure—the “touch”—applied to the slot edge.

In this photo you’ll be able to see that the slot corner has been “sized” away by the UST. I suppose this is why some Harp-Techs call it “burnishing.”

You can also verify the sizing process by plucking the inside edge of the slot. You will notice that your fingernail will snag against the ultra fine ridge of brass that you had just formed with your UST.




Oh, am I too late—don’t despair! ;o) 
First peer into your light source (light table) under magnification, check to see if you hadn’t inadvertently pushed the reed off its rivet access. This would most definitely cause the misaligned reed to hit and click against one side of the reed slot. In this photo you’ll notice the middle reed has a disproportionate amount of light in the bottom right corner. This means the left corner is clicking against the reed plate.

If this is not your case, then look carefully, and you will notice a burr that completely blocks the light form shining through. This is the point where the reed slot is making contact with the edge of the reed.

If the reed is misaligned, simply turn your reed wrench (http://rsleigh.com) in the opposite direction until an equal amount of light appears on both sides of the reed.

To remove burrs, position the UST flat underneath the reed and up against the misaligned ridge. Gently slide the UST forward and back until you “push back” the nasty burr. Take your time, stop, and check frequently by plinking your reed to see if the reed cleared properly.

Another effective technique is to gently slide—forward and back—a .001” shim in between the burr and the reed.

Additional Benefits

From time to time, you will discover reeds that are slightly too short for the length of the slot, causing unnecessary loss of pressure. Easier than stretching the reed, I found the UST to be a fabulous tool for closing the gap on the leading edge of the slot (free end of reed). With all extreme edges eliminated around the tip of the reed, I can expect smoother airflow as well.

Hidden from view, is the all-important “Zero Point”—to coin a Dick Sjoeberg term. Zero Point refers to the gap, the distance between the bottom of the rivet end of the reed and top of reed plate. The optimum is .002” (0.05mm).

I found the UST to be extremely effective in setting this distance. Position the UST along the ridgeline of where the reed meets the rivet pad. While applying even, downward pressure, slide the UST left to right. Check the gap with the .002” feeler gauge.

After you have successfully (relative term, isn’t it) sized all twenty slots, proceed with reed profiling and tuning (not covered in this issue).

Closing Thoughts

If you endeavor to build consistently superb playing harmonicas, then mastering the art of sizing reed plate slots should be on top of your “must learn” list. As for me, along with my Richard Sleigh reed tools (ref: Harmonica Sessions August 2009), the Dick Sjoeberg Ultimate Sizing Tool (UST) is never out-of-reach on top of my workbench. I highly recommend you order one today: www.masterharp.com

Celebrity Hands

Guessing who’s hands these belong to should be a “no-brainer” (if you listen to the Rolling Stones).

Printable Version

“Play the notes people want to hear” © 2008

Kinya Pollard
The Harpsmith

Musician & Harp-Tech
Harmonica Masterclass Workshop Instructor
Mel Bay’s Harmonica Sessions Columnist
www.bluesharmonica.com Harp-Tech Expert


  • Winslow Yerxa said:

    Kinya – this looks great and is an improvement on the router blades I’ve been using. But how can the reader OBTAIN this tool? A link or other reference would be greatly appreciated.


  • Dick Sjoeberg said:

    For those interested of buying the UST, please email me at


    Dick Sjoeberg

  • Bernhard said:

    I would like to know
    - if the tool will work with Seydel’s steel reeds
    - if the tool is in stock


  • Dick Sjoeberg said:

    - The UST works perfectly with Seydel steel reeds
    - They are available from stock and due for immediate shipping.

    Dick Sjoeberg

  • Dick Sjoeberg said:

    I have got several requests if i do PayPal. I do PayPal. For those interested of ordering a UST, please use my verified PayPal account
    info@wawamusic.com. Before making any payment please contact me at

    Dick Sjoeberg