My First Straight Key

I purchased an MFJ-550 to test the waters of Morse Code.  I didn't want to spend a lot at first.  If I grow to master and enjoy Morse Code, I plan to eventually use an Iambic paddle.  While I didn't want to spend $100+ on a key I would likely never use much, a straight key seemed like a great way to learn fundamentals.

The MFJ-550 looked decent.  Some of its components are made from metal.  It's only $15, so I wondered how good it could possibly be.  I fashioned a base from Corian using my 6040 CNC machine.  That added some much needed weight to the frame so it remains firmly in place as I clumsily hammer out what I hope will some day be Morse Code.

I noticed the plastic frame of the key is quite flexible.  I secured it tightly to its new rigid base to reduce flex.  This helped some.

I soon decided a new knob would be more comfortable and printed a few variations to try.  A much larger knob with a convex top feels much more ergonomic than the smaller, smooth, concave knob of the original equipment.  The 3D printed knob isn't as glossy, but much easier to grip and operate.  You can see it pictured immediately below - second from the left and also in the picture of the final key configuration below it.

The cable I bought from MFJ was also on the cheap side, so I made sure to secure it to the base with a 3D printed strain relief.  The wires are very thin they seemed likely to break with repeated bending or vibration.

I started using my key on CWCOM and met Gerry there.  He is the author of Morsepower Blog, and shares a lot of very helpful information there.  His help made it much easier to improve my straight key.

I found consistent, accurate keying to be a challenge.  Gerry assured me that a properly tuned key would make a big difference.  I read his page on straight key tuning and it made a lot of sense.  I inspected the MFJ-550 and noticed that the hammer and anvil (contacts) were not square with each other.  When I pressed the key down, the contacts precariously touched each other on only their corners.  I had to press the key hard to to make a solid connection, and success varied from one try to the next.

To tune my key, I put the lever in a level configuration and measured the extra gap between contacts.  I printed a shim of 0.8mm and secured it between the plastic frame and bottom of the anvil.  The screw that attaches the anvil to the frame can be removed from the bottom of the frame.  I then used sandpaper to match each contact face to its mate as Gerry outlines in his blog.  This made a big difference in how easily and consistently the contacts operated.

After tuning, I set the gap small and the spring tension light.  The result is a relatively short, smooth, light action.  A light touch works well for this key as the lever isn't rigid enough to consistently operate under a heavy fist.  Looking forward to more practice on CWCOM.