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Torsion Bar Key Project

Posted: Fri Apr 24, 2015 9:49 pm
by admin
I built two straight keys a couple of years ago based on plans by Rich (WB9LPU) called the Simple Straight Key Construction Project. This was my first time building a key. With Rich's well written detailed instructions I was able to build some nice working straight keys with my own two hands using simple tools. I was hooked !! Recently I ran across the Torsion Bar Key by W1SFR and was fascinated by it and had to build one for myself. This thread will chart my progress. -Joe

W1SFR TBKII
http://kx3helper.com/single-lever-keys/

Detailed plans for Torsion Bar Key here.
ARRL QST Archives Search
Dec 1982 - QST (Pg. 22)
Torsion Bar Key, The
Author: Leary, Thomas, W0VTP

Simple Straight Key Construction Project
https://sites.google.com/site/wb9lpu/ECI-KEY9.pdf

Re: Torsion Bar Key Project

Posted: Fri Apr 24, 2015 9:52 pm
by admin
Brass and drill rod (torsion bar) arrived today. First step is to cut pieces to size and square everything up on the belt/disc sander. I had the base cut by the factory but it still needs squared up on the sander.

I buy all my metal from Online Metals (http://www.onlinemetals.com) Good prices and fast shipping !

Below is the metal list. I ordered two base plates in case I made a mistake. There is plenty of material for mistakes or for building two keys, whichever comes first! NOTE : Have base cut .125 inches larger in each dimension to allow for machining. (2.25 x 3.625)

1/8" 01 DRILL ROD - 36" $1.69 1 $1.69
0.25" x 0.5" Extruded C360 H02 Half Hard Brass Rectangle Bar - 11" $4.15 1 $4.15
0.25" Hot Rolled C464 Naval Brass Plate - 2.13" x 3.50" $8.22 2 $16.44
0.25" Extruded C360 H02 Half Hard Brass Square Bar - 24" $3.95 1 $3.95
0.25" Extruded C360 H02 HALF HARD Brass Round - 24" $3.02 1 $3.02
20 GA .032" C260 HALF HARD H02 BRASS SHEET - 0.25" x 24"


I order hardware from McMaster-Carr (http://www.mcmaster.com) Good prices and fast shipping ! Note : I economize by buying longer screws and cut them down to size as needed. You will need to cut some screws in half for this project. Same goes for the Shoulder Spacer insulators. You will need to cut them down to size.

1 92313A106 Type 316 Stainless Steel Cup Point Set Screw, 4-40 Thread, 1/4" Long, Packs of 25
1 92313A190 Type 316 Stainless Steel Cup Point Set Screw, 8-32 Thread, 1/4" Long, Packs of 25
1 91145A138 Nylon 6/6 Unthreaded Shoulder Spacer with Flange, Long Barrel, #4 Screw Size, .500" Length, Packs of 100
1 92741A100 Brass Round Knurled Thumb Nut, 4-40 Thread Size, 3/8" Head Diameter, 1/4" Overall Height, Packs of 25
1 92443A110 Brass Binding Head Slotted Machine Screw, 4-40 Thread, 1/2" Length, Packs of 100

Re: Torsion Bar Key Project

Posted: Sat Apr 25, 2015 7:15 pm
by admin
Spent 2 two hours in the shop this afternoon carefully cutting, squaring and cleaning up all the pieces. Starting to look like a key ! Still a long way to go though. Next step is to make some drill templates build some simple jigs so I can accurately drill holes.

tbk_step1.jpg
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Re: Torsion Bar Key Project

Posted: Sun Apr 26, 2015 7:01 pm
by admin
Spent a few more hours in the shop today with the key. I created a drill template by using the original QST article. I blew the diagram up on my photo copier by 155% to match the dimensions of my parts. Your percentage will vary depending on the actual size of your finished parts. This saved many hours of finding and marking holes by hand. I punched and drilled all of the holes on the base plate and upper torsion bar support. They fit together like a glove ! The secret is to take your time to punch and drill as accurately as your eyes and machine will allow.

tbk_step2.jpg
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Re: Torsion Bar Key Project

Posted: Sun Apr 26, 2015 7:05 pm
by admin
This is what it looks like after fiting the upper torsion bar support with the base. Everything is lined up nice and square. So far so good.....

Re: Torsion Bar Key Project

Posted: Tue Apr 28, 2015 12:06 am
by engineercm
Joe, it's already a beaut. You're quite the craftsman. Of course, that goes along with being a CWOP.

Re: Torsion Bar Key Project

Posted: Tue Apr 28, 2015 2:07 am
by admin
Thanks Clark ! Anyone can build this key with some basic tools and lots of care and patience. This is a fun key to build. It's my first paddle. I'm waiting for some set screws, special brass screws and insulators to come in. Working on the finger pieces now. I'm scaling down my Begali HST finger pieces. Trying not to reinvent the wheel. I will try to get it finished and on the air in a week or two.

Re: Torsion Bar Key Project

Posted: Wed Apr 29, 2015 2:28 am
by admin
It's alive ! I spent a couple of hours in the shop tonight carefully drilling and tapping the holes to mount the torsion bar assembly and lever arm to the base. I wanted to test the tension so I threw together some makeshift contact posts and hooked it up with jumper wires. I gaped the contacts to about .3mm. Even without a finger piece it really exceeded my expectations ! Very smooth and responsive with just about the right amount of spring tension. The lever arm returns back to the center position nicely. I plan to try a brass torsion rod at some point to see what the tension is like compared to the steel drill rod. I made a short video. https://www.youtube.com/watch?v=nQU1OBYYaHo

Re: Torsion Bar Key Project

Posted: Fri May 01, 2015 7:02 pm
by admin
Spent some time in the shop the past couple nights working on the binding and contact posts. The contact posts were too close together so I had to machine the posts down to 3/16. Not fun. I will make a note of this issue on the drawing for future builds. The plastic flanged shoulder spacers worked perfectly for insulating the posts. Just cut them down to .125 and put one in the top and bottom of the hole. I changed the binding posts from the origianal plan to simply use 4-40 thumbnuts and a screw for dit and dah contacts. The thumbnuts are insulated from the base the same way I did the contact posts. The ground post is still .25 square bar like the plans called for. Works and looks pretty cool. Saves some work too. I wanted a single finger piece so this is what I came up. I used some Zebra wood I had laying around. I milled it down to .25 inches thick and mounted it to the lever arm with two 4-40 screws. It works and feels good. I will have my Son machine me some nicer looking pieces in his shop.

tbk_finger_piece.jpg
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Re: Torsion Bar Key Project

Posted: Sat May 02, 2015 8:16 pm
by engineercm
Great piece of work (in the good sense). I love your comments about "milling" and "laying around". You must have quite a machine shop.

There's a guy at Dayton that sells finger pieces out of different kinds of wood. They are gorgeous.

Will you add some kind of finish to the base of the key?

Clark