Evolution of the --- Dot Speed Control
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Making a speed control is not a difficult process. I have provided detailed info below on how you can make your own round dot arm trombone speed control using off the shelf hollow tubing. You can even make one if you dont own a drill press. Provided your handy with basic hand tools and have a decent vise with a V grove for holding tubing. www.onlinemetals.com now has two outlets in the US. They are the single source for anything you might need for metals.
The concept for the speed controls came about after many years of frustration trying to slow down the dots on speed keys. The idea was to attempt to distribute the weight along the dot arm equally. To balance the dot arm so that it can produce higher quality dots. And to also provide a way to extend part of the weight beyond the end of the key. Extending the weight further behind the key allows lighter weights to be used. If you load up the dot arm with heavy weights in an attempt to slow down the dots, the key can become clunky and awkward to send with.
It evolved into three experimental designs.
1. For the round dot arm, a hollow tube that slips over the round dot arm and acts as a trombone to allow the end weight to extend several inches beyond the rear of the key for slow speeds.
2. For the flat dot arm, an aluminum body with a slot milled to fit over the flat dot arm. A weight rod slides back and forth in the aluminum body to vary the speed.
3. For the larger round dot arms on the McElroy/TAC keys, an aluminum body that fits over the dot arm -- with a weight rod that slides back and forth in the aluminum body to vary the speed.
Pictured below from top to bottom:
1. Top picture shows the experimental Mac/Tac speed control using a nickel silver weight rod that slips inside a larger trombone section. The trombone section then slides inside the aluminum body for a dual slide. Which can extend the weight up to 5 inches behind the key if desired. Its shown with two small brass weights. Having a weight at the front and rear balances the design as the body slides back and forth on the dot arm. Its fairly easy to duplicate on a drill press.
2. Pictured second from the top -- is the flat dot arm version with its sliding weight tube. You can see the milled slot for attaching to the flat dot arm. Its not easy to duplicate but it can be done using a "V" block to hold the aluminum body as the slot is milled. Then the V block is transfered to the drill press for drilling the various holes. And finally the V block is moved to a manual tapping device for the hole tapping.
3. Pictured at the bottom is the round dot arm hollow tube and as shown -- there is a weight at the front and rear of the device to help keep it in balance for best quality dots. Its easy to duplicate using off the shelf hollow tubing. The item can be drilled on the drill press and then the two holes tapped to accept the 8-32 nylon thumb screws. Fairly easy to duplicate with items usually found in a home shop.
What follows is detailed info on how to make your own trombone speed control as shown in the bottom picture above:
1. The round seamless tubing can be obtained from www.onlinemetals.com
You will need the .025 diameter by .03 wall brass or aluminum tubing and make a ferrule out of .375 dia by .065 wall tubing. Cut off a small length of the ferrule material and ream it out slightly with a size D drill bit. A complete 115 piece set of drill bits can be obtained from http://www.cdcotools.com/index.php for a very reasonable cost. Cut a length of .025 tubing 3" long and attach the ferrule to one end by first drilling out the ferrule with the size D drill bit using a power hand drill. It should be a very snug fit over the .025 tubing -- where you have to tap it on with a hammer. Taking care to not bend the tubing. The ferrule needs to be very tight snug fit to the tubing. It may take you several trys to get one thats correct. Reaming out the ferrule end with a larger drill bit helps to start the ferrule onto the tubing. The drill press vise I like to use is the grizzly.com H7575. Its the perfect size and has accurate V groves for holding tubing. The tubing with the ferrule can then be placed in the V grove of a drill press vise and using a 1/8" drill bit, drill a hole through the center of the ferrule and immediately place an 8/32 tap in the drill press chuck and tap the hole by turning the drill press chuck by hand. That will keep the tap running straight in the hole. Then do the same for the other end of the tubing. I use a 1" long 8-32 nylon thumb screw in the ferrule as that extra length allows attaching a standard small weight to the thumb screw. If your local hardware store dosnt have the nylon thumb screws you can obtain them from McMaster.com for a reasonable cost. If your fairly good around shop tools and have a decent drill press with a V groved drill press vise, you can make your own hollow weight tube fairly easily. Grizzly.com has their small milling machine at a reduced price in 2010 and its an excellent value. If you have a drill press equipped with an X-Y cross slide table from Grizzly, it allows you to move the vise back and forth easily. The grizzly G8750 X-Y compound slide table is 63 lbs and works really well with a drill press. It may take several attempts to make a decent speed control before you have one thats acceptable. The trick is to tap the 8-32 holes at front and rear of the speed control all the way through both sides. That way you dont need a special bottoming tap. The below picture shows the Grizzly H7575 drill press vise on the G8750 63 lb compound slide table. I equipped the drill press with a keyless chuck from CDCO Tools. Which allows fast changes between a center drill and the drill bits. All the holes should be started with a center drill. CDCO tools provides an excellent set of center drills. The below picture shows a V block in the vise that holds the item to be drilled. I use V blocks whenever possible as you can remove the V block and place it back on the vise while retaining the same position of the work piece. The vise jaws were made to run parallel with the drill bit chuck by setting it up with a magnetic dial indicator.
As far as the flat dot arm on the Lightning and Champion keys, its very easy to make a speed control.
The rectangular weights for the flat dot arm have 8-32 threads all the way to the bottom. All you need do is attach the same 1/4" hollow tube to the bottom of your existing weight using a short 8-32 screw. Use a file to shave off half of the 1/4" tube where it contacts the bottom of the weight so that it fits snuggly on the bottom of the rectangular weight. So in no time at all you can both a round dot arm and a flat dot arm key equipped with your home made speed control. You could even make them if you dont own a drill press if you can live with the holes not being perfectly straight.
You can use 000 steel wool to burnish the surface and it will give the brass a nice burnished appearance. Or polish them by placing the tubing in a power hand drill and use standard polishing compound. Coat the finished speed control with Krylon Crystal Clear coat to preserve the surface.
If you desire further info you can reach me via email: extendadot@gmail.com
Frank W7is
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