Monday, December 19, 2011

Cable Splicing Clamp

 To form the looped end on the control cables using a 5 or 7 tuck splice method, or on bracing cables using the solder wrap method, the cable end must be held firmly while doing the work.  To hold the cable end you need a Cable Splicing Clamp.  The clamp is held in a vise while the other end of the cable is pulled snug during the splicing operations.  The clamp at right is from a 1930s Nicholas-Beazley catalog K.  The tab on the right is clamped in the vise and the wing nut on it is tightened to keep the clamp from rotating.  The wing nut at the top is used to move the center slider to clamp the cable securely in the curved jaws.  Back then a gallon of clear dope sold for $1.85.

 This picture from "Aviation Mechanics Made Easy" Vol. 4 pg. 526 (c1942) shows a clamp in use  on a control cable.  It also shows the other tools needed to form the splice, a marlin spike, rawhide mallet, and wire cutters.  You also need a hardwood block to pound against when tightening up the tucks.
 This clamp is from a 1944 Supply Division catalog pg. 75.  That same gallon of Berryloid dope was then $2.65 although a new Sensenich prop. for a J-3 was only $35.
 The one I've decided to use as a model to make my own is one I borrowed from Rich Wilbur who is restoring 2 WACO NINEs.  He made this one in A&P School so it seemed like something I should be able to copy.  I've had this for a year but couldn't find a piece of 1" steel to make the holding block on the vise end.  While making some tools for the Cessna 140 project I realized this block could be made from 1/2" x 1" mild steel like the clamp base piece.  All I need to do is screw 2 pieces together to make a 1" block.  In the end this is probably a better idea since it solves the problem of how to install the bushing which holds the block and clamp base together.
The 2 block halves were cut 1-1/2" long, ground smooth on one side, and squared up on the ends.  The Base piece is also cut from 1/2" x 1" mild steel 3" long.  The Jaw piece at the end is the same size but cut from 1/4" thick mild steel.  The pivot bolt is 3/8" - 24 UNF x 3" long.  The 2 Slider bolts are 1/4"-28 UNF with a grip length of 2-5/8".  The threads need to bottom out in the Jaw plate.  The ends get ground off smooth and staked in place.
The first part is the Knob for tightening the clamp to hold the cable.  It's a round disc of steel 1/4" thick, 1" in diameter, with a 3/8" - 24 UNF threaded hole for the bolt, and knurled on the edge for a better grip.  I started by drilling and tapping the hole in the end of a piece of 1/4" x 1" mild steel bar stock from Tractor Supply.  It's easier to drill and tap the bar than the finished disk.
A 3/8" hole was drilled in a piece of oak to use as a pivot to grind a nice round end on the bar.  The 1" end was then cut off the bar.  By making 2 45 degree cuts and then a square cut across the bar the piece is close to the desired finished (round) shape.
By using the same process but with the board clamped in place and moved closer to the belt in small increments the knob was turned to a nice round shape.  I have no way to knurl the knob so instead I used the band saw to cut into the edge of the knob about 1/32'' deep. Cuts were made dividing the edge into quarters, then eighths, and then 16ths.  It makes a nice grip surface.  The top and bottom edges were filed to soften the corners.

After using the Splicing Clamp to make about 10 cables, for my Fly Baby, I decided I needed to stop and make a larger, easier to grip, tightening wheel.  I originally made the wheel from the same 1/4" x 1" bar stock used for some of the parts.  It seemed clever and would work fine with flexible cable.  With the non-flexible 1x19 cable it was just too hard to get the cable tightened against the thimble.  You could do it but it took a lot of wiggling the cable while turning the wheel.

I decided I needed a wheel closer to 2" in diameter with nice big knurls for a good grip.  I also wanted to keep it 1/4" thick to have a reasonable number of threads.  If it wears out I may need to make one from 3/8" thick steel.
 The only piece of 1/4" steel I had was on some tools for making wire ferrules for the WACO internal bracing wires.  I decided it would be fine with a 2" hole in the base since I just clamp the base to my work bench.

I located a pilot hole for the 2" hole saw then used the saw to draw a centerline to layout a pattern of holes for the knurls.  It certainly took the guesswork out of where the center of the holes should be.

 I center punched a pattern of 12 holes, pilot drilled them with a 3/16" drill and finished them with a 5/16" drill.

 To round the edges of the holes, it makes more comfortable knurls, I countersunk the holes with a 1/2" center drill, steeper flutes.  Then I lightly countersunk then with a 1/2" twist drill.  It really makes a nicely rounded edge to the holes.

 Back to the 2" hole saw to cut out the wheel. I cut half way from each side and when it got close just pounded it out with a light hammer blow.  I didn't want to risk this 1/4" slug flying around.

It's looking like a thumb wheel.

 I cleaned up the outside radius with the belt sander and the chamfered the edge at 2 angles, sort of like with the hole edges.

 The remaining burs were cleaned up with the small sanding drum on the Dremel tool.  It needs to feel good in your hand and no sharp edges.
 The hole was tapped with a 3/8" fine thread to spin on the center bolt.
I had a little trouble getting the 3 bolts apart since I had put Loctite on the threads and cut off the head of the 3/8" both after tightening it in the clamping bar.  A little heat took care of the Loctite.  I greased the threads and the pivot with Molykote to keep the friction low.

A much nicer wheel.

No comments:

Post a Comment