more construction; trapeze upgrade
So i finally got around to upgrading my trapeze. The previous one i had built did not have bar ends, and i eventually decided that i really wanted them. So finally one night i went down into the shop with the intention of cutting and grooving a new replacement bar, and then disassembling my trapeze and swapping the new bar in. But the original trapeze had been a prototype design to begin with, and in the time since i had built it i had come up with several design improvements. Plus, the original bar was 1-1/8th inch, and was pretty darned heavy already. So instead of simply swapping the bar out on the original trap, i decided to do a complete do-over and produce Trapeze Design Rev 3, with a 1 inch diameter bar. (Rev 2 was only on paper, and never built.)
The new trapeze is a cable core design, which uses a two-part donut-like assembly which acts as both a rope thimble and a captive collar for the wire rope core. The cable passes through this assembly, around a groove in the bar, and back out again. The rope is then passed around the thimble part of the donut and backspliced into itself, about 6 inches away from the thimble (so you can undo it and inspect the cabling without needing to undo the splice). Rope eye is then lashed together and down to the bar. Cable is 3/16ths 7x19 construction, vinyl coated. Rope is 3/4 nylon 3-strand laid.
Much of this process i took photos of. So, much like the recent entry about the hoop, here is a photo log of its fabrication. Some of the assembly was done at craft nights at other folks houses, which is why there are so many different backgrounds in these shots :-)
Step 1. (not shown) Cut off a 36 inch piece of 1-inch diameter 303 stainless steel rod stock. Stick it into your lathe and cut 2 grooves in it, each 1/4 inch wide and 1/4 inch deep, each 6 inches in from one of the bar ends.
Step 2. Make the funky donut thimbles. Step 2 takes longer than Step 1...
A) Start with a length of 2.5 inch diameter 6061T6 aluminum rod stock. Slice off 4 discs wide enough to be 5/8ths inch wide after they've been faced flat.
B) Chuck up discs in lathe, face them off:
producing these:
C) Drill 1-inch holes in the center of these (not all at once; about 8 different drills used):
D) Each one of these is now mounted on an expanding arbor, and we use a radius tool to carve out
a 90-degree cut of slightly over 3/8th radius.
This leaves us two sets of these:
Stick them together and you get this:
They're held together with 3 1/4-20 socket cap screws in a bolt circle. To lay out and drill the bolt circle accurately, i needed a way to hold these pieces down on the milling table, while making it possible to drill/countersink the holes in an accurate and repeatable fashion.
E) I made a jig to hold/align them that fits into my milling vise. Pick up the edges of the jig with an edge finder, and then you can easily move to the exact center of the piece being held in the jig.
piece fits over hole, then plug fits into piece and hole, then bolt holds it all together.
F) Then spot-drill locating holes and drill out the bolt circle.
g) Now that we have the bolt circle drilled, we can use the holes, along with some setup blocks, to make a locating jig on the milling table, to allow us to mill out the slot that the cable will pass through:
Here is a shot of the two finished thimble halves, and one end of the bar.
When assembled on the bar, the donut-thimble looks like this. The cable will go through the slot, around the bar (in the groove), and back out again.
Each thimble has two set screws on the bottom side, to prevent the bar from rotating around inside of the thimbles. (making of set screw holes not shown)
ASSEMBLY:
I've already crimped a 6-inch cable loop at one end of the cable. slide cable loop over thimble parts and bar.
And then into groove in bar.
Now push thimble parts together.
Tighten bolts. The cable loop is now trapped in the groove in the bar.
Tape the cable loop.
The rope i used is 3/4 inch nylon, standard 3-strand laid twisted braid. The cable runs through it along most of its length, up until the eyes at the bar and rope thimbles on the ends of of the trapeze lines. Getting the cable through the center of the twisted rope was sort of annoying.
Backsplice the eye loops. Nylon is slippery stuff. 9 tucks. Oy. klingonlandlady had just cooked up a mondo pile of brussel sprouts as i was starting to do all of the splices. I ended up playing this mental game where i would do a row of tucks, followed by eating a brussels sprout as a reward. (i *like* brussels sprouts. Yep, i'm weird. but you already knew that.)
Loop the eye around the thimble, then lash down to the bar with 3mm cord.
Do both sides. Splice the eyes at the top of the ropes (not shown).
Structural assembly is now complete.
Wrap some cloth padding strips around:
Put some red suede covering around the hanging thimbles:
Add red suede covering around bottom of ropes/padding, and tape the bar.
Finished product here:
The new trapeze is a cable core design, which uses a two-part donut-like assembly which acts as both a rope thimble and a captive collar for the wire rope core. The cable passes through this assembly, around a groove in the bar, and back out again. The rope is then passed around the thimble part of the donut and backspliced into itself, about 6 inches away from the thimble (so you can undo it and inspect the cabling without needing to undo the splice). Rope eye is then lashed together and down to the bar. Cable is 3/16ths 7x19 construction, vinyl coated. Rope is 3/4 nylon 3-strand laid.
Much of this process i took photos of. So, much like the recent entry about the hoop, here is a photo log of its fabrication. Some of the assembly was done at craft nights at other folks houses, which is why there are so many different backgrounds in these shots :-)
Step 1. (not shown) Cut off a 36 inch piece of 1-inch diameter 303 stainless steel rod stock. Stick it into your lathe and cut 2 grooves in it, each 1/4 inch wide and 1/4 inch deep, each 6 inches in from one of the bar ends.
Step 2. Make the funky donut thimbles. Step 2 takes longer than Step 1...
A) Start with a length of 2.5 inch diameter 6061T6 aluminum rod stock. Slice off 4 discs wide enough to be 5/8ths inch wide after they've been faced flat.
B) Chuck up discs in lathe, face them off:
producing these:
C) Drill 1-inch holes in the center of these (not all at once; about 8 different drills used):
D) Each one of these is now mounted on an expanding arbor, and we use a radius tool to carve out
a 90-degree cut of slightly over 3/8th radius.
This leaves us two sets of these:
Stick them together and you get this:
They're held together with 3 1/4-20 socket cap screws in a bolt circle. To lay out and drill the bolt circle accurately, i needed a way to hold these pieces down on the milling table, while making it possible to drill/countersink the holes in an accurate and repeatable fashion.
E) I made a jig to hold/align them that fits into my milling vise. Pick up the edges of the jig with an edge finder, and then you can easily move to the exact center of the piece being held in the jig.
piece fits over hole, then plug fits into piece and hole, then bolt holds it all together.
F) Then spot-drill locating holes and drill out the bolt circle.
g) Now that we have the bolt circle drilled, we can use the holes, along with some setup blocks, to make a locating jig on the milling table, to allow us to mill out the slot that the cable will pass through:
Here is a shot of the two finished thimble halves, and one end of the bar.
When assembled on the bar, the donut-thimble looks like this. The cable will go through the slot, around the bar (in the groove), and back out again.
Each thimble has two set screws on the bottom side, to prevent the bar from rotating around inside of the thimbles. (making of set screw holes not shown)
ASSEMBLY:
I've already crimped a 6-inch cable loop at one end of the cable. slide cable loop over thimble parts and bar.
And then into groove in bar.
Now push thimble parts together.
Tighten bolts. The cable loop is now trapped in the groove in the bar.
Tape the cable loop.
The rope i used is 3/4 inch nylon, standard 3-strand laid twisted braid. The cable runs through it along most of its length, up until the eyes at the bar and rope thimbles on the ends of of the trapeze lines. Getting the cable through the center of the twisted rope was sort of annoying.
Backsplice the eye loops. Nylon is slippery stuff. 9 tucks. Oy. klingonlandlady had just cooked up a mondo pile of brussel sprouts as i was starting to do all of the splices. I ended up playing this mental game where i would do a row of tucks, followed by eating a brussels sprout as a reward. (i *like* brussels sprouts. Yep, i'm weird. but you already knew that.)
Loop the eye around the thimble, then lash down to the bar with 3mm cord.
Do both sides. Splice the eyes at the top of the ropes (not shown).
Structural assembly is now complete.
Wrap some cloth padding strips around:
Put some red suede covering around the hanging thimbles:
Add red suede covering around bottom of ropes/padding, and tape the bar.
Finished product here: