Bending 3/8 Copper Tubing

[n3lrx]

I'm making an Old Buzzard open wire tuner.
Anyone got suggestions on winding the coils? I'm using 3/8 copper tubing (refrigeration line) to make the matching coil and I seem to be making a mess of it. I'm winding it around 3" O.D. PVC pipe but it keeps kinking on me.

[Steve - WB3HUZ]

Fill the tubing with sand or kitty litter (no kidding).

[KB2WIG]

Try filling the tubing with sand...  no joke.  The sand exerts some pressure on the inside which is supposed to help prevent kinking...  fine sand works better i've been told..  

 Maybee try to bend the tubing in a semicircle on a larger form and then work to reduce the radis of curvature?  

Maybe you can use a larger dia.  ??

 klc

[WBear2GCR]

Yeah...

You likely can't make such a tight bend with 3/8"... perhaps with 1/4"??

Two tricks I know of:

1)freeze water in the line before the bend (not so good for this round and round thing)
2)put sand in the line before bending - fine sand here.

You really just need to make up a "slip roll" type of affair. Three rollers, with a round groove in at least one to guide the tubing. that and a crank... feed it in, it comes out bent... the distances between the rollers determine the circumference of the bend...

Good news... Harbor Freight sells one that mounts on the edge of a bench for ~50bux.

Trick three... run an asphalt roller or equivalent over the tubng - it's now flat ribbon, wind that. 

Trick Four - perhaps the right amount of HEAT[/b] applied as it is being bent over a  solid (pipe?) form might work... I'm thinking of a pipe on two bearings/pillow blocks/lathe, with a follower roller affixed just before the tubing reaches the pipe, the pipe being rotated dead slow under power, and HEAT being applied as it reaches the bend.... but the Harbor Freight tool is easier and faster.


Trick 5 - you can use/make a "bender" that is merely a pipe, with a way to clamp the tubing and an arm with a roller that runs around the pipe for like 1/2 of the circumference, then you'd have to index the work in half turns as you bend it... but the supply would have to move with the bend or you'd reverse kink it... if you turned the pipe, roller fixed -  that's a variation on Trick 4

I'd think that some copper flashing, sheared into strips would be more than sufficient... flat being easier to work with??

                _-_-WBear2GCR

PS. oh, another way to go is to make a much bigger, loose coil, like say 6-12" diameter - then affix one end on the form and rotate it around until it pulls down to a smaller size - but again if it's really 3/8" OD, then a 3" diameter is probably too tight.

[KF1Z]

Yep, the sand trick usually works well.....

Also anneal the copper first, to soften it.....the easier it bends, the less kinking.

So, straighten the length out anneal it (propane torch, heat the copper to almost dull red or at least color changes... you can dump cold water on it afterwards, but won't make any difference other than quicker cooling).......

Fill it with sand.... BUT BE CAREFULL not to bend it around much... you will work harden it before you get the coil formed!

Now go ahead and wrap the coil..... \

shake out the sand.....


You'll notice that if you make a mistake, and try to 'unwind' it.... the copper has work hardened, and will become hard to work with again......


Anyhow... have fun!

[n3lrx]

A 3 roll bender would be nice. First I'll make it simple, but here's what I'm eventually gonna try to do.

I'm making a sorta-tina-jj type tuner. But instead of alligator clips I was thinking of having the inductor fixed as usual, but Plexiglas or Teflon sheets on both ends. Each corner of the plastic would have a piece of all thread floating in bearings and a bearing and slip contactor on the all thread that connects to the coil. As you turn the shaft, the slip contactor slides up and down the shaft as it slides along the outside of the coil instead of the coil revolving and a wheel following along.

Also in doing so you'll have your four independent feed points to the coil. 2 for the inputs and 2 for the balanced line. You can tune  up one without moving the other.

I've seen similar things done to load towers on AM Arrays so I figured I'd try to make one myself.

[KL7OF]

A "square coil" is easily made with a standard hardware store variety tubing bender.  The copper tubing is formed into a coil with each coil loop having straight sides and 90 degree  corners formed with the tubing bender.   EASY and no kinked tubing...

[K1KFI]

I plan to make one of these too...Is it any easier to bend around a 4 1/2 inch form like the one Brent made? when you get it, its already in a coil; so, if anchored in a big vise, I'm thinking it should be fairly easy to form around the pvc pipe? The fine sand, available across the street in the cranberry bog sounds like a great idea!

 
K1kfi/Cliff

[WA1GFZ]

I lay it out on the floor and roll the form over the pipe to form a coil. I didn't use sand so it did go a bit flat. 3 or 4 inch pvc pipe makes a good form. Close wind it then spread the turns when your done. Spacing between turns should be at least 3/16 or the Q will suffer.

[KL7OF]

Why 3/8 dia tube?...1/4 inch will handle plenty of power................. I just had to try filling the tubing with water and freezing it...then winding a coil.    The temp has been hovering around zero here for a week, so it was easy to try outside in the big sky freezer.   Guess what?.... It doesn't work very well... . I really  like the edge wound coils found in Gates and other TXs  but I have not attempted to wind one (yet)...

[W2VW]

I lay it out on the floor and roll the form over the pipe to form a coil. I didn't use sand so it did go a bit flat. 3 or 4 inch pvc pipe makes a good form. Close wind it then spread the turns when your done. Spacing between turns should be at least 3/16 or the Q will suffer.

Roll your coils in stereo. That always gives spacing. Just unscrew one coil out of the next to separate. You need a matched set for superior coupler designs anyway.

[k7yoo]

THE BEST ADVISE ON THIS WHOLE LIST IS TO ANNEAL THE COPPER BEFORE DOING ANYTHING. HEAT THE WHOLE COIL AS HOT AS YOU CAN GET IT AND QUENCH IMMEDIATLY IN A BUCKET OF WATER. THE STUFF IS LIKE RUBBER UNTIL YOU WORK HARDEN IT AGAIN. I USED TO RECYCLE BSA & TRIUMPH SOLID COPPER HEADGASKETS THIS WAY. WORKED FB
SKIP

[WA1GFZ]

Man been a few years since I've played with either one of those head gaskets.
I helped two buddies build choppers years ago trumpet 750 and BSA 850 stroker. I wouldn't drive either one when they were done.  I did go on the back once at about a buck and wanted to wipe after it was over.
Like going down the road on a vertical sheet of plywood.

[WU2D]

I made snow shoes out of PVC pipe by pouring hot sand into the pipe with a stopper on the end. The sand is heated in an old aluminum kettle on a Coleman stove. You wait 60 seconds, pull the stopper releasing the sand, and the PVC is like spaghetti. You quickly put it around the form and it sets into any shape in a few minutes. 

Now if we could just do that with copper.

Mike WU2D

[WA3VJB]

Example of superior coupler design.

[WBear2GCR]

I made snow shoes out of PVC pipe by pouring hot sand into the pipe with a stopper on the end. The sand is heated in an old aluminum kettle on a Coleman stove. You wait 60 seconds, pull the stopper releasing the sand, and the PVC is like spaghetti. You quickly put it around the form and it sets into any shape in a few minutes. 

Now if we could just do that with copper.

Mike WU2D

Sorry, OM, a bit of QRM and fade on ur last over...

Say what? Snowshoes?

Oh, You mean you made the frame of snowshoes by heat bending PVC pipe??
Every try to make a larger bit of pipe flare significantly by this method?? Wondering if this could be made to happen... they mold acrylic and Lexan into bubbles for skylights and into hot tubs...

           _-_-bear

[W2VW]

Example of superior coupler design.

Match chicken cutlet or even metal patio furniture with that.   

[n3lrx]

Does Uncle Jed know you stole his still??

LOL