Bend chart for 3/8" aluminum tubing

[Charles L. Cotton]

Does anyone have or know of a bend chart for bending aluminum tubing? I need the set-back numbers. A friend and I are building 2-meter LFA yagis and are having a hard time making the end pieces for the driven element loop. The bends aren't coming out the right size in terms of spread; i.e. keeping the two driven elements correctly spaced. Here is a link to the LFA loop design. http://www.g0ksc.co.uk/making-the-lfa-loop.html" onclick="window.open(this.href);return false; We've tried the method shown, but it doesn't work, the end piece is too short. We've added the depth of the 3/8" slot on the bender (approx. 3/8") and the end piece is too long. If we have to, we'll just stay with the trial and error method, but a bend charge would sure speed up the process and save material.

This is the bender we are using: http://www.lowes.com/pd_331956-943-6657 ... facetInfo=" onclick="window.open(this.href);return false; BTW, if you need one, get a bender with longer handles or use cheaters! It's mighty tough to get the bend started.

Does anyone know of a bend chart showing the set back for tubing this small? I know they are available for conduit, but I can't find one on the Internet for tubing.

Thanks,
Chas.

[puma guy]

There should be some old instrumentation/electrical fitters here on the forum. The tubing bender you show is for1/4" - 3/8" tubing. Are you using 3/4" or 3/8" aluminum? Is the width between the long elements critical? If not you couldn't you bend the end pieces to what ever dimensions and radius are calculated by the bender, make two and fit with the long pieces? The drawing indicates swaged type connections is that how you are joining the pieces? Also would it be possible to bend each end of the long pieces, leaving some extra and then cut to meet the dimensions. That would mean just two joints instead of four and less hassle to fit to parallel longitudinally. BTW is this thin wall tubing or rigid?

[Charles L. Cotton]

There should be some old instrumentation/electrical fitters here on the forum. The tubing bender you show is for1/4" - 3/8" tubing. Are you using 3/4" or 3/8" aluminum? Is the width between the long elements critical? If not you couldn't you bend the end pieces to what ever dimensions and radius are calculated by the bender, make two and fit with the long pieces? The drawing indicates swaged type connections is that how you are joining the pieces? Also would it be possible to bend each end of the long pieces, leaving some extra and then cut to meet the dimensions. That would mean just two joints instead of four and less hassle to fit to parallel longitudinally. BTW is this thin wall tubing or rigid?

The subject line had a typo, we've bending 3/8" thin wall aluminum. The measurements are critical, in fact the designer said to cut them to the exact length which seems a bit overkill. That said, the spacing between the two driven elements is critical. The two driven elements are made from 1/2" aluminum and the end pieces are the 3/8" that slide into the 1/2". A single bent 1/2" won't work because we tune the antenna by sliding the end pieces in and out. Once tuned, they will be secured with a single screw in each.

Chas.

[powerboatr]

http://www.sheetmetalguy.com/" onclick="window.open(this.href);return false;
try that link
I have a ASA aviation mechanic handbook and tried searching for it online to no avail as far as reading whats inside
i took photos of the pages for bending alum with the setback, and you may be able to add in the total thickness of the tubing to get a real world "K" number for the setback
is its 3/8 soft tubing...I know, but is it 3/8 OD or ID.
aircraft tubing is sized OD, as in a #4 (4/16ths)is 1/4 od with 1/8 wall thickness which equates to 1/8 id ,
then flex hoses are listed as their ID for size

[powerboatr]

last attachment

also i was thinking
if the 3/8 tube is designed to slide into the 1/2 tubing
and that is how you tune i suspect the antenna, the set screw is already calculated for interference or its gain correct
the setback amount may not be that critical because you have the ability to shorten or lengthen the inserted end and the other end you could trim to size after the bending is done
ONLY IMO
if your going to be using a bender for precision bends, get a real good one from http://www.aircraftspruce.com" onclick="window.open(this.href);return false;

http://www.aircraftspruce.com/catalog/t ... 470-fh.php" onclick="window.open(this.href);return false;
http://www.aircraftspruce.com/pages/to/ ... bender.php" onclick="window.open(this.href);return false;
or some other supplier that deals with close tolerance tools
a universal bender for all sizes 1/4 through 3/4 is to sloppy imo

anywho
hope it helps

[mrvmax]

http://www.swagelok.com/downloads/webca ... -13-43.pdf
This manual lists the offsets/gain adjustments (page 23, 7/16 for 3/8 tubing), it is much harder using the benders you have Charles. The Swagelok benders are much better and easier to use for precise bends.

[RX8er]

I've got a buddy in the machine shop at Gulfstream Aerospace. If you send me the ID, OD, tubing metal type, length between the bends and the tool using to bend, he has a computer program that will give the exact star and end dimensions needed for the bend.

Also, to keep from collapsing the tube when you bed it with a very tight radius, fill it up with water and freeze the tube leaving one end open for expansion. Then, the bender won't crush the tube.

[mrvmax]

Also, to keep from collapsing the tube when you bed it with a very tight radius, fill it up with water and freeze the tube leaving one end open for expansion. Then, the bender won't crush the tube.

That is why the Swagelok benders have rollers.

[RX8er]

Also, to keep from collapsing the tube when you bed it with a very tight radius, fill it up with water and freeze the tube leaving one end open for expansion. Then, the bender won't crush the tube.

That is why the Swagelok benders have rollers.

Yes, I agree.

I saw the tool Charles got from Lowes, hence why I recommended freezing them first if he's had an issue with crushing the tube. I know with copper and brass the bends he's making, it would never happen unless you freeze or go with Swagelok.

Charles, I think most auto parts stores have the Swagelok or a similar roller based tubing benders. I know the Napa near me does as I used them when I redid the brake lines on my boat trailer.

[cheezit]

chas we bend lots of 316ss seamless at work, i think your issue is a poor quality tool . look for an imperial bender second choice would be ridgid.
measure and mark the tube make your first bend, measure your next bend. line your marks up with the "L" on the bender and use a speed square to make sure it square.
also always keep your bends to the left it makes things easer.
hope this helps you

[RX8er]

Freezing works, clean dry sand is faster - pack it full, bend slow.

The only problem I have had trying the sand method is that the sand not being packed tight enough. I did see some really fine grain sand offered up from someplace not long ago just for this though. I think if it is fine enough and you can plug the ends good, it'll work.

[Charles L. Cotton]

Thanks guys, I think we have the problem solved.

Regards,
Chas.