I use lots of K & S brass in my models. To soften the tubing for bending (aneal) I heat it with a small propane torch. The brass "work hardens" after it is bent. You can also purchase soft tubing from K & S which is very easy to bend, so heating is not necessary. If you are going to paint it anyway you can also purchase K & S aluminum tubing which bends easily.

The water monitor on my Coast Guard boat has some "tricky" bends. This is the only picture I have on hand of it. It is kind of a corkscrew.

Phil, Not long ago I posted a link on this site to a recent video I made on bending small plastic brass/copper tubing. This involves making a small bender tool. (The tool is optional but handy.) The tool is essentially a pully sheave shape with the diameter equal to the radii of the desired bend in the tubing (need to compensate for the spring).

The "secret" to preventing the flattening or oval shaping the cross-section of the tubing can be accomplished several was as mentioned in other replies. However, using a close fitting extension spring is probably the best bet. Using a filler in the tubing to prevent the distortion would require close to 100% density of the filler to avoid shifting of the filler.

The close fitting compression spring worked very well for me on my last build which used .093 inch OD brass tubing, with some pieces having multiple bends.

Solid rod works better than tubing but I use the ID of the tubing to strengthen the joints by adding smaller diameter rod inside the joints. This is because this boat is a Springer tug which needs to take a little bumping. Drawing shows the concept of the cross joint (same for a "T" joint).

Lew
Florida 😎, USA😍

Video link for bending:

I find using bowden cable works for me available in most sizes i use old motorcycle cables

For thin tubing I anneal first and then insert solder wire, it comes in various diameters, and bend over a suitable curve.
When done retrieve the solder wire. The brass is frequently surface marked afterwards.

I checked on the internet for cleaning brass and came across this, using an aluminium foil lined container and hot water and baking soda for getting a polished / clean surface.
I have not tried it yet but will soon.

Roy

I use brass rod not tubing so much easier. Also depends on the how sharp of a bend and tubing diameter. Tubing bender for larger "R" this photo is of my 47 CG MLB I'm building. the front railings are tubes, aft are rods

Fill tube with sugar before bending I was told, it helped but didn’t make a real smooth bend.

Others have used heat to soften the tube during bending process.

I was using copper 1/4” tubing to run sheet lines when building my Emma sailboat. Which is still waiting for it’s first day on the water, once the hand heals it will happen.

I always used some small bore bending springs which fit outside the tube.
Mine are from K&S and are available from Hobbies UK or most model shops. As already mentioned you should anneal the tubing first.

Hi Phil, a few years ago I had this need and I was about to buy a pipe bending tool like the one in the link.
I didn't need it anymore so I didn't buy it anymore, so I can't tell you how good and effective it is.

https://www.amazon.it/Toolwiz-Curvatubi-manuale-3-1/dp/B07TT28B56/ref=asc_df_B07

Hi
As Stotty1111 said you must anneal it first.
I have filled the tube with water then freeze it, used a set of bending springs, used a pipe bending tool that is used for car brakes pipe, also used brake pipe as this is sofe copper it can be bent by hand but will not take a tight bend.
Fred

If the tube is wide enough, block one end with solder, fill tube with fine dry sand, tamp it, then block other end with solder and bend away, probably best to anneal the area to be bent before you start!
Tony