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Tubing Bending

In most situations our tubing can be cold-formed (bent or flared) without damage providing some form of tubing wall support is part of the bending process. Annealing (softening) should only be required if extremely tight radius bends or complex shapes are needed.

.018" Tubing:

We have successfully cold-bent the .018" diameter tubing over a 1/16" diameter mandrel. This produces an "after spring back" bend of about 10 N-Scale inches which seems small enough for most electrical conduit work, street lights, and general lighting applications. After forming, microscopic inspection showed no evidence of surface cracking either on the extension (outer) or compression (inner) surfaces.

In this test, we used internal tubing wall support by sliding our (N2112) .012" diameter stainless wire inside the tube prior to bending. Once formed, removal of the wire is best accomplished by pulling the wire through a .012"-.014" slot cut in a scrap piece of brass, aluminum or other sturdy material. Allow the tubing face to butt up against the far side of the slot, then pull the wire through using pliers. Doing it this way puts all of the stress on the tubing face and eliminates the possibility of accidentally distorting the tubing shape you've just so carefully created. Only gentle support of the tube is required during this "extraction" process. Alternately, if you don't have a hobby saw that will produce a .012"-.014" sawed slot, tightly clamp two pieces if scrap material in your favorite vise so that there is a gap between them that the .012" wire will slip in but the tubing won't. Make sure they're clamped tight. If you're performing bends of much larger diameter than 1/16", the stainless wire can probably be reused.

It is likely that tighter bends than the 1/32" radius (1/16" dia.) we performed would successfully cold-form as well, but keep in mind, the sharper the bend, the harder it becomes to pull out the support wire. Trial and error will tell for sure.

After our test above, we easily threaded a twisted-pair of our red/green #38 magnet wire up and around the bend by simply pushing the wire. If we had flared the tubing end first, we could slide on a lampshade, solder on a Micro LED and this would look great sticking out of a building over a door.

.025" Tubing:

Having a wall thickness of only .003", this tubing can be very easily formed using .019" diameter stainless wire as an internal wall support. Detail Associates provides this .019" wire to most hobby shops under their part number 3506. Limit bends to a minimum of 1/16" radius for best appearance (1/8" diameter bending mandrel).

.032" Tubing (.0025" wall):

Relative to its diameter, this tubing has an ultra-thin .0025" wall. As a result, this tubing is also very easy to bend. Use #22 (22 AWG) copper or music wire for wall support. If not available, stretch a length of bare #20 copper wire so that it just fits inside the tube. This will also straighten the copper so it's easy to work with. We recommend limiting the radius of the bend to 1/8" (1/4" mandrel).

.032" Tubing (.006" wall):

This tubing can be easily formed using .019" diameter stainless wire as an internal wall support. Detail Associates provides this .019" wire to most hobby shops under their part number 3506. Limit bends to a minimum of 3/32" radius for best appearance (3/16" diameter bending mandrel).

.042" Tubing:

Having a very thin .0035" wall, this tubing is also very easy to bend. Use #20 (20 AWG) copper or music wire for wall support. If not available, stretch a length of bare #18 copper wire so that it just fits inside the tube. This will also straighten the copper so it's easy to work with. We recommend limiting the radius of the bend to 1/8" (1/4" mandrel).

.050" Tubing:

This tube has a thicker wall (.004") and is larger in diameter and therefore harder to bend (but not much harder). Using #18 (18AWG) solid copper wire (readily available at any hardware or lighting store) as an internal tubing wall support, we cold-formed over a 1/4" rod with total success. No evidence of damage. We used a similar support wire extraction process, also with success. This tubing has an N-Scale outside diameter of exactly 8 inches, so a larger radius bend such as this would probably suffice for most situations (curved drainage pipe sections, ornately shaped sign post, vent pipe on a building, who knows?). It really depends on where you cut it after bending. Smaller radius bends shouldn't be a problem.

.065" Tubing:

Our .065 diameter tube can be cold-formed using #16 (16 AWG) bare copper wire for internal wall support. We don't recommend cold-bending to a sharper radius than 1/4" (1/2" mandrel) for good appearance. Tighter bends can be performed, but remember, as the tubing size increases, removal of the wall support, or forming wire becomes increasingly difficult. An external bending spring or miniature tubing bender can also be used.

.083" Tubing:

This tubing has a slightly thicker wall at .0055". For internal wall support, use #14 (14 AWG) solid wire. We recommend lubricating the wire with a light oil prior to insertion, to make removal easier. Because of the wall thickness, we do not recommend forming to a sharper radius that 1/2" (1" mandrel).

.095" Tubing

If you want to bend this tubing using internal wall support, use #12 (12 AWG) solid copper wire. As with the .083" tubing above, we recommend lubricating the wire with a light oil prior to insertion, to make removal easier. We do not recommend forming to a sharper radius that 1/2" (1" mandrel). Annealing this tubing will make tight-radius (1/2") bending much easier. Large radii can be formed without annealing.

Tubing Flaring

Making a small flare in the end of the tubing isn't very difficult. If you're using the smaller (.018") tubing and plan to make lights using the lampshades, it's desirable to put a small flare at the lampshade end. This gives the shade a good resting surface for the epoxy joint bond.

The easiest way we've found so far is to slide a .012" support wire into the tube with a slight bend in the wire so it will stay in position in the tube. Clamp the tube firmly in a pin vise with the end of the tube just protruding past the jaws of the pin vise (about 1 tube diameter or so). Position the support wire slightly recessed from the end of the tube (maybe even with the pin vise jaws or slightly farther in. Make sure the tube is tightly clamped by the pin vise.

Now, clamp the pin vise with tube and support wire in your bench vise preferably with the tubing end facing up.

Choose a carbide scribe, compass scribe pin, dental pick point, small steel pin ground to a tapered point, or even a ordinary straight pin. This will be your "flaring tool". Place the pointed tip into the tubing end and tap firmly (but not too heavily handed) on the back end. You may need to inspect and repeat tapping to get the slight flare you want, but once you've done this one time, it's seems easy to repeat the process. If we find a better or easier way, or someone suggests one, we'll be happy to post it.

Flaring the larger tubing works fine using the same procedure. If you need a large flare (a ship's funnel vent on deck, or ?), you should consider annealing the tube end prior to flaring. This will bring the tube (portion you've annealed) to a "dead-soft" condition and allow much easier working. Keep in mind however, in any case, there is only so much that the tube will stretch before it start to split. Trial and error is the guideline here.

Annealing

While not required for most bending and forming situations, should you need all or part of a tube to be in the "dead soft" condition, the following procedures will achieve this.

Laboratory grade annealing:

For "proper" annealing, the manufacturer recommends using a reduction oven with preferably, a nitrogen atmosphere to prevent oxidation, and "cooking" the tubing at 2100-2300 degrees F for 3 hours. Then allowed to naturally cool (heat off, still in oven) to room temperature. This will maintain material surface brightness and alloy composition.

The hobby method:

A detailed discussion with the manufacturer or our intended uses in the hobby marketplace yielded a much more down-to-earth process.

In a well ventilated area, using your favorite butane torch, heat the tube (or portion you want annealed) to a bright "cherry" red and allow to cool to room temperature. Carefully (remember, it's soft now) drag the tube through fine steel wool to return the surface to a bright condition. Wipe the tube clean with a tissue and alcohol. Voila... annealing is finished!

Remember, this tubing is in it's softest condition now and can easily be damaged. If you need to re-temper the tube, you can try a reheat and water quench, but hardness is tough to control so results may vary. Again, trial and error here.

Last modified: May 04, 2008