This post is about hand rolling of circles, rings, tubes, pipes, curves, tapers and cones in titanium and stainless steel hardened alloy foils and thin sheet.
Introduction
Small sheet metal rollers are expensive and bulky and have such a short rolling mouth width. They use 3 geared rollers that rotate in synchrony to force the sheet to feed between them and bend the sheet down under one roller and deforming it between the other two.
In another post on hand tools, I briefly describe an alternative simple and cheap hand tool that can be used to roll a variety of curves in titanium and stainless steel foils and thin sheet metal. It simply uses a force applied to a thin long rolling rod, applied by moderately strong hands and fingers. The rod (~10mm diameter) presses against the foil and the soft sealed cell rubber pad on a rigid anvil. This can deform the foil to the point where it is permanently bent in a smooth curve. Several rolling passes can achieve progressively deeper curvature.
I will try to explain in this post the wide variety of curves that can be formed with this and similar homemade tools that are derivatives of this simple curve forming tool. The curves can range from short tapers or cones to long flue pipes.
A versatile hand-rolling tool
At first sight, it might be expected to be only able to roll strips of metal with a similar or lesser width to that of the blue sealed cell foam pad. “This was its intended use for making narrow rings and short tubes as connectors and adaptors for backpacking stoves. These items are finished to become stable and strong components using miro spot welding.
I have found that this type of rolling tool can do so much more and so it deserved this post of its own.
The rolling pin
The rolling pin can be a strong piece of ~10mm hard and smooth stainless steel pipe or rod. It is used to press and roll the foil against a sealed cell rubber pad on a rigid anvil. In most simple situations, the roller should be substantially longer than the width of the anvil. This means that it can be pressed and rolled with confidence, control and considerable force from the underside of all four fingers on each side of the roller. With heavier foils and sheet metals, the palms of the hands may need to be used.
Alternative ‘drag roller’. The hand-rolling described above puts a heavy load on the fingers. Consequently, I came up with this simple ‘drag roller’ with a fat and soft handle. It can be comfortably held in one hand and the other hand can hold the work. It means that the full force of arm muscles can be applied to the work. It does not roll, but rather it can skid over the metal easily and still has the desired curving effect. I put a trace of olive oil on the skid-surface to make the skidding even easier. “It is much easier to use than the roller.”
Why have an anvil?
Firstly, the anvil is needed to provide solid support and anchorage for the sealed cell rolling pad.
It also allows the roller to be rolled at an angle to horizontal for rolling cones and tapers (More on this later).
Lastly, it also provides clearance for the rolling pin to flex downwards while applying its strong rolling/bending force to the foil (and rubber).
If all my words about the rolling process don’t quite make sense to you, possibly this Instagram video may do so.
Width limitations of the rolling pad
At first, it would appear that a wide anvil and wide rolling pad would be the most versatile tool. However, this is not so and this is why I continue to most often use the little one shown in the above photos, although I do use wider anvils and pads (discussed later) for some tasks.
The narrow anvil and pad provide much less resistance to the curving deformation of the foil. Consequently, it makes it much less stressful on the fingers/hands and allows sensitive and controlled rolling of the desired curvature.
The forces resisting deformation come from both the foil and the rubber, so even with a narrow strip of foil and a wide anvil and rubber pad, the resistance will be much greater than with a narrow rubber.
A wide rubber with a narrow anvil can work quite well, but it is much harder to keep the foil strip on target in the centre of the anvil when it is hidden.
Wider anvils and rolling pads can be used, but then a greater rolling force must be applied by the flat portion of the hands.
Once the width exceeds ~120mm the hands (mine at least) can not comfortably provide an adequate rolling force to form tight curvatures, with hardened titanium and stainless steel foils that are only 0.1 mm thick. However, don’t despair as infinitely wide rolling is still possible.
Using a thicker rolling pad
Using a thicker rolling pad is another way of rolling the curvature into wider or thicker foils. However, it comes with the disadvantage of the curve becoming less smooth.
Segmented Rolling
Segmented rolling can be performed on a narrow anvil and pad and is only limited by your patience and the width and stiffness of the rolling pin. I routinely form tubes of 10-60mm diameter in lengths of 150-250mm and occasionally up to 450m long from 0.1mm thick hard stainless steel foil. Rolling a 450mm wide strip with a 600mm long roller only leaves 75mm each end for your fingers, so you need to be careful not to cut your fingers.
This wide rolling can be done in stages, gently and evenly curving the sheet of foil at one end. Then moving it progressively over the padded anvil and rolling the whole length in adjacent segments. The process can be repeated again from the starting end, as many times as needed to achieve the desired curvature.
“This process may sound like an implausible method to use, but is amazingly simple and the foil almost tells you where it needs a little more rolling to make it even.”
I weld up tubes that are formed in this way and then put them back onto the bare anvil and roll the seam very hard. Then I roll the tube with the pad on the anvil for a finishing rolling. I do this to make them fully round and applying very strong and concentrated rolling effort into overlapping joint line along the seam. This line is always somewhat flat because it is not possible to curve the very edges of the metal by this rolling method ( or a formal 3 roller rolling machine). However, when welded together they can be rolled into a suitable curvature, just like any other part of the sheet. They just need concentrated rolling force, achieved with a narrow anvil, on account of the double thickness of metal at the joint.
Rolling tapers or cones
I confess that I have a growing love-affair with cones. They are particularly suitable for stove making where:
- A metal tube must tightly fit and seal into a round hole that is punched through another stove part. With a suitable taper, the tube can be easily docked into the round hole and be pushed in a little more to make the join tight and have a good seal.
- Tubes of a different or similar diameter must be connected tightly together.
- Tubes of the same diameter must fit tightly together, one-inside-the-other. A small taper on one end of a tube can make their docking easy while ensuring a tight fit.
I hope that you are sold on tapers. I found that the above segmented rolling technique, when done unevenly along the width of the foil, will form a conical shape.
Please go to this link for more details on curved and welded foil stove fittings.
Infinite tube ‘roller’ for flue pipes
Curving a long roll-up flue pipe for a backpacking tent heater/stove is a particular challenge if it is to be done very well. The need for good pre-forming of a flue pipe prior to the development a new pipe shape memory by/heating is detailed in my post about heat memory shaping of roll-up flue pipes with an alcohol flame lance. The pre-rolling is described in another post. Roll up flue pipe curving by hand rolling
Tim
