Material for bending straps

[HoGo]

Hello folks, I'm toying with some new ideas about making rib bending of difficult woods less stressful and need some new strapping. Perhaps also building some bending jigs and fixtures...
I've used ordinary roofing galvanized sheet but that gets kinked after some use and doesn't hold the bends as smooth as it used to. I found some suppliers of presision metal sheet shims and they offer quite a variety of metals.
I suppose stainless spring steel would be the best choice, but do I need it hardened/tempered or not? What do you think? Also what thickness? Most commercially sold straps are 0.012" (0.3mm) or 0.01" (0.25mm).
Thanks.
Adrian

[sunburst]

I have some stainless steel straps made from shim stock and they work very well with no memory or kinking... they remain straight/flat. They also don't stain woods that have tannin. I don't know whether the stock was hardened, but I suspect it was. I also don't know the thickness right off but I'll try to remember to measure when I'm in the shop.

[Richard500]

Hardening not necessary, if I understand these are used the way they are in other woodworking bending. Plain type 304 stainless (which is not hardenable, anyway) should be fine, and will not transfer iron into the wood, which can create finish problems. The 300 series is non-magnetic, which is how you can tell what it is. The only detail is that ss is not as easy to drill as other materials, so to fasten the ends, you need good drills or a punch. If you bend the ends to seat clamps, it also won’t work harden and break. Best cut to length with good shears or hacksawn. Sheet metal shops have scraps and shears. It can also be brazed and spot welded if you wish, although I remember that you are a tool minimalist, which is cool.

[HoGo]

What I'm looking at is 1.4310 (here in EU), which should be type 301. They have also hardened in 0.25mm thickness, which is just about right and price difference is rather minimal.

[sunburst]

The stuff I have is magnetic and it measures .006"

[HoGo]

The stuff I have is magnetic and it measures .006"

That is much thinner than what the luthier suppliers sell. I've got some wrist reflective straps that have blue steel shim just about 0.006" thick inside. Those seemed too thin to me as I was used to 0.5mm (0.020") thick galvanized sheet offcut.
I was thinking about building side bending jig similar to Ellis in the future and that would require some strength for smooth bends.

[j. condino]

Perforated stainless steel sheet is my favorite. It is available in all kinds of thicknesses. The main benefit of this over all of the other materials is the perforated holes. They allow you to maintain the strength aspect but they allow moisture to evaporate rather than get trapped inside the "bending sandwich". I've used stainless and blue spring steel, aluminum, flashing and galvanized and this is by far my favorite. When you use it in a big guitar (or double bass!) sized side bender, the sides are almost dry when you pull them out rather than needing to sit in a mould overnight to dry.

There is a guy on ebay who usually sells it in guitar sizes and you can also get it from any of the online metal shops:

https://www.onlinemetals.com/en/buy/...rforated-sheet

[HoGo]

Perforated stainless steel sheet is my favorite. It is available in all kinds of thicknesses. The main benefit of this over all of the other materials is the perforated holes. They allow you to maintain the strength aspect but they allow moisture to evaporate rather than get trapped inside the "bending sandwich". I've used stainless and blue spring steel, aluminum, flashing and galvanized and this is by far my favorite. When you use it in a big guitar (or double bass!) sized side bender, the sides are almost dry when you pull them out rather than needing to sit in a mould overnight to dry.

There is a guy on ebay who usually sells it in guitar sizes and you can also get it from any of the online metal shops:

https://www.onlinemetals.com/en/buy/...rforated-sheet

I couldn't find anything of that kind in usable thickness locally. I wonder if it bends smoothly despite the holes? I can have holes laser cut into standard starp as well and keep solid smooth edges without "half" holes.

[Richard500]

The perforated idea sounds good, although I don’t think it would be useful in steam bending thicker stuff. I checked, and in the US anyway, there’s a huge variety, going down to .006” and some with almost microscopic holes. Expensive. Adrian has it right about ‘half holes’. Can make handling really nasty, like having a serrated kitchen knife everywhere.
So, rather than any of the above, what’s wrong with a porous inner strip (anything fibrous) that can wick moisture out? And of course, the opposing form should also be ventilated. Just musing on this.

[cwood3]

Just as a side note, I received my bending iron and bending strap from Luthier's Bench this past Saturday. I just measured the strap and it is 0.3mm (.012") thick. It is stainless steel.....and very nice.

[HoGo]

The perforated idea sounds good, although I don’t think it would be useful in steam bending thicker stuff. I checked, and in the US anyway, there’s a huge variety, going down to .006” and some with almost microscopic holes. Expensive. Adrian has it right about ‘half holes’. Can make handling really nasty, like having a serrated kitchen knife everywhere.
So, rather than any of the above, what’s wrong with a porous inner strip (anything fibrous) that can wick moisture out? And of course, the opposing form should also be ventilated. Just musing on this.

Maple ribs don't require all that much water for bending so there's no big problem. The small amount needed for bending will dry out pretty fast. For bass the width of ribs is huge compared to thickness and residual water or uneven drying may cause waves across the rib if it is not supported firmly all across in a form of some sort. Collings solved this by using counterforms with ventilation holes to hold bent ribs till they cool and dry. But IMO some small amount of springback is not that critical if you build around fixed form. Or you can slightly overbend the sides to start with.

[HoGo]

Just as a side note, I received my bending iron and bending strap from Luthier's Bench this past Saturday. I just measured the strap and it is 0.3mm (.012") thick. It is stainless steel.....and very nice.

That's interersting as they claim they DON'T use stainless for the strap and thickness is 0.2mm (0.007")....

[cwood3]

I say it's stainless......................it's "shiny".....but it is magnetic, so probably not 300 series SS. My caliper reads .3mm......but it's not a Starrett.....

It bends rib material well.................maybe it will rust if I don't take care of it

I like the handles......