Making Circular Forms/Bending

2296 Views 1 Reply 2 Participants Last post by OnealWoodworking, Nov 21, 2015

Arbee

Discussion Starter · Nov 20, 2015

I'm a member of another forum for musicians. Regularly a newbie (like me here) posts a question asked and answered 10K times before.

I don't want to be that jerk to you experts here. I did try searching this first. I will glady accept etiquette lessons here as I'm new and don't know protocols--although I've gotten excellent friendly responses so far.

That said, the subject concerns bending wood, or wood like items like MDF, versus kerfing: the pros and cons.

The subject expressly does NOT concern the bending of Trex and other composite deck like items, as, to my limited understanding, that's done with heat more than steam, using equipment specifically design by composite decking manufacturers like Trex.

https://www.youtube.com/watch?v=hIfYHQC80Lc

With scope of topic understood, when faced with the need to make a round table skirt this past summer I choose kerfing over steam bending. I haven't done the latter, and it would have probably involved, in addition to making myself a steam box, the help of others when bending the wood, along with a premade jig and a whole lot of clamps I don't own.

I had much better luck using MDF than wood, I suspect due to the consistent man-made nature of the former. I found it to bend much more consistently as long as my kerfs were evenly spaced and equally deep into the material being bent. A simple ratchet strap helped form the kerfed wood.

But I have to think that kerfing has drawbacks over steaming, correct? For one, removing material as kerfing does is bound to make the kerfed item weaker--even though I did glued all the kerfs once the circle was formed. I had to be very careful to fully support the kerfed piece along its length before shaping or risk it snapping under its own weight and kerfed weakness.

And I have to think that when bending wood into complex shapes (e.g. twists), steaming is the only way to go.

Are there disadvantages to steam bending apart from the tools and manpower needed, and the difficulty and safety of working with heat, and the need to work very fast?

Is little to no strength lost on a piece that's been steam bent? Can one re-steam a piece that hasn't set into exact specifications and does the piece's strength "take a permanent hit" each time its steamed? When I say strength, of course I mean after the piece has cooled and dried.

I've heard that bending wood can result in consistencies from desired shape and that it's a bit of an art let best left to those experienced in same--like taping drywall. Is this urban myth?

Clearly, as wood takes to nails and screws better than MDF, that certainly has to be one advantage wood offers in this process.

Thank you.

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Oneal-Woodworking

· #2 · Nov 21, 2015

Arbee said:
But I have to think that kerfing has drawbacks over steaming, correct? For one, removing material as kerfing does is bound to make the kerfed item weaker--even though I did glued all the kerfs once the circle was formed. I had to be very careful to fully support the kerfed piece along its length before shaping or risk it snapping under its own weight and kerfed weakness.

And I have to think that when bending wood into complex shapes (e.g. twists), steaming is the only way to go.

Are there disadvantages to steam bending apart from the tools and manpower needed, and the difficulty and safety of working with heat, and the need to work very fast?

Is little to no strength lost on a piece that's been steam bent? Can one re-steam a piece that hasn't set into exact specifications and does the piece's strength "take a permanent hit" each time its steamed? When I say strength, of course I mean after the piece has cooled and dried.

I've heard that bending wood can result in consistencies from desired shape and that it's a bit of an art let best left to those experienced in same--like taping drywall. Is this urban myth?

Clearly, as wood takes to nails and screws better than MDF, that certainly has to be one advantage wood offers in this process.

Thank you.

I have done a metric crap pile of circular stair handrails without ever touching a steamer. Laminating a bunch of skinny slices together is generally how that is done and it works like a charm. Same thing applies to the circular stair skirt boards. It is ten times easier to laminate several skinny pieces around a curve until you get to the thickness you need than it is to fool around with kerfing or steaming a single board that is 3/4" thick to begin with around the same curve.

The tighter the curve - The skinnier the laminations you want (depending on the particular wood of course and how easy it is to bend)

The steamer I do have currently was made from a BIG piece of PVC pipe, a burner from an old turkey fryer, and an old propane tank that was decommissioned and turned into a vessel to boil the water in. If I just GOT to steam some 12' long (or longer) strips to make them do what I want them to do - I set it all up and go to town.

Steaming is just one method of helping a piece of wood bend and not always the easiest to employ.

You should also consider laminations of hard woods or plywoods (mentioned above), bendable plywood with a veneer of your choice as the last visible layer applied to your form, or Kerfing (as you have already experienced).

Gluing the kerfs like you mentioned above is always a good idea to help strengthen things after they are formed. Bondo or epoxy both work equally well for this sort of thing as you really only need to fill the kerfs with something hard and stable. I like bondo as it is relatively easy to work with, cheap, and dries as fast as you wish (mixing proportions and such).

Best of luck with your project Sir. :smile:

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