Building A Steam Bent Drum
Steam bent shells are considered among the most desireable because of their acoustic properties and simplicity of design. However, they are not easy to build, and as a result, most builders choose a different method. Because of this, there is far less information on how to build them than other methods.
Also sometimes called 1 ply shells, steam bent shells are made from a single piece of wood. A special box is made to produce and control moisture and the piece of wood is placed inside and carefully monitored. After the right amount of moisture is achieved, the wood is removed from the box and wrapped around a mold. They generally have a scarf joint which is glued together to complete the circle. (For more info on scarf joints see:http://en.wikipedia.org/wiki/Scarf_joint)
More wood types are available than the ply method.
Uses hardly any glue at all.
Considered by many to have great sound, although this is subjective.
The legendary Radio King snare was built using this method.
Perhaps the most difficult to keep in round. Because of this, they often have reinforcement rings.
Limited shell thickness - difficult to make thin or thick - needs to be somewhere in between.
Grain is horizontal which some believe doesn't produce the best tone, although this is highly debated.
Not as much information on how to build them because fewer people use this method.
Special tools required:
A box where moisture can be added, controlled and measured.
A mold around which the wood can be wrapped and a method of applying the pressure.
DISCUSSIONS FROM THE DRUMSHED FORUM
When I saw a video on YouTube, I decided to give steam bending a try. They show a mold that seems about the same diameter that the rough shell ends up with.
Today I went to my wood supplier and he told me the molds should be about 10% smaller than the end result. Is this true? And if so, how does it work with a male mold? I think I'll end up with the last part of the wood not bent - it seems impossible to me. Another question.
On YouTube they first bend the shell, then glue it to the right size, after that lathe it to the right size.
I plan to bend it first, then remove the aluminum plate, glue it and make it to the right size on the same mold.
Put the mold with the shell in my lathe, lathe the outside, remove the mold, then lathe the inside.
Will I be able to remove the mold after gluing? The mold is made of several layers of scrap wood about 18mm thick.
I have a book on bending wood, "Wood Bender's Handbook" by Zachery Taylor. (Sterling Publishing Co., inc. New York isbn 0-8069-9702) It says nothing about the 10%, but I guess you need to over-bend the wood a bit to end up the correct size.
It also says you need to support the outside while bending. They say you want to crush the inside and not stretch the outside, so you can buy steel bending straps with stops at the ends of the wood. The stops prevent the wood from stretching.
You probably know these guys: www.baptist.nl. They have a webshop too, and they sell creme de la creme for woodworkers, including the bending book and straps.
I've done a search and not found much as to how steam bent shells are done. Is it as simple as steaming the wood and then bending it and putting it in the mold and gluing the edges, or is it more complicated?
You think that sounds easy????
Steam forming wood is an art form in itself!!! You can't do it over a boiling kettle!!!
...it looks relatively easy and cheap to set up. However, I think that actually producing a usable shell is extremely hard. For one thing, shells are really thick for wood bending, so you'd have to have a very solid mold (thickness is relative to bending diameter, of course). There is also the difficulty of getting a good joint. Then, to top it all off, you have to put the shell on a lathe to get it perfectly round.
I thought a steam bending set up was a million dollar piece of machinery the way people have talked about it.
Nah, it's not that expensive to get set up. A few hundred dollars if you get the bending wheel made for you, plus the materials for the drying forms.
Once the blank is bent and has dried the rest is straight-forward machining processes. It's the bending that requires an intuitive touch, where art and craft blend together. Sure, the rest of the steps take finesse but that comes with practice. Knowing how much to sand the scarf, etc.
Why not put the wood in a bath with boiling water for a while and bend it afterwards? Frankly speaking, I didn't try it out myself. But this is how it's done in the veneer and plywood industry to flatten fresh rotary-cut veneers!
Moreover, 90 to 100 degrees C is the best temperature for making wood bendable. At higher temperatures wood starts degrading seriously, in case of using a gas stove it's hard to control temperature.
That is: making the lignin plastic, so that the wood stays in shape after the wood gets out of the mould. (Bending has nothing to do with heating the fibers - it's purely about softening the lignin, molecules in wood which act as 'glue' between the fibers).
I have seen a lot of posts that say, because the steam bent wood is not in its natural position, the fundamental pitch gets higher and "choked". I was at the Hollywood Drum Show and got to see some Vaughncraft shells firsthand. I actually picked up a couple of the shells (carefully) and tapped on them. If anything, it seemed like MORE sound came out of them than would be expected from a ply shell.
I really dig steam bent single ply shells...a lot. They do get a sound out of them that is different than a segment or stave shell. I think they actually have a bit of a lower fundamental tone. They have a very "warm" sounding quality to them. Part of this could have to do with the grain running horizontally and the fact that it's a single piece of wood. I'm also not sure if these shells get lathed down or not. Maybe one of the guys who visited Vaughncraft knows.
I don't know about Vaughncraft but I seem to remember reading somewhere that Craviottos are bent then lathed to perfection.
Yes, they're lathed. I talked quite a bit with Steve, who does the bending & lathing at VaughnCraft, and while there are certain steps he couldn't talk about, I did get the info that lathing is a step. How could it not? Steam bent wood is bound to be a bit out of round & the finished product is so perfect.
I don't buy that the argument that steam bent shells are under pressure and therefore sound choked. I doubt they actually are under pressure. I don't think that if you cut through a steam bent shell it would spring back into a straight board. I remember reading that the process of steam bending actually changes the bonds between the wood fibers, meaning that whatever shape the wood dries in it will retain. There may be a little spring back, since the wood is bent to a fairly extreme diameter, but it would be very little.
Jdrose (from Vaughncraft):
In order to properly bend wood you need to raise the temperature of the wood (all woods are different, but 350 degrees and above usually works) to change the complexities of the lignin in the wood. The bending process involves wet wood that we treat with chemicals (again this depends on the type of wood) and steam heat (done under a pressurized unit). This makes the wood easier to bend and then you have the key of how you raise and lower the temperature at which each wood properly cures and over what period of time.
We lathe the inside of the shell (for proper adherence of the re-ring) and the outside of the shell for diameter (13.875", 13.750", etc.) and to 'clean up' the shell. We then sand the outside and the inside of the shell (up to 1500 grit).
This is what I have read about bending wood...
1. Use air dried rather than kiln dried wood. Apparently kiln dried wood fixes the cells so as to not be able to become pliable.
2. Steam for 1 hour per inch of thickness. That's a number that seems strange to me. It would imply then that a 1/4" thick shell could be steamed for only 15 mins. before being ready. That seems remarkably short, but I have never done it, so.....
3. I was planning on using a scarf joint for the seam. Any opinions on how long the overlap should be? I was thinking 2"-ish. Should it be more? Could I get away with less? My thinking behind this whole project is that if stave shells have 10% of the glue of ply shells, which IMHO is good, then if a steam bent shell has 10-15% of the glue of a stave shell then that's even better!!...?
4. I was planning on bending around an internal mold (that is, bending the shell around the outside of a mold) and clamping but not gluing. Then once the wood is dry, I would undo the clamps at the seam a bit, glue, and then re-clamp to dry. Does anyone know of an appropriate glue that would allow me to glue the wood while still wet, or is my original plan the better option?
Number 1 isn't correct. I used to bend kiln-dried exotics all the time when I was building acoustic guitars.
I've heard that you can't use kiln-dried woods for steam bending, but I have no idea if it's true. Bending a 14" diameter is pretty extreme, especially for thicker wood, maybe that's why you need air-dried lumber.
The problem with 4 is that you will have to make a new mold whenever you want to change the thickness of the drum, which if you are planning to make many (Which I presume you are) you will have to make many different molds.
I came across the same info about 1 hour per inch of thickness, didn't make sense to me either. It made even less sense when I steamed a 3/8" piece of oak for 90 minutes, and it still split when I tried to get it in the mold.
I used Elmers 'Ultimate Glue' (http://www.elmers.com/product/produc...sp?pCode=P9405 ) on my stave shell, and it worked great. I tell you this because, it actually needs moisture to do its thing.
When you build your steam box, use old "junky" wood (it doesn't matter what the box looks like). Also, put a few dowels through the box to set your wood on, and it also allows some steam to escape. Make sure the opening is at the opposite end of the boiler.
As far as your boiler, I used an old, EMPTY propane tank. I removed the valve, let it sit for a few days (to air out the horrible odor that is added to propane) then inserted a piece of threaded pipe where the valve was. Then I drilled a hole in the bottom of my steam box, set the hole over the pipe, and voila! Best heat source is a camp stove, something similar to these (http://www.cajunmarket.com/Cajun-Coo...r-Gas-Cookers/ )
I was researching this topic a few months ago. Here's something I found http://www.megspace.com/lifestyles/njmarine/Steam.html It has instructions on building a steam box out of PVC. I think it would work well for your first attempts, since it would be a little cheaper and easier than building a box out of wood. There's some other great information on the site too. They also say to steam wood for one hour per inch of thickness.
Problem with PVC, or at least what I was told, is you need to use high temp. PVC. Another problem is, finding it. I was going to use 6" PVC for my box, but the only place I could find that had it had a minimum order (of a pallet). I used old fence boards and some plywood to build my box, total cost, about $10 (beer is included in that price).
(In regards to bending 1-ply steambent shells) Éhow do you guys calculate the diameter so perfectly to get a good scarf joint?
Generally, once you bend the "steamed" board you need to let it cure, or maybe "set-up" would be a better term. The best way I know of is to place it inside of a "sono-tube" that is of similar I.D. to the O.D. of the bent shell immediately after it is bent. It stays in the tube for a few weeks (or more depending on conditions) until it pretty much drops out on it's own. Then you position it and glue up the lap joint to slightly over the desired O.D. Once the glue has cured, it then gets turned inside and out on the lathe to true it up.
I have never had the opportunity to check out a solid shell snare. I was wondering how the ends are joined? Both ends cut at a 45-degree angle and glued? Or Use some small biscuits and glue? Or Dove tailed?????
There are no joints on a 'solid' shell, because it's a solid piece of wood. I assume you're asking about a 'single ply' shell, referred to by many in the shell business (deceptively so) as 'solid'. A 'single ply' shell is typically joined with a scarf joint. Closer to a 22.5 degree angle (for a typical shell thickness) than a 45 before being trued on a lathe or sanding fixture.
DISCUSSIONS FROM THE DRUMTOWN FORUM
These are not drum specific but there is a lot of info on these sites. And there are tons more if you go looking.
Bending wood is a skill like anything else, practise and experimentation is key. Anyone can do it if researched thoroughly and practised. One needs to learn what is involved, every type of timbre will have unique properties. Lengths appropriate per drum size, scarf joints and jigs to cut them, then the forms to bend the wood to, need to be created.
But I think anyone can do it, if they are willing to spend the time and money to achieve the knowledge, and build the appropriate equip't to do so.
I have dabbled in it on and off for a few yrs, and it's fun, the only reason I haven`t done drum shells, is the expense to have practical molds/presses to do them successfully, home made happen stance rigs just don`t cut it.
What I can tell you for sure is, you need to use live steam, not just fluffing clouds of white water vapour into the chamber and hoping it'll work, time per inch(thickness) plus live steam equals success, with practise and experimentation of coarse. Just remember, steam burns exposed skin very quickly, proceed with caution and wear really good thermal work gloves. PDGood:
This is a non-drum website, but some of the ideas may apply:
For information on where to purchase steambent shells, see the Supplier's page on this site.