drilling holes for bamboo joints

[headcase]

Hi Bamboozlers
Im new to this forum. Please forgive me if I ask an obvious question. I have noticed the way bamboo furniture, chairs in particular are made. The joints are made by drilling holes and inserting a bamboo bar (say a crossbar for chair legs for example). What puzzles me is that the hole is a tight fit with the bar. How is such a hole drilled so cleanly? The inserted bar does not appear to have been pared down to fit, so an exact hole cutters must have been available for that particular diameter. Given the very wide variation in culm diameters this would need hundred of different drill or hole saws, clearly not practical. So there must be some special adjustable tool used to drill such a precise socket. I saw this particularly in Angelese in the Phillipines but the locals wouldnt tell me where their workshop was!!

I am guessing that they use a standard hole saw and then have a set of reaming tools used with a carpenters brace??

Anyone any ideas? The joints are very strong and use small nails to fix them in position while still green. They are then lashed at the joint with bamboo lashings.


rgds

headcase

[Mark Mortimer]

Hello Headcase,
In making my furniture, I need to make many joints like you describe. I have a series of holesaws, going up in 3-4mm increments. This is a very expensive way of doing it! But it does save time. Even then, the fit is probably not tight. The tolerances needed are to within fractions of a millimeter. So I use a tool I made myself, by filing down an old chisel, with which I take of shavings from the hole I just made. Even if I had hole saws which went up in diameter in very fine increments, I'd still have to do a bit of shaving of the hole, as I've never seen a piece of bamboo which is perfectly round, there's always a bit of an oval or irregular shape in it. If you want the fit to be really tight, you need the hole to follow the insert all the way round.
In Victor Cusack's book "Bamboo World", which if you haven't already got I heartily recommend, he talks about the Bali furniture makers, who do without power tools altogether. They simply make a hole with a chisel, roughly shape it, then increase the size with a curved blade, designed to suit the purpose, until the insert fits. They do this very quickly, sitting on the floor, with their feet and legs as a vise! I am not so skilled so rely on expensive tools (maybe that's why I'm not so skilled.)
One more thing, all the cutting tools need to be razor sharp. And they blunt very quickly, as there is a lot of silica in the epidermis of the bamboo, which blunts edges in a jiffy. My hole saws I have to take to a guys who sharpens them, but I'm constantly using a sharpening stone on any of the knife edges I use.
Anyway, hope this helps. Let's see some of the stuff you make, please.
Cheers, Mark

[Mark Mortimer]

By the way, Headcase,
I'd be very surprised if the furniture we are talking about is ever made with fresh green bamboo culms. The green bamboo would shrink a bit as it dries, and all the work put in to making a tight joint would be wasted, as it would become loose and slack.
Where did you see them using green bamboo? It is more important to use properly dried bamboo if you are using clumpers, as runners do not undergo shinkage to the same degree.
Cheers,
Mark

[headcase]

Hi Mark
thanks for your informative reply. I live in central thailand where there is a lot of bamboo. Traditional construction methods are very wasteful and crude. They dont have the same indigenous skills as you Balinese. Consequently the bamboo clumps are very under-utilised because structures rarely last 3 years and are limited to field huts (gratoms) or crude fencing. As we know, properly treated bamboo can have a life of 10, maybe 20 years. The clumps are largely going to waste and have nuisance value as they drain the surrounding land of nutrients and also, according to local lore, make the ground acidic and unsuitable for rice. I have been studying ways to make a better jointing system instead of a crude lap joint. I have been testing a plywood web (gusset) and also an interesting type of ball joint (imagine something equivalent to the human skeleton say the knee joint, after all bamboo stems do resemble bones). Certainly I am aware of the silica problem and its potentially disastrous effects on an expensive bimetal hole saw kit (which i have just managed to acquire). I dont really have the means to resharpen these very easily - bit like trying to resharpen a hacksaw blade. Equally, like yourself, I dont have the skills or the patience to shape these holes manually although I am sure the local craftsmen could be taught the skill (but that would hike the cost and IMHO be a backward step). I am looking for ways to apply modern technology (say making a special cutters with tungsten carbide tips). This isnt so improbable as I have made similar tools before and these tips are readiliy available as lathe machine accessories. I have also seen an old design for a tapered reamer (the type used to make a flute or a windsor chair leg for example). The are really quite simple to make and use a hacksaw blade- with its teeth as is- as the cutting edge. Cheap and effective and easily maintained. Similarly i propose a wooden mandrel to which a strip of emery cloth can be glued. This can be used in a power drill for fine tuning the hole.

As for fixing the joint, I dont like nails and prefer the use of hardwood dowel pins say 4mm 6mm or 8mm. I think these should be glued. PVA glue is reaily available but perhaps Cascamite (Humbrol) would be better for water proofing? It is a urea formaldehyde and the basis of marine ply.

I dont suppose its practicable to , say, scribe an outline around the hole to be made and then use a stanley knife to scrape off the skin inside the circle. Would this help tool bit life?

As for green bamboo, I may have been mistaken and assumed the piles of green bambo were for immediate use

I'd be pleased to correspond on the subject. Apart from my bamboo joint work I am currently designing a bamboo playpen for my 6 month old daughter as a matter of urgency. She's a holy terror already, fingers into everything. I also have a design for a traditional cradle and hammock in bamboo on the back burner.

Incidentally how do you boil up 3 meter poles in water for 2 hours (insert into an oil drum and invert after 2 hours? surely not?

Would it be advisable to knock our all the internal diaphragms and use a long handled scraper to remove most of the internal wax first?

regards

Headcase (aka Lung Chang)

[TribalWind]

Hi headcase

good ideas up there ,
i havent done all that many joints like this with bamboo,yet.

the few i have done i used a cut-off of the piece to be the Tenon,traced its perimeter onto my would be "mortise" took the bulk out with a large spiral drill bit,or a side-cutting bit in my dremel rotary tool.then 'sneak' up on my line by using the drum-sander wheel bit for the dremel..it works great for fine tuning and cant say it took very long at all. joints(well most) were tight as a drum.

a pic of the drumsanding attachment.
http://www.mytoolstore.com/dremel/407-438.gif

of course the joints i was doing were small .up to an inch or so..if you work with the big stuff then use a normal drumsander bit in a drill gun or even a trim-router for faster rpm...

[headcase]

bamboo joints

I have come to knowing that the path I searched has been well trodden already (as is so often the case). The study of joints in bamboo hs been exhaustively researched by

DESIGNING AND BUILDING WITH BAMBOO

Jules J.A. Janssen

research report 20

http://www.inbar.int/publication/main.asp

lots of great stuff there as you may well know.

It seems that preservation is the key issue and its difficult and expensive to treat long poles, except by the traditional methods of submerging them in swamp water for 3 months.

Much of the problems of treating and using bamboo go away when you split the poles into strips. Its much easier and quicker to treat strips. I am looking at laminating strips to make square section poles.

advantages

a Regular size , no taper and can be thickness to standard dims

b Easier to treat with preservative, no phsical barriers

c Easier to machine as the integument contains silica has been removed

d easier to make joints in square section

e More predictable strength of material

f Easier to design from standard tables for wood

g Can be made rot, termite, proof throughout using cascamite urea formadelhyde glue

the downside is that - its not bamboo anymore!!!!!!!! its a composite

but maybe we can overcome this by using bamboo veneer?

I have yet to try and cost this process but normal construction timber is made from the Malaysian Rubber tree. Its semi hard wood, very straight with few knot holes. Its also very expensive, comparatively. They also use Eucalyptus wood (blue gum). Its poor quality and has a habit of becoming brittle and fracturing unexpectedly.

In thailand you need a special license for any kind of woodworking machinery. Such licenses are expensive and prone to graft (its to do with inhibiting furniture production from endangered timber). However, no special license is needed from processing bamboo.

Anyone interested in cooperating in this project please post.

rgds

Headcase

[Mark Mortimer]

Hi there Lung Chang,
Have a search on the net, as there are many Chinese and Indian companies who use and sell/make machinery for processing bamboo. They mainly use them to make bamboo parquet, but they can be adapted.
here's just one link that I happen to have in my favourites:
http://www.tifac.org.in/nmba/proj_mach.htm
Bamboo becomes a completely different material when processed. You are right, it no longer is "bamboo". You can of course find a middle ground, like using splits which are not machined and still have the skin on, like I use in my fences. But it is difficult to mass produce anything this way. I for one, am building a business which aims to use bamboo as close as possible to it's integral structure, but making it all less labour intensive. This only comes with practice and the develpoment of tools and techniques which work for me, at any given time.
Anyhow, let us know how you get on with your plans.
Cheers,
Mark

[headcase]

Bamboo machinery

Hi Marks
Thanks for your reply
FYI I find ingeneral that the indian subcontinent is generally an unsatisfactory area for trade and info particularly from Thailand. Its a mindset thing. The site you suggested is all development ideas and not any really info. China is a much more fruitful source, generally speaking and easier to deal with.
My work is on hold at the moment while my fish ponds are being excavated (one must eat) but will revert in about a month's time.

rgds
Lung Chang

headcase

[Mark Mortimer]

Hi Lung Chang ,
In one of your previous posts you said this:
"I have also seen an old design for a tapered reamer (the type used to make a flute or a windsor chair leg for example). The are really quite simple to make and use a hacksaw blade- with its teeth as is- as the cutting edge. Cheap and effective and easily maintained."
I am intrigued. Can we have a bit more information?

[Vijaykunchum]

Hello folks. I have gone through the same frustrations working with bamboo. It's always a challenge. Recently I have used a p.u. based low foam adhesive and I find the result encouraging. Here is what I did. I used bamboo saw dust(one could use any saw dust) and added a little quantity of this adhesive to the saw dust. Made the mixture into a cylinder and pushed into the end of the bamboo. Allowed it to dry for two days. This adhesive tends to foam a bit as it starts drying. This proved beneficial as the material expands and fills the void nicely. After it dried out I drilled a 8mm hole with a spade saw. The hole turned out perfect. Now I intend to insert mild steel pipe into the hole and fix it with nuts and bolt from the side. This should give a very strong joint. Another option is to use a piece of wood turned to 8mm dia and fix it into the hole with the same adhesive. This practically gives me a great flexibility in designing. For joints across I intend to use shorter length of the pole. Like the joint for a chair at the seat position. Instead of taking one long pole for the back, I intend to take a welded pipe slightly bent and insert the back, the leg and the seat portion. This should give me enormous strength and also allow me to use short lengths of bamboo. I will post photos as soon as I make one of the products.:)

[spacevenu]

hi, instead of this if u woved bamboos through the cable is long lasting tensile joint. i will load my experiment snaps soon.