Thursday, March 24, 2016

Where the money is

You know, science is about truth searching, isn't it? Well, think again. Money is given to universities to advance a certain agenda, the agenda of those who have money or power (which are usually the same).

Saw tensioning is worth of study as any other subject, but since you make more money selling disposable circular saws to big companies, that's where the science is. Said in other words, you are not gonna get funded to study the tensioning of a ryoba so we need to divert some of the colloidal suspension money into it.

Usually the first step in a research project is to check out the literature and share it with your friends so you start talking the same language. This is what we are doing here.

Our first paper in this study is "Understaind Saw Tensioning" by G.S. Schajer appeared in 1984 in the journal Holz als Roh- und Werkstoff. Here's the link.

I just copy paste the interesting quotes to give you an idea of what the paper is about.

This paper describes the various techniques of circular and band saw tensioning, and explains how they work. It also discusses many of the significant contributions to the literature in this field.

Circular saw tensioninginduces stresses in the sawblade such that the periphery is pulled into tension. These stresses alter the saw vibration fiequencies, and when favorably dis- tributed, they can significantly improve sawblade stability.

The traditional way of tensioning both circular and band saws is by hammering their surfaces. The hammer blows in- dent the saw steel and squeeze it laterally in the plane of the plate. These highly localized deformations induce the tensioning stresses. Harmmer tensioning is very much an art, and great skill and experience is required to achieve good results. When done well, hammering can be as effective as more modern methods. However, hammer tensioning is usually not recommended for general use because the results can be very variable. Also, the hammer blows make the saw blade surface uneven and can initiate fatigue cracks.
A small induction generator heats the sawblade close to the collar to a temp rature in the range 30-80 C. This modest temperature does not cause any permanent changes, such as occur during heat tensioning. Thermal expansion of the heated central region of the saw induces tensile stresses in the unheated outer region. These tensioning stresses exist only while the central region of the saw is kept warm. When the induction generator is turned off; the saw returns to its original state. In practice, the induction generator is controlled so as to maintain a set temperature difference between the inner and outer regions of the sawblade.

Food for thought.

The pictures is from another paper and presents the analysis I plan to make for a ryoba with a shaped surface. These are the normal modes for a circular saw, the way it displaces out of plane. Any vibration of the blade can be decomposed into a sum of these modes, like a string in 1 dimension if you catch my drift.

 What you want to do in a saw is to dampen the low frequency modes so the vibrations are high frequency and low amplitude, thus your kerf is straight. Do you achieve this by carving the centre of the blade with the sen? by doing a surface hardening with a burnisher? I bet you can, I bet you do.

Saw tensioning is an obscure subject, but not because being intrinsically difficult or magical, but because the economic conditions of the world had made the subject not worth of research effort while at the same time making the people who knew this art redundant and obsolete. To change this means to work in a lateral way to usual university/research work, freed from corporate interest, based on friendship and love for knowledge. As it used to be, as it should be.

Stay tuned.
This paper describes the various techniques of circular and band saw tensioning, and explains how they work. It also discusses many of the significant contributions to the literature in this field. 

Tuesday, March 22, 2016

Chilean maple

Since nobody said a thing about FEM solutions for teeth geometry of saws, I assume you either don't get it or don't see the point of it. So back to wood pictures.

We have this wood here in Chile, Lenga (Nothofagus Pumilio) which is very similar to maple in grain, colour and overall feeling. It even has some flaming to it.

I bought one 2x6 and cut it into pieces, brought one to Valparaiso and left the rest in santiago. I wanted to make the connection for the legs of the bench downstairs but the piece was too short. So why not make some scrolls?

I don't have a printer nor violin patterns, so I just eyeballed the dimensions of the scroll using some values I found in internet, it's a tad too wide for a violin, that much I can tell.

 But what I'm interested on is trying out the tools in the wood, see how it cuts and where it breaks. How well defined the chamfers can be made with the knife, and how's the grain to behave when carving the scroll. Call it an exercise if you wish

 The grain orientation is not the best for a scroll but you can get a fair idea of how it would perform.  The short grain there at the bottom of the back side was too weak. And I always have problems carving those parts where the grain comes in two directions.

The tools used and dog's approval

Didn't scrape or sanded anything, nor did the other half. No files used either. The wood  needs to dry a bit more, so I'm cutting the blanks and getting a template for the scroll. That small spokeshave came real handy. Now look for a log of flammed lenga and let it sit for 10 years while I build my violin making workshop.

Friday, March 18, 2016

Why japanese teeth are better

Bad teeth are better than no teeth, but sweet ass teeth is what you look for in a smile.

Western saws cut, and ugly teeth do smile, but japanese are better and we know it. Why? The secret is as usual a fragile balance between two opposite forces, and japanese craftsmen know to walk on the tightrope.

Let's start with a western saw pattern, projected onto two dimensions for the sake of simplicity.

The gullet space is where the saw dust goes once you start cutting, so the more space there is, the more you can cut with each tooth.

Say we instead of using a triangular file to sharpen, as in western world, we use one file for each side of the tooth, as is done in developed places like Chile.

 That looks more like our mountains here. Which is better in the sense that gives you more space where to put the sawdust so you can cut more with each tooth. But, here starts the contradictory principle to play, as you make the teeth pointy they become also weaker. The strength of the material is proportional to the area (volume in 3D) of the teeth, so as you increase the angle they become weaker... something you don't want in your mouth, weak teeth.

Not clear? Well, let's solve the plane stress relation for a fixed material with different geometries and see if you get it. (Red is the deformed geometry, black the relaxed position)

I'm applying a force on the left facet of the teeth, always the same force, and checking the deformation of the teeth. As the teeth becomes more pointy, they also deform more in the tip. Eventually they can reach their breaking point and pluff. Cappicci?

So what you do? You can change the geometry of the teeth such that they are strong yet have plenty of room for the sawdust. How you do that?

Indeed, you create a third facet that increases the strength of the teeth since it supports it from the back, that's where the force of the wood on the teeth is going.

Like this:

Without the third top facet the tooth become weak and useless.

Now, since we have a strong tooth and plenty of space to put the sawdust, we can put more teeth per inch and remove the same amount of sawdust as the western pattern, only faster and easier.

This is maybe an exaggeration but you get the idea, as long as you have enough gullet space you can put more teeth and cut faster.

did you like that fem plot? Me too, I'm coding later a japanese teeth pattern and show you why it's better to cut chumasaru rake and what's the best angle for the top facet. And maybe in a few days we go 3D.

I will continue dwelling in saw sharpening for a while since it's been too long that I promised to make a write up and send a pdf of it to the guys who took the class in NL. Sorry for the delay but I was busy learning how to do this FEM analysis, amongst other things.

Wednesday, March 16, 2016


With that quincho standing there back south I can focus again in the several projects that have me imagining things before going to bed.

One of those is the violin making workshop. Ya know, all the little cute tools.

Yesterday I tried the spanish file on the blade. Today was a fast chiseling of some hardwood flooring Keiran found on the street here in valpo, seems to be sycamore, or a chilean wood I don't recognise.

The blade is kinda fat, I wanted to take it to the university and mill 2mm off the back, but god I cannot wait so it's as thin as my boredom filing allowed me.

I ground a kind of ura on the back but there was a back bevel that made my work a bit useless. I did some "engraving" on the blade too. I call this blade "forest of bamboo in winter as seen by Klimt when we was visiting Ralun". Or kanna-chica if you want.

 I started with a 10x10x3cm piece of wood and just morticed the middle real fast. Then used a keyhole saw to cut the grooves.

20 min or so later it was cutting some lenga.

 Then I sharpened it and cut some laurel

After that put a piece of purpleheart in front of the mouth

and put it next to a 70mm one for a sense of the size.

(And make you jealous if you recognise the blade.)

Tuesday, March 15, 2016

Paying debts

This one is mostly for Jason.

Or for those people interested in getting the bang for they money regarding japanese/chinese diamond stones.

Or interested in saw geometry.

Or files.

All the pictures that come next are good things:

 a fast cutting saw for wet wood.

not well jointed but works ok. The steel is thick.

a sk-11 flattening diamond stone after a year of use, 12 students, and many many beers before taking it out of water.

It rusts, as you ca see, and those rust spot grow and peel off the diamond coating.

 it started quite soon back in Graz, if I used it for sharpening metal. As long as there are no metal particles on the thing, seems to work quite well.

 those spots will gouge your sharpening stones, but won't come off so don't worry too much. It's still usable but ordered a new one a week ago already. Only for stones and maybe can get some of that powder that makes water iron friendly... any idea what I'm talking about? saw it somewhere, it must be a base or an acid, will ask a scientist when I find one.


spanish files. They cut fast, get one if you find them in your local hardware shop. Erizo, porcupine in español.

That's another mini kannami in the making.

Monday, March 14, 2016

hot springs

 We did laundry today

and in the evening to the hot springs

it looks cools but feels better

Because yesterday we were putting some up with some shit

and covering with blue plastic for the time being. 

Saturday, March 12, 2016

Almost there

Getting tired of blogggin of this, shit is coming along. 

The morning was spent on fiting those half lap bevel, man we are doing something wrong cause we spent far too much time and energy putting in, putting out, trying the fit.

 Anyway, the winter will come and a simple roof will do, and that's what we are doing tomorrow together with putting everything up.

Lots of screws, circular saws and nails. I guess I could build a "chilean" house in a few days.

We cut the posts to lenght, 220 till the start of the tenon, and loaded the truck.

 And rode with em

 the view is as usual priceless.

That's where everything will happen tomorrow

Stay tuned.

Friday, March 11, 2016

Back at it

Welcome once again, to Sebastian's House of Joinery.

We took a plane, Keiran and I, and arrived yesterday to Puerto Varas, where the food is great and the weather is awesome. Valparaiso is already cold and cloudy and Santiasco is smoked and hot, so escape here even for 4 days feels like fucking heaven.

Nico had some health problems in argentina that delayed his trip to the end of the world so could not make it... and David is back in Berlin building his own workshop. Hope to see pictures of that soon.

Anyway, we arrived to pv, got some beers and burgers, and came here, to "home". Wood was where we left it.

Today we wanted to fit the tenons of the columns on the mortises and by 11:30am we had 2 done. At 4 the job of the day was done and we were ready to swim. Feels good to have rested for a few weeks and the back doesn't hurt when you move beams around. Job was sweet, as it should be.

 That's the first tenon going in.

It was so hot that measures were taken

the centre lines don't lie

looks cool, isn't it? maybe a new tattoo? Japanese joinery tattoo porn, I like that.

  and around 5pm we were here

That's how it looks down the river

and this is up, direction argentina

I was swimming like 15 minutes, really nice water man, I'm telling ya.

Come next year to join us, we planned to come here to the river one day for bbq and spoon carving or some shit like that, working next to the water, swimming, checking out the birds.

Thursday, March 3, 2016

Some toolmaking

Yeah, been busy. Now I'm also doing some brain wave data analysis since the postdoc, the house, the dog and the workshop didn't ask for enough.

Anyway, today before lunch and after dinner had some time to cut a new blade for this:

I bought a set of 10 spoke shaves from japan and half of them were really crappy. The other half was nice and ready to use, almost.

The protruding blade is one I changed from one of the ones I have, that still needs some work.  The other 5 are usable already and the sixth was my "old" spokeshave. (Why somebody needs 10? Well, stair-making is your answer.)

So, the day started with going down to Christian to buy a cutting disk. And figuring out a way to put it in my grinder.

Christian is my new friend, owner of the hardware store (the only hardware stone with beer and electronic music of the world I guess). I will invite his place to the blog next week.

Cutting was really easy, a stiffer disk would have been nice. But it worked not half as bad as I was expecting and after some 30 min work with the saw, I had 3 pieces.

The hand cranked grinder was awesome, way slower than a dremel so the steel didn't get hot at any point. 

A comparison with the original blade. Seems like carbide welded into steel. Not sure what it is but it's laminated. 

 Then we went for lunch at a stupid vegan restaurant with a french girl Julia met in Argentina when she went to extend her visa... cool girl, new rule of my life: never again go to vegan restaurants.

We spent a few hours out, then Julia did some yoga and I had to be silent, so I napped.  Around 9pm this was were I was... I thought about a kanji but decided against it and mark it with a dot. One dot, first blade, and so on.

I need to uradashi a bit more the centre... there are some small rust spots there.

 and the spoke shave wasn't used before. so I had to open the mouth a bit.

I like the square-ish shape

Ohhh... I almost forget. Spent like 1 hour filing the back of the blade, it was like 3 times the thickness of the original blade, which didn't look to tapered to be honest.

Need to find a use for the remaining 2 parts of the old blade. And I have a few other old blades that may visit the cutting disk... I'm really into small kanna at the moment. I also found a wood that's the chilean equivalent of hard maple, lenga it's called. Looks more springy than the other woods I've seen here and with a purple heart insert in the may just do it.

(and before you say anything, no, it's not real sharp. I was just busy today setting the bevel angle, there is still some work to do to call it done.)