Episode 108 DadoStop!

Had a look at the blade(s) after the fact, and found out where the significant cascading sound comes from when the brake activates.  12 separate tungsten carbide teeth ripped loose of the blade.  Most presumably are due to the spacer blades not being in direct contact with the aluminium brake, so were able to move when the blade was (rapidly) decelerating, and knocked the teeth off as they slid past.

It is a good effort, stopping that much spinning steel on a dime!

The Boris Goldberg Kerf Chair

This is pretty cool – a chair created on a CNC machine using kerfing as the technique to give it shape.  Opens one’s eyes to all sorts of possibilities.

Glueups Progressing

Much of the evenings this week have involved short trips out to the shed for the next small step, primarily glue ups.  Sure have gone through a bit of glue this project!

Sink Lip

I cut the opening in the top of one unit for the sink using the Worx Sonicrafter.   To stop the sink falling through (and add strength), I created a rebated mitred lip around the sink.  I don’t have four corner clamps the same, so ended up using both the corner adapter on the Quick Grips for to corners, and the Woodpeckers Mitre Clamp Set for the other two.  Interesting comparison – the Quick Grips were more convenient, the Woodpeckers did a better job.  The design of it really allowed the corner to load up and get pulled together.  I also made good use of the Woodpeckers Mitre square.

Woodpeckers

I can really see how having the Woodpeckers Mitre Clamp set mounted to a jig would give a very good result.

Dry Fit

Tried the sink out (and no surprise), it fitted like a glove.  No surprise because I’d already tried a couple of times already 🙂

Mitre Inserts

I wasn’t happy how the mitres went – not close enough for what I wanted.  I’ve not had good results from mitre joints so far, and this one was no exception.  Nothing wrong with the clamps, everything to do with my technique.

So I decided to try another idea.  I ran the sink back over the saw, with the blade carefully set to the height just to cut through the top, and created a kerf at each corner.  Into that, I inserted and glued a piece of Solomons Queen Ebony.  Once it is dry, I will sand it flush.

Reinforcement

Finally, before I ran out of time, I added some support to the front and rear edges of the trays – didn’t want to risk a split/breakage when loaded up and in operation.

Still seems so much to do, progress is dragging.  And Christmas is only a few days away!

The Secret Language of Saw Blades

Ever gone to purchase a sawblade and wondered just what all the codes are engraved on the side (or printed on the packaging)?

There are a surprising number of variables that are possible with saw blades, so many versions that can be considered.  Some are irrelevant when choosing between one blade and another – they distinguish between a blade suitable for wood vs plastic (for example).  Some blades do cross over – the Flai Mustang for example, which will have variables that suit both materials.

For example: ATB D250, K3.0 B30, Z40, H10

ATB

ATB = alternating top bevel – this blade has its teeth set so it is like a chisel, with one tooth cutting to the left, and the next to the right of the kerf.

You could have 4+1 (4 ATB teeth, plus one FT (flat tooth) as a raker tooth, flattening the bottom of the cut).  An ATB blade leaves a V groove in the bottom of a partial-depth cut, and the 4+1 is a way to resolve this, leaving a flat-bottomed kerf.

Other options include HATB (or HiATB), where the teeth are even more angled which is good for melamine, and timbers prone to tearout, TCG (triple chip grind, also known as triple cut, FT (Flat Top), HG (hollow ground)

D250

D stands for diameter – size of the blade in mm.  A 250 blade (or to be exact, a D254) blade is 10″

K3.0

This is the kerf of the blade, measuring across the teeth.  This does not mean the blade will actually cut a 3.0mm wide kerf however. Blades have runout (just how flat is the blade, and during use just how flat it remains as the temperature of the blade changes).  Saws (tablesaws or circular saws) also have runout, and it is a combination of both that will dictate exactly how wide a kerf you will get.  If you want to know it exactly each time, you have to measure it whenever you change blades.  The next time you mount the same blade, it could be different depending on at what point of rotation that the saw is vs the blade.  It is much easier just to do a test cut and remeasure if it is that important.  This concept is greatly (and deliberately exasperated) for a wobble dado blade, which is designed with a large amount of runout which can be dialed in, creating a dado (or wide trench).

B30

This is the size of the bore – the hole through the middle of the blade.  Depending on your saw you can either get a blade that specifically matches your saw, or one that is larger and get some saw blade bushes (or reducers) to match both the blade and you particular saw.  They are not as convenient (but are still easy to use), and they allow you to purchase blades that are suited to your needs without necessarily being made for the size bore you require.  Of course, if the hole is smaller than your arbor, you have a problem! Getting back to dado blades for a sec, when using stacked dados, I would strongly recommend getting one where the bore is correct for your saw – there are enough things to juggle without also having to try and manage a bunch of bushes as well.

Z40

Z stands for the number of teeth.  A ripping blade can have around at little as 24 teeth, a crosscut blade as many as 100.

H10

H is the hook angle (or rake angle). Large hook angles are an aggressive blade, particularly for ripping soft timbers.  Small, zero or even slightly negative for crosscutting hard timbers.

 

These are just some of the variables and codes that can be written (engraved) onto the blade.  They may not all be listed, and some blades may list a whole bunch more.  If you know these at least, you are well on your way of being able to distinguish between one blade and the next.

 

Some other variables include top clearance angle, top bevel angle, gullet size, gullet plug, expansion joints, noise reduction slots, max operation RPM, carbide type, base blade material, blade coating, body thickness and so on.  We’ll stick with the most common concerns at this stage!

 

Calibration

For some operations on the Torque Workcentre, such as surfacing, you want the shaft of the router (and therefore the bit) to be perfectly perpendicular to the working surface of the workbench.

You can certainly achieve this by trial and error, but I prefer a less empirical approach, and thought that the way that you can accurately set a drill press table would also work well here.  Using the Carbatec Deluxe Alignment System, mounting it in the collet of the router and (non powered!!!!) rotating it around you can easily measure where it is high, and low.

Dial Gauge Calibration

Ignoring whether it is forward or back, adjust the Y axis rotation until the high and low points are exactly parallel to the Y axis.  Then work with tilting the tool until there is almost (to no) movement of the dial gauge throughout.

Calibration

Somehow I managed to get the rotation to happen at just the right place, that the point of the dial gauge missed every single hole.  Didn’t imagine that’d be possible!

I was originally wondering if there was a way of using a laser mounted in the router, but the dial gauge is going to give a pretty good result!

The sort of laser I was thinking is actually a kerf-laser from a saw – it is normally mounted on the arbor next to the blade, and the spinning saw turns on the laser.  If this was instead mounted on a shaft like is done with some slot-cutting router bits, I thought this might be a way of projecting a horizontal line, perpendicular to the router shaft.

Kerf-laser

Table of Blade Measurements

I have added a page to the Battle of the Blades review which gives a table of all the blade measurements side-by-side. Table of Blade Measurements

There were a few unusual measurements that came out of it, but all in all, it is the performance of the blade that really counts. Other than perhaps carbide thickness, which gives an indication of how much resharpening the blade can take.

One item that offered some correlation between the measurement and the cut quality was blade runout.

There were a few blades with a significant degree of runout, and each also gave a poor finish. I only get to test one blade from each, so I can’t say whether it was just a rogue blade, or batch, or if that is typical. It really did highlight the fact that it is definitely worth testing a new blade’s runout before putting it to use, and if you are not satisfied, return the blade.

The typical runout found was 0.005″ / 0.13mm. The lowest was a remarkable 0.002″ / 0.05mm. The highest was 0.030″ / 0.76mm. That blade literally screamed when it was run unloaded, with the noise going from a typical unloaded (but running) level of 95dB to 105 – 110dB after a few seconds. Not sure if one resulted in the other, but it is interesting.

It is not just the blade runout that affects the quality – variation in tooth width (the kerf) plays a large role as well.

I didn’t get into the angle of the grind and how it plays a part in quality – perhaps a job for another day.