If you’ve bought a miter saw in the past few years, you might have noticed the LED “laser” that came with it. The goal was to show where on the piece the saw was going to cut. But over a year or two, you might have found the laser to have drifted or skewed into a crooked line. [Fisher] decided that his after-market laser wasn’t entirely accurate enough and added a shadow line instead. (Video, embedded below the break.)
The blade has a thickness (known as kerf), and with a laser to one side, you can only accurately cut on one side of the line. A shadow line works differently. By shining a line at the top of the blade, you get a mark where the blade will cut precisely. You can also see your marks as the laser doesn’t shine over them. Previously, [Fisher] had tried to use LED strips, but after a comment suggested it, he found a sewing light on a gooseneck. It worked great as a small compact light fitting the blade housing. After some quick modifications, hot glue, and duct tape, the light was installed, and the wires were routed while still allowing the saw its full range of motion.
The result is impressive, with a clear shadow on even darker hardwoods. Just the few test cuts he made seemed entirely accurate. Of course, you can always go deeper down the hole of accuracy and measurement. But overall, [Fisher] has a great little mod that speeds up his workflow more accurately.
43 thoughts on “If The Blade Sees Its Shadow, It’s Another 64th Of Accuracy”
What’s a 64th in Olympic-sized swimming pools?
About the width of a banana slice.
An Imperial or Metric banana ?
If you feel a slight disturbance in The Force, probably imperial.
400u (396 and 7/8 micron, exactly).
64th? That means 63 swimmers are above you in the standings.
Well 1/64in is 79349.6 beard-seconds, so that converts to 0.00000793496 Olympic sized swimming pool lengths
I was hoping this involved Fresnel lenses or something. Correct me if I’m wrong, a Fresnel lens on the light would make the shadow appear sharp much earlier, and give better contrast too, right?
It’s certainly possible to stimulate an infinitely far away light source with a point source and a lens, but it requires specific spacing and the right kind of lens, and in general would be more complicated and more expensive and more bulky. So I think it made sense to try this way first, and the results are probably “good enough.”
I was thinking the same thing – a collimated light source would work much better at a longer working distance. The quick and dirty way to build something reasonable would be to just use a strip of narrow beam LEDs in 5mm packages. 15 degree is pretty easy to find. For example: https://www.digikey.com/en/products/detail/creeled-inc/C503D-WAN-CCBEB151/4793679 is pretty cheap and available.
It’s a really quick modification if you watch the video…
On another note:
I highly doubt that lamp will stay secured to its place because hot glue sets much too quickly when used on aluminium because of the quick heat transfer.
Guess vibration will make it fall into the blade sooner or later…
I’m sure the “alabama chrome” will be right behind the hot glue. But as a proof of concept, it’s perfect. I think two small screw holes through the metal housing into the light’s plasic shell would work ok. Similar for clips to hold the wires.
I’ve had good success with glueing aluminimium with hot snot, but you have to pre-heat the aluminimiminium or you have to use enough hot snot to heat up the aluminiminiimiuum with that.
And of course you also have to clean it. If the hot snot only adheres t the sawdust inside the guard it won’t work very well.
I’ve glued a spoon / knife rack to ceramic tiles with this (in a rental apartment, so I could not drill holes in the tiles) and it’s holding up for years now.
Yep, pre-heating and a degreased surface is the way to go!
That’s the new trend in commercial miter saw.
Nice hack! But FYI those stick on cable guides are trash. If they have ANY shear load on them the will fall off within a month or 2. Serious, 1 ethernet cable is enough to pull them off.
I’ve had mixed success with different adhesive strips. Some are nigh permanent. Unless you mean the specific one’s they’re using.
Maybe there’s some brand that’s good, but I’ve never seen it. I was an industrial engineer when I was younger, and I saw these used many times. All different brands and types, every installation fell apart at some point.
Adhesive needs preparation for it to work properly. Clean the area, stick on the cable clip, then leave it 24 hours before adding the cable.
Why not just touch the blade down on the workpiece before you start the cut? If the edge of a tooth is on your line, you’re good to go.
That’s fine if you’re only concerned where the cut starts. Which, 90% of the time is indeed all you care about.
If your line and saw blade are at the same angle (they should be), you should only need one point of reference. The cut should start and end on the same line.
Tape measure and pencil don’t go well in the same sentence with accuracy. If you want accuracy you need to stop measuring.
Pencils can’t make a line anyway. Just a smudgy widening shape as the point wears down.
That’s why I rotate the pencil while drawing with a straightedge, (like I learned in Drafting class)
Aren’t the sawblade teeth proud of the shade of the sawblade’s body (and thus the shadow line)?
They are, but – at least on my saw with a shadow-line LED built-in – they are visible in the shadow.
reminded again of the usa being pretty much the only country in the world with inches and those weird fractions..
And accuracy with a drop saw is just practice, and occasionally end stops on the bench.. :-)
Weird fractions? You mean those numbers to the right of the binary point?
“numbers to the right of the binary point” – Touché – Nice one, I never thought of it like that!
In all honesty, I always though the USA rejected the imperial system on 16 December, 1773, in Boston, when they threw some tea into the harbour. Seems not everyone did though.
There were multiple attempts to bring the metric system to the colonies, unfortunately they were defeated by pirates, storms and short-sighted politicians. One of the first attempts at bringing the kilogram to the USA was struck by a storm. The ship ended up off Montserrat where it was attacked by pirates who threw the kilogram over the side as junk.
That would have been a feat since the metre was first defined 20 years later in 1793…
Well, it ain’t rocket surgery since the inch is exactly 25.4mm. And 1/64 inch is exactly 396 and 7/8 microns :-)
please remove this because lawiers cut you
He is not physically modifying the saw, he is just adding functionally where there was previously none. Just like the “add-on laser light next to the blade.
Great hack! Out of the box, my Ridgid 12″ miter saw uses this method of projecting the cut line instead of a laser. It has worked great for me.
I sue s shadow line while sharpening clipper blades on a lap wheel. It vibrates a lot. Laser just wiggles a bunch. Yeah I could balance the wheel.
I like this idea a lot. Wondering – if you look at the light (time 6:21), would that tend to get somewhat coated in fine sawdust? Especially for sappy or moist wood? I’d think the crisp shadow line would get diffuse over time. Maybe frequent swiping with a soft brush would keep sawdust at bay…
Yes! Glue camel hair bristles to the saw blade to whisk those particles away as the are produced!
Y’all are aware that most newer (in the last 10+ years afaik) miter saws are sold with an led shadow line guide, and dewalt sells one as an add-on to any of their saws made in the last 18+ years.
I have one on my dewalt miter saw and I love it.
My mitre saw is years old an still perfectly accurate. I’m not going to buy a new one for a light
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