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My table saw doesn't have a depth gauge. What is the quickest way to set it to a precise depth for e.g. cutting slots or dados or clean looking rabbets?

I tried using calipers to measure the blade height but it is difficult to make sure the blade is rotated so a tooth is at peak height.

Currently the way I am doing it is eyeball it, test cut through scrap, measure actual depth with calipers, adjustment by eye, repeat until I'm close enough. It isn't exact and it is very inconvenient.

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    Plus every test cut I make increases the chance of my table saw blade becoming sentient, slicing my neck open and rolling away to terrorize the city. – Jason C Nov 1 '15 at 19:18
  • It has begun. – Jason C Nov 2 '15 at 2:15
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    I feel that you are not following our suggestions properly if that is your results. – Matt Nov 2 '15 at 2:43
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    Something to watch out for is that every gearing mechanism has some backlash, whereby a clockwise turn followed by an identical counterclockwise turn might not return the blade to the exact height it was before. If you can "creep up" on the final height without overshooting and having to go back, it might be easier to get to the final position without frustrating oscillations. – Eric Lippert Nov 2 '15 at 20:19
  • Here is a thing I'm playing with now based on LosManos' answer below. I botched two of the slots but so far it seems promising. If it works out I might switch to mr mdf. I also want to experiment to see if I can consistently use the top of the splitter as an indicator instead. – Jason C Nov 5 '15 at 14:27

10 Answers 10

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What is the quickest way to set it to a precise depth for e.g. cutting slots or dados or clean looking rabbets?

I think you're already pretty close to doing it.

Usually what I do is get it close to the measurement that I want using a tape measure, spacer block, test piece, or something else just by looking at it. Rotate the blade (power off!) to see where the top of the cut is.

When you think you have it close, run a test piece through the saw and measure with an accurate device (calipers are good for this, though a combination square works just fine). Or, you can measure against the piece you are fitting it to, which is a better idea since you can custom fit it. Keep fine-tuning it until you have the cut at the desired depth. Sure, it burns through some scrap pieces until you get the settings dialed in right, but that's what the scrap bin is for!

3

Not an exact answer to the question but this should help you get precise in 2 cuts but should be very helpful in this situation and would also help you get to know your table saw. This information should also partner well with other answers here.

I cannot speak for all table saws but many are dial/wheel based for vertical adjustment. Turning that wheel a full rotation should be an exact, measurable change. In that every full rotation should move the blade up or down the same amount.

Make a pass onto a test block (The blade would need to have flat top teeth for this to work well!). Use a caliper with a depth gauge to measure the depth of cut. Then turn the wheel one full rotation to raise the blade and cut again on the test piece. Measuring again, and subtracting the previous cut depth, should give you the depth change of one full wheel rotation! I would suggest repeating the test to see if you get the same results.

While this does not help with the first cut exactly it does make fine adjustments more precise!

  • This is a great idea. I will try this tomorrow. Should also be able to find zero by making test cuts until the blade just barely scratches the boards. – Jason C Nov 2 '15 at 2:12
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    @LosManos I think that might be a bad idea from a safety point of view as there are very few reasons to change the height of the blade while operating. You would also have the OPs problem of trying to figure out the top of the cut so you might be tempted to move the board from that position. – Matt Nov 2 '15 at 13:12
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    @Matt Starting the machine would sort of defeat the purpose; the piece would stay in place until it flew away. (unless the air turbulence made it wobble beforehand and make the procedure even worse) Instead keep the machine off and turn the disc by hand. – LosManos Nov 2 '15 at 13:35
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    It is a procedure similar to when adjusting an electric jointer. Similarly; if you plan to fiddle around with fingers close to the business end of a jointer while it is running you better be a Very quick learner. – LosManos Nov 2 '15 at 19:20
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    @JasonC so that is how the 5 foot blades got away? – Matt Nov 3 '15 at 3:26
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Depth gauges can be used to set the height of many different tools, table saws, routers etc.

I got the Incra gauge myself and they can be found for under $20. Incra Depth Gauge

  • In a mere 3-7 business days, this will be in my hands. I'll still have the peak tooth height awkwardness, though, but maybe a precise reference will make up for that inconvenience. – Jason C Nov 2 '15 at 22:39
  • @JasonC I hope you enjoy it. I think it's wide enough to fit across a couple teeth. And is should be infinetly easier than trying to use a tape measure. Let me know how it works for you. – bowlturner Nov 2 '15 at 23:28
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    There are lots of other measure-the-exposed-blade solutions, including using dial calipers, or a compass and a ruler, or a set of standard-height blocks, or a v-gague (stepped or not). Warning: unplug the machine before using any of these! – keshlam Nov 3 '15 at 2:40
  • I got the gauge today. It is a great little tool. But no luck with the table saw. There is still the peak tooth height thing. I can rotate the blade under it but this gauge is made of plastic (good for not scratching your wood, not so good for holding against sharp, angle toothed saw blades) and the blade scratches up the face, so that's no good. There isn't enough surface on the gauge to really attach an extension to either. But it is handy for measuring test cut depth if you cut the outside of a board and leave the cut profile exposed, much easier than calipers. – Jason C Nov 12 '15 at 15:33
  • @keshlam Holding small straight board against the top of a standard height block and checking the blade that way is a good idea. I don't have a set of blocks though. But maybe I should get some. The low grade ones are reasonably priced and way more than accurate enough for this job. – Jason C Nov 12 '15 at 15:38
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For the same height repeatability you can attach a piece of right angled and dimensionally stable scrap to the fence as a sacrificial board. Raise the blade until right height.
Unless your cut is very low you now can measure against this former-scrap-now-jig without having to make sure a tooth is in the topmost position. Just raise the blade until it makes contact with the scrap-jig and you're at right height.

My first thought was that one can use this single jig piece for any height but then realised that it has to be level. Or curved exactly as the blade.

  • Just to clarify, you mean to cut it partially, so that the curve of the blade is visible in it? – Jason C Nov 3 '15 at 21:13
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    Yes. The same would be possible with the blade hidden inside too but then something might fall into the hole and destroy the accuracy. – LosManos Nov 4 '15 at 7:42
  • So I made this. I botched two of the slots but I'll redo it tomorrow. The others are accurate to .005", for now. If this works out I might use marine grade MR MDF instead. I also should take smaller steps to smooth the ridges from the angled blades. I want to add an extension for the lever effect you mentioned in your other answer. So far so good though. – Jason C Nov 5 '15 at 6:29
  • I wonder if I can use the top of the splitter instead. I'll have to experiment to see how repeatable its position is. – Jason C Nov 5 '15 at 7:11
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Interesting problem. I think that you can just as effectively measure the distance of the arbor (center of blade) in order to make the adjustments you desire. I have not tested this solution, but intuitively it seems to make sense (I have no such problem as, my Shopsmith saw has a finely-adjustable stop device on the table height adjusting column.) If your insert has some room alongside it, or if it is zero-clearance but you can remove it easily, I would suggest the following:

  • Grab your arbor wrench (hopefully, one of those nice flat and parallel-to-the-blade-face jobs - the flatness is important here.)

  • Get another straight, rigid, thin slat, something like a 6"" aluminum ruler, a rare-earth magnet, a marking knife, and a length of adhesive ruler tape long enough to measure the deepest non-through-cut you'll want to make (with satisfactory resolution - 16ths, 32nds, whatever.)

  • Adjust your depth of cut to exactly 0" somehow - your choice of method, and take your time, you'll only need to do this once.
  • Remove your insert if necessary so that you can reach down to the
    arbor nut with the wrench.
  • Reach down with the wrench and engage the arbor nut as though you were going to loosen or tighten it.
  • Lay the ruler down on the table so the end touches or almost touches the face of the arbor wrench (their faces will be at right angles). Plunk the magnet down on top of the ruler to hold it in place.
  • Rotate the wrench (and blade since they're engaged) so that the wrench is vertical.
  • Scratch a reference mark into the arbor wrench along the top edge of the ruler. This is your zero reference. Remove the wrench from the arbor nut.
  • Apply the ruler tape to the wrench with zero positioned at the zero reference and the numbers increasing in the direction of the wrench opening (center of blade).

You now have, in the form of the taped arbor wrench, the ruler, and if needed, the magnet, a tool for measuring the amount the blade cuts above the table. To set a cut depth:

  • Remove your insert if necessary
  • Grab your taped wrench and ruler, set the ruler on the table next to the opening.
  • Apply the wrench to the arbor nut and rotate to vertical with one hand, cozy the ruler end up to the taped side of the wrench with the other. Apply the magnet if needed.
  • Let go of the ruler, reach over (while keeping the wrench vertical with first hand), and adjust your blade height (and thus the wrench height - it's connected to the arbor) until the edge of the ruler is alongside your desired depth of cut.
  • Remove wrench and ruler, replace the insert, and make your cut.

Best I could come up with, I think it'll work for a lot of people, and is a dirt-cheap solution. Cheers!

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Take two pieces of wood of the height you are aiming for.
Put one at 1/4 and one at 3/4 of a distance from the blade.
Take a Very Straight Piece of scrap (extruded aluminium maybe) and lay on top of these. Put a finger on the piece closest to the blade and slowly raise the blade.
When the blade tries to raise the Very Straight Piece the lift distance is amplified in the end farthest away from the blade.

enter image description here

  • Ah, but this still runs into the problem of making sure the tooth contacting the horizontal piece is at peak height. I have an idea based on your other answer though that I am going to try to construct today. This answer, using the leverage to amplify the movement, gives me an idea for an improvement too although I'm not sure if I can build it. – Jason C Nov 4 '15 at 14:38
  • @Jason To start with I would turn the disc by hand. If the construction then worked to my liking I would consider something like the sacrificial board jig to make the contraption cooler. You have a very valid point regarding finding the teeth at peak height and I hope for you to solve it and tell us all. – LosManos Nov 4 '15 at 15:21
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  1. Make two blocks of wood of the same height as the desired depth of the dado.

  2. Use a square to make sure they are parallel.

  3. Unplug the saw.

  4. Place the two blocks on either side of the saw blade and lay a steel rule across them.

  5. Weight the assembly by placing a weight like a peanut butter jar or something on each block.

  6. Raise the blade until it just touches the steel rule when you turn it by hand.

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If you're looking for real repeatable precision, a device like the OneWay Multi Gauge is a good solution, and very handy for other setups around the shop as well, such as planer blade height:
https://oneway.ca/products-category/miscellaneous/Multi-Gauge

OneWay Multi-Gauge

With a measuring device like this one, you can rapidly achieve repeatable accuracy withing .001", which is more than adequate for woodworking joinery.

Notice the wide flat tip on the dial indicator. This is absolutely required for sweeping the peak tooth height (only sweep blade teeth backwards to avoid scratching the indicator tip.

Also notice that the body extends far enough back to not rely on the red insert being exactly co-planar with the table top.

I've tried lots of methods for this sort of thing. Using this device is the only one that doesn't drive me crazy :)

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I tried using calipers to measure the blade height but it is difficult to make sure the blade is rotated so a tooth is at peak height.

There are a couple ways to improve the accuracy of this measurement:

  • Mark the blade. Remove the blade from your saw. Find two teeth that are directly opposite each other, and then use a good straightedge and a fine-tipped permanent marker to draw a line right on the blade from the tip of one tooth to the tip of the opposite tooth. Repeat on the other side of the blade if you think you might work on that side sometimes. Re-install the blade. If you rotate the blade (with power off, of course) until the line on the blade is vertical, you know that that tooth is at it's highest point.

  • Setup blocks. Stack up some combination of machinist's setup blocks to match the desired height. Place these next to the blade, raise the blade until it's a bit lower than the top of the blocks, and then start rotating the blade back and forth looking for the top of the arc. Gradually raise the blade until the top of the arc is just tangent with the top of the blocks. For extra accuracy, you can place a piece of very flat scrap (plywood and MDF are often very flat) on top of the blocks so that the scrap hangs over the blade. Raise the blade gradually until the top tooth just kisses the scrap as you rotate the blade back and forth.

For the best accuracy you should of course measure from the table rather than the insert, since most of the work will ride on the table. But the insert should be dead even with the table anyway, and if a couple thousandths of an inch make a big difference, you're working with the wrong material.

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The solution is simple: a sundial. Affix a light source, piece of tape on the table saw and measure the shadow. Leverage the precision of light.

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    I'm not sure if this is supposed to be a real answer or is just a joke? But if it's supposed to be real, you really need to add more detail about how this is supposed to be done. – Charlie Kilian Jan 22 '18 at 4:47
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    Are you serious? This is exactly what I do. I've never heard of a forum punishing people for simple effective solutions. Go ahead and delete it, stack doesn't deserve to have solutions anyways. – wtwe Jan 23 '18 at 19:02
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    Okay! I honestly had never heard of this method. My apology for assuming you were trolling us. Can you add more detail about how you do it? I have never heard of this method and would be very interesting to learn something new. – Charlie Kilian Jan 23 '18 at 20:15

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