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Sloped dado?

2K views 11 replies 11 participants last post by  lateralus819 
#1 · (Edited by Moderator)
I was using my dado set the other day to cut a slot to fit my digital caliper to use as a gauge to calibrate my table saw. So that means I was using my mitre gauge and a sacrificial fence to cross cut a shallow ~5/8" dado in a thin strip of hardwood. The width came out perfect (yay!), but upon closer inspection I noted something very weird. The dado depth was not consistent. That is, at one end of the cut it was deeper than the other (not left to right, but front to back). I have tried to think through how this is physically possible and have come up with nothing. I have adjusted my throat plate to make sure it is flush with the table.. and beyond that I don't have any real way of determining how this could happen.

Any thoughts?
 
#2 ·
Gerard, what sort of hold down did you use? I've sometimes had small pieces "Climb" the blade a bit. Only other thought would be if the blade dropped, did the dado slope up or down?

Hello from the 'Dorf just a bit south of ya!
 
#3 ·
I can't recall offhand in which direction it sloped, but that's a good question. I will do a test cut this week and see.

As far as hold down…. umm… does my hand count? I didn't have anything providing pressure directly over the groove so I suppose a climb of the cut would be possible (and that also gels quite nicely with my understanding of how physics work, whew). What type of hold down would be best in this situation?

I bought my cooktop in the 'Dorf!! Come up to the Norf side sometime and we'll make some dust.
 
#4 ·
I think climb cut has to be it assuming flat table, flat inser . I've had that happen on dados and it befuddled me. I don't trust dado blades anymore so I go to my trusty Record router hand plane to clean up. :)
 
#8 ·
Not much to add to the previous posts except to add that you might want to set up a level for your table. Set the level exactly horizontal and parallel to the blade then measure the distance from the bottom of the level to each end of the table.

Have fun! You are in a big wide world of woodworking now, there are more than 3 ways to skin the bark off a tree!
 
#10 · (Edited by Moderator)
This is a reason the radial arm saw is sometimes
preferred for cutting dados.

In any case, it's an interesting problem and it's
good that you noticed it. Noticing and addressing
these things is how we learn to excel at the craft.

A dado cut can push the work up if the feed rate
is too fast and downward pressure on the work
insufficient or inconsistent as the work is fed. A
loose height setting can allow the blade to go
down under the pressure of removing the material…
the blade sort of tries to "run away" and gravity
helps it. I have seen this happen with a benchtop
saw.

You might try rabbeting the end of a board with
your dado set at full width. This way you can observe
the cut from the side as it's happening and consider
your feed rate and how you're applying hold down
pressure. Check the rabbet, cut the rabbet off and
cut another rabbet. Are they all going to be perfect
or is there going to be some variation and why?

Sometimes in working with machines I think of myself
as a ship's engineer. Over time fussing with machines
one learns their quirks and how to compensate. It's
an interesting part of the craft for me.
 
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