How deep does everyone here cut their dadoes? On an example ~3/4 plywood carcass where you are cutting dadoes for shelves? If you asked most woodworkers their answer would most likely be Ό with a few people saying 3/8. That is the general rule I have always heard, 1/3-1/2 of material thickness. Well I have a confession to make
My name is Jonathan and I dont care how deep my dadoes and rabbets are. There, I said it. I feel better. Whew! *wipes sweat from brow* (the more experienced among us can probably tune out now, they likely already know what I am about to say)
I have virtually every setup gadget ever made for table saw and router this side of the very expensive Angle Wright. I rarely use them anymore. They gather dust in a drawer in my workbench. I ceased to care how much material I am removing from my carcass sides. It is the least important measurement on my plywood carcasses and realizing that has saved me time and frustration in my projects.
Now, this is not to say that I just grab my outside dado cutters and a chipper or two for the table saw, toss them on in haphazard fashion, give the handle a few cranks and let her rip. That is far from the truth. I just finally realized one day that the amount of material being removed was far less important than the amount of material that is left, for most casework.
It really does not matter if your dado is Ό in depth, 3/16 in depth or whatever. Somewhere between 1/8 and Ό is sufficient for most all of our purposes, and that is the size of mine. Dadoes ranging in depth from 1/8 and Ό when I am working with ~3/4 plywood are perfectly fine. I used the squiggly line because it is never Ύ. Plywood generally ranges between 11/16 and Ύ. At least the stuff I buy is. I know everyone speaks poorly of big box sheet stock but my local Lowes usually carries pretty good stuff. The Home Depots here in the Indianapolis area carry sheet goods that probably would not even make good firewood though. The one problem with it is variations in thickness. It is usually around 11/16, sometimes a smidgen more.
I have gone through all of this long-windedness to let you know that I cut my dadoes to a depth that makes sizing my other parts the easiest. So in ~3/4 plywood I cut them to a depth that leaves me with exactly ½ of material remaining. I also use no measuring tools to measure the height of the cutters above the table saw surface. Crank it up until it is 1/8 or so above by just eyeballing it and cut a test dado in a scrap piece from the same sheet and then take my calipers and measure from the bottom of the dado to the opposing, outside face and since it should be greater than my magic ½ I crank it up a bit and recut. Rinse, lather, repeat until you have exactly ½ of material remaining and then cut all of your dadoes possible with this width of stack.
If you do not have calipers you can still get extremely close by using two pieces of scrap. Cut your test dadoes on both pieces and then place them back to back with the dadoes facing out and measure the combined thickness of both remaining pieces together and shoot for 1 exactly. By using two pieces you automatically account for and lessen the effect of cumulative error. Not as precise as calipers, but it should work plenty well for machining wood.
So, some of you may be asking why not just measure the plywood, subtract ½ and set your cutter height to that? Well, it comes back to cumulative error and not wanting to overcomplicate things. I do it this way because it is easy, simple, fast and it works. If you measure, measure, do the math, measure and then cut, you leave yourself open to cumulative error and you are making it a lot harder than it needs to be. You are also buying expensive setup tools that are never where you remember laying them down at last and then wasting time while looking for them and then by the time you do find them I have already cut my dadoes and started glue-up (as soon as I find where I set my glue down at last .I really need to clean up my shop also, lol).
The next question is why am I being so anal-retentive about leaving exactly ½ of material? It makes your entire remaining math SO MUCH EASIER! You also should not care how deep the dadoes are by now! We all work off of a set of dimensions right? Or at the very least we have a set of outside dimensions in mind and some plan for scale and placement of the rest. Let us think about a simple bookshelf for a moment. We want to make it 30 wide. If you use my method when it comes time to cut your fixed shelves then you know they should be precisely 29 in length. If you cut them Ό in depth you will probably end up with something approximately 29-3/32, if you can even measure that closely. I on the other hand did not even have to go search for my tape measure that is not where I remember laying it down when I went to go look for the glue .. That is also assuming that you set your cutter height to exactly Ό. Any amount you were off by you can double it and that would be your cumulative error. Those errors will all show up at the end when the bookshelf you wanted to be 30 in width is now 29-7/8 or 30-1/16 and that throws off every measurement from then on. It also could end up like a bookshelf I built once for myself where I messes up and cut my last piece to 28-1/16 instead of 29-1/16 and had to re-cut all my shelves and ended up with a bookshelf that was narrower than planned by exactly 1.
This method works even better on drawers because by the time you end up measuring for them often times little errors have added up or you may have had to adapt along the way (compensate for mistakes in other words) and now your drawers are an oddball size. Drawer bottoms can also be a pain to measure for. Now that I quit caring how deep my grooves are also I leave myself with Ό of material on my ~1/2 plywood drawer stock and when I measure my drawer I subtract ½ and cut my bottoms (I usually take off an additional 1/16 to make them easier to slide in and since they are plywood I also glue them into place.
It works for rabbets also. When I rabbet for plywood backs I leave myself with ½ of material like on my shelf dadoes and then I measure my carcass, subtract 1 from the width and whatever allowances I need to make from the height if any and cut my plywood back. I do not have to take inside measurements with my tape measure that never seem to turn out quite right.
I know this was terribly long-winded and I appreciate anyone that made it this far. I am coming down with a head cold or sinus infection and for some reason I was not able to sleep and felt like writing. This was also a little tip I wanted to pass on to the newcomers so that 5-10 years down the road they were just realizing this on their own. Every set of plans out there and every woodworking show always says Ό dado for this or Ό groove for that. Even his Normness always says he cuts a Ό groove for drawer bottoms and I always wonder if they arent more like 7/32?
My name is Jonathan and I dont care how deep my dadoes and rabbets are. There, I said it. I feel better. Whew! *wipes sweat from brow* (the more experienced among us can probably tune out now, they likely already know what I am about to say)
I have virtually every setup gadget ever made for table saw and router this side of the very expensive Angle Wright. I rarely use them anymore. They gather dust in a drawer in my workbench. I ceased to care how much material I am removing from my carcass sides. It is the least important measurement on my plywood carcasses and realizing that has saved me time and frustration in my projects.
Now, this is not to say that I just grab my outside dado cutters and a chipper or two for the table saw, toss them on in haphazard fashion, give the handle a few cranks and let her rip. That is far from the truth. I just finally realized one day that the amount of material being removed was far less important than the amount of material that is left, for most casework.
It really does not matter if your dado is Ό in depth, 3/16 in depth or whatever. Somewhere between 1/8 and Ό is sufficient for most all of our purposes, and that is the size of mine. Dadoes ranging in depth from 1/8 and Ό when I am working with ~3/4 plywood are perfectly fine. I used the squiggly line because it is never Ύ. Plywood generally ranges between 11/16 and Ύ. At least the stuff I buy is. I know everyone speaks poorly of big box sheet stock but my local Lowes usually carries pretty good stuff. The Home Depots here in the Indianapolis area carry sheet goods that probably would not even make good firewood though. The one problem with it is variations in thickness. It is usually around 11/16, sometimes a smidgen more.
I have gone through all of this long-windedness to let you know that I cut my dadoes to a depth that makes sizing my other parts the easiest. So in ~3/4 plywood I cut them to a depth that leaves me with exactly ½ of material remaining. I also use no measuring tools to measure the height of the cutters above the table saw surface. Crank it up until it is 1/8 or so above by just eyeballing it and cut a test dado in a scrap piece from the same sheet and then take my calipers and measure from the bottom of the dado to the opposing, outside face and since it should be greater than my magic ½ I crank it up a bit and recut. Rinse, lather, repeat until you have exactly ½ of material remaining and then cut all of your dadoes possible with this width of stack.
If you do not have calipers you can still get extremely close by using two pieces of scrap. Cut your test dadoes on both pieces and then place them back to back with the dadoes facing out and measure the combined thickness of both remaining pieces together and shoot for 1 exactly. By using two pieces you automatically account for and lessen the effect of cumulative error. Not as precise as calipers, but it should work plenty well for machining wood.
So, some of you may be asking why not just measure the plywood, subtract ½ and set your cutter height to that? Well, it comes back to cumulative error and not wanting to overcomplicate things. I do it this way because it is easy, simple, fast and it works. If you measure, measure, do the math, measure and then cut, you leave yourself open to cumulative error and you are making it a lot harder than it needs to be. You are also buying expensive setup tools that are never where you remember laying them down at last and then wasting time while looking for them and then by the time you do find them I have already cut my dadoes and started glue-up (as soon as I find where I set my glue down at last .I really need to clean up my shop also, lol).
The next question is why am I being so anal-retentive about leaving exactly ½ of material? It makes your entire remaining math SO MUCH EASIER! You also should not care how deep the dadoes are by now! We all work off of a set of dimensions right? Or at the very least we have a set of outside dimensions in mind and some plan for scale and placement of the rest. Let us think about a simple bookshelf for a moment. We want to make it 30 wide. If you use my method when it comes time to cut your fixed shelves then you know they should be precisely 29 in length. If you cut them Ό in depth you will probably end up with something approximately 29-3/32, if you can even measure that closely. I on the other hand did not even have to go search for my tape measure that is not where I remember laying it down when I went to go look for the glue .. That is also assuming that you set your cutter height to exactly Ό. Any amount you were off by you can double it and that would be your cumulative error. Those errors will all show up at the end when the bookshelf you wanted to be 30 in width is now 29-7/8 or 30-1/16 and that throws off every measurement from then on. It also could end up like a bookshelf I built once for myself where I messes up and cut my last piece to 28-1/16 instead of 29-1/16 and had to re-cut all my shelves and ended up with a bookshelf that was narrower than planned by exactly 1.
This method works even better on drawers because by the time you end up measuring for them often times little errors have added up or you may have had to adapt along the way (compensate for mistakes in other words) and now your drawers are an oddball size. Drawer bottoms can also be a pain to measure for. Now that I quit caring how deep my grooves are also I leave myself with Ό of material on my ~1/2 plywood drawer stock and when I measure my drawer I subtract ½ and cut my bottoms (I usually take off an additional 1/16 to make them easier to slide in and since they are plywood I also glue them into place.
It works for rabbets also. When I rabbet for plywood backs I leave myself with ½ of material like on my shelf dadoes and then I measure my carcass, subtract 1 from the width and whatever allowances I need to make from the height if any and cut my plywood back. I do not have to take inside measurements with my tape measure that never seem to turn out quite right.
I know this was terribly long-winded and I appreciate anyone that made it this far. I am coming down with a head cold or sinus infection and for some reason I was not able to sleep and felt like writing. This was also a little tip I wanted to pass on to the newcomers so that 5-10 years down the road they were just realizing this on their own. Every set of plans out there and every woodworking show always says Ό dado for this or Ό groove for that. Even his Normness always says he cuts a Ό groove for drawer bottoms and I always wonder if they arent more like 7/32?
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