There are a couple of ways to perform dado cuts with a table saw. The very best way is with a stacked dado head. This is a pair of saw blades separated by a suitable number of what are called chippers. A chipper is a somewhat 'S' shaped bit of metal wider in the middle with a hole through it to slide over the arbor on the table saw. At the tips of the 'S' the metal of the chipper is widened. These days this is usually done with a piece of carbide. The thickness of the chippers varies and there are washers otherwise called shims which can also be fitted between the blades and chippers or between the chippers. You add chippers and shims between the blades until you get the width you require for your dado cut.
A second way uses a dado blade also often referred to as a wobble blade. This is a blade mounted against an angled, I don't know how else to describe it. It forms a sort of wedge in such a way that you can turn this device to alter the amount of wedge that the wobble blade rests against. This has the effect of tilting the blade so when it turns it wobbles from side-to-side thereby cutting a wide groove as it passes. the width can be adjusted by adjusting the shape of that wedge and thus the displacement of the wobble. There are issues with this approach, perhaps the most significant one being that the floor of the groove will not be absolutely flat but rather slightly arced. The third way that comes to mind and the one I often use for a single application mostly because I am lazy is to set the edge of the blade to one edge of the desired location of the dado and lock in the rip fence then push the board through. You may set it a little short then move the fence in very small increments to accurately locate the one edge. You then just keep moving the fence about the width of the saw blade and sequentially run the board through until you have traveled the fence the required distance for the width of the dado you want. This has the disadvantage that often the floor of the dado will be a little like corduroy which I argue leaves a place for excess glu to inhabit. It is also fairly easy to get your groove just a little wider than you wanted. All of these methods require that the saw is free of a blade guard of course. The real dado sets also require a table insert with a wider hole for the blade to protrude through. Usually dado sets are smaller, 6 or 8 inch diameter. The stacked head saws the two outer edges while the chippers chisel out the middle something like a planer would do. Setting the depth of the dado is generally easiest using a table saw because of the size of the table. My favorite method uses a step gauge one of my daughters sent to me a couple of Christmases ago. This is a flat bar of aluminium more or less trapezoidal in shape. Each sloped end has a series of quarter inch steps cut in it, at one end they are offset by an eighth of an inch so on one end the steps are 8th inch, 3 8th inch, 5 8th inch and so on. The opposite end are quarter inch, half, three quarters and so on. I figure usually 3 8ths depth in 3/4ths inch panels so I set the gauge on the table top and raise the blade until it is just touching the appropriate step. I spin the blade by hand listening for the evidence of it just barely skimming the appropriate step then lock that height in. I don't and never have owned a wobble blade I expect it might be a little tougher to set that way. I also use my step gauge to set router bit height. You cannot or rather you should not ever attempt to mount a dado style cutter into a hand held circular saw. This leaves you with one or two variations on my lazy man's dado done on the table saw. You can and do however continue to use the blade guard on your circular saw. Cutting a dado with a circular saw can be done in at least a couple of ways. Using a pencil mark of course is the traditional way, both sides of the dado are marked and you saw between the marks in several passes. Few of us can do that but we can use a saw board or straight edge and measure to locate it at one edge of the dado and then cut, then move the straight edge or other guide over incrementally and continue until you have the width you require. You might use a pair of cutting boards particularly one made for the motor side and one made for the outer edge of the saw then align them and clamp them so they form the outline of the dado you want to cut then just run the saw between them in several passes removing material until the dado is clear. Another way is to cut the two outer walls of the dado channel and, depending on how wide it is, make a couple of more cuts between the wall cuts then take out the waste with a chisel. If you set the depth into plywood to about the junction of laminations you can often get the natural fiber separation to help you get a really nice bottomed dado. Setting the depth of the dado with a hand held circular saw can be a little more problematic than on a table saw. This is because the blade rarely comes very close to the shoe plate so gauging the absolute depth can be confounded. If you can see there is usually a scale on or near the depth lock, it is at best approximate even for optically enabled humans. The other problem is holding everything, the saw upside down, a gauge balanced over the gap in the shoe and the spring loaded blade guard ot of the way while you manipulate the depth lock control. It is easier if you hae a small sheet of material the desired thickness of the depth of the dado you want to cut, then set the saw on this sheet, retract the blade guard and slide the blade up against the cut edge of the sample depth board then raise or lower the saw until you feel the tips of the blade are at the same depth as the sample thickness and lock the machine to that depth. A step gauge can be used and I have often done it but it is just a little difficult. Cutting a rabbet can be done in the same way, it is nothing more than a dado with a missing side wall. I hope that I have addressed your questions satisfactorily. I don't want anyone to think for a moment that any of my posts represent the only or even necessarily the best method or technique. I am neither professional nor trained. I have had a certain amount of experience in these things and that is all. It is my hope that not everyone will have to use up all that time making many of the same mistakes I have made. Dale Leavens, Cochrane Ontario Canada [EMAIL PROTECTED] Skype DaleLeavens Come and meet Aurora, Nakita and Nanook at our polar bear habitat. ----- Original Message ----- From: William Stephan To: [email protected] Sent: Friday, November 02, 2007 11:18 AM Subject: Re: [BlindHandyMan] Circular or table Dale, great post. Can you talk a little about cutting dados? I've never really grasped how to get the right depth with a circular saw or table saw either. Thanks! Bill Stephan Kansas City, MO (816)803-2469 William Stephan -----Original Message----- From: "Dale Leavens"<[EMAIL PROTECTED]> Sent: 11/1/07 8:43:07 PM To: "[email protected]"<[email protected]> Subject: Re: [BlindHandyMan] Circular or table Hi Dale, I had a table saw long before I finally got a circular saw however I did have a jig saw which I used a lot for reducing plywood and other sheet goods down to manageable sizes. Thing is that even with a very big and top end table saw, wrestling sheet goods, even relatively light ones like quarter inch plywood around on a table saw is not only difficult but does add significant injury risk. You can add infeed and outfeed tables if you have enough shop space but it is still damn difficult and although I did quite a bit of it as a younger man I don't much fancy it today. If you are likely to do a lot of cabinet work into the future or where you need a high degree of accuracy to finished panels the table saw is what you want. Excellent work of most types can be accomplished with a hand held circular saw and a little care. It becomes somewhat more difficult to reproduce a series of identical cuts than with the fence on a table saw but again using jigs or other measuring sticks and such it certainly can be done. One can even cut dados and rabbets with care but it is more difficult. One can of course buy both a decent circular saw and a router or two and still have a pretty good chunk of change from the price of a decent table saw. A table saw certainly can be used safely by the blind. There are different techniques depending on your confidence and skill complement of course. You may wish to use path finding techniques to ensure safety, knowing that the blade is always in the same place means if you need you can locate some safe part of the machine like the far right near edge of the wing and near rail of the fence then follow that back to the fence and down to the switch for example. If on the other hand you are a little more sure of yourself you might, as I usually end up doing, kick the power switch on with the toe of my shoe. My saw is a 1975 vintage with a standard light switch for power. Kicking it off while controlling work and waiting for the blade to spin down sometimes requires a little imagination. Modern machines usually have something like a recessed push button for on and a big square panel you can hit with about any body part to turn it off. The beauty of a table saw is that it is relatively easy to set the rip fence to a suitable distance with a ruler or what ever, even an already cut piece can be slid up against the blade and the fence slid up to it. Using a circular saw with a decent shop made jig can be quite accurate too provided it is the sort where the base comes out where the saw has cut it flush so you can tell exactly where the blade will cut. Otherwise you must include an offset to the edge of the shoe for aligning the guide as I have to do since I still haven't got around to making such a jig. I recently saw a jig designed for cross cutting with a pivot for locking in an angle. It is interesting in a way, I well remember observers goggling my makeshift jigs in some kind of wonder and now 30 years later they sell them in major department stores albeit rather more refined (and expensive) than the blind pioneered of necessity. Unless you expect to continue a vigorous hobby into the future I think I would hold off the table saw. You will always want a circular saw anyway. It is well worth while to buy a good quality one. This can be said of all tools and it is also true of a table saw only a decent table saw will cost in the range of 800 to 1000 dollars. A cheaper one will disappoint and you won't be wanting to use it a lot. If you really get into the work you will soon regret not having bought a better one and your money will be wasted. It may discourage you from continuing. You can get a darn good little 7 and a quarter inch circular saw for a hundred and fifty bucks or less, I really like my little Makita MAG model for about a hundred and twenty five, good quality, light, toolless blade change, it is available in right and left side blade and should remain accurate as it is a well made tool. Doubtless there will be other opinions, there are a lot of stamped steel table saws for a couple of hundred bucks out there and I don't intend to get into a debate on that. I have used them occasionally on a job site and they work well enough where 8th inch accuracy is adequate, light to shift onto the bed of a pickup truck and not a big loss if they get knocked around a bit but beyond construction carpentry I don't like or recommend them. I hope this is helpful. Dale Leavens, Cochrane Ontario Canada [EMAIL PROTECTED] Skype DaleLeavens Come and meet Aurora, Nakita and Nanook at our polar bear habitat. ----- Original Message ----- From: Dale Alton To: [email protected] Sent: Thursday, November 01, 2007 8:20 PM Subject: [BlindHandyMan] Circular or table Hi gang, I am contemplating purchasing a circular saw or a table saw. I know I have to cut some plywood to make a counter for the wet bar I am in the midst of, and yes if you like keg beer come on over. I am also thinking about making a little cupboard type of thing to put by my front door. The thing I don't know for sure is which saw would be better for me. Are table saws safe for a total to use? I think I would get the use out of either but don't know what would be best. Any help would be greatly appreciated. Dale [Non-text portions of this message have been removed] [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
