Dado Techniques

      Router and jig, or table-saw with dado blade set? Cabinetmakers discuss choices and methods. May 22, 2006

Question
Which method is better to dado the top and bottoms of the case to side pieces: with a dado blade or router set up with undersized plywood straight cutting bit? Looks like the router would be better than sliding your material across the table saw and possibly scratching the veneer.

Forum Responses
(Cabinetmaking Forum)
From contributor J:
I only have one table saw and would love to get a second just for dados. With that said, I have a dedicated router table set up with the undersized plywood bit you mentioned. It works great and is very fast. Also, the router cuts much cleaner across the grain, producing far less tear-out. The problem is I go through a lot of those bits. I always factor in a bit (or two) when I'm bidding the job. I've tried Freud, CMT, and others, but have found the el-cheapo carbide bits that Woodcraft sells last almost as long and are about half the price.



From contributor L:
I get no chipout from my Freud 8" dado set. Had it for 15 years and only sharpened recently after dadoing a lot of melamine. I don't have too many problems with scratching the veneer, though it happens every once in a while. I would, however, be cautious if I was dadoing pre-finished ply.


From contributor P:
I use a Forrest dado 8" and I never had a problem with tear out. As far as scratching the veneer, as long as you keep your top clean and free of stuff that might scratch, I don't see a problem. I have done pre-finished this way and it worked fine. It was for cabinet interiors, which aren't really seen unless it is a lighted interior. The flatline finish was nova pre-finished, which is a very durable finish and I use a dc which helps get rid of anything that might scratch. I might be a little worried if it were pre-finished with nitrocellulose.


From the original questioner:
Thanks for the responses. I do have two table saws set up. The second saw I use mainly with a moulding head installed. Another concern I had with using the table saw, was sometimes the plywood is not perfectly flat and may not have a consistent depth dado all the way through without holding a lot of down pressure. Either way is not a concern - I am fortunate enough to have a 3,000 sf shop in my backyard and I do have two Unisaws. I was just looking at it from a pro and con standpoint. I like the idea of using the router better, but was not sure if those undersized router bits really worked. I did go out today and purchase a set of CMT plywood bits and I guess I will find out if they work okay.


From contributor D:
I'm contemplating how I cut my dados. Currently I use a dado blade in my TS. I've read some shops use an over-arm router setup. That way, they always have a consistent width of material left over. For example, if you set the distance between the table top and the bottom of the bit, say 3/8", that will always remain constant no matter how thick the plywood really is. If you need a cabinet exactly 12", just cut your top and bottom to 11 1/4". Seems pretty accurate to me.


From contributor B:
I have used routers exclusively in the past, but just purchased a Freud dial-a-width dado blade that I haven't used yet. I have the same questions as you. I like the clean cut with the straight router bit. I haven't had any depth issues, but the cost is an issue, as I also plan to go through at least one bit for every job. I started out using the 600 series PC router and found that it bogged down too much, which I also think dulls the bit quicker, and had to go out and buy the 800 series PC. Always wondered about the dado blades and if I could run through jobs any faster with little or no compromise in quality. Dado blades (good ones) being quite expensive, I never had the chance to try it out, but the Woodworker's Show was in town last week and I just sold a big kitchen, so I thought this would be a good time to find out. I am a little bit worried about scratching the surface of my pre-finished ply, but then I slide the same stuff across the router insert, too. Maybe putting some masking tape on the surface of the saw would help. Don't know if this helps or not, but you're not alone.


From the original questioner:
Just tried the CMT bit and the jig I made to line it up. The bit is dead on accurate. I was surprised. I made a sled that fits the width of my pc router and put Plexiglas on the bottom and routed the groove through the Plexiglas, so all I have to do is line the groove up with my pencil mark (Plexiglas so I could see through it) and it works great. I made it 30" long so I could use it on upper or lower cab sides. I think this is the route I am going to take.


From contributor R:
I use the Freud Super Dado set and it works great. No tearout, flat bottoms. The problem I run into is cutting a dado into the middle of a long cabinet side for a fixed shelf. It can be tricky keeping the work piece against the fence. Like you said, getting a consistent depth is a problem when the wood's not flat. When possible, I use a push block (the same kind you use with a jointer) right over the saw blade. I recently got a Festool router and set it up to use with their saw guide. I haven't quite figured out a foolproof way to measure and position the router and guide yet. The cuts are pretty good, but not as good as my Unisaw with the Freud. All that said, I have cabinetmaker friends who laugh at me for doing dados at all.


From contributor T:
I try real hard not to use dadoes these days, but when I did, I preferred using a router hand-held with a guide. Router because of tearout and hand-held to follow the not-flat plywood. Try Whiteside router cutters from Librawood or Router Bits On The Web. Great cutters at a good price.


From contributor E:
Give the router bits from Her-Saf a try. They make dado bits with replaceable carbide cutters that are quite reasonable. The cutter has four cutting edges so it can be rotated and the carbide cutter is fairly cheap. Under 5 bucks, I think. I get mine from Carbide.com.

From contributor E:
I use the Her-Saf bits for cross dadoes in all sides. I use a Freud dado set for making the 1/4 inch groove to capture my backs, and bottoms of drawers.


From the original questioner:
I see some of you do not use dadoes. Let me ask you a question. If you have an upper cabinet and the side is going to be the finished end panel as well, how do you fasten the top and the bottoms to the sides and have a strong joint? I understand that you can use the pocket screws on the top because you would not see the pocket screws, but what about the bottom of the upper cabinet? Do you just let the pocket screws show or do you nail through the side of the end panel? I have seen people nail through the end panel and the nail filler looks bad when finished. The pocket screw holes would not look real good either on the underside of the bottom. Or do you have the pocket screw holes on the inside of the cab bottom? Just curious about how the pros do it.


From contributor L:
I usually use dadoes and rarely use pocket screws for my plywood cabinets (FF I use them all the time). But you use the pocket screws on the top and the bottom and then put a finished 1/4" piece of ply on the bottom of the cabinet to hide the holes and joints and can scribe it to the wall for a flawless bottom.


From contributor J:
I use a pre-finished 1/4" panel on the ends and bottom to cover up all those pocket screw holes. I use pre-finished birch plywood for my boxes and pocket screw them to the face frames from the outside. I rabbet the face frames to receive the cases and make it 1/4" wider if it will be a finished end. I attach the finished end panels with construction adhesive and brads, or crown staples if it's in an area that won't be noticeable. I like this method because I can finish just the face frames and end panels and don't have to worry about bringing the whole cabinet into the spray room. We can also leave the cabinet knocked down until just before installation.


From contributor Y:
You might want to look into a Hoffman PDS 32 dowel machine to do those bottoms; not cheap, but fast and accurate.


From contributor T:
I biscuit join sides to bottom and top, then biscuit join face frame to the cabinet.


From contributor I:
We use a panel router, with the Her-Saf cutters. The router cuts perfectly square, is easy to set stops for repeat cuts, and uses a spring to keep the router tight to the plywood for perfectly uniform depths. We stop dadoes and notch the pieces that go into the dado on a dedicated router table for a clean look on the face of the cabs.

Her-Saf and Safety Speed Cut both make good machines. I picked mine up used 10+ years ago and it still works perfectly. There is no setup time ever, except when changing router bits for different width cuts. Quick, easy, great results. No setup time on the notching router table, either - it cuts 3/16" every time. We use a notched piece to set the depth of the panel router, so that is a snap too.



From contributor K:
What are undersized plywood router bits and what are they used for?


From the original questioner:
They are smaller in diameter to accommodate the thinner plywood material. 3/4" plywood is not 3/4"; it is around 23/32".

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