What do I need to know about cutting dovetails with a router jig and plywood? I have cut dovetails just fine in hardwood with this setup. I’m trying to make a little stool for my son’s class project. I’ve seen plywood dovetails before and think it looks cool. Every time I’ve tried, I get terrible tearout and splitting. I’ve tried wrapping the surface and edges with blue masking tape and that didn’t make a difference. Help!!
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Replies
MOM,
Two solutions to your problem. One, use baltic birch plywood for your project. The veneers are much thicker and tearout usually is minimal. Two you can use a backer board on the vertical board if your jig allows it. Just adjust the clamping mechanism not the fingers and your pins should be fine. A lot of shavings and a lot of wasted wood for plywood, but it will work. I'm not sure regular 1/2" plywood is strong enough to support dovetails, but I have never tried it. I've dovetailed baltic birch for utility drawers many times and it make a great drawer box, but it eats bits because of all the glue. Make sure your bit is sharp. Whiteside makes very sharp bits and are reasonable.
Terry
terrylee86,Thanks for your help. I have since tried to wet the plywood - didn't help either.How thick is baltic birch plywood? Most of my tools came from my dad's workshop after he passed. He made beautiful cabinets for his workshop and the drawers are dovetailed plywood boxes. I have to assume he used the Leigh jig that he owned. Although I could probably use a sacrificial piece on the outside of the board, I'm not sure I could use one on the inside because it would change the size of the cut.I am using a Whiteside bit that looks to be very sharp.
How thick is baltic birch plywood?
Sizes are metric-half inch is really 12mm.
Baltic birch plywood comes in many thicknesses. 1/4" (6mm) 3/8" (9mm) 1/2" (12mm) 5/8" (15mm) 3/4" (18mm) I am not sure if those metric dimensions are exact because my supplier( Toledo Plywood ) sells it as english dimensions. They sell it in 5' x5' sheets or 4' x 8' sheets. Forestgirl is right about the plys being smaller, but that adds to it's strength. The plys are all the same dimension including the face plys and they have no voids internally. Nice stuff to work with, I can even run it throug my wide belt sander.
Terry
terrylee86 and forestgirl,Thanks for your help. I'll have to get some and try it out.
I haven't tried dovetails, but here's some half-inch BB ply with fingerjoints:
View Imageforestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Thanks for the information forestgirl and cadiddlehopper.I could try fingerjoints. Might be easier on my router bits and less wasteful. I assume it's done on the table saw. Looks pretty straightforward. Anything special I should take into consideration?
If you want a real treat, buy the Freud Box-Joint Cutter. It makes 1/4" and 3/8" flat-groove (no "bat-ears" like you get with a dado set) box joints.
You can do box joints either on a router table or on a tablesaw. Although I have a sled for my router fence, I chose the tablesaw, using the Freud Box-Joint Cutter. You need a tallish fence on your miter gauge, and a slot and a key. Here are pictures of my set-up:
Auxiliary fence mounted to Incra 1000 miter gauge:View Image
Key and cutting slot. I got frustrated trying to cut a 1/4" x 1/4" piece of wood, so opted for aluminum stock, but that wasn't really necessary (discovered afterwards that my splitter had slipped out of alignment, creating havoc). There's a series of steps to making the two slots and starting the fingerjoints. I don't have a web link handy, but if you drop me an email, I can send a scan.View Image
The joints I made were a bit too tight, though the box did go together. The teeny fine adjustments can be a challenge, but once it's right it's fun.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 3/7/2007 11:54 pm by forestgirl
those look very good. nice tight joints and no tearout.
Thanks! They were actually a little too tight, LOL, but I'm learning. My first efforts produced those little "flags" on the exit side, but re-read the instructions and scored with a knife for the next set, eliminating the flags.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
yes on the scoring. that helps with machine cut dovetails as well.
I have learned most of my woodworking with real wood as opposed to plywood, and when I try to do something in plywood, I have all sorts of problems, mainly tearout. It seems as though it is a medium that is best suited to machines. Every time I touch it with a rasp or a plane, there is instant tearout. Scoring seems to work sometimes, but is that the only way?
Going back to wood,
Pedro
Not much experience here, but just instinctively I can't see a plane working on plywood. The thiness and orientation of the wood in the plys would, it seems to me, completely defeat the mechanics of a plane. Same, more or less, with a rasp.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
I plane plywood edges all the time. A really sharp low angle block plane works the best. Clamp a block of scrap on the end so you don't blow out the side. Works great.
Len
Thanks, Len. So that would work on "proud" fingerjoints? Everyone told me to make 'em proud, but for the plywood I cheated and made 'em flush.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Hope you do not mind me butting in, but if you do a good job making them flush then why make them proud? You are not likely to want to sand or plane down the sides or front using ply so flush is good in my book.
This sound like one of those half truths, if you were copying Chippendale then of course you would cut proud and fit. But plywood? Daft I call it.
All the best, M
Yes, skew the plane and it should slice the plywood just fine.
Well, by looking at your finger joints, you have that figured out, did you finish them. or are they done when put together?
Pedro
"...did you finish them. or are they done when put together?" Not exactly sure what you're asking there. If you meant "finish" as in shellac, whatever, this was a pure utility box (coffee, etc) for our far-from-new pick-'em-up truck, so I felt free to fool around. I put one coat of shellac on it, and then wiped some cherry gel stain on just to see what would happen. Wasn't pretty, so it goes well with the truck. <grin>
If you meant finish as in doing anything else to the fingerjoints, nope, they're just as they were. Too tight, but not bad for the first try.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Ya, what I meant was did you have work them after joining. I am very frustrated with working with plywood. There are different techniques to working it. More to learn. Funny, I have a truck just like that!
Thanks, Pedro
Edited 3/11/2007 11:41 am by ptu
Pedro, a miscellaneous tidbit -- I know you can joint plywood on the power jointer. I've cleaned up burned edges that way (poor saw technique, LOL). To prevent tearout, joint a few inches in one direction, then turn the panel around and come from the other corner.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
The glue in plywood is very destructive to jointer blades. After doing this a few times (over 30 years ago), I never did it again. I don't know if carbide jointer blades are immune to the damage or not.Cadiddlehopper
Caddy, carbide jointer blades will deal with plywood and its glues no problem. I keep that little 6" machine there mainly for that.Philip Marcou
"I keep that little 6" machine there mainly for that." Creep! <grin>forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Forestgirl,
Thanks for the tip. The learning curve for nice work with plywood is new and steep to me. This stuff I get ($89.00CDN a sheet) has the "birch" veneer layer of 1/2 mm on either side. Not much to work with, frays very easily, the middle is full of delamination gaps, and the sheet warps when you bring it inside. I don't want to know what realy good plywood costs. I Imade a carcass for a computer cabinet out of it, and ended up ripping out the delaminate areas and bows, and gluing the pieces back together. The joint was still not flush all the way, but I covered it with a lath. Not what I had expected to do. I think I will stick to real wood.
Pedro
Wow, that's reallllly discouraging. Have you looked around to see if you can find some Baltic Birch plywood -- seems like it shouldn't be too much more expensive than what you paid, and would be much higher quality. Don't know what the Canadian situation is with BB ply. What part of the country are you in??forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
I live in the Yukon, and we have a limited availability of good stuff. The construction grade plywood is okay, its the fancy stuff that isn't good. Its one of the advantages of living in the north.
Pedro
Mom, I continue to discourage dovetailing plywood. Finger joints have a much better chance of holding up to use. In a finger joint, there is actually SOME long grain to long grain contact for a decent glue joint. Dovetails in ply wood provide virtually NO such surface. As far as I am concerned, plywood never should be dovetailed.Cadiddlehopper
"The veneers are much thicker and tearout usually is minimal." To clarify, the outer layers of veneer may be thicker than on regular plywood, but given that there are more layers, in general the layers are thinner. For instance, 1/2" BB ply I count 9 layers, but regular ply 5. The outer layers in the regular ply are barely visible on-end they're so thin.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Baltic Birch Ply, when properly "backed up", will take dovetailing by a jig with repeatable success. You MUST back it up. Something of equal width, fitted in the jig. And, as terrylee mentioned, plan on thrashing your dovetail bit - smoke is not out of the question. Even carbide is no match for BB Ply glue.
When fitting the sides, use a wooden block (under your mallet) that covers the entire width of the ply stock. That will help prevent damage (blow-out).
It's doable.
Countless thousands of utility grade Baltic Birch drawer boxes and furniture pieces sitting in Montessori schools from sea to shining sea precede you. Go make some more.
Hi handymom,
I'm a little late to the party. As other's have said use baltic birch. However, not all baltic birch is the same. I buy mine from a plywood and hardwood supplier. I've had to buy some from a local lumber yard once. I won't do that again. The baltic birch was a fraction thinner than the plywood I had bought from my regular supplier. Messed up the all the settings I had carefully made.
Back to your question. Baltic or Finland ply works fine for dovetails. Always back it up and you should have a problem.
BTW. I usually only do half-blinds in plywood so if I do get some blow out it's usually buried in the joints. Here's some pictures of a set of under bed drawers I did for a client.
Enjoy.
Len
One thing that hasn't been mentioned is to use a sharp bit. I was making box joints in Baltic birch plywood using a dado set this weekend, with no tearout. When I was trimming parts to fit with a slightly dull regular saw blade, I got quite a bit of tearout.
I had actually started to make the joints using a router, and got so much tearout that I switched to the dado. The bit rotation direction relative to the surface grain direction was a factor, but I suspect the sharpness of the dado set relative to the router bit was also important.
Umberto Eco, The Island of the Day Before
I've enjoyed reading all of the replies. The project has changed a little and we aren't going to do the finger joints after all. When I do try them, I will be fully prepared with the right material and know-how!Thanks forestgirl and everyone else!
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