Dado cutting on Maple veneer Plywood

[Michael Ginsberg]

I am about to make some wardrobes out of 3/4 stain grade Maple Veneer Plywood that cost an arm and a leg. I need to make crosscut dadoes using my new 1400 EQ router. I have brand new Freud carbide plywood bits. I don't want to get tare -out on the thin veneer. Should I rout right through masking tape, score the plywood first with a knife, or just use the bit as is with no preperation to the wood? I have not had much experience with crosscut routing on veneered plywood.  Also, what speed should I use on the router?
THANKS

 

[Jesse Cloud]

Shouldn't be a problem if you bought quality ply, which it sounds like you did.  But here's a few odds and ends to think about anyhow....

Search through the Fog for "OF1400 base"  and you will see a few threads discussing how to use the 1400 on a rail.  The base that comes with it won't extend all the way down to your plywood with the base on top of the rail.  Festool provides a plastic "outrigger" that is intended to support the 1400 in this situation, but many of us have had trouble with it.  There are several workarounds, from shimming to making your own base, to buying another base that compensates.  Take a few trial runs on scrap just to get the feel of whatever you decide to do.  And don't trust the depth setting!  Measure it directly with a caliper.

If your dado goes all the way through the ply, you can have tear-out when it exits.  Solution is to clamp on a sacrificial strip of wood where the exit would normally be, then you get the tearout  on the strip, not your wardrobe.

Always a good idea to take light passes, at least in the beginning.  Use a steady medium speed feed rate.  If the router starts to chatter, slow down.

For positioning your dado, there's a raised vertical line on the middle of the 1400 base.  It aligns exactly with the center of the cut.  You can just mark the centerline of your dado and align the router to it this way, no measuring needed.

If you are doing through dados, on at least one side, clamp the two sides of the wardrobe together, carefully aligned, be sure your rail is square to the piece, and route them both at the same time.  Saves time and improves accuracy.

To answer your specific questions, I would set the router speed to the highest speed.  I never use tape or a score, but they sound good, though a lot more work....

Hope some of this helped.

 

[Michael Ginsberg]

Thanks Jesse. The front of the dado is going to be stopped a 1/2  from the front edge of the wardrobe. I was going to apply solid maple trim to the front of the plywood to cover the endgrain of the plywood shelf, also hide the curve of the end of the dado. For the back, I am planning to cut  a 1/4 rabbet on the table saw with a dado head for the plywood back. So , I wasn't concerned about tearout on the back end of the through dado.

 

[ccarrolladams]

When using a router to make dadoes (grooves) especially in plywood, the tear-out is mostly produced by the climb-cut. When you make a rabbet, the climb-cut side of the bit is not cutting, so life is good.

One approach is to use a bit smaller than the finished dado. Arrange the climb-cut away from that side of the dado, then make the final pass on that side moving the router in the opposite direction. Back in the days when employers could use dado heads, there was no climb-cut.

Another approach is to cut each side of the dado using a guide rail and a TSxx saw. Then use a slightly small bit, so neither side is actually cutting any wood.

Most of my business is building custom cabinets, almost always from expensive veneer plywood. We were still allowed to use dado heads when I owned my previous shop. When I went back into the cabinet business in 2006 I bought a pair of TS55, several guide rails, a CT22 and a pair of OF1010. One of those was kept set up to drill shelf-pin holes. I kept the other set up to be guided by a rail.

I saved a fortune in damaged material by cutting each side of the dadoes using a TS55 and a rail, then moving the rail over using a machined spacer. As the final step I used the router to remove the rest of the material from the dado. This method worked well. It also was a major factor in my buying CNC routers as soon as I was able to move my business into a very large factory building. With the nested router the CNC is programed to use an under-size bit, make one pass and then the other pass moved over and going in the opposite direction. Any decent CNC routing software is set up for this opperation.

 

[Michael Ginsberg]

CCARROLLADAMS,
Thanks for the suggestion. I like that idea especially since I have a TS55REQ. BUT... What about the front of the wardrobe that has the stopped dado? I can see your idea working very well for a through dado. The parallel cuts made by the saw blade will very different than the router bit path. Does that matter due to the fact that the trim will cover all of them? Also.. How would I have the saw make the parallel cuts stop at the same spots consistantly throughout the project?

Michael

 

[ccarrolladams]

CCARROLLADAMS,
Thanks for the suggestion. I like that idea especially since I have a TS55REQ. BUT... What about the front of the wardrobe that has the stopped dado? I can see your idea working very well for a through dado. The parallel cuts made by the saw blade will very different than the router bit path. Does that matter due to the fact that the trim will cover all of them? Also.. How would I have the saw make the parallel cuts stop at the same spots consistantly throughout the project?

Michael

Festool makes an adjustable stop for the guide rails. I used one of those when making stop dadoes. Then to square up the stop dadoes I used a chisel.

Thinking in terms of a dado head, the two cuts with the saw are like the blades of the dado head. The router bit is like the chippers used between the blades of the dado head. In the case of a TS55, the fine tooth blade has a kerf of 2.2mm so all you need do is select a router bit about 4mm smaller than the finished dado.

 

[Max Neu]

I use a panel router for my dado's,I use a downward spiral cutter and get zero tearout.

 

[Worm Drive]

I use a panel router for my dado's,I use a downward spiral cutter and get zero tearout.

I second using a down spiral bit.

 

[Michael Ginsberg]

So, you both are saying I should use a spiral down bit for the entire stopped dado? Not using a regular plywood sized straight bit? Again, the dado is stopped in the front of the side panel. You are suggesting not to use the saw? I have the proper accessaries to attach the router to the guide. I need to make about 24 consistent dadoes for this project.

 

[Max Neu]

If you use something other than a downward cutting bit,you will have to take unnecessary steps to prevent tearout, standard straight cutters will require scoring first.

 

[Kevin Stricker]

How about routing your dado before applying your edge banding?  Then no problem with the stopped cut, you just have to make a filler strip that sits in the dado when you trim your edge banding assuming you are using a bearing guided bit.

Double check the width of your "undersized" router bits against your plywood, I find they almost never are an exact match.