Cove-and-Beading Fixture

Canoez

Paddle Bait
I was asked by another member to post some information on the cove-and-bead cutting fixture that we use in my class. Before we get too far into this discussion, it is indeed possible to build a canoe by putting a bevel on the strips with a plane. Using the cove-and-bead is a matter of choice. I'd prefer that this thread didn't become a debate on the use of cove and bead, only a discussion of different ways to apply them.

That being said, if you are only building one or two boats, it probably isn't necessary to go to this extreme to put the cove and bead on. With my own boats, I had a router table with a single router cutter at a time and made two passes on the strips - I cut the bead first and made a fence that had a mating cove to keep the strip in place when I made the second pass. What id did discover was that putting the cove feature in was a bit fussy - I felt like I needed to be a safe-cracker to make it right. Were I to design a fixture for a single router like this again, I'd make the fence on a pivot with a threaded rod to adjust the distance between fence and cutter to allow for fine adjustment.

When I was asked to teach the class, I knew that I needed something better and I made this fixture. The fixture had done well for us over the last 5 years, but it has some short-comings that I'd like to point out - I am planning on making a new fixture that incorporates the things that I point out here. I also want to point out that this fixture was designed as it is for a few reasons.


  • We need to feed strips in a linear fashion in the shop for work-flow reasons.
  • We need to be able to adjust for different widths - we sometimes apply cove-and-bead features to feature strips that are up to 1-3/4" wide.
  • The fixture needs to be fairly idiot-proof.
  • The fixture needs to be nearly bomb-proof.
  • The fixture needs to be reliable.
I also designed around Porter-Cable 690 routers as that is the equipment I had available - any router would do. We use Woodcraft's cove and bead cutters which are 1/4" shank. We have a new set of cutters with 1/2" shank which should be a significant improvement. Here is a picture of the fixture's top:

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Here is an oblique view of the bottom:

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As you can see in the pictures above, the fixture is primarily made from pieces of 3/4" Cherry plywood left over from another project along with some scraps of solid Cherry and a few pieces of hardware from McMaster-Carr Supply. This is one of the changes that I would make - the plywood does OK for staying flat, but chipping and abrasive wear around the edges can be an issue. I'd probably use a synthetic panel from perhaps Garolite or solid-surface counter-top material.

Here is the base-plate with the top section removed:

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This base plate is about 18" deep and 30" wide. The router that comes up through the hole in the base-plate is the bead-cutting bit. It only is able to move up and down. There are three screws that are counter-sunk into the plywood to be sub-flush that hold the router to the plate. The two side-pieces are dovetail slides and are glued and screwed to the base plate. When assembled, a slip of paper was put between the top plate and these two side pieces to allow the top to slide smoothly. The three holes in the upper left and right of the plate are threaded brass inserts to lock the top plate in place. The adjustment of the top plate is a "gross adjustment" between the two router cutters and sets the width of the strip. You can also note several contacts where the cove cutter has hit the base-plate - this was deliberate - we were making narrower strips (3/16") using a 1/4" cutter. This is another improvement - I would have a groove here for the cutter in the base plate. Here's a detail of the corner of the plate:

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The brass threaded inserts are clear in this picture. Here's an improvement - I'd probably use UHMWPE for the dovetail blocks to make it slide smoother. We waxed the two surfaces and they're not bad, but could be better. I'd also have them spaced more closely - they can jam if the top slide moves at a slight angle. One other design issue would be idiot-proofing to prevent the two cutters from ever making contact - limited to 1/8 strip width minimum.
 
Here's the top slide assembly:

1zccyv5.jpg


What you see here is two sets of slots on the outside which have a wing-nut with a shoulder that goes into the threaded insert on the base plate. It locks the spacing between the cutters and sets the strip width. There are also two vertical fences for clamping feather-boards. The router itself sits on a slide which allows you to move the cove cutter with respect to the fence. The dovetail set-up is just like the base plate and has it's own pair of screws to lock it in place (just above the router) At the top of the fixture is a fine adjustment.

Here's some detail:

2daest1.jpg


In the back of the slide with the router is a threaded inserts. The screw that goes into it is 1/4-20 - every screw rotation is 1/20th of an inch and allows a fine adjustment of the cove depth. The strip that is screwed to the plate and is roughly vertical in this image has a clearance hole in it. Washers sandwich this strip and a nylock nut holds the screw in place with respect to the strip.
 
Here's the underside of the top assembly:
24b7y8l.jpg


What you see are relief cuts and guards - you would have to work pretty hard to push your finger into the cutters as they are protected by the top plate. The damage to the left of the cove cutter that you can see is not from hitting anything - that's from erosion by the chips flying about. I'd put a piece of UHMWPE in this location so it would be replaceable. The clearance at the bottom is to allow your fingers room to turn the fine adjust screw. I'm planning to put in a dust collection opening in the top slide (extending vertically in the picture) to allow connection to a shop-vac or the shop's dust collection system.

A replaceable section on the fence with a bead section to protect the somewhat fragile cove edges on the outfeed would be great too.

The other improvement that I would make is to add threaded inserts to the fence and the base plate for locking feather-boards in place. We use two on the infeed and two on the outfeed. currently they're held in place with quick-grip clamps, but two screws per on a 45° slide angle would be great.

Another large improvement would be a power supply box with two outlets and a switch to turn routers on and off at the same time - for safety.

A power feeder on this would be awesome too. :)

While I seem to be tearing my own work apart here - it has worked very well - we've put about 12 linear miles of strip through this thing with good results - the improvements would make it both better and safer.

I'd love to hear what other suggestions folks have.
 
I think my only worry about the UHMW would be warp or sag - I'd want a more rigid base to support it. Ideally, I'd like something about 1/2 thick for the base plate. Wouldn't be bad for inserts or fence material, however.

Then again I am pretty fond of my low angle block plane.

Troublemaker. :rolleyes::D
 
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It's interesting that you posted this topic a few days ago because I just started milling my strips and my buddy and I came up with a similar setup using bearings and shock cord.

Enjoy
 

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