Does anyone have any suggestions for edge miter joinery

[Red F]

We don't have a CNC at work, but I'm trying to convince them otherwise. The company that I work at has a table top with apron where all of the edges are mitered. They've been doing all of the angles on a shaper. It drives me nuts to see them done this way. The top is plywood, and the aprons are solid wood. After they glue up the top, they take it to a bandsaw and cut notches where metal legs protrude through.

They originally were making the apron from plywood too, but got a lot of tearout on the corners after they were finished.

I've test cut one of the tops on my machine at home and it works great. I'm convinced that there must be a trick to locating the apron pieces so that they are aligned tight. I'm not having any luck inside my own head, and most of the folks here think in metal not wood.

Thank you to everyone for all of your help.

[scottp55]

Possibly using a miter fold like this if the sizes will allow?
http://forum.vectric.com/viewtopic.php?f=28&t=25413

[bleeth]

The issue with the aprons is you have to machine 3 edges and therefore holding it still is an issue.
You can solve this using a vacuum puck system using a high vacuum low air vacuum instead of trying to hold it to the table with a high flow vacuum.

Positioning the pieces for repeatability is strictly a jig system. aligning the length is easy and if you think about using a removable block for one end you will have it.
Align unmachined edge against fixed stop and slide to L shaped removable block that aligns with end of fixed stop. Turn on vacuum and pick up removable block. Run tool(s).

Initial setup is touchy but for standard repeatable parts it is darn quick once set up. Particularly if you have a tool changer to do the notches with a straight bit and then your miter bit (or vice versa).

If every table is a different size you are into more programming but since you are using vacuum pucks for holddown it's not to tough to set up.

Note: If they have a decent shaper and power feeder it's not really a bad system.

[Red F]

Thanks for the replies. My problem isn't as much of a work holding issue, but a glue-up alignment issue. I thinking that a miterlock bit may be what we try next. Has anyone tried running those on a CNC? I've never run one CNC or otherwise, but I've heard they can be a pain to setup.

Scott I've thought about doing a miterfold, and seeing that link helps. But for durability, the aprons need to be from solid wood. With ply, the veneer is quickly sanded through and chips easily.

Rereading your post Dave, I'm thinking maybe a block in the notch during glueup could align the apron.

Thanks again for the suggestions,
Blaine

[jTr]

28698


This is no joke. I've made countless pieces, including a very large entertainment center with floating shelves 24x60" with torsion box construction mitered exactly this way. In those instances, I've inserted dowels from underside when not visible for piece of mind, as they bear several hundred pounds of weight.(sorry, photos are not readily available).

Your piece appears to receive little in the way of load bearing stresses, so I feel this is ample. Remember, glue is the only thing holding the plywood together, yet we have the utmost faith in it. For material thickness you're using, there is a lot of glue surface there. Try it on some scraps and you'll readily see the ease of machining, alignment and flawless fold results are hard to beat. Just need a clean accurate miter and a helper for the larger stuff.

Jeff

[curtiss]

I saw a countertop the other day that had a piece of hardwood glued to the front / exposed edge.

Laminate was then glued to the top surface and front edge and then a 45 degree router bit cut that back and exposed the hardwood again.

Looked very nice compared to a 90 degree laminate front corner.

[RickW]

If I understand you correctly, the problem is not so much cutting the miter, but aligning the pieces during glue-up. Is this correct? How are you aligning and clamping them now?
For ease of alignment, I'd recommend that you switch to a lock miter bit on the shaper. The advantage to that is you only have to clamp the pieces in one direction, and the pieces align very well. The drawback is that the bit must be set up correctly, which can take a while. One piece gets run horizontally, and the mating piece gets run vertically.I have used a Freeborn lock-miter bit on my Delta heavy-duty shaper to shape both plywood and solid wood parts and the system works very well.
The whole top could certainly be cut and miter-folded on a CNC.However, the grain of the end pieces would run vertically, instead of horizontally like the sides.That may be acceptable; it depends on your design criteria.
Hope this helps.
Rick W

[myxpykalix]

I made a jig like this for holding, clamping and gluing miters using a kreg jig clamp