Brainstorming a Modified Door Frame Joint

Is there a quicker and easier way to machine the joints for a raised-panel stile-and-rail cabinet door? Here's a handful of possibly useful ideas. May 22, 2007

Is it possible to clamp door frame pieces and rout and slot cut inside edge for raised panel doors without using stile and rail router bits?

Forum Responses
(Cabinetmaking Forum)
From contributor L:
Sure, why not? But you may have to square out the round inside corners to fit the panels in. You can get a set of router bit door cutters for around $100. It'll make your life easier than doing it the way you propose.

From the original questioner:
The reason I asked the question is that I like the holding power of biscuit joints over coped stile and rail, and the raised panel corners could be rounded over easily to match slot cuts.

From contributor L:
I have coped door joints that are 20 years old and still look like day one. How strong do you want the joint to be? Are they hitting your doors with cars or something?

From contributor M:
Your inside edge detail corners would be rounded, not coped - it would look like an MDF door. Also, you can't convince me that a biscuit joint is stronger than a proper fitting coped rail and stile.

From contributor K:
I think you are misguided about biscuit joints. The biscuit is basically an alignment tool and doesn't add much strength to a joint. It does provide a little more glue surface, but nowhere near the glue surface provided by a cope and stick joint. Joint failure in cope and stick doors is usually from someone starving the joint for glue to prevent squeeze out.

From contributor P:
If I understand what you're saying, it's very easy and I've done it many times. I modified my homemade mortising jig to accept a longer board. I do it this way instead of using a slot cutter because it's easier to control the start of the cut on a stopped groove.

The board to be grooved stands on edge and the router plunges into the edge and you just cut whatever length you wish. It's a very simple setup and basically consists of two wide platforms on either side for the router base to rest on, edge guides atop this to make a guide, a couple of bolts with wing nuts, a couple of clamps for extra stability on long boards and stops that can be moved. I use a spiral upcutting bit.

When you think about it, the groove for a panel is nothing more than a long mortise. I've always wondered why there isn't a commercial jig for doing this. It would be simple to make and I bet it would sell quite well. I'd buy one if it solved the clamping problems.

From contributor W:
A biscuit is not as strong as a properly made cope and stick. It all has to do with the surface area for the glue to bond.

From contributor T:
I assume you do not usually make doors. Just take your parts to a cabinet shop and ask them to machine them for you.

From contributor S:
Just curious, are you putting a profile on the rails and stiles? I would put biscuits at the low end of the scale. Stub tenons would be better or dowels or even maybe a spline that fits the groove that you are plowing for the panel. Coped stick is a modification of the best way, which I would say is mortise and tenon, and the profile on the inside of the rails and stiles and coped.

From the original questioner:
I build raised panel doors in the traditional way at this point and it works fine. Just looking for a faster way and sometimes you must look outside the box.

Thanks for the responses. I am a residential builder and sometimes (when time permits) I build the cabs for my spec homes, so this is not my forte, but I find myself enjoying it more and more.

From contributor J:
I just wanted to comment on some not so accurate information being passed along on this thread. There have been a few responses claiming biscuits do not add strength to a joint, and this is absolutely false. In testing of different door joints, biscuited doors (using two biscuits per joint) outperformed the typical coped joint by a long shot. Regardless of what people think or believe, this is factual, tested, and proven. I personally use coped joints, though, as they are more than strong enough for most cabinetry.

From contributor F:
As to slotting the inside of a frame for a panel with a bearing guided cutter… I worked in a shop once that made a certain door style by rabbeting out on the back side of a door frame for the raised panel to be let in and then skinned off. They had been squaring out the rounded inside corners left by the router bit for many years by hand with chisels. The youngest of the crew thought outside the box and suggested simply chopping the four panel corners at 45 degrees and leaving the rabbet round in the corners. I don't know about double biscuits, but single ones aren't even as strong as dowels, let alone the glue area of a cope and stick joint.

From contributor Z:
Just wanted to add another two cents to the biscuit argument. One important thing that nobody mentioned is that biscuits are designed to swell up from the moisture in the glue. The swelling provides a mechanical bond in addition to the chemical bond from the glue. They're pretty darned strong. I still wouldn't use them for doors, except maybe mitered ones.

From contributor F:

My view on the swelling is, if you merely wet them with water and assembled, do you think you could pull it apart in a week? Also, effective clearance between parts for aliphatic resin glue is between .004" and .006". I would wonder if the precompressed biscuits would leave adequate clearance for glue after the water in the glue swells them?

A shop I worked at for a short time decided to build a set of face frames with biscuits. The frames had several joint failures after being sanded in a wide belt. Single biscuiting in this case.

From contributor Z:
I dunno, contributor F. I'm gonna try it. Interesting question about the glue joint, though. I would think the clearance shouldn't be an issue. I doubt the squeeze out is any more than when you clamp edge-glued boards in a panel glue-up. How do you biscuit a face frame? Wide stiles and rails, I'd guess?

From the original questioner:
Size FF biscuits are designed for face frames, hence the name. They will work in 1 1/2" stock.

From contributor F:
The thing about glue clearance or, more correctly, glue thickness is… When you clamp, say, two boards together as in making a wider panel, if the proper pressure is applied to the clamps, you will get a glue-line from .004" to .006" thick. On the other hand, too much clamp pressure will thin out the glue line and is said to cause a "starved joint." However, when it comes to a mortise and tenon type joint, the fit of the joint itself must be substituted for clamp pressure in the equation, thus .004" to .006" clearance. In the case of biscuits, they have been compacted in advance so as to swell. I only know I have seen them fail under torque; I do not know what their final thickness is in relation to the biscuit slot at the point of glue hardening.

From contributor J:
As usual you guys are bringing up some interesting perspectives on this subject. I'm guessing here, but I would think the pressure of the biscuit swelling into its opening when glued would be similar to the pressure exerted to boards clamped edge to edge. I can't see where the biscuit would exert too much force creating a glue starved joint. But again, it's just my opinion.

Regarding the strength of biscuits, I've been trying to recall where I got the info I posted previously. It finally came to me so I have pulled out the book to reference that article. Unfortunately there was no testing on single biscuit applications. But surprisingly to just about everyone, the three biscuit application outlasted even mortise and tenon construction. When the joint did finally fail at 3000 psi, it was the surrounding wood and not the biscuits that failed. One caveat being that when the biscuit joints failed, they failed completely, while some of the other joints tested held together after failure.

The test covered loose tenon, mortise and tenon, dowel, and tongue and groove joints along with the biscuited joints. And yes, even the two biscuit joint was stronger than all other joints, including dowels and coped (tongue and groove, in this case). More importantly, maybe, is that all the joints were plenty strong enough for a typical cabinet door.

For anyone who's interested in the details of this, the article is found in "Practical Design: Solutions & Strategies" published by Taunton Press. I believe the articles contained in the book come from Fine Woodworking Magazine so you may also be able to find it there. I recommend reading the article if you're interested, as there are many aspects and limitations of the testing that are far too lengthy for me to go into here. Suffice it to say it's interesting reading. And as I said before, I'll stick to my coped joints, as sometimes it's good to stay inside the box:)

From contributor F:
Interesting information on two biscuit joints being stronger than full mortise and tenon, which can be much longer than a biscuit's penetration into each side. Just want to say that the fit of a tenon or a biscuit is not a "pressure" thing… it is a space thing. There needs to be from .004" to .006" space left for optimum glue thickness according to data I have read on the strength of aliphatic resin glue.

From contributor Z:
Contributor F, remember, biscuits have an embossed grid on the surface, so the joint will probably never be starved. I wonder what caused the joint failure you saw. Maybe the glue wasn't cured before it went into the widebelt?

From contributor I:
Contributor J is correct about the article on biscuit strength compared to other joints. I've read the same article. Double biscuits did quite well on strength.