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Panels - join w/ biscuits?

Matthew_Campbell's picture

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I'm building a traditional frame and panel exterior door. My question has to do with the panels. The wood is red oak. I will need to glue some boards together to make the 9" wide panels. Should I join them together with biscuits or just butt the boards together and glue? My panels will be 3/4" thick.

Lastly, how much expansion room should I leave in my dado slots for the panel to expand with the season, 3/16"?

Thanks for any advice, Matt

Mike_King's picture

(post #106177, reply #1 of 15)

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Some people say that biscuits help with alignment, Matt. Others claim they add strength. If you use a jointer or jointing plane, and get a good precise match on your glue edges, you don't need anything more. I don't use anything but jointed edges for fitting, and medium clamping pressure. If you insist on biscuits or dowels, then you can't make any placement errors..

Matthew_Campbell's picture

(post #106177, reply #2 of 15)

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Thanks Mike. I was thinking of planing down my panels a little heavy (> 3/4") then joining them, and running them thru the planer once again to finish them off to the final 3/4" thickness. I thought that also might take care of any alignment problems.

Having never done that, is that a no-no?

Sgian_Dubh's picture

(post #106177, reply #3 of 15)

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Your plan is quite a normal procedure. It's done all the time if you have the machinery to cope with it, or you are happy to do the necessary handplaning on one face before thicknessing! However, it's easier to run the joined faces over the overhand surface planer (jointer) to get one face flat first, if it's wide enough, then run the stuff through the thickness planer.

The one serious problem with running joined boards through a thicknesser without getting a face flat first is that you have no guarantee that you'll end up with flat boards. What you get is often acceptable enough, but there is always that real chance of ending up with stuff that is nowhere near flat, therefore hard to mould and machine accurately to make door panels. It's less important for table tops of course.

rob.kelly's picture

(post #106177, reply #4 of 15)

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Matt--unlike many, I have actually built hardwood frame and panel exterior doors. Lots of them. Some thoughts follow.
1) An exterior door should be 1 3/4" thick, with a 5/4 thick panel, a little thicker if you're using a 15* raised panel cutter, in order to get a defined landing on both sides. 3/4 is way too skimpy for a 7/4 door. It's OK for a 1 3/8 passage door if you use a 5* cutter on the panels, but 1 3/8 is too thin for an outside door even though some modern construction uses them to save $$.
2) Don't use biscuits! Let's say your door is a traditional six panel 80" door, and your panels are 8", 22" and 26" high. You are going to bury 1/4" in the rail on each side, so add 1/2" to the length and width of the panels. Counting saw kerfs, you can cut your panels out of 2 boards, 9 1/2" wide and 58" long. Glue up 2 boards that size, face joint them and plane to thickness. Use one for each vertical row of panels and the grain flows from one panel to the other all the way up the door, if you use the panels in the order you cut them. You don't use biscuits because of Rob's Law of Migrating Biscuits: "No matter how well you plan and measure, one or more of those biscuits will be revealed by the panel raising bit."
3) My grooves are 1/2". With the 1/4" bury in the groove, this leaves expansion space of 1/4" all around. Since this is more than you need, when I glue up the door I put a 1/4x1/4" pc of wood in the groove on the bottom short side of each panel and on one of the long sides, that which is 'down' when the door is glued. Then if the panel gets glued in place from leaking glue, at least it's in the center.

Matthew_Campbell's picture

(post #106177, reply #5 of 15)

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Rob,

My door won't have raised panels. They will be flat panels. That will leave only a 1/4" of wood on each side of the panel after cutting a 5/4 slot for the panel. Is that enough?

I'm doing a flat panel door because of preference.
I can understand the need for a thicker panel because of it being an exterior door, but a 1/4" left over doesn't seem like a lot.

Matt

CStanford_'s picture

(post #106177, reply #6 of 15)

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Nope, you don't need biscuits. You need a good jointer (electric) or a good jointer plane (and the skill to use it well). Joint the edges until they will stack on edge with virtually no light shining through the edges and your glue-up will be a dream.

That's it. It's that simple.

rob.kelly's picture

(post #106177, reply #7 of 15)

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Matthew--A 12" wide piece of oak will shrink 1/2" from a full wet as-cut condition to fully air dried [inside a barn] 2 years later. So if you start with air dried or KD, 1/4" is OK. The trouble is positioning the panels. A raised panel is tapered to center it, but a flat one can move all the way to one side or the other. That's why I suggest using the block in the groove to keep it approximately centered. If your groove hides 1/4" of panel all around, that is plenty for a 9" panel. There will be NO appreciable movement in the direction parallel to the grain, so don't worry about up and down shrinkage. One more thing--put your rails and stiles together with floating tenons; they allow more latitude in glueup and are plenty strong. I've been using them for years and never a problem.

Dale_Page's picture

(post #106177, reply #8 of 15)

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rob.kelly: what's a "floating tenon?" I use m&t a lot for traditional New Mexico furniture and wonder if this makes things easier. Thanks, Dale in NM

Sgian_Dubh's picture

(post #106177, reply #9 of 15)

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Make a mortice in both parts and machine a piece of timber to fit. E.G., mortice the rails end grain. Mortice the stile. Fit a loose or floating tenon. Slot mortisers are a popular tool for this job, and so are routers. Some people swear by them. They have their place, but so too does a traditional mortice and tenon. Sliante.

Dale_Page's picture

(post #106177, reply #10 of 15)

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Thanks. Dale

rob.kelly's picture

(post #106177, reply #11 of 15)

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Dale, with a floating tenon, you get long grain to long grain glueing on both sides of the tenon. This gives you so much glued area that the small amount of extra area you would get from fitting the tenon exactly and glueing the edges is not significant in terms of overall strength.So I make my floating tenons about 1/8" less high than the mortise and a sliding fit as far as thickness, so before everything sets up I can adjust to my register marks with a series of hammer taps. Also it gives the excess glue a place to go. I slightly chamfer the edges and ends of the tenon so they don't hang up during assembly.

Dale_Page's picture

(post #106177, reply #12 of 15)

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I think I understand how they're made now. Thanks for the time to answer. One thing, though: If you're attaching two members at 90 degrees to each other with a floating tenon, how is it that you get long grain to long grain on BOTH mortises with the same floating tenon?

rob.kelly's picture

(post #106177, reply #13 of 15)

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Think of a rail and stile (both 4.5" x 7/4") at rt. angles. Make the mortise in both pieces. Put in the tenon. On the rail, you have long grain to long grain, with the grain direction parallel. On the stile, still long to long, but grain direction perpendicular. None of the end grain glue on stile, mortise or tenon is load bearing. If you just did a butt joint with no tenon, strength would depend on an end grain to long grain glue joint. Very weak. Add 4 biscuits to the butt joint, and you have your original weak joint + abt. 8 sq." of good glue surface, counting each side of the biscuits. Contrast this with a 5" x 3" tenon, which gives you 30 sq." of surface.

Dale_Page's picture

(post #106177, reply #14 of 15)

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Thanks, Rob. I thought you were saying a floating tenon was better at holding than a regular tenon. Now I understand the fitting ease of the floating tenon and the glue holding properties of both compared to a butt joint. I appreciate all the time you guys took to answer this. Dale in NM

Alan_Krause's picture

(post #106177, reply #15 of 15)

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I am looking for advice on the safest way to use a router and or shaper to place a cope in a arched or cathederal rail and to safely raise the corresponding raised panel. It seems that freehanding the pieces is unsafe with the chance of some serious kickback. The panels have been reduced to 9/16 inches and the rail is 3/4 inch.
Thanks to anyone that can help.
Al