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Redwood gate by a rookie

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Blog entry by NapaMike posted 06-23-2008 03:26 AM 2976 reads 1 time favorited 5 comments Add to Favorites Watch

Help! I am starting my second attempt at a redwood gate. Arched top rail (long grain) with rails & stiles that frame loose slats in a groove in the rails & stiles. The gate opening is 39”. Location Napa, CA. All the rain comes between Dec to March then dry for the rest of the year with very dry summers.

The 1st attempt was with horizontal long-grained arched top rail half-lap glued to long grain stiles = long-grain to cross grain. As I should have known the cross-grains split with swelling when soaked in winter rains. The next try will use full length stiles with mortise & tenon into the rails.

Questions:
1. How much expansion should be expected for overall width with redwood, meaning how much gap is needed per side of the opening; 1/2” per side?
2. For the floating slats would opposing rabbit or tongue & groove joints work better to prevent warping?
3. How can the swelling for either junction be predicted? I am concerned about tongue swell splitting out grooves.
4. If I use 1×6 slats what width groove in stiles and rails would be needed when wet to prevent split out?
5. Are there tricks with glued exterior mortise & tenon joints to prevent split out when they expand in the rain, meaning just glue the ends or over size the mortise to some degree to allow it to swell?
6. Can all these expansion problems be taken care of with sealing?



5 comments so far

View Todd A. Clippinger's profile

Todd A. Clippinger

8901 posts in 3567 days


#1 posted 06-23-2008 09:36 PM

A gate should not have huge amounts of swelling left to right because it is not one solid piece of glue up like a table top. That would be several pieces of wood glued side-by-side and they all move in tandem. You are actually making a frame with a floating inner panel. The frame contains the inner panel and they can move independently of one another.

Please understand that I build for my area. I live in Billings, Montana and we get rain in the spring and extremely dry summers. The ambient humidity may be 10 to 15%. This may be similar to where you are at. I usually gap my work close to 3/8” but 1/2” seems a little heavy. The nice thing about fences, decks, and gates is that you can get away with these things because that is the nature of the projects, they are refined rough carpentry.

The groove that accepts the slats will need to have drain holes drilled clear through the bottom so as not to hold water. I have seen the slats in 3 ways: tongue and groove, ship lapped, and simply laid side-by-side. My personal favorite is tongue and grooved, but that is just personal taste. Certainly the key to success with any of these is that none of them are laid tight together. There has to be a little slack. The same goes for creating a tongue and groove. It is outdoor construction, not fine furniture making.

Your observation of the cross grain blowing apart is accurate. But, mortise and tenon do not work the same way that a half-lap does. If you do M&T, the mortise slot can be made slightly larger than the tenon. The tenon can be pinned with dowels in two locations. For example; the top pin would fit tight and the lower pin would go through a slotted hole in the tenon. It would hold the tenon fast in the mortise at the opposing angle, but it would allow for the movement side to side as the rail expands. That is why the mortise slot is slightly larger than the tenon to allow for the movement. The cheeks of the tenon would fit firm, the shoulder would have room to move one direction for seasonal expansion in the mortise. (I hope this is not confusing.)

No, the exterior finishes will not really help reduce the movement of the wood. The conditions outside are too harsh and extreme. Indoor furniture is kept in a climate controlled situation and avoids the extreme changes in moisture and temperature levels. The finish on indoor furniture is more apt to slow the exchange of moisture content in the wood, but that is because the changes indoors are not as extreme.

I am sure others may be able to expound on this information for more points of view.

-- Todd A. Clippinger, Montana, http://americancraftsmanworkshop.com

View NapaMike's profile

NapaMike

4 posts in 3332 days


#2 posted 06-24-2008 02:15 AM

Thanks Todd. I really appreciate your experience and thoughts. When you over size the M&T are you talking 1/16” or 1/8” per side or something else? Do you end glue the tenon or full glue? Is an expanding glue like Gorilla glue helpful or harmful?

View Todd A. Clippinger's profile

Todd A. Clippinger

8901 posts in 3567 days


#3 posted 06-24-2008 03:43 AM

I had 1/8” in mind, but only to one side. If the tenon is pinned in place on, let’s say the top of the rail, that causes the movement to go all to one side. That is why the lower hole in the tenon for the pin is slotted, to allow the tenon to expand and contract in the mortise.

Because of this movement, think a moment about the top rail and bottom rail that have grooves to hold the slats. This means that the grooves will have to be deep enough to allow the slats to properly be contained as the rails expand and contract. The slats and frame, in general, will swell side to side more than in thickness.

Be very particular about picking your lumber for the door parts. Observe the growth rings on the end of the board and get the pieces that indicate as close to a quartersawn cut as possible. These pieces will be more stable overall.

Gate doors are notorious for sagging, especially if made of redwood. Support cables and metal frame parts are most often incorporated into my designs anymore because the doors are almost guaranteed to sag over time. The wood mostly seems to shrink here in Montana and the parts starts getting sloppy. The joints start getting worn out as the gate is continually lifted and dropped to compensate for the sag and this only exacerbates the situation.

The great thing about Gorilla Glue is that it is impervious to water in exterior projects. I also have full faith in the TiteBond III for outdoor applications.

-- Todd A. Clippinger, Montana, http://americancraftsmanworkshop.com

View Todd A. Clippinger's profile

Todd A. Clippinger

8901 posts in 3567 days


#4 posted 06-24-2008 05:18 AM

I went back and read my first answer and I did use the term “shoulder” incorrectly in describing the tenon. But I do think that you are understanding my explanation.

-- Todd A. Clippinger, Montana, http://americancraftsmanworkshop.com

View NapaMike's profile

NapaMike

4 posts in 3332 days


#5 posted 06-24-2008 07:32 AM

Thanks again

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