Shiplapping Pressure Treated Wood

[Jozef Kaslikowski]

This isn't a fine woodworking question, but it is at least still somewhat on topic. I have recently finished a cow trough made entirely from 2xX pressure treated boards. Since this particular feeder was for ground corn, it needed a somewhat leak proof bottom. I enlisted some help and we ripped 8 2x6 boards 12' long twice to make a ship lap joint. I need to make some more of these feeders but doing that again does not appeal to me in any way. The boards are just too heavy, long, and usually warped to work with safely and efficiently on the tablesaw.

Can I get a 3/4" rabbeting bit for my router and just run it down each side? I have never tried routing PT wood and I will definitely do it outside and wearing a respirator, but will this be too hard on my router? Are there any other concerns with doing this?

What about making half lap joints on the same wood? I was thinking of making a jig that I could clamp to the board in question with a hole small enough to stabilize the router and then just plunging a straight bit (with a collar?) to remove a section and then moving it along the board to complete the removal in 2-3 steps.

[Kendall Landry]

Let it dry and it cuts/routes fine.
Thats too much routing to do.
Put your worm drive on it. That's what I'd do.

[Michael J. McDermott Jr.]

Did'nt know Pressure Treated Lumber was Approved for Feeding Livestock ???

[Kyle Kraft]

Yeah, I second that. If you won't eat your dinner served on a nice plank of PT lumber you shouldn't make the cattle eat theirs on it.

Don't be offended, just my take on the matter.

[Jozef Kaslikowski]

I wouldn't get offended at that concern. It is an issue to consider. I didnt really explain the entire use/design of the feeders. They are movable temporary fixtures that are dragged around with a truck or ATV. They are not covered with a roof and are painted on top of the pressure treated wood. The feed is not stored touching the wood, it is poured from a bucket and is immediately consumed. The chemicals are really a non-issue as far as leeching into the feed.

[David Keller NC]

"Can I get a 3/4" rabbeting bit for my router and just run it down each side? I have never tried routing PT wood and I will definitely do it outside and wearing a respirator, but will this be too hard on my router? Are there any other concerns with doing this?"

I just finished doing a bit of this (routing) in PT yellow pine. Yes, you can do it this way, but in general you'll have to take at least 2 passes to get a 3/4" deep by 3/4" wide rabbet. Taking all of that in one big chunk will be very hard on your router and the bit.

If the bottom of the trough doesn't have to be water-tight, just feed-tight, there's an alternative method of construction you could consider - a spline joint. You would need a slot cutting bit for your router, and you'd need to rip one of the PT boards to get your splines, but there's a lot less wood removal involved in the construction. One other way to get the splines is to use outdoor marine plywood. It's more expensive and may not last quite as long as the solid wood PT splines, but there's no knots and no warpage.