[OP]
Member
I got a great deal on some large, mostly clear, Doug fir Timbers that I am planning to use for a split top roubo.
7x14x12/16ft.
I was debating between re-sawing them and laminating in some larger pieces (perhaps 6” wide) to help prevent movement. Alternatively I could saw them 12” wide and use as is, one per side of the bench.
Should I be worried about that twisting / moving with the split top Roubo design?
Last edited by Steve Lake; 09-01-2022 at 12:48 PM.
Contributor
Are these timbers fully dried?
My thought on re-sawing would depend on what way the grain is running and what you have to do the work.
Some Doug Fir a neighbor gave me dried for a few years before doing any work on it.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)
Contributor
I'd second the moisture content question. I remember someone did some modeling somewhere that showed that workbench-sized slabs take at least human lifetime to dry, like 80+ years or something, and that the center will never truly dry. So if the slabs were cut somewhat recently you'll probably have to flatten them somewhat often until they settle down, and then maybe every year or two for quite awhile after that. (That being said, I consider flat-ish fine for a workbench. If you're really into flatness, probably steer away from the slabs altogether.)
If it's all the same and you've got the bandsaw, support, and muscle on had to do it, I'd personally re-saw to maybe 8/4 let them dry a few weeks in the shop, check the moisture, then laminate.
Contributor
A 2" thick bench top is more than enough for how I use a bench. I never use a sledge hammer on top of it, so 7" thick is just silly. Trendy, but silly.
[OP]
Member
The Timbers are stamped KD-HT, so I assume they are kiln dried. With something this big I assume with with kiln drying the centre is still not going to be dry..
I have worked on a couple big heavy benches and do love it. I have another 2” top maple bench but it just doesn’t have the mass for working with hand chisels and saws without it moving around.
They were sitting in a yard and are pretty straight/flat at the moment. I do worry that as soon as I saw them down it might cause some movement. I only have a 12” jointer planer so I was planning to at a minimum saw them to 12” so I don’t have to hand plane the entire top.
Contributor
By the way Steve, Welcome to the Creek.
Seven inches is a overly thick for a bench top. Holdfasts have trouble working with benches thicker than about four inches.
Some kilns also use negative air pressure to extract moisture from lumber. It can be less expensive and much quicker than using heat alone.
Hand planing is a workout. If you want to avoid hand planing you could cut the timbers to 4X7 to run through your jointer to make a laminated top.
Just remember in a few years you may want to run a hand plane over the top.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)
Contributor
You must really wail away at your tools. I built my bench in 1989 and it hasn't ever moved. The base is heavier than the top, and the top has a thicker rim around the 2" thick top.Originally Posted by Steve Lake
workbench.jpeg
Contributor
Can you get a picture of the entire mill mark? The blob of text that has the KD-HT nomenclature? On Doug Fir construction lumber KD-HT is not an uncommon mark, but it is generally kilned down only to 19-20%.
Contributor
At 7" x 12" those timbers will be drying out for years. If you want a reliably flat bench start with dry material. You can get a rough idea of the overall moisture content by weighing the pieces and comparing that to their projected dry weight based on standard tables.
Contributor
I went digging in my WWPA guidebook last night. There is another mill mark that can be used on Doug Fir, "MC-15" for wood at 15% moisture content and lower. So in theory the KD piece(s) the OP has could have been kilned down to anywhere "between 16 and less than 20 percent moisture content." In practice I am used to seeing fresh Doug Fir stamped KD measure 19%MC.
So the next questions are how straight is the grain and how few are the knots? What else could a timber that generous be used for?
[OP]
Member
Here are some photos of the timbers. I was also planning to use another of these (a longer 16ft one) for materials for some shoji screens I am making, if I can resaw enough clear VG out of it. There are some small knots in the top one, less visible in the other two. The grain on the side is fairly nice vertical grain. It looks like I was mistaken as well and they are actually 14x6 rather than 14x7.
IMG_4745.jpgIMG_4750.jpgIMG_4749.jpg
One thought was to make the two top slabs on a split roubo removable. I'd use the traditional through double tenon joint, but draw bore it or use a through wedge from the side and cut a small recess for access to tap the dowels/wedge out from behind, removing the top so it could be run through my jointer/planer as needed.
Contributor
Well, those sure look like Doug Fir to me, though the mill mark does not include the trademarked triangle with the big D up top and the smaller FIR on the lower line.
I do notice they are both (in pic 2) more or less flat sawn and starting to split along the center of the grain line.
I have done something at my end that doesn't let me see your pics and respond on the same screen. BRB
Contributor
So a couple observations.
The CB or GIB or DB with the oval shape is probably the mill mark. If that really is Doug Fir, I don't see why they left off the trademarked triangle outline with the big D up top and the FIR in the lower half of the triangle. The edge grain in your second pic looks a whole lot like D Fir, though the end grain in pics one and three honestly don't.
TAD (thoroughly air dried) does appear in my WWPA grading guide. Neither of RFP or TAC do appear in my guide.
I don't understand why there isn't a species mark. Even if it is not DFir, Larch (big L) and Lodgepole Pine (big L big P) have design values so they can be used in engineered construction. Leaving the species mark off means the mill has to sell at a lower price.
Your timbers do both display splitting (end checking this year) near the peak of the smallest growth ring. This will only spread as the timbers continue to dry - in my experience with Doug Fir. I don't see any significant knots and I don't see a lot of runout as pictured.
I don't see your location in your profile.
Without a species mark from the mill to specify design values and incorporate them into say a timber framed building, work bench top is probably a good choice. I would not use either of those as one piece split top slabs. Ass/u/me-ing they really are one of the western softwoods, my expectation is the end checks you see will only get bigger and longer as your existing timbers continue to season. Probably fine as say a top plate in a timber famed garden shed, but also likely disastrous for a bench top.
At my place, and I have actually done this, I would first cut somewhat overlength for your desired bench size... Full disclosure I had a 6 foot piece of 16/4 Doug Fir that was 14 inches wide... then rip down the center of the grain line to have pieces with FOHC end grain. Free of Heart Center Cut. There is a church in either Alabama or Mississippi with a very similar name, but if you can filter those hits out and just focus on wood working you will see what I am talking about.
For my piece I crosscut at 36", then ripped on the peak of the growth rings. I have all four legs for my next workbench seasoning for over a year now, one pair at roughly 16/4 x 36 x 6 and the other pair at roughly 16/4 x 36 x 8. But all four of my legs are FOHC end grain.
For a bench top I would do the same. Rip down the middle, maybe rip twice to get rid of all the splitty bit, wait if you can, then laminate just two pieces together to make your top halves.
Having been there, done that, I don't deal with pieces that big anymore unless I am building a barn. What I do now is peruse the DF 2x4 at the homestore, every time I go, looking for work bench top parts and vise chop parts. 2x4 Doug Fir will thoroughly season in two years.
You got some nice looking timbers there. If they really are a western softwood at ~19% moisture they are going to keep moving for several more years.
[OP]
Member
Thank you, that is very helpful advice!
Despite the lack of mark, I’m fairly certain they are DF. I’m in Vancouver and Doug Fir is almost exclusively used for timber frame building around here as there are endless amounts milled nearby.
Last edited by Steve Lake; 09-03-2022 at 9:23 AM.
Member
I would re-saw those one time each, (or perhaps twice each, if you want a wider top) expose the VG for the bench top, and bury the checks in the glue joint. Will make a great bench top.
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