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Holtzapffel Bench #5: 8/4 < 2 (Lessons in Math)

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Blog entry by Olaf Gradin posted 2454 days ago 1026 reads 0 times favorited 5 comments Add to Favorites Watch
« Part 4: Plane Old Planes Part 5 of Holtzapffel Bench series no next part

My grade school arithmetic left me with some rather incomplete lessons in the basics. I learned yesterday that 8 / 4 is not equal to 2 in the real world.

I took my rough-dimensioned ash over to a friends shop yesterday to get some time on his 8” jointer and planer. As we began to surface the slightly more than 8/4 boards, it quickly became apparent that I was not going to get the thickness on these boards that I had hoped. A small amount of bow and twist on a board nearly 4’ in length causes your usable thickness to go down quite dramatically when jointing for flatness. I learned some very valuable lessons in those few hours at his shop. Unfortunately, they came too late for my bench lumber as I had already picked it out and purchased it.

When picking out your lumber, you want to measure the thickness at the thinnest point on the board. That’s not always readily apparent, so it’s a good idea to take several measurements along the board – both sides – to find it. Use that thinnest measurement to a) go towards your dimensioned needs and b) negotiate board feet (ergo price). You’ll want the thinnest part of the board to be about 1/4” bigger than your final dimensioned stock. That means, you may have to buy 10/4 boards to get 8/4 after jointing and thickness planing. I hate to be so wasteful, but wood is an organic beast and doesn’t adhere to the expectations of “dimensioned” lumber requirements. Clearly, it also helps to buy boards that have been rough cut to accurate thicknesses up front. Using more reputable hardwood suppliers with better machinery will undoubtedly yield better results.

I also learned to keep your fingers away from out-feed rollers on a thickness planer. The idea was to lift the boards coming out of the planer to minimize snipe, but the shorter length rails were finishing their cut just prior to the last roller. I grabbed for one thinking I would be able to lift it up and out only to find that the planer was still feeding it. Two of my fingers found themselves between 8/4-ish ash held by a planer and a steel feed roller mounted to said planer. Needless to say, my fingers gave first. A painful lesson, but not the worst that could happen. At least I still have them!

You may recall that I had originally intended to hand plane these boards entirely. As such, I had cut them to within an inch of their final length and width to do this work. That waste threshold isn’t sufficient for machinery planers. Snipe from a thickness planer can eat up the ends of your boards if you’re not careful with your technique. Even with care, end snipe will always be present to some degree.

Regardless of my frustrations with the dimensioned stock, I must move on. As my friend told me, don’t worry over the dimensions. It’s a workbench and doesn’t require such rigid requirements as I am intending. Just get the lumber flat and go from there. Worst case, I laminate another wood inside of my glued-up pieces to get the thickness wanted and a decorative touch! In any case, I’m ready to move on to another part of this project. It’s time to glue-up those legs and cut the stretchers and rails to their final dimensions…

-- It takes a viking to raze a village. &mdash Blog'r: http://www.gradin.com



5 comments so far

View rjack's profile

rjack

110 posts in 2481 days


#1 posted 2454 days ago

Olaf,

I’m glad to hear that you are making good progress! I have my legs glued up but I need to do final machining on them.

-- Roger - Havertown, Pennsylvania

View John Gray's profile

John Gray

2370 posts in 2512 days


#2 posted 2454 days ago

Great post please keep us updated.

-- Only the Shadow knows....................

View Todd A. Clippinger's profile

Todd A. Clippinger

8768 posts in 2726 days


#3 posted 2454 days ago

If I want 4/4 finished I buy 5/4. Also always figure more material than you need.

It is based a good bit on experience but 25% over is a good starting point. By the time you straightedge boards, make a bad cut, and have the grain make a board dance after releasing tension in it you will find 25% isn’t that much over.

On a project that requires 15bf that is only 3.75 bf extra

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

View Thos. Angle's profile

Thos. Angle

4435 posts in 2589 days


#4 posted 2453 days ago

I always allow 1/3 when I bid and sometimes don’t use that much but it’s seldom. I’m messier than Todd.

-- Thos. Angle, Jordan Valley, Oregon

View miles125's profile

miles125

2179 posts in 2632 days


#5 posted 2453 days ago

8/4 will usually net 1 3/4” when dressed (the thickness of most exterior doors if you notice).....But sometimes they come plump or a little skimpy in the rough.

-- "The way to make a small fortune in woodworking- start with a large one"

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