Ever wondered how to figure out how much material you need to buy for a project? A board foot estimate is a start, but consider laying out your parts on cutting diagrams as well for greater estimating accuracy. Here’s what to keep in mind.
Tags: diagrams, lumber selection, project plans, woodworker's journal magazine, woodworking
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on Monday, May 23rd, 2011 at 10:27 am and is filed under Sheet goods, Shop Tricks, Video.
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Great equation to know… Are there any exceptions to it?
How do you calculate the sawblade width into the drawings? You have many different widths and the boards on the outer edges don’t get cut twice. If ripping 1″ strips out of a sheet of plywood you won’t get 48.
The graph paper doesn’t take that into considerartion.
You do have to account for saw kerfs on cutting diagrams. You can’t butt the parts right next to one another unless you allow them to be slightly oversized to begin with when you lay them out on the diagrams, then cut to final size once the plywood is broken down into more manageable workpieces. This is often what I do when laying out parts–leave things 1/4 or so longer and wider than final size, then trim them precisely.
In Carpentry, (Such as framing.) you can get away with cutting ‘on the line.’ In Mill-work, or Cabinetry, you ‘cut beside the line.’
With that knowledge in mind, the next step is to know what width of kerf the actual saw blade you will be using, ‘cuts.’ Blades can defer slightly between sharpening houses and the type of blade it is, such as Hollow Ground Planner or Ply. (Anywhere from 1/16 to slightly over 1/8th.)
Make a cut on scrap and measure the width with a Box rule or Draw tape.
That dimension, is then added to the length or width of the piece being cut, depending on which direction one is progressing with the series of cuts.
It can also be figured into your drawings when creating the pattern too.
Hope that helps.
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