Raising The Bar in Shop Accuracy

[Sawduster]

Like Cabinetman, I try very much to limit the amount of measuring I do. Even built-ins seldom require outside dimension accuracy of 1/16th inch. With initial case perimeter parts and the like, it is more important that opposing pieces are cut to identical lengths than to an exact lengths. So I mark the first piece and use it to set up a stop to cut all like pieces. Grooves and dados and the like are marked from the piece they will house, and opposing pieces are marked simultaneously by clamping them down next to each other and carrying the layout marks from one to the other. Shelves etc. are fitted by either glueing up or dry assembling the pieces that will house them, then an actual shelf is put in place and marked for length. Again, this initial piece is used to set up stops for all like pieces to be cut.

Regardless of the rule you use for transfering measurements, there is a degree of error both in taking the measurement and in applying the measurement to the piece to be cut and more times than not, these errors will accumulate rather than cancel each other out.

A very sharp marking knife is the cat's meow for marking since it should leave a nearly hair thin line. Even with that hair thin line one must determine whether to split the line, take the line or leave the line when making the cut. This is determined by how the line was obtained and the relationship of the parts. You can not get this accuracy using a rule or even digital calipers.

Got some additional stuff on measuring, marking and laying out on http://www.sawdustersplace.com/Marking/Measuring.htm of my website.

[JimD]

The best measure for a part is the other part it mates to. For instance, I am currently making plantation shutters. The louvers need to be 1/16 shorter than the rails (that have lose tenons). It matters a whole lot more that there is the 1/16 difference than that either piece is exactly a particular dimension. Make one or the other and then use it to set the stop for the next part. When I fit the shutters to the window, I try them in the window. I make them a bit big and then trim to fit.

I also cut a bit long, when I can, and then trim to final size. I frequently use old buisness cards up against my stop to make something a bit smaller. On the rip fence of the table saw (BT3100 of course) I use the micropositioner to nibble up to the final size.

A negative hook angle carbide blade helped my radial arm saw. A stick-on tape on the fence for my stops helps me get at least rough dimension and acts as a double check of the final setting.

I like the looks of engineering squares but plastic drafting triangles seem plenty accurate and are a lot cheaper. I try to put one at each saw - then I always have one handy.

Some cheaper combination squares are quite accurate but not every one in the pile at Sears or where-ever. Tapes are the same way at the end. When you can, check a bunch of squares with a drafting triangle and tapes with a steel rule and fine the one in the pile that is accurate and then buy that one.

Jim

[gwyneth]

Got some additional stuff on measuring, marking and laying out on http://www.sawdustersplace.com/Marking/Measuring.htm of my website.

Jerry, that's great info you've presented--could be a handout in a class (except it's probably more useful).