The Price of Precision

[LCHIEN]

For me the advantage of these kinds of bars is to move or offset an item an exact amount from a previously fixed position.

For example, mortising. Using either mortiser or a drill press that you follow with a chisel.

Say you want a mortise 1/2" wide with just a 1/4" mortising bit or a 1/4" drill bit.
I'd drill or mortise the first row using the fence.
Then I would slip my 1/4" aluminum 12" bar between the workpiece and the fence. This will instantly move the workpiece exactly 1/4" over without having to move the fence or fuss with any measurements and the resulting mortise will be exactly 1/2".

[All Thumbs]

Agreed - on metal or cast items. But very good on wood. Wood cannot be expected to be operated with the tolerances of metal.

There is a thread here some 10+ years ago in which I had a pict of a Japanese friends' wood shavings. (The pict is now gone). The shavings were so thin that you could easily read magazine print through the ribbon.

I commented on that to Maeno and took some shavings home to make that picture. Maeno said, (in Japanese of course) "Oh, that plane wasn't as sharp as it could be. I will call you to come back when I sharpen it."

A few weeks later, he called and I went back to his house. Bear in mind that Japanese planes are not adjusted by a knob or lever, but by tapping the sides or ends of the block lightly with a hammer, causing minute movements of the cutter - and eyeballing the results.

Well, Maeno did that with me watching. Then he said (had to repeat a couple of times for me to understand) "This piece of planed wood has been setting out for a couple of days. After a piece of wood is planed and is flat, humidity changes over a couple of days will raise the soft vs hard of the grain. What once was flat will now be ridges between the two." With that, he planed away the raised ridge of the soft wood and little strings/strands came off. That had to be close to 1/5000 of an inch or even up to 1/10000 as you mentioned.

He eyeballed the settings and came up with that, no trial and error!

My point wasn't that we need .0001" precision for woodworking, but rather that they're charging for .0001" precision in their jigging but supplying .001". And I think people that scoff at thousandths when it comes to woodworking may be surprised at how poorly a tenon fits into a mortise when the former is 1/64" smaller than the latter.

[woodturner]

I agree... I think we often don't see the material for what it is. Many of us get the idea that 'machine-shop' precision is essential to good workmanship with woodworking.

I think it also depends on application and timing. For example, a dovetail where the tail is within 0.001" of the pin dimension won't fit together. However, a dovetail with a 1/64" gap will seem sloppy and poorly fitted.

But cut the dovetail to a 0.005" clearance (seems to be about right, in my experience) at the end of the day, quit for the day, and try to fit it the next day and is it unlikely to fit as well, due to the overnight expansion and contraction of the wood.

I aim for around 0.005" precision when cutting joints, but more like 1/64" on saw cuts. I think it is difficult to get more precise than that on essentially any saw, even high end industrial saws. The higher end saws have better repeatability (make the same cut with the same setup exactly the same) but are still limited in accuracy by the flex of a spinning blade.

Better yet, in most cases, is to cut to fit - we really care about tight joints and work that looks good, rather than work that meets a specific dimension, in most cases.

[TimTucker]

For those looking for a much, much cheaper alternative there's the Harbor Freight option (saw this recommended on one of the reviews for the Kreg setup set a while back):

http://www.harborfreight.com/60-piece-keystock-assortment-67540.html

[woodturner]

For those looking for a much, much cheaper alternative there's the Harbor Freight option

Those are keystocks rather than machined setup bars. The accuracy is not there - they are die cast piece that can vary in precise dimension. Should be accurate to 1/32" or so, if that is enough for what you are doing. Bigger problem may be variation between pieces of the "same size". If you only need one for your setup and 1/32" or so is accurate enough, they maybe OK.

[durango dude]

I'm pretty happy with my Kreg setup bars - although the Veritas 1-2-3 block is on my Christmas list.

As I do more and more woodworking, I learn to match, rather than to measure.

Wish I could 'splain that statement - but really - you just have to believe me.