jig for cutting blanks on a table saw

Pretty good for English. Not a lot about rulers. LOL

--=20 Will R. Jewel Boxes and Wood Art

power of accurate observation is commonly called cynicism by those=20who have not got it.=94 George Bernard Shaw

I must apologize - I forgot the following..

When multiplying or dividing -- the percentage of error adds absolutely, when adding and subtracting, the absolute error adds absolutely.

That would make it clear why you have the rules about guard digits and places of precision.

For example if you multiply two number together, (and you had been able to make the measurements and obtain the two numbers to 5% accuracy...) The resulting answer would be accurate to 10% -- so any digits beyond the first decimal place would be guard digits or used for rounding...

So you could haver 5 decimal places of precisi All kidding aside -- you should remember this when doing calculations when you multiply or divide measured numbers.

Adding or subtracting..

1 1/2 (+- 1/16 ) + 1 1/4 (+- 1/16) is 2 3/4 (+- 2/16) or

2 2/4 (+- 1/8 ) in other words... Because it is the ABSOLUTE SUM of the two estimated errors that is the error factor. SNIP ....... ================================= We all (or at least the veteran wood/ metal/ etc. workers) know that any tolerances will accumulate in the direction that will totally defeat any attempt at assembly until the entire project has been modified to the point where it is no longer identifiable as the original concept showed it on the plans (if any plans were actually drawn!) {:-)

Ken Moon Webberville, TX

I thought that's what I said ?

Rught you got it! LOL

for those who care

precise is an absolute measure ie .005 inches accurate is a percentage reference ie .005 inches per foot

ergo it would be imprecise to describe a language as inaccurate

Otto

Otto:

Couldn't resist this (not that it's not an electrical joke thread... -- although we could induct "the other group" and really give this discussion a positive charge...)

As I have been working on the latest project and turning over the design in my mind I have been trying to draw a bead on this "accuracy and precision thing". Not to put too fine a point on it but one can grind on the issues until you develop the skill to put a finer point on your instruments of operation. In other words if one is going cut to the quick, and not shave the truth, or skew the situation (lest it spiral out of control), it would be best to take harbor in a comfy cove and contemplate the issues carefully. Anything else would be but a finial on a turners philosophy in addressing the issues with sufficient sharpness.

If that is clear, read on.

ottomatic wrote:

Not necessarily. IMO It would inaccurate and imprecise to say the above..

First: "i.e." Is I believe -- "id est" (That is to say -- "That is") in Latin as I recall -- pretty foggy on my Latin these days and too lazy to look -- how is that for an imprecise answer.. LOL i.e. -- the "periods" count and "ie" is an inaccurate depiction of the contraction. )

So If I may be so bold this could be better:

** .. accurate is a percentage reference -- e.g. The measurement is 1.02 feet - precise to two places and accurate within +/- .005 inches. If one is describing a single measurement. (An observation.)

Here we can/should/might give a precise amount of _an estimate of_ the observable error. Since it is a measurement.

or

The measurement is 1.02 foot - precise to two places and accurate within

2% per foot of length after all applicable calculations. If one is describing a what could be called a calculation method used to arrive at a figure. This is assuming we had used multiplication or division to arrive at this number.

If we only used addition or subtraction, it would be best (more acceptable) to state a +/- error figure. (Not necessarily symmetric as in: within +.05 inches, and within -.1 inches)

Note that statistical methods would use all the arithmetic operation classes and we would therefore be compelled to say something of this nature in other situations:

e.g. I asked the classs to measure a 4.50 inch stick of wood and record that number along with their estimated error. After analysis I determined that they were with .05 inches of the correct answer 80% of the time and had a greater error the remaining 20% of the time. In other words the class can be counted on to take a measurement with an accuracy of 1.5% in a similar situation -- at least 80 %of the time.

**

The above would -- I believe -- be more correct. Assuming I was taught correctly -- and I make no guarantees -- especially after considering my past professors carefully, and considering my scholarly record -- which was disgraceful at best.

...Since one is describing a particular example (for e.g.) -- not a stating a general principle (Or is it principal? hmmm LOL) So therefore it was an inaccurate depiction of the principle, and imprecise thinking.

And other far more knowledgeable people who frequent this group could of course pick me to tiny pieces.

The point is that is quite difficult to precisely describe this issue without a lot of thought - and requires _far_ too many words to make it fun (* or accurate).

And now I think I will run rather than waiting for a well deserved shot, and a cranky reply. ROTFL

And now -- back to the lathe.

What can I say to that... ?

Was there an idea that said "you can prove a theory is you can dis-prove the opposite" I think it would be easier to define imprecise and inaccurate. It maybe accurate to define imprecise as a long list of inaccuracies. But it would be inaccurate to define inaccurate as a long list of imprecision, (if one were measuring 45mm long bolts with a 1m long stick with no graduations.) But its all semantics (and loads of fun) and genarally people understand whats going on. mick

Over the weekend I used a jury rigged approach based on some of the designs but much simpler.

I had a piece of 1/2 inch baltic birch plywood that I had made a mistake in cutting.

I knotched one end with a cut wide enough for my bandsaw blade and several inches deep.

I drilled a few holes in to receive a finish nail that I cut short so less than 1/2 an inch would stick out when driven through a hole from the other side of the plywood.

Then I mounted a chunk with a shallow hole drilled in what I thought should be the center and moved the plywood until the chunk was nearly contacting the blade. I made sure that the hole with the nail was lined up with the tip of the blade and then clamped the plywood to the bandsaw table.

The approach does not require anything more than a few holes because I can reposition the plywood so the center is in the correct place.

The plywood is stiff enough that there is no flexing.

After a couple smaller chunks I put a large piece of dry elm log almost

9 > At one point I remember seening the plans for a jig to help cut blanks

So much easier when the jig maintains the cutting edge tangent, isn't it?

I built a similar jig but had trouble with the bandsaw making the turns. I have an 18" saw with a 3/4 inch blade.

What blade size did you use?

Thanks Mike

I have a Jet 18

I use timberwolf blades that I buy directly from timberwolf. I like dealing with them because they keep a record of all the blades I've purchased. I just ordered some more 3/inch (RK blades I think invoice is on my desk at work) but if your unsure just explain to them what your doing and they will be able to suggest the correct blade.

They were runn> I built a similar jig but had trouble with the bandsaw making the turns. I