Dealing with decimals

[tablesawtom]

How many of you use either a dial or a digital caliper? This is also in response to an earlier post about a oneway gig.

I worked in decimals all of my life so it is second nature but I am sure some of you convert using either a conversion chart or a calculator. I was asked by my 11 year old grandson about diameters and fraction last week He said he hadn't had any of it in school yet. So I hope this helps at least one person.


So my first question is how many pennies are there in a 1/2 dollar. The answer is 50 and if a person was adding or subtracting one would right is as .50.  if one was reading a dial indicator in thousandths or a dial or digital caliper it would read .50 and add a zero or .500.

Second question how many pennies in a quarter answer 25 and add a zero or .250

If you are using a digital caliper to measure a piece of wood just out of a planner and it is supposed to be 3/4 of an inch then it is 25 cents, 25cents equals 50 cents and 25 cents equals 75 cents. And add a zero or .750 I hope it is using what you have known all your life in a different way because you do this kind of math in you head every day.

!/8 and 1/8 equal a quarter and 1/2 of 25 cents is 12and 1/2 cents or .125.  so 3/8 inch is .12 plus .25 or .37 and add the .005 or .375.  And 5/8 inch is 1//2( 50) plus 1/ 8 ( 120 or 620 and add the .005 or 625. Again a head job with a little practice.

1/16 is 1/2 of 1/8 or .062 because 1/8 is .125.

1/32 is .0312 Don't worry about the .0002 and rounded off is .03

and 1/64 is .0156 don't worry about the .0006.

lets say you have a beading bit in a router table and you roughed the radius in and you now have a round over. The depth of the cut left is 1/16 inch. Now here is where I part company with several here on the form I go with accuracy and the general thought train is it is only wood. I would use the gage pictured and raise the cutter .062



You can say that that kind of accuracy isn't needed but down the road lets say that it is 1/2 of a drop leaf joint. If the thickness of the wood .75 and the radii starts 1 /16 down from the top then if I use my gage and set the top of the cove bit at .625   above the top of the router table then the tops will match because the top surfaces Datum of the wood first cut was cut referencing off the datum of the router table (top) If different thicknesses then it is just a math problem when setting the cove bit.

If I cut the first  joint the way I do, then I can come back a month latter, and cut the other half if the joint and the tops will match. Yes I know wood expansion can come into play but in the 1/16 it is so little it won/'t inter into the equation.

It is using fractions, dismals and such to produce a nice piece of work. If what I wrote make any sense to you,  just imagine the possibilities.

Tom



imagine

[tablesawtom]

Lets say you are cutting a rail and style using a set of cutters. You have cut all the pieces using the first bit. You set the second bit height and hopefully did a test cut and there is a mismatch. The distance is measurable with the gage pictured and the cutter then can now be raised or lowered that amount again using that gage without any hassls , no trial and error until it is correct.

[JGrout]

And what if you can accomplish something like this without a one way gauge? 



the unit above was a retrofit piece in a historical site remodel and had to be the exact size the one above is on the perimeter. Additionally, the knives and the guide bearing were not perfect, in fact the  differentials  all had to be worked out as the guide bearing and the cutters were dissimilar by a given fraction (5/64" IIRC) yet the interior joinery is accurate. the Joint elevations are all the same as well. 

 we all use decimals and fractions to construct actual pieces. The radius of all the parts was determined with the help of a calculator It is just part of life in the trade. 

I wonder if you would have heart failure if I said I used a simple protractor  to get all the angles and a stick with trammel points to set the arches.  

BTW I did.....

Joe

[Steve N]

After those Nuns spent all that time whacking my knuckles teaching me inches. I have dial calipers with SAE reads. I understand all that Metric is supposed to be childs play, Dum child here evidently

[Marc]

Im with steveN... rulers on the knuckles. Math was/is my worst subject. Decimals close to an inch i get, like .50,,,.25 As embarrassing as it is,,im completely lost after that. My digital caliper fixes it. As a kid i never would have guessed that decimals would be important to my hobbies...engine work, metal lathe and woodworking. I get it to work,,but i struggle.

For me,,,the biggest problem i have using dial indicators or calipers, etc...is no one ever "physically " showed me how to use them correctly. I can get 2 or 3 different measurements and never know which is correct. Too much thumb pressure on my caliper and i can watch a .53 turn into a . 50

[Arlin Eastman]

Tom

Like you I have dealt with fractions and  decimals all my life since I should say 2 grade but for my job all of it and even now.
I do not know how anyone making something can not use one or the other.

[CLETUS]

 I was asked by my 11 year old grandson about diameters and fraction last week He said he hadn't had any of it in school yet. 

I spent 8 years as a machinist... to this day I still convert all fractions to decimals in my head. We went through the fraction stuff with my son this fall... trust me, converting to decimal is not allowed.

[daddo]

I just don't always use the zero's.

.5 is the same as .50.
If I am rounding to .5 then I might use .50 to tell me I rounded it off so if there is a problem with my fit, I'll know to go back and see I was really at .498.

[Wizard of Oz]

Being a machinist by trade, I find decimals much better to work with. The only problem is I tend to think just a little too close for woodworking (it doesn't have to be +or- two thousands).

Oz

[tablesawtom]

T o JGrout no, I would not be surprised and I would not have heart failure if you  said you used a simple protractor to get all the angles and a stick with trammel points to set the arches. I commend you on the fine work. I know nice work when I see it. And I am pleased to see some of your work and I hope others are too.

Quote: and we all use decimals and fractions to construct actual pieces.  Yes I am in prefect harmony with you. Yes we all use decimals and fractions. But if a person put the board though a planner. And he wants the finished dimension to 3/4 inches. And he is using a digital caliper to check the out come. I would hope a person should be able to measure something if only with a tape measure.

1. Maybe this person has a full time job that doesn't uses fractions, decimals, or even a calculator. Now lets say he has misplaced his calculator: What is wrong with me saying one can do the math in his head.  What is wrong with me asking how many pennies are in three quarters ( actual coins) and the answer which 99% of the adult world can answer is 75 .

2. Now the dial or digital caliper reads in three places  And if I say add a zero  What is wrong with that? How did I commit heresy and why must I be put in my place.  And if the measurement is .765  that means that .765-.750=.015 and .015 if you look at the post is 1/64 so the person lowers the cutter head 1/64. Is there something I said  which must be contradicted? I don't want or expect it, but I would be nice to hear someone say GEE I never thought of putting the 2 together. You have made it easier for me.
 
Quote: The radius of all the parts was determined with the help of a calculator It is just part of life in the trade.   It seems that you are allowed to bring a calculator into the picture, Which being a recent invention but I am not allowed to call a great tool( gage ) to the attention of woodworkers who might not recognize its uses to help make things easier. It certainly  is not a tool of my profession. And how resent are the protractors we use today.

I am not the enemy. I am not the know it all, I am not trying to cause problems. I don't want to argue. I know one can lead horse to water but I can't make him drink. I can write about datums which at least 90% have never heard off. Of 
how to measure and make things easier so that if a person has to make one over he or she can do it much easier. 

And finally to JGrout and to the rest  who miss read what I wrote, I wish you would actually read what I wrote, not just speed read to find something wrong but take time to read and ponder what I actually wrote. Test what I wrote to see if it is good before being against it.   

Tom