Relative Dimensioning
The Power to Improve your Accuracy

By David Knipfer
April 13, 2005

A while back I wrote about the concept I call 'relative dimensioning'.

Simply stated...  relative dimensioning is a collection of techniques to determine the size of various WW parts without the need to measure anything directly.

IMHO relative dimensioning is a very powerful tool...  and has the ability to greatly improve the accuracy of about any WW machining task you need to do.

Using the power of relative dimensioning is a fundamental tenant of work in my shop...  on par with sharp tools and attention to details.

Sooooo...  in the spirit of sharing...  I'm writing now to explain a second basic type of relative dimensioning.

First...  a quick review... 

The first type of relative dimensioning is what I call 'measuring without numbers'.

This is where you determine the size of parts without using any tools that have numbers on them.

The example from my previous post was cutting some drawer bottoms to size...

My drawer bottoms are fit within blind grooves...  so measuring the width and length of a bottom directly would be quite a task.

Using a set of calipers to find the dimension...  then transfering that dimension to your table saw...  well...  this is a simple and highly accurate thing to do.

It's the power of relative dimensioning.

Now...  another kind of relative dimensioning... 

Size of parts based on each other...

This is the second type of relative dimensioning...  using parts you have already made to determine the size of new parts.

There are hundreds of examples of how the power of this particular method can be applied...  here I'll share one to get you thinking...

I'm building a new jewelry chest for a customer...  a box of drawers with doors if you will.

Wanting to use knife hinges for the doors, I know from past experience that the total carcass length needs to be 0.070" longer than the final door length...  this makes for a sweet swinging knife hinge installation.

Soooo...  the doors are built...  and it's time to cut the carcass parts to final length.

Two options here...

Option 1...  Measure the length of the doors (about 16 - 7/16"), then add the clearance (0.070"), total them up...  and find a way to set a stop on my saw to that exact number.

Bad choice.

Option 2...  The power of relative dimensioning...

I cut the carcass sides to the exact required length by simply using the doors themselves plus a piece of scrap to fix a stop on my saw.

The edge of the door is flush against the blade...  the piece of scrap is equal to the clearance I want...   and there goes the stop.

Remove the doors and cut the carcass sides to that dimension...  and they will be perfect.

Now...  I do not know exactly what the actual dimension is...  but I don't care.

It's the power of relative dimensioning.

There are many other forms of this technique as well.

I'll share more later.

For now...  think about how you can use the power in your own work...

Anytime you reach for a tool with numbers on it...   try and find a way to use relative dimensioning.

Thats all for now.


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