Thread: Hole spacing
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Old August 20th 11, 09:57 PM posted to rec.woodworking
Doug Miller[_2_] Doug Miller[_2_] is offline
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First recorded activity by DIYBanter: Apr 2011
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Default Hole spacing

In article , "Paul" wrote:
My math skills are non existent beyond basic math, and I'm trying to figure
out how to space holes evenly along a center line in an area. Let's say I
have a rectulanglar block, 6" long ,less 1/4" on each end for a border and I
want to evenly space 6- 3/4" holes. How do you figure that? My
daughter-in-law says you can do that in one of those cheap home design
programs. That would be ideal for me. Anyone use one of those programs that
knows if they can be used for that? Thanks.


Well, this *is* basic math: all you need is simple arithmetic (addition,
subtraction, multiplication, and division). What complicates this one is the
use of a measuring system that's approximately a thousand years old.

You have a total of 6" less two 1/4" borders = 5 1/2" to put the holes in.

Six 3/4" holes take up 6 * 3/4" = 4 1/2" of that 5 1/2", leaving 1" for spaces
between the holes.

Since there are 6 holes, there will be 5 spaces between them. You have 1"
total to make 5 spaces, so each space will be 1/5".

The distance between the centers of the holes will be 3/4" (the width of the
hole) plus 1/5" (the spacing between holes) -- this will be difficult to
measure with tapes or rules marked in inches.

I suggest you choose one of the two options below instead.

Option 1
-----------
Increase the size of the borders by 1/32" to 9/32". This will leave you 5
7/16" to put 4 1/2" worth of holes in, leaving 15/16" to divide among five
spaces between holes.

15/16" divided among five spaces = 3/16" per space -- and *that* you *can*
measure easily. This gives you a distance between centers of 3/4" + 3/16" =
15/16".

So mark the center of the first hole at 9/32" (the width of the border) plus
3/8" (*half* the width of the hole) = 21/32" in from one end. (3/8 = 6/16 =
12/32; 9/32 + 12/32 = 21/32)

Subsequent holes are centered every 15/16" from the
21/32 + 15/16 = 21/32 + 30/32 = 51/32 = 1 29/32
1 19/32 + 15/16 = 1 19/32 + 30/32 = 1 49/32 = 2 27/32
2 27/32 + 15/16 = 2 27/32 + 30/32 = 2 57/32 = 3 25/32
3 25/32 + 15/16 = 3 25/32 + 30/32 = 3 55/32 = 4 23/32
4 23/32 + 15/16 = 4 23/32 + 30/32 = 4 53/32 = 5 21/32

Option 2
----------

Redo everything in metric. It's SO much easier.

A number of years ago, I was in Toronto on business. Having utterly failed in
my attempts to find a metric tape measure at home, I asked one of the guys I
was working with where I could find a hardware store. He wondered why; I told
him -- and he asked in honest bewilderment what on earth an American would
want with a metric tape measure. My answer was that I'm a woodworker, and
solving problems such as this is FAR easier with measurements in millimeters,
rather than fractional inches -- as you're about to see, too.

It's much easier to find metric tapes in American hardware stores now than it
was in the 1980s. So go buy yourself a tape measure that has dual scales
(inches and millimeters). That will make it easy to see the relationships
between the two systems.

Then remeasure. You will find that:
- your block is 152mm long.
- you want a 6mm border at each end.
- you want to evenly space six 19mm holes.

152mm less two 6mm borders leaves (152mm - 6mm - 6mm) = 140mm.

Six 19mm holes occupy 6 * 19mm = 114mm

You have (140mm - 114mm) = 26mm available for the five spaces between the six
holes, so there will be (26mm / 5) = 5.2mm between each hole. Ignore the
point-two millimeters; you can't measure that fine anyway.

The holes will be centered every (19mm + 5mm) = 24mm.

The first hole should be a distance of 6mm (the width of the border) plus
9.5mm (half the width of the hole -- round it off to 10mm) = 16mm in from one
end of the board.

Subsequent holes are centered every 24mm after that:
16mm + 24mm = 40mm
40mm + 24mm = 64mm
64mm + 24mm = 88mm
88mm + 24mm = 112mm
112mm + 24mm = 136mm
And looky the the last hole is (152mm - 136mm) = 16mm in from the end, same
as the first one.

Isn't that a lot simpler?