How straight is straight?

Charlie, You are correct about wood: that 0.002 is way past where you
need to be. However, for machining steel parts, 0.0002" is really nice.

Also, seems to me that if your stratig ege reference has an error of up
x, then your jointer can be up to square root of (2 x squared), root
mean squared (RMS). If you join two pieces that also gets RMS'ed so the
error is potentially twice the eror in the original reference straigth
edge.

Still not very much, but just for completeness, we ought to make note
of this effect -- unless this analysis is wrong -- and it sure could
be.....

Yes Doug -- you hit the point of the discussion right on the head. I've
noticed that these threads take on a life of their own and usually
morph into completely different discussions. In this case, it has, at
least, stayed constructive.

Nate Perkins notes:

>[email protected] (Doug Miller) wrote in
>news:[email protected]:
>
>> Gotcha. And quoted directly from that page:
>> "Product Description Specifications: Edge straightness .0002" per
>> foot."
>
>Sheesh.
>
>0.0002"=5 microns off straight over a foot
>0.002"=50 microns off straight over a foot
>
>For reference, a human hair is about 100 microns thick. Talk about
>splitting hairs.

And anyone who REALLY gets their tools set up to .002" is way past where they
need to be when working wood.

Results on the best days are going to be within 1/64" or so, with the very,
very, very occasional dip to 1/128". Unless you're making a damned small box,
moving it from bedroom to kitchen when the dishwasher is in use will make it
move nearly that much.

With my eyesight as it is now (fairly good except for excessive floaters), I
doubt I could see a difference between 0.0002" and 0.002" on my table saw table
even if the straight edge would show it. And if I could, I'd still leave it
alone.

Charlie Self
"One of the common denominators I have found is that expectations rise above
that which is expected." George W. Bush

"Mike Marlow" <[email protected]> wrote in news:WtdFd.140$aa6.59
@fe61.usenetserver.com:

>
> "Never Enough Money" <[email protected]> wrote in message
> news:[email protected]...
>> Charlie, You are correct about wood: that 0.002 is way past where you
>> need to be. However, for machining steel parts, 0.0002" is really nice.
>>
>> Also, seems to me that if your stratig ege reference has an error of up
>> x, then your jointer can be up to square root of (2 x squared), root
>> mean squared (RMS). If you join two pieces that also gets RMS'ed so the
>> error is potentially twice the eror in the original reference straigth
>> edge.
>>
>> Still not very much, but just for completeness, we ought to make note
>> of this effect -- unless this analysis is wrong -- and it sure could
>> be.....
>>
>
> It sure is an entertaining analysis. It has all the right components -
> numbers, multipliers, square roots, abbreviations and a way to put all of
> those together. Hell, it doesn't have to be accurate, it sure looks
> impressive as a formula.

All it needs is an addendum calculating for 220/240/440V, wire gauge, and
whether we need three or four leads...

Patriarch,
who IS kidding...

Charlie Self wrote:
> Nate Perkins notes:
>
>
>>[email protected] (Doug Miller) wrote in
>>news:[email protected]:
>>
>>
>>>Gotcha. And quoted directly from that page:
>>>"Product Description Specifications: Edge straightness .0002" per
>>>foot."
>>
>>Sheesh.
>>
>>0.0002"=5 microns off straight over a foot
>>0.002"=50 microns off straight over a foot
>>
>>For reference, a human hair is about 100 microns thick. Talk about
>>splitting hairs.
>
>
> And anyone who REALLY gets their tools set up to .002" is way past where they
> need to be when working wood.
>
> Results on the best days are going to be within 1/64" or so, with the very,
> very, very occasional dip to 1/128". Unless you're making a damned small box,
> moving it from bedroom to kitchen when the dishwasher is in use will make it
> move nearly that much.
>
> With my eyesight as it is now (fairly good except for excessive floaters), I
> doubt I could see a difference between 0.0002" and 0.002" on my table saw table
> even if the straight edge would show it. And if I could, I'd still leave it
> alone.
>
> Charlie Self
> "One of the common denominators I have found is that expectations rise above
> that which is expected." George W. Bush


First, a human hair isn't necessarily 100 microns. red
heads may be down to 60 microns, lots of black hair is 150
to 200 microns.

Second about 1/128" Hell, breathing on the wood will make
it move that much from just absorbing moisture. And working
out the math, if you are 1/128" short you are truly a "hair"
short or maybe "two hairs" short or more accurately you are
one black and curly short. Oh yuck!

Old Nick wrote:
> On Thu, 13 Jan 2005 00:09:13 GMT, "George E. Cawthon"
> <[email protected]> vaguely proposed a theory
> ......and in reply I say!:
>
> remove ns from my header address to reply via email
>
>
>>Second about 1/128" Hell, breathing on the wood will make
>>it move that much from just absorbing moisture. And working
>>out the math, if you are 1/128" short you are truly a "hair"
>>short or maybe "two hairs" short or more accurately you are
>>one black and curly short. Oh yuck!
>
>
> What's yuck about black and curly man? My wife has black curly hair on
> her head. Seems OK to me <G>

I thought someone would descend to a lower level. ;-)

"Australopithecus scobis" <[email protected]> wrote in message
news:[email protected]...
> On Fri, 14 Jan 2005 22:23:42 -0800, CW wrote:
>
>> You can't see 0.0002" with your eye.
>
> > Yes, you can, easily.
>
> [This keeps coming out sounding argumentative, and it's not meant to be:)]
>
> Can you tell 0.0002 from 0.0003 by eye "easily?"

No, but that was never the issuse.


>When you say "easily," do
> you mean bright light shows 'twixt straightedge and work? In astronomy we
> deal with arcseconds; there are limits to what the eye can see.

References to astronomy don't make you look good. For various reasons, I
have learned to dismiss the astronomy types.

> Older eyes
> have more trouble. Can old farts here see 0.0002 easily?

I can. YOu would have to live with my eyes for a day to appreciate that.

> Is that amount
> small enough that temperature (coefficient of thermal expansion) matters?
>
For a guy in his woodshop, no.

Why bother with straight? Play with it. Straight lines are boring. Use an
angle grinder with a carving blade in it and go for it.

"gregg" <[email protected]> wrote in message
news:[email protected]...
> Charlie Self wrote:
>
> Hi Charlie,
>
> Especially when you consider that 200 years ago people were using wooden
> planes, and big-slab wooden benches - which weren't leveled with a routah
> and sled - to make furniture that is excellent by any standard.
>
>
>> And anyone who REALLY gets their tools set up to .002" is way past where
>> they need to be when working wood.
>>
>> Results on the best days are going to be within 1/64" or so, with the
>> very, very, very occasional dip to 1/128". Unless you're making a damned
>> small box, moving it from bedroom to kitchen when the dishwasher is in
>> use
>> will make it move nearly that much.
>>
>> With my eyesight as it is now (fairly good except for excessive
>> floaters),
>> I doubt I could see a difference between 0.0002" and 0.002" on my table
>> saw table even if the straight edge would show it. And if I could, I'd
>> still leave it alone.
>>
>> Charlie Self
>> "One of the common denominators I have found is that expectations rise
>> above that which is expected." George W. Bush
>
> --
> Saville
>
> Replicas of 15th-19th century nautical navigational instruments:
>
> http://home.comcast.net/~saville/backstaffhome.html
>
> Restoration of my 82 year old Herreshoff S-Boat sailboat:
>
> http://home.comcast.net/~saville/SBOATrestore.htm
>
> Steambending FAQ with photos:
>
> http://home.comcast.net/~saville/Steambend.htm
>

"Never Enough Money" <[email protected]> wrote in message
news:[email protected]...
> Charlie, You are correct about wood: that 0.002 is way past where you
> need to be. However, for machining steel parts, 0.0002" is really nice.
>
> Also, seems to me that if your stratig ege reference has an error of up
> x, then your jointer can be up to square root of (2 x squared), root
> mean squared (RMS). If you join two pieces that also gets RMS'ed so the
> error is potentially twice the eror in the original reference straigth
> edge.
>
> Still not very much, but just for completeness, we ought to make note
> of this effect -- unless this analysis is wrong -- and it sure could
> be.....
>

It sure is an entertaining analysis. It has all the right components -
numbers, multipliers, square roots, abbreviations and a way to put all of
those together. Hell, it doesn't have to be accurate, it sure looks
impressive as a formula.
--

-Mike-
[email protected]

[email protected] (Charlie Self) wrote in
news:[email protected]:

> Nate Perkins notes:
>
>>[email protected] (Doug Miller) wrote in
>>news:[email protected]:
>>
>>> Gotcha. And quoted directly from that page:
>>> "Product Description Specifications: Edge straightness .0002" per
>>> foot."
>>
>>Sheesh.
>>
>>0.0002"=5 microns off straight over a foot
>>0.002"=50 microns off straight over a foot
>>
>>For reference, a human hair is about 100 microns thick. Talk about
>>splitting hairs.
>
> And anyone who REALLY gets their tools set up to .002" is way past
> where they need to be when working wood.

Yeah, my point exactly. Most people have no concept how small 0.0002"
really is. You can't see 0.0002" with your eye. You can't reliably see it
with the best optical microscopes. It's so small that any amount of
routine handling will throw it out of tolerance.

So why pay extra for 0.0002" tolerance in Starrett vs 0.002" tolerance from
Lee Valley? Beats me.

"CW" <[email protected]> wrote in
news:[email protected]:

>
> "Australopithecus scobis" <[email protected]> wrote in message
> news:[email protected]...
>> On Fri, 14 Jan 2005 22:23:42 -0800, CW wrote:
>>
> >> You can't see 0.0002" with your eye.
>>
>> > Yes, you can, easily.
>>
>> [This keeps coming out sounding argumentative, and it's not meant to
>> be:)]
>>
>> Can you tell 0.0002 from 0.0003 by eye "easily?"
>
> No, but that was never the issuse.
>
>
> >When you say "easily," do
>> you mean bright light shows 'twixt straightedge and work? In
>> astronomy we deal with arcseconds; there are limits to what the eye
>> can see.
>
> References to astronomy don't make you look good. For various reasons,
> I have learned to dismiss the astronomy types.

Really? What types don't you dismiss?

>> Older eyes
>> have more trouble. Can old farts here see 0.0002 easily?
>
> I can. YOu would have to live with my eyes for a day to appreciate
> that.
>
>> Is that amount
>> small enough that temperature (coefficient of thermal expansion)
>> matters?
>>
> For a guy in his woodshop, no.

Sure it does. Look up the CTE of a good stainless steel. Assuming a
2ft bar, the linear CTE is about 3x the tolerance for every degree F.

Now try the same with the elastic modulus. :-P

You want to pay extra money for a 5um tolerance, go for it. I'll save
my money and buy something useful.

"Nate Perkins" <[email protected]> wrote in message
news:[email protected]...
> "CW" <[email protected]> wrote in
> news:[email protected]:
>
> >
> > "Australopithecus scobis" <[email protected]> wrote in message
> > news:[email protected]...
> >> On Fri, 14 Jan 2005 22:23:42 -0800, CW wrote:
> >>
> > >> You can't see 0.0002" with your eye.
> >>
> >> > Yes, you can, easily.
> >>
> >> [This keeps coming out sounding argumentative, and it's not meant to
> >> be:)]
> >>
> >> Can you tell 0.0002 from 0.0003 by eye "easily?"
> >
> > No, but that was never the issuse.
> >
> >
> > >When you say "easily," do
> >> you mean bright light shows 'twixt straightedge and work? In
> >> astronomy we deal with arcseconds; there are limits to what the eye
> >> can see.
> >
> > References to astronomy don't make you look good. For various reasons,
> > I have learned to dismiss the astronomy types.
>
> Really? What types don't you dismiss?

Most anyone but astronomers.

>
> >> Older eyes
> >> have more trouble. Can old farts here see 0.0002 easily?
> >
> > I can. YOu would have to live with my eyes for a day to appreciate
> > that.
> >
> >> Is that amount
> >> small enough that temperature (coefficient of thermal expansion)
> >> matters?
> >>
> > For a guy in his woodshop, no.
>
> Sure it does. Look up the CTE of a good stainless steel. Assuming a
> 2ft bar, the linear CTE is about 3x the tolerance for every degree F.
>
> Now try the same with the elastic modulus. :-P
>
> You want to pay extra money for a 5um tolerance, go for it. I'll save
> my money and buy something useful.


You're proving my point.

On Fri, 14 Jan 2005 05:47:30 GMT, "George E. Cawthon"
<[email protected]> wrote:

>Old Nick wrote:
>> On Thu, 13 Jan 2005 00:09:13 GMT, "George E. Cawthon"
>> <[email protected]> vaguely proposed a theory
>> ......and in reply I say!:
>>
>> remove ns from my header address to reply via email
>>
>>
>>>Second about 1/128" Hell, breathing on the wood will make
>>>it move that much from just absorbing moisture. And working
>>>out the math, if you are 1/128" short you are truly a "hair"
>>>short or maybe "two hairs" short or more accurately you are
>>>one black and curly short. Oh yuck!
>>
>>
>> What's yuck about black and curly man? My wife has black curly hair on
>> her head. Seems OK to me <G>
>
>I thought someone would descend to a lower level. ;-)

Now, now, trolls' accusations not withstanding, this is a civilized group
populated by gentleman (and proper ladies). [besides, that would have been
waaaay too easy :-) ]



+--------------------------------------------------------------------------------+

Now we'll just use some glue to hold things in place until the brads dry

+--------------------------------------------------------------------------------+

On Fri, 14 Jan 2005 22:23:42 -0800, CW wrote:

>> You can't see 0.0002" with your eye.
>
> Yes, you can, easily.

[This keeps coming out sounding argumentative, and it's not meant to be:)]

Can you tell 0.0002 from 0.0003 by eye "easily?" When you say "easily," do
you mean bright light shows 'twixt straightedge and work? In astronomy we
deal with arcseconds; there are limits to what the eye can see. Older eyes
have more trouble. Can old farts here see 0.0002 easily? Is that amount
small enough that temperature (coefficient of thermal expansion) matters?

--
"Keep your ass behind you"
vladimir a t mad {dot} scientist {dot} com

On Fri, 14 Jan 2005 05:47:30 GMT, "George E. Cawthon"
<[email protected]> vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

Damn!

"Nate Perkins" <[email protected]> wrote in message
news:[email protected]...
> Yeah, my point exactly. Most people have no concept how small 0.0002"
> really is.

True


> You can't see 0.0002" with your eye.

Yes, you can, easily.

> You can't reliably see it
> with the best optical microscopes. It's so small that any amount of
> routine handling will throw it out of tolerance.

Depends upon your routine.
>
> So why pay extra for 0.0002" tolerance in Starrett vs 0.002" tolerance
from
> Lee Valley? Beats me.

Depends on the intended purpose.

On Thu, 13 Jan 2005 00:09:13 GMT, "George E. Cawthon"
<[email protected]> vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

>Second about 1/128" Hell, breathing on the wood will make
>it move that much from just absorbing moisture. And working
>out the math, if you are 1/128" short you are truly a "hair"
>short or maybe "two hairs" short or more accurately you are
>one black and curly short. Oh yuck!

What's yuck about black and curly man? My wife has black curly hair on
her head. Seems OK to me <G>

On Fri, 14 Jan 2005 05:47:30 GMT, "George E. Cawthon"
<[email protected]> vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

>> What's yuck about black and curly man? My wife has black curly hair on
>> her head. Seems OK to me <G>
>
>I thought someone would descend to a lower level. ;-)

Aaah! That stuff between my toes.......

Charlie Self wrote:

Hi Charlie,

Especially when you consider that 200 years ago people were using wooden
planes, and big-slab wooden benches - which weren't leveled with a routah
and sled - to make furniture that is excellent by any standard.


> And anyone who REALLY gets their tools set up to .002" is way past where
> they need to be when working wood.
>
> Results on the best days are going to be within 1/64" or so, with the
> very, very, very occasional dip to 1/128". Unless you're making a damned
> small box, moving it from bedroom to kitchen when the dishwasher is in use
> will make it move nearly that much.
>
> With my eyesight as it is now (fairly good except for excessive floaters),
> I doubt I could see a difference between 0.0002" and 0.002" on my table
> saw table even if the straight edge would show it. And if I could, I'd
> still leave it alone.
>
> Charlie Self
> "One of the common denominators I have found is that expectations rise
> above that which is expected." George W. Bush

--
Saville

Replicas of 15th-19th century nautical navigational instruments:

http://home.comcast.net/~saville/backstaffhome.html

Restoration of my 82 year old Herreshoff S-Boat sailboat:

http://home.comcast.net/~saville/SBOATrestore.htm

Steambending FAQ with photos:

http://home.comcast.net/~saville/Steambend.htm

In article <[email protected]>, [email protected] (Charlie Self) wrote:
>
>And anyone who REALLY gets their tools set up to .002" is way past where they
>need to be when working wood.
>
>Results on the best days are going to be within 1/64" or so, with the very,
>very, very occasional dip to 1/128". Unless you're making a damned small box,
>moving it from bedroom to kitchen when the dishwasher is in use will make it
>move nearly that much.
>
>With my eyesight as it is now (fairly good except for excessive floaters), I
>doubt I could see a difference between 0.0002" and 0.002" on my table saw table
>even if the straight edge would show it. And if I could, I'd still leave it
>alone.

All of which is correct, but misses the point of the thread. The original post
asked, in essence, why is the Starrett more expensive, yet less accurate, than
the Lee Valley; this was shown to be a misconception. Whether the 2.5x greater
accuracy of the Starrett is needed for woodworking is a different discussion.

--
Regards,
Doug Miller (alphageek-at-milmac-dot-com)

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