Marking sheetmetal

[Michael Horowitz]

I want to mark sheetmetal for bending.
Can't use a scribe because I'll weaken the metal.
Magic Marker is too thick.
Pencil doesn't show.
What do you use? - Mike

[Morgans[_2_]]

"Michael Horowitz" > wrote in message
...
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

Fine point gel (.5mm) Pentel ink pens.
--
Jim in NC

[Morgans[_2_]]

"Michael Horowitz" > wrote in message
...
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

Pencil is also not to be used because the graphite will combine chemically
with some types of sheet metal, and make it weak on the line. I don't
recall for sure which type, but I think aluminum.
--
Jim in NC

[Scott[_1_]]

Fine point sharpie magic marker.

Scott


Michael Horowitz wrote:
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

[stol]

Michael Horowitz wrote:
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

Sharpies work great, come in several line widths and wipe off easy... I
used dozens while building the "beast" of mine..


Ben
www.haaspowerair.com

[Stealth Pilot]

On Sat, 16 Sep 2006 11:05:24 +0000, Scott >
wrote:

>Fine point sharpie magic marker.
>
>Scott
>
>
>Michael Horowitz wrote:
>> I want to mark sheetmetal for bending.
>> Can't use a scribe because I'll weaken the metal.
>> Magic Marker is too thick.
>> Pencil doesn't show.
>> What do you use? - Mike

1st choice as scott says.
2nd choice, stick some tape on it and mark the tape. remove after
bending. btw leaving on the protective plastic sheet is just as
effective.

[Stache]

Michael Horowitz wrote:
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

>From an old gray hair tin bender, use a #2 pencil it will show. To get
the proper bend allowance and set back lilne I use a #2 pencil some
will use a Graphite pencil, but it is very ligh. I would suggest
wiping the sheetmetal surface clean then the pencil will be more clear.

Stache

[flybynightkarmarepair]

Michael Horowitz wrote:
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

I use a fine point Sharpie, me, but I get annoyed when they dry out.
Before Sharpies, there were metal marking pencils, developed for just
this purpose, with non-corrosive pigments. You can still get them:

http://www.office1000.com/discount/pencils-marking.html

[Morgans[_2_]]

"Michael Horowitz" > wrote in message
...
> I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

What type of metal are you bending?
--
Jim in NC

[RST Engineering]

Depends entirely on what tolerance you are marking/cutting/bending to. I
want my students to be able to cut/bend to ten thousandths accurately and
the only way to do that is to scribe. THen again, we are only building
electronic chassis out of aruminum (5052H32) and we don't worry much about
it cracking under vibration.

When I build small airplane parts and have to hold that sort of tolerance,
I'll lay on a thin coat of machinist's bluing and scribe very carefully so
that I only cut the paint and not the aluminum itself.

Doing it on a wholesale level, I might be tempted to lay down a spray paint
of some sort in a dark color and scribe the paint, then wash the paint off
with solvent.

I've never used one, but I've seen professional tinbenders use a special
metal-marking pencil that does NOT corrode or otherwise weaken the surface
of the metal.

Jim


"Michael Horowitz" > wrote in message
...
>I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike

[Reggie]

RST Engineering wrote:
> Depends entirely on what tolerance you are marking/cutting/bending to. I
> want my students to be able to cut/bend to ten thousandths accurately and
> the only way to do that is to scribe. THen again, we are only building
> electronic chassis out of aruminum (5052H32) and we don't worry much about
> it cracking under vibration.
>
> When I build small airplane parts and have to hold that sort of tolerance,
> I'll lay on a thin coat of machinist's bluing and SCRIBE very carefully so
> that I only cut the paint and not the aluminum itself.
>
>************************************************** *****************88
Keep your cotton picking hands / scribe OFF any aeroplane!!!

Stick to Non aviation L'etronics....

If you bought a chassis from budd, you would be ****ed if they
cracked..

Reggie

[Don W]

RST Engineering wrote:
> Depends entirely on what tolerance you are marking/cutting/bending to. I
> want my students to be able to cut/bend to ten thousandths accurately and
> the only way to do that is to scribe.

If you can bend aluminum to a 1/10,000" tolerance
you are the MAN. You must have some really
talented students.

When I was building parts we could machine to +/-
..001" and grind or polish to +/- .0005" on a very
expensive part. Likewise for drilling you could
drill to +/-.001 and ream and polish to +/-.0003
or so.

A very fine tip pencil leaves a line that is .004"
wide--which is also the thickness of a piece of
20# bond paper. A very fine tipped scribe
probably leaves a line in the Dyekem that is .002"
wide. You would have to measure it under a
microscope to be sure.

I'm really pleased to hear that technology has
progressed such that sheet metal can be bent to a
tolerance of +/- .0001". That is 2.54 microns
which is down in the area of the metal linewidths
of the semiconductor chips in your computer.

Wow, who would have thought.

or maybe you meant .010?? ;-)

Don W.

[RST Engineering]

"Don W" > wrote in message
. ..
>
> RST Engineering wrote:
>> Depends entirely on what tolerance you are marking/cutting/bending to. I
>> want my students to be able to cut/bend to ten thousandths accurately and
>> the only way to do that is to scribe.
>
> If you can bend aluminum to a 1/10,000" tolerance you are the MAN. You
> must have some really talented students.

That's not the English of it. Ten thousandths is far different from one ten
thousandth. Ten of the little thousandths rather than one of the tenth part
of a thousandth. 0.010 as opposed to 0.0001. Two orders of magnitude
difference. Get it?


A very fine tipped scribe
> probably leaves a line in the Dyekem that is .002" wide. You would have
> to measure it under a microscope to be sure.

An optical comparator would tell me quite easily.


>
> or maybe you meant .010?? ;-)


That's what I said and what I meant. {;^0

Jim

[RST Engineering]

Who in the hell are you? Oh, I see, a googlegroups groupie. That explains
it.

Jim



"Reggie" > wrote in message
oups.com...


>>
>>************************************************** *****************88
> Keep your cotton picking hands / scribe OFF any aeroplane!!!
>
> Stick to Non aviation L'etronics....
>
> If you bought a chassis from budd, you would be ****ed if they
> cracked..
>
> Reggie
>

[Orval Fairbairn]

In article . com>,
"Stache" > wrote:

> Michael Horowitz wrote:
> > I want to mark sheetmetal for bending.
> > Can't use a scribe because I'll weaken the metal.
> > Magic Marker is too thick.
> > Pencil doesn't show.
> > What do you use? - Mike
>
> >From an old gray hair tin bender, use a #2 pencil it will show. To get
> the proper bend allowance and set back lilne I use a #2 pencil some
> will use a Graphite pencil, but it is very ligh. I would suggest
> wiping the sheetmetal surface clean then the pencil will be more clear.
>
> Stache

NOT ON ALUMINUM! The graphite from the #2 pencil will galvanically
corrode aluminum. Use a Sharpie and clean with either lacquer thinner or
denatured alcohol after you are done.

[Jim Carriere]

stol wrote:
> Sharpies work great, come in several line widths and wipe off easy...

Sharpies wipe off nicely with denatured alcohol and paper towel, which
also cleans up wet epoxy, the manufacturing markings on sheet metal,
Permatex, regular dirt... and isn't excessively toxic.

[JJS]

"Michael Horowitz" > wrote in message
...
>I want to mark sheetmetal for bending.
> Can't use a scribe because I'll weaken the metal.
> Magic Marker is too thick.
> Pencil doesn't show.
> What do you use? - Mike
>
Word on the RV lists is that blue fine tip Sharpies are the way to go. For
some reason the blue ink lasts longer. Sharpies' lives can be extended by
injecting lacquer thinner with a needle and syringe once they start running
out of ink. Van's says that for a mark that needs to show through primer it
is ok to use an electric "vibrating" engraving pencil in spite of
admonitions against marking with a scribe.

Joe Schneider
Cherokee 8437R
RV-7 in the works



----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Don W]

RST Engineering wrote:
> "Don W" > wrote in message
> . ..
>
>>RST Engineering wrote:
>>
>>>Depends entirely on what tolerance you are marking/cutting/bending to. I
>>>want my students to be able to cut/bend to ten thousandths accurately and
>>>the only way to do that is to scribe.
>>
>>If you can bend aluminum to a 1/10,000" tolerance you are the MAN. You
>>must have some really talented students.
>
>
> That's not the English of it. Ten thousandths is far different from one ten
> thousandth. Ten of the little thousandths rather than one of the tenth part
> of a thousandth. 0.010 as opposed to 0.0001. Two orders of magnitude
> difference. Get it?

yeah, I got it the first time. Just having a
little fun with you. Was it good for you too?

That's why some people call it ten mils, or .010",
or... sometimes ten one thousands of an inch, etc.


Don W.

[Drew Dalgleish]

On Sat, 16 Sep 2006 20:37:39 -0500, "JJS" <jschneider@re
movecebridge.net> wrote:

>
>"Michael Horowitz" > wrote in message
...
>>I want to mark sheetmetal for bending.
>> Can't use a scribe because I'll weaken the metal.
>> Magic Marker is too thick.
>> Pencil doesn't show.
>> What do you use? - Mike
>>
>Word on the RV lists is that blue fine tip Sharpies are the way to go. For
>some reason the blue ink lasts longer. Sharpies' lives can be extended by
>injecting lacquer thinner with a needle and syringe once they start running
>out of ink. Van's says that for a mark that needs to show through primer it
>is ok to use an electric "vibrating" engraving pencil in spite of
>admonitions against marking with a scribe.
>
>Joe Schneider
>Cherokee 8437R
>RV-7 in the works
>
>
Cumon Joe a shapie costs a dollar do we really need to make it last
longer ?
>
>----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
>http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
>----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Morgans[_2_]]

"Drew Dalgleish" > wrote

> Cumon Joe a shapie costs a dollar do we really need to make it last
> longer ?

They don't last very long when you forget and leave the cap off, do they?
<g>

There is a version of a marker that clicks like a retractable ink pen,
though, and they work pretty good. The problem is that the point is not
nearly as sharp.

Anyone ever try to sharpen a sharpie? It seems like there should be a way,
somehow.
--
Jim in NC

[.Blueskies.]

"Don W" > wrote in message ...
: RST Engineering wrote:
: > "Don W" > wrote in message
: > . ..
: >
: >>RST Engineering wrote:
: >>
: >>>Depends entirely on what tolerance you are marking/cutting/bending to. I
: >>>want my students to be able to cut/bend to ten thousandths accurately and
: >>>the only way to do that is to scribe.
: >>
: >>If you can bend aluminum to a 1/10,000" tolerance you are the MAN. You
: >>must have some really talented students.
: >
: >
: > That's not the English of it. Ten thousandths is far different from one ten
: > thousandth. Ten of the little thousandths rather than one of the tenth part
: > of a thousandth. 0.010 as opposed to 0.0001. Two orders of magnitude
: > difference. Get it?
:
: yeah, I got it the first time. Just having a
: little fun with you. Was it good for you too?
:
: That's why some people call it ten mils, or .010",
: or... sometimes ten one thousands of an inch, etc.
:
:
: Don W.
:

How about 1 hundredth of an inch?

[Dave[_2_]]

".Blueskies." > wrote in message
m...

> How about 1 hundredth of an inch?
>

That was my thought when I read the whole silly thread. The problem is that
hundreths are not a "popular" dimension. It seems that in popular notation
the instant you segment an inch you are dealing in thou. So, asking someone
to remain within "ten thou" is instantly understood by almost anyone. By the
time you go the nest step and get into tenths people usually revert to
fractions and start dealing in /32s or /16s.

In any case stay away from pencils, I'm not that careful with a scribe, and
sharpies are common. I've got two sitting on my desk.

[Jim Logajan]

Orval Fairbairn > wrote:
> NOT ON ALUMINUM! The graphite from the #2 pencil will galvanically
> corrode aluminum. Use a Sharpie and clean with either lacquer thinner or
> denatured alcohol after you are done.

Why can't you just clean off the pencil marks?

Also, doesn't a galvanic reaction require an electrolyte between the
metals, so if you didn't erase or clean off the pencil mark but primed
and/or painted over the aluminum surface, no salt water or other
electrolyte could get in there to produce the galvanic reaction?

[Morgans[_2_]]

"Jim Logajan" > wrote
>
> Why can't you just clean off the pencil marks?
>
> Also, doesn't a galvanic reaction require an electrolyte between the
> metals, so if you didn't erase or clean off the pencil mark but primed
> and/or painted over the aluminum surface, no salt water or other
> electrolyte could get in there to produce the galvanic reaction?

The danger of using pencil for aluminum is not a "maybe" kind of problem.
The pencil works it's way into the molecules, and can not be cleaned off,
completely. It is an accepted fact, known to materials engineers as a
unacceptable practice. I don't know if it is really a galvanic reaction, or
something else, but people *way* smarter than you and me have proven the
problem. The metal will become brittle at the pencil line, and with enough
stress, *will* cause a crack to start.

Why risk it? Why argue? Use something else to mark your aluminum. Period.
--
Jim in NC

[Orval Fairbairn]

In article >,
"Morgans" > wrote:

> "Jim Logajan" > wrote
> >
> > Why can't you just clean off the pencil marks?
> >
> > Also, doesn't a galvanic reaction require an electrolyte between the
> > metals, so if you didn't erase or clean off the pencil mark but primed
> > and/or painted over the aluminum surface, no salt water or other
> > electrolyte could get in there to produce the galvanic reaction?
>
> The danger of using pencil for aluminum is not a "maybe" kind of problem.
> The pencil works it's way into the molecules, and can not be cleaned off,
> completely. It is an accepted fact, known to materials engineers as a
> unacceptable practice. I don't know if it is really a galvanic reaction, or
> something else, but people *way* smarter than you and me have proven the
> problem. The metal will become brittle at the pencil line, and with enough
> stress, *will* cause a crack to start.
>
> Why risk it? Why argue? Use something else to mark your aluminum. Period.

And --- DO NOT USE A SCRIBE!!! Scribes, no matter how careful you are,
will damage the aluminum and create stress raisers. They can also damage
the Alclad coating and provide a path for corrosion.

It is not a matter of IF a piece will fail at a scribe line, but WHEN --
due to fatigue.

The admonition against pencils in aluminum shops also holds for engine
shops. The easiest way to fail a hot steel part is to mark it with a
lead pencil. The steel glows red hot and absorbs the carbon from the
mark, creating an instant stress concentration. An old friend related
how he saw a Lockheed Constellation exhaust manifold with a crack in the
shape of "OK", due to lead pencil.

[[email protected]]

Drew Dalgleish wrote:

> Cumon Joe a shapie costs a dollar do we really need to make it last
> longer ?

Sure, it's only a buck. But it only quits at night or on the
weekend when the stores that sell Sharpies are all closed.

Dan

[[email protected]]

Orval Fairbairn wrote:

> The admonition against pencils in aluminum shops also holds for engine
> shops. The easiest way to fail a hot steel part is to mark it with a
> lead pencil. The steel glows red hot and absorbs the carbon from the
> mark, creating an instant stress concentration. An old friend related
> how he saw a Lockheed Constellation exhaust manifold with a crack in the
> shape of "OK", due to lead pencil.

The steel absorbs the carbon and becomes brittle, whereupon it
cracks after being flexed while in use. The carbon doesn't cause a
stress concentration; that's caused by scratches or nicks that
interfere with the lines of stress in a metal part. A nick in a metal
propeller is an excellent example of a stress riser, as is a scratch in
an aluminum skin.
For a steel to be hardenable, it needs a carbon content of at
least 0.4% carbon. That's not much. Few steels have as much as 1%. 0.6%
is commonly found in hand tools and spring steel, and a steel having 1%
might be found in ball or roller bearings. A pencil mark could raise
the local carbon content a lot, probably to much more that 1%
,especially on a hot item like an exhaust manifold where the heat
allows rapid and deep absorption of the carbon.
Aircraft tech schools will teach you to leave the pencils at
home when working on aluminum.

Dan

[Peter Dohm]

>
> Drew Dalgleish wrote:
>
> > Cumon Joe a shapie costs a dollar do we really need to make it last
> > longer ?
>
> Sure, it's only a buck. But it only quits at night or on the
> weekend when the stores that sell Sharpies are all closed.
>
> Dan
>
It also quits just out revenge because you failed to cap it securely--for a
ridiculously short period of time. :-(

The obvious solution is to stock spares.

Peter

[Jim Logajan]

"Morgans" > wrote:
> "Jim Logajan" > wrote
>>
>> Why can't you just clean off the pencil marks?
>>
>> Also, doesn't a galvanic reaction require an electrolyte between the
>> metals, so if you didn't erase or clean off the pencil mark but
>> primed and/or painted over the aluminum surface, no salt water or
>> other electrolyte could get in there to produce the galvanic
>> reaction?
>
> The danger of using pencil for aluminum is not a "maybe" kind of
> problem.

I'm not doubting galvanic reaction involved at all. Nor the inadvisability
of drawing a pencil line and leaving it there.

> The pencil works it's way into the molecules, and can not be
> cleaned off, completely.

This is the claim that bothers me. But assume it is true. I would expect
the rate of corrosion to be roughly proportional to the ratio of the
size of the exposed cathodic material (graphite) relative to the size
anodic material (aluminum). This ratio is usually expressed C/A, (where
C is the cathode surface area and A is the anode surface area). And I
did find a source on the net that verifies that [1]. So even if one
couldn't clean it all off, the corrosion rate would be greatly reduced.
And if the surface were sealed before any electrolyte (e.g. salt
water) could be introduced, no reaction would take place.

> Why risk it?

Not asking anyone to risk anything.

> Why argue?

Because rules of thumb are okay when deeper understanding takes too long
to impart to the practitioner, but understanding the deeper nature of
the problem allows so much more to be accomplished.

[1] http://www.ocean.udel.edu/mas/masnotes/corrosion.pdf

[DonMorrisey]

At the risk of beating this subject to death, use a sharpie, however a
Fine Point Sharpie is too thick. An Ultra-Fine Point Sharpie makes a
line approx 1 MM in width.

Don...

[J.Kahn]

Morgans wrote:
> "Jim Logajan" > wrote
>> Why can't you just clean off the pencil marks?
>>
>> Also, doesn't a galvanic reaction require an electrolyte between the
>> metals, so if you didn't erase or clean off the pencil mark but primed
>> and/or painted over the aluminum surface, no salt water or other
>> electrolyte could get in there to produce the galvanic reaction?
>
> The danger of using pencil for aluminum is not a "maybe" kind of problem.
> The pencil works it's way into the molecules, and can not be cleaned off,
> completely. It is an accepted fact, known to materials engineers as a
> unacceptable practice. I don't know if it is really a galvanic reaction, or
> something else, but people *way* smarter than you and me have proven the
> problem. The metal will become brittle at the pencil line, and with enough
> stress, *will* cause a crack to start.
>
> Why risk it? Why argue? Use something else to mark your aluminum. Period.


I've always puzzled over why John Thorp called for using a pencil to
mark lines in his "building the T-18" articles from the mid 60s. Surely
they know about it then?

John

[RST Engineering]

You are kidding, of course? You are marking a line 40 mils wide and
expecting a piece to come out to 20 mils or better accuracy?

Jim



"DonMorrisey" > wrote in message
ups.com...
>
> At the risk of beating this subject to death, use a sharpie, however a
> Fine Point Sharpie is too thick. An Ultra-Fine Point Sharpie makes a
> line approx 1 MM in width.
>
> Don...
>

[RST Engineering]

Because he knows what in the hell he is talking about?

Jim



"J.Kahn" > wrote in message
.. .


>
>
> I've always puzzled over why John Thorp called for using a pencil to mark
> lines in his "building the T-18" articles from the mid 60s. Surely they
> know about it then?
>
> John

[Montblack[_1_]]

("RST Engineering" wrote)
> You are kidding, of course? You are marking a line 40 mils wide and
> expecting a piece to come out to 20 mils or better accuracy?


If the line were 20 mils thick, where would you cut? The middle of the line?
The edge of the line?

But yes, a thin line is nicer.


Montblack
"Good enough. No one in the front row will ever notice it."
Theater set construction motto! <g>

[Gig 601XL Builder]

"Montblack" > wrote in message
...
> ("RST Engineering" wrote)
>> You are kidding, of course? You are marking a line 40 mils wide and
>> expecting a piece to come out to 20 mils or better accuracy?
>
>
> If the line were 20 mils thick, where would you cut? The middle of the
> line? The edge of the line?
>
> But yes, a thin line is nicer.
>
>


When I started building I made up my on rule so I'd know which side to cut.
I always cut on the left edge of the mark. My reasoning is because I'm right
handed I will be holding the straight edge with my left hand and marking
with my right. With a very few exceptions this rule has served me well.

If I think there will be a question I put a little < on the right(as opposed
to left) side.

[Ernest Christley]

RST Engineering wrote:
> You are kidding, of course? You are marking a line 40 mils wide and
> expecting a piece to come out to 20 mils or better accuracy?
>
> Jim
>
>
>
> "DonMorrisey" > wrote in message
> ups.com...
>> At the risk of beating this subject to death, use a sharpie, however a
>> Fine Point Sharpie is too thick. An Ultra-Fine Point Sharpie makes a
>> line approx 1 MM in width.
>>
>> Don...
>>
>
>

And if you could put the bend within 10 mils of where you intended every
time, would anyone care?

If the designer calls for that amount of accuracy in anything other than
bearings, it's time to find a new designer. I was told by a old-time
sheet metal worker that unless the plans state otherwise, standard
accuracy requirements are 1/32". That's plus or minus .03125 in either
direction for a .0625" window.

On parts that I do want to cut straight because I want them to be
pretty, I mark with a sharpie against a metal ruler, then aim for the
side of the line. The metal ruler limits where the sponge on the tip of
the marker can go.

[Ebby]

I take needle nose pliers and pull the point out about an 1/8 in or so then
use my razor knife to repoint the wick. Works for awhile and the wick is
over an inch long so it still. hmmmm. well it still wicks!

"Ebby"
Hatz Classic s/n37
Camden, NY

"Morgans" > wrote in message
...
>
> "Drew Dalgleish" > wrote
>
>> Cumon Joe a shapie costs a dollar do we really need to make it last
>> longer ?
>
> They don't last very long when you forget and leave the cap off, do they?
> <g>
>
> There is a version of a marker that clicks like a retractable ink pen,
> though, and they work pretty good. The problem is that the point is not
> nearly as sharp.
>
> Anyone ever try to sharpen a sharpie? It seems like there should be a
> way,
> somehow.
> --
> Jim in NC
>

[RST Engineering]

"Ernest Christley" > wrote in message
m...
> RST Engineering wrote:
>> You are kidding, of course? You are marking a line 40 mils wide and
>> expecting a piece to come out to 20 mils or better accuracy?
>>
>> Jim
>>
>
> And if you could put the bend within 10 mils of where you intended every
> time, would anyone care?

I care very much. If you got a chassis from me and it had 20 mil gaps in
the corners, you'd think I was the sloppiest designer in the world. All my
freshman students bend within 10 mils on everything to pass the course.
Most of them can hold 5 if they try.



>
> If the designer calls for that amount of accuracy in anything other than
> bearings, it's time to find a new designer.

I *BEG* your pardon? In my part of the world, 0.0 is within 50 mils, 0.00
within 20 mils and 0.000 within 5 mils.

Jim

[Ernest Christley]

RST Engineering wrote:
> "Ernest Christley" > wrote in message
>> And if you could put the bend within 10 mils of where you intended every
>> time, would anyone care?
>
> I care very much. If you got a chassis from me and it had 20 mil gaps in
> the corners, you'd think I was the sloppiest designer in the world. All my
> freshman students bend within 10 mils on everything to pass the course.
> Most of them can hold 5 if they try.
>
>

Oh, no. Now you done gone and did it.

First, I need to make sure we're talking apples to apples. A mil is
1/1000th inch. Consulted http://www.onlineconversion.com/length_all.htm
just to make sure.

1 mil = 0.001 inch

I have here in my hot little hands (queue paper rattling for the ditto
heads) one gen-you-wine "RST-443 Panel Mount Intercom", the serial
number being 1014, which went together perfectly and works wonderfully.
I LIKE it, and you can't have it back. Starting at the front right
corner and proceeding counter-clockwise, the gaps in the bends on the
lower half of the chasis measure .020, .030, .032, .035. The bends in
the upper half required a different technique. The edge of an envelope
fit loosely in the gap of the rear corner bends, the envelope measuring
..010.

We must be talking different measurements; either that, or I have
extremely low expectations and you're headed out to chew some hides in
your quality control department. 'Cause, I think this box is tighter
than a cheerleaders butt.

> [i]
>> If the designer calls for that amount of accuracy in anything other than
>> bearings, it's time to find a new designer.
>
> I *BEG* your pardon? In my part of the world, 0.0 is within 50 mils, 0.00
> within 20 mils and 0.000 within 5 mils.
>

I have only a couple measurements on my set of plans that call for a
specific tolerance. One is for the pins locking the gear leg halves
together. The other is for the wing lock pin. The rest are just
measurements with the smallest being with 1/16". Everything broken down
into feet, inches and fractional inches. But no "plus or minus"
anywhere. So I asked a recently retired machine shopman and sheetmetal
worker, because, heh, if you can't trust somebody that's been doing it
40yrs, who can you trust? He told me 1/32" if not specified. Does the
difference come down to how the numbers are specified? Fractional
inches resolve to 1/32, and decimal inches have the tolerances you state?

[Dave[_2_]]

"Ernest Christley" > wrote in message
m...
He told me 1/32" if not specified. Does the
> difference come down to how the numbers are specified? Fractional inches
> resolve to 1/32, and decimal inches have the tolerances you state?

I've watched this thread with some interest, I like being accurate but I'm
realistic. I have no doubt that Jim Knows what he's talking about. On the
other hand I'm fairly sure I can live with the accuracy that a Sharpie
affords almost any time. The most accurate project I've had recently was
replacing an engraved bezel. it had to inlay with no gaps and had four holes
for push studs. I took no measurements at all. I simply filed to shape, no
gaps, no slop.

[.Blueskies.]

"Ernest Christley" > wrote in message m...
: RST Engineering wrote:
:: >
: > I *BEG* your pardon? In my part of the world, 0.0 is within 50 mils, 0.00
: > within 20 mils and 0.000 within 5 mils.
: >
:
: I have only a couple measurements on my set of plans that call for a
: specific tolerance. One is for the pins locking the gear leg halves
: together. The other is for the wing lock pin. The rest are just
: measurements with the smallest being with 1/16". Everything broken down
: into feet, inches and fractional inches. But no "plus or minus"
: anywhere. So I asked a recently retired machine shopman and sheetmetal
: worker, because, heh, if you can't trust somebody that's been doing it
: 40yrs, who can you trust? He told me 1/32" if not specified. Does the
: difference come down to how the numbers are specified? Fractional
: inches resolve to 1/32, and decimal inches have the tolerances you state?

Where I work , unless otherwise stated, we tolerance to:
Fractions ±1/64
0.0 ± 0.010 (10 mils)
0.00 ± 0.005 (5 mils)
0.000 ± 0.001 (1 mil)
We do make assemblies where we hold clearances of 50 micro-inches (µin) (Oh no, not another one!)

[RST Engineering]

Blueskies, you and I are in the same world. When something finished product
is only six inches long with 4 bends and four corner notches, if you can't
hold ten mils your product looks like it was built with Bondo.

As for Mr. CHristly's measurements (and I'm glad he likes the little box; we
sure sell a hell of a lot of them) when he doesn't have the original
dimensioned print in front of him, and is making measurements with
envelopes, how he can say a measurement is off by so many mils without
knowing what it is SUPPOSED to be is beyond me.

If he is referring to the corner gap, I just went out and looked at a sample
of 10 from the last batch of 100. THe corners are water-tight to the point
where I can't see sky through them. How he has a 30 mil gap in his is
somewhat of a mystery.

Jim




".Blueskies." > wrote in message
...
>
> "Ernest Christley" > wrote in message
> m...
> : RST Engineering wrote:
>
> Where I work , unless otherwise stated, we tolerance to:
> Fractions ±1/64
> 0.0 ± 0.010 (10 mils)
> 0.00 ± 0.005 (5 mils)
> 0.000 ± 0.001 (1 mil)
> We do make assemblies where we hold clearances of 50 micro-inches (µin)
> (Oh no, not another one!)
>
>
>