# What is the best aluminum for heat sink?

wrote:

That would be 180 degrees, not 90.
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But 90 degrees to the mirror's surface, which is optically flat.
Cheers, James Arthur
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wrote:

Obtaining a square is easy. Take two EXACTLY equal length 'rods' or other suitable flat and true faced edge. Tie them together at one end, and separate the other end by exactly 1.4145926536 * the length used for the two faces. They will be precisely 90 apart.
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Well yes, Jasen Betts implied that (in sed) when he said "Pythagoras". But is that how reference squares are really made?
I can imagine checking a standard with Pythagoras, but you can't just bolt three rulers together. There are gotchas. Like, you need three perfect straight edges, and you have to mate their reference surfaces exactly.
If you try to bolt three pieces of precision-length bar stock to make a perfect reference square, you can imagine the inaccuracies that would result.
Cheers, James Arthur
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The following assumes that you have a surface plate of sufficient flatness. There are existing ways to make them starting with three of the same size, but I won't go into them here.
So -- start with a lathe and some steel perhaps about 4" diameter. Turn it to be a true cylinder -- measure the diameter at both ends and several other places near the center and make sure that they are all the same diameter (and use a toolpost grinder to get a really nice finish). Without moving it in the chuck, turn the end flat, recess all but about the outer 3/16", and then use the toolpost grinder to grind that outer rim truly flat. Part off the other end where it was held in a chuck as this is neither the right diameter. Ignoring the parting-off part, you have a cylindrical square. Set the ground rim end down on the surface plate, and you will have a reference which is as square as you were able to measure with the micrometers for the diameter of the workpiece. These are made commercially, but usually from hollow iron castings to minimize the weight. I have a couple of these of differing sizes and weights.
Brown & Sharpe used to offer one which had one end truly true, and the other a precise angle off, and a series of markings chemically etched into the cylinder to allow you to measure just how far off square you are -- measured in steps of 0.0002" up to 0.0012". The dimensions of this one are 6-1/4" high, 2-1/2" diameter, accuracy within 0.0001" and 6RMS surface finish. The part number was 599-558-6, and the price was \$160.00 back in 07/1972, when the catalog which I have in hand was printed.
Enjoy,         DoN.
--
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DoN. Nichols wrote:
[turn a 4" cylinder, recess all but a 3/16 rim on the base, finish & true the rim with toolpost grinder]

Thanks DoN, that's the quickest and easiest suggestion yet.
James Arthur
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Such an exercise is detailed in one of Guy Lautard's Bedside Readers. Both how to generate a reference square and how to check one. Neither one involved tubs of water(except for hardening) or mirrors. You DO have to have a true straight-edge first. For a rough check, with no other squares needed or available, you can take your straight straight- edge, put it on a piece of paper, park the square on top and draw a line the length of the perpendicular blade. Flip the square and repeat. The difference out of parallel is twice the offset of the end of the blade.
Also detailed was lapping a square and how to make a cylindrical square.
Stan
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snipped-for-privacy@prolynx.com wrote:

Thanks for the scoop and the references!
Cheers, James Arthur
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On Fri, 8 May 2009 10:51:35 -0700 (PDT), snipped-for-privacy@prolynx.com wrote:

Oh wow. Actual application for high school geometry for constructing a perpendicular bisector.
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I think the caliper jaws would be more useful for parallelism, and perpendicular was determined by comparison with a toolmakers square.

First, make a surface plate or three.
Then scrape three rectangular bars into straightedges against the surface plates.
Then choose an end of each of the three straightedges to be the perpendicular faces.
Scrape the three ends into conformity with one another while the straightedge faces are also on the same surface plate. The process is very much like the process by which one generates the surface plates.
I think this and related methods were originally invented by opticians to make prisms, the difference being that they ground things together rather than spotting and scraping.
Joe Gwinn
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Joseph Gwinn wrote:

I thought in SED that some variation of rubbing three cubes' faces against each other on a surface plate might do the trick, but I didn't press it.
The bottom surfaces of bars I-III are first scraped flat. Then, sliding on a surface plate, faces a-c are rubbed against each other in rotation, making their profiles square with their bottom surfaces and the surface plate. (Fig. 1)
---------------------------------------------------------
====== (view in Courier or other fixed font) FIG. 1 ===== unfinished edge / .-~-~--~-~-~-~-~-~-~-~--. .-~-~-~--~-~-~-~-~-~-~-~-. | | | | | I. a.| |b. II. | | | | | |_______________________| |________________________| \ straight edge .---~~~~~~~~~~~~~~~~~~~--. | | | III. c.| | | |________________________|
---------------------------------------------------------
Okay, so a, b, and c form right-angles to their straight-edged bottoms. Cool.
Now, if just rubbed together by hand, faces a-c are possibly rounded profiles, right?
--------------------------------------------------------- =====FIG. 2 ===== straight edge / --------. I. / ) ----------. / ) <~~~ a. (viewed from above) ----------' ---------------------------------------------------------
I'll have to ponder this a bit further to figure how to make all faces flat and square to each other.
Super accuracy from simple tools--elegant.
Thanks!
James Arthur
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Once you have two opposite faces flat and parallel, make a fixture with an indicator point directly above a similar-shaped stop. Push the block up against the stop and read the indicator. Invert the block you're making and repeat. The difference between the indicator readings is twice the squareness error of the end of the block over the distance between the point and the stop.
jsw
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On Sat, 9 May 2009 08:36:14 -0700 (PDT), Jim Wilkins

It's cool that you can generally do arbitrary-precision measurements of dimensionless properties with pretty much just patience. For example, you can match resistors to any precision at any ratio with simple equipment. Ditto weight and distance ratios.
John
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Jim Wilkins wrote:

Got it. So you make the first measurement like this:
(View in Courier or other fixed font)(angle exaggerated for clarity)
indicator __ / \_____ .-------. <~~ top is scraped flat |_____)/ | __/ / | / block | / | / | .-. '-------------' <~~~ bottom is scraped flat and parallel | | .----------------. | | | |<~ surface plate '-' '----------------' \ stop
then flip the block over, & make the 2nd measurement.
Slick.
Thanks, James Arthur
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wrote:

A block placed into the chuck of the lathe, can have a pretty damned flat face cut onto it, and a subsequent hand held lapping can be accurately performed on it. That makes one face true, and finely polished.
Then, it can be milled on the other face with a surface grinder or mill. A vertical mill would be nice as it would achieve a better surface quality than a horizontal mill would, and it would be kept more parallel to the bottom face. Back over to the lathe to mount up, and it should lap as true as the other face, which is a test of your upchucking capability. :-)
Now, you have two parallel faces, and if you mounted it into the lathe very carefully, the sides will be perpendicular to those two faces.
You could then continue upchucking different faces of the cube and facing them off with the lapping device you'll want to make for the tail stock of the lathe. :-)
I agree... upchucking is fun.
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pythagoras' theorem.
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Groan! Is that like when somebody says "ve have vays..." ?
I once worked in a place using a combination shear and punch, and when they first instructed me to weld jigging onto the work surface I got a big knot in my gut.
Cutting it off with an angle grinder to reset for the next part gave me a twisted gut too.
I quickly adapted, got quick at it and cycled through many dozens of different parts and jigs.
I am now back to thinking it was so very wrong.
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Greegor wrote:

Ouch! Groan back atcha!

Ah, the fine art of production. It's amazing how refined it is, and yet we continue refining it year after year: smaller, lighter, cheaper, faster.
It's inspiring.
Cheers, James Arthur
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wrote:

Iz it zafe?
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On Wed, 06 May 2009 18:00:36 GMT, James Arthur

I used to hang around an optics company that had a bunch of the slow wet grinding tables that made things flat. There is also an inherent (no external artifact) way to make perfect cubes, but I don't recall what it is. That shop was making the retroflector optics that one Apollo mission left on the moon, in a grungy shop behind the River Rondezvous bar at the foot of Carrolton Avenue, right near the levee, in New Orleans.
John