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Chariots of Fire

Keeping things parallel and square

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I  had a recent question about what I use in making 90 degree angles when cutting plastic.  Here are some of the tools and techniques you can use in doing that.  In the photo are the following:

A template for triangles, squares circles and hexagons.

An adjustable compass

A steel ruler in inches and millimeters

An Xacto square 3" x 4" marked off in 64ths

30/60/90 and 45/45/90 drafting triangles.  

These tools can be used in a number of ways to make cuts square and true.

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Above I have a piece of plastic sheet stock that is laid on one side and the Xacto square laid next to it.  Holding them together it is easy to draw a line anywhere on the plastic that is 90 degrees to the edge that is laying flat.  Never assume that you have a 90 degree edge on a plastic sheet.  It may look square but it might be off just enough so if you try and make a line 90 degrees to the edge lying flat it will not be parallel to the edge that is standing up.  Check it to be sure and mark it off so that you can trim it to 90 degrees.

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Another way is to use two triangles.  In this case I chose to make a line that is 90 degrees to the two parallel lines and to do so at the tick mark.  Start by laying one triangle against the horizontal line.  Hold it there and put a second triangle against the slanted side of the first triangle.  Hold the second triangle firmly and slide the first one down until the right hand edge is at the tick mark and draw the line.  This works because the triangle has a 90 degree corner.

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Don't have triangles or a square?  Use a compass.

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Here we start with laying out a horizontal line and want to make a perpendicular line to it a #1.  Open the compass to any comfortable space and draw a tick mark on each side of mark #1 (2).  Now open up the compass some more so that the space between the point and the pencil lead is greater than between #1 and #2. 

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Put the point of the compass on #2 left and draw an arc.  Then put the compass point on #2 right and draw another arc so that they cross at #3.  Connect the point where the arcs cross with the tick mark at #1.  The line you draw will be 90 degrees to the horizontal line.

As will any measuring.  Measure twice and if you are not sure measure again.  Don't be the guy that measures twice and finds that it is "still too short"!!😁

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That reminds me of the basic geometry lessons in school (elementary?) . And we thought back then that we would never find real-life application for all those things we learned. :D

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Drafting was one of the first classes I took in College in the 60's. Learned all this at a drafting table. Too bad they don't teach drafting the old fashion way anymore.  Now days it is just "plug it " into the computer and print it out.  Computers are ruining our minds.  Making it too easy. 🤪

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Its important to know how to do the process manually. For many years the only way to do math calculations was paper and pencil or a slide rule. With a slide rule you needed to estimate your answer. Not understanding the basic process Can only lead to nonsensical answers. Plus if the power is off you won't be able to get the answer you need.

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Paper, pencil and a slide rule.... That's how we landed on the moon....🤪 

....and back home again.. 😁👍

Edited by Deuces ll

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2 hours ago, Deuces ll said:

Paper, pencil and a slide rule.... That's how we landed on the moon....🤪 

....and back home again.. 😁👍

Can you imagine the stack of blueprints that made up the Saturn V, LEM, and crew module?.  I wonder if they were ever digitized or if they are rotting away in a crate in some warehouse. 😬

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On 10/19/2020 at 11:06 PM, Pete J. said:

Can you imagine the stack of blueprints that made up the Saturn V, LEM, and crew module?.  I wonder if they were ever digitized or if they are rotting away in a crate in some warehouse. 😬

They say we now have more computing power in our cell phones than they had back when we sent the astronauts to the moon.  And they had a whole room full of computer hardware!

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and battleships.   Also learned drafting in high school on a board

  Still have the drawings

Use a small adjustable carpenter's square to check for squareness on truck chassis.

 

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8 hours ago, Chariots of Fire said:

They say we now have more computing power in our cell phones than they had back when we sent the astronauts to the moon.  And they had a whole room full of computer hardware!

Not true!  Your watch has far more computing power.  I took my first course in programing in 1967.  We used a Philco 2000.  One of the most advanced computers at the time.  We could only run rudimentary calculations using programs written on punch card, batch processed over night.  A hundred cards(lines of code) was a huge program.  I recall my instructor starting the class with this line.  Computers are not smart.  They are 3 year old idiots who can think really really fast and only do precisely what you tell them.  

  The computers that were used for the space program were for telemetry only.  They were an outgrowth of computers that the Army developed to compute artillery trajectory tables.  There was no CAD.  The design and construction was all done with pencils on paper and blueprints. 

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1 hour ago, Pete J. said:

Not true!  Your watch has far more computing power.  I took my first course in programing in 1967.  We used a Philco 2000.  One of the most advanced computers at the time.  We could only run rudimentary calculations using programs written on punch card, batch processed over night. 

Philco?  The same company that produced TVs for the consumer market?

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Not my watch!  It still only tells me the time!😆  And the day of the week if I adjust it for 30 day months and for February!

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38 minutes ago, Chariots of Fire said:

Not my watch!  It still only tells me the time!😆  And the day of the week if I adjust it for 30 day months and for February!

I don’t even own a watch! My smartphone has one

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8 hours ago, peteski said:

Philco?  The same company that produced TVs for the consumer market?

Yup, thing was the size of a house.  Back then there were only a few companies making mainframes.  Philco was one of them. I suspect that this was a hold over from WWII when they were a huge government contractor for electronics. 

Just did a quick search for the Philco 2000.  It was the first highly transistorized high speed computer.  They were also the leading manufacture of transistor radios at the time.  Pretty much took Texas Instruments baby and ran with it. 

Edited by Pete J.

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Nice trick with the two triangles Charles, I have not come across that one before. Ok,  Back to layout basics... I need to make a 90 degree angle from 2- 45 degree bends (mitres). I made a simple jig bent from a sheet metal strip. It is bent at 90 degrees- 22.5 degrees = 67.5 degrees. I clamped it in the vise along with a large file. Slide the two edges to be joined against the file at the pre-determined angle and the joint (in this case) will be a perfect 45 degree  angle. Once you have the proper angle bent as a guide, repeating the mitre angle is easy!

Edit: A flat piece of metal in place of the file with your choice of sandpaper clamped between it and the angle may work even better.

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Edited by NOBLNG

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Now that's a great tip! And how did you determine the 67.5 deg for bending?  I understand the math but how was it accomplished to make the jig?

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I have a small (12”) press brake/shear/roller that I used to bend the metal. It could possibly be done carefully with just a bench vise and a hammer?😬 To get the angle bang on I used a combo square/protractor. I used the same method with a compass that you used for the perpendicular line to split the mitre angles when laying out these fenders. Here I needed 180 degrees from six 30 degree mitres.

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Edited by NOBLNG

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A good quality tool like the one above can get quite expensive, in the high $200 range and may be more that what we need for modeling.  Starrett makes a very precise protractor that can also be used for under $75.  I got one for working on my benchtop mill and lathe.  Very nice tool for the money. 

By the way, when working on the small scales that we do, precision is everything.  Good measuring tools will save a ton of frustration.  Don't be afraid to spend the money for quality when it comes to measuring tools. 

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On 10/22/2020 at 4:28 AM, peteski said:

Philco?  The same company that produced TVs for the consumer market?

The same company that made AM radios for the Ford Maverick in 1972.... I remember that car very well...

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11 hours ago, Deuces ll said:

The same company that made AM radios for the Ford Maverick in 1972.... I remember that car very well...

This is the Philco  radio I remember.  Lots of them around when I was a kid.(pre TV).Vintage Philco Radio/Turntable

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There is no substitute for well made tools. I still have some excellent tools that I bought when i was an apprentice way back in the early 1960's.

Micrometers by Moore & Wright, and Starrett, a combination set made by Brown And Sharpe, Engineers rules by Rabone Chesterman and General, and a Vernier Caliper made by a Swedish company named Eskilstuna.

Have used them all my working life, and still use them today on my scratch built modelling projects and various DIY jobs.

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