CARDBOARD SLIDE RULE

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About: Hello Everyone! I am a GrandParent that loves to build “things” and I am also an engineer!

HELLO EVERYONE!

As an “old school engineer”, I studied the first 3 years of my engineering degree with a slide rule. I witness how the first electronic calculator introduced in 1972 (HP35) almost immediately caused the sudden death of my calculating tool. Even so, I used my slide rule until 1975 and have always been amazed by it and how it works... It has a genius design! I still have my original slide rule and even use it from time to time... (see picture)

Later on, I became a college professor and was always amazed by the difficulties my student had for “feeling” the numbers. As an example I could ask them estimate the volume of a glass of water and will get answers in the order of several cubic meters! When challenged they will immediately reply showing me their calculator “Look! It is the answer I get with my calculator.”

I am now convinced of how useful is a slide rule and started to look around if any is available and found out they do not make them anymore. Simple electronic calculators have such a low price that nobody seems to be interested in a slide rule that cannot add or subtract. ... by the way, adding and subtracting are the only operations a slide rule cannot do. For learning these operations, an abacus is the best!


A slide rule would help to have better “thinking students”, I decided to built one! Instructables has at least 2 similar projects posted. I study them them and decided to built a simple, cheap and challenging slide rule that would be of use for students of middle and high schools. Even better if it is a project they could do with their teacher!


Many thanks to the authors of these instructables!
https://www.instructables.com/id/Custom-Slide-Rule...
https://www.instructables.com/id/Making-Your-Own-S...

Supplies:

The supplies are simple and easily available. I list the ones I used but it was only because I already had them at home.
- Cardboard (thick and thin)
- 180-220 paper
- White Glue
- Acrylic transparent paint spray

The tools you need with this Instructable are:
- Cutting board
- Xacto knife
- Metal ruler

Teacher Notes

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Step 1: SLIDE RULE SCALES

The real secret of a slide rule are the scales! They are the ones that “perform” all the calculations. Fortunately, the internet is full of sites that provide good quality pdf scales we can print.

As my calculating tool is designed for middle and high school students, I selected the following scales
- basic scales (C and D)
- square value scale (A And B)
- cubic value scale (K)
- inverse scale (CI)
- trigonometry scales: Sin/Cos (S), Tan/Cot (T)
- logarithm scale (L)

I found all these scales in the instructable posted by Phil B.

https://www.instructables.com/id/Making-Your-Own-Slide-Rule/

The template is for a “paper slide rule” but I was unable to make it work properly, probably because my paper was not thick enough.

I printed my template on 180 paper

Note:
You can customize your own slide rule with the scales you will need and even do it using both sides. In this case, we only use the top side.

Step 2: CUT OUT THE PARTS OF THE SLIDE RULE

Using your Xacto Lnife and metal ruler, cut out the 3 parts of your slide rule and glue them to a thick and stiff piece or cardboard. to prevent it from wtapping, set it to dry under heavy weight. Due to the nature of the project, I considered that using my 2 books of Calculus as weight was appropiate.

Once dry, trim out any excess.

Step 3: MAKING THE SLIDER AND SIDES

1. Take a piece or thin cardboard and glue the slider over it. Be sure to have enough thin cardboard on top and bottom of the slider to later glue to your other parts. Do not forget to put some weight over it to keep it from wrapping.
2. Locate the top and bottom parts and separate them from the slider with a thin piece of cardboard or paper so it will move easily.
3. Trace. The outside of both pieces on the thin cardboard and cut it to size
4. Trace a parallel line on both sides of the slider and they will mark your slider edge. Cut it out and you will have the pieces that go under your top and bottom parts.
5. Glue the top and bottom parts. Please, note that my final picture shows the top part bellow and the bottom part above (my apologies)

Step 4: MAKING a SPACER

Glue a strip of 180 paper under the top and bottom parts to create a spacer that will ease the travel of the slider

Step 5: ASSEMBLING THE SLIDE RULE

1. Assemble your slide rule making sure that all number “1” of scales C,D,A,B line up
2. Put glue ONLY on the top and bottom sides
3. Set the assembled slide rule over thick and stiff cardboard
4. Check the alignment again
5. Slide out the slider
6. Let it dry under weight

Step 6: CHECK IT OUT!

Once the glue is dry, trim the excess cardboard and you can slide the slider into position. By now, you have a perfectly working slide rule (minus the cursor). It may be necessary to work out the slider to make it slide easily from side to side.
As the slide rule has only one working side, I used the back side to put up some useful conversion factors.

To preserve the printing of the scales, I sprayed several thin coats of transparent acrylic paint. Do it on a well ventilated place.

Step 7: MAKING THE CURSOR

This final step is crucial for the accurate performance of the slide rule.
1. Measure the distance between the left most mark on any scale and the edge of the slide rule. In this case, it is 12 mm
2. This means that the maximum width of the cursos is the double of the above distance: 24mm
3. Is selected to do a cardboard cursos so I made a frame 24 mm width and the length corresponds to the width of the slide rule PLUS 2 cardboard thickness
4. Originally I made a frame for the bottom part of the cursor but then decided for a full piece of cardboard
5. For doing the hairline, cut out a piece of transparent plastic and trace a line over the number 1 of the top and bottom parts of the slide rule. Draw a line wth a marker over the trace an clean the plastic. Now you have a double hairline.
6. Glue the cursor frame locating the hairline right in the middle and trim the excess transparent plastic
7. Locate the bottom part of the cursor right on the edge and very careful align the hairline with the number “1” of te top an bottom parts and glue it into place.

Step 8: FINAL ADJUSTMENTS

Now it is time to adjust your slide rule...

In my case, the width of my slide rule was not constant and the cursos fitted right in one end but was loose on the other end. To correct this, I glue a trim made of thin cardboard and then sand it to the correct size so the cursor travels freely but in a tight matter, it should not wobble as we move it.

Step 9: FINISHED AND TIME TO ENJOY IT!

The slide rule is complete!
Time to brush up on the ability of using it!
I placed a simple table of useful conversion factors on the back of my slide rule! They always come in handy!

Final picture... my 2 slide rules!

Note:
I am considering glueing additional small cardboard pieces at the edges of the slide rule to work as stoppers of the cursor

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    28 Discussions

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    Syncopator

    18 days ago

    Many slide rule users are not aware of the fact that their principle is that of mechanically adding logarithms in order to multiply.
    You remember log tables, don't you?

    4 replies
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    billbilltSyncopator

    Reply 15 days ago

    YUP.. USED LOG TABLES A LOT UNTIL HAND HELD CALCULATORS WERE DEVELOPED THEM AS A KEYBOARD FUNCTION... (CHARACTERISTIC, MANTISSA..ETC...ETC...)
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    cparedes2302Syncopator

    Reply 18 days ago

    I do!
    And I still have my old little Log table booklet similar to the image
    Many thanks for checking my instructable

    Tablas de Coppetti.png
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    Syncopatorcparedes2302

    Reply 17 days ago

    I wouldn't be able to use log tables now, I've completely forgotten how to use them!

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    cparedes2302Syncopator

    Reply 17 days ago

    no kidding! I am sure you take a look at it and it will come back in a second!

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    billbillt

    15 days ago

    This Pickett model N1010 Trig was my favorite.. Thanks for sharing!...

    SLIDE RULE.jpg
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    dickworrall

    18 days ago on Step 2

    It brings back memories. I went to electronics school for 2 years in the 60's. The slide rule is all we used for calculations.

    3 replies
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    pmartelcparedes2302

    Reply 15 days ago

    Thanks for the link to these different slide rule scales!

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    pmartel

    16 days ago on Step 9

    Still have several, including a circular slide rule, Having a physical rule is nice, but I'd like to point out that there are slide rule phone app.

    1 reply
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    cparedes2302pmartel

    Reply 16 days ago

    Many thanks for pointing it out!
    I do have the app on my cel and tablet, and use it!

    My “secret agenda” could be to have the middle school student interested in building and using his own slide rule (straight or circular) so they train the brain in “number management”. The idea is to have the students perform mental calculations instead of just keying in numbers.

    ... just a thought...

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    GordM2

    17 days ago

    I still have my K&E Deci-Lon. Excellent piece of human ingenuity and design. I marvel at it every time I use it. The 'slide rule' and the carpenter's 'steel framing square' are two awe inspiring devices that are so overlooked in today's world. Well done.

    1 reply
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    cparedes2302GordM2

    Reply 17 days ago

    I totally agree! Many thanks for your comment!

    Our youngsters should be made aware of how ingenuity helped humanity before the computer age! I am still convinced that it would be of benefit for them if we teach them how to use a slide rule and have them use it in middle and high schools. I gave my neighbor’s kid the slider de rule and he was immediately interested!

    Greetings!

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    lclaiborne

    17 days ago

    Not an engineer, but for the young - the SR 71/72 Blackbirds were built using slide rules. Also the Apollo spacecraft. No wind tunnels, no computers, just brains and slide rules. Stunning amounts of engineering greatness were done this way.

    Cool project! It’s a good skill to know a slide rule, requires thought.

    1 reply
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    cparedes2302lclaiborne

    Reply 17 days ago

    Many thanks for your interesting comment! In those days, everything was done with slide rule.

    Greetings!

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    belcher1

    18 days ago

    If you would like a real one, there are bunches of them in antique stores. I have 2! Most don’t know what they are anymore.

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    cparedes2302belcher1

    Reply 18 days ago

    Many thanks! I was not aware of.... remember, I am just starting
    I will check them out!

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    Phil B

    18 days ago

    Thank you for making reference to my Instructable using this same downloadable file. I did a couple of other Instructables. One was on refurbishing a circa 1955 Dietzgen I bought for $2.50 plus shipping at eBay. The other is a tutorial on using a good slide rule. Two years ago at age 72 I was planning the loading of our household goods for a move across the United States. We had various stacks in our garage. I used a 10 inch plastic K & E slide rule to calculate the cubic footage of each stack. My wife fretted that we needed a bigger truck. I calculated it all a second time with the slide rule. The slide rule told me the truck we rented would be 80% full when loaded. My slide rule calculations were correct and the move went well without a larger truck. That K & E slide rule is now in my workshop for quick calculations. I could use the digital calculator on my smartphone, but I reach for the slide rule instead without thinking about it.

    1 reply
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    cparedes2302Phil B

    Reply 18 days ago

    Your instructable was decisicive in convincing me to build my slide rule. Many thanks for posting it as I am sutre it has inspired many others. I checked your other instructables and now I am "inviting my friends" to give me their slide rule so I can restore it... and keep it!!

    I have use the slide rule with my students and they were always amazed how "a piece of plastic" could be so accurate and fast! Have a great day!