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Magnetic Cylinder Square

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Alexander McGilton

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#1
This is my own copy of the suburban tool magnetic cylinder square. The base is made from a 2.5" diameter one inch thick hardened 1045 steel having a thou under bored hole and recess . The shaft is a 3/4" piece of drill rod with a 1/2" hole for weight reduction that has been pressed into the base. The recess bored out of the bottom of the base where four magnets are placed with an aluminum ring and the void is filed with epoxy. Just after assembly there was little over a thou of error in squareness, this was measured by test indecator from base to tip the revolved four time in 90deg increments. Corections were made by lapping the base in and repeating the measurements. It now holds an error of less than .0001" referanced both to itsself and to an angle plate that was measured optically.
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Tozguy

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#2
Just curious as to how you keep the magnetic surface clean. Do you have a trick for taking metal chips off the magnet?
 

Alexander McGilton

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#3
That is what the epoxy is for, it makes a smooth surface that the chips can be wiped off of. Lapping a magnetic surface is somewhat tedious as it gathers all the lapped dust.
 

Bob Korves

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#4
Nice work, Alexander. It somehow did not register to me how simple (if time consuming) such a tool is to make, and how it is self proving, much like my diesel engine wrist pin made into a cylinder square. I think I will need to make one like yours. After borrowing and using a couple of the style you made to check the squareness of angle plates, I now understand how useful they are.
 

Bob Korves

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#5
Did you consider using a ring or cylindrical magnet? Just thinking that it could be easily glued in. Approximately what total pull strength do your uninstalled magnets have, compared to the weight of the entire tool?
 

Alexander McGilton

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#6
For the strength, I needed only add 100g or so on the tip for it to slid down the angle plate. I drilled the lightening hole after discovering this. I could have used the cylindrical magnets as I had for the target mirror project, but I had these rectangular ones on had. Originally I was going to use hard drive magnets though those were too powerful.
 
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