how to cut round plexiglass

[darkspeed]

Bridgeport vertical mill + rotary index table

Rotate the index table to cut the circle, then tilt the table 90deg and drill the holes at exact degree marks around the radius

This is if you was a very stable high speed motor

[NTesla]

I have built several electric motors (e.g e-Orbo,  of concept designs) using Plexiglas rotor discs. Here is how I make them - without having access to a lathe which would probably be ideal:

1. Equipment needed:

- Vertical drill press - the larger the better. You want one that has enough  area on its drilling table (the vertical column gets in the way) so that you can drill a hole in the centre of your cut plexiglass sheet.

- Disc sander that has a table (e.g. http://www.ryobitools.com/catalog/power_tools/corded/BD4600). This is for finishing off the circumference of the rotor disc plus its a great tool to have

- Jigsaw (e.g Bosch or Makita) with a blade suitable for cutting plexiglass.

- Saw horses for placing the plexiglass on.

- Clamps for securing the plexiglass on the saw horses.

- Square sheet/off cuts of Plexiglas (e.g 8-15mm thick) with the protective adhesive layer on both sides - this is important for measuring and protecting the Plexiglas during construction. I got a few off cuts from a guy who used it for safety glass in racing cars.

2. Either use a school draughting compass to directly draw the circle onto the sheet or if you have some good drawing software, use it to make a 1:1 drawing that you print out and then glue to the sheet as a template (remember you should be drawing/gluing to the sheets adhesive layer not the sheet itself). Remember the diameter of your rotor must not exceed the working area of the drill press table.

It is important to accurately draw NOW the positions of any other components that will go on the rotor disc (e.g magnets). Note that even if the circumference of your rotor disc is not cut exactly, if the components are positioned on it correctly, that may be what is important.

3. Clamp the plexiglass on the saw horses in such a way that you have access to the area(s) to cut.

4. Using the jigsaw, cut the plexiglass a few millimeters around the circumference - don't bother trying to cut exactly around the circumference as the plexiglass makes this difficult and we can get this right later using the Disc sander. Tip: A larger area you cut around will make it easier to handle when drilling the centre hole.

5. Drill the centre hole of the rotor disc using the vertical drill press - it is crucial you get this correct so practice on a spare piece first, use good lighting, and if you can, clamp the rotor disc down first. WARNING: Drilling holes in plexiglass can be dangerous because the drill bit tends to bite into the plastic - DO NOT use drill bits intended only for wood. If you cannot clamp the plexiglass to the drill press table wear protective gloves - it goes without saying that you should ALWAYS wear protective eye wear!

6. After drilling the centre hole, finish off sanding the circumference of the rotor disc using the Disc sander - if you can't get sufficient accuracy an alternative is to use the vertical drill press. Use a bolt that fits snuggly through the rotor disc centre hole and secure it with a washer and nut, then use the bolt like you would a drill bit - you sand the circumference of the disc by holding a sanding block next to the circumference while the rotor disc rotates on the drill press. Use coarse grit sand paper intially and limit the speed of the sander else friction will create lots of heat and melt the plastic.

7. Once you are happy with the rotor disc, you can then peel off the protective adhesive coating - you will now have a nice and clean rotor disc for use! Tip: If you are going to glue anything on the rotor disc that needs to be secure (e.g magnets), BEFORE you take all of the protective adhesive off, use a modeling knife to scribe the areas that need to be glued (cutting through the adhesive layer). Then peel these areas off and sand them to increase the surface roughness for a better glue seal.

Done!

As I said at the beginning, an appropriate lathe machine would be preferred, unfortunately I can't justify the cost of one right now!

Hope this helps!

[Mk1]

How big do you need it ?

[ckreol1]

Great instructions, thanks.  I posted them up to my site, electropub.wordpress.com, under "other stuff"--for easy reference.

The size I'm looking for is between 9 and 12 inches diameter.  I'm not sure on the thickness.  I think 3/8ths inch would be good.

I don't have any experience with plexiglass.  What is a source that others have used for plexiglass in the USA?

[DeepCut]

I do it simply and cheaply and they come out fine.

I use a jigsaw (fitted with a plastic cutting saw, 20 TPI or more).

I buy the plastic in squares.

Then keep cutting rotated squares until you are left with a circle that you can sand any irregularities from.

The centre-hole is found by marking corner to opposite corner, where the two lines cross.


Gary.