cutting circles

[jgoldader]

Howdy--

What do you do to cut out circles, or washer shapes, from styrene sheet?

I've really tired of cutting my circle template with X-acto knives, and of scribing endlessly without getting through the sheet. Is there some sort of cutter that could handle up to 40-mil styrene? 20-mil would be okay, I could just cut out two pieces and laminate them together.

Thanks!
Jeff

[Wug]

Hi jgoldader,

What diameter? For small diameters a punch and die set is best.

For larger diameters you have a few options. Olfa and other manufacturers make circle cutters. They're like a beam compass with a hobby blade. I bought one years ago and only used it a couple of times. It seems best for circles that are at least a few inches in diameter.

I usually use dividers or a compass with points on both ends. I have a bunch of them in a variety of sizes. Try to find the strongest stiffest ones you can. I scribe the circles a little oversize then chuck them in a drill to sand them to final size.

If you are unbelievably lucky you might find a hole cutter drill bit in exactly the right size.

Mike

[jgoldader]

Hi jgoldader,

What diameter? For small diameters a punch and die set is best.

Ah--good question. Sorry I wasn' specific enough.

I have a punch set for small diameters, but I'm usually cutting circles ranging from 1 cm to about 6 cm in diameter (call it 1/2 inch to 2.5 inches).

Jeff

[ajmadison]

For cutting the larger circles, I use a pair of "dividers". Technically a compass is a point & a pencil. Olfa makes a nice adjustable circle cutter with a blade for the sizes you indicated. But its designed for paper, not sheet styrene, and is about as effective as a carpenter's compass with a no. 11 blade holder in place of a pencil. But going the dividers route versus a circle template is slightly faster in two ways. If you don't mind cleaning up the center hole, you can really dig in with the compass, speeding up how quickly you can score the sheet for eventually getting your circle out. For 40 thou sheet and up, another trick I use, is that eventually the divider's punch the center point all the way through your sheet. Flip your plasticard over, and insert your divider center point into the hole on the opposite side and make a second score from the opposite side.

If you can't clean up the center hole, and I've had parts that were like that, you can superglue a piece of sacrificial scrap over the proposed center point. After your circle has been popped out, stick a knife point under the scrap, pop it off, and clean up the glue remnants. But this trick only works if you use CA.

Finally, another trick I use for creating circles in the 7mm to 1.5 cm range is to take a section of tubing the right diameter and glue it "edge on" to your plasticard. Roughly cut the plasticard around the tubing. Then spin with your fingers, the tubing & the rough polygonal shape against sandpaper until you've got a nice circle. In this case, Plastruct tubing works better than Evergreen, because the Plastruct tubing is harder and thicker than typical sheet styrene. When your circle is ready, stick a knife point between tubing & your circle and pop it off the end of the tube. Takes some practice, but when your circle is done, its really done, its not just roughly cut out, but has a smooth edge.

[Kylwell]

All depends on the Olfa.

For smalland I mean really small, circles a punch & die set is king.

For larger circles, the Olfa or similar devise works fine.

For really large radius' I have an attachment for a 6 foot length of aluminum that works.

[Rocketeer]

Finally, another trick I use for creating circles in the 7mm to 1.5 cm range is to take a section of tubing the right diameter and glue it "edge on" to your plasticard. Roughly cut the plasticard around the tubing. Then spin with your fingers, the tubing & the rough polygonal shape against sandpaper until you've got a nice circle. In this case, Plastruct tubing works better than Evergreen, because the Plastruct tubing is harder and thicker than typical sheet styrene. When your circle is ready, stick a knife point between tubing & your circle and pop it off the end of the tube. Takes some practice, but when your circle is done, its really done, its not just roughly cut out, but has a smooth edge.

What a clever idea! Circles in the 1/8 to 1/2 inch diameter range are the bane of my existence; this sounds very useful.

[TazMan2000]

Its kind of a poor man's way of doing it...but it works for me before I got my lathe.

If you require something perfectly round, try putting a screw (and a couple of nuts on either side of the styrene) through a rough cut piece of styrene. Secure a power drill to your bench and then mount the styrene disk to the chuck. Make a makeshift tool rest using a few pieces of scrap wood, and secure that down to your workbench. Use a suitable tool to shave down the plastic to your required diameter and sand. Warning...the plastic shavings make a heck of mess.

TazMan2000

[Kylwell]

Its kind of a poor man's way of doing it...but it works for me before I got my lathe.

If you require something perfectly round, try putting a screw (and a couple of nuts on either side of the styrene) through a rough cut piece of styrene. Secure a power drill to your bench and then mount the styrene disk to the chuck. Make a makeshift tool rest using a few pieces of scrap wood, and secure that down to your workbench. Use a suitable tool to shave down the plastic to your required diameter and sand. Warning...the plastic shavings make a heck of mess.

TazMan2000

In other words... Look around...Can you form some sort of rudimentary lathe?

[AbsoluteSciFi]

For circle cutting I cut from the same angle and take my time- turn the sheet often, and always use a sharp blade. Patience. I try not to cut too deep early into the cutting, I can't really use a template, and circle cutters only go so deep- But they can start you off. Ninety percent of the circle is percieved by the topmost edge of the circle- so getting that part right is key.

[Andrew Gorman]

I usually use a gasket punch-
http://www.amazon.com/SHARP-HOLLOW-PUNC ... B000Q7AVL0
For bigger discs the Olfa beam compass circle cutter works well.
Lately I've accumulated enough model car wheels, poker chips, tiddly winks and other disks I haven't needed to make a custom sized circle for a while.