Drawing/cutting "LARGE" perfect circles/semi circles

[Negativecreep0]

This might be a dumb question but, how would I got about drawing a perfect circle or semi circle. It is on a rather large scale like something that a regular compass couldn't handle? How would I tackle drawing and cutting this semi circle/circle perfectly? thanks for any help

[Level42]

Indeed a stupid question.

Get a nail, get a wire. Put nail in center of circle, attach wire, attach drawing tool to other end of wire. Hold wire straight. Draw circle

 

[toasty]

Ancient people used to drive a stake into the ground, attach some rope to it, pull the rope taut, and walk off a perfect circle that way.  I assume you're not looking to do anything on that large of a scale, but the same principle ought to work with a nail, some string and a pencil.

Or you can just find something round that is the size you're looking for and trace around it.

EDIT: ^^ looks like Level42 beat me to the punch...

[gamecreature]

Drafters have a tool called a "beam compass" which is essentially a metal bar with a pin on one end and an adjustable holder for the drawing tool on the other. You could probably fabricate one out of stuff you have in your house, unless precision is a must.

[leapinlew]

nail + string = Brilliant!

The easy solutions escape me sometimes. I walk around the house looking at everything - pickle jar lid, trash can lid, cd, etc. I'll do the string/nail method next time though.

[fatfingers]

nail + string = Brilliant!

The easy solutions escape me sometimes. I walk around the house looking at everything - pickle jar lid, trash can lid, cd, etc. I'll do the string/nail method next time though.

Like my mom always used to say:

There's the easy way, and then there's fatfingers's way

[mark shaker]

nail + string = Brilliant!

The easy solutions escape me sometimes. I walk around the house looking at everything - pickle jar lid, trash can lid, cd, etc. I'll do the string/nail method next time though.

Hey! A man should never, and I mean NEVER, pass up the opportunity to buy a tool, simply because the job can be done with stuff you have laying around!

What you need is a good set of Trammel Points.

http://www.amazon.com/gp/search/ref=pd_sl_aw_tops-1_tools_14412276_2/102-0661372-4190530?search-alias=tools&keywords=trammel%20points

   - Mark

[MYX]

Circular Saw   

[vorghagen]

Circular Saw   

There has to be some kind of penalty for posts like this.

[Brax]

I'm a draftsman by trade so I lean towards a beam compass. The one I have will draw 36" circles. It's surprising how large of a circle you can draw since you only need the radius. The string and pencil trick is certainly a close second.

As for cutting a circle, the easiest/best way is to use a circle cutting jig with your router. Perfect every time.

http://www.woodworkingtips.com/etips/etip102000sn.html

[mccoy178]

I'm a draftsman by trade so I lean towards a beam compass. The one I have will draw 36" circles. It's surprising how large of a circle you can draw since you only need the radius. The string and pencil trick is certainly a close second.

As for cutting a circle, the easiest/best way is to use a circle cutting jig with your router. Perfect every time.

http://www.woodworkingtips.com/etips/etip102000sn.html

This is the method I use for circles.

[severdhed]

string and nail works for me...as for cutting them, i have a circle cutting atachment for my dremmel, it worked really well for cutting the hole for my trackball.

[rbarr110]

I have to go against the concensus of using string, but, depends on how you use the string.

Using string your pen/pencil/marker can do this --->   /    or    \  when you want it to be -----> |

The size can be greatly affected by the slant of the pen/pencil.   /|\

I personally use a piece of wood lath or aluminum flat bar with holes drilled for the nail, and one for the pen/pencil just large enough to fit the tip of the pen/pencil through.  That way little or no tilt can occur.

Maybe I am just anal retentive, but thats my personal preference.

[RickDIII]

I'm a draftsman by trade so I lean towards a beam compass. The one I have will draw 36" circles. It's surprising how large of a circle you can draw since you only need the radius. The string and pencil trick is certainly a close second.

As for cutting a circle, the easiest/best way is to use a circle cutting jig with your router. Perfect every time.

http://www.woodworkingtips.com/etips/etip102000sn.html

This is the method I use for circles.

This is the single best way I know for cutting circles.  If you look at the screenshot on the link you will see that the jig is cut to length where the pivot point needs to be.  If you extend the back end of the jig you can drill new pivot points later if you need to do different sized circles. 

This method will give you perfectly cut circles and arches!

[arcadegamenut]

Circular Saw   

There has to be some kind of penalty for posts like this.

Actually, I saw a video on google of a man demonstrating this could be done.

[leapinlew]

I have to go against the concensus of using string, but, depends on how you use the string.

Using string your pen/pencil/marker can do this --->   /    or    \  when you want it to be -----> |

The size can be greatly affected by the slant of the pen/pencil.   /|\

I personally use a piece of wood lath or aluminum flat bar with holes drilled for the nail, and one for the pen/pencil just large enough to fit the tip of the pen/pencil through.  That way little or no tilt can occur.

Maybe I am just anal retentive, but thats my personal preference.

Mount the string low on the pencil - real low, like on the lead. Slant shouldn't matter then.

[rbarr110]

Mount the string low on the pencil - real low, like on the lead. Slant shouldn't matter then.

Yep - thats why I said it depends on how you use the string.

Also, I should have said, I like using wood or aluminum since it is rigid and doesn't have the potential of going slack and also affecting the circle.

[nostrebor]

String/wire stretches.

Go to a few home shows lumberyards and pick up the freebie yardsticks they all give away. Drill hole for pencil in one end, so pencil fits tight. Add holes as needed for nail or ?? pivot point. Accurate and free.

[DrewKaree]

Circular Saw   

There has to be some kind of penalty for posts like this.

There is.  You end up dropping your own cab

Sorry MYX, I just couldn't resist!

[vader]

String/wire stretches.

Go to a few home shows lumberyards and pick up the freebie yardsticks they all give away. Drill hole for pencil in one end, so pencil fits tight. Add holes as needed for nail or ?? pivot point. Accurate and free.

I like this idea....slanting is not a issue then

[Howard_Casto]

Personally I just make a router jigg and cut at the same time I measure. 

1.  Get yourself a nice sheet of 1/8 inch plywood. 

2.  Remove the plastic base plate on your router

3.  Trace the plate on your plywood.

4.  Use a yard stick to draw a large rectangle extending from your plate tracing (4 feet is good). 

5.  Cut out the whole rig, drill holes in the plywood where the screw holes were on your plate and screw the plywood back on instead of the plate.

Now what you have is a compass set with a router on the end rather than a pencil.  You can use a yardstick to measure for the pivot hole to drill.  Your circle will be twice the width of the length from your hole to the inside edge of te router bit. 

When you are ready to make your circle you put the piviot hole in the apropriate place and literally screw the whole thing down by putting a screw through the pivot hole and attaching it to the piece of wood you are cutting.  Now it's impossible to cut a bad circle as your router is locked in a circular path with no "wiggle room". 

You have a small hole to deal with from where you mounted the rig, but that can be filled with putty and no one will ever know.  This method can be used for outside cuts as well, you just get a scrap piece of plywood the same thickness and butt it up against the piece you wish to cut. 

[nostrebor]

If you search "router trammel" on google you'll get a few online versions of what Howard says above. Router is the most accurate way of cutting a circle, bar-none.

[Negativecreep0]

what about semi circles and ovals like we see in KNIEVEL's CP designs?

[DrewKaree]

what about semi circles and ovals like we see in KNIEVEL's CP designs?

Those are just decorative surrounding elements for his buttons.  Those aren't actually cut out.  To do what you're seeing in that image, you need to get that answer in the artwork forum from someone knowledgeable in Photoshop, Corel, Paint Shop Pro, or some other image-tinkering program.

[DrewKaree]

....but if you really want to know how to do it, drill a series of holes (in a straight line, obviously).  When you've created the size oval you need, using a chisel (or a jigsaw or a file/rasp or a.....), remove the peaks left over to make the sides of your oval smooth and straight. 

If you have a drill press, they often make mortising attachments that can remove the waste between two points.  Using that method, drill a hole on either end of the oval you wish to create, and using the mortising attachment, remove the waste between the two holes.

[Negativecreep0]

haha i didn't mean on the art I meant like do arcs liek the shape of KNIEVELS cp. I hope you dont think im that retarded................ gulp

[mccoy178]

On an oval of that size, I typically make a template out of plywood or mdf, tack it to the original with brad nails or clamps(depending on the surface), and use a flush trim bit.

[Negativecreep0]

yes but how was that template made in the first place? String and nails?

[mccoy178]

Well, in that picture, you could use a protractor to make the half circle since it is so small.  Once it's drawn, a jigsaw and sand paper are my weapons of choice. 

[Negativecreep0]

umm small enough? that curve is 36" where have you seen a protractor that big? and besides protractors are for perfect circles not semi circles?

[mccoy178]

Okay, okay, I missed that.   To make a circles up to 5', I bought a 5' metal yard stick at Lowe's.  I have various sizes of rulers and yard sticks.  I use one of those router attachments to cut circles up to 24"'s.  To make curves that big, I buy 1/4" foam board that has 1/2" squares on it and draw the curve out.  I made a header for my bookcase/entertainment center that had a 5' French curve in it and that is how I did it.  I just traced the pattern onto my wood, cut it with the jig saw, and spent my good ol' time sanding it smooth.  A belt sander can really take off the wood.  I then used a smaller sander once it was very close.

BTW, with a protractor, I was just reading the instructions........yep, it does semicircles also.  Says here, you can stop it anywhere you want. 

http://www.greatbigstuff.com/draftingtools.html

Also, I think I meant a compass:


http://www.lowes.com/lowes/lkn?action=productDetail&productId=142040-1431-1405&lpage=none

From the website:
"Add a longer 1/2" dowel for larger diameter circles"

Sorry, I should've just found this in the first place.

[NiteWalker]

My router circle cutting jig:

I made it out of 3/8" lexan. It's calibrated for a 1/2" straight bit and a 1/4" pivot. 1"-24" diameter holes and discs. Works great.

I don't draw no stinkin holes! I rout them!

To make a curve like on knivel's cp, just use the same yardstick and nail or whatever. What you're looking for is the radius. A circle cutter can do those too. Or a compass like the one from lowe's.

[BackAgain]

You can also make a circle cutting jig for your bandsaw, like this one:

http://www.blish.com/Product/ProductInfo.aspx?ProductID=102143

Cuts perfect circles every time, just as good as a router jig.  It can be much faster; it depends on your tools.  If you're using a router to cut a circle in 3/4" plywood you're going to have to make several passes (the wood is too thick to do it all at once).  With a bandsaw it will be done in one pass.

[NiteWalker]

That's another way to cut circles. They won't be as clean edged as the router jig though. I don't have a bandsaw (yet!) but when I do I'll be sure to try it out. You can do circles on the table saw in a similar method too.

I'm also biased towards the router

But all are acceptable methods of creating circles. The router just gives the cleanest cut. I'd rather take 3 passes with my plunge router and have a perfect circle than do it on the band or table saw and have edges to clean up.

IMHO, nothing cuts as clean as the router. Best tool in the shop.

[Kemet]

For larger radius curves the best things are symetrical and asymetrical drawing bows.  These are perfect for the front curves on cps.  They look like a bow from bow and arrows but the wire part is adjustable in length, thus tightening or loosening the curve. Once locked in place they make repeatability easy.