Scribing circles?

red5angel · Post by **red5angel** » Mon May 21, 2007 11:06 am

Anyone have a good idea for easily scribing small circles? I need to scribe some circles on an irregular surface from about 1/2" to around 1 1/4 inches in width. I don't have a steady enough hand to draw the circles and do it free hand and it's important I get thes clean.

TREKKRIFFIC · Post by **TREKKRIFFIC** » Mon May 21, 2007 11:46 am

red5angel wrote:Anyone have a good idea for easily scribing small circles? I need to scribe some circles on an irregular surface from about 1/2" to around 1 1/4 inches in width. I don't have a steady enough hand to draw the circles and do it free hand and it's important I get thes clean.

Have you got a circle template ? You can also try a compass with a finishing nail in place of the pencil to scribe the line.

Post by **TER-OR** » Mon May 21, 2007 12:59 pm

Scribing templates are the way to go. Tape it down securely first.
The SM store sells a couple templates. A compass might be required for the >1" circle, though.

Go Flight · Post by **Go Flight** » Mon May 21, 2007 2:10 pm

You could also pick up an Olfa circle cutter. Just substitute a pin or the like for the blade - http://apps.webcreate.com/ecom/catalog/ ... ctID=25204

Sparky · Post by **Sparky** » Mon May 21, 2007 2:13 pm

Got in the circle scriber onezero reviewed, it came all the way from the UK. I got the deluxe box set; it comes with an extender to make bigger circles and different blade chuck for cutting bevels.

I saw a similar product at target I believe the cost is similar but I don't know the quality or ease of use difference. It looked more complicated that what I got.

The SM review:
http://www.starshipmodeler.com/tech/jl_circle.htm

Kylwell · Post by **Kylwell** » Mon May 21, 2007 3:18 pm

The big issue here is the 'irregular' surface. Template is about the only way to go and this is probably the best scriber for such use.

red5angel · Post by **red5angel** » Mon May 21, 2007 3:41 pm

The olfa looks like something I'd be comfortable using on this job. I have hand scribers in my work kit now but they're not going to work well for this job I'm doing. If I can't find an olfa-like cutter I may have to jury rig something from a compass.

Sparky · Post by **Sparky** » Mon May 21, 2007 3:46 pm

tool shop brand, at menards, has a big stick and needle style compass.

ah they call it a beam compass.
http://www.amazon.com/Alvin-Co-BEAM-COM ... 58&sr=1-61

red5angel · Post by **red5angel** » Mon May 21, 2007 4:21 pm

lol, that things waaaay too big for my needs at the moment. I'm doing a scratchbuilt miniature of the Enterprise A. the Primary hull is only about 1 1/2" across so it's got to be small and decliate like!

I was thinking about experimenting with thick paper clips tonight if I get the chance

Lt. Z0mBe · Post by **Lt. Z0mBe** » Mon May 21, 2007 8:58 pm

I had the same issue on my Box O' Crap build. I took my circle template and used them to make another template out of .015" or .010" styrene. It was flexible enough to confirm to the nacelle yet rigid enough to hold the scriber needle tip.

I hope this helps.

Kenny

Woody · Post by **Woody** » Mon May 21, 2007 11:04 pm

I like to use a pair of drafting dividers for circle scribing.

red5angel · Post by **red5angel** » Tue May 22, 2007 9:10 am

what's a drafting divider?

futch · Post by **futch** » Tue May 22, 2007 9:23 am

drill a hole in some .01 styrene sheet.
tape the sheet to the surface.
when the surface is curved, i use Blue Tac to hold the template in place(here in the US it is yellow and called poster tac I think).
scribe away.

alternatively, i found an eraser masking template is also useful. it is made of super thin stainless steel and comes with pre-punched holes, lines and other odd shapes. it costs about $1 in school supplies.

Woody · Post by **Woody** » Tue May 22, 2007 12:22 pm

red5angel wrote:what's a drafting divider?

http://img.photobucket.com/albums/v140/ ... d86172.jpg
second one from bottom.
http://img.photobucket.com/albums/v140/ ... re2006.jpg
In action.

red5angel · Post by **red5angel** » Tue May 22, 2007 5:48 pm

woody, that's exactly what I was thinking of a few days ago! where would one come across something like that? hobby shop maybe?

Woody · Post by **Woody** » Tue May 22, 2007 5:58 pm

I buy them off ebay. I bid on drafting kits and get them for cheap. Drafting is mostly done on computers now days so there are tons of old drafting sets out there. I have also seen them for sale at places like Hobby Lobby.

Warped Speedster · Post by **Warped Speedster** » Wed May 23, 2007 5:08 am

One thing to remember about circle cutters and drafting compasses. They are really great for circles about one inch diameter or larger. Any smaller than that and they can get a little stressed with the tight bends. As they flex and twist the cut radius shortens, sometimes quite a bit, giving an irregular shaped circle. They always flex a bit no matter what size circle you're making, but you don't see the imperfections so much in larger diameters. But it's pretty hard to make a really perfect 1/2" circle. They will always twist more in a small circle and any flexing of the tool will be much more noticable in the small diameter.

Solid and strong is always better for cutting. It's straighter and easier.

For scribing really small circles I usually make a special cutter just for the job. I use a short piece of metal or some stout plastic that won't twist (as much). Then drill the pivot point at one end and poke a sharpened nail through it and superglue it. If you're using metal just superglue the nail to the side of the metal. Then glue a No. 11 cutting blade at the other end. 1/4" square Evergreen is good for making little blocks to glue to the metal or plastic to give a 90 degree surface to glue the blade to. It's really pretty easy to do and the results are worth it, especially when you're scribing a bunch of cuts all the same size. Make a bunch of different radius cutters and you have em for lots of other tiny jobs later.

As already mentioned, the template method is good too for small circles. And it doesn't leave a center pivot hole to be filled in. Although I find it hard to lock a template in place sometimes. If it wanders during a cut, you're screwed. As an alternate method, you could make an outside (reverse) template. "Lightly" tack weld (glue) a car wheel or a steel washer or something to the surface to give the desired radius you want. Then just scribe around its ouside edge. It's easy to flick off the piece later and sand away the tack. I've used this method a lot and it's a good way to get a small radius scribed exactly where you want it.

Woody · Post by **Woody** » Wed May 23, 2007 12:20 pm

Templates made from scrap styrene are great for small holes.
http://img.photobucket.com/albums/v140/ ... 10d1b2.jpg
Note the smaller locating holes.

red5angel · Post by **red5angel** » Wed May 23, 2007 2:08 pm

I'd thought about creating the templates in styrene, I have a template with all the circles I need on it now made of styrene, problem is in my experience it always tends to shave off styrene as you go.

I think I've come up with a solid plan though, since I plan on making a mold and casting the parts for myself, I figure I can start by making a mold of the piece without the lines, make a couple of casts, then try doing the lines on those. that way I can experiment with different ways of doing it if the first try doesn't work out, and I don't have to worry about screwing up my master.

Woody · Post by **Woody** » Wed May 23, 2007 4:24 pm

red5angel wrote:I'd thought about creating the templates in styrene, I have a template with all the circles I need on it now made of styrene, problem is in my experience it always tends to shave off styrene as you go.

Notice the tool I'm using? It is round so it doesn't cut into the template.

futch · Post by **futch** » Thu May 24, 2007 1:02 pm

Woody wrote:
red5angel wrote:I'd thought about creating the templates in styrene, I have a template with all the circles I need on it now made of styrene, problem is in my experience it always tends to shave off styrene as you go.
Notice the tool I'm using? It is round so it doesn't cut into the template.

ditto. start off light. you dont need to gouge out the panel line on the first pass.

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Scribing circles?

Scribing circles?

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