Drawing Large Dia Circle

A long piece of wood with half or one inch holes drilled along half the wood, pencil size. then a nail nailed in the other end, put pencil in one of the holes for the diameter you need, then draw the the curve positioning the nail end in the board to be drawn on.

oops! read the bloody post. :-)

A piece of wood dont cost an arm'n'leg. :-)

Two pieces of wood screwed together in the middle to form a compass set. ( a V shape) Hammer a nail in the end of one piece to form a pivot point for the centre of the circle, and drill a hole and put a pencil in the other piece to draw your arcs' with.

This won't work so well if you are working on a baseboard for a layout, but if you are working on paper, draw out the layout on A4 (or use CAD) and print/photocopy it onto acetate. Pin the paper up on the wall and use an overhead projector to throw an enlarged image on to the paper. It's one technique used by signwriters.

Owain

: I could bodge something with a nail as a pivot and drill several holes : at various radii for a pencil but was just wondering if there is : anything a little more professional available that wont cost an arm and : a leg.

A nail and a piece of string?

Ian

The device you want is called a trammel bar compass. It is a high tech version of a piece of wood, a nail and a pencil. The main difference is that the pencil and pivot point are each mounted on clamps that can be attached to a rule, allowing more flexibility than a series of drilled holes.

Colin Bignell

That's how my grandad used to do his railway layouts. Just be careful not to wind the string around the pencil as it sweeps out the arc. It's easy to do and of course it changes the radius of curve from start to finish.

: Ian Johnston wrote: : : > On Tue, 19 Jul 2005 15:26:18 UTC, snipped-for-privacy@mwfree.net wrote: : > : > : I could bodge something with a nail as a pivot and drill several holes : > : at various radii for a pencil but was just wondering if there is : > : anything a little more professional available that wont cost an arm and : > : a leg. : > : > A nail and a piece of string? : : That's how my grandad used to do his railway layouts. Just be careful : not to wind the string around the pencil as it sweeps out the arc. It's : easy to do and of course it changes the radius of curve from start to : finish.

Isn't that a way of drawing an evolute spiral, or possibly an involute?

Ian

So, no transition curve then?

Chris

A genuine trammel set, bought from eBay. This is a pre-war draughtsman's instrument, a pair of small clamps that go onto a wooden stick (a wooden yardstick is about ideal). One has a spike, the other a pencil, spike or ink pen. Better ones also have a screw micro-adjust for radius.

I've got two of them, one a pair of heads only (bring your own stick) the other has an extensible metal rod, up to about 18" max. Both were under a tenner.

Make your own compass with 2 battens drilled and bolted together at one end. Smack a 2 inch nail in one free end and cut the head off with a hack saw and sharpen with a file. Preferably a masonry nail which might be better sharpened on a angle grinder. Then glue on a pencil to the other free end.

Arthur

You can dom eiter if you wish, just takes mucking about with penholders of the appropriate diameter. Bit OTT for railway layouts though.

Rather than drilling holes for the pencil, cut a pencil-width slot along most of the length of the batten. Tnen drill a load of holes across so you can insert a couple of bolts with washers and wing nuts to clamp the pencil at whatever radius you want.

Hmm. I'd stick with string and pencil option.

Jacob

Thanks for all the useful suggestions. I hadn't thought of actually making a large compass. I used the string idea before but found keeping the tension equal tricky so that would be ok if precision wasn't required.

Kevin

You need a rod and some screw on clamps...I have seen this somewhere but can't remember where..got a mate with a lathe? Its a simple job if you have...