# Drawing an accurate radius on benchwork

Discussion in 'HO Scale Model Trains' started by tetters, Nov 9, 2007.

1. ### tettersRail Spiking Fool!

Hi guys, I tried the search function honest. The search function keeps giving me an error message, i.e. I didn't type in the minimum word length in order for it to work. anywho...I digress.

How do you gents draw accurate curves on your benchwork if the center of the radius off of the benchwork? I'm trying to concoct ideas in my head, however was wondering if anyone here had some tried and true methods.
2. ### Gary S.Senior Member

What I did: I took my camera tripod and set it up, used some trial and error measurements to get it positioned at the center of the radius, then took a string with a loop and put it around the tripod shaft below where the camera would attach. Then it is a simple matter to draw the curve from there. Now, don't pull too hard or you will topple the tripod!

Don't forget about the tangents into the curve!
3. ### MasonJarIt's not rocket surgery

If your benchwork is fixed, and you have room beside it, you can put your centre on a tripod or other temporary set-up. If this is not feasible, you can create templates from plywood or even cardboard. The bonus of this is that you can get two radii in one template. Picture a 1/4 circle cut out of ply, but only 2" wide - the inner radius could be 28" (for example) and the outer would then be 30".

The other alternative is to use something like XTrkCAD planning software that allows you to print your trackplan "full size". You can then tape the printout right to the benchwork to transfer it.

Andrew
4. ### tettersRail Spiking Fool!

Thanks guys...the tripod idea was what I was looking for. :thumb:

scratches head...now why didn't I think of that???
5. ### PWRR-2207Rogue Islander

Triangulation on goal...

I use a Carpenter's Square and an isosceles triangle to find the center of the circle for an arc between two points (sic a curve connecting two tracks). Picture probably explains better than 'trig-speak':

If the center falls outside a solid location to place a nail or screw, you can take two strips of wood and use the point where the wood strip centers intercept or go with Gary's tripod tripod idea but use strings of equal length instead of the dotted lines shown above to locate the center.

If you are using easements, I recommend going with the MasonJar's 'printing out the track plan' idea.
6. ### doctorwayneActive Member

I screwed a board onto the benchwork, using a single screw, so that it extended out into the aisle, then positioned my radius tool (a long stick with holes drilled in it at set intervals) so that it seemed to be in the approximately correct area - the single screw allows to board to pivot so that you can reposition the pivot point for the radius tool. Then clamp the board in place while you try different radii for the location. Of course, this only works for inside curves: You could use a cardboard template for outside curves, and since you'd have to make it for the outside curve, be just as well-off using it for the inside ones, too. :-D
To be quite honest, I sawed up a couple of sheets of 3/4" plywood into expanding curves, starting at my minimum of 30", and working up to, in 2" increments, 48". The curves were laid out starting at the narrow end of the sheet, and the majority were in the 32" to 38" range, as these sizes seemed like they would be the most useful for my particular situation. With an armload of curved roadbed, I just walked around the room plunking down the widest ones that would fit in each particular location, and with a room like the one shown below, you can bet that there are a lot of curves. Sorry, but I don't have a trackplan.

Wayne
7. ### tettersRail Spiking Fool!

Jeepers...why didn't I think of this one??? Must have been tired after building another turnout last night after getting the kiddies to bed. All great ideas gents...once again thanks! I've got a carpenter's square, a framing square and a 40" metal ruler all sitting at home. I should have figured it all out. slaps head!

I used big pieces of cardboard and drew radius templates and cut them out for the radiusis according to my trackplan. Using the trackplan, accutrately locate and draw the straight tracks,connect them with the template and your done.

Loren
9. ### 60103Pooh Bah

I took a piece of 1x2 and clamped it to the roadbed or bench work and then added bits of wood in the approximate place to get the pivot up to the same height as the roadbed. Then I add another clamp so that it doesn't move.
10. ### myltlpnyMember

That's just what I did. I connected the straight sections to the curves much like using sectional track. I butted the sections together and use a short piece of plywood and screws to back up the joint.
11. ### MCL_RDGMember

By a cheap wood yard stick...

...or get a piece of cardboard strip from a long box. Poke a hole near one end for a nail or pin. Measure (or not) a distance that you want for a radius somewhere down the length (you can even add a second measure, or as many as you want for that matter, for multi-track mains) poke a hole where you need the center of your track and smash a pencil in the hole. Pivot the stick around the pin/nail. In drafting they called it a "beam" compass.

You can also use a piece of string tied around a pencil and tethered to your benchwork with a nail to make uniform radii. Don't cut the string short- leave it long and wrap it around your pivot point.

I hope you can picture what I'm typing. I see it. But then again, laying around on the floor, staring up at the naked bulb in the ceiling can do that to you.

Mark
12. ### 60103Pooh Bah

If you don't need curves larger than 36" radius, a meter stick is good (Canadian yard sticks now have a yard on one side and the meter on the other; the length is 39+"). You can get devices that clamp on the yard stick to make it a compass. I just drill holes in it. I have a hole at 1" that takes a pencil, then pivot holes at the R+1" marks for nails. I add extra holes each side of the 1" mark to mark either rail positions or end of ties (depends how I'm feeling.) I also make holes each side of R+1 to mark roadbed edges.