what does the radius af a curve mean? EXAMPLE: atlas Dash 8-40c has a min. radius curve of 22"- how do i tell how sharp my curves are?
This is going to be dificult to explain verbally so bear w/ me. The radius is 1/2 the diameter. For a 22" curve drive a nail into the table top through a yardstick… Measure 22" and put a pencil on the yardstick at that point. Swing the yardstick around the pivot and the pencil will mark a 22’ radius curve. To figure the radius of a curve already laid, measure a 12" straight line across the arc of the curve. With a square draw a line towrds the center of the curve at the 6" point of the straight line. Repeat at another point on the curve. Where the two lines cross is the center of the curve and the radius is the distance from where the two lines cross to the curve.
If your curves form complete loops or semicircles, it’s a simple matter of measuring center to center… Anything less than that you’ll need to find the center of the curve arc and measure from there… If you are talking prefab track (bachman, atlas, etc) sections (not flex) it’ll either be 22 or 18 in most cases. 22 will be the wider of the two. If you want to make a template for measuring, take a peice of poster board or other large sheet of something easy to cut and a yard stick (or something else you can mark off inches on)… Hold the 0 of the yardstick at one point while drawing an arc at about 22 3/8 Inches and another at 21 or so inches (like you would with a large drawing compass) and then cut out the piece… The outer edge of that peice will be equivilant to about the outside rail on a 22" radius. Holding the template to the rail, you will discover one of 3 things… First, your track is 22" radius. Second, your track is less than 22" radius (template ends resting on rail but rail moves away from template in the center of the template). Or third, your track is greater than 22" radius (template center will rest on rail but the ends will not)…
Get all that??
Good luck,
Jeff
okay, so couldn’t i just measure a circle of track(to get the diameter) and divide by 2 to get the radius?
Are you using Atlas sectional track? If so it is marked on the back.
the Radius is the distance measured from the center of the track (where the nail holes are located) to the center of the circle. The radius is also 1/2 the diameter. If you have for example a 4 foot wide sheet of plywood on a penninsula in HO scale you could put a 22’’ radius curve on there with about 2 inches on either side of the board left. I know that 4’’ = 48 inches and 1/2 of that is 24 but you dont want to put the center of your track right on the edge of the board (one rail and 1/2 the ties would be hanging over the side)
If you are drawing out the track plan on a sheet of wood a trick ot use to make your curves just right is to take a string and measure it out a little longer than the radius of the curve you want (eg 22’’ radius cut string 26") Tie a loop in one end and a pencil to the other. Find the center of the circle (a curve is just a small part of a complete circle) and hammer a small finishing nail into the wood. (if the center of the circle is not on the layout you can hammer the nail into a piece of wood that is about the same height as the layout) now measure again from the nail to the pencil and make sure that it is 22’’ If it is not then roll a little string up with the pencil till it is the right distance. Now you have just made a large compass for drawing out your curves. Hope this helps.
Yes.
If you don’t have a full circle or half circle to work with, start with a guess. From the center of the track (between the rails), measure off 18 inches towards the inside of the curve.
Now pick a spot at the far end of the curve, and find the point where an 18 inch mark meets the first mark. From this point, the distance to the center of the rails will be 18 inches in any direction of they are 18" radius curves. If not, repeat the process with 22" measurements and keep upping the ante till you get a match at three or more points.
Yes you can measure circle of track and divide by 2.
circle measured 44" you have 22" radius
Circle measures 36" you have 18" radius
- so can i measure from the center of the circle to the center of the track and the resulting measurement would be the radius?
thanks everyone, I’m gonna go measure those curves right now- be back in a few minutes to tell ya what i found
the curves are 18"- even though atlas says the min. radius for the dash8-40c is 22" will it negotiate a 18" curve(without derailing)?
It may or may not… I’m not real familiar with the Dash8-40c but if they have 6 wheel trucks and the wheels are spaced far apart, it will likely have problems. I’ve seen locos with the same spec run fine on 18" radius and others won’t… Your best bet may be to find one in a hobby shop and test it there…
Jeff
i occasionaly have problems with my Atlas U33C (6 axle)derailing on curves. My Athearn AC4400 (6axle)rides these curves fine(usually). I’ve never a a 4-axle derail on a curve…EVER!
That’s because the radius is too small. The trucks are binding or interfering w/ the steps or underframe. If you do want to run 6 axle on the small radius, you may be able to remove some material to clear the trucks. I would only do this if you have no other alternative. Best rec. is not to run them under a 22" radius.
Even if you can negotiate the curve with the engine only, you are sure to have derailment problems with rolling stock.(the coupler swing will be too great)
Bob K.
well there’s no way i can switch to 22" curves- on the old table there is only about 2" from the track to the edge of the table on each side- an i doomed to 4-axle? i may just stick w/ athearn for my 6 axle locomotives since the AC4400 stays on curves 95% of the time ,Thanks everyone
Bummer on the radius thing. You could always put the six axle units in storage (model a small engine terminal) and use a four axle unit to run a local. Anybody know if BNSF have any SW 1500’s or equivalent?