We are bidding on replacing some sign faces that are attached to an existing pylon sign. The top of the pylon has a radius arch shape. Directly below the top arch the sign panel arch matches the pylon arch exactly. So in order to replace the sign we would have to duplicate the radius. The only way I know how to do this is to take a tracing off the existing sign. Only problem is it's up 30 feet in the air. We would have to rent a lift just to reach the area to trace the radius. Is there another way to duplicate a radius?
Posted by Dawud Shaheed (Member # 5719) on :
find out who did the original.
Posted by David Harding (Member # 108) on :
There are a couple of ways to do it via geometry, depending on how the radius is handled. I'll do a step-by-step sketch up on how to do this.
Posted by Jon Jantz (Member # 6137) on :
No, Jean... you wouldn't HAVE to rent a lift... there are other ways of measuring it....
[ March 30, 2009, 02:06 AM: Message edited by: Jon Jantz ]
Posted by Bruce Bowers (Member # 892) on :
Jean, I am sure David is going to use the same method I would. Feeling lazy today I will let him do the work... Hahahaa!
I would use a van ladder or a tall ladder and a helper to get your measurements. A little expense up front will save you much grief later.
Measure your width of cabinet. Measure the overall height. measure the the flat portions of the sides. don't forget to measure your retainer width.
Using these measurements to make a computer rendered drawing. I have done many of these.
Posted by Dale Feicke (Member # 767) on :
I don't know, Jean; the radius at the top of the sign could be any of a bunch of inches in diameter. It could also not be a true radius, maybe being flatter on the down slopes than the top curve.
I'd want to spend the extra money to make the real measurements and tracings. Remember what the faces are going to cost and how much it will cost YOU if they are not right. I don't see where anyone except the company who originally did them would have an advantage in this respect.
Posted by Doug Allan (Member # 2247) on :
For what it's worth, I made a $5000 mistake last year, by interpolating a measurement from a photo. That makes the cost of an actual measurement go down in my mind for the rest of my career!
Posted by David Harding (Member # 108) on :
Here's my step by step on doing with software what I used to do with compass and straight edge.
To do this construction, you will need precise measurements of the width of the sign, the shoulder height to the start of the curve, and the height to the top middle of the sign. With these three measurements, you can construct an accurate radius. You are still doing this at your own risk because the other company may have produced this with flat spots as Dale mentioned.
Below are two scenarios, assuming each one is a true arc. One is actually a semi circle on top of the sign that ends tangentially with the sides, the other is a section of circle with cusps where it intersects the sides of the sign.
This is how I set up my workspace.
I draw two boxes in scale, one the size of the rectangular portion of the sign, the other the total height of the sign but half the width.
Draw a line and rotate it 90 degrees. Make sure it snaps exactly at the shoulder and top center.
Drag the line larger until it intersects the center line of the sign.
The intersection point is the center of the circle that will make the arc section.
Start the editing process.
Finish trimming, welding, and adding the retainer contour.
I'd superimpose this over a minimally distorted photo of the sign to check and see if there's any obvious anomalies. Also, on installation, bring a router or laminate trimmer with a flush cutting bit with a bearing on it. If the face is slightly large, the router will trim it to match the can. Be sure to allow for expansion clearance.
[ March 30, 2009, 07:34 PM: Message edited by: David Harding ]
Posted by Jean Shimp (Member # 198) on :
David, Thanks so much for your step by step. I will definitely print out and keep this on file. The radius on the sign in question REALLY looks like a true radius, but like Doug, I could end up with a very costly replacement if I trust the photo. The original sign maker in long gone and the property owner has no drawings on the sign for reference. Coincidently I also have another sign with a radius to duplicate but it's at ground level. I'll use this method on that.
Posted by Mike South (Member # 4523) on :
Forget the fancy math, just go measure it. You can also confirm face type, rigid, flex etc. Lamp spacing for proper lighting with new face etc. Can't assume anything is square or one of the sign is larger then other.
Posted by Tony Vickio (Member # 2265) on :
I'm with Mike. I only see one sure way to order new faces with no worries.
Measure it!
Posted by Ken Henry (Member # 598) on :
What if.....and it's a rather BIG ONE, the curve you're seeing ISN'T a segment of a circle, but rather a segment of an ELIPSE or OVAL ? That would throw everything off, since the radius won't give the proper curvature.
Actual measurements and/or tracing is the only SAFE way to go.
Posted by David Harding (Member # 108) on :
Even with measurements, it is necessary to generate some computer files for production, permitting, etc. The steps above will help to get things very close to actual and also to verify.
I've field measured numerous odd shaped faces for retrofit, including many Granite ones. I'll set up my measurements similar to what I show below.
I'll plot the measurements in Corel and then generate a curve to match.
For really weird shapes, I have a piece of matte .020" clear Lexan, approximately 4' x 10'. I'll hold that up against the face and mark everything on it with a pencil. I then precisely measure that clear template and plot it on the computer. When my Lexan template is not being used, it gets rolled up and secured with tape.
Following is a picture of a retrofit we did using measurements, photos with minimal distortion, traced pattern on Lexan, and computer generation.
Posted by Doug Allan (Member # 2247) on :
great job David!
Posted by Ian Stewart-Koster (Member # 3500) on :
So, Doug, what was your costly mismeasurement all about?
Posted by Darren Salyer (Member # 10761) on :
OK, I've lurked long enough!! Time to jump in and introduce myself. While not a sign guy yet, I'd like to use my CNC machine to start doing some sign work. My experience is 20+ years as a trim carpenter/cabinetmaker. I'd love to be able to do some CNC signs with a tenth of the talent I've been observing here. To add a little info to the topic, a simple formula to calculate a true radius when the width and rise from a shoulder is known is as follows: To get a radius from the rise and spread.
S=Spread R=Rise
(S/2)Squared + (R)Squared/R(2)
Example:
S=36 R=8 Radius=24 1/4" Hope this helps someone, and that I fit in here. Darren Total Home Remodeling www.asktotalhome.com Posted by Ray Rheaume (Member # 3794) on :
DO NOT ASSUME THAT A FORMULA WILL WORK!!! Get the money for the lift, include it in the price, make it a separate fee....whatever it takes to get up there and KNOW what you need.
Tape measures and traces work for a reason. They are TRUE! They are also a better assurance you won't be doing it twice.
Ask me why I know this... Rapid
Posted by Russ McMullin (Member # 5617) on :
So Darren steps out of the shadows to make his first post, and he gets hit with all caps and triple exclamation points. LOL.
Hey Darren, welcome to Letterville. Keep posting. You will fit in just fine. Your experience with CNC should give you the ability to make some really cool stuff.
Posted by Jon Jantz (Member # 6137) on :
Welcome to Letterville, Darren. You'll fit in great. No worries...
Just keep making suggestions and if the poster doesn't follow them, don't feel bad. I doubt Jean will follow my suggestion in this post either, but I don't let it get me down...... Posted by Ian Stewart-Koster (Member # 3500) on :
Who's Jean? (or which Jean is that, JOn?)
Welcome Darren. Yes, that's the formula for the radius, given the dimensions of a chord of a circle, but as Rapid was meaning- maybe it was an oval/ellipse, not a circle, or maybe it was drawn manually with differing degrees of arc in different places.
I've had frames made up where I gave the engineering shop a template with a perfectly radiused curve, but which they botched up the frame of, so that ultimately I had to make the face to suit their structure, which was markedly different from my original.
Fortunately, with experience, you learn to expect them to muck things up, and you hold off on your side of the production until they have finished, so you can adapt what you do to what they did. You can't presume they'll be as good as you hope they'll be!
(does that make sense...!?!)
Posted by Brad Farha (Member # 931) on :
Do not use any formulas for estimating the radius! Tell the customer that you will need to take actual measurements, and have them pay for that in advance.
