Scroll development question

[HWooldridge]

I was wondering if anyone who does a lot of scroll work has a good mathematical formula for determining stock length. My method is to first draw the scroll on the table then use a dressmaker's flexible measuring tape to determine the finished length. For a simple tapered tip, I subtract double the material thickness from the final length, so a C-scroll from 1/2" stock that must complete at 28 inches would start with 26 inches on the assumption each end will draw by an inch.

This method normally gets me pretty close to the table sketch but the other night, I had an S-scroll finish about two inches longer than it should have so I'm having some doubts about the validity of my theory and would like to know if anyone has another technique.

Thanks, Hollis

[brianbrazealblacksmith]

The reason the dress makers tape doesn't work is because it is not the same thickness as your material. You'd have to make a scroll out of 1/4" material and measure the outside of that if you are making them out of 1/2" stock. You have to measure from the center of your material. One thing about scolling though is they are easy to tweak and make fit into the box.

[Dodge]

There are some add-ons available for Google sketch-up that do a nice job of figuring stock lengths. You just draw the scroll ( one of the add-ons) and the stock tool does the math. Sketch-up is a free download (Just google it) and so are the add-ons. Sorry I can't remember where the add-ons come from. Maybe someone here will fill in the blanks ;)

[John B]

Mark out your scroll shape and use a piece of non stretch string, or soft wire to conform to the centre line position on the scroll, then make adjustments for the type of scroll end you are proposing to use.

Another way if you are going to be making many scrolls, is to make a set of scrolling jigs, and note/stamp on the lengths used to produce a scroll on it, these can be then used to calculate the length to be used

[divermike]

also make 1 extra of each size, and mark the length on it and hang it, the next time you will have it to compare, after a while you have a bunch and it's easier to figure out, and it's nice to have them laying around for design purposes as well. Good luck and good hammerin.

[TASMITH]

There is a mathematical formula called the Clackson scroll method.

L = Pi x s x n^2

L - represents length of stock required

Pi - 3.143 (rounded off)

s - spacing between the turns

n - number of turns in the spiral (squared)


Example: spiral with 3 turns spaced a 1/4 in apart


L= 3.143 x 0.25 x 3^2

L= 3.143 x 0.25 x 9

L= 7.071 in

Or just over 7 inches of steel to make the spiral


Terry

[HWooldridge]

Terry,

That is exactly what I was looking for - thanks very much. I'll try it and see what happens. The old timers didn't have CAD and they probably didn't like "cut and try" any more than we do so I figured there had to be a formula.

I have about 30 scroll forms I've made over the years and they are all marked with the stock requirement (for example, "snub, 1/2, 15" denotes type of scroll tip, stock size and length). However, it's fairly common that other sizes are needed for new jobs and I was looking for a starting point to prevent trial and error.

Mike, keeping an extra scroll is a good idea. I would even say a person could make a range of stock sizes - maybe 3/8, 1/2, and 5/8 - and bend each one over the form as the look will change dramatically depending on the size of the parent bar. As you said, a good design tool.

Thanks for the replies...H

Edited March 9, 2009 by HWooldridge
content

[TASMITH]

Hollis,

I have used this formula and it works well for even spaces between the scrolls. You have to fudge the starting length some though if your spaces between the spiral are expanding a bit on each turn, but it gives a pretty accurate starting point and saves a LOT of trial and error waste of stock over some of the other methods I've tried.

Terry

[firebug]

You can go to Lowes, Home Depot and look in the tool department. It should be around the other measuring devices such as tapes, rulers, squares etc. Look for a gray in color electronic measuring device shaped like a FAT pen with a red wheel on the bottm. The top is wider than the bottom. You can then turn it on and trace the C- scroll, S-scroll, ring, whatever shape it is and get a very accurate measurment. The tracer wheel is about a 1/2 inch round and works GREAT. You can trace drawings or other peoples finished scrolls and use the measurment to replicate the design. They are not cheap, about 50.00 bucks but the time and wasted material you save will pay for it in about a day or two if you do a lot of scroll work like me. It has a built in scaler too, it is used to figure footage on blueprints also. Example, 1/4 inch equals on foot.

[Ed Thomas]

Firebug, I did a search and found one of the more common devices as you described to be called the "Scale Master Classic", available online and in stores. Are you actually using this for measuring scrolls and such? I'm wondering how accurate/reliable you have found it to be? Seems like one of those gadgets that could get addicting in a hurry and very useful if it is consistent.

Terry, that formula doesn't seem to take the expanding rate of the scroll into account. If the expansion is linear, I suppose you could take the start and end and average them, but most, such as the fairly common Fibonacci rate, aren't linear. I'm so danged rusty on the higher math that my head hurts on this stuff anymore. But my instinct is that the error Hollis got on the 'S' scroll is due to this expansion; the amount of error then being doubled as the rate stopped and then reversed. Does that make sense, or do I really have to hit those particular books again?

[firebug]

They are VERY accurate. Worth every penny. I gave my last one to Hofi and promptly bought me another one the same day. I use it all of the time. It has a "custom" mode that simply measures in inches as you roll it around the design. The wheel is thin and small which helps it to be easy to roll around different shapes. I usually measure the scroll more than once and it is the same each time. If you make scrolls for projects especially ones that must fit into certain areas it will pay for itself fast.

[HWooldridge]

Well, I went out and bought a Scale Master tonight at Home Depot - $64.81 including tax. It gives similar readings to my dressmaker's tape but is much faster and easier to use. I am currently working on a gate with 28 scrolls, 10 of which are complex (multiple ends) so I used the gadget to measure one chalk outline on the table. The finished scroll was within 1/4 of fitting the drawing and that was easy to tweak to size. Anyone who does architectural work should consider getting one of these; my wife and I were joking about going to court over custody since she wants to use it for quilt patterns - but actually, I'm smarter than that and will just leave it in her studio until I really need it

Thanks Firebug - a great suggestion...Hollis

[TASMITH]

Ed,
You are correct in your math. This formula was designed with the idea that your scrolls would be linear. In my second post on it, I did caveat the fact that if the distance between the turns increased as you formed the scroll that it did in fact change the starting length. This is an OLD formula however that does give at least a base starting point to make a scroll and as I stated earlier it has helped me a lot. Of course with the new measuring devices available now it makes the old formulas even more obsolete, but they are still there for people to try. Sometimes its' just fun to try the 'OLD' ways.

Terry

[Alwin]

One other technique, though probably not as good as the electronic measuring device, is to use a roll of solder. You just form the solder into the shape, straighten it and measure.

[Ferrous Beuler]

You could also use a traveler as smiths have done for centuries. Make them in smaller sizes than the standard 12" if you like. Remember to measure down the centerline.
I think this was a tuesday night BP once upon a time?

[ornamental4766]

i knew a blacksmith down in Charleston SC. that did most of the wrought iron gates, fences, handrailings etc. down there. His name is Philip Simmons. He has been a blacksmith journeyman for about 55 years. What he would do is take a piece of stiff wire thats easily bendable and he would draw a "to full scale" size of the scrolls that he wanted to make on his shop floor with soap stone then he would take a piece of the wire and bend it around the drawing on the floor he made with the soap stone and cut off the access then he would straighten out the wire and that would give him the length of stock he needs to do a scroll etc. But here is what i did to save myself a lot of time and frustration. Call the company KING ARCHETECTURAL METALS Baltimore Md. and get a catalog of there different ornamental pieces. All they do is make ornamental pieces for these ornamental shops to just weld them together. My suggestion is this: look through the catalog and pick out a scroll or etc. and get 2 of them that is the size of scroll you want to make. Then cut the rest of the scroll off that you don't need and grind down the flare on the ends until it is the same width as the rest of the piece and weld one on top of the other then weld the scroll pieces on a 1/4" thick steel plate leaving about 8" extra plate all the way around. KEEP YOUR IRON HOT AND HAMMER HIGH.

[CRAFTBENDER]

The reason the dress makers tape doesn't work is because it is not the same thickness as your material. You'd have to make a scroll out of 1/4" material and measure the outside of that if you are making them out of 1/2" stock. You have to measure from the center of your material. One thing about scolling though is they are easy to tweak and make fit into the box.

I like your method. I'm bad about not writing things down, so if I need to see how much material is in a scroll, I set some dividers at .2 and walk around the scroll at the center of the material. Two, four, six, etc. On bigger scrolls you could set the dividers wider. Same thing if it is drawn out on paper.