Oh great and wise Orchidians, I’m the one writing the book. I’m

stuck with a problem. If I have a 6mm bead and I want to make a

bead cap for it, how large would I cut the sheet metal and to what

diameter would I take it to when I dap it. Let’s suppose I have

disk cutters and a block and dapping punches and a dapping block.

I’m thinking that there must be a formula for this, but I can’t find

one. I’m going to thank the Orchid list in my thank you page and

I’ll thank anyone who can give me the answer by putting their name

in the book and sending them a copy. I have an October 15 deadline

and yes, it’s really being published by a real publisher. Thanks in

advance for your help. Christine

For determining the size disc needed for a bead cap, see

Silver-Smithing by Rupert Finegold and William Seitz, 1983 (still in

print). The authors present a method for determining the disc-blank

size needed for forming a bowl - which also is useful for

determining the disc size needed for any half-sphere size or less.

The authors present a graph that illustrates the method better than

words alone, but for your 6-mm bead:

-Draw a horizontal base line under a 6-mm circle,

-Draw a line perpendicular to the base line up through the diameter

of the circle,

-Draw a horizontal line through the diameter of the circle parallel

to the base line,

-Determine how far up the circle/bead you want the bead cap (your

choice), and draw a line from this point across the circle parallel

to the base line.

-Anchor the compass on the base line where it touches the circle

center line. Place the pencil end of the compass on the point where

the bead cap height is marked on the circle. Draw an arc from this

point down to the base line. Make another arc from the other side

(or make a big circle through both diameter points).

-Measure in-between the points made by the arc on the base line.

This is the disc size needed.

This method provides an estimated size because it does not account

for the thickness of the metal or the variable amount of stretching

during doming. However, most bead caps are made of thin metal and a

shallow dome does not stretch the metal very much. I included a

chapter in my book on determining the disc size needed for a

half-sphere. As well, I presented the disc size needed for 10

commonly used bead sizes. I suggest you include not only the

Feingold-Seitz method, but also (or at least) provide a table

listing the disc size needed for certain size bead caps. This is

easy enough to do and would be appreciated by your readers.

As a general rule, place your bead in a dapping block die that is

the same size; dome the bead cap only to the next largest die.

Again, this varies with the thickness of the metal and the

incremental die sizes available in your die block (it varies).

I hope this is helpful.

Nancy

`Oh great and wise Orchidians, I'm the one writing the book. I'm stuck with a problem. If I have a 6mm bead and I want to make a bead cap for it, how large would I cut the sheet metal and to what diameter would I take it to when I dap it.`

Christine, there are two answers to this, the easy one and the righ

one. Lets look at the easy one first…

Thinking just in two dimensions (easy, OK?), the bead is a circle

of 6mm diameter. We want a strip which can be bent into a curve of

3mm radius, so that it fits snugly against the circle. Suppose we

want the strip to cover half of the circle. Now, the circumference

of a circle is Pi times diameter, or inthis case 3.14 times 6, say

approximately 18mm. Wanting to cover half the circle we take half

that length (9mm) and form it to a 3mm radius curve. If we wanted a

smaller cup, say covering just one third of the circle, we would

take a length equal to one third of the circumference. Fine, in

theory.

Going up one stage in realism and complication, but still in two

dimensions, lets say the strip is to be made from material that is

1mm thick. We require the internal radius to be 3mm, so we would

use a punch with a 3mm radius end. On the dapping block we would

use the hole of 4mm radius, to accommodate the material thickness.

Note that this is purely a geometric argument, and assumes that

there is no distortion of the strip other than pure bending i.e. the

dapping does not cause thinning and elongation. OK so far?

Now, in real life we we work in three dimensions, and there is

distortion. We can still take the geometric method as a starting

point. So now we cut or punch a circle of 9mm diameter, use the same

punch of 3mm radius and the same 4mm radius hole in the dapping

block. In all probability you will not end up with a perfect

hemisphere though. More likely a hemispherical lower portion with a

sort of collar around the top, possibly wrinkled, that would have to

be cut or ground away.

Point is though that at least you had a starting point. Now, if

this was for a one-off that would probably be the end of the story.

But if you were wanting to make a lot you would have to look

critically at how much excess material there was, and make your next

disk accordingly smaller. Then try to form it in the dapping block

using exactly the same amount of force on the hammer and the same

number of blows. But since there will always be some variation in

the forming process you would need to always use a disk that you

knew would give a slightly oversize result, so that you could cut it

back. If there is only a small amount of material to remove the

easy way is to rub the whole circumference in a circular and figure

of eight pattern on a pice of rathe coarse wet and dry paper, used

wet, supported on a flat surface.

Hope that helps, and Good Luck.

Kevin (NW England, UK)

I can see some problems with the doming technique presented by Kevin

and suggestion that the discs should start out oversized. A bead

cap, sometimes purely decorative, generally is thin metal and, with

a small hole, is used to center a bead with a larger bead hole onto

a thinner strand with smaller beads. If the disc is too large (and

hit with a dapping punch that is too small), then the dome rim will

be warped as described by Kevin. But, a bead cap rarely is a plain

dome that can be sanded down past a warped or excessive size. Often

pierced, it is much easier to pierce a design on a flat disc than

after doming. And, for matching pairs, two or more discs can be

stacked and pierced as a unit. If a disc is slightly domed, the

pierce design can be over the entire surface without much worry

about distortion - as the arc of the dome is increased, the

stretching (and often destruction of the design) increases from the

disc center outward.

Also, many bead caps are scalloped into four or five lobes, as in

the petals of a flower, so that the caps will fit a range of bead

sizes. The lobed wire bead caps (decorative only) I recently made

were gently pressed, not hammered into the dapping die. These caps

extend beyond the bead diameter to overlap and were soldered in

place (that was tedious) but they could have been used on a wide

range of bead sizes. (It’s a necklace on my website.) Anyway, if

you start with the correct disc size and don’t get carried away with

forceful doming, you can make uniform and decorative bead caps

without much final finishing at the cap rim. I do agree with Kevin

about the estimated disc size being only a starting point. Whatever

method you use to determine the correct size, you need to try it out

and adjust accordingly. Hope this just adds a few more points.

Nancy