| Two views, inside and out, of the results of the first sinking
pass. I take some care to keep the bowl reasonably symmetrical, but great
precision is not required yet. |
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| The center is heated and driven down. Then, to gain greater
depth and to smooth the bowl form out, I do another sinking course, this
time from the center outward. I take greater care to keep the bowl uniform;
I especially do not want any great amount of warping, or "potato chipping",
where the bowl is curved more on one axis than the other. |
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Time for a depth check! I like to keep track of the depth and width
of the blank as it forms. I use flexible steel rulers -- very handy things
to have for hot sheet metal working. The blank has been sunk all over
its surface, using the shallow block. At this point, it's depth is about
3". |
| Since this will be a "peaked" helmet, with a sharp apex, I may as well
make provisions for the peak now, while the blank is shallow, and the
interior is easily accessible. I mark the center while the blank is still
warm, using metal rulers and welder's soapstone. Dividers also work fine. |
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| I reheat the center, and switching to the narrow, deep sinking
block, I drive down the very center of the helm. I use a long, thin bossing
hammer for a couple of heats. I punch down about a 2" diameter region
this way, making it about an inch deep. I have to be gentle! It's easy
to thin the metal too much, hammering with such a skinny hammer in such
a limited area. |
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The blank is now fully sunk, with a "proto-peak". Dimensions: average
15.5" diameter, 4" deep. The rim actually tends to shrink during this
type of hot sinking; I've lost 0.5" of diameter. Since the plan is
to make a 7" high helmet, I now have a bowl that is over half the finished
height - not bad! At this point, it's time to begin raising. (Total time
needed to sink was about 1.5 hours.) |
