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Glassblowing Fin Molds
Fin Molds are similar in concept to Optic Molds except that fin molds do not have an outer wall.An analogy would be the difference between a regular car (with a hard-top roof) and a convertible -- the convertible has no limit as to how tall you can be.
There is rather very little available written material about Glassblowing Fin Molds,
so I wrote to CMOG, and here is the informative response I received back:
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Tony,
The exterior fin mold, sold under the name "raggiere" (Italian for "spokes" I believe) is a tool you used to be able to buy from Carlo Dona. I suspect they make them custom, so one could get just what they need. The blades are customarily very thin (maybe 16 gauge), and are sharpened along the interior to a blade-like edge. One specific use of this mold is in the technique of "Merletto", where cane patterns are forced into the mold, and the fins help "cut" the color pattern, and with glass manipulation, and perhaps another time into the mold, create a more randomized looking surface. I've seen Davide Salvadore do it here before, but I suspect many contemporary Italians may have this technique in their tool box. Good Luck, Harry Seaman Corning Museum of Glass (CMOG) |
Dimensions:
| Height | 8.5 inches |
| Outside Diameter Width (at top) | 7.25 inches |
| Outside Diameter Width (at bottom) | 6.5 inches |
| Thickness of Base (Bottom of Fins) | 0.5 inches |
| Thickness of Fins | 3/16" |
| Length of Fins | 2 inches |
| Weight | 14.5 pounds |
| Inside Diameter Width | 3.25 inches |
| Inside Depth | 6.75 inches |
| Diameter of Nut at Bottom | 0.75 inches |
| Note: the Nut in the bottom is 1/8" above the bottom of the fins,
to provide a perfect recessed area for the punty to be attached! | |
The image below shows a cross-section of the mold design.
The center orange rectangle is the circular disk that all the fins are welded to.
This disk forms the perfect depressed area to punty-up to!
Also, the base is at a 5-degree angle to the vertical ribs.
Here are some calculations relating the size of the mold to the number of fins:
| Basic Calculations Concerning the Mold Shown Above | ||
| Inside Diameter (at top) | 3.25 | inches |
| Inside Radius (at top) | 1.625 | inches |
| Inside Circumference (at top) | 10.210 | inches |
| Inside Area (at top) | 8.295 | sq. inches |
| Inside Height | 6.75 | inches |
| Volume of cylinder (approx) | 55.996 | cu. inches |
| Weight of HOLLOW Cylinder (approx) | 3.270 | pounds |
| Note: Weight of sample piece is 2.85 pounds, so equations good! | ||
| Thickness of one fin at 3/16 inch | 0.187 | inches |
| Number of Fins | 15 | fins |
| Thickness of 15 fins at 3/16" each | 2.812 | inches |
| Average Gap (at top) between fins | 0.493 | inches |
| If we increase size of the mold (and add one or more fins) | ||
| Inside Diameter (at top) | 4 | inches |
| Inside Radius (at top) | 2 | inches |
| Inside Circumference (at top) | 12.566 | inches |
| Inside Area (at top) | 12.566 | sq. inches |
| Inside Height | 8.000 | inches |
| Volume of cylinder (approx) | 100.531 | cu. inches |
| Weight of HOLLOW Cylinder (approx) | 5.759 | pounds |
| Thickness of one fin at 3/16 inch | 0.188 | inches |
| Number of Fins | 16 | fins |
| Thickness of 16 fins at 3/16" each | 3 | inches |
| Average Gap (at top) between fins | 0.598 | inches |
| If we increase size of the mold (and add one or more fins) | ||
| Inside Diameter (at top) | 4.5 | inches |
| Inside Radius (at top) | 2.25 | inches |
| Inside Circumference (at top) | 14.137 | inches |
| Inside Area (at top) | 15.904 | sq. inches |
| Inside Height | 11.000 | inches |
| Volume of cylinder (approx) | 174.947 | cu. inches |
| Weight of HOLLOW Cylinder (approx) | 10.304 | pounds |
| Thickness of one fin at 3/16 inch | 0.188 | inches |
| Number of Fins | 20 | fins |
| Thickness of 20 fins at 3/16" each | 3.750 | inches |
| Average Gap (at top) between fins | 0.519 | inches |
| As we continue to make the mold larger, we add more fins | ||
| Inside Diameter (at top) | 5 | inches |
| Inside Radius (at top) | 2.5 | inches |
| Inside Circumference (at top) | 15.707 | inches |
| Inside Area (at top) | 19.634 | sq. inches |
| Inside Height | 10.000 | inches |
| Volume of cylinder (approx) | 196.350 | cu. inches |
| Weight of HOLLOW Cylinder (approx) | 11.812 | pounds |
| Thickness of one fin at 3/16 inch | 0.188 | inches |
| Number of Fins | 20 | fins |
| Thickness of 20 fins at 3/16" each | 3.75 | inches |
| Average Gap (at top) between fins | 0.598 | inches |
| As we continue to make the mold larger, we add more fins | ||
| Inside Diameter (at top) | 5.5 | inches |
| Inside Radius (at top) | 2.75 | inches |
| Inside Circumference (at top) | 17.279 | inches |
| Inside Area (at top) | 23.758 | sq. inches |
| Inside Height | 11.000 | inches |
| Volume of cylinder (approx) | 261.341 | cu. inches |
| Weight of HOLLOW Cylinder (approx) | 14.618 | pounds |
| Thickness of one fin at 3/16 inch | 0.188 | inches |
| Number of Fins | 24 | fins |
| Thickness of 24 fins at 3/16" each | 4.500 | inches |
| Average Gap (at top) between fins | 0.532 | inches |
| As we continue to make the mold larger, we add more fins | ||
| Inside Diameter (at top) | 6 | inches |
| Inside Radius (at top) | 3 | inches |
| Inside Circumference (at top) | 18.850 | inches |
| Inside Area (at top) | | sq. inches | |
| Inside Height | 12.000 | inches |
| Volume of cylinder (approx) | 339.292 | cu. inches |
| Weight of HOLLOW Cylinder (approx) | 17.719 | pounds |
| Thickness of one fin at 3/16 inch | 0.188 | inches |
| Number of Fins | 24 | fins |
| Thickness of 24 fins at 3/16" each | 4.5 | inches |
| Average Gap (at top) between fins | 0.598 | inches |
| Note: even at a 4" diameter close to the bottom, the 24 fins would still be 0.336 inches apart | ||
Calculations based on glass which weighs 0.094 pounds per cubic inch = 162 pounds per cubic foot (1728 cubic inches per cubic foot)
Chris Rogahn using a Plasma Torch to cut the fins of the new Fin Mold!
Final Design for 12" Tall 20-Fin Glassblowing Fin Mold - 5 Degree Angle
Note: Shown Below reduced Size, Click for Full-Size 2550-pixel x 4200 pixel image @ 300 DPI = 14" Tall Image
Bill Of Material (BOM) for 20-Fin Glassblowing Fin Mold
| Description | Source | Price $USD (February 2009) |
|---|---|---|
| Hot Rolled A36 Steel Flat Bar 3/16" Thick x 3" Wide x 36" Long
Qty 8 Pieces (24 Feet Total Length) A36 is a low carbon hot rolled mild steel with good welding and forming characteristics. This material is often substituted for 1020 and other low carbon steels. This material has a rough scaled finish. | eBay
Midwest Metal Warehouse 1-866-669-6444 | $5.81 each x 8 = $46.48
Plus Combined Shipping |
| Mild Steel Base Plate- 1/4" (0.25") Thick x 10" x 10"
with 9/16" Cornerd 3/4" from Edge, A36 Alloy | eBay
Discount Steel 800-522-5950 | $6.00 + Shipping |
| Mild Steel Flat Bar (Strap) 1/8" Thick x ½" (0.5") Wide x 36" Long | Home Depot SKU 478-997 | $3.49 |
Jim Moore Fin Mold with Detachable Fins I believe the only fin mold that is currently sold commercially is Jim Moore's detachable fin mold (shown in the image above) which allows each of the 24 fins to be individually removed, so you are not limited (as with a cast optic mold) to one specific shape/design.
The fin mold is 9½ inches deep and 5 inches across at the top.
The Jim Moore fin mold can be purchased directly from Jim Moore Glass Tools
In addition, the Jim Moore fin mold is available with either Curved fins or straight fins. This particular type of fin mold is not to be confused with an "inside" fin mold used for goblet-making
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glassblowing web page at 173.12.39.201 last modified: May 31 2009 |