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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:
 
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)

 
Glassblower.Info - Glassblowing - Fin Mold - 15 Fins - Top View
 
Glassblower.Info - Glassblowing - Fin Mold - 15 Fins - Inside View
 
Glassblower.Info - Glassblowing - Fin Mold - 15 Fins - Side View
 
Glassblower.Info - Glassblowing - Fin Mold - 15 Fins - Bottom View
 

Dimensions:

Height8.5 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 Fins3/16"
Length of Fins2 inches
Weight14.5 pounds
Inside Diameter Width3.25 inches
Inside Depth6.75 inches
Diameter of Nut at Bottom0.75 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) 8.274 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

Glassblower.Info Glassblowing Detachable Fin Mold

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.
It tapers slightly and there is a large radius in the bottom.
The mold is a large one and many people use it to make pumpkins and squash.

The Jim Moore fin mold can be purchased directly from Jim Moore Glass Tools
or through their distributors such as Olympic Color Rods.

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
(image shown below) which is used to make faceted goblets.

Glassblower.Info Glassblowing Fin Mold for Goblet-Making


 
At 20:36:49 April 27 2017 displayed this www.glassblower.info
glassblowing web page at 173.12.39.201 last modified: May 31 2009