The Infinite Rim Mold
™ is a new style of graphite mold
that has tapered holes, rather then the traditional hemispherical cups. I came up with this design after analyzing the way that I
was using traditional cup-style molds - using the rim of the hole for rounding, rather than the cup. The
problem with using the rim of a traditional cup-style mold is that many times the cup sizes available are just not right for the marble being made.
This usually causes one of two situations: either the marble goes down into the cup too far and the glass binds or catches on the rim, or too little of the marble fits into the cup, resulting in inefficient or negligible rounding.
In the past, some marble makers have solved these problems
by having graduated sets of graphite ring molds made. Although the desired
result of having the right size "rim" for any size marble is achieved
with this method, the rings themselves are fairly fragile, and a full set is
extremely expensive. I decided there had to be another solution.
first thought was that a single tapered hole would allow me to round any marble
as if it were riding on the rim of a traditional cup-style mold.
Theoretically, a tapered hole provides an infinite number of "rims"
because a sphere will contact the inner surface of a cone in a circle [Figure
1]. Therefore, no matter how much glass is in the gather, spinning it in a conical
mold should make it round! Unfortunately, there is a major design flaw in trying to
use just one tapered hole for all sizes of marbles - namely, the marble can't be
rotated horizontally if it's too small. This is because when the marble goes too far down into the hole, the punty hits the rim of the mold!
The design I ended up with is a series of overlapping, round bottomed cones,
providing an infinite possibility of "rim" sizes that currently span
from approximately 3/8" to over 6" (Custom molds can be
developed.) Each Infinite Rim Mold
™ is designed to round any marble within a given size
range. I mathematically designed the hole angles so that any marble that fits into the hole will be rounded as if it were being rounded on the
optimal size cup rim or ring mold, therefore avoiding all of the problems that arise when rounding
marbles. And best of all, because of the design, these are absolutely the easiest graphite molds
to use! The marble practically rounds itself!
I LOVE this mold! It's the best darn mold
- Josh Sable
Referring to a prototype 2" Infinite Rim Mold
When I decided I wanted to have these molds produced I approached Dan Grumbling
with the design. Dan had made some of my traditional cup-style molds, and
in my opinion they were some of the best quality molds on the market. Dan
uses only the best quality graphite, has excellent craftsmanship, and his attention
to detail is superb. Well... Dan and I spent the next 5 months designing and
prototyping all of the rest of the details of the molds to make sure that we had
the best molds possible for the money.
- The molds are made from EDM graphite - the best, slickest, smoothest graphite available.
- The graphite is attached to the handle using the same type of band-clamp mounting system that Dan had been using
on his traditional molds. This system has several advantages.
- The handles are custom-turned titanium which provides a lightweight,
durable handle that won't burn, warp, or conduct heat. And the
attachment method provides for a non-slip, twist-proof attachment. The handle will never
slip or twist - guaranteed!
- Minor wear and tear is easily maintained: For example, if your punty always contacts the rim in the same place because of the
angle you hold the mold, it may wear an indentation in the rim over
time. If this occurs simply loosen the band, spin the mold to a new
position, and retighten the band.
- If the graphite mold gets broken in a fall, or severely damaged for any reason, it can easily be replaced by
loosening the band, removing the graphite puck, slipping in a new puck, and
retightening the band. This saves on some of the cost of buying a
completely new mold in the unfortunate event that it's necessary.
- Each handle is 12 inches long overall to accommodate different working styles. Some people
like to choke up close to the mold, while others like to hold further back on
the handle to keep their hand away from the heat.
- The handle is counterweighted with a
custom-fitted, swirled, pewter-like knob on the end. On the smaller
molds this places
the balance point very close to the center of the overall length and makes the
easy to maneuver.
- NOTE: Molds
can be order without handles. Also, custom mounting brackets
designed to hold the mold on the work surface can be ordered directly from Dan
Grumbling when ordering the molds. This is especially important with the
larger sizes. Contact Dan for details via the order
There are currently eight molds available. The smaller sizes are contained in
a multi-hole mold, and the larger sizes are in individual molds. Below is a
table showing the hole sizes and the corresponding range of marble sizes that
can be made using each hole.
||Approximate Marble Size Range
||3/8" to ~ 5/8"
||1/2 to ~3/4"
||5/8 to ~ 7/8"
||13/16 to ~ 1-1/4"
||1-1/8" to ~ 1-1/2"
||1-1/4" to ~ 1-3/4"
|1-5/8" to ~ 2-3/8"
|2-1/4" to ~ 2-7/8"
|2-5/8" to ~ 3-1/2"
|3-1/2" to ~ 4-5/8"
|4-1/4" to ~ 5-3/4"
|5-1/3" to ~ 6-15/16"
Click on the item number to view the
Dan Grumbling is my official manufacturer of The
Infinite Rim Mold
™. All purchases for molds must be
placed directly with Dan and must be only for molds. Please don't combine marble purchases with mold purchases.