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Casting tiny holes, channels, tubes

Hi, I am going to cast in gold and platinum some watch bracelet
segments with very tiny holes for pins. The holes are to small and
long to be filled with investment. I thought about putting inside a
metal wire inside the wax model. But it may stick to gold or platinum
or even melt together with them while pouring hot precious metals to
flask. I want to avoid drilling holes in casts. Any suggestion how to
do it? Thank you.

With sand casting one can use a graphite rod, which is easily
drilled out later. This is not likely to survive the burn out
process, so you will have to use something that can do so, has a
higher melting point than platinum and can be removed later
chemically with say acid. The two things that come to mind are
niobium and tungsten. Niobium would require pretty potent acids which
are likely to dissolve the platinum also. Tungsten I believe can be
dissolved with concentrated hydrogen peroxide.

Good luck,
Scott Garrison


I’ve used hard (4H) pencil leads for mechanical pencils to hold open
hinge tubes for casting with excellent results. The harder pencil
leads seem to hold up the best through the entire burn-out and
casting process, although a bit of drilling is usually called for to
knock out the remaining pencil leads from the cast hinge tubes.

The pencil leads come in a wide variety of thicknesses, and some will
fit the wax tubes exactly. Leave a bit of the lead sticking out of
each end of the tube being cast, for the investment to grab onto.

Jay Whaley

I want to avoid drilling holes in casts. Any suggestion how to do
it? Thank you. 

Well, Jaroslaw, sometimes you just gotta bite the bullet and drill
your castings. Leave little dimples in your waxes for center punch
marks. There’s no way any metal wire is going to be removable,
whether it fuses or not. Think of the tightest fitting glove
imaginable. Even if you can fill the holes with investment, what
generally happens is that the metal goes rushing through and breaks
your teeny tiny pillars of plaster, which then mixes into the metal
and becomes porosity. This is especially true with platinum, because
of the density. Just drill them…

With your wax model pre-holed, push in investment slurry in the holes
with syringe or by other appropriate means and carry on investment
and further processes, as usual. Hope u succeed in your endevours.


I have heard of people using the thin graphite rids used in drawing
pencils - the ones that use the 0.5mm “leads”. I expect it would
work just as well with gold but I also expect you would have to
finesse the burnout cycle so wax is burnt out but the graphite
doesn’t burn too much. I think it would be pushing things at platinum
burnout and casting temperatures. There are also thicker “leads” for
clutch pencils which might work as well.

I haven’t tried it though.
All the best

In my experience casting small tubes is a no no, You would be best
to draw down chenier. Are the bits you want to cast, round or square
or??? Make or buy chenier and put a steel piano wire of the pin
diam. required through the chenier, wax well, internally and
externally and draw through a drawplate round or square, to the
desired size, withdraw the wire, and cut your lengths as required.
This is a watchmakers job, they usually order links from the company
agency. But I have made up approx copies which were good enough as
the original were not available.

David Cruickshank

I have also used pencil leads to make fine holes in castings. You
need old pencil leads, the modern ones use a plastic carrier rather
than clay and it will burn away. They will obviously need to be
drilled out afterwards. I came across this tip in Jewelry Casting by
Murray Bovin. Full of useful info. You can test them by just putting
them under the torch and see if they survive. E-Bay often has older

Tim Blades

i use small titanium wire. it dosnt stick to the inside of the
casting and can be pulled out afterward. the other trick i use is to
thread a long piece of waxed floss through each of the holes, after
pouring the investment carefully pull the thread out and it will
pull the investment into the tubing.

Brian Nilson
B&RN Design
Storrs, CT.

You are right not to attempt to invest the holes but you should
conquer your fear of drilling. This is really the only way to get
the proper hole for your links. If you try to use a wire, even
stainless, it will warp, get firescale and ruin your casting. Just
form a small dimple in your wax where you want to drill before
investing. Setup a firm holding jig to do your drilling.


Bit of an oxymoron!

Brilliant Idea using pencil leads, Jay. I would never have thought of
it as I would have thought the carbon would burn out. I sent a post
yesterday from Aus, usually a day behind others. But:

Thinking about it during the night, here we have to match some
existing links and I still would try to fabricate rather than cast. I
was imagining single tubes / links but watch links are often double
tubes, so I would work out a diameter that when compressed to the
point that the internal long oval formed would allow me to insert two
steel wires, (to be removed but of the same diameter of the pins) I
would then further compress each link on one side so it was slightly
concave, forcing the steel wires apart and giving a slightly convex
face to the eventual outer surface. Withdraw steel wires and insert
your gold pins through the links and the side interlinks.

I would never have thought of it as I would have thought the carbon
would burn out. 

That’s why the choice of the type of pencil lead you use is
important. Part of the lead’s survival is because the “carbon” is in
the form of graphite, not charcoal or something, and graphite is a
bit more resistant to burning away (though it slowly does) As one
poster pointed out, a number of the easily found brands are quite
flexible. These have softer plastic binders, and they will not
survive burnout. You want to get older types which aren’t so
flexible, and get as well, the “hardest” grade lead (like 4H or 6H,
etc) you can find as well. The harder ones have increased clay in the
binder, so that also helps the graphite to survive.

I cannot say I’ve done this much. But some 20 years ago, I had
occasion to do this while casting a whole bunch of bracelet links,
and needed the hinge tubes to be open enough after casting to allow
accurate and easy drilling. The pencil leads I used then were older,
somewhat brittle, and a harder grade, and worked like a charm. More
recently, (ten years ago perhaps) I had occasion to do it again, but
that time, the more recent leads, though the same “hardness” grade,
were the more common fairly flexible types, and a number of them
didn’t survive…

Take from that what you will.

When I need to do this now (not all that often) I skip the pencil
leads and just use copper wire or iron binding wire, steel wire, or
even the shanks of old broken drill bits of the right size, etc. High
enough melting point to survive casting with any gold or silver
alloy, they oxidize during burnout, so the cast metal doesn’t much
fuse to it. Then, after casting, leave it in a suitable acid
overnight. In the morning, the wires are gone. Redrill to clean up
the holes, and you’re set.

Peter Rowe

Just a share:

One way to get high quality graphite lead is to order or purchase
refills for mechanical drafting pencils. These are all very high
quality graphite. I have a stockpile of them from school and also
from a neighbor who drafted maps & such. I use them all the time
inside tubing when soldering knuckles on hinges, or for casting,
glass bead making, etc., and they work excellent and hold up well
with heat.

I believe Hobby Lobby caries them too, but they are also easily
ordered through Blick Art Supply or any other drafting supply house.