Drilling and Pinning Tall Molds
 

I make a lot of molds that are hinged. I remove 1/4 inch of material
leaving a 1/4" tall, by 1/2" wide radius boss at one end along with pockets
for the mating bosses on the other half of the mold. I found that it was
slower to use a 2.5D process with an endmill to do that than to use a round
over mill, but I get a very accurate repeatable result, and do not have to
account for the lead angles on a round over mill and waste part of the
remaining mold surface for a big clearance slot. Anyway, its automated and
it works really well so I can be doing other things while its machining.

After all the primary work is done I drill and pin the hinge bosses along
with my other secondary work. Alignement pins, clamping screws, extra
hardware installation, etc.

When I first start I made some drill jigs out of aluminum with a clamping
screw to hold it in place. It worked, but I had to be sure I clamped the
same side on both the top and bottom of the mold, and if the thickness of
the molds varied much so did the center alignment of the hinge pin. They
were all made as double jigs. Use one side for top and the other side for
bottom. It worked, but it had its issues.

I was always looking for a faster easier way. I played with the idea of
setting up the little mill drill with a self centering vise and after
finding center just clamping down the ways and leaving it there with a work
stop for the molds. After much research I found most self centering vises
that were priced in my budget just weren't up to the task. They would get
you close, but not to my desired tolerance.

I resigned myself to clamping the mold in a vise, indicating off of it, and
then drilling (Hurco or Tormach) or spiral milling (Speedmaster) the hinge
pin holes. The little X4 Speedmaster mostly only gets used for engraving my
trademark and the occasional custom engraving work for a customer so it was
always available for that. Spiral interpolate the clearance size, then
spiral interpolate from there to full depth for the press fit. Its faster
to spot and drill on the Tormach or the Hurco, but the Hurco is down and the
Tormach has been very busy lately.

Well a couple weeks ago I finished two hinged custom molds for a customer
that are 17 inches tall. I also cut a test mold to experiment with. I'm
glad I did. My first that was to just scribe and drill on the drill press.
Nope. I set a 12x12x12 right angle plate on my surface plate, and clamped
the mold to it. I right a cylinder square to make sure it was straight, but
I could feel the dril press flexing a little when I was drilling. Anyway,
the cumulative errors other than that were not good. That test mold works,
but you have to use the handles to pry it open and pry it closed. Between
flex, drill wander, scribing accuracy, and who knows what all else it just
doesn't swing open and closed easily enough. Add on that the mold has
mating "spacers with a close fit (.0005-.001 clearance) and everything has
to line up pretty well.

The molds have been sitting on my assembly bench for a couple weeks while
other molds get finished and shipped.

This morning I had a weird sort of idea. Mount it to the right angle plate,
and mount the right angle plate to a face plate on the 14x40 lathe. I'd
either have to remove the bed gap or clip two corners on the right angle
plate, but the lathe is pretty rigid and it will drill straight (enough) if
I center or spot drill to start the hole. The problem is aligning the lathe
to the work pieces. Twice for each mold. I have no idea how I would
indicate that in.

Then I had a better idea. Make drill guides. Not one like my old ones that
clamps to the outside of the mold, but one that is an exact fit to the hinge
boss itself and clamps to the face of the mold. The hinge bosses are pretty
consistent. They vary by lot less than half the clearance of the hinge pin
clearance hole. If I make the guide deep enough I could even hand drill the
pins at that point. I'll have to make two of them, but so what. Its
automated. LOL.

Drilling and Pinning Tall Molds
 

********
I suppose I should clarify that none of my mills has enough Z axis clearance
to spot and drill these mold hinges. The Tormach is close, but not after I
install a tool holder. Even in a spindle collet, I'd have to make custom
extra short drills. The Hurco came up a couple inches short even with the
knee cranked all the way down.
********

"Bob La Londe" wrote in message ...

I make a lot of molds that are hinged. I remove 1/4 inch of material
leaving a 1/4" tall, by 1/2" wide 1/2" radius boss at one end along with
pockets
for the mating bosses on the other half of the mold. I found that it was
slower to use a 2.5D process with an endmill to do that than to use a round
over mill, but I get a very accurate repeatable result, and do not have to
account for the lead angles on a round over mill and waste part of the
remaining mold surface for a big clearance slot. Anyway, its automated and
it works really well so I can be doing other things while its machining.

After all the primary work is done I drill and pin the hinge bosses along
with my other secondary work. Alignement pins, clamping screws, extra
hardware installation, etc.

When I first start I made some drill jigs out of aluminum with a clamping
screw to hold it in place. It worked, but I had to be sure I clamped the
same side on both the top and bottom of the mold, and if the thickness of
the molds varied much so did the center alignment of the hinge pin. They
were all made as double jigs. Use one side for top and the other side for
bottom. It worked, but it had its issues.

I was always looking for a faster easier way. I played with the idea of
setting up the little mill drill with a self centering vise and after
finding center just clamping down the ways and leaving it there with a work
stop for the molds. After much research I found most self centering vises
that were priced in my budget just weren't up to the task. They would get
you close, but not to my desired tolerance.

I resigned myself to clamping the mold in a vise, indicating off of it, and
then drilling (Hurco or Tormach) or spiral milling (Speedmaster) the hinge
pin holes. The little X4 Speedmaster mostly only gets used for engraving my
trademark and the occasional custom engraving work for a customer so it was
always available for that. Spiral interpolate the clearance size, then
spiral interpolate from there to full depth for the press fit. Its faster
to spot and drill on the Tormach or the Hurco, but the Hurco is down and the
Tormach has been very busy lately.

Well a couple weeks ago I finished two hinged custom molds for a customer
that are 17 inches tall. I also cut a test mold to experiment with. I'm
glad I did. My first that was to just scribe and drill on the drill press.
Nope. I set a 12x12x12 right angle plate on my surface plate, and clamped
the mold to it. I right a cylinder square to make sure it was straight, but
I could feel the dril press flexing a little when I was drilling. Anyway,
the cumulative errors other than that were not good. That test mold works,
but you have to use the handles to pry it open and pry it closed. Between
flex, drill wander, scribing accuracy, and who knows what all else it just
doesn't swing open and closed easily enough. Add on that the mold has
mating "spacers with a close fit (.0005-.001 clearance) and everything has
to line up pretty well.

The molds have been sitting on my assembly bench for a couple weeks while
other molds get finished and shipped.

This morning I had a weird sort of idea. Mount it to the right angle plate,
and mount the right angle plate to a face plate on the 14x40 lathe. I'd
either have to remove the bed gap or clip two corners on the right angle
plate, but the lathe is pretty rigid and it will drill straight (enough) if
I center or spot drill to start the hole. The problem is aligning the lathe
to the work pieces. Twice for each mold. I have no idea how I would
indicate that in.

Then I had a better idea. Make drill guides. Not one like my old ones that
clamps to the outside of the mold, but one that is an exact fit to the hinge
boss itself and clamps to the face of the mold. The hinge bosses are pretty
consistent. They vary by lot less than half the clearance of the hinge pin
clearance hole. If I make the guide deep enough I could even hand drill the
pins at that point. I'll have to make two of them, but so what. Its
automated. LOL.

Drilling and Pinning Tall Molds
 

I have not cast metal since jr high shop in 1965.

But I have been watching MYFORDBOY on youtube.
He is some old brit that never says a word, but casts Aluminum the way we were trying to do it in jr high.

Fun to watch.

Drilling and Pinning Tall Molds
 

On 11/5/2018 2:56 PM, clark wrote:
I have not cast metal since jr high shop in 1965.

But I have been watching MYFORDBOY on youtube.
He is some old brit that never says a word, but casts Aluminum the way we were trying to do it in jr high.

Fun to watch.

Â* That would be about the same time I got my first taste ... but we
didn't get to pour , or even watch , just made the mold and Teacher
poured after school . Now I have my own foundry setup , and have cast al
and brass . Currently working on a forge furnace so I can beat on some
steel . Check out castinghobby on yahoogroups ...

--
Snag
Yes , I'm old
and crochety - and armed .
Get outta my woods !