Molding & Casting a Prop Bracer

The mold and final cast part.

The mold and final cast part.

As someone who has gone to GenCon quite a few years and knows several of the GMs of major events, I’ve started getting asked to make props…  This year I have decided to expand my experiences in molding and casting in order to make one of the props.  The prop requested was a “Bracer that looks like it is made of Amber – part of the shell of an insect”.  Thankfully I was afforded quite a bit of creative leeway beyond that.

 

In the past I have used Smooth-on products, but one of the members of the Makerspace mentioned they were a distributor for Alumilite, so I thought I would give them a try.  This was my first experience with most of the Alumilite products.

 

I ordered the following supplies:

UMR 12 oz.

Alumilite Dye 1 oz. Red

Alumilite Dye 1 oz. Yellow

Mold Putty – 15 2 lb. Lt. Blue

Amazing Clear Cast 2 gal. Kit Clear

Synthetic Clay

 

Other items I used:

PVC Pipe form

A form made out of a 3″ PVC pipe shaped to look like a human arm.

3” Diameter PVC Pipe – Approximately 18” long

3” Diameter Hose Clamp

Plaster Bandages

Vaseline

Disposable Mixing Containers

Stir Sticks

Steel Wire (to hold the mold together)

Syringe

Drinking Straw

 

I wanted to make a “generic” bracer that would fit either arm, not a right or left arm bracer, so I didn’t want to do a life cast of my arm first – it would be too specific.  Instead I picked up a piece of 3” pvc pipe, cut a section out of most of it (leaving a part connected) and then used a hose clamp to tighten the open end down.  It turned into a really good stand-in for a human arm.  The shape is close enough that it is recognizable, but is not left or right arm specific.  (Note that the screws in the picture were added at a later stage)

 

Once I had the basic form for the arm, I used the synthetic clay to create the shape of the bracer.  I was going for an organic look, so I wanted curves and no sharp edges.  The biggest challenge I had was trying to smooth out the sculpt.  I still need to figure out the right technique.  Sadly, I forgot to take pictures of the sculpted bracer.

 

The form and original covered with mold putty.

The form and original covered with mold putty.

Once I had the sculpture complete, I added some screws around the edges as alignment points.  I was careful to make sure the heads were close to the PVC so they would not get stuck in the molding material.  Then I got to try my first new material – the Mold Putty.  I really liked the idea of it – take two parts, hand-mix, then just push it onto the original.  It essentially worked exactly that way.  I thought the mixed consistency was almost perfect for my application.  Unfortunately, the biggest difficulty is being sure not to trap air in it – particularly when placing a second mixed batch next to an already placed batch.  I ended up with some imperfections in the final mold because of this.  Would I use it again?  Yes, but I think I may also try other approaches – either a box and pourable rubber, or brush-on rubber.

 

The mold with half of the mother mold present.

The mold with half of the mother mold present.

Given the way I wanted to cast the bracer – standing vertically – I wanted to make sure that I was able to hold the rubber mold to the arm form well.  So, using the plaster bandages, I made a two-part “mother mold” for the rubber mold.  First, I coated everything with Vaseline as a release agent, then I covered half of the arm piece with plaster bandaging, making sure the edges were particularly strong, and that the top edge, where I would be creating the second half of the mold, was also quite smooth.  After the first half of the mother mold cured, I then coated the edge of the plaster with Vaseline to make sure the other half would not stick to the first half.  Once I was done placing the Vaseline, I then coated the other half with plaster bandages.

 

Once all of the plaster dried, I used a sharpie and drew lines across the edges of the plaster.  These lines are so that I could realign them easily after I took the mold apart to remove the original sculpt.

 

After I removed the original sculpt, I realized I forgot something major…  A way to get the resin into the mold.  Oops!  After a bit of thought, I decided the easiest way to get the resin in would be to drill some holes through the PVC pipe and pour it in that way.  Ideally, I would have designed pour holes and vent holes into the original design of the sculpt.  Something to remember for the next one!  In order to try to control the fluid a bit better, I used straws to extend the holes out.  Bendy straws would have been good – I’m not sure how effective straight straws were.

 

Using the volume of clay from the original sculpt, I did a rough guess at how much resin would be needed to fill the mold (~12oz).  I measured out 6oz of each of the two parts, added one drop of red and six drops of yellow to one of them, then mixed it.  I used a syringe to suck up the mixed resin and transfer it into the mold.  It worked quite well, although it was a bit disconcerting because of the number of bubbles that were exposed during the suction process.  Thankfully, as soon as the resin reached normal pressure the bubbles disappeared.

 

The raw bracer prop as removed from the mold.

The raw bracer prop as removed from the mold.

The resin takes 24 hours to cure.  24 hours wondering if it turned out.

 

And after that full day of waiting, I de-molded it.  Quite the pleasant surprise!  I think it may have slightly too much red, so I’ll have to correct that for my next iteration.  I’m still debating about sanding and buffing it in order to get it to be more glass-like.

Rooster

 

IMG_2028

The rooster head above was cast in aluminum at the space on July 25th.  Steps of the process are outlined below.

First, carve rooster out of plasticine modeling clay.  The clay comes in many forms and can be purchased at most art stores

IMG_1992

 

Next, make a 2 part mold.  The left image shows the plasticine rooster in a bed of sand, dusted with parting compound.  (parting compound helps separate the 2 parts to remove the clay core)

I then mixed up a batch of resin bonded sand (90 Mesh sand, resin and catalyst) and covered the clay core (about 2 inches high)

The right image shows the cured resin bonded sand with the clay core still in place.  I re-dusted with parting compound and mixed another batch of sand.  Note the 3 dimples that were added to help “key” the mold when reassembling.

IMG_1993 IMG_1994 

After the second batch of sand cured (24 hrs) I split the mold apart revealing the open mold on the left and the clay core in place on the right.  Removing the clay, you can see the 2 halves of the mold ready to be reassembled for casting.  Note the “key” locations on the right image.

The pour hole (sprue) that was carved into the middle of the neck for pouring the metal, is not shown.

IMG_2006 IMG_2007

After pouring the metal, allowing some cool time, you can see the mold broken apart in the left image.  Remove the pour sprue, and clean up the flashing (seen in the right image) and with a little polishing, its good to go.

IMG_2012 IMG_2013

I encourage everyone to try it out!

Inexpensive Ceramic Shell: Aluminum Casting with Drywall Joint Compound

We’ve been aluminum casting at the Milwaukee Makerspace since November, and I have cast several things since then.  For simplicity, we started by using a lost foam casting method, wherein the form to be cast is fabricated in Owens Corning Foamular 150 (Styrofoam), and is then tightly packed in a reusable, oil bonded sand called petrobond.  The molten aluminum is poured directly on the styrofoam, vaporizing it.  Because the mold is made of sand, the surface texture on the cast aluminum part has the “resolution” of the grain size of the sand.

Ceramic shell is another technique often used in art casting.  The positive of the form to be cast in metal is first created in wax, which is then dipped repeatedly in a silica slurry, that slowly builds up to the desired ½” thickness.  The surface detail reproducible is much smaller/better, as the silica has a much finer “grain size.”  The piece is then put in a kiln to burn out the wax and harden the silica, thereby forming an empty mold.  Typically the mold is cooled, inspected for leaks, patched, and then is buried in regular sand.  Note that to avoid fracturing the mold, it must be heated before pouring.  With all these steps, this process is relatively time consuming and is also somewhat expensive.

Recently, I read a blog post about a quick and low cost ceramic shell alternative that substitutes one or two coats of watered down “Hamiltons White Line Drywall Texture mix” for the tedious ceramic shell process outlined above.  While I couldn’t find that exact product, 4.5 gallon buckets of Sheetrock brand lightweight drywall joint compound (DJC) are omnipresent.  Note that some bags of quick setting drywall joint compound are actually just plaster, and cannot be substituted. I first assembled all the parts needed to make a quick test of the process.  I decided to make some aluminum packing peanuts:

Aluminum_Peanuts_parts

I hot glued the pyramid shaped sprues to the round cup and to the peanuts themselves:

Aluminum_Peanuts_together

I removed half of the 43 Lbs of DJC from the bucket, and poured in 10 lbs of water, taking care to mix it thoroughly with a spiral paint mixer connected to a drill.  Then, I just dipped the whole styrofoam assembly into the bucket, let it dry overnight, and dipped it in a second time.  Immediately after the first dip, I took care to brush the surface of any especially undercut areas, to prevent air bubbles from sticking to the surface.  In the future, I may consider pulling a vacuum on the bucket of DJC to de-gas it.  This may help prevent the formation of air bubbles on the surface of the styrofoam parts.  In addition, I could have first dipped the assembly in surfactant. After two dips, the 1/8” thick shell on the assembly looked like this:

Aluminum_Peanuts_coated

It was a week before the next aluminum pour at the Makerspace, during which time I poured a half ounce of acetone into the mold to dissolve the polystyrene packing peanuts and styrofoam, producing an empty mold.  This step is only necessary when casting packing peanuts, as their polystyrene tends to rapidly expand out of the mold and catch fire, while the pink styrofoam (also polystyrene) is made for homes, and so is much better behaved.  I buried the now-empty DJC mold in ordinary sand, and Matt W fired up the Bret’s furnace, melted a #16 crucible of aluminum, and poured it (Thanks guys!).  After fifteen minutes, I pulled the mold out of the sand, and found the DJC was a little darker.  The act of pulling the mold out of the sand an leaving it to cool over night left it somewhat cracked:

Aluminum_Peanuts_cast

The DJC crumbled off so easily that I didn’t even need a brush.  Also, I noticed that there is more yellowish surface tarnish on pieces left in the DJC to fully cool.  I recommend removing the DJC immediately after the aluminum solidifies.

Aluminum_Peanuts_cleaned

After making a few more, I’m almost ready to safely pack valuables, such as my “Marquis, by Waterford” crystal stemware:

Aluminum_Peanuts_in_use

Finally, check out the phenomenal surface detail that this process can reproduce.  For scale, this peanut is 1.5” long.  The surface texture on the front face is about ~0.002”!

Aluminum_Peanut_closeup

Thanks to Jason G for this last photo.  Also, a big thanks to Dave from buildyouridea.com for letting me know that one or two dips will do it!

FEAR

 

I’ve updated Robert Indiana’s iconic sculpture “LOVE” for our times!  While “Love” may have been an appropriate sentiment from 1964 to 1970 when the 2D and 3D versions were made, I think that the revised text is more appropriate for the 2000′s and 2010′s. Fear is 8” tall and 4” deep, and while not a monumental outdoor sculpture, FEAR appears fairly sizable on a table top.

Fear, which is solid aluminum and weighs over 7 lbs, was cast last Thursday with quite a few other pieces.  The great thing about having an aluminum foundry at the Makerspace is that the whole thing cost about $7!  - $4 for propane, $1 for Styrofoam, and $3 for some Rotozip bits.  If FEAR were cast in bronze, it would weigh over 20 lbs, which would cost $200 for the metal alone.  As it is, we melted down old heat sinks, stock cutoffs and hard drive frames, so the metal is essentially free.

In the spirit of Indiana who made his own font, I drew FEAR up in Inkscape using Georgia Bold, but I increased the height of the Serifs a bit.  Shane helped me with the file manipulation and G-code generation (Thanks!), so I could use the CNC router to cut FEAR out of styrofoam.  I exported FEAR’s hairline thickness outline as .dxf so it I could bring it into CamBam to generate the G-code. The outer contour of FEAR was selected, and the following settings were chosen:

  • General -> Enabled -> True
  • General -> Name -> Outside
  • Cutting Depth -> Clearance Plane -> 0.125 (inches)
  • Cutting Depth -> Depth Increment -> 1.05 (inches)
  • Cutting Depth -> Target Depth -> -1.05 (inches)
  • Feedrates -> Cut Feedrate -> 300 (inches per second)
  • Options -> Roughing/Finishing -> Finishing
  • Tool -> Tool Diameter -> 0.125 (inches)
  • Tool -> Tool Profile -> End Mill

Identical settings were chosen for the inner contours of FEAR, with the exception of General -> Name -> Inside.   Then, I just selected “Generate G-code.”  Check out the real-time video of Makerspace CNC router running the G-code and cutting out the 1” thick Styrofoam (Owens Corning Foamular 150).

After cutting four 1” thick pieces, they were stacked and glued together.  I buried the foam FEAR in petrobond, and then attached Styrofoam sprues and vents.  For a more complete explanation of the quick lost-styrofoam casting process, check out this post.   Stay tuned for details of our next Aluminum pour, which will be in January in the New Milwaukee Makerspace!

 

Hot Stuff! Aluminum Pour Night.

 

To quote the Iron Worker on THE SIMPSONS,  ”Hot stuff, coming through!”
I was pretty excited that I finally made it down to the Milwaukee Makerspace last night to attend an aluminum pour! I’ve seen a couple of the videos and really wanted to get in on some of that hot metal casting. I have what’s called a “speed-ring”, a metal ring that holds a soft-box for photographic lighting, and I wanted to make a copy of it.

So far, much of the casting has been using a “lost-styrofoam” method. A shape is carved from foam and set in sand, and the aluminum melts the foam as it’s poured in. But I wanted a COPY of an existing item. I asked Bret about it, and he said we could try an experiment of pretty much just pressing the ring down into some sand. An X channel was then added in the middle as a point for the aluminum to pour into and spread out into the shape.

I built a wood box for my item, and we filled it with oily sand, packed it in there, and added the X-trough. My item didn’t pull out of the sand quite as well as I had hoped, but hey, it’s an experiment…

Outside, the aluminum furnace was roaring away, heating aluminum to a delightful orange liquid. The first pour made it through Kevin’s FEAR art piece, my piece, and another members. Later, a second pour took care of Phil’s hand-casting series (which turned out great!)  and the rest went into an ingot mold.

Once my piece was cool enough, we pulled it out to take a look at the results. Not perfect, but not bad for a first time, and an experimental casting at that. There was quite a bit of extra metal, but most of that could be easily trimmed off with the bandsaw. Other members were taking photos of their work. It was obvious that everyone was pretty proud of their individual castings. Even without being the one pouring out twenty pounds of molten metal, it was still a pretty macho experience just to be part of.

If you too want to come play with crazy hot metal, come on down to the Makerspace next time we do an aluminum pour!

Aluminium Casting Night

This past Thursday was another great aluminium pour! I came prepared with a mold I made at work (benefits of working at a minerals company). I can’t show you guys the cast I made, cause it’s a Christmas present, but I can show you the pour!

Be on the look out on the Milwaukee Makerspace Calendar for future Aluminium pours on Thursday night at 7:00, or just come on by any Tuesday or Thursday night at 7:00 pm for our Open Meeting and Builder’s Night Out. See ya there!

Makerspace Aluminum Casting Foundry

I arrived at the Makerspace on Thursday without an idea of what I would cast in metal, and in less than two hours I was removing my piece from the steaming petrobond! Check out the fruit of two hours of labor cast in metal!

That’s right! The Milwaukee Makerspace had its first (and second) aluminum pour on Thursday! Thanks to the hard work of several members, the Makerspace now has a fully functional aluminum casting foundry.  The custom built propane and diesel powered furnace melted an entire #16 crucible of aluminum in less than 20 minutes.  Check out Brant’s video to see our fearless foundry foreman leading the two pours!

To get the foundry running quickly, we’ve started out by using a lost-styrofoam casting method.  That is, styrofoam is carved into the desired shape and then a sprue and vents are attached with hot glue(!).  This assembly is placed in a wooden form, and is surrounded by tightly packed petrobond, an oil bonded, reusable sand.   Then, the molten aluminum is poured directly onto the styrofoam sprue.  The styrofoam is instantly vaporized by the 1250 degree Fahrenheit aluminum, which fills the void in the petrobond formerly occupied by the styrofoam. The air and perhaps even some of the styrofoam residue escapes from the mold through the vents.  We’ll be phasing in bonded sand and lost wax casting soon, so stay tuned for those details.

Eventually we’ll be having aluminum casting classes; however, we’re definitely going to be having aluminum pours on alternate Thursday evenings for the next few months.  Join our mailing list / google group to get more details.  Metal pours are spectacular to watch, so feel free to stop by to see the action around 7 or 8 pm, or join the Makerspace and participate!

Makership Update

Wingnut

It’s been just under a month since we announce Frank as our first Makership recipient, and he’s been busy!

I just wanted to share these two great images of his work, featuring a “wing nut” and some skull rings.

Skull Rings

Pretty cool! Frank said he’s still getting the lay of the land at the Makerspace and figuring out who is who and what all the equipment does, but it’s good to see some progress being made.

And speaking of progress, if you want more updates, check out his blog, iFabr1kat3, where he’s documenting much of his work.

Casting Furnace Update

Despite summer vacation and other obligations, work continues to progress on the Casting Furnace.  In the past few weeks Bret has pinched the end of a metal brake line tube used to feed the furnace diesel fuel and installed a needle valve to better control the fuel flow rate.

Brant has been milling and machining parts for a mechanism that will both lift the lid and turn it out of the way when someone steps on a foot pedal.  The next steps will be to finish the foot pedal, weld it to the rig, and secure the lid to the top of of the lifting post.  Bret also plans to improve the casting tongs so they are more easy to use.

For more information, see the project wiki page: http://wiki.milwaukeemakerspace.org/projects/casting_furnace