Introduction: How to Cast and Machine Aluminum Rollers
My buddy and I have been talking about casting aluminum for a while and I needed end caps to stuff into the stainless steel rollers I had knurled for a grain mill. It seemed like a perfect match for a project.
So I am in the process of building a monster grain mill (later instructable?) for my brewing hobby. Yes, I can buy a mill for $150 give or take but then where is the fun in that?
Things to consider before beginning:
You are dealing with molten metal. It is serious. Do not attempt while intoxicated or on the way to such a state. Imagine that feeling you get when you burn your tongue on cheese of a pizza that was eaten too soon after coming out of the oven. It is like that only times 10 on whatever the metal has dropped onto. It is really hot. We took the precaution of using welding gloves, eye protection, leather aprons, work boots, long pants even thought it was 90+ degrees out.
Here are some of the things you will need to duplicate this adventure:
-foam insulation board (from local hardware store) this is the open cell stuff that shapes well
-drill press, while not required technically, very helpful
-drill the size of the following bolt
-files and rasps
-steel bolt and washers
-flame thrower (the kind they use to melt tar on roofs) like this
-crucible (we are using 1/2 inch 4x4 steel square stock with a 1/2 inch plate welded to the bottom) for holding the melted aluminum
-firebricks or regular for making a furnace/oven to heat the metal in
-desktop lathe made or bought
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Step 1: Making the Lost Foam Template
Using the foam insulation and a sharp blade, cut squares roughly larger that the final roller diameter by maybe 1/8 of an inch and mark the center point. from the center mark the radius of the final diameter with a line.
Step 2: Start the Foam "milling"
Using the drill press, drill a hole slightly smaller than the bolt you are going to put through. I used a lag screw actually, but in hind sight, a bolt might have been better so I could clamp the foam between two fender washers to keep it from slipping. Put the bolt in the chuck of the drill press.
Step 3: Cutting the Foam
When you fire up the drill press the black line drawn will create a dark ring on the spinning piece. You can kind of see it in the photo. That will give you the rough idea on where tyou want to be quickly. You could have trimmed it up before chucking it too, that would work as well I am sure.
Step 4: Tools for Shaping...
for the course work I used the back of a file to do the major cutting. Then switched to a file to clean that up. A rasp could also be used to bring it down quickly. Sanding blocks could also work well. I used the back of the file to hollow out the roller to use less aluminum and look cool. I also milled a recess for the bearing to sit in.
I would stop every now and again with some calipers to make sure the outer diameter is still good. The last photos is the prototypes all lined up (one has a gouge from forcing things).
Step 5: Casting Day
Before burying the "lost foam" templates in plain ol playground sand (we tried sand, sand and lime, sand, lime and plaster of Paris. all seemed fine to use), we glued on a a sprue that the molten aluminum would flow into to the roller cavity from the surface. More on that in a later step.
Step 6: Heating Up the Metal
We used four fire bricks per course staggered to build our "furnace". It is temporary and I am sure more efficient onces can me made, but this worked for what we needed.
You can see the crucible in the furnace and the torch coming in at the bottom. (ha, just noticed the image is upside down...).
You can use regular brick, I guess the just end up cracking quicker. Hopefully these hold up until I get around to building a better furnace.
Step 7: Pouring Into the Mold
We learned something I will share with you now. Make a volcano around the sprue with sand. this will help keep the aluminum going into the mold. You can see it worked good in the second photo, but later pours we didn't do this and the aluminum went everywhere. You can see the part just after we quenched the heat out of it. We are so proud at this point.
The bolt you see in it was pounded free. Seems steel wont melt with the aluminum. :-)
Step 8: Machining the Roller
I put a bolt through the center and bolted it with a bunch of washers, then put the bolt in the lathes chuck.
Step 9: Milled Smooth
I milled the sides and one face just to keep it clean :-).
Rinse and repeat 4 times.
Here you can see it in the roller. Soon you can see it in the mill when I finish that project.
Let me know if you have any questions or have feedback on this instructable.