Project assignment 01 First dish

Project objective.
To have the student step through the tasks of setting up a vertical axis pivot, making profile cutters, erect a sand pit and carve a green sand mold, mix concrete, pour concrete and finishing a dish.

Assignment outcome.
Student has a basic understanding of how to build with liquefied concrete into a green sand mold.
One has also built their first concrete dish during the assignment.

Setting up a vertical axis pivot.

We'll be needing a small block of wood and a 6 inch nail and a couple of screws. Cut the nail head off with a hacksaw and smooth off any sharps there. Select a drill bit slightly smaller than the nail and use this to make a nice vertical hole at centre of a small block of wood. Hammer the nail securely in and check it is PERFECTLY vertical to the base by using a square against it.
The block also has holes drilled on each end all the way through. Into these holes goes screws long enough to secure the block down to your work surface. This "pivot post" is secured to what will soon be the base of your sand pit. I'd recommend you use a half sheet of plywood as the base for the sand pit. My plywood base rests on a stack of wood pallets high enough to be comfortable to work at. This stack is carefully levelled up with wedges as needed. Refer to "The sand pit" for more details.

Making profile cutters

Please review tutorial "The drawing" tutorial if you have not already studied this page.
I will be providing the pattern for the profiles at this point in time. This is because pattern making for multi dishes is an advanced skill and not needed by a new student to get you started.
Please download and print to heavy paper the pattern drawing provided here.... Assignment 01 profile-drawings.PDF

Materials list: Perspex sheet..1.5 mm. * hardware shop.
150mm X 10 mm aluminium tubing. * also hardware shop or metal supplies.

Watch the video below, it will walk you quickly through the task of making profile cutters from the pattern drawings.

The patterns first need to be cut from the paper. These are then placed on the Perspex and marked out with a permanent marker pen. Cutting the Perspex sheet is best done with a dremal type tool. Use a metal cut off wheel and carefully cut out the two profile shapes. The cut edges can be cleaned up with a hand sanding as needed.
You'll now be fitting the aluminium tubing to the axial edge of the profile. Take a 150 mm length of 10 mm tubing and cut it carefully lengthwise with a hacksaw. You'll need to clamp the tubing horizontally in a vice and slowly slice the tube its entire length. Take your time on this. You need the tube to look like the one seen in the video above.
The Perspex needs to be a tad wider than the cut in the tubing. This makes a tight fitting join... Press the axial edge of the profile downwards into the slot of the tubing while it is on the vertical pivot pole. Then, tie it well to the profile cutter with string (as seen in the video above). This can be reinforced if required by using some super fix glue however, keep in mind that the tubing is rather a pain in the ass to slice open and so I tend to recycle the few split tubes I have whenever a new profile cutter is needed.

Erect a sand pit and carve a green sand mold.

Take a look at the profile cutter and we see it is 25 cm's. So, the dish is 50 and the sand pit needs to be a circle generous enough to around it. Lets make the hoop about 70 cm in diameter.
Please review "The sand pit" tutorial if you're not done so already.

Your pivot post is anchored into the sand pit base, plastic edging hoop is on and adjusted approximately to preferred size, ribbon strap attached and then sand is added and compressed until a desirable depth of sand is reached, i.e. a little deeper than the top horizontal profile edge. To save a lot of time, you can roughly scoop out sand that approximates the profile volume, however do not "over cook" this digging. It is necessary to carve with the profile towards the end.
We're aiming for a nice stable and compressed sand mold surface. If your sand is not damp enough it will fall away, collapse even, so be sure the sand is moist enough. Using a water spray bottle is an effective means of adding water into your precious shape without causing any grief. You'll know when the carving down with the profile is complete because the bottom of the profile is resting / rotating on the pivot block. Notice the small "tab" on the bottom of the profile is about 1 cm tall. This allows us to have 1 cm of sand covering the floor of the mold....

Mix concrete.

You'll be needing clean dry sand and a fresh bag of cement powder. (Once the bag is opened it has to reside in an air tight container) Sieve the sand )and the cement powder if it is not fresh) before mixing them together as one dry mixture. Also have plasticizer available for use and premix this fluid into half a bucket of water.
Mix up your concrete as demonstrated in the video tutorial below and all should go well. If you add too much water just add more cement mixture to correct the brew.

Pour concrete.

Make use of a spatula and feed concrete onto your sand mold from the bottom up. The profile cutter also helps as your guide as you build the dish. Build up the walls in a spiral layer till you've over shot the brim. Use the profile cutter to carve down and make a nice surface.
Follow the tutorial below and you'll be fine. Also, learn quickly from your mistakes and you'll find your joy in this task... :-)

Finishing a dish.

Remember you need to leave the newly made dish in the sand pit for 3 days before removing it! It is still VERY delicate so handle with utmost care. Rinse off and lightly wet sand. If there is deep crazing on the outer surface, now is the time to make a small concrete slurry and fill those cracks closed. In the photo below you can see they have been filled with a black fill. Let this dry off for another couple of days before removing excess and giving the entire dish a final wet sanding.

Youtube support tutorial for Assignment one

Well done, you first bowl is completed and assignment achieved. I hope you'll practice by making another dish or two before we move onto making a functional whirlpool dish in Assignment two

Link to Project assignment 02 Single whirlpool dish.