Your welcome Nick.
When it came to building the core box, I had to find a way to simplify the complex shape into a few easy to make flats and curves.
Strange as it may appear at first sight there is only 3 simple shapes involved;
- a rectangular prism ..................................the water jacket
- 2 bell shapes with flat, parallel sides...........the crank cavity
- 3 cylinders...............................................the cam recess & cylinders
The parting lineIs important because I need to get the core out (and be able to use the core box again) so I elected to put the main parting line parallel to the crank axis.
Having decided on a parting line, lets start with the most complex of the simple shapes,
The crank cavityStarting with a block of 2" x 2" of brown stuff, (about a 6" length is enough) draw one half of the bell shape on the end grain to mark where you need to remove the inside of the bell. You can see the marker line in some of the photos below.
Cut the 6" length in half or into two full lengths of the finished core. Take one side (now the cam side) and drill a 7/16" hole where the cam recess is to be. Then smooth up all the contours with some sawdust making devices.
Water jacketTake a bit more of the 2"x 2" and cut a wide channel in it, then cut that to be the same lengths as for the crank cavity. These will form the sides of the water jacket.
CylindersThe remaining shape is the two cylinders. T make these it is just a matter of drilling/carving/filing the two 3/4" holes down through all the parts assembled so far.
Top & Bottom core printsSo far we have only accounted for two sides of a 6 sided core box. At the top and the at the bottom of the core we need some core prints, (protrusions that can support the weight of the core until it can be suspended in a sea of the liquid metal.
For the top core prints I made two cones, drilled into the top board. These need to be accurately (who im I kidding this is W### ) aligned with the cylinders. I made a core print drill to do this, which may sound like a waste of a spade bit but I'll probably use it on future core boxes.
The bottom needs some core prints also, to support the core in the mould. This comprises of two tapered recesses in the bottom board.
Between the two tapered recesses and also glued at right angles to the bottom board is a 12mm wide divider that will form the center main bearing support web.
This may sound all very complicated but its not really, I'm just organising wood to be where I want aluminium and sand where I don't, and building it one bit at a time.
Dare I say? its a bit like the reverse of machining. Instead of machining off the bits I don't want I'm gluing on the bits I do. (and hacking off the bits I don't want too)
The last two sidesThese are just two flat boards or at least they w### be if the water jacket didn't stick out either end of crank cavity. This problem is easily solved, again with a ball nose bit to carve out the extra bit to make the water jacket longer.
Assembling the core box & Ramming upThe core box parts
The Water jacket
The crank cavity
top and bottom boards
side boards to line up all the bits and start ramming up the core sand
Fully Assembled ( you can see here the intricate w##d craftsmanship they'll be admiring for centuries to come)
Ramming up (I think you can see the table is still shaking from the vigorous ramming up)
releasing the core
In this state the core is very carefully transfered to the oven. For instructions on how to prepare the oven for concurrent achievements there is another useful thread HERE
http://www.modelenginemaker.com/index.php/topic,878.msg9924.html#msg9924The core sand is not normal green sand, its a tried and tested formula I got from Tel.
basically, when mixing the core sand, do the same as for green sand. Except, just substitute a couple of ingredients. Replace the bentonite with flour and add molasses to the water, in a mix of 1:10 -( add a bit more if you like the Anzac biscuit smell. Just don't taste them else you'll have to make more!! No need to any way, I can tell you, their just like eating sandwiches at the beach
)
After baking, the core will happily support its own weight between its extremities.
next post I'll drop it in a mould cavity.
Thanks for dropping in.
Bez