I guess that this was the first real job for my foundry, a Z axis saddle for my CNC router.  so a pattern was machined up out of hardwood to produce the casting required.  It turned out that I couldn't make a mold from the pattern ( lack of skill - still learning ), so a match plate was made up so that the pattern could be mounted to aid in the production of a mold, about this time I was also trying out silicate bonded molds, CO² cured.  This turned out to be a lot easier than using petrobond sand and molding boxes, the molds could be made days or weeks in advance of a founding session.

Here the pattern is mounted ready for making the mold, sadly I didn't take any photos of the actual mold making process, I can only guess that I was too engrossed in the work.

Making the mold is very similar to making a normal sand mold except that you dont need to make a false cope, the mounted pattern does this for you.  The process of making a silicate bonded mold is quite simple,  the gates,runners & sprues must be formed at the same time as the pattern so you will need a selection of wooden formes, I use pieces of 90 deg dowel glued together to form half round sections that can be placed into the molding box before ramming up.  

Ramming of the sand mix is similar to green sand, once you are satisfied with the ramming, I prick the half mold all over using a 1.5mm rod right down to the pattern or the whole depth of the mold, once this is done the mold can be gassed with CO²  , I use welding gas as it comes in small containers and is quite cheap.  Gassing the mold takes about 30 seconds, after which the sand mix has hardened enough to strip the mold, the mounted pattern is removed and the loose patern replaced, the whole is dusted with parting dust and the other half of the mold made in the same way.  The two halves are separated and all the formers are removed, any minor changes can now be made, core's glued in and the two halves of the mold glued together using a fast drying silicate based glue, any open holes are now sealed by gluing some kitchen paper over them to keep out creepies.

This picture shows the casting after it has been stripped from the mold with the runners,gates and riser still attached.  Stripping the castings from silicate bonded sand molds is quite difficult as the mold keeps its strength, I have found that wetting the mold helps with this, BUT it must be allowed to cool quite a bit first.

It may even be possible to recycle the sand if you had enough space to dry the sand before re-use,  at the moment my local waste recycling center will take the used sand.  Silicate bonded sand is one of the most environmentaly friendly molding sands after green sand. 

Here we have the pattern and the casting with all the gates and risers removed, I generally leave new castings a couple of days before I start to machine them.

 This shows the casting part machined, the main face was machined first by clamping the casting by means of two steel dowels through the cored out holes.  The casting was then clamped to an angle plate to machine the two end surfaces, lastly the casting was clamped with its main face down in the lathe and the two holes were bored out to the correct clearance to take the linear bearings.  The central hole was also drilled and bored out in the same setup to take the nut for the leadscrew.