Method of pattern making

This really is just a sequence of photograps showing the steps taken to create a pattern suitable for use in sand casting.  The component that I am making is a bearing housing that will clamp two angular contact bearings and provide a square flange that one of my nema23 motor mounts will fit.  The opposite end of the bearing housing will have a round flange that will bolt to the CNC machine frame.

Three pieces of hardwood of appropriate size are glued and clamped overnight,  the woodglue used is a resin based exterior grade glue that once dry is stronger than the wood itself.

The wood blank is centered in a four jaw chuck and the outbound edge supported with a center, ( helps by reducing the clamping force required by the chuck ).  I tend to use simple HSS tools for this kind of work as it is very easy to create simple form tools and radius tools.

Working along the wood blank creating the required profile, before swapping the chuck for a three jaw and reversing the component to turn the end that will form the square flange. 

Here the turning is complete, notice that there is a protrusion at each end of the pattern, these are to form core prints in the mold to locate a sand core that will form a hole within the cast component.  Doing this will save a lot of machining time,  reduce the volume of metal required to pour the casting and will ensure that the casting will have a roughly constant wall thickness ensuring a more even cooling of the casting and hence a higher chance of success.

As above but painted with celulose sanding sealer,  I find that this tends to harden the wood grain making it easier to sand to a fine finish.

The pattern here is now having the square flange formed on the larger diameter using the mill.

This is the finished pattern, it still requires several coates of sanding sealer to harden the surface of the wood a bit more before it is given a coat of gloss paint.

Here we have the new pattern next to the pattern for the nema motor mount.

Once the pattern is finished I will continue this article with the actual mold making and casting session.