Re: [CAD_CAM_EDM_DRO] Machineable wax - answer to Ian's question

Ian Wright wrote:

> Thanks Bill,
>
> I hadn't realised this use for cnc before but now I just can't wait to get
> my mill finished and working (its getting very near now!).
>
> Just one question more - where you are making wax models with more than one
> part to them (as Jon, I think, described), or are fixing parts onto a wax
> sprue for casting, how do you fix the parts together? Is there some magic
> 'glue' or do you just use a hot knife and hope?

For investment casting, the wax patterns need very little strength. For
lost wax casting, the models need a level of strength depending somewhat
on the size of the part, or the cope. When ramming, you could break the
pattern apart.

> One of the applications I
> can see my mill being used for is making wrist watch cases and so this would
> involve fastening the four strap lugs onto the body - all in exactly the
> right position and orientation and without any lumps and bumps at the join.

This is fairly tricky stuff. You might want to make a metal pattern, glue or
solder the strap lugs on, and then make a rubber mold from this. You might
even use wood patterns. The rubber mold would then cast complete watch
cases. There might be some trickery to the pin holes in the strap lugs, but
these could be handled with simple core pins in the rubber mold.

But, I wouldn't be too confident that the strap lugs could be attached to
the wax pattern with good results. This is usually done when assembling
the sections of an engine block, where the cosmetic fit is not a big concern,
and a number of critical surfaces will be machined later.

Jon