Casting Ruler

[AndrewMawson]

Kirk,

I suppose it depends on the scale of your casting operation and the metals that you are casting, but for me both for iron and aluminium, the shrink allowance is comparable with the oversize caused by rapping the pattern in green sand -( this is on fairly small castings)

Up to a certain size I suspect that you can compensate quite adequately by consiously rapping more or less before you withdraw the pattern

[generic]

Here's a pic of calibrations applied in the mill with a drag point using the DRO.
Although it is a little time consuming and never a production method, it does work well.

Gene

[Roy]

The extra space made by a bit of judicious rapping would give you somewhat more oversize than the pattern would produce, but it may not work in all circumstances, and it may also produce a mold with one portion of it that is not in consistent or correct relationship to other portions. Only you can tell that. A quick and easy way to add extra to a original part that intended to be used for a pattern, if shrinkage is of concern is to use that sprayable putty filler. It comes in a spray can and sold at Wal MArt etc or auto parts stores. Its like a thinned down bondo in spray form.

What kind of small engine parts do you cast Andrew.Steam or IC? I have cast a few parts for the steam engines I produced. I also cast quite a few parts using the origonals from a kit so I had spares and parts to make a few more engines from.

[AndrewMawson]

Who said engine parts [img]/ubb/images/graemlins/shocked.gif"%20alt="[/img] Most of my casting to date has been making missing bits for obsolete machinery but just before Christmas I did do a run of 25 1" diameter aluminium silicon pistons for David Boote for his i/c engines (see M.E.)with quite intricate core for the innards- but that was sodium silcate bonded sand. Most recent exploit is experimenting with lost wax - bronze casting of lions for Daughters 'A' level art project.

[Roy]

I sure don't know where I picked up engine parts from your post.........or from any other post as far as that goes.. [img]/ubb/images/graemlins/confused.gif"%20alt="[/img]

[Harold_V]

Roy,

What more can you tell us about the spray putty filler? I've not heard of it. Does it sand well? Cure time? Solvent type?

I'll try to check it out when we get to town next time, but meantime, anything you could provide would be most welcome.

Thanks,

Harold