Have you ever cast your own parts

[maxi19]

You have to be careful with the design of your pattern if you are having a hollowed out underside on a neck, the supporting ribs between the hollowed out sections can cause quite drastic 'sinks' in the finished casting during cooling.

I served my apprenticeship in the toolroom of a foundry, during which we had to go through the 'moulding and pattern making' shops It is quite a technical process.

Best Regards Ron Mc.

[Bent]

Ron, thanks for that valuable tip! Ok..so say you take sinks into the equation...would it suffice if I cast the piece 1/8" over-thickness?
Educate me

[maxi19]

Good afternoon Bent,

it's the different volume of material at these areas and the different cooling rates that mainly causes it, especially at the intermediate rib positions. The moisture content in the sand if it is not uniform can cause serious problems, I have seen metal being poured into a moulding box where the sand was too moist and it immediately erupted back out like a fountain as the moisture turns to super heated steam.

A neck, being a long fairly slim component would require a good runner, sprue and venting at either end of the mould, the cavities would be better made as a 'core' system to try and eliminate the sand being washed along from the mould.

It would be interesting to know what percentage of rejects there are on 'Emmons' necks and they are being made professionally.

I think a 1/4" oversize on your external dimensions would give you a chance of machining the thing straight and flat as you would probably find that the casting would have quite a bend in it.

Best Regards Ron

[Farmer]

Bent, maybe another way to avoid shrinking would be to make the top side of your flask deeper so it would hold more sand then after assembling the flask back together you could cut a trench connected to your pouring hole to hold aluminum outside the mould to take the shrinking. you would have to melt more aluminum than you accually need.

Ron, have you ever tried this? I have increased the size of the pour hole, after I had cut the original hole, to keep my part from shrinking. Sometimes I think shrinking has to do with the mix of the aluminum also. I think the above idea will work, but you need to increase distance between the top of the flask and the part. Ron, I would like your opinion on this....what do you think?

Shobud, you might be able to cast an end plate with the tuner hole in your pattern... Watch all you can on u tube about sand casting. It gets pretty involved trying to explain how to do all you need to do.....

I wonder if Emmons are die-cast ?????? Mike

[shobudmaverick]

If I ever eally try to cast anything it will probalbly be the keyhead and maybe endplates and pedals but it sounds like the neck can be a very complicated piece if you are not good at casting.

[maxi19]

Hi Mike,

from what I can remember (back in days of yore) the shrinkage takes place during cooling at which time the metal is solid or semi-solid so a 'head of metal' would be unable to fill the problem area.

Patterns are made over size as the cooled casting is smaller than the pattern, the shrinkage is different on different metals ie cast iron, brass, aluminium etc and 'formulae' exists to work out the specific pattern sizes for these different materials to allow for general dimensional shrinkages in the casting, however the configuration and shape of a complicated casting like a neck or similar item with multiple differing volumes and bracings creates different shrinkage rates at different points in the casting causing sinks and stress cracks.

You would really have to expirement, your drawing shows the basic principle of moulding but on a long slim item such as a neck it would be advisable to have feeder runners, running alongside the item as well, allowing metal to flow in at several points instead of relying on the metal flowing straight through from A to B.

I was not a 'moulder' but a 'tool-maker', but we were required to have an understanding of the companies products and learn something of 'moulding' and 'pattern making'.

I hope I am making sense here and am of some help.

Regards to all Ron Mc

[Farmer]

Ron, I don't want to hijack this thread, but I think what we are doing is letting other people interested to read this stuff. I have probably cast aluminum for about 25 years on and off. Got most of my instructions in high school in shop class, and my Dad worked at a local foundry, so I got a veriety of education. Of course our instructor was not a foundry man, but he tought us pretty well. I remember casting a ShoBud replcia and it had a shrinking spot. Someone said to increase the size of the pour hole, so I did that and it fixed it. Everything will pour different, so you just have to try different ideas.... Mike

[shobudmaverick]

Thanks for all this information.I have enjoyed reading all these post and I always write down all this stuff because it may be valuable info when I decide to try casting something.

[maxi19]

Good morning Mike,

I entirely agree, the process is really 'trial and error', even in the foundry section of where I served my apprenticeship errors occurred and several castings were ok and some would have faults and all done by the same moulder.

I'm afraid the results,(pardon the pun) are not cast in stone and you will get failures, you just have to try again and not lose heart.

Regards Ron Mc