Tips/Techniques Pattern Taper Question

[jcdammeyer]

Instead of paying over $50 for a 4" piece of solid 6061 Al that is 3.5" diameter and boring hot most of it I thought I'd cast something that looks like this:
In this case the draft tapers (3 degrees) run opposite to each other to make pulling out the green sand simple.

Alternatively the tapers go in the same direction.

Here's a quick sketch that might help explain.

In both cases the parting line between cope and drag is at the bottom although the one on the left could be turned around and pulled leaving the tapered cavity and inside part. The one on the left as drawn has the inside part suspended from the cope while the one on the right rises up from the drag and the cavity is in the cope.

I feel like I'm missing something here.

 

[Bandit]

Instead of paying over $50 for a 4" piece of solid 6061 Al that is 3.5" diameter and boring hot most of it I thought I'd cast something that looks like this:
In this case the draft tapers (3 degrees) run opposite to each other to make pulling out the green sand simple.
View attachment 51567

Alternatively the tapers go in the same direction.

View attachment 51568

Here's a quick sketch that might help explain.

View attachment 51569

In both cases the parting line between cope and drag is at the bottom although the one on the left could be turned around and pulled leaving the tapered cavity and inside part. The one on the left as drawn has the inside part suspended from the cope while the one on the right rises up from the drag and the cavity is in the cope.

I feel like I'm missing something here.

I would put the whole piece in the drag (bottom) with the taper as in the left drawing, but turned over. This way, as the drag is supported, it is much easier to remove pattern after a firm rapping and repairs to the mold are generally also easier, not having to deal with the riser and pouring sprue and venting holes which tend to weaken the cope anyway.
This maybe a perfect time to try a foam pattern, as it does not need to be removed. Melts and gases off as the molten Aly is poured.
All of the above will depend on how deep your drag and cope box's are.
Just my 5 cents worth, a nickle for your thoughts type thing, no pennies in Canada anymore.

 

[jcdammeyer]

I would put the whole piece in the drag (bottom) with the taper as in the left drawing, but turned over. This way, as the drag is supported, it is much easier to remove pattern after a firm rapping and repairs to the mold are generally also easier, not having to deal with the riser and pouring sprue and venting holes which tend to weaken the cope anyway.
This maybe a perfect time to try a foam pattern, as it does not need to be removed. Melts and gases off as the molten Aly is poured.
All of the above will depend on how deep your drag and cope box's are.
Just my 5 cents worth, a nickle for your thoughts type thing, no pennies in Canada anymore.

Thanks. I reversed the taper and printed a second one. Once I finish cleaning up the second one I'll see which pulls more easily.
Not a fan of lost foam or PLA. Dislike the smell. Not for green sand as it leaves residue. And with regular sand needs the plaster covering which is really a lot of work. And if the pour fails have to create the pattern all over again.
OTOH, a friend of mine even made a special floating sand container. He'd turn on the air pump (shop vac?) and then just press the pattern into the sand until just the sprue and riser stuck out. Turn off pump. Sand settles and ready to pour. He also used a modified JGRO CNC router to make all his patterns with hot wire.