The Shop > Metal Stuff

lost pla/pattern castings ?

<< < (2/7) > >>

Joules:
Prints can still be porous and you have the fine layer lines that can also trap the plaster, don’t assume prints to be water tight is my experience.

LOL, I read the title lost PLA casting, and then the description of using the PLA parts for patterns, so some contradictions here.

picclock:
Hi Joules

Thats coz I don't have a clue what I'm doing :scratch:. Take your point about porosity but doesn't seem to be present on my prints. Layers seem well fused. Main problem I have had with 3d printing is warping of the plastic. Not sure how to sort that :-(

I think most of the bits would be pattern cast (see, i'm learning), but one or two would be best cast properly, likely with risers and green sand, or plaster of paris mold in a sand filled bucket for stability. For those baking the mold upside down to purge the plastic from it seems a good idea. But I really have no clue .. .

Just trying to get it right in my head before I decide to go ahead.

Could be a good project for the winter.

Best Regards

picclock

Joules:
I am just finishing up some patterns for sand casting.  Generally a solid parts warps more than a shell print.  Not shell as in single layer, but in this case 3mm thick walls.  The two parts are printed flat then welded together, dowels locate the two halves.  The edges get filled and smoothed off.  My example below has primer for the first rub down to see where the voids are as the print is quite course at 0.15mm layer.

vintageandclassicrepairs:
Hi All,
picclock,
I have a friend who makes sculpture's from bronze castings using the "lost wax" method
I know very little about casting but one thing I have learned from talking with him is that
plaster of paris has to be baked into basically porcelain before molten metal is poured into
the mould
If molten metal is poured into air dried POP it will boil any remaining water instantly and the POP
will shatter  :bugeye:

John

vtsteam:
Okay, picclock good title change.

You'll probably need to incorporate draft in any conventional pattern to release it from plaster, and a mold release as Joules pointed out, and even then, some pieces can be a real pain to release.

Surface finish is pretty critical with plaster -- more so than with greensand (and even that benefits from the highest finish possible).

Copper containing metals need a LOT higher temperature than aluminum and behave differently as well. Hence the suggestion to start simply w/ Al .

If I remember correctly traction engines have diagonal treads on the rear wheels, and I can't imagine pulling a pattern intact out of plaster with that configuration, if treads are included. Lost wax (general term here) methods would work.

Be aware that if you try to pour to top off a simple mold without sprue and gates lots of difficulties can arise. Shrink cavities for one. Or the opposite -- an overpour and surface run-off with lots of excess to cut off and machine back. It doesn't save time or effort to machine a big bunch of lumps compared to cutting off a gate or two where the rest of the casting is close to finished in proportions because it was fully enclosed in a mold..

Or both at the same time: cavities and lumps -- the most likely scenario. I find the best patterns to direct pour are long sticks of something I intend to cut into lengths for some job. Sort of like making your own extrusions. I think it makes sense there. Or pouring round or square section shaft stock. Anything a lot deeper than wide with a spoilage allowance at the top makes sense -- and the nice thing is, you often don't need draft because it's easy to rap a shape like that.

Anyway....my experience in that type of casting.

Navigation

[0] Message Index

[#] Next page

[*] Previous page