Poor Casting Detail


#1

Looking for the Holy Grail here. Cannot get nice, defined details to cast and we have tried many different things. I’ve included some photos. Lettering is the hardest.
Using Plasticast and burning out longer and trying to keep parts clean etc… all the tips i’ve seen.

ANYONE getting great casts with lettering??? Any and all help is appreciated! Thank you in advance.
-JR


#2

what do your printed patterns look like?

Are you burning out the printed patterns? Or using a printed pattern to ram sand?
Or were these cast in investment?

Off the cuff I note that the letterforms do not appear to be Drafted… they Should be drafted at least 5 degrees…

The flaw in the S looks like an inclusion flaw. that is, some small bit of the investment forming some narrow detail in a letterform, ( perhaps the missing hollow in the lower loop of the S- or the missing hollow in the “a” ) got knocked loose by the force of the flowing metal and swept into the channel that should form the lower loop of the S.
The Circular flaw in the M is weird… I would have to see the printed pattern, but that does not look like a casting flaw.
The missing hollow in the U and other letters is, again due to either you investment forming a bubble here and not filling in the hollow- Or the investment in the hollow was broken loose by either the inflowing metal- or possibly by the expansion of the printed pattern during burnout.

Can you clarify your process and post pictures of the printed pattern? What resin are you using?


#3

Hey Sculptingman,
we have a CAD design made of the jewelry piece, we then print at 25 micron in castable wax resin. we do a thorough wash in alcohol and let completely dry. We tree them up and use plasticast investment. good mix, vacuum, pour, vacuum and let dry.
ramp is set to formlabs recommended burnout with an hour added to the 1350 degrees ramp. cast at 1150 degrees.

here’s the formlabs schedule:
Insert Flasks 0 min 150 °C 302 °F
Hold 60 min 150 °C 302 °F
B
Ramp 100 min 2.2 °C / min 4 °F / min
Hold 120 min 371 °C 700 °F
C
Ramp 180 min 2.0 °C / min 3.6 °F / min
Hold 280 min 732 °C 1350 °F
D
Ramp 100 min - 2.2 °C / min - 4 °F / min
Hold
(casting window)
Up to 2
hours
512 °C
or casting temp
954 °F
or casting temp


#4

What you are seeing is damage caused by the expansion of the resin before it starts to burn. Both Castable Resin and Castable Wax Resin expand markedly during the initial warm-up and the plaster isn’t strong enough to resit the expansion. Small circles such as the centre of letters get crushed during this phase and the resulting bits then fall to the bottom of the mould cavity and cause a rough surface. The only way to fix it is to use expensive 2 part dental plasters that can resist the expansion but they are expensive and difficult to remove.