I plan to start sand casting aluminum in flat pieces such as plaques with logos and text. I will be 3D printing the patterns in PLA. Design will be on FreeCAD or Fusion 360. Is there a standard or rule of thumb for the amount of draft necessary for removing the pattern cleanly from the sand? Also, for the 3D printers out there, would it be better to print a thinner face of logos/ text and adhere that to a wood base to save on print time/ material. The best wood for patterns thread just reminded me of that. I anticipate the pattern thickness to be between 1/2" to 3/4", some may be thinner for starters. TIA
I have heard it is usually between 1 and 4 degrees. I usually use tapered end mills, most commonly ~ 3 degrees of taper. How much draft is needed varies quite a bit, supposedly. The hardness and smoothness of your pattern, and the nature of your sand - and, how careful you are - factor into the matter. I suspect there is more than what I listed. How much more - I do not know. Note that I've not done 3d printed patterns, only wooden ones. I've heard printed patterns can be "grabby."
Thanks, I was kinda thinking 3-5° that I heard somewhere, somewhere. I just started printing test pieces, ton more to test and learn yet. I will probably have to smooth a print of layer lines which could involve sanding, filling and or coating. Most probably the pattern will be coated with paint at the least but there are other coatings also.
I think the best answer is "as much as possible". On my plaques cut in wood or PVC on the CNC (I've not used a 3D printer) I always profile cut with a taper router bit with a 10 degree included angle, so, 5 degrees. I generally have no problems pulling them with some exceptions. Inset grooves and capture areas in letters can create some issues if they're too deep or have sharp inside corners. Pete
Letters, especially, want the finest facing sand you can get. I've done enough, uh, stuff with letters to want well upwards of a hundred mesh in general. This Teton-Black place had, briefly, some 180 mesh Olivine sand. I wish I could have gotten a few bins of it.
Within reason. I've done alot of work recreating items with text on them. It has all ways been a challenge especially when trying to duplicate the font. One issue I continue to run into when cad modeling the text is that when the line drawing is extruded with draft you can run into alot of trouble with sections overlapping/intersecting themselves creating geometry errors. The higher the draft angle and the smaller the font, your more likely to run into these aggravating nuisances. I have run anywhere between no draft at all on resin prints where the printer by design will create the necessary draft, to 15 degrees on shallow fff prints. Larger fonts make things a bit easier but small stuff can drive you absolutely 100% chock-full of nuts. I'd print the whole thing and not letters to attach at a later point. Why should I do the work that the printer will do for me while I watch TV or catch up on some sleep? Filament is cheap and my time is sparse...
I like to glue letters on. I have printed multiples so I can change the text. I glue them on with white glue. Plenty of adjustment time. I use thinned water soluble wood filler to paint on the letter. The liquid forms a nice radius at the joint with the backing. The inside of an A, for instance, molds easiest if the cavity is a shallow dish.
You'll find flat patterns are a pain to pull from the sand. Make them match plates. https://forums.thehomefoundry.org/index.php?threads/new-plaque-match-plate.1208/
I use 5°, always Make a matchplate if you can if you are doing lettering, professional pattern letters are a Lifesaver, Hairline are the easiest to Pull, they are Halfround, so you cannot get more draft, Flat or sharp face gothic are your next best choice , be wary of any other fonts, some are a Pure 8itch (tablet) if you are doing something simple and tall, like a billet, a single degree of draft is plenty V/r HT1
I like at least 1.5 degrees for my green sand castings. If there is plenty of room I’ll use 3 degrees. I’ve yet to make a match plate pattern. Any time a pattern doesn’t pull cleanly, I start looking it over carefully to find if I have failed to get draft in that area—-it happens and almost always explains the problem, if encountered. I am usually pretty generous in tapping the pattern prior to drawing it out of the sand. But, I have a couple patterns with convex features where the sand will fracture or letters fracture if rapped too much. Vertical gentle tapping on the draw spikes seems more important than “clearance” tapping in most cases. Graphite rubbed onto and worked into a pattern surface seems to really help. I use “Seed Slik” graphite powder used in agriculture. A pound goes a long way and is pretty cheap. Softly rammed sand is a lot easier to damage drawing a pattern compared to firmly rammed sand. Denis
++1 on the graphite. I'm glad to hear of that particular kind/brand being used, as I was plotting to buy some when money permits. Is it a fine powder, or..?
Extremely fine. I think you can find their spec on their website. But my spec for it is “damn fine.” Denis
