I’m getting into more work that demands draft angles. I’m looking for advice and any guidance on adding or designing with draft in mind.
I noticed rhino has a draft option but that doesn’t work for what I’m doing since my parts need draft in more than one orientation. Or maybe I need more information on it. I’ve used it in the past and it was ok but doesn’t seem to work on what I’m currently doing.
I did look at FreeCad and it has an add draft tool that looks pretty cool one can even add formulas in it. I’m wondering is there an add draft command for Rhino or is it being considered for V9?
The concept of a magic “add draft” tool for most of the things people do with Rhino is laughable. You just design stuff with the right angles to them. You can use DraftAngleAnalysis to check if you missed something.
If you create an extruded feature like a boss in other cad, you create a draft very easily by picking the outside or inside faces and draft them a very specific amount. For injection moulded parts there are generally accepted draft angles for interior / exterior features, polished or textured etc. With a draft tool it’s trivial to create an x° draft on a rub or boss, with Rhino it requires quite a few more extra steps.
Draft angles… what for? Vacuum-forming plastics? Slip-casting porcelain? Injection-moulding magnesium? Casting chocolate with silicone tools? No 3D software has magic tools. You need to find out from your client, what materials and production processes are to be used, and which draft angles are recommended for what purpose.
Thanks for your tips,
I did look at freecad’s draft tool as I have the program it works but not intuitively for me also I’m not a freecad user so it’s a very alien program to me, I prefer to stay in Rhino.
In Rhino I can construct my part with drafts it seems Rhino is pretty good at all of this and I was able to fillet the inside pockets even. But as @ftzuk pointed out the pockets and interiors had to be worked on and thought out it’s not really that trivial. I tried to give all surfaces a 1 degree draft, some of surfaces are less but all surfaces have draft.
@Lagom and @ftzuk
It’s the whole part. We are having the part 3dprinted and the molds are made out of plaster then duplicated in silicon for when the plaster mold wears out. It’s pretty traditional hand work we’re trying to automate/update. Also we’re trying to lessen the parts weight by adding pockets, traditionally the back is all filled in making the tiles heavy. The fabrication process is slip casting (pouring liquid porcelain into a mold). I gather injection molding is the closest thing to what we’re doing, but not that advanced.
I’ve attached my part. There is also first attempt at a mold mock up but I’m concerned about the tile part being moldable, (in plaster as two part mold).
I appreciate any advice and criticisms and thanks for your answers thus far. Molding test.3dm (4.4 MB)
I worked with plaster moulds and slip-casting quite a bit, where CNC or 3D printed models were finished with a very smooth surface finish, then sprayed with a water repellent release agent, then plastered to make moulds. The clay models or 3D printed models had varying draft angles from 2° to almost 60° (shallow dish-like LED light reflectors, dual-cast bisque white inside/bisque black outside). So, there was no “best” draft angle.
Not at PC now but as a very crude generalisation: draft tools work best on surfaces that are straight in at least one direction. So a cylindrical boss is fine because it’s straight in the vertical. You can draft that. However, if the boss had a radius on the top edge the draft wouldn’t work.
For the shape @laggung1205 posted (not sure if that’s your file or not) you couldn’t use a draft tool to draft the outside - you’d need to model that draft as part of your design. But the ribs inside - that could definately be done with a draft tool.
Rhino is a bit frustrating in this regard. I like to give parts to toolmakers with consistent drafts for specific model features. This is trivial in other cad but requires more steps in Rhino.
Awesome work @Lagom and thanks for sharing your images and advice.
I’m going with a 1° draft as the parts are smallish and need to be grouted so too much deviation is not good for the tile setter.
No that’s @Lagom file, my rhino file is attached to my post above his, the file is named molding_test.3dm . My part is a cavetto molding I added draft and filleting to the pockets.
The other half of the mold has draft that will work. The draft needs to change direction at the parting surface. The way you have designed the parting is going to make that difficult. If you can simplify the parting it will be a lot easier to make the draft correctly.
The easiest way would be to make the part all in one half of the mold. The other half would just be a cover that has just the flat surfaces of the one side of the part.
If its required for some reason to have parting split somewhere in between so that both sides of the mold have opposing draft it would be best to make the parting something simple like a flat plane.
The way you have designed the parting it can be done but it will require a lot more skill and work.
The mold maker did a visit today and I am completely redoing the mold according to much of what you said
Yes that’s how I’m doing it now, I’ll post something when complete. My mock up mold was a test and as you said makes it more difficult and has problem areas.
Can’t thank you enough for your sound advice and for taking a look at the model and mold.
But what I was thinking in my previous post was to change the direction of draft on the 4 outer walls. That would make the part and the mold look like this: Mold_opposite_draft.3dm (4.4 MB)
Which way is best for your application I can’t say but both ways are easy to model in Rhino.
Because the draft in that mold is going the wrong way so that the part can not be drawn from the mold. The draft analysis tool shows the draft is inconsistent with the rest of the mold.
Yes this is exactly the way I had to redesign the mold, after discussion with the mold maker, I’m glad the original part was ok. Thanks for your file, gratifying to see the correct way to do it and that I’m on the correct track.
Also thanks for the example file Mold_opposite_draft good to learn an alternative.
@ftzuk thanks for taking a look at the original part.
. Sunday brain not working.