Dear designers, I love what you do! Without you I wouldn't have so many amazing puzzles to play with and admire.
That being said, there are a few things you could do to make my life (and perhaps the lives of others in the future) easier...
Alright so maybe this isn't really a love letter. There really are a few small things that could really help in the polishing of parts.
First, I should recap how parts get polished.Shapeways' Process:
Shapeways uses diagonal-cut cylindrical ceramic media similar to this:
ceramic_media.jpg [ 64.64 KiB | Viewed 910 times ]
Because of the diagonal-cut to this media, it can partially reach recessed areas of your parts. Also, the media wears and leaves a powder which does an okay job of wearing parts too. This is a great media for Shapeways to use because it's fast and only one step. It does a good job of smoothing parts and shining them up at the same time.My Process:
I polish in three stages. The first stage is very coarse grit (think volcanic sand) and the second stage is extremely fine grit (think powdered sugar). Both of these stages need good flow of grit through the parts and they do a great job of reaching all of the areas of a part. For the third stage I use porcelain spheres which do a great job of wearing / smashing down the external surfaces until they shine.
There are three big problems with my process that require a lot of manual labor or planning:1)
Grit, especially the coarse grit, can get trapped in pieces or just not flow well through the pieces which causes them to wear very unevenly.2)
The porcelain spheres can get jammed or stuck in pieces so badly that it takes upwards of 15 minutes PER PIECE to remove the spheres and even then, sometimes they have to be cut or drilled out.3)
Very large pieces with sharp points, or large, highly non-spherical pieces can wear very unevenly. A "large" piece is a piece where any dimension of the piece measures 30mm or more.
I believe these issues can be addressed by designers without much additional work.Dealing with very large pieces:
If your puzzle has large pieces with sharp points, it really helps to re-enforce the piece. One option would be to shell the piece to 1mm or greater. Preferably about 1.5mm. This can drive up the cost of the part though so another option is simply to reinforce the tip(s). For example:
mlc_reenforce_tip.png [ 46.56 KiB | Viewed 910 times ]
The red portion really should be re-enforced. The three corners around that tip and then the other three below those around it are also good candidates for re-enforcing.
The two tips on the big edge piece in the back of the image are also great candidates for re-enforcing.Enabling great powder flow:
The more powder drain holes your pieces have the better. This is true when Shapeways cleans the nylon powder media out of your parts and it's especially true when I tumble your parts. I have run into parts with a single powder drain hole that have been horrible nightmares to tumble. Imagine waiting for a giant hour glass to drain grit out of it, one grain at a time. Now imagine pieces that only drain when shaken violently. Now imagine me standing at my kitchen sink violently shaking pieces for hours to drain the grit out. Now imagine a T-Rex standing at my kitchen sink with arms so short he can't even grasp the parts. Okay so maybe I made up the T-Rex thing...
Parts that fill out with powder that don't drain well tumble very poorly. They get weighed down and wear unevenly. Here are a few examples of powder-drain nightmares:
powder_trouble.png [ 1.56 MiB | Viewed 910 times ]
These are large parts with large chambers that fill out with powder and only one (or two) drain holes. The hole size on these is great because they don't allow porcelain spheres in, but they also don't really allow powder out very fast. For the part on the left, the hole is also at the apex of the curve. Powder doesn't want to drain out of the top of an inverted curve. If the top of the curved surface is the only (good) option, it's better to make the hole a long rectangle or to add a few other holes where you can.
Designing with small spheres in mind:
Porcelain spheres are, by far, the best stage for quality results in the polishing process. Unfortunately they're also, by far, the most work to clean up after. I use 3mm porcelain spheres. They actually vary from about 2mm to 3.5mm but the majority are in the 2.8-3.0mm range.
There are two options for making parts porcelain-sphere friendly:1)
Don't let ANY spheres into the parts2)
Make holes so big that spheres flow really freely in and out.
This means holes need to either be smaller than 2mm or larger than 5mm. Anything in the 2-5mm range causes horrible nightmares. Here are a few nightmare examples:
sphere_trouble.png [ 3.54 MiB | Viewed 910 times ]
This is a 3mm powder drain hole. Now the part is packed with spheres and the only way to get them out is to drill / cut a larger hole.B)
This part has the same problem as A.C)
There is a sizable chamber in the corner of this part and the opening is an irregular shape roughly large enough to allow a 4mm sphere in. Now the corners of this part are packed full of spheres and it takes a lot of manual dental-pick and air-compressor work to get the spheres out.D)
The grating on this part is roughly 3mm in width which allows hundreds of spheres in but getting them out is a huge amount of work. The only reasonable way to get all the spheres out is to cut into the part.
The best way to allow powder flow without allowing sphere flow is to make drain holes that are between 1mm and 1.75mm in size. If you use rectangular drain holes (my favorite) then you can make rectangles that are Xmm in length but only up to 1.75mm in width. If in doubt, ask yourself: can a 2mm sphere make it through this hole? If yes, the hole is too big.
If you can't make small holes (and there are lots of legit reasons why you can't) then try to make sure holes are big enough to allow 5mm or larger spheres through. This makes getting packed spheres out very easy.Ideal parts:
Here are some example parts that are perfect for both powder and spheres:
powder_sphere_perfect.png [ 1.62 MiB | Viewed 910 times ]
These parts allow great powder flow but don't allow spheres to get into the parts.Example interaction with a designer:
Ben (of benpuzzles fame) was kind enough to work with me on his Master Little Chop design. Allow me to quote a bit from our interaction:
There are basically three guiding principles for reviewing a design to try to make it tumble as well as it can. Ask yourself:
* Are there any highly non-spherical parts with sharp points that will wear too quickly (you don't want this)
* Will a bunch of 3mm spheres get packed into the pieces (you don't want this)
* Will powder flow through and drain out of the pieces easily (you want this)
For the 3mm spheres, you either want no spheres to be able to get into the pieces, or you want the spheres to get in and come out very easily.
The 3mm spheres actually vary in size from about 2mm to about 4mm and they can get packed very dense. I see the holes in the bottom of the pieces are somewhat big, definitely big enough for lots of spheres to get in:
mlc_bottom_holes.png [ 59.91 KiB | Viewed 910 times ]
Unfortunately the pieces have big enclosed chambers and the spheres will get into every crevice and be very, very hard to get out. The corners and the edges will be especially troublesome. I'd suggest making the bottom holes only 1.75mm in diameter to prevent spheres from getting in them at all. The other options would be to make the holes even bigger and to make other holes on the parts that spheres could get in and out of. That way the spheres would get in but it would be easy to get them all out. Unfortunately there isn't a lot of room for additional 5mm + holes elsewhere on the pieces. I think a better strategy is to avoid getting the spheres in them in the first place.
For the holes in the parts, since they are going to be made smaller, it's important that powder can get in and out of the parts other ways. I'd suggest adding rectangular drains like so:
mlc_big_piece_slots.png [ 63.66 KiB | Viewed 910 times ]
The skinny part of those rectangles should be between 1.0 and 1.75 mm wide and they can be however long the part can support. dimensions like 1mm x 6mm or 1mm x 4mm would be fine. They'd be too small for spheres to get in but big enough that powder could get in and out easily.
Here are all of the places I'd suggest adding these drains:
mlc_center_drains.png [ 54.94 KiB | Viewed 910 times ]
mlc_small_triangle_drains.png [ 50.01 KiB | Viewed 910 times ]
mlc_house_drains.png [ 43.72 KiB | Viewed 910 times ]
Finally, if you want to make your design polish-friendly and you aren't sure what to do, I'd be happy to consult. Feel free to PM me with questions!