Tolerances of moving parts, or how close is to close.

So I am currently working on a model of a Ghost from the game Destiny.

You can see my progress here,
https://www.therpf.com/showthread.php?t=294486&highlight=ghost

And I am doing the finishing touches on the modeling, and the one thing I'm double checking before I send a few parts off to get printed are tolerances between all the parts. Especially when it come to parts that I know are going to be painted. I want to take into account how much the paint is going to eat up my tolerances.

I have been roughly adding .2mm between all parts that are going to be touching or interlocking, and I also plan on painting it with an air brush and lacquer paint. so my question is, will I need more space between parts? How thick are paint paint coats usually? any advice for painting models with moving/interlocking parts?

if i have say, a pin or axle that fits into a hole just so, i simply don't paint the shaft or the hole. some people build up their paint super thick which may be a problem with tolerances.
i try to lay paint as thin and fewest coats as possible. i usually don't run into that problem...good enough for government work.
sometimes i find paint in the works causes an "interferance fit" which is tight at first but wears out a little so the parts are not too floppy and loose.
but i reckon you got planes and such laying flat parallel to each other (with a pivot or fulcrum on one edge)? i guess it wouldn't hurt to fret about that then....

modelcitizen said:

if i have say, a pin or axle that fits into a hole just so, i simply don't paint the shaft or the hole. some people build up their paint super thick which may be a problem with tolerances.
i try to lay paint as thin and fewest coats as possible. i usually don't run into that problem...good enough for government work.
sometimes i find paint in the works causes an "interferance fit" which is tight at first but wears out a little so the parts are not too floppy and loose.
but i reckon you got planes and such laying flat parallel to each other (with a pivot or fulcrum on one edge)? i guess it wouldn't hurt to fret about that then....

Click to expand...

Some areas won't be seen, but others could.

Im dealing with these spacers that are sitting in the grove I have designed into a sphere, so that it the posts that ride in those groves, but it still will look like a complete sphere.


so I don't plan on over painting it, but I want to keep the illusion that I is a complete sphere.

For example



this area that Is blue will be mostly covered up. however as these posts and spacers spin around the sphere, you'll be able to see them, and so I want them to look as everything else does. and it's areas like that, where I'm worried that everything is going to be too tight.

aye, then you're going to have to do some paint tests first and see what your painting style and thickness is going to be.

as I have it in my head I am going to do a glossy black under coat, and a top coat of my metal finish. and MAYbe a clear on top of that. However now as I think about it and play with it. I don't know if I hate the idea of leaving those areas just painted black...



Also... this sphere is only 65mm in diameter. so its not that big... I might be splitting hairs here.

if you can avoid paint altogether...that'd be best bet.
polished black raw medium (err, just read metal finish paint).
well then. make it out of metal! splitting fractions of hairs, aye

What process are you going to use for printing? That affects the tolerances you need to use.

With FDM printing, the tolerance of the actual print depends highly on the quality of the machine/nozzel extruding the plastic. As well as the orientation of the part. Parts slide well along the layer lines, but not as well perpendicular to the layer lines. The 0.2mm clearance you have is typically good enough, if the parts actually come out to the designed dimensions.
The material matters too somewhat. FDM Nylon is strong and self-lubricating, but harder to paint. PLA is typically very forgiving, but can actually jam up on moving parts as the dust from it tends to easily melt.

I would add at least 0.1mm of tolerance for any areas that you know will have paint against another moving surface. Your actual paint will also affect the friction, some paints a stickier than others. The lacquer you want to use can become very hard and work well on moving parts, but only if allowed to cure fully.

SLS 3D printed parts are more precise to actual designed dimensions, and since they are nylon, actually self-lubricate and get smoother over time. I use 0.2mm for close fit moving parts (Knobs), and 0.3mm for looser fit moving parts. (Hinges) No tolerance or 0.1mm at all for press-fit parts. SLS nylon absorbs paint and dye, so you can paint/dye some objects without affecting the thickness. But if you want a high gloss surface, you have to use a filling primer and sand it smooth.