Printing a Moving Part


#1

I’ve been doing some experiments recently in how to best print moving parts on the Form 1.   As you can see in the picture, they can come out really nicely with the high surface finish.  One thing I’ve noticed, though, is that you should try to avoid moving the parts around until the parts are completely dry from the IPA bath.  If they’re still a bit stick or soft, the parts can scuff by rubbing up against each other – which is not ideal.

Once the print is dry, though, the parts definitely move nicely against each other.  Over time, I’ve seen some wear patterns, so I think it might make sense to put a layer of acrylic spray onto anything that will get a fair amount of use/friction.


#2

Martin, have you had a chance to polish the clear resin to see if it gets crystal clear?


#3

Aric,

I’ve done some experiments with this.   The surface out of the printer is already very smooth, but it can be further refined with 1000 or 2000 sandpaper.  That still leaves the surface somewhat opaque, however, from the sanding.  The best result I’ve gotten is to instead wait for the object to dry and then to spray it with a glossy acrylic spray.

FYI, one thing I’ve tried that has _not _worked well is  using a buffing wheel and my Dremel.  I may be going about it wrong, but that seems to mostly mar the surface.


#4

Awesome, thanks!


#5

Polishing plastic is tricky.  I am involved with people building large scale model aeroplanes and they use special polishes to work with plastic.  Using a Dremel and the polish that comes in their standard kit is typically for metals, but some hard plastics can be tackled as long as it is prevented from generating too much heat from the friction generated with the buffer.  The more abrasive and finer the polishing wheel the higher the risk of melting the plastic.  Is there any information on the melting point of the cured resin??.

Model makers are very resourceful and hove found some brands of tooth paste and a light buffing wheel or soft cloth work very well.  This is something I will be experimenting on when I get the Form1 and the clear resin.  Not sure how long that will be yet !


#6

hey martin -

awesome print!  it got me wanting to make my own hub - while i’m still waiting on my printer - would you take a look at my version to see if it would make a valid print?  I’ve attached the .form file in hub.zip and the .stl in huber.zip

thanks in advance!

keith

hub.zip

huber.zip


#7

I am having trouble with varying clearances based on positioning and print angle. For example, one piece has two sections mirrored at a 90 degree angle, the moving piece positioned on the vertically on the z axis printed entirely together while the one parallel to the build platform printed separately. Has anyone figured out a general rule for clearance that works on every axis?


#8

So I assume you had the bearing print side ways so supports attached to inner race, outer race, and balls?  What clearance did you have all around the balls?


#9

I am also very interested in the clearance you used. A ball race I just tried to print horizontally is basically fused together. I’m now going back to the printer specs, and given the horizontal resolution of the printer being .3mm so I am going to re-do the model with that amount of clearance, but I’m interested in others experiences.


#10

I have found success using a 0.1mm gap for moving parts/fitting parts together as well on an Objet printer. I am not sure how small a feature the Objet can maintain. 0.3 mm could be a good trade-off, but I think one could go smaller if not printed horizontally. 
Also, I think there is a way to vapor polish plastic after fine sanding (600 to 1000 grit?) using a beaker, bunsen burner and super glue, but I will need to research that more in depth. I’m not sure when I will able to get info back to this thread through, maybe check on-line?


#11

@Willian, Adrian, Temujin, et al.  - I’ll be posting a design guide soon to answer all these questions and more!

For a press fit, 0.1 mm of clearance works great. If you want your parts to smoothly rotate, you should use 0.2 mm.

And to save yourself a possible post-processing challenge, keeping support points off of mating surfaces and press fit features is a good idea.


#12

I’m up to 0.4mm clearance on the attached scad (allows you to change dimensions) or .stl (where you can’t) file, and it still isn’t coming out free. Is there some trick to cleaning in the IPA, or is the resin around the balls getting some light bleed that is partially curing it? I am trying to free them right after the IPA bath, since you can see the bridging material, and I don’t want to let it set.

I would also note that the supports don’t always position properly for the balls. Is there a way to force supports into particular places?

Feel free to use and play with the files in the interests of learning.

Ball_Race.scad

Ball_Race_0.4mm.stl


#13

Woohoo, success. After having one printer die on me, and the next one being DOA, my new one printed a ball race (the 0.4mm file above) beautifully. There is too much clearance at 0.4mm (so the balls can come out) but at least I was successful. I have also printed a set of nested, cut spheres which came very well http://www.thingiverse.com/thing:208308. Scad file is on thingiverse, so feel free to leverage.


#14

Oh, and one final note - I have been scrubbing the finished print in the alcohol bath with a toothbrush to get the goopy layer of resin off the surface, and my surface quality has gone up considerably.


Retro Form 1+ Guide
#15

Do you brush the print before or after removing the supports? I am guessing after otherwise there may still be resin buried between some inner supports you cant get at with a tooth brush?


#16

I have ended up doing both. For everything except the most delicate parts, I scrub what I can after a 10 min soak, then remove the supports, then scrub the areas where the supports are. I have found that a fair amount of resin can collect around the supports, especially when printed with a “more dense” setting.

I have been using a set of hand carving tools to scrape, cut and otherwise clean up prints like this. Getting the spheres free from each other wasn’t easy, and one of the bridges cracked when I was trying to lever it free, but it was easily fixed with superglue. Getting the internal supports out was tricky too. I spent a fair about of time in SCAD, rotating the inner spheres so I could get both base support and a few internal supports working.


#17

@adriankunzle,

it’s a very interesting thread. have a few questions I would like to try something like this myself.

what is an scad model?

regarding your method for cleaning up the parts with a toothbrush,don’t you find that you are creating small scratches to the parts if you attempt to brush them right after they have been printed.I find that sometimes even with my finger I create small scratches on the recently cured resin and have been reluctant to use a tooth brush for this reason.

Lastly, it would be nice and helpful to see a last a screen shot of your preform setup. I want to see te support structure and how you guys are dealing with the islands all the free parts create.
Otherwise, I’m glad I found this thread, and Congrats on the great works. It’s really motivating in terms of what can be done w this. printer.


#18

Read through this thread and want to comment on the polishing of the clear resin.

Just a bit of history: I was a gunsmith for several years and later converted my shop and skills to jewelry making and metalsmithing.

That said. I have successfully polished a flat support piece off of one of our models just as an experiment. First, make sure the part is well cured. Second, wet sand the part with successively finer abrasive paper to a 600 finish.

Note: As with any sanding and/or polishing operation, one always sands or polishes in a different direction from the prior grit. So if your 400 grit sanding was from right to left, your 600 grit sanding would be from top to bottom. This helps you avoid ripples and also lets you see when you have removed the sanding scratches from the previous grit.

At this point I used ZAM polish on a 10" loose muslin polishing wheel, running at 1800 RPM. The wheel must be kept clean by occasionally using a buff rake and as stated in Nigels post, the part must not be allowed to get hot by heat generated by friction of the wheel. To avoid that you need to use light pressure when presenting the piece to the wheel and keep your wheel clean and well charged with polish.

Not everyone would have or want a polishing motor that can spin a 10" wheel but all other conditions/cautions would apply.

One general note, machine polishing relies on SFM, (surface feet per minute) thus the 10" wheel @ 1800 RPM. So, if you are using a smaller wheel, it will need to run faster to accomplish the same level of finish as a larger wheel running slower. The only problem with small wheels running fast (as with Dremel) is that you have a greater chance of over heating the plastic, thus melting it and getting deep “drag” marks on the piece you are trying to polish.

Hope this info helps.


#19

Cesar - a scad model is something produced by OpenSCAD (www.openscad.org), and awesome 3D modeling tool.

On the tooth brush thing, I have found that taking the “soft” layer off, reveals a fully cured layer. It is often the soft layer, that when allowed to cure, is what bonds the pieces you want separate together. I haven’t worked out the dimensionality of the resulting pieces, so can’t tell you whether the softer layer is meant to be there or not.

The item was printed a while ago, and I don’t think I have the setup. What I did do was position the spheres in the modeling too (SCAD) in a way that allowed for easier support. One of the outer holes shows a bit of both inner spheres and a gap. It is that hole that should be oriented “down” toward the plate of the Form 1.

I hope that helps.


#20

thank you. i will have to try it.