Looking for info: Modeling an object with moving parts
 

Looking for info: Modeling an object with moving parts  

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Bill Lugg
(@bill-lugg)
Active Member

I'm in the process of conceiving a tool that will have to have a couple of integral moving parts in it (well, it doesn't have to, but it would be convenient if it did).  I'm looking for info that could guide my modeling, preferably specific to the Prusa MK3S and have so far been largely unsuccessful in my searches.

Currently the design is forming in my mind only - I've visualized a mind's eye view of it, but I've been loathe to begin modeling as I'd rather have the parameters necessary for printing success understood before I begin.

Any help the group can provide would be greatly appreciated.

Thanks

Bill Lugg

This topic was modified 1 month ago by Bill Lugg
Bill Lugg...
Posted : 25/10/2020 11:54 pm
Area51
(@area51)
Honorable Member

I think you have to be more precise if you want help in this forum.

Have a look at my designs on Thingiverse or on PrusaPrinters ;)...
Posted : 26/10/2020 3:55 am
Neophyl
(@neophyl)
Noble Member

Well first thing I would do is download one of the tolerance prints and print it in the material you want to make your model in.  That will tell you what sorts of clearance you need to design in so that integral parts dont fuse together during printing.

Beyond that though, dreamland 🙂 is correct that more specific details of the design would be needed.

Posted : 26/10/2020 1:45 pm
Bill Lugg
(@bill-lugg)
Active Member

@neophyl

Understood, so here goes...

I am a model railroader.  I build the bed the track lays on from quarter inch thick strips of spline standing on edge and glued together following the path of the track alignment on my layout.  After the roadbed is glued, planed and sanded, I need to mark a center line on it - this is where my currently imaginary tool come in.

Since the roadbed can vary in width, the tool needs to be able to expand and contract maintaining the marking pencil in the center. So, I envision it composed of two geared racks with the marking pencil inserted in the center of the gear, all of this sliding in a holder that would retain the racks and include the bearings (holes) that a boss on the gear would ride in.  Each rack would have a rounded tang hanging over the side of the roadbed that would allow it to slide along as the pencil makes its mark.

So, my questions are during the design process how much clearance do I need to provide between each of the moving parts?  I don't have the MMU upgrade for the printer, but I assume I'd need to use disolvable supports.  Is that possible without the MMU?  What else might I be missing (this is my first foray into this kind of print)?

HTH, and thanks for the help.

Bill Lugg

Bill Lugg...
Posted : 26/10/2020 2:21 pm
Neophyl
(@neophyl)
Noble Member

So in effect a centre finder but for railroad tracks ?  Is there any reason a normal centre finder wouldn't work ?

For example

https://www.thingiverse.com/thing:1811187
https://www.thingiverse.com/thing:2746107
https://www.thingiverse.com/thing:2199356

Sorry without a visual of the track bed I'm having trouble visualising it.

For a tolerance test a quick search found this one https://www.thingiverse.com/thing:3556301   You print it out in the material you want your to be in (pla/petg etc).  Once finished you then try and move the parts.  The smallest gap that moves is how close parts can be printed together before they fuse.  That gives you an indication of the gap you need to leave inbetween parts to get them to print ok.

MMU or soluble supports are not needed in many many cases.  Just look at other examples of models without supports that move.

You can actually print some amazing things.  A google search will show many

https://www.javelin-tech.com/blog/2018/05/3d-print-moving-components/
https://all3dp.com/2/3d-printed-joints-the-basics/
Plenty of examples here https://tutorial45.com/3d-printing-objects-with-moving-parts/  

Posted : 26/10/2020 2:47 pm
Bill Lugg
(@bill-lugg)
Active Member

@neophyl

See, this is what happens when you give a retired engineer an expensive toy to play with.  He begins conceiving contraptions that are far more complex than necessary to solve a simple problem.

The third item in the list in your reply would do nicely for what I need - no moving parts and adjustable to varying widths of roadbed.  The first photo on that page is almost exactly what my roadbed looks like before I do the finish work on it, albeit mine is a bit wider.

Thanks for the links.  I always seem to forget to look on Thingiverse first.

Bill Lugg

Bill Lugg...
Posted : 26/10/2020 3:48 pm
Neophyl
(@neophyl)
Noble Member

@luggw1

Lol, I think we have all been subject to that.  The half mythical story of the nasa pen vs the russian pencil springs to mind.

Checking out the tolerance stuff and parts clearance is useful anyway though as it gives a better understanding of just what our expensive toys are capable of.   Which is always a good thing.

Posted : 26/10/2020 4:01 pm
Area51
(@area51)
Honorable Member

@luggw1

Good choice selecting the third on the list - I made some in the spring when repairing some wood around the house. Real fast to find the center when drilling holes... and so nice simple...

Have a look at my designs on Thingiverse or on PrusaPrinters ;)...
Posted : 26/10/2020 11:10 pm
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