3D printing using a CNC machine

[jamesterm]

Ok, so let me try to throw an idea out to you.  I know several of you have 3D printing experience so hopefully you know where I'm coming from.

The idea is to 3D on something that has already been 3D printed, let me answer why.  The biggest Achilles heel to 3D printing is the weakness of layer adhesion.  I say that in spite of this test which adhesion appears to work amazing on only one printer, but this printer stepper motors can't handle pet-g filament properly, so I don't use pet-g for it.  One thing I do is print parts that I like to perform some mechanical function, and if the mechanical function requires tensile forces I have to be aware of the orientation of the print.  If I have tensile forces in multiple directions I have a problem.  I've worked around this before by putting "cross grain" lines of filament via doodle pen, and this works, but is a bit messy.  So here we are with this idea.  I could use all the same CNC techniques to actually make cross grain layers.  The result would be similar to plywood vs. regular wood.  This would almost be a perfect fit except I don't have programmable feed control of the doodle-pen's extruder, but then how compatible is gcode from CNC machine to 3Dprinter?  Perhaps the UGS and gcodes could run on it?  Hmmmm I may have a go on it.    I think about these things because I have a part I need to reprint again that broke because it can't handle some forces that cause tension on the layers.

[jamesterm]

While this might work... I remind myself that a 3D printer has its strengths and so does a CNC machine.  This particular part (called the rocker motor mount) has broke at least 4 other times, because its geometry has no easy way to print in an ideal  orientation.  I'm not going to say anymore about it, but to say I'm not pursuing the idea here of a stronger 3D printed part, instead I'll have a CNC solution to work along side a 3D printed solution at the point where the tensile strength is needed.  Also, I may do a fold-mold, where I 3D print a mold on both ends of the CNC cutted lexan to be folded, heat up the lexan to fold it, sandwiched in the mold, and then drill holes from the mold guided holes for precision.  I'll have a new post for this when I cross this bridge.  Thinking about this a bit more... I probably only need a 3D mold for one side.

[Bruce]

What if you cut the part from a big piece of HDPE or something similar?  HDPE at Amazon link 1" thick 12x12

[jamesterm]

Nov 9, 2018 3:39:47 GMT Bruce said:

What if you cut the part from a big piece of HDPE or something similar?  HDPE at Amazon link 1" thick 12x12

Ah I see what you mean... it would avoid needing to fold.  I'll think about this some more, and resume it in the curivator thread once I cross that bridge.  Thanks.

[jamesterm]

Ok for reference:
--link1--
--link2 (just part)--
--link3 (rendering)--

So in the part link 2 you can see where I tried to doodle pen repair the part due to breaking at the joints.  In Link 3 you can see how I need a counter twist to withstand the rotation of the planetary gears.  Now the amount of twist force needed should only be the skid of the rubber tire on the surface, and if that were the case none of this would be an issue; however, what I've been doing is manually twisting the pods where everything is in reverse and the counter twist has to be strong enough to make the motor turn (with no power on)... this breaks the part.  So I've increased the load requirements for the part given this as it's convenient to do if I need to push the robot around with no power. 


Reading the previous entries above, my goal was to figure out how to make the part stronger, but this is one of those cases where I'm addressing a symptom but not really the root cause.  So look at link1.  Instead of trying to mount the motor mount to the above versa frame, I can make use of the other holes in the corner braces.  So the solution can be simply to put either #8 or 1/4 20 screws into a threaded mate of the mount itself.  This addresses the torsion moment directly and with a compression solution (when used in conjunction with 3D printed spacers as needed)... as you know 3D printing's strong suit is great to handle compression.  At some point I'll followup this post with that design solution.

 

[jamesterm]

This is the design change I mentioned in the previous entry, this offers compression enforcement for torsion moments. What can't be seen is that the screws screw into a 3D printed threaded holes so screws have a nice strong seal. The corner braces are enforced as they are bolted onto disc pads. It will be a while before I can get to this, but I'll post an update once I have it installed.

[rowiac]

Since your 3D printed part is failing at the base of the two tabs, what if you remove the tabs completely and replace them with metal plates bolted further down the body of the part? Alternatively you could thicken the tabs in the high stress area--if you are using Fusion 360 you could try the stress analysis tools. Or, you could attach separate 3D printed tabs that are printed flat so that when installed it would avoid the layer separation problem you are seeing.

With 3D printing the ideal is to make one part do everything because it is easy to print complex parts. But sometimes multiple parts is a better way to go.

My 2 cents...

[jamesterm]

Nov 29, 2018 23:34:27 GMT rowiac said:

Since your 3D printed part is failing at the base of the two tabs, what if you remove the tabs completely and replace them with metal plates bolted further down the body of the part? Alternatively you could thicken the tabs in the high stress area--if you are using Fusion 360 you could try the stress analysis tools. Or, you could attach separate 3D printed tabs that are printed flat so that when installed it would avoid the layer separation problem you are seeing.

With 3D printing the ideal is to make one part do everything because it is easy to print complex parts. But sometimes multiple parts is a better way to go.

My 2 cents...

I agree, I can remove the tabs completely.  With this new design, if you look closely at the picture in the previous entry I do have screws and spacers that attach to the part from the corner braces... thereby accomplishing the same geometry as you suggested, but without the need of redundant material.  

On the last sentence both are true when put together that is, 3D printing printing complex parts, but in multiple parts. Sometimes I make the geometry first then I figure out how to print it, by cutting it into multiple parts.  This becomes necessary when considering the orientation of the print as I avoid having tension that can split the layers.  Now that we have a CNC machine the rules have changed! I can blend CNC parts where tension strength is needed, so I can do this with Lexan.

Back to first point... I can remove the tabs, as now they have not had the primary use case they once had, but I'm keeping them in for being aesthetically pleasing to the eye.  I guess you can say there can be art in STEM... STEAM, and still not lose focus on the primary load requirements on the parts. 

 

[rowiac]

Dec 3, 2018 20:34:12 GMT jamesterm said:

Now that we have a CNC machine the rules have changed! 

I've been 3D printing at home for over two years, but I just started CNCing, and I agree, it has opened up a whole new set of possibilities.

[jamesterm]

Assembling this was a little challenging, I had to take it off the versa frame to get a grip on getting the spacers aligned, but as you see here... it could fully be mounted as-is so there is no worry of it breaking as the spacers will give the compression forces needed to resist torsion loads!