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Re: Jumping into 3D printing from CNC

PostPosted: Thu Feb 08, 2018 9:56 pm
by jferguson
One other thing NOV. The MakerGear M2 is a machine tool not something concocted of aluminum extrusions found in a catalog. within the limits of this sort of process, it is hard to imagine anything which could provide greater precision. Very likely spending a lot more money wouldn't get you the order of magnitude precision improvement you can get with CNC cutting. I started out with a small printer very cleverly designed using plexiglass sheets. It was cheap, $175, and made PLA prints inside a 3.25 Inch cubical volume. It worked quite well and I still use it for small one-off stuff. But the M2 is SO much better in terms of temperature control and absence of printing artifacts that it was well worth what it cost.

I run it with an Octopi (raspberry Pi) which has a camera. I can have a look at how it's doing over the course of an evening by calling it up in a browser on my laptop.

Re: Jumping into 3D printing from CNC

PostPosted: Thu Feb 08, 2018 10:50 pm
by insta
JNOV wrote:
Also, dual-material support is a pain in the butt. Don't approach the process anticipating you'll use it successfully. It is far, far better to print multiple pieces and assemble them afterwards.

That's very helpful information -- thanks. Dual-printing with support materials was the main considerations (aside from the cost, hassle, and limitations of working with resin) that pushed me toward FFF and away from SLA.


Single supports work way better than you might think they do, though. Just know that you're not going to get a CNC finish on the supported area.

Re: Jumping into 3D printing from CNC

PostPosted: Fri Feb 09, 2018 1:55 am
by JNOV
Roger -- thanks again!

Re: Jumping into 3D printing from CNC

PostPosted: Fri Feb 09, 2018 1:55 pm
by ednisley
JNOV wrote:a part with a cylindrical extension that needs to be close to exactly 1/2" in diameter to fit a bearing


Unless the bearing is almost completely unloaded, I'd design a socket for a shaft made from a real rod with an actual defined OD, anchor the shaft in the socket (epoxy FTW!), then Loctite the bearing ID on the shaft OD.

Printed with the shaft sticking up vertically, the bearing load will stress the shaft parallel to the layer lines and it'll snap off near the bulk of the part. A half-inch shaft will have 30-ish extruded threads (12 mm with 0.4 mm threads) and any significant horizontal load is expecting way too much from ordinary layer adhesion.

Here's a horrible example on a larger scale:
https://softsolder.com/2016/11/29/kenmore-progressive-vacuum-tool-adapters-second-failure/

Image

I redesigned the adapter around a chunk of PVC pipe to distribute the stress and it's worked fine ever since:

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Printed horizontally, the shaft will be (at least) slightly misshapen from the support material and require way too much putzing around to get even a crappy fit in the bearing ID.

Conversely, you can print a Good Enough(tm) socket for the bearing OD, if you have room for plenty of bulk around the recess. Just clamp the plastic part in your bench arbor / drill press, heat the bearing uncomfortably warm, and ram it into the hole:
https://softsolder.com/2017/10/18/nema17-motor-and-bearing-mounts/

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Use 3D printing to produce complex shapes, but don't depend on it for high strength or precision fits.

Re: Jumping into 3D printing from CNC

PostPosted: Fri Feb 09, 2018 3:44 pm
by JNOV
That's an amazingly helpful analysis -- thanks. I hadn't even considered layer adhesion versus lateral stress, but after reading your explanation, I can see that it's going to be a major issue in a number of the use cases I was contemplating.

Re: Jumping into 3D printing from CNC

PostPosted: Fri Feb 09, 2018 7:47 pm
by ednisley
JNOV wrote:it's going to be a major issue


Nah, you'll embed little bits of precision & strength in your 3D printed widgets. After a while, it'll look exactly like you know what you're doing. [grin]

Along those lines, if you don't already know about threaded brass inserts, they should become your BFF:
https://softsolder.com/2016/02/03/knurled-metric-inserts/
https://softsolder.com/2017/04/28/badge-lanyard-reel-mount/

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Anchor 'em with epoxy, rather than (trying to get) a precision fit suitable for a spendy ultrasonic setter.

Re: Jumping into 3D printing from CNC

PostPosted: Sat Feb 10, 2018 5:35 pm
by JNOV
Thanks for the tip, Ed. (And thanks for the link to your webpage -- lots of interesting reading!)