Advice on Design of Bearing Interface for 3D Printing

[doowus]

Hi guys, I hope I posted this in the right place, I'm looking for some advice on a design I'm currently working on. 

I'm making a USB microscope wall mount that will function similar to many computer monitor mounts, with an attachment at the end to hold a small USB microscope at a constant height across my entire soldering workstation. I will be 3D printing all of the main components and as such have designed with FDM printing in mind. It will use other common components as well like standard M3 socket head cap screws and 608 bearings. I've purposely over-designed for its use case as I want to be able to adapt it for use with other things in the future and potentially have modularity with other popular designs. 

The issue that currently has me stumped is how to design the interface between the arms of the mount and the 608 bearings on the base. (Cross Section pictured below). It needs to have a tight fit on the inner race of both the bearing above and below it so when the pin used to hold the arm to the base is tightened it eliminates vertical play in the arms. I want each part to be easily printable without supports in the slicer and so having a protrusion on both sides of the arm makes this impossible. I could print them as separate shims that are put in place during assembly but I would really like to keep the overall complexity and part count down.

If anyone with experience designing for FDM 3D printing has a better idea or a simpler way to achieve this with I would love to hear it, I'm pretty new to Cad modeling and design in general so any advice on this would really help me out.

Let me know if I need to upload the files themselves and I can do that, not sure on the best practice for these forums yet.

Thanks!

[etfrench]

Here's how I would do it:

[etfrench]

Why don't you want to use supports?

[doowus]

Interesting. I don't want to print with supports if at all possible because I want to reduce the amount of post processing and support removal needed. If It can be done without support, I will do it that way. printing using supports in holes is also a pain for removal and I've found its harder to keep dimensional accuracy when printing in the orientation you have above without sanding/more post processing.

I think I may not have been totally clear on which component I'm having trouble with. I'm fairly happy with the design of the bearing block and the wall mount parts, but the arm with the protrusion on either side is what is bothering me. I want clearance from the bearing like I have, but I don't want to print the arm on its side for the reasons stated above.

Thanks for the response btw

[etfrench]

I don't think you can insert the bearings in your current design because there is a lip on the top and bottom of the seats.  Switching to a flanged bearing will allow using a simple hole. 

Cura, Prusa Slicer, and SuperSlicer (Which I use) all have tree supports that you design and they can limit the amount of post processing needed.  Cura also has a new organic tree which may work even better.  The arm is going to be moving so slow that any imperfections in the seats won't matter.

If you use a drill jig, you could print the arm like this, then drill the center hole:

There would be a tiny bit at the bottom of the V to cut off.

[davebYYPCU]

Print the arms without the spacers, but with combine cut keys.

Print inserts (bearing spacing long) with a key.  No supports required

Might help....

[cShutsy · Accepted solution]

Personally I would probably just use 8mm washers ($0.10) as spacers.

If you really wanted to minimize the bom you could do something like:

Offset the bearings so they sit proud of the block on the inside. Then the only thing the arm can rub on is the outer race, which can be prevented with a shallow circular groove in the arm. It would be an overhang on the bottom but I've had success printing stuff like this. 

[etfrench]

That would certainly work for the arm:

[doowus]

Interesting, I hadn't considered using a flanged bearing, That may be a good route to take for simplicity. I should be able to insert the bearings as the top and bottom lips will have clearance to the bearing by a small amount. (I haven't added that clearance to the design yet which is why it looks perfectly flush to the outer bearing race in the cross section view). I use superslicer as well and am familiar with tree supports but would like to avoid it entirely for ease of printing if I ever publish the design. I'll have a look at the way you've designed it with a drill jig and see if it works for me.

Thanks for the reply!

[doowus]

Very cool. I like the idea of keying it, I could just set the depth of the slot to determine the correct depth of the keyed sleeve. Basically uses it as a bushing then. Will try this out and see how it is.

Cheers

[doowus]

I think this would be perfect! I like that it doesn't add any more components and is just a feature on the top and bottom face of the arm. I can add a chamfer like @etfrench has in his design below to eliminate the need for support for the overhangs. Thanks for the tip!

Edit: You make a very good point bringing up 8mm washers, if I can't make a recess work I may go that route. I guess I am pretty hardline on keeping the BOM down as much as possible. The bearings are certainly overkill for this use case but I may adapt this design later for something that will require very smooth motion. (Figured too much precision/smoothness now will be better than not enough for a future design)

[doowus]

I think I like this approach the best. Allows for the clearance I need as well as not introducing any new parts or requiring supports. I am going to try this out in the design but this seems like a simple and elegant way to get what I'm looking for.

Thanks everyone for the help!