3D-Printable cover for 7x10/14/16 Minilathe Apron Gears

**Elizabeth Greene** · Feb 27, 2023, 08:59 PM

I pulled my lathe apron apart for maintenance and made this 3-D printable cover for the gears in the apron.

3D-Printable cover for 7x10/14/16 Minilathe Apron Gears-img_20230222_170618747_hdr.jpg

3D-Printable cover for 7x10/14/16 Minilathe Apron Gears-img_20230222_170649499_hdr.jpg

3D-Printable cover for 7x10/14/16 Minilathe Apron Gears-img_20230225_164239012.jpg

I put the download up on Thingiverse.
https://www.thingiverse.com/thing:5871566

Anyone that needs one and doesn't have a 3d printer, PM me. I'd be happy to print you one.

Question: How do I know how much clearance to put around a screw hole when designing a part? I've read about press fits and slip fits in the Machinery's handbook, but I'm struggling to connect that hypothetical knowledge with real-world designs. Specifically, this part uses M4 screws for mounting and I added (I think) 15% of the diameter for clearance around the fastener. Still, I had to drill out the cover get the screw to fit. What am I missing?

I can (and will) brute-force the problem by printing an array of holes of various sizes for my next project, but I'd like to understand the "right" answer too.

Thanks all.

**BuffaloJohn** · Feb 28, 2023, 01:47 PM

It depends on many things, size of hole, printer parameters, etc, etc, etc... I stick to comon sizes and print tests to get it right. There is no magic formula...

**Elizabeth Greene** · Feb 28, 2023, 07:12 PM

Originally Posted by BuffaloJohn

It depends on many things, size of hole, printer parameters, etc, etc, etc... I stick to comon sizes and print tests to get it right. There is no magic formula...

I asked another designer today and he suggested I change the slicer to print exterior perimeters before the interior perimeters. Supposedly this reduces the tendency of imperfect interiors to squish the exteriors out of tolerance. I'll give it a try and see what happens.

**DIYer** · Feb 28, 2023, 07:57 PM

Thanks Elizabeth Greene! We've added your Lathe Apron Gear Cover to our Lathe Accessories category,
as well as to your builder page: Elizabeth Greene's Homemade Tools. Your receipt:

Lathe Apron Gear Cover by Elizabeth Greene

tags: lathe, 3D printing

**BuffaloJohn** · Feb 28, 2023, 10:27 PM

Originally Posted by Elizabeth Greene

I asked another designer today and he suggested I change the slicer to print exterior perimeters before the interior perimeters. Supposedly this reduces the tendency of imperfect interiors to squish the exteriors out of tolerance. I'll give it a try and see what happens.

I have not found that to work. Why - well there is always a little squish involved in printing. And - you have the other things which just stack up.

I have made a few of these:

3D-Printable cover for 7x10/14/16 Minilathe Apron Gears-20230228_211807.jpg

which have holes of different sizes that I can test the screws with. This was one that I did for PLASTITE screws (from McMaster - torx plastic screws) and I was trying to figure out the best hole for #4, #6, and #8 screws.

Also, I have made screw holes be hexagonal rather than circular - thought it might help. But - also, I can print hexagons on their side as well, does not violate overhang angles.

**Biggus1942** · Mar 1, 2023, 07:21 AM

If you are using Ultimaker Cura 4.4.1 slicer you can change the tolerance of holes by doing the following.
Click on preferences /Configure Cura, In the window that comes up click settings. On the top right hand side pick Custom selection from the drop down menu. Then Settings from the list on the Left. Scroll down to Walls and continue to near the end of the Wall section and tick the boxes for Horizontal Expansion and Hole Horizontal Expansion. This will show you these options in the print settings menu you get when you are preparing to print. You have to save these settings and pick it from the Profile drop down to use it. I have only needed to use the Hole Horizontal Expansion. With my printer I find that a setting of 0.25 works for most of the metric holes and threads I use.

**Elizabeth Greene** · Mar 1, 2023, 07:37 AM

Originally Posted by BuffaloJohn

I have not found that to work. Why - well there is always a little squish involved in printing. And - you have the other things which just stack up. I have made a few of these:
...

Also, I have made screw holes be hexagonal rather than circular - thought it might help. But - also, I can print hexagons on their side as well, does not violate overhang angles.

Thanks, that's the direction I was leaning. For vertical holes, I use "Teardrops". These are circular holes with the top pointed into triangles at 45 degrees. I'll try hexagons and see how that works.

Originally Posted by Biggus1942

If you are using Ultimaker Cura 4.4.1 slicer you can change the tolerance of holes by doing the following.
Click on preferences /Configure Cura, In the window that comes up click settings. On the top right hand side pick Custom selection from the drop down menu. Then Settings from the list on the Left. Scroll down to Walls and continue to near the end of the Wall section and tick the boxes for Horizontal Expansion and Hole Horizontal Expansion. This will show you these options in the print settings menu you get when you are preparing to print. You have to save these settings and pick it from the Profile drop down to use it. I have only needed to use the Hole Horizontal Expansion. With my printer I find that a setting of 0.25 works for most of the metric holes and threads I use.

I use Cura so this is perfect. I'll give it a try too. I'd be ecstatic to have a solution that doesn't require modification to the models.

**Biggus1942** · Mar 1, 2023, 07:45 AM

I just printed your gear cover and the settings produced 4mm holes with clearance. Nice cover. Thanks.

**Elizabeth Greene** · Mar 1, 2023, 08:14 AM

Originally Posted by Biggus1942

I just printed your gear cover and the settings produced 4mm holes with clearance. Nice cover. Thanks.

Awesome! Glad it worked. If you install it on your lathe, note that you don't have to disassemble the half-nut and gib assembly. I did because I needed to clean out the half-nuts. If you do pop them off, they have a preferred orientation so mark which one goes on top. I didn't do plan for that and had to do it twice.