Buy SO2 Mechanical kit, adapt for ballscrews

Talk about all things CNC
etxbkst
Posts: 216
Joined: Mon Sep 02, 2013 7:54 am

Buy SO2 Mechanical kit, adapt for ballscrews

Post by etxbkst » Tue Feb 03, 2015 2:25 pm

What are the thoughts on the feasibility of adapting a SO2 mechanical kit to ball screws? Would the screws themselves add a significant amount of rigidity? Max XY usable XY would be in the 12" area.

WillAdams
Posts: 8596
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
Contact:

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by WillAdams » Tue Feb 03, 2015 2:43 pm

I've been curious about this sort of thing for a long while as well, but was considering threaded rod as more in my budget.

My concern here is (AIUI) the machine design is currently well-balanced w/:

- plastic wheels
- belts
- not too heavy aluminum extrusion

and one isn't pushing any of the components past its rated capacity --- once one replaces the belts w/ rods, then the wheels become a limit and one may begin causing excess wear --- replace them w/ steel wheels, and one then needs hard-coated or steel rails, at which point one has pretty much replaced the entire machine (save for the plates and motors).

That said, the original pre-Kickstarter design used threaded rods.

I'm still trying to puzzle out what to do once I get an SO3, and reverting my SO1 into its original size (anyone got a spare 375mm rail?) and then converting it to use threaded rod is something I've been considering, esp. if I can work up a design which keeps it reasonably compact.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by cvoinescu » Tue Feb 03, 2015 2:45 pm

Ballscrews are overkill. The other components of the machine aren't rigid enough for the ballscrews to make a difference over, say, trapezoidal (Acme or metric) leadscrews, or even well-tensioned belts. In my opinion, the only justified upgrade for general use would be wider belts, and maybe trapezoidal leadscrews for certain applications needing low-load, very precise positioning (e.g. machining very small parts with sub-millimetre endmills).
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

etxbkst
Posts: 216
Joined: Mon Sep 02, 2013 7:54 am

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by etxbkst » Tue Feb 03, 2015 2:48 pm

cvoinescu wrote:Ballscrews are overkill. The other components of the machine aren't rigid enough for the ballscrews to make a difference over, say, trapezoidal (Acme) leadscrews, or even well-tensioned belts. In my opinion, the only justified upgrade for general use would be wider belts, or maybe trapezoidal leadscrews for certain applications needing low-load, very precise positioning (e.g. machining very small parts with sub-millimetre endmills).
I want to carve/engrave silver, and I'd like to be able to use possibly sub-millimeter endmills to achieve fine details. You feel like Acme screws could do just as well?

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by cvoinescu » Tue Feb 03, 2015 2:53 pm

My experience is not with extremely detailed work, but I really don't see how ballscrews would be any better than trapezoidal screws with anti-backlash nuts. You can buy motors with built-in screws quite cheaply. The only reason I'd go with ballscrews would be if they were less expensive than the trapezoidal screws (say, if I already had them from another project, or someone gave them to me).
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

etxbkst
Posts: 216
Joined: Mon Sep 02, 2013 7:54 am

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by etxbkst » Tue Feb 03, 2015 2:54 pm

cvoinescu wrote:My experience is not with extremely detailed work, but I really don't see how ballscrews would be any better than trapezoidal screws with anti-backlash nuts. You can buy motors with built-in screws quite cheaply. The only reason I'd go with ballscrews would be if they were less expensive than the trapezoidal screws (say, if I already had them from another project, or someone gave them to me).
OK, good to hear, especially since ballscrewa are so darned expensive!

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by cvoinescu » Tue Feb 03, 2015 2:56 pm

I'm not saying that ballscrews aren't better than trapezoidal screws -- they are, but the rest of the machine is nowhere near rigid enough for that to matter. :)
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

etxbkst
Posts: 216
Joined: Mon Sep 02, 2013 7:54 am

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by etxbkst » Tue Feb 03, 2015 3:33 pm

cvoinescu wrote:I'm not saying that ballscrews aren't better than trapezoidal screws -- they are, but the rest of the machine is nowhere near rigid enough for that to matter. :)
So here is the question. Given the nature of the SO2, will screws add any sort of rigidity?

Edit: I'm thinking jettison the wheels and go with linear bearing rails. Of course this then pretty much makes buying a shapeoko kit pointless.

Hans
Posts: 290
Joined: Tue Dec 25, 2012 5:19 am
Location: Connecticut, USA

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by Hans » Tue Feb 03, 2015 4:24 pm

etxbkst wrote:So here is the question. Given the nature of the SO2, will screws add any sort of rigidity?
Yes. The flexibilities of the wheels, the belts, and the frame add together. If you stick a ballscrew on there, the flexibility of the belts is reduced to effectively zero. How much does each factor contribute to flexibility? Nobody's done a complete study but I think they are close enough to balanced. I'm guessing on a 1'x1' work area machine you'd lose 1/4 flexibility going to ballscrew and another 1/4 going to ground rails. You've doubled the stiffness, but you can still only take a 2-lb finish cut and I think that's a generous figure.
Shapeoko #1,123

cvoinescu
Posts: 4442
Joined: Thu Jul 19, 2012 6:50 pm
Location: Camberley, UK
Contact:

Re: Buy SO2 Mechanical kit, adapt for ballscrews

Post by cvoinescu » Tue Feb 03, 2015 4:34 pm

I assumed you'd keep the wheels. If you replace them with something else, then you need to replace pretty much everything else, so, as you said, there's no point in even buying the kit in the first place.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Post Reply