Basically, yes. There are a few ways to do it, but yes. If you look at the kickstarter above it shows how they do it.
This is why linear scales (optical and magnetic) are used for DRO’s. Even so, 600 pulse/r degree optical encoders really cheap ($15) and more than adequate enough across the distances we’re talking about, but difficult to use in these circumstances. Buying a “closed loop stepper driver” and an appropriate stepper with an encoder is a cheap way to get what you want. If you’re driving for absolute maximum productivity, makes more sense than a stepper systems…but honestly if you’re into needing maximum productivity to the point of not being able to slow down a little to avoid skipped steps, you should probably be using a difference machine.
DRO’s use scales like these
The issue is that there is no means of feedback to simple cnc controllers like GRBL. You can either do it at the stepper/servo, or do it at the controller. It’s easier at the servo with a controller like GRBL.
Makes sense to me (and apparently @Vince.Fab). Interesting discussion though - thanks! Here’s a DRO system for mills. Do you know of anyone who uses them on CNC machines for position feedback?
That’s the problem really - the GRBL software can’t do anything with that feedback. You could hook one of these up, but it would only be as a monitoring tool (and a really slick way to calibrate), but not a integral part of of the control systems.
Do all CNC machines use GRBL software?
Many of the machines use Mach2/3/4 instead of GRBL and there are many proprietary systems too. When I look at the processors available for VCarve there are dozens.
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No, but SO, SO2 and SO3 does. Many home machines use Mach3 and 4.
When you get to commercial machines, basically think of each one as bespoke - they all “speak” g-code, but often have significant enhancements for a given machine to drive toolchangers, 4+ axis, sometimes multiple spindles, modern machines are pretty amazing.
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Awesome - I want one of those! Does anyone use position feedback?
The LoboCNC did (use positional feedback).
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After googling lobocnc, it amazes me how far technology and industrial-quality parts availability for the hobby market got in the past decade.
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Yeah, I think the next two big advances will be:
- sensor technology — someone is going to work up an elegant way to use sensors to markedly improve reliability of steps/cutting
- 4th axis — the PocketNC is amazing, but I think a 4th axis is the sweet spot for functionality — the problem is, lathes are heavy and expensive
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I’d think that improvements in rigidity would be a better improvement for our machines. If position is lost, it’s typically while cutting and the damage may be done.
I think those positional sensors are best suited for fast, low load machines like pick and place machines, where positional corrections make all the difference (before material is affected).
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I don’t see how we’re going to increase rigidity w/o markedly increase weight and cost and shipping.
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HDZ is a good start. Linear Guide Rails on X and Y axes next?
The second moment of inertia of the existing aluminum X and Y Axis extrusions likely provides more than enough rigidity. To improve accuracy, some claim that steel timing belts are a worthwhile upgrade too - possibly avoiding the expense and hassle of ball screw drives on those axes.
2019-12-03 Update
All about precision linear guide rails.
All about precision ball screws.
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Any thoughts on the Centroid Acorn controller? It advertises hybrid loop operation but unsure what that means.
Still, imo we shouldn’t be pushing even close to 18lb cutting force during operation. The @gmack workbook really helps to keep load values in check. And usually its bad cam (crash) that causes load spikes to skip steps.
Ridgidity - the stock machine is really well balanced right now and imo there is a clear spot in the market for a MDZ (medium duty Z). Not sure if I ever posted my bolt on linear bearing upgrade Z plate that’s 9mm belt drive on here.
Linears are a huge step up but also don’t really seem feasible to mass produce upgrade kits unless a good amount of the s3 design changes. Setup can be a pain…a friend of mine has been having a ton of trouble adding X rails on his openbuilds machine.
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Are you monitoring spindle input and/or output power for that? Too bad the Centroid Acorn apparently doesn’t support that!
I’m interested in your MDZ design. Could you please provide details (PM or here?) The more I think about spindles for woodworking on Shapeokos, the more I like this one, but it would require modifying the Z plate - might as well be your design!
What in particular was the problem? In my opinion using 20mm linear rails works best with 20series v-slot extrusions. 15mm was a nightmare to install.
@gmack when using the 1.2kw 60k I definitely factored in spindle load but with a 1.5kw 24k it’s much less important. The constant TQ limit needs to mesh with your cam and how long you sustain loads, a couple different ways to go about shifting everything.
The is the design and needed a little chop of the rails I had and a closed loop 9mm or open loop belt clamps. The 15mm rail bolt pattern lines up perfectly with a couple top and bottom holes already on the rear plate. Spacing is nice.
@BartK yeah…I not sure why but he is using low profile 12mm. That coupled with extrusion flatness is wrecking his setup. Slides good until bolts are torqued. Hes using the C beam and imo 15mms would have been the smallest I would have gone with. Oh well, lessons learned!!
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So you only use the calculator to predict your cutting forces, not to estimate them from measured/monitored spindle cutting power draw? 
Extrusions are tricky 
I’ve reused so3 xl’s long extrusion as a gantry on my cnc, but turned out to be nowhere near as flat as i need it be. Nothing I can complain about since they aren’t really meant for installing linear rails. 8020 extrusions will definitely have much tighter tolerances. Today did a mockup fit of 25mm HIWIN rail onto 100x50mm extrusion and it’s a massive improvement. Misumi sells few models of their extrusions with surfaced faces and they aren’t horribly expensive.
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