Nomad with deep DOC, shallow WOC

The HGR15 sized rails are rated for some pretty heavy loads already.

Spacing the rails and bearing blocks further apart reduces the leverage that the spindle loads have over them when loaded in X and Y. At what spacing it becomes the mounting materials which are deflecting more than the rails becomes the key question there. HiWin do publish deflection loadings for their rail blocks.

Ideally you’d want flat face contact for the spindle holder to the Z carriage, or any tramming adjustment. You can rotate this, ideally with eccentric or set-screws pushing the spindle mount to rotate into X alignment and then lock it in place with the main bolts.

The Y alignment is harder, either you rotate the X rail mountings at the Y plates or have to do things with spacers & shims. Like on the Shapeoko there doesn’t seem to be any obvious bolted joint that allows for Y alignment of the spindle bracket.

You may have trouble using all the Watts of the spindle even in a super-Nomad. Unless there’s a big saving buying it all in one go I might grab a CW3000 or clone first.

I believe Mechatron are decent enough to specify the required flow rate and supply water temp for their spindles.


HIWIN stiffness specification:


  1. HG15 with preload class ZA is considerably stiffer than HG20 with Z0.
  2. those stiffness values are huge, compared to everything else on that machine…

It’s probably not worth spending extra effort to try and make bigger rails fit. It may be worthwhile to consider buying well-defined quality however. I’m not sure all of the aliexpress vendors know which preload class they are selling. (Tuli, that you linked to earlier, looks pretty reliable).

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Thanks, that sounds like a good idea, much simpler than the things I was looking at.

I think I can deal with Y alignment where the plate attaches to the X-axis carriage. I think I’ll have to use right-angle brackets, so I can just leave a little bit of wiggle room in the holes for them.

How about a PC water cooling loop? Just a couple of radiators, fans and a pump? I’m looking for quiet and I’m afraid these larger chillers will be too loud. Have you used one? Do you maybe know how loud they are?

Yeah, that I’m definitely doing. I’m not buying random stuff from AliExpress for sure.

The problem for me at the moment si that Tuli charges a bunch for machining the ends of the ballscrews. Dold Mechatronic sells ballscrews pre-machined for a much better price but they have literally no specifications for their ballscrews…

Just in case you have not seen it, we had a thread a few months ago about the CW-3000, how loud/quiet it was with and without mods, alternatives solutions people have used, etc… It’s running near my desk as I write, after adding fan control I can’t hear the fan anymore, but the pump itself is not silent, so it really depends where your personal threshold for quietness is.

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Thanks! I indeed hadn’t seen that thread. It looks like that cooler would suit me just fine. The 50ish dB you report is plenty quiet. My concern is more 60-70dB like the compressor I bought.

Have you considered an electric fan cooled HF spindle as discussed here? Their ER-20 collets would allow you to use larger cutters for higher MRRs without increasing forces.

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Also please note that you can go up to 5/16" (8mm) tooling in an ER-11 collet:

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Yup - and 9/16" with an ER-20 collet.

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Yes, I considered Sorotec’s various offerings, including the Teknomotor products. Two categories I ruled out entirely:

  • HSD and Elte had a worrying lack of specs (even basic things like runout)
  • Teknomotor’s “HF Motor” spindles only have 18k RPM and claim low tolerance for axial loads

That left the Teknomotor electrospindles. Those looked good and I like that they have electronic fans but I noticed that they’re larger and heavier than the Mechatron spindle (4kg for 800W vs. 2.4kg for Mechatron) and when I searched around, I couldn’t really find anyone who’s used one.

I did consider the ER-20 collets. I’ve seen a bunch of my machinist YouTubers using indexable tooling and thought that surely I should have it too but when I read up on it, it didn’t seem like a clear win. The Nomad is a small machine and I don’t think I can physically fit in pieces of stock large enough to use such large tools.

As for larger endmills, that’s true but most of the endmills I’ve seen have recommended surface speeds around 500m/min, which I already get with 6mm tools at 30k RPM. And again, bigger tools work great for bigger pieces but the Nomad can’t physically fit a whole lot in there.

And I know I sound obsessed when I talk about MRR but I don’t really need anything extreme. The Nomad currently maxes out at ~0.5cm³/min before it hits its limits, which is… Insufficient… But with the new spindle, the 30k RPM alone allows me to get ~9x MRR over the stock spindle, while keeping the same cutting forces. That means a job that previously took the whole day takes just an hour now.

With a Nomad that’s no longer like a blob of jelly and the improved spindle, I might be dreaming, but it could be possible to push it to 42cm³/min of MRR (84x stock). At that point, the modded Nomad can do in an hour what takes a stock Nomad 2 weeks. That comes with peak forces of ~82N but with axes built on ballscrews and linear rails, maybe it’ll be okay?

To be clear, even if it’s possible, I don’t think I’ll routinely push the Nomad that hard, I just wanted to think about what might be theoretically possible.

And back to ER-20, I won’t have it now but since I have flexibility, I can always swap in a new spindle in the future, just to try it out.

I’ve also been tempted by the idea of some insert tooling but Luke’s very helpful post here damped that enthusiasm quite a bit;

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Wouldn’t it be 3X MRR (3X Speed/Feed)?

When I put it into Millalyzer, it showed ~1/3rd of the force on the spindle even with the tripled feed rate, so I could bump up the depth of cut 3x as well while keeping the same force.

Maybe you forgot to triple the feed rate?

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Ah, sorry, you’re right. Usually I have Millalyzer on feed per tooth mode and it does it for me but apparently I didn’t when I did this.

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Can you actually use a 5/16 for 8mm??? Its darn close… never even thought of that!

I haven’t had a problem using them interchangeably — I mean, I’d like to see the production line which reliably holds specs where 5/16" == 7.9375 millimeters is significantly differentiable from 8mm — scarcely 2 and a half thousandths.


That’s less than the size and runout tolerance on many of the collets.


So I realized that there’s a major deficiency in my current design: It lacks supports for the ballscrew.

This isn’t a problem for the ballscrew itself but at the moment, the design puts the entire weight of the spindle and all the axial load and vibrations directly onto the stepper motor shaft. I think this is a bad idea. It was fine for the regular Nomad but the regular Nomad’s Z-axis carriage doesn’t weigh very much and the spindle isn’t made for axial load anyway.

I was also looking through the datasheets for the rails and I think there’s another problem: the required vertical parallelism of the surfaces the two rails sit on (the allowed height difference between rail 1 and rail 2).

The TBI datasheet says I get 120µm tolerance for Z0-preloaded blocks but their image also shows a 500mm separation between the rails. When I look at the Hiwin and CPC datasheets, they calculate this using an equation of the form tolerance = <constant> * separation, where tolerance is 4e-4 for CPC and ~2.6e-4 for Hiwin. If I assume TBI rails are governed by a similar equation, the constant would be 0.120/500 = 2.4e-4. With my current 88mm separation, I get:

Brand Constant Tolerance
CPC 4e-4 35µm
Hiwin 2.6e-4 23µm
TBI 2.4e-4 21µm

And to add to the complexity a bit more, there’s variance in the heights of the carriages themselves. For the standard-precision carriages, the carriage height tolerance is usually ~100µm, “high” and “precision” are ~30µm, “super” precision ~15µm and “ultra” ~8µm.

Theoretically, those numbers should be subtracted from the flatness tolerances above, so I even if I go for the “ultra” precision carriages (which cost ~2x), I still need ~27µm flatness for the mounting surface.

I could try machining this on the Nomad but I fear trying to get that level of precision out of the Nomad would drive me to insanity.

@spargeltarzan, do you have any clue how expensive it would be to get a plate with those tolerances machined at Spanflug or Weerg? I’d ask but I’d have to ask them for a proper quote and not just use the automated tool.

Or is there somewhere I can just buy mounting plates made for this?

Or am I overthinking things and it’s totally fine to just ignore the specs and throw the rails on a faced plate of Aluminium?

Shim it to win it buddy

Hmm, not a bad idea. It looks like I can buy rolls of 10µm steel pretty easily and by stacking them I should be able to get the rail to within tolerance.

Is there a way to do it without a surface plate though? I’ve been putting off buying one because they’re so heavy and expensive.