Xzero Raptor CNC build - linear rail and ballscrew selection

[Mattia]

Hi folks!

I'm slowly figuring out which bits and pieces I need to finish a Aluminum kit CNC router set I received most of* (missing one ballscrew and all the linear rails, plus motors/electronics) years ago. Following some measuring and collecting info from old build threads I've figured out the Hiwin HGR20 series with HGH-CA and HGH-HA carriages, as all the bits and bobs were designed for this. X axis is 1200mm, Y 790mm and Z 300mm.

Local suppliers (DamenCNC in NL or Sorotec in Germany) are eyewateringly expensive; following recommendations from folks here I requested a quite from The main differences are that the local folks provide High accuracy (H) carriages (tolerante 0.03mm); BST provides C grade standard (tolerance 0.1mm). One has Z0 and the other ZA preload. Considering this is an aluminium gantry router that is intended primarily (>90%) for use in wood - although I do want enough accuracy to do detailed shell inlay (guitar fretboards) for example - I would think that the BST C grade with ZA preload should be a perfectly good solution. Am I right, or is there any good reason to spend double the money for higher accuracy linear rail systems?

The ballscrew mounts and measures (and the two big end bearings that I did receive) suggest the machine was designed for a 25mm ballscrew, though I'm not sure what pitch would be appropriate. From what I gather 2510 was the original design spec but I can't really confirm. I'm not really sure about the pros and cons of a 2505 vs 2510 for a CNC gantry router this size (only 1200mm travel)

[AndyGuid]

Hi Mattia,
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I'm replying mostly to bump up your sensible query in case it gets overlooked.
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Based on the size of your machine 2510 ball-screws would be far heavier than ideal or needed IMO.
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I would be thinking of 1610 or 2010 or even 2020 for this size machine, but hope someone with proper knowledge comes along to answer you soon.
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It always helps those replying to threads if you're able to post images or plans.
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Good luck from down under,
Andy

[Mattia]

Thanks Andy!

To spice things up and help draw some interest, here are a few shots of what I have - I've put together the gantry and base (just bolted it up, no loctite, no attempt to really level or line things up) just to get a sense of the size of the whole machine, and to get accurate measurements of the clearance between the 8080 profile and the gantry sides to figure out the required linear rail bits and pieces. Once I've got a little further down the road I may start a build log to document things for my future self and simply for fun, and to get some input if/when I get stuck along the way.







The ballnut housing has a 40mm diameter hole, which suggests a 25mm leadscrew to me. That would line everything up with the machined holes in the endplates. Overkill, perhaps, but what would the major downside be other than the need for a lot more power? I need to dig up all the other bits and pieces and pre-assemble the Y and Z axes to see if I even have all the required hardware for mounting everything. If not, that's going to take some interesting reverse-engineering, or re-engineering. The backing plate and uprights on the gantry are milled aluminium, the base (which the ballnut housing is attached to) is 2020 profile, bolted in. Being a woodworker, I'm mostly impressed by how heavy things made of metal end up being. The plan (and mounting bits and pieces) is to fit a Teknomotor electrospindle (2.0 or 2.2kw), which weighs a good 8kg. The Z and Y axis run on 20mm HGR rails with 2 'long' carriages (50mm bolt spacing) per axis, the gantry runs on 20mm rails with 4 'short' carriages (36mm bolt spacing). The Y-axis ballscrew seems to be a 1610 with supported bearings on both ends, the Z-axis bottom is unsupported. The machine is very similar to this one, which is a slightly different variant by the same builder/designer:

https://www.youtube.com/watch?v=9SG_6aKASUU

I've seen some references to improved Z-axis designs over something like this, but I figure I"ll start with what it was designed to do, as I know quite a few guitar makers who have done well with this machine. For now I'll likely direct drive the axes and consider geared reduction if I run into limitiations/want to upgrade things, once I've gotten it all up and running...

[Kitwn]

Another guitar is on my (ever longer) list of things to make with my CNC router so I'll be interetsed to see how you get on.

[JAZZCNC]

The ballnut housing has a 40mm diameter hole, which suggests a 25mm leadscrew to me. That would line everything up with the machined holes in the endplates. Overkill, perhaps, but what would the major downside be other than the need for a lot more power?

The only slight draw back is lower acceleration, a thinner lighter screw will accelerate quicker with less power required. Depending on what motors you fit this will be hardly noticeable for the most part unless you are doing lots of point to point moves or short moves like in 3D jobs.

Bigger isn't always better or can be called over kill, because all it's doing is crippling the performance and costing extra. It adds nothing to the machine but weight and money.!

If it was me I'd be fitting 2020.!

I'd also be looking to stiffen up the gantry. Although the Aluminium cross plate may look strong because it's a thick piece of aluminium it's actually not because it's just a flat and unbraced so at that width it will vibrate when cutting, this vibration will transfer into the spindle so will show in the cut quality.
Also don't be fooled into thinking the rails will stiffen it up because they won't and don't. What it needs is a perpendicular brace across the back to make it like "T" on it's side.!

[Mattia]

The only slight draw back is lower acceleration, a thinner lighter screw will accelerate quicker with less power required. Depending on what motors you fit this will be hardly noticeable for the most part unless you are doing lots of point to point moves or short moves like in 3D jobs.

Bigger isn't always better or can be called over kill, because all it's doing is crippling the performance and costing extra. It adds nothing to the machine but weight and money.!

If it was me I'd be fitting 2020.!

I'd also be looking to stiffen up the gantry. Although the Aluminium cross plate may look strong because it's a thick piece of aluminium it's actually not because it's just a flat and unbraced so at that width it will vibrate when cutting, this vibration will transfer into the spindle so will show in the cut quality.
Also don't be fooled into thinking the rails will stiffen it up because they won't and don't. What it needs is a perpendicular brace across the back to make it like "T" on it's side.!

Thanks for the tips! Is there any real downside to a pitch of 10mm vs 20 or 25? If I’ve understood it right, it means less torque if I’m using servos at a given speed, vs running higher rotations and getting more power at the cost of lower top speeds. My assumption was that unwound not be hitting top speeds (in terms of motor rotations) with either solution. I was looking at these motors for all three axes:

https://www.sorotec.de/shop/JMC-Serv...ml?language=en

Running the lot off an EdingCNC board.

I had seen cross braces for the gantry i. Other builds, will see about adding one, thanks! It can double as a mounting spot for the energy chain as well. Any suggestions as to dimensions? Intuitively I would prefer something like 20mm thick 100mm wide solid bar, drilled and tapped every 50-60mm, to a piece of extrusion. Or is something thicker or wider a wiser choice?

[JAZZCNC]

Thanks for the tips! Is there any real downside to a pitch of 10mm vs 20 or 25? If I’ve understood it right, it means less torque if I’m using servos at a given speed, vs running higher rotations and getting more power at the cost of lower top speeds. My assumption was that unwound not be hitting top speeds (in terms of motor rotations) with either solution. I was looking at these motors for all three axes:

https://www.sorotec.de/shop/JMC-Serv...ml?language=en

Ok well when I said 2020 I probably should have given you more info to why and how I'd use them, also I didn't know the motors you where using so didn't want to go too far with it. But with you using Servo's then it's even more important, esp those motors so I'll explain more.

I would use a larger pitch mostly so I could put a ratio(2:1) on the screw to reduce the rotation speed, this lowers any chance of whip on longer screws it also increases the torque, thou this is offset slightly by lower torque of higher pitch. A 20mm pitch with 2:1 ratio will give you the same Resolution and speed as a 10mm pitch but half's the screw rotation speed.

This will become more important to you because your using 3000Rpm motors which is way too fast for a long ballscrew and the fact your thinking to use 25mm which have a lot more inertia it becomes even more important.

Also I don't think those motors are powerful enough to handle a 25mm ballscrew with direct drive, or even 20mm for that matter. They are only rated 0.57nm, I've looked at the manual and I can't see any where the peak rating. Thou Often it's 200% of the rated value for a few seconds which means at best you'll only have just over 1Nm for a few seconds to accelerate and de-accelerate the axis which isn't enough for a heavy gantry changing directions at higher feeds.

However, with only 36V I don't think they will be the most powerful things in the world so I doubt they will give you high peak rating for any usable length of time. If they had decent Peak ratings I'm sure they would have stated them, even if just as a marketing tool.
Now If they where 200V 180W or 200W Servos then they would just about be ok, but even still with a heavy gantry and 25mm screws direct drive it would a close thing.!

If it was me and you really wanted servo's then I'd go with proper 400W servo's. 200w would work but you can get 400w for nearly same money.

I had seen cross braces for the gantry i. Other builds, will see about adding one, thanks! It can double as a mounting spot for the energy chain as well. Any suggestions as to dimensions? Intuitively I would prefer something like 20mm thick 100mm wide solid bar, drilled and tapped every 50-60mm, to a piece of extrusion. Or is something thicker or wider a wiser choice?

Just a piece of 20mm x 100mm like you suggested would be good. I wouldn't bother with the extrusion.

[Kitwn]

A 10mm pitch screw has to rotate twice as fast as a 20mm pitch for a given linear gantry speed and will suffer more whip as a result. gearing the motor speed down 2:1 on a 20mm screw will give the same motor speed as 1:1 on a 10mm screw but will double the torque driving it. This means the maximum linear force available to push the gantry will be the same in each case.
Less whip but the added complexity of a reduction belt drive.

EDIT: Dean beat me to it!

[Mattia]

Gotcha, slowly wrapping my head around it all. I would guess those 180watt motors (they also have a 200watt and 400watt variant) would probably work well enough for the Y and Z axes with their 16mm ball screws, or would it be a good idea to look for more power for all three? Once I get the bits and pieces a little more together I’ll take a few more pictures and sketch up some options for the X axis screw.

Also need to check the mounting holes as milled into the machine - I think they’re NEMA23, which fits the 180w but not the 200 or 400w models of those drives (6060 frame sizes). The 400w is also higher voltage (48 vs 36 nominal).

[JAZZCNC]

Also need to check the mounting holes as milled into the machine - I think they’re NEMA23, which fits the 180w but not the 200 or 400w models of those drives (6060 frame sizes). The 400w is also higher voltage (48 vs 36 nominal).

Nema 23 motors are 57mm and 60mm frame is the same as Nema 24 but in both cases, the hole centers are the same at around 47.14mm so unless the plates are machined for the outer frame size they should still fit.