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.

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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-Servo-Motor-with-integrated-driver-180-Watt---36-Volt---3000-1-min-7908.html?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-Servo-Motor-with-integrated-driver-180-Watt---36-Volt---3000-1-min-7908.html?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.

[Mattia]

Based on your recommendations, I ordered the rails and carriages from Fred at BST - excellent communication, great pricing and quick turnaround. Time from payment to delivery was 8 days (paid Sunday evening, received Tuesday the following week).

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I'm going to test bolt things together this weekend to measure up various bits and pieces and see how she slides. I'm going to get someone local to machine a few bits of aluminium for the extra bracing on the gantry. Do you guys lubricate the carriages before putting them into operation? They feel like they're a little 'dry' out of the box, but not sure if that's the ZA preload I'm feeling?

Now it's down to selecting the ballscrew for the X axis. Some folks on a Dutch forum suggested going for dual ball screw to prevent the gantry from racking. Gantry width is 800mm, and as mentioned I plan to mount a 2.2kw Teknomotor spindle. This machine was originally designed with steppers in mind. Will adding servos (with their potential for greater acceleration/rapids) make a duals screw with individual drive a more stable solution? If so, 2020 or 2010 for both, or downsize to 16mm screws?

Also, is there any significant upside to getting a C5 ground ballscrew (e.g. a TBI from Tuli) vs a C7 screw from Fred here?

[JAZZCNC]

Do you guys lubricate the carriages before putting them into operation? They feel like they're a little 'dry' out of the box, but not sure if that's the ZA preload I'm feeling?

Grease them when your ready to use the machine, there is enough grease inside them for setup etc but not enough for running.
The stiff and notchy feel is quite normal, when greased and in use under weight they run smooth.

N
ow it's down to selecting the ballscrew for the X axis. Some folks on a Dutch forum suggested going for dual ball screw to prevent the gantry from racking. Gantry width is 800mm, and as mentioned I plan to mount a 2.2kw Teknomotor spindle. This machine was originally designed with steppers in mind. Will adding servos (with their potential for greater acceleration/rapids) make a duals screw with individual drive a more stable solution? If so, 2020 or 2010 for both, or downsize to 16mm screws?

Also, is there any significant upside to getting a C5 ground ballscrew (e.g. a TBI from Tuli) vs a C7 screw from Fred here?

At 800mm your at the limit of a single screw and personally I would use twin screws, esp if using servos.
Regards the screw size then it depends on the length, if over 1100mm then I would use 2020 with a 2:1 ratio, again even more so if using servos because of the higher RPM's servos run at. The ratio will half the screw speed but bring the resolution and federate back inline with 10mm pitch.
If between 1000-1200mm You could use 1616 and do the same but the difference in cost isn't worth taking the trouble, and if over 1200mm then 20mm is the best choice.

Just getting C5 rolled screws over C7 is worth it and ground goes a step higher but so does the cost. End of the day it's down to how a good a machine you want and your budget. BUT.!! . . .Just remember the machine is only as good as it's weakest link so even if you fit C1 ground screws they won't take up any slack in other weak areas so it could easily become wasted money. The goal and secret to a great machine is a balanced machine, if your going to fit C5 level then the rest of the machine needs to be built to C5 level.

[Mattia]

Grease them when your ready to use the machine, there is enough grease inside them for setup etc but not enough for running.
The stiff and notchy feel is quite normal, when greased and in use under weight they run smooth.

Thanks for the confirmation!



At 800mm your at the limit of a single screw and personally I would use twin screws, esp if using servos.
Regards the screw size then it depends on the length, if over 1100mm then I would use 2020 with a 2:1 ratio, again even more so if using servos because of the higher RPM's servos run at. The ratio will half the screw speed but bring the resolution and federate back inline with 10mm pitch.
If between 1000-1200mm You could use 1616 and do the same but the difference in cost isn't worth taking the trouble, and if over 1200mm then 20mm is the best choice.

Just getting C5 rolled screws over C7 is worth it and ground goes a step higher but so does the cost. End of the day it's down to how a good a machine you want and your budget. BUT.!! . . .Just remember the machine is only as good as it's weakest link so even if you fit C1 ground screws they won't take up any slack in other weak areas so it could easily become wasted money. The goal and secret to a great machine is a balanced machine, if your going to fit C5 level then the rest of the machine needs to be built to C5 level.

Looks like 2020 and dual screws are in my future! Will shoot Fred a message to ask about pricing on a couple of ball screws with bearings, which I'll mount inside the base up against the 8080 profile. And try to find someone local who can help me machine the frame end pieces to fit the two new ballscrews and add mounts for a pulley system with the motors inside the base, which should save a fair amount of room. I'm also having a bit of a sketch to see if I can mount the Y axis motor so its on the T extrusion I'll add to the back of the gantry to stiffen up the top. Although that will probably be a more long term plan since it would probably require replacing the screw - I don't think the end extends past the side enough to mount a belt pulley...

I think one of the biggest potential areas where there's a risk of loss of precision is the X axis (longest rails, 1200mm) which are mounted to unmachined extrusion. The base face plates have two accurately machined notches that the rail ends rest in, however, so I figure I'll use those as reference points for vertical and horizontal alignment at the two ends. The Y and Z plates are flat and have machined surfaces and edges the rails can mount to, so that's much less of a concern/challenge for now.

Also, anyone have a tip on what timing belts and pulleys are appropriate for this kind of build? Or a good source of basic info on the upsides and downsides of various systems (eg T5, T10, AT5, AT10, HTD??). Even just some photos of a 2:1 geared drive system on a DIY machine would be helpful...

[routercnc]

Joined late so just my summary thoughts.
One of my early machines was 600 wide and used a single screw and you could push each end of the gantry back and forth noticeably. I tended to cut in the centre line to hold a tolerance. So anything over 600 would be a double screw for me.

I used T5 belts on an earlier machine but use exclusively HTD 5 now. I prefer the tooth profile on HTD and believe the shape is optimised for high torque.
It has been a while since I looked into it but it think the AT types are somewhere similar in profile but I find the HTD work well.

Although I’ve only ever used rolled screws I have never found them to be anywhere close to being a limiting factor on the overall machine. So in my view rolled threads can be used and still make a very good machine.

[Mattia]

Thanks all! I've dry-assembled the Z axis, didn't get around to the other two just yet. Looking and feeling good so far. I've been dabbling with Fusion360 (not quite 'got' it yet, but working on it) trying to come up with a design for mounting a pair of 200w servos for the x axis (on the assumption that two 400w servos for a gantry this size would be rather overkill).

What I'm considering is mounting two 2020 ball screws inside the frame alongside the extrusion, face mounted to the end frame pieces using FK/FF mounts, having the lock nut on the fixed end recessed into the frame. Then mount a 40 tooth HTD5 pulley on the ballscrew. The idea is to find someone who can machine the end frame for a recessed 60mm motor mount with elongated bolt holes to allow for tensioning the 20 tooth pulley on the motor.

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The way I've sketched it now leaves 7mm thickness for the motor bolts, with a 3.5mm recess for the round flange surrounding the motor's shaft. I'm guessing I should oversize the slots and recesses somewhat since it doesn't need to press fit in place and I'm not sure how tight the tolerances on the average 60mm frame motor are (0.5mm per side, or total? Suggestions welcome). Will this leave enough meat for the motor? Would 5mm be enough as well? How long would you leave the slots for belt tensioning? I've gone with 6mm slots for M5 bolts that are 16mm long. Too much? I'm a little concerned about the clearance at the edge of the hole to the recess for the plate around the shaft. Also need to work out exact positioning for this so the belt preferably does not run across the bolt caps, though an offset mount would mean less leeway in terms of taking up belt slack. Comments on this plan welcome. I'm also wondering whether to start a separate build thread or just keep all the questions here - I'm finding the dialogue very helpful in making decisions!

[Mattia]

So I've dry-assembled the gantry (all the mechanical bits except for the currently missing X axis ballscrew(s)). I was hoping I might be able to convert at least the Y axis to 2:1 belt drive as well (placing the motor on a bracket on the to-be-built gantry brace) but the ballscrews I have feature some pretty non-standard machining. Both ends are simply turned down with a retaining C-clip in a groove on the floating end, which is a nice snug fit in the holder; the fixed end is apparently only 'locked' in place by the flexible coupling, no retaining nut of any kind. Since the coupling can't fit through the machined holes as is (the bolt stick out just a little, need to file a small corner into the frame so it can pass), the Y axis is particular simply slips back and forth. The fixed ends do have a tapped hole in the end. Not very reassuring in terms of being able to adjust for backlash.

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Thoughts? I guess this works well enough considering there are quite a few of these machines floating around out there, but it isn't super reassuring. I'll use 'standard' FK/FF machining and supports for the X-axis. But I may request a quote for a new Y axis ballscrew at least.

[poldi]

Dag Mattia!

How is your project going??

Would be glad if you could advise on following...

- Did you opt for a C5 screw?
The thing is, Damen only offers C7 screws. Is that because you can even out the tolerance in software? But I guess t makes sense to get C3 bearing blocks to get rid of bearing backlash?

- Are you happy with the 10mm pitch / lead?
- Is it recommended to use a double ballscrew nut on 1200mm length? Dameter 20mm?
- Did you pay any customs fees when ordering from BST?

Thanks in advance!

Greetz
poldi

[Mattia]

So, time to revive! Sorry for the no reply Poldi, life and lack of funding got in the way again. I’ve spent the time actually designing some models (guitars) I can cut, so that’s an extra push to get this done.

I’ve got the servos hopefully arriving tomorrow - 4x 400w deltas, 2 for Y, one for X, one with a brake for Z. Plan is 2:1 belt drive, 15mm HTD5 belts.

I’m revisiting the Ball Screw issue now the motors are locked down - will likely get rolled C5 TBI ball screws from Fred at BST. The question is: 2020 and 1620 for Y and X, or 2010/1610?

The motors can hit 5000rpm, but are in their optimum range up to 3000rpm. This would yield a theoretical maximum of 15-25m/min for 10mm, or a whopping 30-50m/min for the 2020 screws, juuust within the critical speed for screws that size (lengths 1200 and 790mm, as a reminder). With the 17 bit encoders and the fact I will mostly do wood, I’m not particularly concerned about accuracy for either - I do need to do accurate fret slots, but figure this should still be more precise and repeatable than my slotting templates and a saw.

What I can’t quite estimate is whether the frame (with a slightly beefed up gantry) will be able to handle the super speeds of the 2020 option, and whether I may be better off with the still really more than fast enough 2010 option at these dimensions, sacrificing ultimate speed for better acceleration for possible 3D carving in my future. Or is there so much excess torque (spec’d at 3x baseline, so 3.8 NM @ 3000 rpm, but tailing off rapidly above that) that the speed gains are worth it, and design for the option to swap to 3:1 gearing in the unlikely event I want an in between option? For the Z, I’m guessing 1605 is plenty quick even with 2:1 belt reduction.

The main use will be guitarmaking (bodies - mostly arched tops - necks, inlay, acoustic bridges, fret slots and jigs/tools/templates). Maybe light metal milling (brass, aluminum) for jigs and for prototype guitar hardware. I will likely also do some sheet good cutting for smallerfurniture projects, and want to dabble with some V carving/3D carving as well. With the ample power I’m pumping into the machine, what would you guys go for in terms of XYZ pitch?

[Mattia]

Small bump.

Motors have arrived! Shiny! And HEAVY. Will wire them up for a quick test this weekend or early next week (time permitting).

I’m the meantime, anyone care to weigh in on the ballscrew sizing issue? Going to shoot Fred a message soon to get a quote, since I’ve got the plans for the small amount of extra machining/brackets needed for the servos worked out now…