NordicCNC's build log

[NordicCnc]

Change log
10.3.2020 - Z-axis ratio changed to 2:1. Removed 48V power supply from component list. Added Delta 400W servo motors to component list.
4.3.2020 - Ballscrew dimensions changed.
4.3.2020 - Motor and power supply alternatives added.


Hello,

I’ve decided to start a build log in order to collect all the advice I receive in one single place. I found myself having to go back to all my posted questions, to refresh my memory quite often.
The idea is to build a good CNC milling machine for myself that I will use for my own projects. I plan to take a modular design approach when building this machine. What this means I can explain in another post upon request! Note that this just an approach that I will use for fun and it will not be a deal breaker if it turns out to be too complicated or doesn’t succeed for other reasons.

Machine requirements
The machine will be designed based on following requirements:
- The budget is undefined but I prefer to stay below 8000€.
- Stiff enough to machine aluminium with good tolerances and surface finish. What I mean with good finish is that the finished product should not have a terrible surface. If I can achieve the same surface finish as in this video, I would be more than happy: https://www.youtube.com/watch?v=xyVr35pgx7s
- Fast feed rates for machining large wooden sheets.
- Auto tool change spindle is preferred. Possibility to downgrade to a manual tool change spindle if the budget requires it.
- The footprint is not critical but is preferred to be as small as possible for the following working area: Y-axis (base frame): 1400mm, X-axis (gantry): 1000mm, Z-axis (spindle axis): 200mm.

Machine control and software
- I already own a Mach3 license and will continue using it. In the future I can upgrade to Mach4 if I find it necessary.
- Interface cards Ethernet SmoothStepper (ESS) https://www.cncroom.com/interface-cards/ess-mb3. This I already own. Breakout board will be MB3.
- MB3 breakout board: https://www.cncroom.com/interface-cards/ess-mb3.
- The MB3 and ESS will be powered with a 24V, 150W & 6.3A power supply: https://www.sorotec.de/shop/Power-su...A-Heng-Fu.html
- Delta servo motors (400W, 3000rpm) with brake (for Z-axis): https://www.aliexpress.com/item/3267...23d152a8ZJcwMZ. - Was JMC 180W servo motor.
- Delta servo motors (400W, 3000rpm) without brake (for X- and Y-axis): https://www.aliexpress.com/item/32671356516.html?spm. - Was JMC 180W servo motor.
- 3kW Auto tool change spindle with BT30 tool interface combined with a 3.7kW VFD: https://www.ebay.com/itm/3KW-220V-AT...r/264448370955

Z-axis design & components
The solution I will be using to allow for the heavy ATC spindle is to keep the Z-axis weight as low as possible. Linear rails, ballscrew & bearings, and servo motor will all be mounted on the rear plate. The ballscrew nut housing and guide carriages will be mounted on the front plate. This is based on the advice that there is not much difference between front/rear mounting when it comes to stiffness. Yes, it is slightly stiffer with front mounted linear rails, but this is a compromise I need to take. The gantry clearance will be 200mm. Anyway I will still be able to surface components up to a height of 240mm and with a diameter of around 160mm, since it will be possible to raise the tool above the bottom of the gantry. I could also decide to make the rear plate longer to further increase the height if I want.

Components that I plan to use:
- Aluminium tooling plates
- HIWIN linear rails: 20mm
- Delta 400W servo motor, with brake - Was JMC 180W servo motor.
- Ballscrew: 1605 - Was 1605 or 2005.
- HTD 5M pulleys with a 2:1 ratio Was 3:1
- 3kW Auto tool change spindle

X-axis design & components
The gantry will L-shaped and be made with 120x80 or 160x80 aluminium profiles. Aluminium keys will be inserted into the t-slots and then the profiles are bolted together from the bottom. Side plates will be used to mount the profiles together from the side. I am still debating if I will go for high gantry sides combined with aluminium profiles similar to JAZZCNC’s design, or with raised gantry. Linear rails with be top/front mounted to get maximum gantry clearance and maximum spacing between the guide carriages. It will also allow for Z-axis vertical tram. The ballscrew will be placed on the rear side of the gantry to stay clear of chips.

Components that I plan to use:
- Aluminium tooling plates
- Item equivalent aluminium profiles
- HIWIN linear rails: 20mm
- Delta 400W servo motor, without brake - Was JMC 180W servo motor.
- Ballscrew: 2010 - Was 1610 or 2010.
- HTD 5M pulleys with a 2:1 ratio

Y-axis design & components
I’ve learned that it is recommended to make a welded steel frame and use epoxy levelling to get flat surfaces for the linear rails. It is also cheaper. I consider myself a good welder and I have the possibility to make a welded steel frame. Does the welded frame have to be stress relieved or is that not required? I am not sure where I would find any local company that could do that for me. If I go for the welded steel frame, what are the recommended box section dimensions?

The machine will have be moved to my own garage at some point in the future (2-3 years from now), since I am building it in my parents garage. This is the main reason why I am still debating on using aluminium profiles for the base frame. With aluminium profiles I would be able to disassemble it and assemble it again once I move to my own garage. If I decide to use aluminium profiles I will probably use 120x80 or 160x80 aluminium profiles.

To allow for easier alignment of the linear rails I am planning to mount them to the top of the base frame. The guide carriages will be mounted together with separate aluminium plates, which will allow for some adjustment of the X-axis gantry to get the machine square.

Components that I plan to use:
- Aluminium tooling plates
- Item equivalent aluminium profiles
- HIWIN linear rails: 20mm
- Double Delta 400W servo motor, without brake - Was double JMC 180W servo motor.
- Double ballscrew: 2010 - Was 1610 or 2010.
- HTD 5M pulleys with a 2:1 ratio

Continuing forward
I will start posting updates of the design as it progresses. Any advice is very welcome.

[jarjar]

Hi,

Some comments in no particular order, assuming you want to build a decent machine and not a toy:

- 1400 x 1000 x 200 mm is a _huge_ working area. I would expect a machine that size to weighs at least 1500 kg.

About servos:
- those 180W JMC servos are toys and seriously underpowered if you want decent speeds. If you want to go servos, use some proper ones. Delta servos are cheap and good. You need to size the motors depending on the max feed/rapid rates and accelerations you seek. 400W is probably the bare minimum.
- Personally I expect a router this size to be fast, I would target 30m/min (1000 ipm) and maybe 0.5g accel.

About ballscrews:
- 10mm pitch ballscrew would be the minimum I'd use, without any reduction. With servos direct-drive is the best and the cheapest. Good pulleys are expensive, and add unwanted inertia to the system. Servos are usually rated at 3000rpm, with 10mm pitch this gives you a max speed of 30m/min.
- 5mm pitch ballscrew is acceptable for the Z axis. Again without reduction. If you really want pulleys for space issues, use 1:1.
- Ballscrew diameter: you need to calculate it depending on the desired max speed. A ballscrew 1400mm long that don't whip at 3000rpm with fixed-floating ends is around 60mm diameter... If this sounds too big you can go with rotating ballnut (complex) or larger pitch. 20mm pitch would be ideal and you would only need 32mm ballscrews.

About rails:
- don't bother with anything less than 25mm. For the simple reason that 20 rails use M5 bolts and require tighter drilling positioning tolerances.

[joe.ninety]

Hi,

- 1400 x 1000 x 200 mm is a _huge_ footprint. I would expect a machine that size to weighs at least 1500 kg.

Those measurements are all in MM you know? Do you consider that to be huge? That just seems a little bigger than AndyUKs and a couple of others I've seen on here.

EDIT: Are you saying it's huge for a MILL?

The reason I'm asking is because I was looking to build a machine that had a cutting area that could accommodate 1.2m X 0.8m and the proportions in Nordic's build are about the same as I was calculating.

Cheers

[jarjar]

It all depends on your requirements.
But if you're after speed, good tolerances and surface finish in aluminium, it is, indeed, huge.

[NordicCnc]

Hi,

Hi and thanks for your comments, very much appreciated! I will add my replies below.

Some comments in no particular order, assuming you want to build a decent machine and not a toy:

- 1400 x 1000 x 200 mm is a _huge_ working area. I would expect a machine that size to weighs at least 1500 kg.

Yes it is a huge working area! About the weight, I've quickly added all components to my build with assigned material weights etc. and it sums up to about 200kg right now. I excpect it to be around the 300kg mark once everything is mounted (with aluminium profiles as base frame). Not much is missing so I am not sure if you thought that the whole machine would be built out of steel? Then the 1500kg would make sense.

About servos:
- those 180W JMC servos are toys and seriously underpowered if you want decent speeds. If you want to go servos, use some proper ones. Delta servos are cheap and good. You need to size the motors depending on the max feed/rapid rates and accelerations you seek. 400W is probably the bare minimum.
- Personally I expect a router this size to be fast, I would target 30m/min (1000 ipm) and maybe 0.5g accel.

Yep, I realized this later (NEVER BUY PARTS BEFORE DESIGN IS READY) that I would've been better of getting either 400W JMC servo motors or 400W delta servo motors (seems to be pretty much the same price and specs!) or even stepper motors.

Targeted speed is 15m/min and about 0.25-0.5G acceleration. This I plan to achieve with a 2:1 ratio with 3000rpm and 10mm pitched ballscrew. I will also achieve some increased torque with the 2:1 ratio, which will be helpful for these small beasts of servos.

Here are some references where some people are testing these specific servo motors. According to description section he is running at 12m/min at 0.25G at a 2:1 ratio with a 10mm pitch.
https://www.youtube.com/watch?v=xyVr35pgx7s
https://www.youtube.com/watch?v=nd19IBllD2I&t=32s

Here is another one with some amusing testing. Same video in both links but at different time stamps.
https://youtu.be/ZMxzRn9GrKY?t=330
https://youtu.be/ZMxzRn9GrKY?t=420

About ballscrews:
- 10mm pitch ballscrew would be the minimum I'd use, without any reduction. With servos direct-drive is the best and the cheapest. Good pulleys are expensive, and add unwanted inertia to the system. Servos are usually rated at 3000rpm, with 10mm pitch this gives you a max speed of 30m/min.
- 5mm pitch ballscrew is acceptable for the Z axis. Again without reduction. If you really want pulleys for space issues, use 1:1.
- Ballscrew diameter: you need to calculate it depending on the desired max speed. A ballscrew 1400mm long that don't whip at 3000rpm with fixed-floating ends is around 60mm diameter... If this sounds too big you can go with rotating ballnut (complex) or larger pitch. 20mm pitch would be ideal and you would only need 32mm ballscrews.

I wanted to use belt drive to be able to experiment with ratios, mounting simplicity and to hide the motors so that they are not protruding. Using direct drive with 3000rpm and 10mm would be too much as you said for 16mm ball screws. This is another reason why I intend to use a 2:1 ratio, which would result in 1500rpm.

What calculator are you using to calculate those diameters (link or fomula)? I have not seen anyone in here that size of ball screws! I keep seeing the recommended sizes being 1610 and 2010. I will be happy with 15m/min anyway.

About rails:
- don't bother with anything less than 25mm. For the simple reason that 20 rails use M5 bolts and require tighter drilling positioning tolerances.

If I go for the aluminium profiles on the Y-axis (base frame), then I will only have to drill and tap the M5 bolts onto the rear Z-axis plate. This plate size fits well in my shitty CNC router that I built 10 years ago. It can handle the requires tolerances needed for those holes, I am pretty sure.

Anyway, do you think 25mm would be to prefer over 20mm rails for the sake of stiffness?

[AndyUK]

Some comments in no particular order, assuming you want to build a decent machine and not a toy:

Well that really depends on the definition of decent and a toy. Arn't all home machines practically toys when compared to industrial VMCs? Your line seems very arbitrary. Nordic has stated he wants a 'good' surface finish in Aluminium, which really he should be using a mill style machine for - so I see where you're coming from there, but again, define 'good'.

- 1400 x 1000 x 200 mm is a _huge_ working area. I would expect a machine that size to weighs at least 1500 kg.

... Why? This size is about standard for most of the build logs. Huge for a mill, still quite a small router. 1500kg? I think mines about 500kg... Sure added weight helps dampen vibration and makes sense, but there isn't any reason it must weigh that much. And hey - if its on rollers who cares? Lift and move with jacks.

About rails:
- don't bother with anything less than 25mm. For the simple reason that 20 rails use M5 bolts and require tighter drilling positioning tolerances.

That seems like a terrible reason to spend more money. A standard clearance hole for M5 gives you 0.5mm of wiggle. By marking out carefully, setting up the rails with clamps and a dial guage, then using a transfer punch, this is more than enough.

[NordicCnc]

Well that really depends on the definition of decent and a toy. Arn't all home machines practically toys when compared to industrial VMCs? Your line seems very arbitrary. Nordic has stated he wants a 'good' surface finish in Aluminium, which really he should be using a mill style machine for - so I see where you're coming from there, but again, define 'good'.

Hi Andy! Thanks for pointing this out. I will update the starting post with what my definition of good means. With good I mean that after my finishing pass, I want a smooth surface on which you should not/rarely be able to see vibration marks if you don't look extremely closely. The tolerances that you can achieve with a machine also very much depends on the machine operator. You cannot expect to get a good tolerance with roughing passes, even with industrial machines without using some tool compensation or adjusting the G-codes.

[jarjar]

Nordic has stated he wants a 'good' surface finish in Aluminium, which really he should be using a mill style machine for - so I see where you're coming from there, but again, define 'good'.

A "mill style" machine doesn't mean anything. The style of structure (C-frame, fixed gantry, moving gantry, ...) of a machine has nothing to do with its capabilities. Some are just easier to make stiff than others.

... Why? This size is about standard for most of the build logs. Huge for a mill, still quite a small router. 1500kg? I think mines about 500kg... Sure added weight helps dampen vibration and makes sense, but there isn't any reason it must weigh that much. And hey - if its on rollers who cares? Lift and move with jacks.

Just some number I have in mind when someone tells me he wants to build a 8000€ router this size to do aluminium work. A Datron with similar working area is 2.5t for comparison. Stiffness comes with weight when using standard material (metal).

That seems like a terrible reason to spend more money. A standard clearance hole for M5 gives you 0.5mm of wiggle. By marking out carefully, setting up the rails with clamps and a dial guage, then using a transfer punch, this is more than enough.

Indeed I was wrong about that. The clearance is the same for M6 bolts. Still the price difference is low and bigger is always better for rails... It helps for stiffness, ballscrew clearance, and the rails are better supported when mounted on T-slots profiles.

@NordicCNC
You still need a 32mm ballscrew at 1500rpm and 10mm pitch for 1400mm travel. Calculator for critical speed.

[NordicCnc]

Just some number I have in mind when someone tells me he wants to build a 8000€ router this size to do aluminium work. A Datron with similar working area is 2.5t for comparison. Stiffness comes with weight when using standard material (metal).

I've added some clarification to what I mean with good finish. I am not looking to be competitive with a Datron machine, luckily! Maybe an even better description of what I mean by good finish is that the finished product should not have a terrible surface.The surface finish achieved in this video, I would be more than happy with: https://www.youtube.com/watch?v=xyVr35pgx7s

Indeed I was wrong about that. The clearance is the same for M6 bolts. Still the price difference is low and bigger is always better for rails... It helps for stiffness, ballscrew clearance, and the rails are better supported when mounted on T-slots profiles.

Yes, price difference seems to be only about 15-20% for either 25mm or 30mm rails. If it is bringing me added value and it isn't overkill, I think I am ready to go for the 30mm rails.

@NordicCNC
You still need a 32mm ballscrew at 1500rpm and 10mm pitch for 1400mm travel. Calculator for critical speed.

Many thanks for the link! Seems like if I would use fixed bearings in both ends, I would barely make it!

[jarjar]

1. You need to add a safety factor.
2. The root diameter of a 16mm ballscrew is not 16, but 14-15 (outer diameter minus ball grooves).
3. Don't use fixed-fixed unless you know exactly what you're doing. The ballscrew needs to be pre-tensioned properly to account for thermal expansion or you will introduce backlash.