NordicCNC's build log

[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

[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!

[AndyUK]

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.

Don't forget to include the carriages in the cost estimate.

You'd be just about okay with a 1200mm 2010 screw @ 1500rpm.

Those of us using steppers rather than servos don't tend to go above 10m/min because the steppers will really lose torque above 1k rpm. My machine can just about handle 15m/min, but I'm leaving it at 10.

You'll have to find build logs for comparable routers using servos - I don't have any experience with them so won't advise.

[NordicCnc]

Don't forget to include the carriages in the cost estimate.

I quickly compared the 1100mm HGR20 and HGR30 sets offered from BST Motion on Aliexpress (I have seen them recommended a lot here, Fred was the seller) and the prices came down to 210€ vs 265€, if I recall the numbers correctly. Both sets included 2 rails and 4 carriages. Seems like a very good deal to me. Even with VAT added is only like 260-320€.

You'd be just about okay with a 1200mm 2010 screw @ 1500rpm.

Those of us using steppers rather than servos don't tend to go above 10m/min because the steppers will really lose torque above 1k rpm. My machine can just about handle 15m/min, but I'm leaving it at 10.

Sounds good. I will have to see if I go for 2510 or 2010.

What diameter and pitch, ratio and stepper RPM are you running on your machine to achieve the 10m/min?

You'll have to find build logs for comparable routers using servos - I don't have any experience with them so won't advise.

Good advice, thanks. I have looked around here and I will also browse through CNCZONE to see if I can find something similar.



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[JAZZCNC]

The surface finish achieved in this video, I would be more than happy with:

Thought you said wanted a good surface finish.!!. . . . Any decently built machine will give you that finish.

Also:
If you go with 30mm rails and 25 or 32mm ball-screws then you can forget 180w or 400w servos. The extra inertia will freak a 400w servo motor when trying to stop 25mm screws from 3000rpm that are attached to a reasonably heavy Gantry which is sat on heavy bearings with a heavy ATC spindle hanging off it.

The best machines are those that have the right balance of power and weight which means getting the design and components matched. The choices you are looking at now will give you a very unbalanced machine.!

20mm screws and rails are more than enough for a machine this size. Regards the screw size and whip etc then forget whip calculators because they can't and don't account for the whole machine.
If you want proof if 20mm won't whip at 15mtr/min then just ask anyone who's using them on similar sized machine.! . . . . I've built dozens and trust me they don't if properly aligned and with correct end bearings. However, I've told you how to eliminate any chance of whip and still get the speed you require.

Also on that note, you have to factor in the Servos and the extra resolution and power they offer over steppers. This means you can use higher pitch screws and still end up with good resolution compared to steppers. Use this along with applying a ratio and the screw speed can be lowered greatly.

Regards the weight then I think you must have got something wrong because a machine this size will easily weigh more than 200kg, even 300Kg by time it's all finished.