NordicCNC's build log

[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.

[AndyUK]

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.

Whats the maximum weight you'd expect though? I think a 1,500 Kg minimum as suggested in post #2 is a little overkill.

[JAZZCNC]

Whats the maximum weight you'd expect though? I think a 1,500 Kg minimum as suggested in post #2 is a little overkill.

Think JarJar is talking about a different strength machine, esp when he's comparing to a Datron which is a big lump of epoxy Granite. Thou that's like comparing apples with pears when a Datron cost's like £100K.

I'd expect a machine this size to be around 400Kg when finished using the materials and components suggested. It's amazing just how much weight fasteners etc add.

[NordicCnc]

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

Hehe, seems like we have different standards! I think that finish is quite good and I would be happy with that. Of course, I will try to achieve the best finish I can with my DIY build. I will not settle with decent, if I can get good.

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.!

Yes, I got confused with the advice from jarjar. It seemed quite contradicting to the general advice I've seen on the forums. He mentioned that a 400W would probably be the bare minimum. Anyway I don't plan to rotate any ballscrews with 3000rpm. I will use at least a 2:1 ratio, resulting in max. 1500rpm.

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.

As I planned from then beginning, to use 20mm rails. Thanks for confirming!

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 seen those builds, which is why I was skeptical and questioned jarjar's advice about the huge ballscrews.

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.

Correct. About preloading the ballscrew with tension, using double fixed bearings. Is there any guide how to do this? I guess the applied force by tightening the fixed bearing nuts will be critical?

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.

That is exactly what I said, that I expect it to be around the 300kg mark once finished. Probably above! :)

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.

My plan is now the following:

- I will build the machine with motor brackets than can be replaced. This will allow me to at least first test the 180W JMC servo motors. If they are not powerful enough even experimenting with ratios, I will have to buy new motors - probably some 400W servo motors or get stepper motors. This will be an expensive learning lesson, but that is life! I will most likely never buy any parts before design is ready again, lol.
- 20mm HIWIN linear rails on all axis's.
- 2010 ball screws on the Y-axis (base frame).
- 1610 or 2010 ball screw on the X-axis (gantry).
- 1605 ball screw on the Z-axis.