NordicCNC's build log

[JAZZCNC]

Thanks for your advice. I think you forgot to add a picture though?

I will reply back once you have added, as I think things will make more sense to me then.

Skickat från min SM-A530F via Tapatalk

No didn't forget the forum is playing silly buggers again and won't let me upload the pic. I'll try again later.

[NordicCnc]

Ok well first, the ribs on the front plate add virtually nothing but weight because the plate is fastened directly to the bearings with no overhang, it's also short and strong so very little vibrations come from that area.

Regards the plates on the sides then these would help, however, I have a better suggestion. If you look at the pic and at the other machines I've built I always put a cover over the Z-axis. This isn't just to protect from debris it's also structural as it does the same job those plates. You don't need a 10mm plate, I use 3mm for the covers and it's more than strong enough.

The spindle mounting area is limited to the lower area (see the pic, it's the silver area, the black is drawbar cylinders.) However, they are steel and would easily handle another clamp.

Regards putting the spacer plates on the front plate to save weight then I wouldn't do that either because of your shifting weight to the wrong area.
To be honest I wouldn't use spacer plates as it lowers precision and makes it complicated.

Regards Motor brake then I can't answer that because I don't know those motors, but servos are not like steppers where they have a shaft sticking out the back, mostly because this is often used for the encoder.

How the motor handles the weight will depend on usage, but if you plan on doing 3D type work with lots of short moves with high acceleration then I think they 180W motors will struggle with the inertia and you'll get some following errors. Because again servos are unlike steppers where if they lose the position you visually see the lost steps, instead the encoders along with the drives close the loop and catch back up so will always return to exact same place when stopped provided they don't go outside of parameters set in the drives.

However, what you get is a following error which if it stays within following error parameters can trick people into thinking they don't have a problem because if they do a type of work which is mostly 2D the Z-axis isn't whizzing up & down so it gets missed.

JAZZ, I think the way you have installed the pneumatic actuators and the Z-axis cover design is great! The whole machine design is phenomenal.. I hope you don't me taking ideas and copying some features from it?

I've removed my spacer plates now and added a machining to both the rear and the front plate to make room for the bearing and ball screw nut housing. This reduced the overhang by 15mm! It also reduced the total weight a few kg's. Thanks for the tip!

[JAZZCNC]

JAZZ, I think the way you have installed the pneumatic actuators and the Z-axis cover design is great! The whole machine design is phenomenal.. I hope you don't me taking ideas and copying some features from it?

No don't mind at all , go for it.! . . . Thou bare in mind some of these pictures are not of the finished article, the covers, for instance, are still missing some fastenings and slot covers, etc but hopefully show what I've been saying.

[NordicCnc]

Regards Motor brake then I can't answer that because I don't know those motors, but servos are not like steppers where they have a shaft sticking out the back, mostly because this is often used for the encoder.

JAZZ, what motors are you using to drive the ball screws and is the Z-axis motor with a brake? The Z-axis for my machine will be quite the same weight.

If you read one of my last posts in the build log http://www.mycncuk.com/threads/13448...823#post114823, I wrote that I will probably use Delta 400W servo motors and with a brake on the Z-axis. Well now I've got an offer for a full return from the supplier of those JMC 180W with integrated drivers, if I swap them for JMC 400W servo motors with integrated drivers. The problem here is that those JMC 400W servo motors does not come with a brake option.

[JAZZCNC]

JAZZ, what motors are you using to drive the ball screws and is the Z-axis motor with a brake? The Z-axis for my machine will be quite the same weight.

If you read one of my last posts in the build log http://www.mycncuk.com/threads/13448...823#post114823, I wrote that I will probably use Delta 400W servo motors and with a brake on the Z-axis. Well now I've got an offer for a full return from the supplier of those JMC 180W with integrated drivers, if I swap them for JMC 400W servo motors with integrated drivers. The problem here is that those JMC 400W servo motors does not come with a brake option.

The motors are 8Nm Lichuan closed loop steppers using 230Vac mains drives. It doesn't use a break because the gantry is vertical so Z-axis isn't fighting gravity, plus 8Nm is more than enough for this Z-axis even with heavy ATC spindle on it.

Regards the JMC then I've no experience using these motors or drives so I can't comment on how good or bad they are and I haven't looked at the specs, but if I'm honest I wouldn't use motors with integrated drives on a CNC machine. The heat and vibrations from the motors along with cutting debris, esp from aluminum coolant, etc, can't help with life expectancy but for me what's worse is the fact your running long signal wires back to the controller leaving you wide open to issues with interference from noise.

[NordicCnc]

Short update on the Z-axis design! You might notice that the design is heavily influenced by JAZZCNC's build's (e.g. the cover and L-shape gantry), although still very different and definitely no where near his quality!

Modifications:

1. Based on feedback I have now removed the stiffening ribs from the front plate. The reason is that since the front plate is directly mounted to the X-axis bearings with literally no overhang, the stiffening ribs would add nothing but weight. Instead a 3mm aluminium sheet is bent and welded, forming a cover that is structural while also protecting the components and cables from chips.
2. Removed the linear rail spacer plates and added machining to both the rear and front plate, to make room for the BK12/BF12 bearings and the 1605 ball screw.
3. 180W servo motors are no longer a constraint. Now I am thinking about getting Delta 400W servo motors. On the Z-axis I plan to use one with brake: https://www.aliexpress.com/item/3267...23d152a8ZJcwMZ. On the X- and Y-axis I plan to use ones without brakes: https://www.aliexpress.com/item/32671356516.html?spm. All axis with still be geared 2:1, to limit the ball screw maximum speed to 1500rpm.
4. Modified the top bearing plate to account for BK15/BK15 bearings and 2010 ball screw on the X-axis (in design process).
5. Preliminary positioning of proximity switches. The X-axis will only need one, but for the Z-axis I might need 2 if I can't find a location which I can use for both homing/top limit switch as well as bottom limit switch.
6. New Z-axis weights are 45kg (total) and 25kg (moving).

Here is the Z-axis mounted on the draft X-axis design, made with 120x80 Item profiles (I will post a more detailed X-axis design description later):

[Clive S]

Preliminary positioning of proximity switches. The X-axis will only need one, but for the Z-axis I might need 2 if I can't find a location which I can use for both homing/top limit switch as well as bottom limit switch.

Its not easy or practical to put a bottom limit switch on the Z axis as the tool lengths will all vary .

[NordicCnc]

Its not easy or practical to put a bottom limit switch on the Z axis as the tool lengths will all vary .

True but my intention of using one is not to protect the tool itself, but to protect the machine from crashing into the BF12 floating bearing for any unintended reason. On my current machine I've been completely fine without any limit switches, but that machine is made with weaker stepper motors and is only running 4000mm/min at maximum feed rate.

[Clive S]

True but my intention of using one is not to protect the tool itself, but to protect the machine from crashing into the BF12 floating bearing for any unintended reason. On my current machine I've been completely fine without any limit switches, but that machine is made with weaker stepper motors and is only running 4000mm/min at maximum feed rate.

Have you considered soft limits?

[NordicCnc]

Have you considered soft limits?

No I have not, but that should work perfectly with position feedback from the servos. Thanks for the tip!