[Master of nun]

Hi Giz,

The HD's are supposed to be backlash free so I can only suspect that mine are either worn or I'm operating outside of their spec's....from memory it did feel like a flexing rather than a straight out backlash.
your's are huge compared to mine if I remember correctly...although it may be worth your while making a makeshift assembly to test them out before you invest too much time in the real deal.


The vacuum works a treat, I purchased the pump direct from china for around $1200 plus duty and taxes etc. I can pass on the contact info for my supplier if you're interested.

I'm not using the air ram at the present time, it seems to operate fine without it although I could possibly set a faster accel. and speed in mach if I were to use the ram. The ram is still there so if in the future with faster speeds or a ballscrew change I can soon connect the air supply. The intention was to have a large tank under the table that is fed a regulated supply from my plumbed workshop compressor. My thinking regarding the tank is the displaced air from the ram when the Z axis is all the way down needs a very large space ( compared to the ram volume) as to not increase the pressure ( or the effective counter balance applied) in the system.
There could be some kind of pressure relief setup available but I haven't looked into it at all, but this would also mean the compressor would be running a lot more often.


work has been VERY slow for the last few months so I haven't used the router as much as I would have liked....but I will post in the future anything of interest.




Cheers


Liam

[havardak]

Hello Master of Nun!

I have read this thread and admired it for a while now, and have finally desided on starting up my cnc-design again.

I have one question for you; since you have this long z-axis, how does it work when you mill in small objects in for eksample aluminium? Is it rigid enough?

Best Regards,
Håvard K

[Master of nun]

Hello Havard,

I'm traveling at the moment but i'll give you a quick update.

I have tried cutting aluminium sheet òf 1.6mm although only at 0.4mm steps, as I haven't pushed the machine tô hard yet.
I do get some chatter cutting thick mdf, I think thís ís due to the T slot extrusion used at the top òf the gantry....I wouldn't use T slot aluminium in a build thís big I f I were to do it over again.

I have since converted the machine to servo motors ăswell. 400w leadshine motors and drives from Ocean Controls in Áustralia for the X and Y áxís, a massive 130 frame 2.2kw servo from salecnc in china for the Z axis, all thís ofcoarse required a completley diferent gearing set up.

I also have installed the wireless mpg from salecnc, thís is so easy to setup and great for getting aroud a large machine with no cabling I recommend thís company.....very good support.

got to go....

[D.L]

Hi MasterNun, try out the local flea markets for surplus, so far i have found 2 wormdrive reducers 60:1 hangzhou types $30 and $40 a peice (more haggle needed).
Also found an arc welder $25 (it's now a power supply)
A Abwell 150mm vice $30 (almost dead, got screwed)
Industrial switch boxes with large push buttons $5
Benchtop grinder $20

Sometimes getting there too early is no good, it shows you are desperate, just snake on by a few times and let them get edgy.

Derek

[paulus.v]

Hi Master,

Where are all your pics gone? I was wanting to check your rotating ball nut design but sadly there's nothing to see...

[Master of nun]

Hi Paulus


I'm not sure, I hadn't logged into the zone for a long time and they were gone when I did....I've tried to edit them back in, but I'm no longer able to. there must be a time limit to allow this.

here are the photos

[paulus.v]

I'm not sure, I hadn't logged into the zone for a long time and they were gone when I did....I've tried to edit them back in, but I'm no longer able to. there must be a time limit to allow this.

Sad to hear this... From discussions I think it is a nice build.

here are the photos

Many thanks! I like your design, it looks sturdy and compact but you need to use big bearings or thin ballscrew

I made my design based on a build of someone from the uk cnc forum. Here it is: red are the angular contact bearings 72x35x17mm, green the bearings shaft with nuts to preload them, yellow the pulley and the ball nut for 25mm screw and dark grey the steppers nema 23 or 34.

Hoping to have tomorrow the project done and will create a new build thread. You will be very welcomed to give suggestions.

[Master of nun]

[paulus.v]

wow! your "2 axis spindle mount" is awesome (or how's called if has a name).

I was thinking to build something like this in the distant future.
What is your gantry weight, x-y screw diameter and pitch and the x-y-z stepper size or you have servos?

[Master of nun]

The spindle mount is B/C axis...turned out to be a complete failure due to flex in the harmonic drives, I did learn a lot from the exercise though!

I'm not sure of the weight but rough estimate of between 120 and 160kg

X axis rack and pinion 40:1 with 400watt servos, Y axis 10mm pitch 25mm dia. screw 3:1 400watt servo. Z axis 5mm pitch 25mm dia. 1.5:1 2.0kw servo.

Currently only operating as 3 axis machine.

7.5 kw vacuum table.


I need to take some more photos and update this thread as the machine has undergone the servo conversion since this thread was last alive.

[caferbur]

Hi, I do not understand something, what you mean is that failure head design A / B, that failure?

[Master of nun]

Hi Caferbur,

I'm really not sure where the problem was, with the head assembled you can't see what is flexing. I say flexing, because it didn't feel like backlash... All I can put it down to, is using Harmonic drives that were too small for the loads. If I were to place one hand on top of the spindle and the other at the spindle collet, I could flex it back and forth 2-3mm over the length of the spindle (about 300mm).
I'm full time employed at work now so I have little time to fix the problem....so 3 axis it is for now:-(

[D.L]

Hi Liam, I reckon your build is 1st class, really schmicko!
You have provided everybody with a realistic expectation of harmonic drive abilities.
Most robots they come from are only concerned of positional accuracy, not heavy torque arm application.
I'm hoping to build a clone of the Centroid ballscrew head, I need to hit the books on Linux for customising Linuxcnc.
Apparently they deck cast iron engine blocks with that drive mechanism, I'm sure a harmonic drive could not do this.

[caferbur]

And you think of this design .....
Fresadora casera o router de 5 ejes open source

fresadora casera o router de 5 ejes

[Master of nun]

And you think of this design .....
Fresadora casera o router de 5 ejes open source

fresadora casera o router de 5 ejes

That's very neat, thanks for the link.

[Master of nun]

Hi Liam, I reckon your build is 1st class, really schmicko!
You have provided everybody with a realistic expectation of harmonic drive abilities.
Most robots they come from are only concerned of positional accuracy, not heavy torque arm application.
I'm hoping to build a clone of the Centroid ballscrew head, I need to hit the books on Linux for customising Linuxcnc.
Apparently they deck cast iron engine blocks with that drive mechanism, I'm sure a harmonic drive could not do this.

G'day D.L,
Thanks for the praise.

I do believe harmonic drives are suited to the application if the correct size are used, although as you say, milling steel may be pushing them too far.
Thats an interesting concept using the ballscrew. At work here we have an some testing equipment of about the same size, this has a motion of +- 30 deg. using the same idea.

I'll post some photos later.

[caferbur]

You think the pulley system, advantages and disadvantages, compared to your design.

[Master of nun]

You think the pulley system, advantages and disadvantages, compared to your design.

It doesn't look like he has a very high ratio, maybe 5:1, I'd think resolution would be poor.
If I were to build mine again, I too would use belt drive, but probably in two or three stages for a reduction of 30+:1.
The intention using harmonic drives was to make the head more compact.

[caferbur]

Well I want to share something more about my project, I want to take advantage and make a machine that allows me trabajr wood, acrylic, glass and soft metals such as aluminum, I do everything possible to have a good resolution and accuracy in head movement , but I can not clearly define the right system, according to what I've dimensioned harmony system is what gives the head a compact design, but fell short in the strength and movement of the head, really have any idea if I use a system pulley to where I should go with the choice of measures to obtenmer diametrosy a very good resolution, really I'm just starting to get into this cnc and I still have a lot of information, I appreciate everything you bearings.

[MarcusWolschon]

No commercial music please.
It can mean that people in countries where Google has not licensed that song (e. G. Germany).