Messages

3071

Mach4 General Discussion / Re: Setting up Spindle/VFD control Issues

« on: February 15, 2019, 09:59:30 PM »

Hi,
yes that would be simplest and probably cheapest.

48V to 12V is a bit outside the normal realm of linear regulators so you would have to augment the pass transitior
with an external transistor, doable but depending on your electronic skills fiddly.

Another possibility is a switching buck regulator but would require an IC, a Mosfet and an inductor with maybe a few
other smaller components to 'glue' it all together on a circuit board. Again doable but fiddly.

Yet another alternative is a DC-DC converter. This a typical example:

https://nz.element14.com/recom-power/r-78hb12-0-5-w/dc-dc-converter-12v-0-5a/dp/2774032

Useful, elegant and tidy solution for $27NZD plus GST and freight.

Craig

3072

Mach4 General Discussion / Re: Mach 4 and fusion 360

« on: February 15, 2019, 09:23:41 PM »

Hi,
Fusion is used and recommended by plenty of users.

For all that I am dubious about Autodesks motivations about Fusion I can still only complement their commitment
to their stated aims.

If you are prepared to stick with it and get a good Mach4 Fusion post you will be good.

The only other suggestion I have is to use Mach Mill wizard. It produces good code and is very useful for chains
of usefull machine operations. I use commonly for chainging simple operations together to create a Gcode job WITHOUT using
a CAM program at all. It costs $75 USD.

Craig

3073

Mach4 General Discussion / Re: Mach 4 and fusion 360

« on: February 15, 2019, 09:04:08 PM »

Hi,
I have used Fusion briefly. You will have to find out more from the Fusion guys but as it stands Fusion is
producing bad code.

Craig

3074

Mach4 General Discussion / Re: Setting up Spindle/VFD control Issues

« on: February 15, 2019, 08:47:31 PM »

Hi,

Could I use the same trick with the Zener Diode's and the 48v supply or is it too much of a drop from 48-12v? if its ok what value resistor would you use (and out of curiosity how do you calculate that value)

NO! the Zener and resistor will fry up BIGTIME.

A 12V 1W zener will get to limiting heat at 1/12=83mA. If at 83mA you had to drop (48-12)=36V then the resistor
would be 36/0.083=432 Ohm. The dropper resistor would dissipate 36 x 0.083=2.988W.

Either way such a setup wont deliver anything like your required 450mA to a load.

I will give it some thought and make a few suggestions.

Craig

3075

Mach4 General Discussion / Re: Mach 4 and fusion 360

« on: February 15, 2019, 08:20:52 PM »

Hi,
you now at least have it operating in mm.

Now you have Mach operating in one arc mode whereas Fusion is producing code in another mode.

Change the mode of Machs arc interpretation to check it out.

Thereafter it will be necessary to change the Fusion post to generate compliant code.

Go to Configure/Control/General and change arc center mode from Incremental (normal) to absolute.
Run the code again. If it pans out there are instructions in the Fusion forum about changing the post.

Craig

3076

Mach4 General Discussion / Re: Setting up Spindle/VFD control Issues

« on: February 15, 2019, 07:11:32 PM »

Hi,

Just for my understanding and curiosity is it working by the zener diode "bleeding" off any voltage it "see's" above its set value to ground (in this case 10v)

Yes, in fact that is a very good description as to what exactly a Zener diode does.

What I don't understand is how this does not create a short circuit and overload the amp capacity of the VFD 12v output?

Also can you explain what the resistor does for this setup please.

The resistor is between the VFD 12V output and the Zener. In absence of the resistor the Zener would 'short out'
the output and the VFD might not like it.

You are correct, but the 'short' is not quite the normal sense of it. Normally you would short a circuit and force the output
voltage to zero. In this instance you would 'short' it to not 0V but 9.1V (or whatever value Zener you used).
In engineering parlance that is called a 'differential short circuit'.

The resistor is to limit the current in the differential short and drop some voltage, in this case 13.2V-9.1V=4.1V.
It is entirely likely that the manufacturer of the VFD put some current limit resistor or other circuit within the VFD
to protect the output in case of a short circuit. Quality designed and built US, Japanese and European brands
will almost certainly have protection built in. Who knows with Chinese brands? Some are actually very good indeed,
anything made by Delta for instance I rate as good or better than any US, Japanese, European stuff but other Chinese
stuff I wouldn't 'cross the road to piss on'.

Craig

3077

Mach4 General Discussion / Re: Mach 4 and fusion 360

« on: February 15, 2019, 06:55:25 PM »

Hi,
I see the code has a G71 near the top of the file:

Code: [Select]

: (PGM, NAME="2001")
; T5  D=4 CR=0 - ZMIN=-17 - FLAT END MILL
: G90 G40 G94
G17
G71
M26
; 2D CONTOUR1
M9
M26
:T5 M6
M26
S5000 M3
A G71 command should set the units with which the file is to be interpreted as millimeters. If you look in the 'Mill Gcode
Programming' pdf in Mach4s Docs folders there is no entry or description of G71. G71 IS described and supported in
Mach3 but not, to my knowledge in Mach4. In fact G71 is old school and I believe is deprecated in ANSI Gcode as well.

May I suggest editing the G71 to the currently supported G21 and try the code again.

If its effective you may need to tweak the Fusion Post to use G21 rather than G71.

Craig

3078

General Mach Discussion / Re: CNC router specs

« on: February 15, 2019, 06:22:50 PM »

Hi,
there are two areas where hobbyists/newcomers woefully underestimate when talking CNC.

One is the spindle. Most of us go for cheap spindles. Cheap spindles are underpowered, have poor bearings leading
to excessive runout, have low torque restricting the size of tools that can be used and materials that can be cut.

In particular many of the highspeed (24000) rpm spindles (from China and elsewhere) and VFDs are actually quite good
for soft materials and small tools but are hopeless for steel. If you want to cut steel, stainless steel, titanium or any
of the super alloys you'll need a high torque spindle. Your cheap Chinese 24000 rpm spindle just won't do it.

The other area that is underestimated is rigidity. Even if you have an adequate spindle your machine must hold the
spindle rigidly in place to cut the material. If the machine deflects even slightly then the accuracy of the part is shot,
and you'll likely get a vibration which further degrades accuracy and destroys surface finish.

I have made both mistakes. I bought a German made 24000 rpm 750W spindle. It works really well for engraving
(PCBs in particular) and does a good job with smallish (6mm and smaller) tools in brass and aluminum. When I try to
cut steel its not so good. I have cut mild steel with a 3mm endmill at 9000 rpm. I can't go much slower without the spindle
motor from overheating. Really 9000 rpm is a bit fast, without flood cooling the tool burns up. The real problem is though
that the spindle doesn't have enough torque and except with the lightest of cuts stalls the tool resulting in the tool being
snapped.

I really wanted to be able to cut steel so I ended up making a spindle to do it. Its powered by a second hand 1.8kW, 3500rpm,
6.2 Nm continuous (18Nm peak) AC Allen Bradley servo. Its direct coupled to a Rego-Fix (Swiss made) ER25 tool holder in NSK
matched angular contact bearings. Cost me about $2000 to make. It works really well.

That showed up the second problem. I made my mill out of cast iron slabs, approx. 220mm x 60mm x500mm. It has
15mm rectangular 4-point linear guides, C5 ground ballscrews and five phase steppers through low lash (<2 arc min)
planetary gearboxes. The column is made out of solid 80mm x80mm mild steel, note that's SOLID steel, not box
section, and yet it still flexes when cutting steel with my new spindle.

It works well but I have to limit the cuts to maintain accuracy and surface finish. I thought when I was building it that it would
be really rigid, and it is in fact, its just that I didn't appreciate HOW RIGID a machine has to be. I know more now!

The saying that '....only as good as the weakest link' certainly applies in CNC machines, and spindles and machine rigidity
tend to be the weakest links, both of which are expensive to fix, if it can be fixed without scrapping the machine.

Craig

3079

General Mach Discussion / Re: CNC router specs

« on: February 15, 2019, 04:59:30 PM »

Hi,
you don't say what materials you want to cut and at what speeds.

The size an power of the spindle determine the weight and  the cutting forces the machine will be subjected to.
Deciding beforehand that you are going to use this stepper or that stepper for an axis is back to front.
Spindle <determines> Forces <determines> Weight/Rigidity <determines> Axis Components <determines>Steppers/Servos.

Craig

3080

Mach4 General Discussion / Re: delay

« on: February 13, 2019, 07:49:44 PM »

Hi,
I'm far from sure about this but here goes:

When you issue a <FeedHold> Mach enters 'MC_STATE_HOLD'. Thus the GCode interpreter is busy
and cannot process any Gcode.

The only way you can cause Mach to execute Gcode is when 'MC_STATE_IDLE', which can only occurr
if you end the Gcode job or <CycleStop>.

You can test this by loading then starting a Gcode job. Now <FeedHold> and try all the buttons/functions of the GUI,
most of them don't work. That means that the Gcode interpreter chunk is running and therefore the GUI chunk is not.

The only way I could see that would that might achieve what you want is to modify the existing CycleStart() function
in the screen load script, and I may be that you would have a delay whenever you <CycleStart> not just this particular
job.

Craig