Messages

471

General Mach Discussion / Re: treadmill motor for spindle

« on: June 12, 2019, 05:35:50 AM »

If you use one of these motors with something like a KBE controller or one like Jim linked to, BEWARE if you want to link it to Mach 3 to control the speed!  This is because the 0 - 10 V speed control input is NOT isolated from AC mains.  You would have some sort of smoothing circuit that takes the PWM output and derives a suitable variable voltage, relative to the 0 V rail on the BoB.  If you then connect that to the "0 V" on the speed controller, there will be a "loud brown smell" and at least the controller and maybe the BoB and/or your PC will be fried.   You need to have an opto-isolator that can transfer the PWM signal to the speed controller without any galvanic connection, then do the smoothing on the speed controller side.  You can buy isolators from somewhere, but there are also simple a cheap circuits around to build.  I published one which you can find in this thread in the Model Engineer forum:

https://www.model-engineer.co.uk/forums/postings.asp?th=114432&p=1

472

General Mach Discussion / Re: Mach 3 Turn - Machining a Dome with a Wizard?

« on: May 10, 2019, 03:51:41 AM »

Cool!  Any chance you could post the Excel file please?

I use Excel a lot for generating odd curves - most recently the pallet profile for a gravity escapement and an equi-angular spiral cam for lifting the gravity arm of a Synchronome-style clock.

473

General Mach Discussion / Re: Mach 3 Turn - Machining a Dome with a Wizard?

« on: May 09, 2019, 04:18:29 AM »

I'm afraid that some maths is needed when you're doing CNC, even when using wizards!

OK, the flat is consistent with backlash on the leadscrew.  I suspect that either the previous owner used CAM to generate the g-code or wrote it himself.  Probably the latter as the method of generating the dome looks a bit odd - I would make the tool follow the dome profile several times at reducing Z offsets, so it starts by cutting the outer edge and as the Z offset decreases eventually cuts from the centre.  Making the tool follow the right path is a simple G03 command.  Or you could even edit the above g-code.  Of course a problem with cutting centre to edge is that now backlash on the cross-slide becomes a problem, but I have a balllscrew on that!

474

General Mach Discussion / Re: Mach 3 Turn - Machining a Dome with a Wizard?

« on: May 07, 2019, 02:24:14 PM »

Yes I know what you are looking for I think - I was just saying that I have used the wizard and it works - at least in the version I have (I'll check which that one is).

OK, suppose you want a dome with a radius of curvature of 50 mm, so it's a "cap" sliced off a 100 mm dia sphere.  This will be on the end of a 25mm diameter bar.  In the OD Sphere wizard you set the sphere diameter to 100 mm and the Z centre position to -50 mm.  X start is 25 and X end is 0 mm.  Now you need to set Z end to the height of the dome.  The distance of the dome centre to the centre of the bar end and to the dome edge will both be equal to its radius, but the edge will be set back from the bar centre by the height.  If the sphere radius is R and the bar radius is r, then the height h is given by:

h = R - sqrt(R^2 - r^2)

where R^2 is "R squared".

For R = 50 and r = 12.5, h works out to 1.588 mm, so you put -1.588 for Zend.

The only problem with this for me is that it cuts edge to centre, with Z moving in a positive direction.  My lathe has an ordinary Z leadscrew with significant backlash, and the cutting forces would be in the wrong direction.  The X would be OK as it has a ballscrew.  Really a better version would cut centre to edge.  Anyway here's the G code the wizard generates.

G18 G64 G80 G90 G40 G49
M3
G00 X26.2
G00 Z0.6
F30
G00 Z-0.2577
G01 X25
G01 X25
G03 X22.8511 Z0 I-12.5 K-49.7423
G01 Z0.6
G00 X26.2
G00 Z-0.5155
G01 X25
G01 X25
G03 X20.4901 Z0 I-12.5 K-49.4845
G01 Z0.6
G00 X26.2
G00 Z-0.7734
G01 X25
G01 X25
G03 X17.833 Z0 I-12.5 K-49.2266
G01 Z0.6
G00 X26.2
G00 Z-1.0314
G01 X25
G01 X25
G03 X14.7204 Z0 I-12.5 K-48.9686
G01 Z0.6
G00 X26.2
G00 Z-1.2895
G01 X25
G01 X25
G03 X10.7639 Z0 I-12.5 K-48.7105
G01 Z0.6
G00 X26.2
G00 Z-1.4844
G01 X25
G01 X25
G03 X6.3277 Z0 I-12.5 K-48.5156
G01 Z0.6
G00 X26.2
F15
G00 Z-1.5877
G01 X25
G01 X24.9999
G03 X0 Z0 I-12.5 K-48.4123
G01 Z0.6
G00 X26.2
M5
M30

Having looked at this I realised that actually for my hemisphere I used the OD Fillet wizard for the above reason, but that only cuts full quarter circle fillets so won't work for you.  Depending on your backlash you may be OK.  Oh, and I think I have the same version as you - with the original one I used the wizard reliably crashed Mach 3.

475

General Mach Discussion / Re: Mach 3 Turn - Machining a Dome with a Wizard?

« on: May 07, 2019, 04:31:56 AM »

Hi Druidan,

This can be done, I have done it, at least for a hemisphere.  I'll look at the wizards on my machine and see.  What version of Mach 3 do you have?  I know there was an issue with the wizard on an earlier version of "Turn" - I upgraded mine and it worked OK.

476

Mach4 General Discussion / Re: switch an output when G31 (probing) is active

« on: April 21, 2019, 01:41:05 PM »

I assume that you want to generate, say, a logic "1" when the probe input is active (i.e. the probe is touching).  Why do this in a script, why not just use the probe logic level?

477

General Mach Discussion / Re: Mill or Turn?

« on: April 16, 2019, 05:19:46 AM »

If you want "basic turning" capability why not simply have a separate lathe profile for your milling machine, mounting the tool on the table and putting the work in the chuck?  "Turn" is based on "Mill" with the mill laid on its left side then on its back.  You could probably make your own screen.  This could be interesting: http://www.vinland.com/CNC-Mill-Lathe.html

478

General Mach Discussion / Re: mach 3 turn

« on: March 11, 2019, 05:22:05 PM »

Sounds like you're in radius mode rather than diameter...

479

General Mach Discussion / Re: Lathe tool table

« on: February 03, 2019, 09:45:46 AM »

Vince, if you are asking me, it's a combination of a number of macros, some additions to the standard screen set (for example a button to "find stock end" on the manual screen), and a new offsets screen.

480

General Mach Discussion / Re: Lathe tool table

« on: February 01, 2019, 05:10:00 AM »

What you really need to do is have a different reference.  There is nothing sacrosanct about using Tool 1 as a reference, it's just convenient.  My approach is to reference X to an accurate home switch that sets the machine zero at the start of every session; while Z I set with the tool I'm using to the end of the stock using a tool touch sensor.  I do measure and store both X and Z offsets, but the latter are almost never used since I normally only use a single tool per program.  So I can easily reset Tool1 offsets without affecting at least the X offsets for all the other tools.  If you do want to use Tool 1 as the reference, then it's best to make it a "dummy" that's never used for turning - could be for example be made of mild steel just shaped for convenience in referencing.

Might also be useful to see this thread:
https://www.machsupport.com/forum/index.php?topic=39249.0