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331  Mach Discussion / General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course on: October 08, 2012, 08:42:58 AM
Torque and HP are essentially the same thing. HP is just torque over time, and the relationship is linear.

Not exactly. Power is torque times rotational speed. And saying that the relationship is linear is a bit confusing as the speed (RPM) is not a constant itself. Take a stepper motor for instance - peak torque is at zero RPM, where the power is zero, while peak power is at some mid point RPM where torque is substantially less than its peak value.

Hence, the way Terry put it, is the correct way. You are essentially transferring torque. Power has absolutely no meaning here. I could have a 6kW high speed spindle putting out the rated power at 30,000RPM, which means only 2Nm torque, whilst a tiny NEMA 34, 25 watt stepper would have twice that torque at zero speed. Power is the amount of work you can do over time, so obviously the 6kW spindle would do more work in a given time at its lower torque than the high torque stepper.

Dan
332  Mach Discussion / Mach SDK plugin questions and answers. / Re: Impact engraving plugin on: October 08, 2012, 06:53:34 AM
Hi Pasquale,

I don't have a working system. I attempted to build an electromagnet for this purpose some time ago but not completely understanding the physics behind it and wrongly assuming that it ought to be powerful to be able to engrave, I built a strong one. Then I saw that the plunger was too heavy and the coil had to much inductance and I couldn't drive it any fast.  I reduced the plunger and the coil but it still was not enough. Haven't touched it ever since.

Not sure why you said PWM. I was asking about the practical current control in the circuit. What component will be controlling the MOSFET gate voltage? Only way I know of in the configuration you laid out is an Op Amp. But I built such a circuit and found it struggling to pulse the MOSFET at frequencies higher than about 10Khz. I think that possibly the specific Op Amp model was not suitable although it was 1Mhz band width I think.

Regarding the frequency divider, I think that Tweakie and Andrea were getting good results without this. So again not sure why you need it.

Dan
333  Mach Discussion / General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course on: October 07, 2012, 06:05:10 AM
Yes, I have an Emco F1 bench top mill and it uses BT30 holders without the flats and the spring force is sufficient to hold the holders not allowing them to slip.

It would be helpful to know the application.  There is a lot of distance between driving 1/4 roughers thru aluminum and pushing a big face mill across an interrupted cut on stainless.

8mm roughing mill full diameter 4mm deep in aluminium. I am sure I could do twice that depth and the tool wouldn't slip. Don't use face mills on that small machine. Do use slitting saws and had a few times it jamming, but again it's not really a reference as it was stalling the undersized spindle motor (around 5Nm at the spindle).

Dan
334  General CNC Chat / Show"N"Tell ( Your Machines) / Re: A few of my projects.. on: October 07, 2012, 04:06:03 AM
Can you attach your images instead of linking to them as they dont seem to load or atleast not for me, I get a wee bit at the top of each then it seens to stall.
Hood

Yes. The same is here.

Dan
335  Mach Discussion / General Mach Discussion / Re: Encoders config on: October 06, 2012, 02:05:29 PM
Is the error the same on all axes? Are the encoders the modular bearing-less type? If so, the accuracy would depend on the installation accuracy. If a modular encoder is not well aligned you could easily get 40 counts error over a one nominal 4000 counts revolution.

Dan
336  Mach Discussion / Mach SDK plugin questions and answers. / Re: Impact engraving plugin on: October 06, 2012, 01:52:53 PM
I am curious what are you using for current control? Is it an Op Amp?

Also what do you mean by the frequency divider?

Dan
337  Mach Discussion / General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course on: October 06, 2012, 10:04:52 AM
Yes, I have an Emco F1 bench top mill and it uses BT30 holders without the flats and the spring force is sufficient to hold the holders not allowing them to slip.

Dan
338  Mach Discussion / General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course on: October 06, 2012, 06:21:35 AM
Hi Dave,

The BT holders have two flats at 180 degrees which engage with keys on the spindle. See photos earlier in this thread.  In this one you can see the seats for the keys on the spindle:

http://www.machsupport.com/forum/index.php/topic,22080.msg155852.html#msg155852

And this photos you can see the f;ats on the holder:

http://www.machsupport.com/forum/index.php/topic,22080.msg154764.html#msg154764

Dan
339  Mach Discussion / Mach SDK plugin questions and answers. / Re: Impact engraving plugin on: October 06, 2012, 01:13:55 AM
Hi,

I think Tweakie has once mentioned this to me. But I still don't understand this, since as we know the current change rate on a coil is described by:

  i(t) = I0-(R/L)t

So only depends on the inductance...?

Dan


340  Mach Discussion / Mach SDK plugin questions and answers. / Re: Impact engraving plugin on: October 05, 2012, 01:22:36 PM
Can you please clarify how the higher voltage helps in increasing the oscillating speed?

Dan
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