RE: [CAD_CAM_EDM_DRO] CNC newbie questions

> -----Original Message-----
> Hi all,
>
> I'm about to embark on an investment in CNC and have opened
> a can of worms, I think!
>
> I'll be buying a Sherline 2010 mill and proably using
> Sherline's steppers, unless somebody on this list advises me
> that I need better motors.

Congratulation, and remember to buy soon as Sherline is increasing the
price of this item 14% as of October 1 along with a 10% cut in Internet
dealer margins. Net result is that the item will cost 24% more after the
first of the month.

I used to advise people to get larger motors. But, that was based upon
experience using a full step and half step drive where you had lots of
resonance problems and the larger motors with the current set low helped
get around the resonance stalls. Now with the very common use of
microstepping controllers (generally Xylotex for this size machine) I
have found that the performance of the smaller motors has increased
dramatically. I have a Taig 2019CR running with motors that are just
slightly smaller then the Sherlines and the performance is tremendous. I
have also run a Sherline with the same ~114 oz/in motors on 3 axis and
it performed just fine. I have never used the actual Sherline motors,
but have a customer that is using them with a Xylotex based DenverCNC
turnkey control box and he is very happy with the performance.

> Now for the questions: (!)
>
> 1/ Does anybody consider the Sherline steppers to be
> underpowered for the machine? (I assume the main limitation
> is in the maximum usable step rate?)

See above. Yes the end result of too small a motor is your maximum
travel rate is reduced.

> 2/ I'm having trouble understanding the power supply
> requirements that I've seen documented (e.g. in Gecko Drives'
> white paper). Assuming the motor is at rest in the 45 degree
> step position, where the motor will need the maximum current,
> each winding needs to be powered with Iwinding =
> Imax/sqrt(2). From this, it would appear to me that the drive
> power supply needs to provide an average current of 2 x
> Iwinding = 1.4 x Imax This conclusion doesn't gel at all with
> the requirements in the white paper (in that my calcs show a
> MUCH gruntier supply is needed), so I'm confused as to where
> I've got it wrong.

As Mariss from Gecko points our, the number are VERY specific to a
Gecko. Other drives will have other current requirements. The guys that
do the DenverCNC box did extensive testing with the Xylotex drives and
the conclusion is regardless of the voltage you use or the speed you are
driving at the maximum power supply draw was 4 amps.

> 3/ Any suggestions/recommendations as to CNC software? I've
> looked at DeskCNC, Mach2 and TurboCNC. Each seems to have ups
> and downs.

Yes, they all have their + and -. My personal favorite at the moment is
Mach2. I have used TurboCNC for testing and some for driving a lathe
before Mach2 added the feature, but personally find the DOS interface to
be too clunky for my tastes. Plenty of people using it happily and
making great parts though. I also occasionally use DeskCNC. The major
advantage is that the smoothness of the pulse train is the best I have
ever seen which give you major performance advantages in maximum motor
RPM. But, it is not as sophisticated a controller as Mach2. On the other
hand, it has a pretty extensive CAM offering. It also has a superior
probing routine.

> DeskCNC has a serial interface to proprietary hardware, which
> appears to avoid PC hardware compatibility issues, and it
> includes some CAM functionality. I'm not sure about it's
> ability to support 4 axes in either CAM or CNC. I was advised
> that it does but the downloadable S/W doesn't seem to.

Fred (the Master distributor and my supplier for this item) may say
otherwise, but it is only a 3 axis product at this time. The product is
a good value and I find it has a great feature set for the money.
Currently the product is hampered by poor written documentation and a
weak help file. Support on the user forum is pretty good, but is a poor
replacement for lack of documentation.

> Mach2 supports 4 axes but may limit my computer installation,
> since it needs to do naughty things to get Windows to be
> pseudo real time.
> It also doesn't have any CAM, so I'd need to sort a solution
> out there (Suggestions welcome).

Nothing naughty about what it does. It is very similar to what some of
the multimedia programs to a lesser extent. But you are right that it is
a little picky about hardware.

> TurboCNC gives me the option of using a really cheap PC
> running DOS, at the expense of lower step rates. I haven't
> had a chance to look at this closely yet - I don't know
> whether it can handle 4 axis control.

Yes on 4 axis. It is a very nice program if you are happy with DOS
interfaces and no constant contouring. Suits many people and the price
is right.

> At the moment I guess I'm leaning toward Mach2, if I can sort
> out the CAM issue. Maybe I'll have to bite the bullet and buy
> BobCAD/CAM. I have access to SolidWorks so I wasn't really
> that keen on having to shell out for a CAD package I don't
> really need at the moment.

As far as a CAD/CAM package I would suggest you take a look at Vector or
Dolphin. They both offer generous list discounts and the sales tactics
and support are considered much superior to BobCAD.

Tim
[Denver, CO]
Beat the Sherline Oct 1 price increase. Order Now!
New Sherline Prices at http://www.ktmarketing.com/SherlineIncrease.htm

Sherline & Taig products at Deep Discount
Mach1 & DeskCNC with credit card ordering
www.KTMarketing.com/Sherline
e-mail me at Timg @ KTMarketing.com for items not yet listed