Re: New Setup

Hi,
I think most of us on this list would have to agree with James.
There are so many different aspects of CNC that its more practical to get something going then tinker with it after its actually working.
Just the actual mechanical works can be very time consuming.
As could the electronics if thats your passion
or just learning and using various cad\cam software packages
or doing the programming yourself

So make it work firstly, then try to make it go better
And have fun doing it.
Regards
Bob Thomas

--- In CAD_CAM_EDM_DRO@y..., "James Owens" <wotisname@l...> wrote:
> Hi,
>
> I have a question for you, why do you want to reinvent the wheel with a toy machine? This is a rhetorical question and not meant to cause offence to you or other Sherline users.
>
> The internet and this list has all of the answers you need to achieve a CNC solution on this machine without you going to the lengths of designing your own electronics and software. I can understand you wanting to save money but most of what you require is free or for a small sum as shareware. Let me start at the beginning.
>
> You have your light-weight table-top machine. It has very little bulk and if you cough in its direction the head will flap about and does not come with ball-screws to drive the slides. This maybe an exaggeration but you get my drift. The first thing to look at is the way the slides are being moved and to remove as much backlash as possible within your budget. Either throw away the slide nut and make a new one from something like Moglice or fit ball-screws. Next there is the question of driving the leadscrews, servos or steppers.
>
> To keep it simple you are looking at steppers with a chopper driver board. A stepper of 200 steps per revolution on a 14 threads/inch leadscrew will give you steps of 0.00035", if you half step the motor this goes down to 0.00017" which is pretty small. A chopper driver board was published on this list a few months ago. Dan Mauch @ Camtronics does one which will drive all the axis and then there is the Gecko's. I have found a number of circuits using various chips on the internet. No encoder feed-back is required, your driver boards and steppers should be man enough not to lose steps unless you zap them with a pulse train too fast for them to keep up. For software look at TurboCNC, Kellyware or any number of free/shareware programs. All of these drive the chopper boards directly from the parallel port with no extra programming require except setting up. Finally there is the biggy EMC which is free as well. CAM is the next thing in the line, but you haven't asked this question.
>
> Servos are a different kind of animal and if you don't have the knowledge now to design a driver board I don't advise you go there. There are many flavours of servo driver, some expensive, some complicated and some that work almost out of the box. A servo works in a closed loop system with an encoder telling the motor how far it has gone. In basic terms the motor moves, the encoder confirms the move and the electronics correct any over or under shoot. Jon Elson of www.pico-systems.com as I understand these drives they only work under software like EMC or other such software designed to run servo drivers. Then there is the Gecko's which will run with any of the software that will run steppers because they accept step and direction pulses. You will need encoder feed back with servo motors which should be mounted on the motor, however some put the encoder on the leadscrew to try and eliminate backlash. I feel that this practice makes the motor hunt all the time if there is any backlash.
>
> An edge finder, either electronic or manual, will take care of setting up a job on the machine.
>
> There is no need to write drivers, design driver boards or developing digitising probes............... unless you think you can do better.
>
> Regards,
>
> Terry
>
>
>
>
> Hi Folks,
>
> I'm a newbie to the list, and have just ordered a Sherline CNC Ready
> Mill, I live in London, England, so I'm expecting it to arrive here
> within the next month or so. In the meantime, I've been working on
> various plans and ideas for the controller part of the system - which
> I shall be building myself. When I see the huge prices companies and
> websites are demanding for simple parallel port drivers, it just
> doesn't make sense to buy from them when I know I could make
> something far superior for a much lower price.
>
> I have one main question right now before I commit: Steppers or
> Servos? So far I've been leaning towards steppers, driving them with
> the L297/L298 and using a PIC uController to control them and take
> input from digitizing probes etc (it'd be a serial device with an
> error control protocol, and the PIC would take care of ramping
> up/down speed and providing steps instead of the PC, so I could write
> Windows driver software and performance would not be an issue)
>
> I'm just wondering if anyone knows where cheap servo motors could be
> found? Specifically, ones that are NEMA 23 compatible. If I could get
> inexpensive enough servos, I'd most definately go with this route
> rather than trying to hack mouse-encoders onto my finished stepper
> setup at some distant point in the future.
>
> Any advice/tips etc before I release the wispy spirit from power
> drivers?
>
>
>
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