Very basic questions

I have a Harrison lathe and a Bridgeport mill in a workshop at the bottom of my garden and I am purely a 'hobby level' machinist, but I hanker for a computer controlled mill and since I have a very nice Bridgeport, would like to convert that for CNC controlled by LinuxCNC.

At this stage I'm trying to get an overall picture of the hardware requirements, particularly at the PC end and what is required in between that and the actual mill. I have zero experience of any of this and so need to build up my knowledge.

First things first. I have a couple of PCs I think could be press ganged into use for this. Both have parallel ports built-in, but one has spare PCI slots, whereas the other does not. What interface/connections are required? I read that the parallel port is often used. Is that still a viable method? Is that all that would be required or are other connections also required?

As the subject states, very basic questions, but could do with some guidance to help me gain my own understanding of all that is involved.

You can use the parallel port in some applications. You can download an iso with Linux CNC preloaded and run as a live disk to test the latency/jitter.

My PC is older than 10 years and has respectable latency. You can disable bios settings to to cut it down also

What I'm really trying to establish is what connections are required to the PC. Is a single parallel port sufficient, or are multiple ports required and what alternatives are there to the parallel port?

One of my PC options has a parallel port but only one spare PCI slot. Is that enough? If not, then I can discount that as a possibility and instead use the PC with multiple slots available.

Looking at it from another angle, how does the PC connect to the machine (Bridgeport in my case). I'm under the impression that the PC connects to an external box/controller that in turn connects to the various motors and feedback devices on the mill. So how does the PC connect to that intermediate box and what is in that box? Apart from the PC and actual mill, what other actual hardware is required?

I have NO experience of CNC and cannot simply 'guess' what might be required. I'm trying to build up some basic knowledge of what is required so that I can plan to convert my Bridgeport.

Typical systems using a parallel port have:

Parallel port --> Breakout board --> motor drivers (one per axis) --> motors
The motor drivers used depend on the motor type, size and performance requirements

Aha, so the breakout board and motor drivers could/would be housed together in a box/enclosure external to the PC? In which case, just the parallel port is all that is required from the PC?

What are the alternatives for this connection to/from the PC? I believe RS232 is not fast enough and USB hard to make real time. Ethernet doesn't strike me as being ideal for this, but appears to be an option. Is it in fact better now than parallel? What would be used on a modern PC/LinuxCNC setup?

The Mesa cards can be Ethernet or use the parallel cable with advantages to each

To further expand on the parallel port's capabilities. The usual bit banged parallel port, as used with normal parallel port breakouts for software stepping, will be limited to one of 3 I/O configurations, as "Output" with 12 output pins and 5 inputs. as "Input" with 4 output pins and 13 inputs, or "X-mode" with 8 output and 9 inputs (there are no retail breakout boards available that support X-mode),

There are also options from Mesa or Pico Systems that will connect to a parallel port using EPP mode and can expand the parallel ports capabilities immensely.

So, would I be able to control 4 axes of my mill through the built-in parallel port on my PC?

I want to ascertain that I would need no additional PCI card in that PC, in order to control 4 axes on the Bridgeport, in case I want to go to 4.

UKenGB wrote:

So, would I be able to control 4 axes of my mill through the built-in parallel port on my PC?

I want to ascertain that I would need no additional PCI card in that PC, in order to control 4 axes on the Bridgeport, in case I want to go to 4.

Yes the eBay and Amazon cards support 5 axis , it is what I'm using. It has 5 inputs for an estop and limit switch also.

Here is a video, he is a member here as well.



I believe if you use the pwm spindle control option it uses a pin from the 5th axis.