CNC Construction

Does anyone still use a parallel printer port? Consider a USB adapter to be compatible with modern computer systems.

The problem with USB is that the timing is very inaccurate, OK for all the normal devices as they use error correction and buffering, but for driving a CNC Router, not good at all.

If there is no alternative to USB for your computer, then you need to buy a so called "Smooth Stepper", which costs around $150 (the next version will cost $119), to provide the missing timing from the USB connection....

But its far cheaper to buy a plug-in card for a PC or a Laptop, there are several different types, with a parallel port on it. Also cheaper with repair as if you blow the card, just replace it!! And that can happen, especially when you are testing a DIY stepper driver.... ebay is a good source amongst others for new plug in cards, they are still made.....they are no problem to source.

PCI cards cost around $10 on ebay, PCMCIA (Laptops) cards cost around $20.....

So you can buy a lot of cards before a smooth stepper is paid for!!!

The other main reason for buying a cheap Parallel Printer Port Card is also you then have access to more software, a lot of it free, that can drive a printer port, but not USB!!

Another possibility for good Laptops is to use a "Docking Station", which often provides the much needed parallel Printer port.

Do not try so called I/O Expanders that drive via a USB port.....not all correct the timing I am told....if it uses a proprietary connection (Toshiba for example) then this should not be a problem....

Good point, I hadn't considered the latency issue.

Don't worry, you are not the first and certainly not the last.....I have since forgotten who brought my attention to the problem as its probably a few years now!!!

CNC needs vcery exact timing, even running software under Windows can cause problems as Windoze pokes its finger in wherever it can!!

Good CNC Windows software has not been written (my personal opinion, open to correction!) by the Open Source community up to now as far as I am aware. Its mostly only from companies and costs of course....

But who cares, the open source community has written good software under both DOS and Linux, allowing older PCs to still do a worthy days work!!

Excellent, valuable information that has probably saved me a few hours of hair-pulling...

IO would like to hear why it has saved you "hair pulling" please.

By the way, the reasons that USB is not suitable for timing is that a mode of data transfer called "Streaming" is used, which is good for simple data transfers, but not when timing is critical and the data provides the timing as well......

You can read more here:-

http://en.wikipedia.org/wiki/USB_streaming

The "Smoothstepper" unit accepts the streamed data via the USB port and portions it out at the clock speed set up in the Smoothstepper firmware, upto 4MHz, but can be set much slower for a slow CNC machine....each axis can be set different, but that makes little sense for most machines, unless the travel distance of each axis is also different, also seldom....

Not all users are happy with the SS unit and the manufacturer has made many changes to try and get it working better for all customers.....its seems to be getting quite good now.

You can see a list of Firmware fixes if you go here:-

http://warp9td.com/downloads.htm

...and page down a bit.

There is a site loaded with info , forums and tutorials, at www.cncinformation.com .

Sounds like you guys would really like it. Its a start up site and Im sure you could help liven things up.

This site is geared towards diy cnc. There are many nice projects there, give it a try.

Good luck

Condor

The "hair pulling" has to do with some issues I have had with migrating from RS232 to usb for test and measurement acquisition- not directly related to cnc, but to problems with communicating with the outside world with the "new, improved" protocol...

Ah!

Thanks.

I bookmarked a diy machine like this in 'Instructables', a site I like for that kind of stuff. I'll certainly hold on to my old cards, glad I didn't toss them. I always keep an old computer around for backup, can dedicate it to the cnc router when I make it.

I want to make custom screen doors, would like to be able to cutout images. Victorian gingerbread is another chore for the machine. I can understand the x-y printer connection, it's the z for plunging the router that will be the winning trick.

I've been playing with an Arduino prototyping pc board for a variety of projects. The top end version is cheap, about US$35 per basic board.

Arduino Website

These boards are also being used to build one off CNC systems.

Arduino CNC Website

Google "arduino cnc" to see a lot more CNC examples using this board. Arduino is even incredibly simple to program and there's a ton of source code for all kinds of stuff available on the net. It's an open source system so go for it.

Hooker

What you say is partly true, great chips, great boards, but I would guess that most are used to control motors....

Who would want to write their own software to read G-Code files? I am sure there are people who do it, but surely not many......or is there already a forum.....?

Please point us in the right direction.

Most, if not all of the Arduino projects I've seen provide all the source code needed, in the spirit of open source.

For example, the source code for the project in the second link above is here:

Source Code

Of course, I have no idea to what level of sophistication this guy took his code as I haven't taken the time to look at it. He says it's a hacked version of Reprap g-code interpreter. I doubt that that code can even do circular interpretation, but I don't know that for sure. I haven't looked at it, either.

What I like about the Arduino environment is that I can look at other people's efforts and use it, or tweak it, or find something else that might work. I'm not locked into any proprietary system and the costs and limitations inherent in that.

Heck, with an Arduino, you're free to replicate the board itself and include it in a marketable product, which is something I'm involved in right now in a field other than machining.

Oh, and there is an Arduino forum. See the first link in my post above. There's probably some cnc related discussion in there.

Hooker

You are missing the point of my question slightly, I was referring ONLY to interpreting G-Code and driving a CNC machine......properly.

I already know about all the other plus points of Arduinos.......but I actually find PICAXE to be just as good and far far cheaper...but each to his own....

A hacked version of some other code cannot compare to TurboCNC or EMC2 for example, there you have two real professional bits of software for nothing.......just download them and use.....

I want real professional control, but anyone who wants can do what they want with Arduinos or whatever, but not for me personally....

Thanks for replying......

Hi Andy,

No I don't think I was missing your point. I'm just going in a slightly different direction. For example, TurboCNC is good stuff but it's somewhat dependent on technology that's showing it's age. Don't get me wrong, it's got lots of cool stuff (gcode standards, interpolation, etc).

For my purposes, for example, I would truly like to avoid dependence on parallel ports in modern designs. Not a biggie. But we are seeing electronics evolution at work.

I need to look at PICAXE. Never heard of it.

Hooker (and I'm not exactly a novice at nc/cnc. I used to be a multi-axis Part programmer using IBM 370's and paper tape )

Did you read what I wrote about USB and CNC? It needs expensive hardware to work - mostly....some actions are still not done correctly.

Buying a plugin Parallel Printer Port is no problem, as is installing it.....

Older PCs are more than fast enough and really, really cheap, in fact you might get given one or more for free!

All the old DOSs are available online for free as are the early "Wins"......Linux runs brilliantly on older pcs (as it also does on new ones too!! See Ubuntu 10.04!!!)

We will be using PPPs for many years to come......

PICAXE is supported by the British government and is really cheap and all the needed software is free.....there is some other software which might be called "nice to have" which you have to pay for, but even that software is still very cheap.

There is even a free simulator.....

Goto here for more infos and downloads:-

http://www.rev-ed.co.uk/picaxe/

There is also a look alike of PICAXE which is compatible to all the software and even a bit cheaper at:-

http://www.1sorc.com/group.asp?grp=101

It looks as though the original company for KicChip has dissappeared.....