Do you know what "Drip Feeding" is?

Yes, I use it all the time!
No, I haven't a clue!

060707-1620 EST USA

widgitmaster:

Yes I know what it is, and I am of the camp want DNC to be identical in meaning to "drip feed".

I think DNC should not be used for "distributed numerical control" because this creates confusion. Clear definitions are important for effective communication.

We have an RS232 Isolator product, our I232, that is ideal for "drip feed" applications as well as others.

The I232 provides High Baud Rate Capability, simultaneously Long Cable Lengths, and Electrical Isolation.

DNC to do contouring will at times require many very short mechanical moves. At low baud rates, like 9600, this may cause data starvation and the CNC machine to move in jerks. This slows you down, is hard on the machine, and degrades the surface finish.

For more information on the I232 System visit our web site:
www.beta-a2.com

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Gar,
Can you describe precisely what "Drip Feed" is for those who are new or inexperienced!

I believe DNC means:

Direct Numerical Control – A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory.


Eric

060707-1817 EST USA

"Drip Feeding" is a method of sending a CNC program to a CNC machine a few instructions at a time, and there is a handshake process so that the sender knows when to stop sending and when to send more data to the CNC.

The general reason for using "drip feed" is that the CNC program is bigger than the amount of available memory in the CNC for storing programs.

In a general way this is how the process works.

The operator puts the CNC machine in DNC mode. Now the CNC is ready to receive and process incoming CNC instructions.

In the CNC machine is a "first-in first-out" (FIFO) buffer that can store at least a few lines of CNC code. This buffer fills from the RS232 input up to a certain maximum limit, and then the sender is told to stop via a handshake signal. Because of time delays in communicating between the sender and the CNC the maximum limit is set less than the buffer capacity.

When data is in this FIFO the CNC extracts instructions from the buffer as needed. When the FIFO drops below a certain number of characters, then the handshake signal tells the sender to send more data. This continues until the end of the CNC program. Such a program might be 10 to 100,000,000 bytes, but the CNC program memory space might be only 100,000 bytes.

Sometimes in DNC the machine may run several days on one program.

Fanuc machines tend to have a very small FIFO whereas a HAAS machine will use a very large percentage of available CNC program memory space for the FIFO.

This is a quick overview.

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Gar,
Can you describe precisely what "Drip Feed" is for those who are new or inexperienced!

I believe DNC means:

Direct Numerical Control – A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory.


Eric

gar;

I agree that clear definitions are important for effective communication; perhaps you can clarify, please.

widgitmaster gives the definition above and I am confused; I was under the impresssion that the (competing) meanings for DNC are:

DNC: Distributed Numerical Control - A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory

and:

DNC: Direct Numerical Control - a method of sending a CNC program to a CNC machine a few instructions at a time with a handshake process so that the sender knows when to stop sending and when to send more data to the CNC; also known as "Drip Feeding".

Either I have it backwards or widgitmaster has it backwards.

gar;
Either I have it backwards or widgitmaster has it backwards.

Actually, I went to Google and used the define command!

define:dnc

Of the five definitions returned by Google, only one was CNC related!

Direct Numerical Control – A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory.


All I intended to do was to clarify the ambiguous terms used on the zone, because like myself, there are many who just don't know exactly what they mean!

Oh well!
Eric

060708-0639 EST USA

Geof:

You are correct, and the definition from Google is wrong.

DNC used for systems other than "drip feeding" is very uninformative if you look at the various ways people use the term. Some simply mean communication from a computer to a CNC, others means a network of one computer and many CNCs, and so on.

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lol....when I saw this thread I thought it was something to do with coolant! :D

As one who hasn't a clue, something I read on another forum lead me to believe drip feed was along the lines of creating a part from several separate files: complete one file's worth of operations then load another etc.
I thought this thread was trying to define 'drip feed' but it seems to be more about the definitions of DNC. Where does DNC fit into 'drip feeding' ?
Geoff P

As one who hasn't a clue, something I read on another forum lead me to believe drip feed was along the lines of creating a part from several separate files: complete one file's worth of operations then load another etc.
I thought this thread was trying to define 'drip feed' but it seems to be more about the definitions of DNC. Where does DNC fit into 'drip feeding' ?
Geoff P

The way I understand DNC and dripfeed this is more or less correct. Direct Numerical Control DNC is when a program too large to fit in the machine memory is 'dripped' into the machine and executed at the same time. Your description is just bigger drops of program.

Also maybe someone can comment further but my understanding is that drip feeding originated a long time ago before machine processors had enough capacity to execute complex macro calculations fast enough to run a machine at the same time. The calculations to generate compound curves were processed in real time on a big mainframe which dripped the results into the machine. Something similar to having a CAD program simultaneously feed a CAM program which is simultaneously providing code to the machine. Maybe the analogy is a bit stretched but not too far with a bit of imagination.

In this context Distributed Numerical Control DNC is a johnny-come-lately that only became possible with the advent of desk top PCs and large scale network systems. Although I guess the Sun Workstations that were used a few years ago were a bit big to describe to describe as desk top.

060711-0756 EST USA

geoff p:

I believe I gave a fairly good description of how a typical "drip feed" operation works in post #4.

In the most extreme case you have old machines using tape readers. Here the "drip feed" occurs one character at a time. Or maybe you would like to say one block at a time. This would depend upon whether there was an internal buffer used.

As I previously said I do not like the acronym DNC used for anything except Direct Numerical Control ("drip feed") because this leads to confusion of what one is saying.

"drip feeding" is a colloquial term for Direct Numerical Control. But is very useful because it is sufficiently unique in its meaning to avoid the problems with the many definitions of DNC relative to CNC machines. Also DNC has lots of uses besides those in the CNC arena.

The Wikipedia discussion on Direct Numerical Control is a real mishmash of concepts without clear definitions.

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060711-0756 EST USA......The Wikipedia discussion on Direct Numerical Control is a real mishmash of concepts without clear definitions....
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I will second this. I skimmed it quickly and came to the conclusion it is not even internally consistent; which is not surprising considering how Wikipedia operates.

Wow, now I feel real stupid. I looked at the poll and thought "drip feeding" must be when you have your coolant on a continuous feed dripping onto the cutter. And I thought, I work with wood, I don't use a coolant. But then I read further into the posts and found drip feeding was a totally different thing.

I'm glad I started this poll, as there is way more confusion than I ever imagined!

I'm glad I started this poll, as there is way more confusion than I ever imagined!

I think this thread is a good example of the value of having a consistent interpretation of a word or an abbreviation and sticking with it. At various times I have been accuse of being picky in other threads because I have commented on the wrong use of technical terms. My view is that if you want to be understood unambiguously use the correct technical terms and words in the correct context and spell them correctly.

I think, with any specialty, there is a terminology that you pick up as you work in it for a while. My background is in mysical instruments and if I started talking about the chin, the ears or the corners on a violin I wouldn't expect many folks here to know what they mean either. Likewise, I was talking to one of my summer interns about "thumping" liquid helium tanks (which does not mean banging on their sides) and he seemed genuinly amazed at how it works.

When I first started out here I can't tell you how long it took me to figure out the process of exactly how one goes from a CAD drawing to actually making a part on a router table (generating g-code and then using the g-code in something like mach3 etc). But the more I read out here the more I learn. With any luck, someday I will have some understanding of what I'm doing (hopefully before I retire).

A violin maker I know fashioned his own knife sharpening machine by using a gear motor at about 200rpm mounted vertically, several flat interchangable plywood disks mounted hoziontally on the motor shaft with various grades of wet/dry sand paper from 800 to 10,000 grit. The lubrication system he used was to take an old milk jug with a small hole in it (fitted with a tube), filled with soapy water as the coolant reservoir. By raising or lowering height of the jug he controlls the dripping of coolant onto the sandpaper keeping his edgetools cool as he sharpens them.

That's where my misconception of "drip feeding" came from.

So drip feeding in CNC work is like getting your porn on a slow internet connection. Little bits of the picture come through at a time. Dribbling through at a slow feed rate, eventually making up the whole thing. Now I think I've got it :)

....My background is in mysical instruments...

If the typo here was a missing 't' you certainly would have an unusual background. :)

Well, it is said that the violin is the devil's own instrument which does bring it to a spiritual level of sorts. But I did, in fact mean, musical :)

But I would never argue against anyone who would like to attribute any extra qualities to my work.

Thanks Geof

060711-2003 EST USA

HAAS has a very well written paragraph on DNC. Following is a direct quote from p 100 in one of our manuals.

The subject heading is:

"Direct Numerical Control (DNC)"

"As a standard feature, this machine is shipped with a DNC capability. With DNC, there is no limit to the size of your CNC programs. The programs are directly executed by the control as they are sent over the RS-232 interface. Note, that this is the first serial port or the top connector. Do not confuse DNC witrh RS-232 uploading and downloading."

The same RS-232 port is used for both up and down loading programs, and for DNC. In the above paragraph HAAS did not mention the buffering between RS-232 and actual code use, but that is not important to the broad concept of Direct Numerical Control.

Anyone with a Fanuc manual that can show how they define DNC?

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The Yasnac Book I have was printed in 1984 for the MX1 Control. It gives no information on DNC, but always ran it off my Lap Top RS232C. The Programs are in the 900,000 sequence block length and longer at times. Fanuc will more than likely give an almost Identical definition of DNC. The original place where I learned the definition of DNC was the Machinery's Handbook 26th and McGraw Hill. Has a little info on CNC, CAD, and CAM. It also explains the basics of how a CNC works, both electronicly and machanicly. I am very amazed that this one word could cause so much confusion in a place called CNCZONE.

BTW: The Baud Rate of the Yasnac was maxed out at 1200. Very slow compared to todays standards.

Nice Poll Widgitmaster.

I’ve been a software developer since the mid 70’s
In the early 80’s I wrote my first Communications software for the Machine tool Industry.
The Definition of DNC means both of what has been discussed in this topic.

First it Means “Distributed Numerical Control” this is the process of Transferring a Program into the Controls Memory.

Second it Means “Direct Numerical Control” in it’s earliest form, this meant that the CNC control Executed the commands as they were received through the RS232 port.

The Earliest form of Direct Numerical Control was Punched Paper Tape.
In effect, the Tape could be as long as necessary. The program was executed directly by reading in a block of code from the tape, stop the tape, execute the block, read the next block, execute it, and so on….

The Limitation was how much tape you could fit on a Spool.

Very early DNC systems that used a PC also used a BTR (Behind The Reader) device to replace the Punched Paper Tape Reader. Instead of the Control executing the program from a punched Tape, the program was executed from the BTR device which was being fed instructions from the RS232.

Now BTR devices and Punched Tape are rarely seen or used.


There is a use of “Direct Numerical Control” that should more accurately be called “Buffered Input”.
Many controls will now input Data from the RS232 port into a Memory Buffer, the CNC then Executes the Codes from this memory Buffer, as the Buffer is emptied, more data is requested to keep the buffer full. This type of buffer is also known as FIFO or First In First Out.

Some controls use very large memory Buffers, while others use a very limited buffer size.

So basically the Definition of DNC depends on the context of how you plan to use it.

070103-2208 EST USA

vpcnc:

You have provided some very clear definitions.

Big problem is that most persons that use the term DNC provide very little "context" information to clarify what they are talking about. I suspect this results from a lack of knowledge of the possible meanings of DNC, and that clairification is needed.

I have tended away from using the term DNC by itself. I like the term "drip feed" because it quite clearly identfies the subject. When I use "drip feed" there is usually enough "context" that indicates I am talking about data transfer, and not lubrication or coolant.

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Who in year 2007 use drip-feeding !!! Ethernet rules....

M30 <-- rewind tape !!

070217-1721 EST USA

LeonH:

Drip feeding has nothing to do with the communication path.

Drip feeding needs to be used if the program to be run is larger than the available CNC program storage area in the CNC machine.

If the CNC has a hard disk and the CNC program is too large for the available RAM in the CNC, then you will effectively drip feed from disk to RAM.

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Most Pc Retrofit Machines Dont Need Drip Feed,mine Is Mach3 Dell
1000 512 Ram Ethernet To Amd64 Cad Cam Just Pull The Whole Program Over In Adout A Minute No Buffering In,drip Feed Is Normally Hardware Based Cnc Older Like Dynapath, Etc With Almost
No Ram