Question about pre-CNC automatic milling.

[Flynth]

Another beginner question about my horizontal 3k lbs knee mill (a Heckert Fw250), but applicable to countless other machines I think. The question is, when automatic milling with fast return how to prevent dragging a cutter across the work and breaking teeth? Or is it applicable only to some special cuts (and cutters) that are immune to it?

Let me explain what is meant by automatic milling.

My mill made in 1960s (estimated) has a feature of pre-CNC automatic milling. Only one axis can be under power at a time so it is all limited to a single axis. It is "programmed" by placing special plastic blocks on rails that each axis has one of. When the movement of the axis reaches that block it presses on limit switches in a special way engaging a certain function. The functions are divided into two groups. One works when approached from the left (and ignored from right) and the other opposite.

The functions are: stop feed, engage auto feed left or right, engage fast feed left or right. So not a lot of options, but the manual shows some examples how to use it(sorry it is in German, but understanding the text is not necessary).


So let's say you want to set up the work to mill down a surface on Z. You configure the mill to reach a certain spot on X, then return to it's start position. You can repeatedly press the button to start, auto feed starts on X milling your surface until it reaches your predetermined location. Then it fast returns to the start position. Then you move Z axis by hand up, press the button again and so on. You don't have to return manually.

There is a feature of this mill to lower the knee a tiny bit hydraulically, but it's an option my mill doesn't have. So the question is, is automatic milling useless without it? Or are you supposed to watch it like a hawk and lower the knee the moment it reaches the return point manually?

There is zero information about how to use this feature other than few drawings like ones I attached. Can anyone offer any more info?

 

[Karl_T]

Yea, you are going to get cutter marks on the return with that system. No problem EXCEPT for finish cut.

Neat idea for its time - pre computer CNC.

 

[Shotgun]

Carbide cutters were not nearly as much of a thing then, so the reversal wasn't nearly as problematic as I have found it to be with carbide inserts (Heh, a man's gotta try.)
We have a skewed vision of the past. We think everything made back then was done with exceptional workmanship, every edge deburred, every surface ground. The truth is that only the high quality stuff has survived, and the vast majority of the stuff produced is rusting in a landfill or has been recycled. If there were some tool marks from running in reverse, there is a good chance it would have been shipped that way if it didn't interfere with function. The rule then was the same as now. Make money by getting the parts out the door.
If it was to be a precision part, you'd probably set the production line up to do a rough cut, then let the metal season to let it relieve stress by itself. The finish cutting would be at a different station with a different machine and a different operator. The hydraulic add-on wouldn't be needed in this case.
These features were added so that the operator could do something else while it ran. "Watching like a hawk" was never part of the plan.

 

[Joe in Oz]

I would call that a "prodcuction machine" or semi-automatic automatic. In around 1960 I father took me to visit a machine shop where they had "NC" machines, large mills and planers. They were operated by metal punch cards on chains. That was in Germany and the production was precision machine tools. Everything Shotgun said above applied back then too.

 

[Flynth]

I would call that a "prodcuction machine" or semi-automatic automatic. In around 1960 I father took me to visit a machine shop where they had "NC" machines, large mills and planers. They were operated by metal punch cards on chains. That was in Germany and the production was precision machine tools. Everything Shotgun said above applied back then too.

Interesting. Those punch cards are the next stage I think. This machine is German make BTW (East German). And it is the smallest and the oldest design of the series.

It has a 1000mm by 250mm (40in by 10in) table It can only drive one axis with power feed at the time (you switch which axis is driven by what looks like a manual car gearbox). It uses a continuous variable speed pulley system to set automatic feed speed. It has selenium rectifiers and a cabinet full of relays (24 of them, each 8 input and 24 outputs) that looks like an old telephone exchange... It took me 6 months to get it to work as intended electrically. This included reverse engineering it (all the schematics I had were wrong) and using a piece of software called EKTS to simulate relay logic. Im really glad some Turkish guy wrote that piece of software and made it free. Without it I probably wouldn't be able to fix it

The next sizes up are fw300 and fw400. From the manual I read fw400 has 3 drive motors, one for each axis so in theory a much more complex control could be achieved, a control panel full of buttons the size of a two door fridge and it uses some semiconductors in its electronics (thyristor drive for motors). I see some for sale around here from time to time. If I had space for one it would make a great basis for a cnc conversion.

Coming back to my machine. I think you're right this was made to speed up production, but why they made the effort of installing this system in a little(compared with others) toolroom mill I don't know.

I think the previous posters are right "watching like a hawk" was never a part of it. I have to try using that feature again, this time with a different cutter and with remaining axes properly locked.

 

[derfatdutchman]

Way back when I was in tech school, we had an NC Bridgeport mill. Had a big cabinet that set next to it. You could jockey the table and knee around manually by entering the coordinates on the control panel or run it automatically with a paper tape. When the tape reader worked and didn't eat the tape that you spent a couple hours making it was neat to watch it work.