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Electronic leadscrew on a big boy lathe

CarbideBob

Diamond
Joined
Jan 14, 2007
Location
Flushing/Flint, Michigan
Allow me to rephrase. .
Allow me to wonder if you have ever built something like this or any motion controls. All sorts of things get in the way.
What are mech and electric time constants, and this whole z domain thing between the analog world and the digital word just for starts.
I understand that it seems straightforward and so logical. Have been there it that thinking and so sure I could do it.
Jump in and join .. the water is maybe deeper than it appears and you will never know until you try.
Build something and test it.
Have you even done a usable DRO or a basic high response PID servo in a cheapo controller?
It looks so easy until you do it and I one thousand percent understated that thinking.
Lord knows I thought all this cnc and servo stuff would be simple and I just needed higher chips speeds, more processing power and faster sampling. That was 1973.
Bob
 

Strostkovy

Stainless
Joined
Oct 29, 2017
Allow me to wonder if you have ever built something like this or any motion controls. All sorts of things get in the way.
What are mech and electric time constants, and this whole z domain thing between the analog world and the digital word just for starts.
I understand that it seems straightforward and so logical. Have been there it that thinking and so sure I could do it.
Jump in and join .. the water is maybe deeper than it appears and you will never know until you try.
Build something and test it.
Have you even done a usable DRO or a basic high response PID servo in a cheapo controller?
It looks so easy until you do it and I one thousand percent understated that thinking.
Lord knows I thought all this cnc and servo stuff would be simple and I just needed higher chips speeds, more processing power and faster sampling. That was 1973.
Bob

I built a plasma table that I tuned servos for and also tuned the servos on our press brake. I am building a servo driven mill, but that isn't finished so let's not count that. Obviously not the most experience, but more than none.

Do not do the PID loop in the cheap controller. Just use a cheap controller to receive quadrature index pulses from a spindle driven encoder, and output new pulses accordingly. These pulses go to a name brand servo amp, which is where you do the tuning. I like panasonic servos because I can affford them, but I've never used any of their larger ones, if they even make them.

I intend to make a small desktop lathe at some point (400ish pounds) but really have no use for a manual lathe with this retrofit. I'm happy to help someone write code though.

Edit: I have other less relevant experience as well, often with steppers or general repairs. I did make a circuit from logic gates to divide a quadrature signal by 256 to interface to a servo amp with a lower maximum pulse rate, which is kind of relevant I guess.
 

Turbowerks

Cast Iron
Joined
Nov 9, 2018
Location
Windom
Interesting thread (pun) , my take on this would be not knowing the size of the lathe to have the els installed on, rather than overthink this would be take clough42’s research and testing and supersize it if needed to fit your application seems after watching most of his videos on this subject ( sitting home with the covid after effects) he has addressed most of the problems. Although a good old American iron large lathe and its inertia could be a little nerve racking but if your retrofitting a els why not a brake. Jm2cw


When I find it I don’t need it
When I need it I can’t find it!
 

hanermo

Titanium
Joined
Sep 28, 2009
Location
barcelona, spain
ELS and threading

After 5 lashups and 2000 hours I spent 2000€ plus on just the electronics.

Because it is the only way to do it really well.
Imo. Ime.
Lots and lots of experience.

You need to track the encoder aka spindle position in real time to about 200-500 khz, within a 10 steps or so.
Or angular resolution of about 0.02 degrees, maybe 0.03 degrees.
This is difficult, without industrial hw.
With varying spindle speeds .. that have various differing lag times.

I now have an ac servo spindle running 12 khz update loop .. with a more or less perfect spindle speed.
Reacts in 0.00013 seconds, more or less, at 90 Nm of torque.
Just to do good threading.

When the servo pulls the tool out on the x axis, it needs to repeat to about 0.01 mm.
Otherwise, cascading errors cause a dig-in and the tooltip snaps.
This is difficult, without industrial hw.


I just spent 1300 plus 100 € plus 200€ on stuff for my new controller on the mill.
About 2000€ all in..
A VMC I built.
It´s a lot of money.
The reason is that the cheap stuff just does not work.
Properly.

Mine will do good threads to industrial quality, using a high res optical encoder to track the spindle.
Just like the lathe.

It is difficult to do good cnc threads, reliably.
I know of exactly zero youtube videos or amateurs demonstrating "good" threads in steel.
A kit might work at one rpm, but not at another.
 








 
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