Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Fastest1 on December 14, 2009, 08:42:56 AM
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I have just installed a DC-04 and got it working pretty well. I am not getting any response from Peter. Could be that I sent the mail on the weekend or could be computer problems as I have been experiencing all kinds of strange email problems. Almost no email for a week or more including no junk mails then a flood. Anyway, I can use the tach and in manual mode I can attain a 1450 rpm, however under automatic I can only get 1096-1100? I have tried changing the PID values and it did help me to understand what those settings were for, they didnt help. I had read about a trimpot adjustment but the way it was worded made me think it was for the manual setting. Anyone have an idea? I did get to do some threading and it is very close to correct and cool to watch without having to worry if you are going to engage into the correct location manually. Speed control matches the S command perfect until 1100 rpms.
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I have just installed a DC-04 and got it working pretty well. I am not getting any response from Peter. Could be that I sent the mail on the weekend or could be computer problems as I have been experiencing all kinds of strange email problems. Almost no email for a week or more including no junk mails then a flood. Anyway, I can use the tach and in manual mode I can attain a 1450 rpm, however under automatic I can only get 1096-1100? I have tried changing the PID values and it did help me to understand what those settings were for, they didnt help. I had read about a trimpot adjustment but the way it was worded made me think it was for the manual setting. Anyone have an idea? I did get to do some threading and it is very close to correct and cool to watch without having to worry if you are going to engage into the correct location manually. Speed control matches the S command perfect until 1100 rpms.
Hi John,
Not sure what is going on with the emails. I'll go through the spam box and see if they are there.
Under automatic control, the max speed you can achieve is about 5% less than under manual control. This is because the DC-04 needs to steal a bit of the voltage for its own use. The trimpot allows you to decrease the max manual speed to match the max automatic speed if you desire that.
The closed loop control in Mach3 does not work unless things have changed . So I wouldn't bother using that. As to the linearity you need to keep in mind that the DC-04 is an open loop control system. There are a number of things that influence the linearity of the spindle speed. I have done a lot of testing and can confidently say that the DC control voltage generated by the DC-04 (And the other Digispeeds) is linear with respect to the PWM signal it receives from Mach3.
With the DC motors, there is the initial friction of the spindle drivetrain to overcome. This will cause the spindle to turn slower than you would expect at low RPMs.
Then there is the DC motor characteristics at the top end. Once the motor gets to approx 95% of its max speed the response is no longer linear. For a machinist this is usually not as issue as at this stage you basically wantthe spindle to run as fast as possible rather than an exact speed.
Between 10% and 90% the DC motor should be very linear.
You also need to keep in mind that the spindle speed usually creeps up a bit once all the bearings are warmed up, so I suggest that any sspindle speed tuning should be done after the spindle has been run for 20 minutes.
For tuning, I do the following.
- In Mach set the max pulley speed to 1000 rpm.
- Turn on the spindle and set the speed to 1000 (maximum).
- Record what mach is reporting as the actual spindle speed and enter this into the pulley setting.
- Set the spindle speed in Mach to about 50% of the maximum speed.
- Tweek the max value in the pulley setting to get actual speed to mach the set speed.
- If 50% of max is not where you normally operate, then do the tweek at that speed.
Cheers,
Peter.
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Peter
Thanks for the response. I have talked to my ISP but I guess asking questions here puts me on some kind of watch list! Email activations have been ignored also. Anyway I got it running pretty well today. I cut a thread at 20 tpi at 400 rpm on an old sherline with some backlash in x not compensated for and they turned out real well. Maybe not perfect but hell it was my first try and I using a piece of electrical tape across my pulley. I am thinking of using a thinner piece of tape but the indexing was spot on at 400 rpm indicated. I did try it with and without spindle feedback or averaging at different times. Seemed like it did work better without the feedback. Yesterday seemed like the opposite. Anyway it has been fun and I have an insatiable appetite for info when I am in the middle of something so patience might not be my forte. The delay caused me to read a lot of info on wikipedia and here. Nothing I didnt need to do. Do look into my email, it was thru your support on your website.
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Hi John,
Good to see progress is being made. As to the index mark, Mach3 just looks for the transition edge so the width of the mark is not important EXCEPT that it needs to be wide enough. How wide depends on a number of things, including the spindle speed, Mach3 kernel speed, opto sensor sensitivity, etc.
If you are using 1/2" electrical tape, then just leave it at that. No need to make is thinner.
I'll look through my spam later tonight.
Cheers,
Peter.
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Here is a pic of it. Of course the diameters are not relevant to anything. Just testing repeatability of the cutting tip to follow the previous path. Incredible, to me anyway. Obviously I need help in photography too!
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Hi John,
That looks really cool. Even if there is no nut that will fit it. :)
Cheers,
Peter.
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By tomorrow that will all change. I will either measure a bolt or look up the specs and make 1. Thanks for the new found possibilities. Of course I am still trying to find out why I am doing this. I think it is the challenge to say the least.
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John,
You may want to take a look at the write up I did called Threading on The Lathe-Mach3 Turn.
It is located in Members Docs or via SUPPORT> Documentation above. Covers a lot of info.
RICH
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Rich
Do you see something blatantly obvious that is incorrect? I did read that write up more than 2 times. Some of the literature regarding this topic is difficult to read. I always doubted the A.D.D. or hyperactive label but I am starting to have my concerns. At the time I cut those threads impatience had gotten the best of me and I just had to hit "cycle start". You can only hope you are understanding it for so long then its time for action. I actually cut that set of threads many times at many different speeds with various features I didnt fully (or partially) understand and I wasnt really getting the helpful responses to progress. I do find the results in aluminum were much better at 400 rpm than they were for 175 rpm. Also cutting fluid produced the best results. Even though the lathe is a Sherline it is so much more rigid that trying to thread via the mill.
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John,
I don't see anything wrong just didn't know if you were aware of that write up.
What literature is difficult to read? In the write up?
If in the write up, can you be more specific or provide feedback on it.
RICH
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Rich the article was well written just very technical and a few concepts I am not grasping (not that I can think of any one thing right now). This must be a relatively difficult procedure for most of us laymen judging from the responses to the related threads. It wasnt as bad as I built it up to be. I am having fun playing with it now. I did get a 1/4-20 nut and threaded it onto a thread I cut today and it fit better than the bolt I copied.
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Thanks John, unfortunately, all considered, threading is rather technical because it's governed by so many standards
and a rather complex cnc operation. It's when you have problems threading that undestanding of all the info
becomes even more important.
RICH
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Rich, Actually I want to thank you for the effort to explain the threading concept and Peter Homann's DC-04 for making it work for a very reasonable price. I have a very limited math background (high school) and I didnt see the associations at the time. You know the saying "if I knew then what I know now"? Well the girls would have still been irresistable! It is good for the mind to keep learning. I cant imagine the frustration before forums like this and having to use the Dewey Decimal System to find a book that might have some info or not. This place is a god send. Even though I still get frustrated in the middle of the night when no one responds it actually makes me read the directions over and over and over. Eventually I get it. THANKS TO ALL OF YOU! Dont think for a minute this means I have acheived anything. Tomorrow I will babbling about something else, probably a bigger lathe and mill! I threaded a bolt at 500 rpm this afternoon. 1/4-20 that had a feedrate of 25 ipm pretty funny to watch on a Sherline. Another amazing thing was how much the carriage, toolpost and gibs were moving (mostly because I quickly threw the spindle from the mill to the lathe and didnt fix any previous issues yet) and they still cut an excellent thread. Cant wait to tighten it up and test again.
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You can thank ART for taking care of users with punny lathes. A lot of time was spent to provide for spindle slow down and still end up with satisfactory threading. That work took 1 1/2 years to get it right. My first cnc lathe was a Sherline and still have it. You will find that that higher rpm is required to get the power out of the SHerline to minimize spindle slow down. Do a whole bunch of threading on it gradualy working your way up in size and pitch to gain experience. Use 6061 Al and not that gummy stuff and then try the equivilant in steel. Doing that will give you experience on what YOUR lathe system can and can't do. It's easy to thread to "the nut fits" it's another matter to attain a class fit.
Have Fun threading,
RICH
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Rich, The Sherline is a great machine for people who want little stuff. I can see the results of some people who are patient and they are incredible. I can also see where I want a bigger more rigid lathe, not a huge lathe just bigger. But it is a great learning tool. I did read somewhere last night that the aluminum rod (Home Depot stock) was a gummy metal that doesnt machine well. So I will have to get some 6061 and some 12L14 because I hear as a steel it works very smoothly. I really get alot of my metals from a recycler near my house. With that identification becomes an issue. THANKS ART for your work on this and all you do.
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Rich, I was just rereading this thread and realized you asked this question years ago and I never responded. The literature was not difficult to read, it was and is difficult to comprehend. Two different problems entirely, one for which you can not be responsible, me. ;-)
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Fastest1,
The problem is that cnc threading relates to a PC, controller, software, standards, different techniques, hardware, mechanics,etc.
That's true of for all of CNC work. My generalized term for it all is the Lathe SYSTEM. Like everything in CNC it can quickly go from simple to complex. So the wirte-up was a touch on a topic that covered just some of the main components to do a basic thread.
One example of expanding on threading would be for tapered threads, NPT which includes different types and classes.
To cut one to meet / check for tolerance could be a challenge.
A good example of something which gets complex quickly is gears.
So let not your heart be troubled as there a books written on the subject,
BTW, didn't even touch on the design end of threading.
I guess, in general, anyone who writes on a topic is challenged to keep it in perspective and write at some thought level which
may be comprehended.
I only write and can not read ( or spelll) so only the end user will be able to judge! :D ???
RICH