Any machinist here?

Posted by: @ralphxyz

So are there other machinist?

Hi Ralph,

I worked as a machinist many years ago.  I also had a small machine shop of my own.  I hand a really nice South Bend lathe.  I don't recall the numbers, but it was a large floor model.  Probably something like 16 inch by 6' bed?  Or something in that ballpark.  I also had a Bridgeport vertical mill with a J-head.  I wish I had those machines today, but unfortunately I don't.

Today I do have a bench-top combination Lathe/Mill.  It has a 17" swing, but only about 24" between centers.

It's not that best machine by far, but it's been serving me well.   It does have automatic feed on one axis of the lathe only and I've used it for cutting threads.  I never bothered to try to motorize the cross feed.    There are no auto feeds when used as a mill.  Even the main table feed from the lathe no longer works when switched over to the milling mode.

So I'm not going to be able to help you out with your conversion to CNC.   However, if you notice in the picture of my lathe, the table can also be fed by hand using the handle at the far right of the leadscrew as you can see in the photo.  So I could easily install a stepper motor there to make the table feed electronically controlled.  Then I would also be able to use that CNC feature with the mill too since I would still have control over the table lead screw.

I have thought about the possibility of converting this machine over to CNC.  But thus far I haven't really had a need for it.  I'm not planning on using it for mass production, and when doing a single job it's just as easy to do it manually, I think.

But yeah, if I ever had a reason to have it make a lot of identical parts converting it over to CNC might now be a bad idea.   I guess you can also use CNC for doing extremely complicating parts that may be next to impossible to do by hand.  Like if you wanted to mill out a statue or something like that.  Again, I just haven't had a need to do anything that complex.

In any case what you want to do is certainly doable.  I've seen others who have converted manual machines to CNC using stepper motors, etc.   What I have also heard is that there can be some feedback issues.  You might need to employ some fancy control techniques like PID (proportional–integral–derivative) feedback control. 

This is done to avoid overshooting your target and to minimize possible feedback loops that may cause chattering, etc.    From what I understand converting a manual machine to CNC can be quite an art.  That can all depend on exactly what kind of precision you need when all is said and done, and how much play is in your machine.  When cutting metal manually we can deal with some play by simply being aware of it and taking measures to deal with it.   But in an electronic system that uses feedback it can become a nightmare.

There are also two fundamentally different ways to approach the subject.

1. Precise positional feedback
2. Brute goal-oriented plow-through 🤣 

Okay I just made up the second term here.  But the difference is that in the first situation you're actually using positional feedback to insure your tool is actually where its supposed to be.  That's what requires a lot of skill and art.

The second method is more general.   You just start the tool from a known position.  And then have the stepper motor just "plow-through" the intended path of the cut and hope that everything goes okay.  This method can actually work pretty well if the cuts you set up are reasonable.  It's basically the same thing as using the auto-feed on a manual machine.  You just engage the lever and the machine will keep cutting until you disengage the level.  If something goes wrong and you fail to disengage the auto feed, the tool will smoke, the machine will growl, belts will squeal, and you'll either blow a fuse or break the machine. 😮 

With well-designed CNC you typically have the machine sense when things aren't going properly and shut things down automatically, or make other adjustments to resolve the problem.

I realize this probably isn't much help, but I thought I'd chime in just the same.

Best of luck on your project. 👍 

@robo-pi

Hi Robo-pi! Thanks for the reply.

I am following various ELS (Electronic Leadscrew) forums.

I am "thinking" of just getting motorized Z and X where I can Brute goal-oriented plow-through 🤣 cut.

Using this as a learning experience looking forward to learning PID.

I could always buy a commercial kit, that is always an option.

I would like CNC on my mill largely to cut circles and curves.

I am also setting up a rotary encoder on my spindle for RPM.

I am going to need coding help.

Ralph

Just in case you might be interested, I'll tell the story of my homemade DRO.

It's kind of silly so be prepared to have a belly laugh.

I was going to design a serious DRO (Digital Readout for the non-machinists reading this).   I was going to  use an Arduino and rotary encoders as you mentioned.   And this would allow me to do fancy things like having instant coordinate transformations, and pre-programmed data sets for doing repeat operations.

But there turned out to be a problem,....  I'm extremely lazy! 🤣   Well, to give myself a little bit of credit I have limited time as well, so the played a factor in my final decision.

And here's my final decision:

My immediate goal was to have a DRO simply to know when I'm reading the bottom of a hole when cutting an internal bore on the lathe.  This is what sparked my initial desire for a DRO in the first place.   There are  two reasons for this.  The first being that the lines on my manual dials are not easy to read.  And secondly whoever designed this lathe was a complete idiot because there's no way to set the dials to relative zero.  So you need to keep remembering weird numbers that just happen to be at the bottom of your hole.

Solution:

I bought a bunch of cheap plastic digital readout dial calipers.   They were extremely cheap.  Like $4 a piece.  I bought about 5 of them.

6" LCD Digital Calipers

These only measure to 0.01" on the dial, but they are actually much more precise in reality.  I'll explain in a moment.

So what I did was use small C-clamps to attach one end of the caliper to the lathe table and the other end to the lathe bed, or tailstock base.   Obviously these need to be set up for every job and will have a max travel limitation of 6 inches.

But since the bore I was making was less than 3 inches deep this worked really well.

These cheap calipers have a ZERO button so you can zero out the display at any location.  So I ran the boring boring bar into the workpiece until it just bottomed out.  Then I pressed the zero button on the caliper.  Then after backing the boring bar back out I staring cutting the bore.  I just ran the boring bar into the hold until the cheap dial caliper JUST turned to zero.

Now it's true that the readout on the dial caliper only reads to 0.01".   But using it in this way I was able to achieve an accuracy at the bottom of the bore closer to 0.001"  The reason being that I would stop at the very instant the  readout turned to zero.   You could then continue on another 0.01" before the display would change to -0.01".   So it would remain saying ZERO during that hundredth of an inch.  But if you actually stop at the very moment the display turns to zero, it pretty close to having an accuracy of 0.001".

Anyway, these have become my makeshift DRO.   If you came into my shop you might see cheap plastic calipers clamped onto various parts of my machines.  I even use this on the drill press when I want to drill blind holes.   It works really well, and they are easy to set up because when clamping them onto the machine position is totally unimportant because you eventually end up just zeroing the display out and that's what gets everything in sync.    You can zero out at the beginning of a cut and then cut until  you get to the target dimension, or you can set the tool at the target dimension, like I did with my boring operation, and then use zero as the target.

Either way they are actually accurate to about 0.001" if you go by when the digital readout JUST turns over to the number you want.

So as silly as this sounds it actually works.  I think 5 of these cost about $20 and I've been using them everywhere.  I also do a lot of woodworking and I use them like this in the woodworking shop on various machines.

The bottom line is that for $20 and NO WORK at all, you can basically have some form of DRO that isn't too shabby.  It's not as nice as a DRO I might have designed using an Arduino and encoders.  But then you've have a dedicated Arduino with encoders wired onto the machine, etc.  Yes it would be nicer.  But just clamping on a plastic dial caliper when I need a DRO reading actually turned out to be much simpler. Just don't tell any "real machinists" that I did this or they'll be screaming that I'm using junk equipment.  Which of course would indeed be true. 🤣 

But hey, it works! 👍 

It seems to be good enough for the jobs I'm doing.  You can squeak 0.001" precision out of these by just going by when the display just clicks over to the number you want.  If you stop right there you'll be within a mil of where you wanna be.

Of course this has nothing to do with CNC and what you would like to do.  But I thought I'd just share this cheap trick for whatever it might be worth.   $4 a piece how can  you go wrong?   I also use these all the time just for making quick ball-park measurements.  Having 5 of them laying around the shop has proven to be worth the 20 bucks in and of itself.  I find myself reaching for one all the time.  The especially come in handing in the wood shop where the 0.01" inch accuracy is more then sufficient for woodworking.  They also have metric button that serves not only to measure in metric, but it's also an instant converter.  Just dial in the number you want to convert and press the button to get the measurement in the other system.  In fact, I sometimes use them just for that person when drawing things up in CAD.

Posted by: @ralphxyz

Using this as a learning experience looking forward to learning PID.

By the way, Paul McWhorter has a really good course on PID.

9-Axis IMU Lessons

He doesn't get into PID until lesson 26.  It would probably be worth taking the entire course.  Then you'd have all the prerequisite information and experience to fully understand PID. 

Paul's lessons are superb.  He is very good at explaining every possible detail.  You'd be hard pressed to find a better teacher.  He's as good as Bill's DBW videos, with the major difference that Paul makes entire series on a single topic.   So Paul's videos are more like entire courses.  Whereas Bill's videos are typically a one-shot deal focused on just one thing at a time.  Both are great.  Just different styles.   I don't think Bill covered PID yet,  If it did I must have missed that episode.   It would be hard to cover PID in any depth in just a single video I would think.

In any case, Paul's course on the 9-axis IMU sounds like it would be just the ticket for what you would like to learn about PID.  Because, as I say, there's a lot of prerequisite info that you should be aware of before you even look into PID and Paul's course walks you though all of that preliminary info.

Thanks Robo Pi, that is cool, I have seen others that used calipers so you are not alone.

I haveiGaging DRO on my mill, I use TouchDROfor display it works great.

I really cannot get in the habit of using the dials to say nothing about how hard they are to read.

I "should" be able to use the rotary encoders on my leadscrews for position, ha, someday maybe.

I am starting a new thread as I am having problems with the Big Stepper project.

Ralph

Posted by: @ralphxyz

I really cannot get in the habit of using the dials to say nothing about how hard they are to read.

I don't mind using well-made mechanical dials on a good machine.   Especially when they have the little thumbscrew so you can zero them out whenever you want.   My lathe is a cheaper model.  The hole machine was only $2500 brand new.  And I think I even bought some accessories on that same order.  I have a dividing head that I think may have been on that order too.

In any case, I know that my current machine is one of the lower-end machines.   But it serves me well as I seldom need to do any work to within 0.001", especially over a long distance like a long shaft.   Most everything I do doesn't require anymore precision than 0.005" at the at the best.  Save for possibly some press-fit work, but usually press-fit jobs are also fairly short distance cuts.   My machine will hold to 0.001" if  you're really careful with it.   In part because of modifications I've done to it after I bought it. 😊 

I would love to have my old South Bend lathe back.  I had a lot of accessories for that lathe including the taper attachment and a tool post grinder.  It was nice.  No point in crying over spilled milk, (or a sold machine).

Anyway, best of luck on your project, I'm sure you'll get it all sorted out.   You definitely came to the right forum for advice on electronic control, stepper motors, and rotary encoders.