Messages

171

General Mach Discussion / Re: laser cutting ally plate

« on: February 19, 2013, 08:26:11 PM »

I use a commercial shop whose business is mostly laser-cutting.  They have BIG machines!  They won't even do 1/2".

Regards,
Ray L.

172

General Mach Discussion / Re: NeverStall Stepper Motor Controller

« on: February 19, 2013, 01:19:45 PM »

I have always struggled with the logic, and perceived benefit, of such systems.  The explicit base assumption of such systems is that the motor/controller simply cannot provide the torque required to do the job correctly, which means the system was poorly designed from the start.  "Closed loop steppers" seem a crazy expensive and complex solution to poor design.  For less money, you could design the system properly, and never have to worry about losing position.  For about the same money, you could build a servo system, and likely get better overall performance.

And, note that, even in the video, the motors do NOT maintain position.  When the guy grabs the wheels and turns, the motors move.  The only thing that's different is that AFTER he lets go, they return to where they should have been all along.  How is that "unstallable"??

Regards,
Ray L.

173

General Mach Discussion / Re: M3/M4 spindle reverse safety?

« on: February 19, 2013, 01:15:13 PM »

Those contactors can be used to create an interlock that will prevent the motor from reversing *while* powered, but will not prevent the sequence:

Motor on CW, Motor Off, Motor on CCW  (or the reverse)

from being executed quickly enough to blow the controller, due to the fact that the motor could still be spinning at high speed CW when the CCW direction is engaged, which is the real risk.  Preventing a change directly from CW to CCW, or vice-versa, can be implemented with just two DPDT relays, such that one relay is disabled any time the other is enabled.  But the CW-Off-CCW sequence, or its reverse, is also deadly to the controller, if the motor is not allowed to spin down during the Off portion.  That can only be prevented by use of speed sensing, whether direct (e.g. - an encoder, speed switch, etc.) or indirect (e.g. - measuring back EMF), or by ensuring the Off state persists long enough for the motor to coast to a stop.

Regards,
Ray L.

174

General Mach Discussion / Re: M3/M4 spindle reverse safety?

« on: February 19, 2013, 12:27:40 PM »

The biggest problem you face is that it is not enough to simply prevent the rotation from being reversed.  You need to ensure that the motor is stopped, or very nearly so, BEFORE it can be reversed.  This means either ensuring that BOTH directions are disabled for a long enough period of time that the motor is certain to have coasted to a stop, or to actually sense motor speed, and not allow the motor to be re-energized until it has stopped.  Using a timer is the simpler approach, but then how do you "tell" Mach3 that the spindle is not running for several seconds?  This approach would require at least two relays, and a timer, either electronic, or a time-delay relay, and custom M3/4/5 macros in Mach3.  Either way, it's not pretty, and I really think you're much better off simply using a manual reversing switch to make it really fool-proof (well, assuming the operator is not the fool....).

Regards,
Ray L.

175

General Mach Discussion / Re: M3/M4 spindle reverse safety?

« on: February 19, 2013, 11:47:27 AM »

You REALLY don't want to depend on software to protect you from that.  What you need is a hardware interlock, completely independent of Mach3.  If it happens even one time, your motor controller WILL be toast.

Regards,
Ray L.

176

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: February 05, 2013, 11:36:36 AM »

Steve,

Feel free to call or e-mail if you need any help with the KFlop.  I'd also be happy to send you all my code as a starting point/educational tool.  I"m sure there's a lot there you could use, with straight-forward modifications.

This really is the golden age of cheap, powerful little MCU boards, isn't it?  Seems like every couple of weeks there's a new board that's better, stronger, faster, cheaper than the best of the previous week.  My PDB and toolchanger will be built around a lowly Arduino ProMini.  At about $6 each, it's hard to pass up.  I've been wanting to try the Propellor. Not so much because I need 8 processors on a chip, but I'm a multi-processor guy from way back - I was doing HyperCube research at CalTech/JPL back in the '80s, and helped build what was, briefly, the worlds fastest computer, the CalTech/JPL Mark III Hypercube.

I think you've made the right choice re: rotating the head.  But how are you going to drive the Z axis if you fill the column?  Where will the ballscrew go?

Regards,
Ray L.

177

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: February 04, 2013, 06:11:06 PM »

Steve,

No secret - I ordered a Novakon Torus Pro Servo bed mill - 25"X x 15"Y x 12"Z travels, 2HP 3-Phase, AC servos, 500 IPM Rapids, ground ballscrews, linear rails on Z.  Best of all, it's EASY to fully enclose, so first project will be fully enclosing it with 8020 and Plexi, and finally get to use the high-pressure (60 PSI) coolant system I've had sitting in the corner since I built it last year - WAY too messy on the knee mill.  I will, very shortly, rip out the BOB and 86 Mach3, and put a KFlop in it so I can run my CNC controller app.  This is the biggest machine I could find at a reasonable price, and the guys I've talked to that have them are VERY happy.  It seems to be quite rigid, and very accurate.  I hope to also add linear scales, fed into the KFlop, to get a bit more accuracy out of it by compensating for thermal errors.

Regards,
Ray L.

178

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: February 04, 2013, 12:46:48 PM »

I also plan to have a macro that will automatically touch off all loaded tools (I can tell which slots are occupied, and which are not), and load the tool table automatically.  I think that will be a nice convenience, and time-saver.

This was my conclusion also, but it does not seem so easy to do, at least on BT30 where there are holders with very long 'noses' that could then have very long cutters in them. Conceivably the delta could be 6 or 8 inches from a short holder+short tool to an extended holder+long tool.  Seems like moving a touch-off pad (or laser) with a LOT of travel would be the only way to do it.

I spend much more time thinking about designs, and much less time actually building them. And, in most cases, they work almost perfectly on the first try.

Well, my observation is that you built an entire ATC over quite a long period of time with prototype components that were later replaced with final design parts. Now you have designed an altogether different one which, as described, should be quite an improvement on the first. That process seems pretty normal to me . . . . . Just sayin' 

The more common approach I've seen far too often is to rush into construction, then spend months putting on "Band-Aids" for all the things that were not well thought out up-front, and you end up with something more complex, and expensive, than it needed to be.

Seems you have discovered my secret method. Except that after about three band-aids, I scrap the whole idea and start over . .   

Favorite saying;

"Trip of thousand miles begin with one step"
 - Asian probably - don't know who  - circa:  long time ago

"Evrybody is incopetent, just at differnent things"
- Will Rogers maybe?  cira: some time before he died

"I cut it off three times and it is STILL too short"
- my mentor . . . .  explains a lot, huh 

Steve,

My approach to the touch-off macro is to have a "compliant" touch-plate - one you can approach at high speed without risk of damage to the tool.  So, you do an initial high-speed probe, to figure out the rough length of the tool.  Then, back off a short distance, and do a second, slow, probe to measure the length.

If I'd had an uninterrupted period of time to do the ATC, the total time would've been down to a few weeks.  The parts I re-made were more to refine dimensions that I could not measure accurately, rather than fundamental design changes.  The initial design is VERY close to as first drawn.  The new design has a completely different set of constraints, and the MAJOR advantage of being aimed at production, rather than a one-off.  That makes many things practical that were not in a one-off.  The basic carousel design, BTW, is nearly identical, except for the number of tools, reducing the maximum allowable tool diameter (both per the customers request), and the change to internal Geneva (this helped make it more compact).  So, a lot of the initial design has been carried over.  The major change was making the carousel fixed, and adding the transfer arm, which both helped make the whole system more easily adapted to other machines - an important consideration for a "product" I hope to make lotsa money from.  This added complexity, but n0ot much.  This is where all the major design changes are.

Regards,
Ray L.

179

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: February 04, 2013, 12:24:48 PM »

Steve,

I've never once had the need to rotate the head on my knee mill, and I really wish it was rigid.  I would expect anything you can do with a tilting head, you can do just as well by fixturing the workpiece differently, or using a 4th axis.

I agree completely about CNC-ing knee mills.  If I had it to do over again, it's not where I would start - too many compromises.  My new machine is a bed mill.  I think most of the reason there are so many CNC'd knee mills is just that there are so many knee mills out there, and often for very cheap.  Bridgeport probably just took the path of least resistance on their early machines.

Regards,
Ray L.

180

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: February 04, 2013, 10:08:29 AM »

To Anyone: 

- How important would it be to have a manual (pendant or equiv) method of operating the ATC? In practical terms, the carousel has to be loaded with tools and so on. My thinking is that inputting a tool change into the MDI is adequate, but it would be good to know if there are any 'wish list' methods that people would like to have, and/or to know what 'real' ATCs provide in terms of manual operation. 

- How important would it be to have the ATC perform some type of automatic tool touch off?  It would be good to get a discussion going on how this works on machines that have it, and how it might be implemented. I saw one that appeared to use lasers.


To Ray:

- You originally mentioned that you were keeping the Geneva for the carousel in your new design, but your latest description says 'servo' powered.  Are you using that term generically, as in 'motors' (i.e. steppers) or have you come over to the dark side?

- In *easily converting your new ATC to work with 30 tapers, how do you accommodate the drive dogs?

*you always say everything is 'easy'. Flying is easy for a duck. It is a bit of a challenge for a donkey. Depends on how you're equipped, I would say . . . 

Steve,

FWIW - On mine, I will provide a macro or modified screenset to "assist" the user in loading tools.  It will sequence through the slots, bringing the transfer arm to the forward position so the user can put the tool into it, then it will put it in the carousel.  On my current one, I added buttons to rotate and home the carousel to facilitate manual loading/unloading of tools.

I also plan to have a macro that will automatically touch off all loaded tools (I can tell which slots are occupied, and which are not), and load the tool table automatically.  I think that will be a nice convenience, and time-saver.

I kept the Geneva, though I switched from an external Geneva to an internal, for a much smoother motion profile.  It is driven by a real servo motor, with encoder, mostly just because it was convenient, and only a very few $ more expensive (<$5 more) than the plain gearmotor I used on the first one.

When/If I do 30-taper, the tool "forks" on the carousel and transfer arm will have locating tabs for the drive dogs, to maintain proper orientation.  The spindle will be either servo-driven, or I will provide some simple indexing mechanism.  Indexing is already designed into the PDB for the target machines with 3-phase spindles.

The one rule that I have used my entire career is "If it's complicated, you haven't done it right".  I never start building something until I've gone through enough iterations of the design that I am convinced it is about as simple as it can be.  This approach has *always* paid off, and has allowed me to consistently do things in short order others told me I'd never be able to do at all.  I spend much more time thinking about designs, and much less time actually building them.  And, in most cases, they work almost perfectly on the first try.  The more common approach I've seen far too often is to rush into construction, then spend months putting on "Band-Aids" for all the things that were not well thought out up-front, and you end up with something more complex, and expensive, than it needed to be.  ANYTHING can be boiled down to very simple pieces if you think about it long enough.  Just yesterday I figured out how to eliminate one whole motor from the new ATC design, with no loss of functionality or performance.

A few of my favorite quotes:

"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." Antoine de Saint-Exupery (1900 - 1944)

Everything should be made as simple as possible, but not simpler !
--Albert Einstein

Any intelligent fool can make things bigger and more complex... It takes a touch of genius --- and a lot of courage to move in the opposite direction.
--Albert Einstein

Regards,
Ray L.