Messages

451

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

« on: December 30, 2012, 09:45:35 AM »

Steve,

BTW - I'm also in discussions with a machine manufacturer, to potentially design a PDB/ATC system for several of their machines, loosely based on my current design.  There are, of course, a number of things I would do differently on the second go-round.

Regards,
Ray L.

We should throw in together. I'll do the mechanics and you can do the controls. I don't like that part so much . . .

452

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

« on: December 30, 2012, 09:40:49 AM »

Those are the biggies. The rest is, as you pointed out, to keep the machine from chewing its own ankles off.

I would try to design in a failure point to prevent that.  On my ATC, the weak point is the attachment of the tool "forks" to the carousel, which are Nylon screws.  If a major jam were to occur, those screws would simply shear off, and the tool holder, and folk would fall on the table.  The only failure I can see right now with any possibility of breaking anything would be if the PDB tried to engage while the spindle was running in reverse.  Since I've never once had to run in reverse, this one doesn't concern me.  

Running in reverse does present some additional problems. I have a big face mill that runs in reverse, hard tapping of course involves reversing the spindle and I also run certain grinding cups in reverse depending on the setup.

If the PDB were to engage while the spindle is running forward, the drawbar would simply unscrew, dropping the tool and collet.  Not good, but not catastrophic.  Even then, the spindle brake *might* be enough to over-load the motor and stall the spindle, though I have no intention of testing that theory....  

You have the luxury of designing and building for your own use exclusively. I have to imagine the stupidest thing a person could possibly do and then try to prevent it. Her in the States, everything you buy has twelve pages of warnings and one page of actual operating instructions. First you have to say 'do not use this toaster in the shower' and 'do not eat the insulation' and 'do not put the large hot coffee between you legs and then drive out into traffic'. Each one of those idiotic warnings is part of the settlement from a law suit. It is hard to explain to people on the other side of the pond how rediculous out legal system is here.  

Once I get a spindle sensor on the machine, these issues also go away, as neither the PDB
nor ATC will be allowed to engage unless the spindle is confirmed stopped.

Regards,
Ray L.

A HAH!  You are soooo busted my friend! You have more sensors to add.  I'll just puit that beer back on the shelf a bit longer, thank you very much!  

453

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

« on: December 30, 2012, 09:27:36 AM »

Steve,

Here is my ATC code:

#ifndef ATC_H
#define ATC_H

#include "KMotionDef.h"
#include "../Common/CommonDefs.h"
#include "../Common/PDB.h"


Ray L.

Well this explains things a bit. We have counting different beans, methinks.

What you have here is the conductor and the orchestra is elsewhere. You see I would count the libraries as part of the ATC code. Or certainly at least the ones you wrote yourself. I like looking at your code as there is unsally a tasty morsel or two of the 'tips and tricks' variety, but really I was interested in seeing what actual pieces you used for sensing and how those are mounted and while I can see some checks in your code, the routines are not present so it is hard to divine what sensors you are reading and what reaction is called in response to a fail.

For example, I see ATC_PIVOT_SENSE and ATC_LIFT_SENSE but that doesn't explain what you are doing specifically.

You usually have some clever trick up your sleeve and it take some coaxing to get it out of you . . example; the relay switched torque on your drawbar stepper drive. You had to have something slick going on in order for the thing to work the way you described, because there drive does not have that capability . . until you figured out how to add it.

So if you feel so inclined, I for one would love to have some details on exactly what actions you are monitoring and most importantly why you chose those actions and not others and how you accomplish the tasks.  Really the whole methodology and thought process is what I'm after if you are willing to share that. 


                                                                                                                                                                                               

454

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

« on: December 30, 2012, 08:57:22 AM »

Steve
 The second list looks  better to me
I try and interlock things as much as possible on my machines. I am the only person that uses them so its more for machine safety than personal safety that I take that route. The big lathe could rip itself to bits in seconds if something wasnt right and I didnt have a saftety check in to see it wasnt right.
Mills are not so bad in that they wont likely do as much damage to themselves but bent arms or carousels or whatever are still a real possibility so I think your approach is the way to go.

I have gotten a lot of positive responses on the spindle and the ATC including a couple of dealers/manuf who are interested in incorporating them into their machines  (along with the InTurn™ 4th axis). I am seeking product liability insurance at this time with the intent to sell the spindles. I am not able to build a proper 10k + RPM spindle just yet, but that is coming. My immediate concern is the same as yours; primarily torn up equipment and down time, but long term, the serious consequence would be a tool holder coming out of the spindle at 15K RPM and taking a brisk stroll across the shop floor. Mach is not exactly a stable program and PC's in general are prone to tantrums now and then. If the power goes off momentarily, it is hard to predict what a PC is going to do. This happened recently here and air valves were going on and off as the PC tried to get its act together. That's why I have an electric solenoid operated positive mechanical interlock on the drawbar actuator. There is no way to accidentally release a tool. However, an equally important task is to make sure the tool is gripped and seated properly before starting the trip to 15k.

Those are the biggies. The rest is, as you pointed out, to keep the machine from chewing its own ankles off.

 I like doing these things in a PLC, main reason is I find ladder logic, well how can I say it, logical and it comes easy to me. The Chirons ladder if printed out at 100% would take 46 pages of A4 paper, I wouldnt know where to start trying to do all that in VB let alone any other programming language.
Hood

Probably a good bit of that code is for communicating with the mother ship and I won't have that feature . . .

The pair of Mistu drives will help a lot in reducing the coding and the sensor count as they will fault in some of the situations and they have a position reached signal that will serve as the sensor for several of the steps. In taking advantage of that, the controller would not be able to pinpoint a failure quite as accurately, but the operator can snoop around a bit to figure out what stopped the party.

455

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

« on: December 30, 2012, 08:30:26 AM »

Looking good Steve.
I'm not having any of the issues that you are with the Bellevilles but I suspect that it's because mine are external. The coil spring idea In my opinion is the best way to go. As soon as I get the last bits of my tool changer done I'm going to be redoing the drawbar with the coil spring. I see you used a die spring instead of the valve spring.

Pretty much all of my problems with the disc springs was binding and galling in the containment. First they were chewing on the ID of the tube so I made a fatter shaft to keep them centered and off the tube ID and they then chafed on the shaft. I solved that (mostly) by tediously sanding flats on the 'mating' surfaces, but in so doing, I lost a good deal of the already barely adequate travel. Only a few thou off each spring, but there were 60 of them so it adds up to a significant number. The experience was expensive, but useful. I would know what to do differently if I ever have to go 'back to well' in the future. However at this point in time, I'd rather be poked in the eye with a sharp stick than touch another Belleville stack 

If you are using a 30 taper I will give you the part number and source for the die spring (in a PM). I saw the top of your spindle and it looks like it will fit in there quite nicely. If you are using any other taper, including R8, then you will need to select your own spring. The die spring was considerably cheaper and is a single spring which simplifies things. The damping of the multi spring valve spring is not needed in this application. FWIW; I made the washers above and below the spring fro 416 SS. The top washer is .26" thick (not counting the slight relief at the top to clear the snap ring) but it is backed up by a wide retaining nut that slightly overlaps the spring so the washer does not take the stress in a cantilever. The ball holder is undoubtedly the weak link. I have tested mine to 3,500lbs tension so I have the minimum 2X safety factor.

I have a question for you about Pull stud tools. Is the gripper supposed to provide lateral support as well as upward pressure or is the taper supposed to take care of that?

Derek

I don't know the answer to that, but I would speculate that the taper is going to dominate over any misalignment in the gripper. The consequence of a misaligned (or low precision) gripper is that not all of the balls will be sharing the load. For example, if the holes for two of the balls is even .003" above the other two, you will have only two balls holding all of the force (unless you make the gripper body from 'stretchy' material . .  which would be a really bad idea). 

Typically I only accomplish high precision or high finishes where they are necessary, Rough finishes and 'close enough' where it doesn't;t matter and 'normal' everywhere else. The gripper body is one of those pieces that requires precision, particularly in concentricity and the elevation and depth of the ball holes (the depth matters because the round shape effectively changes the height). The outer sleeve has to be reasonably concentric, but is not as critical, in my view, as the ball holder.  The Ball holder is tricky because you can't 'nibble' at tool steel of it will harden up on you so you have to take your best shot with a good setup and sharp tools and measure the result.

456

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

« on: December 30, 2012, 02:29:33 AM »

Actually, the sensors and code on mine turned out to be quite trivial.  The code is barely two pages of dead-simple C that took only maybe two hours to write and debug.

This is a surprise. I have a flow chart that runs for a couple of pages, let alone the coding. Even considering that what is 'trivial' to you is anything but trivial to most people, it would truly be amazing (to me) to be able to control an ATC with two pages of code.

This is the list of tasks that I envision need to be performed on my ATC.  I broke it down two ways; down and dirty and commercial/industrial  (OSHA).  All comments from any reader are welcome.

Simplistic: swing the arm 30 degrees
 
                 drop 4"

                 say a prayer

                 swing the arm another  60degrees
 
                 rise 4"

                 say another prayer

 

Safe:  

 

           Has the carousel reached the correct tool position?
 
           Is there actually a tool in the holder?

           ( we already know the claw is unoccupied because we confirmed that when it put the previous tool away)

           Open the safety interlock on the claw.
 
           Did it open?

           Swing the arm 30 degrees

           Did the claw close? (if it closed, then it has the tool, otherwise it cannot close)

           Is the tool holder safety interlock open?
 
           Release the tool from the toolholder (pneumatic)

           Is the tool released?

           engage the claw safety interlock

           did the claw safety interlock engage?
 
           lower the arm 4"

           did the arm lower?

           Is the mill spindle rotating?
 
           Is the mill spindle at the correct azimuth for tool change?

           lockout the mill spindle operation (can be done a number of ways)
 
           Swing the arm 60 degrees.

           Is the arm in position?

           Release the drawbar safety interlock
 
           Did the drawbar safety interlock release?

           Activate the drawbar actuator

           Did the drawbar actuator open?

           Raise the arm 4"
 
           Did the arm reach position?

           release the drawbar actuator

           Did the drawbar actuator release?

           Is the drawbar safety interlock reset?

           Is the drawbar height correct (i.e does it have the tool gripped correctly)
 
           release the claw safety interlock

           did the interlock release?

           Swing the are back 40 degrees

           has the arm reached position?
 
           lower the arm 5"

           did the arm lower?

           move the arm to the park position.

           allow mill spindle operation

457

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

« on: December 30, 2012, 02:00:18 AM »

Steve,

Nice work as always.  The time I spent playing with Belleville drawbars a few years ago convinced me I never wanted to mess with them again, and is what led to my stepper-driven drawbar.  I wonder why so many VMCs use them?  And huge stacks of them at that.

I hear numbers like 3k to 5k forces for CAT50. I hasten to say that this is just what I read on forums. I do not know the facts on this. However, if these numbers are accurate, then it would be difficult to achieve with a coil spring. Disc springs can be nested thereby multiplying the force.

BTW - I sent you a e-mail earlier today re: KFlop.  Did you get it?

Regards,
Ray L.

Yes, I did. I'm just now getting to my computer chores; e-mail, reading, posting, etc. I'll have a response for you on that e-mail and also your postings here after I have a minute to noodle over them.

458

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

« on: December 30, 2012, 01:48:17 AM »

This post is just some misc stuff that has been completed for the ATC.

Following photos are of the completed carousel mounting arm. In the next few days, I hope to have this and the swing arm mounted to the side plate of the new mill head.



A previously missing detail is the safety interlock for the drawbar actuator. This little guy sports a hardened pin that runs thru a hardened die pin guide bushing and interferes with the actuator movement unless it is retracted. i.e. the drawbar actuator cannot release the tool unless this pin is first retracted. Totalling all of the special parts and the time to design and build this component adds up to a fairly expensive little gadget.  However, safety features are immune from cost cutting and/or production considerations. 

459

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

« on: December 30, 2012, 01:34:11 AM »

Some progress to report.

Ding, dong, the wicked Bellevilles are dead and gone. Long live the spring!

Only after scrubbing BOTH sides of each belleville by hand to create flat mating surfaces would the springs stay aligned when compressed. However, that solution created another problem by reducing the travel to barely what was needed to release the gripper. It still worked, but it would not take much variation in a stud to have a tool hang up in the spindle due to insufficient travel to fully release. Worse, even after all of that effort, the disk springs still chafed on the shaft as seen in the following photo. Using disk springs specifically made for a machine spindle or 'nesting' much thinner springs to get up to the required force might have solved these issues. Nitriding the drawbar and tube would certainly help, but my patience ran out for the whole spring stack arrangement. There may be some compelling reason to use this method in certain cases, for example, in-line nesting of coil springs increases travel, but not spring force. However, for the BT30 spec, I see no reason not to replace a troublesome $60 stack of problems with a $19 die spring and not have to deal with the the spring stack issues at all.



Jumping ahead to the completed components:



Switching over to the coil spring was relatively simple matter of cutting a pocket for the spring and making retainers and guides. The angle in the next photo is intended to show the bottom of the pocket and it makes the snap ring grove look a bit odd, but it is a simple square bottom grove. One of the unsatisfying aspects of the disc spring stack was that with no tool in place, the drawbar would extend all the way up and press against the actuator making the spindle difficult to turn (for belt changes, etc). If the spindle was started in this condition, it would damage the actuator plunger and the top of the drawbar.

In the new arrangement, a snap ring at the top of the spindle makes a positive stop for the spring when there is no tool holder in the spindle. The snap ring is on order so it is not pictured.



And here is the spring installed on the drawbar and partially inserted into the spindle. Most likely, this arrangement could be added to an existing spindle with the spring on top of the spindle. This particular spring was selected for BT30 and the rate is 2550lbs. At coil bind you have approx 2,000lbs and for a gripper with a .21" release travel, you get a max hold of about 1,450lbs. Note that this in not adequate for R8, but larger springs are available that for that application. I have the arrangement set up so that any hold tension from 600lbs to the 1,450 max is available by simply adjusting the threaded retainer cap.

460

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

« on: December 29, 2012, 07:53:28 AM »

Ray, truth be told, I fully expect you to win. I just want the competition to be at the highest level, and I know you are capable of that. I have a selfish motivation, of course, but it also hopefully benefits the many readers of this thread to observe the process.

I think we agree that the mechanics, complicated as they may be, are not the lion's share of an ATC, but rather the control and sensors. I would speculate that those who can build the mechanism are many, those who can create an autonomous and safe control system are few. That's where I see the real competition. The finish line includes all sensors and 'release candidate' level fully functional control code. I also want to follow what Hood and other 'non-contestants' are doing with regard to sensors and control code.

To consolidate your questions from the last couple posts, let me say that yes, I am familiar with 'C'. There are several thousand lines of it in my InTurn™ motor control system. And less volume but far greated intensity code in my balancer. Although I am a lightweight with electronics, I get by with the 90% learn and 10% do methodology. 

I am going to acquire a Kflop board based on your endorsement. Initially, I just want to replace the smoothstepper, but I have similar needs to yours down the road, so the sizeable learning curve is an investment that will pay off, methinks. You mentioned loaning a board, but the way it is worded, I cannot tell if you mean loading an ethernet Smoothstepper or a Kflop board.   

As to machine complexity, I have 4 axis of Mitsubishi J3 series industrial drives (and motors) and the spindle is a Copley Controls Xenus drive pushing a big DC brush motor. I am starting to talk to these devices in real time to get at some of the pertinent staus info they provide and create a 'reactive' system that can act on the data from the drives to adjust the paramaters on a CNC machine in real time. Another machining center feature to bring down to we mere mortals. Hence my interest in your amazing work with the Kflop. Yeah, I did some homework on that.

Anyway, I threw this machine together quick and dirty to get enough Y travel to do a specific project. I have since boxed and welded up the column and now it has decent performance.  My 'permanent' mill will be similar, but larger, much heavier and of course will have the spindle and tool changer from this thread. Since the spindle is completed (except for the die spring) and the ATC is almost done, I am revisiting the pile of parts and the frame design. Today I purchased a 9" x 42" Bridgeport mill table to add to the pile.

There has been no progress on my ATC because I had some unanticipated work to accomplish, however, I expect to start making progress again on the ATC today. I am simultaneously making a new spindle from A6 tool steel, (which will be fully hardened and ground) and ditching the bellevilles. I expect there will be a lot of interest in my big fat die spring because it *probably* can be implemented on an existing spindle which has no way to get the typical disc spring arrangement installed. Next couple days I will post some photos of the ATC assembled on the side of the new head.

I see from the photos you posted that the swing arm has been eating its Wheaties. Very nice piece!  I also note the pivot has an upper and lower mounting. Double nice. Significant improvements from the prototype, as one would expect. Q: curiosity, how did you form the smooth curve in the skirt?