Messages

291

General Mach Discussion / Re: Odd stalling or stuttering, loss of position

« on: September 30, 2012, 12:55:28 AM »

Why are you running the kernel at 45kHz?  You should use the lowest kernel speed you can, and maintain your rapid speed.  There is *no* advantage to running the kernel faster than necessary to enable the maximum pulse rate you'll actually use.

What acceleration are you using?  Setting acceleration too high is a good way to cause lost steps.  You should determine what acceleration *appears* to give the best performance, then back off 30-50%, to provide plenty of margin.  If you set it to the maximum that *appears* to work it will NOT be reliable.

Regards,
Ray L.

292

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

« on: September 28, 2012, 07:21:24 PM »

   Made a bit more progress today - only had a couple of hours of shop time.  I rigged up a power supply for the Geneva motor, and did several dozen complete "manually sequenced" toolchanges (pushing a button to power the Geneva, flipping a valve to actuate the lift).  I see no significant problems whatsoever - it seems to work very nicely, even when fully loaded with heavy tools.  I got one half of the guide pin done - a 1/2" tapered pin - mounted on the side of the head, and just need to make the "socket" part that goes on side of the pivot arm.  This will ensure absolutely precise vertical positioning of the forks, and provide a hard stop for the pivot arm.

Regards,
Ray L.

293

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

« on: September 28, 2012, 11:30:52 AM »

Very nice.

The only advice I would offer is to put an upper support on the arm pivot pin. That is a long lever and when you get that carousel loaded with tools, it will put quite a moment load on the pin. Aluminum is not the best choice for the mount, in my view, due to the modulus of aluminum. Your mechanism moves a load vertically at the end of a long arm. This arrangement will induce significant vibration and aluminum has little ability to damp that. An upper support on the pivot pin would address both the moment on the pin and the vibration (bouncing) of the loaded carousel.

An upper support would convert the moment on the lower bracket to compression and put the upper bracket in tension. The pin force would be converted from moment to shear. Moment loads are a bitch to calculate, while shear is easy, so there is an ancillary benefit as well.

 
The whole mount bracket, and probably the arm, will be re-made once it's all working.  I already had to modify it once, so it's a little "hacky" already.  Though it is surprisingly strong just as it is.  Also, the small amount of slop/flex it allows is not really a problem, as there will be a tapered pin and socket on the side of the head to ensure precise alignment of the ATC to the head.  I wanted to support the pivot pin with a U-shaped bracket, but didn't have any material large enough to make that, so built what I could with what I had on hand.  Most of the time, when making something like this, I'll do a quick and dirty prototype (what this is), to verify dimensions, fit and functionality, then refine the design, and re-make most/all of the parts for the final "product".

edit: one other comment; You probably already have something in mind for this, but just as an observation, the shafts running thru the arm at the carousel would benefit from bellows or a scraper type o-ring to keep the nasties (evidenced by the wall behind the carousel) from jamming the movement.

 

The clearances are tight enough I doubt anything could get in there, but I will do something to at least prevent accumulation of crud up there.  Something as simple as a sheet-metal shield, covering the "front" (when parked) and top, would do the job.  It would also be easy to fit lip seals on the top and bottom of the arm.  Note the "main" shaft does not move, only the two smaller "guide rods" move.

 
Got a nice "bonus" - yesterday PM I spent a few hours tweaking a few of the parts, and adjusting things up carefully.  I was originally afraid I might have to lose up to 1/2" of quill travel, but now have it to where I'm losing only about 1/10", and, with a simple mod to the lower support for my quill drive (just counter-sinking some screws), I can easily recover that 1/10", and lose no quill travel at all (I currently have just a hair under 5").

294

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

« on: September 27, 2012, 04:06:32 PM »

Making good progress on the ATC.  The whole carousel and "lift" mechanism is working now.  The only major missing pieces are the air cylinder that swings the ATC into position under the quill, the side covers for the carousel, and all the "sensors".  Lots of little details to take care of (like that ugly stack of cr@p on top of the air cylinder in the last photo), but I see no reason this will not work very nicely.  Operating it manually, it very reliably locks onto the tool, yanks it out, and puts it back in.

Regards,
Ray L.

295

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

« on: September 23, 2012, 03:15:44 PM »

Steve,

Just for your amusement, here is the current state of my ATC

Well, if I am to be amused, I must get out my RED pencil   . . . kidding, of course. Your work is always first class and logically conceived.

Interesting thing is that what you have is something of a hybrid between the typical moving carousel arrangements that I have seen and with what I am doing. You move the carousel . .  so far fairly conventional . . . .  but as always there is the 'Kabibble Twist' on it. You move it with an arm! That removes one of my objections to the travelling carousel concept . .  that being the carousel hanging over the table. This is the first arrangement I have seen with an arm swinging the carousel. Very clever indeed.

Couple questions if you don't mind (not to worry no RED pencil here);

1) Another of my quibbles with the DIY setups is lack of protection for the taper (or 'stud' I suppose in your case). Do you have any plan to protect those surfaces from swarf?  Do you consider that a must have or optional?

Yes, the carousel will be enclosed (a circular top cover, and 4" high side covering, so the tool holders are completely enclosed top and sides, with only longer tools exposed.  There will be a rotating door to uncover the selected tool, operated by a simple cable as the carousel swings into position.  I think this, alone, will suffice for keeping crud away from the tool holders.  If not, it will be easy to rig a Plexi or sheet metal shield between the back of the table and the front of the carousel when it's parked.

2) What kind of sensors are you planning? At what points in the process do you recon a confirmation is required before moving to the next step?

I haven't worked out all the details, but I will be using a combination of microswitches and Hall sensors.  Switches will be used to ensure the arm moves to both extremes of motion.  This will allow me to stop operation if the arm jams for any reason.  Also to ensure the carousel "lift" mechanism moves full travel, so I can stop operation if the tool does not move fully into, or out of, the spindle.  There are Hall sensors on the Geneva to indicate it is "in position", and also one to indicate it is positioned at tool 1.  This will allow me to "home" the carousel, and track position during moves.  I also expect to have a hall sensor to detect a toolholder  is present in the selected position, so I can tell that it correctly was loaded into the spindle, or extracted from the spindle before proceding.  I think that should be enough....

3) Probably you would get around to this eventually, but I am impatient so . . what will drive the Geneva?

The Geneva is driven by a simple DC gearmotor, about $35 from McMaster.  I hope to have that mounted and working no later than tomorrow.  I did prototype it a few months ago, and it worked perfectly - very smooth and quiet, and very precise positioning, with near zero torque required to rotate it.  The motor I'm using is not blindingly fast, but adequate - about 1 second per tool.  This should make the worst-case toolchange time maybe 15 seconds,. and the more typical (sequential) probably under 10 seconds.

4) did you make the holders in the carousel or are they a Tormach part?

Made my own, though they are very similar to the Tormach (kinda have to be....).  They're cheap and easy to make, and a designed-in failure point in case of a jam.  They're attached with #10 Nylon screws, so a jam should simply rip the fork off the carousel, breaking only the screws.  Note that I could very easily fabricate a new carousel disc, and tool forks (no more than half a day's work), and switch the whole thing over to 30-taper.  No other changes should be required, other than perhaps extending the vertical travel of the carousel, which would just mean swapping out the air cylinder.

5) Will you use a sparate PLC to control the sequencing or will it be integrated into your Kflop system?

Sequencing will be controlled entirely by the KFlop for now.  Until I run out of I/Os (and I'm not that far....), there's really no reason to do otherwise.  Once it's working, moving the functionality to a dedicated micro would be really trivial, and I'd probably just go to a simple RS232/RS485 serial interface (as I'm already doing on my pendant).

6) How do you do the thumbnail - to - full size photos?

I don't....  I just attach the photos using the built-in function on the forum.

296

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

« on: September 23, 2012, 02:02:19 PM »

Steve,

Just for your amusement, here is the current state of my ATC - I finally got some time to work on it yesterday.  It's mounted on the machine, and, operating it manually, it appears to work perfectly - the forks slide on and off the tools very nicely, and the tools slip in and out of the spindle effortlessly.  I hope in the next few days to get the top plate of the housing done, which will let me mount the geneva motor, and see how that all works under power.  Then, it's just a matter of mounting the two air cylinders - one long one to swing the ATC to the spindle, and back to the park position behind the table, and the second to push the carousel down for ejecting tools from the spindle.  I'll also need to re-make my Y/Z way cover, to make it narrower so the ATC can get back as far as possible when parked, and re-make my coolant "collar", which right now mounts to the bottom of the spindle, and interferes with the ATC.

Regards,
Ray L.

297

General Mach Discussion / Re: How much stepper power do a 1-1/2 HP Bridgeport need to do a good job ?

« on: September 23, 2012, 01:56:41 PM »

OH.... I can see in the specs. for the 3 drivers that they ll accept 80 volt DC input, do you advice that ill buy three additional 80 Volt Switchmode supplyes for the steppers or are we just talking marginal improvements here ?

Leif

Speed will increase, roughly, proportional to voltage, up to a point.  So, 80V will buy you 20-30% more than 60V, but then you also have to be concerned about whether that 80V rating has any real margin on it.  If not (which is common in Chinese designs), then an E-Stop when the machine is running at full speed could blow the drivers.  Personally, I wouldn't throw any more money at it until I saw how they worked.  You can easily swap out the motors later, and with a better motor 60V might be OK.

Regards,
Ray L.

298

General Mach Discussion / Re: How much stepper power do a 1-1/2 HP Bridgeport need to do a good job ?

« on: September 23, 2012, 11:37:35 AM »

Those steppers will work, but their performance, particularly in terms of rapid speed, will far well short of stellar.  Those motors are VERY high inductance, which, on it's own, severely limits top speed.  Further aggravating the problem is the fact that the power supply, at only 60V, is WELL below the ~150V required to get the best performance those motors are capable of.  My guess is you'll probably be limited to rapid speeds well under 100 IPM.

Though the drivers allow micro-stepping up to 256X, this is essentially useless.  You'll want to use the 8X, or at most 16X setting, to keep your pulse rates reasonable.

Regards,
Ray L.

299

General Mach Discussion / Re: burned a servo

« on: September 23, 2012, 01:50:28 AM »

What motor polarity is correct is determined by how the encoder is connected, as well as what rotation you consider to "correct".  You cannot go purely by wire colors.

300

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

« on: September 21, 2012, 12:07:20 PM »

Steve,

Like Terry, I too question the real-world value of a super-fast toolchange time.  I can't imagine that it would save more than a few minutes per day at the cost of significantly increased complexity, and opportunity for disaster, due to higher speeds, and generally higher precision required.  I think you can quickly get to the point where doubling speed will take 10X the time and 2X the cost, to make it as reliable as a slower, simpler machine.

Re: the speed of a Geneva, this, too, I think is a bit of a red herring.  Perhaps a high-speed Geneva will always be a bit slower than a max-performance direct-driven mechanism, but I think the overall difference in toolchange time would still be small.  I'm running mine VERY conservatively, and it runs under a second per tool pocket.  So, even with a 24-tool carousel, max seek time would be 12 seconds.  I'm sure I could easily double that.  Beyond that point, you have to start worrying about the tools flying out as the thing moves.  The biggest job I ever did only used about 12 tools, and that one took hours to run, so an additional 3 minutes in seek time would be lost in the noise.

Certainly doing a variable-tool-size chain-driven machine is quite do-able, but, again, at considerable cost in terms of complexity.  You'd have to not only program each tool length, but now the "pocket" width as well.  And, setting up a job will mean a fair amount of disassembly/re-assembly to move the tools to their required positions.  Or, have pre-configured slots of different sizes, but then you have to deal with mapping tool numbers so each tool lands in an appropriately-sized pocket.  My biggest tool is a 4" face mill, so I just sized all the pockets accordingly.

Regards,
Ray L.