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1341

Show"N"Tell ( Your Machines) / 4th axis - show and tell - pictures

« on: November 21, 2008, 03:11:04 PM »

We started talking about 4th axis rigs in another thread and agreed to post pics when they were done. Finished mine today. Comments welcomed.






It works great and I used the indexer manually to make the timing pulley and then used the powered rig manually to grind a new Z axis ballscrew end down to .5", but I have not cut anything with the this finished CNC operated rig yet, so jury is still out on how tight it can hold azmuth during machining operations, but I'm hoping that for my purposes it will do fine.

1342

General Mach Discussion / Re: Having a small problem with mach3

« on: November 21, 2008, 02:39:26 PM »

I don't know if this has any relation to your problem, but I've been evaluating Mach3 and I had exactly the same result you got; namely what appeared to be random deviations from the desired path . .

It did not occure in any programs that I wrote but did appear in any wizard programmed code.

Eventually I noticed that there was a pattern to it. The tool was turning WAY early like you do in your car if you were driving REALLY fast, and that led me to check into the feed rate, motor speed and accelleration settings.


I use feed per rev and the wizard put out IPM, so the wizard stuck the feed at say 50 in the code which is 50inches PER REVOLUTION in feed per rev. That's what was causing the tool to go off path in my case. I would not swear to it, but I don't think I got any errors . . . it just ran fine, but with the tool doing exactly what yours is doing.

In messing around trying to figure the problem out, I notuced that (if I am remebering right) that the accelleration set in the motor tuning also can cause the tool to meander is Mach thinks the motors need more time to accell decell than they really do.

So you might check your motor tuning settings and see if something has changed there.

1343

General Mach Discussion / Backlash - very slow movement with every change of direction - Normal?

« on: November 21, 2008, 02:15:09 PM »

I'm trying the backlash function and it seems odd behavior to me.

Jogging the axis back and forth results inthe backlash being taken up at a very slow movement regardless of the speed setting in the backlash config box, or the feed rate commanded.

Am I missing a setting somewhere or is this the normal behavior?

I cut aluminum at 6,500 RPM .002 per rev feed on a 5/16" end mill. The extreme slowdown during backlash takeup is going to be a problem methinks.

1344

General Mach Discussion / Re: GROUNDING - what is the correct way to ground a CNC machine?

« on: November 21, 2008, 04:04:48 AM »

Thanks for the info, guys.

I was looking for a little more specific 'how-to' for CNC rather than general rules. You know "Grounding for Dummies" type of help.

I am adding a fourth Gecko 203V to my control box right now and I want to know that I have the grounding set up correctly. Gecko says to ground their driver frames and I assume that means to earth ground, even though the are not at mains and have a 5v side. I have them all mounted on a .090" aluminum plate as a sink and I plan to attach that plate to earth ground via the unused ground wire in a 16/3 power cable coming from the 36vDC  power supply's earth ground terminal which goes directly to the earth ground center prong on the wall plug. I know the ground is good in the outlet.  Gecko says to feed each drive separately all the way back to the power supply so I've added the necessary cables to do that.

Also the system has a minaric variable speed DC drive which is installed in an separate aluminum box along with it's associated relays, pot and a CNC interface board that (supposedly) produced the control voltage for the drive to follow. The box is fed 115vac from the wall outlet and also 12v for the relays from a two wire 12v outside source and 5v which is supplied via the breakout board in the control box directly to the CNC speed controller. hot and common from the 115VAC goes to the board terminals and the green ground wire is bolted to the chassis and these run in a 16/3 cable to a grounded outlet.

So far, with the exception of the Gecko's, which are isolated, I have kept the 12v and 5v stuff off of the earth ground as I'm imagining that a short to ground on the 115 side would fry any 12v or 5v (including the laptop) that was on the same ground. I don't think this is correct and I'm wondering what the correct procedure is to ground the laptop and the breakout board, or even if they should be grounded. The geckos are all opto isolated, and the breakout is opto isolated on everything except the specific gecko connections (it is a gecko specific board).

So I take it that all of the 'big' stuff just goes to earth ground individually. My remaining question is how exactly do I ground the 'electronics' side. There is no terminal or screw that says 'this one goes to earth ground' and that the level I need help on, unfortunately.

1345

General Mach Discussion / Re: random e stop error

« on: November 20, 2008, 05:03:41 AM »

From the "stab in the dark" department;

I just started a thread on grounding that you may want to follow. Grounding and also shielding are apparently serious considerations in CNC.

One example in my experience was the Z axis motor randomly bumping a step while it was stopped. It was located adjacent to the variable speed controller which was in the original plastic box. After reading that these controllers can be very noisy electrically, I moved the controller and associated switches and relays into a separate metal box located off the machine. All that goes to the spindle is the 120v dc power feed from the controller box.

So far, that seems to have cured that problem.

1346

General Mach Discussion / GROUNDING - what is the correct way to ground a CNC machine?

« on: November 19, 2008, 06:36:23 PM »

I need some advice or direction on the correct proceedure for grounding my CNC conversion.

There seems to be a lot of potential for problems if the mill is grounded to the computer to the breakout board to the 5v source to the stepper power supply, etc , etc.

For example, what goes to earth ground?

1347

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 18, 2008, 10:29:47 AM »

Keeping in mind that I'm a newbee, and this may not be a great idea, it goes like this;

Take a situation of a machine that has two basic setups that are vastly different; one is normal full table travel for general work and one has a 4th axis rig that takes up almost half of the table (of a baby mill).

My combination homing/limit switches are on a phono jack that just plugs into my CNC controller box. I think it would be a simple matter to add another switch in a position appropriate for the 4th axis work envelope, chain those together on a separate plug and have a second XML file for 4th axis projects. The xml could have the approproate limits for the 4th axis envelope and any other changes that may benafit that type of work.

So as a part of the 4th axis setup, I simply put the rig on the table, plug in the appropriate limit/homing switch chain into the CNC controller and start Mach with the 4th axis XML. Now I have fast homing and limits appropriate for the 4th axis envelope.

Maybe I'm missing something, but this seems like a very usefull proceedure.

1348

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 16, 2008, 05:13:12 AM »

Excellent info!

Having the switch in the middle of the table seems like the perfect solution for homing. Presumably you would have to make sure you were on the correct side of the switch before homing? And I also presume you then could not use the same switch for both homing and limits if the switch were in the middle of the table, so you're back to multiple switches and associated wiring, yes?

That still leaves the issue of machine protection. In my scenareo with the 4th axis rig, wouldn't it still be wise to have a physical switch positioned to stop the travel before the spindle hit the 4th axis chuck if something went awry?

I like the idea of sliding swithces and/or moveable slotted triggers. That would make it very easy to position a limit switch for example. . when the 4th axis rig is set up on the table.

1349

General Mach Discussion / Re: 4th axis issues, please have a look?

« on: November 15, 2008, 06:33:35 AM »

Dave,

I hope you start a thread (with pictures) of your 4th axis setup.

After some consideration, I sold my rotary table and went with a stepper powered spin index. For my purposes, the trade of in accuracy for speed was useful. I have two full steps per degree. I don't know what the max RPM is.

I just got it going last night and it's first job was to grind the last 3 inches of a new ball screw down to .5" diameter and then the tip to .375 for treading. The I ground a flat for  set screws.

Made quite a mess, but it worked great!

1350

General Mach Discussion / Re: Can someone explain the current draw of these stepper motors, please.

« on: November 15, 2008, 06:15:15 AM »

That's what I did, Ray.

The Y axis is working OK now, but I think I am going to put jack screws on the bearing block and do a fine adjustment without the table on the machine to get the ball screw lined up properly. The machining on the front of the base is not perpendicular to the ways, so the accuracy in the bearing block is defeated.

I had read a lot about binding ball screws in my intial homework before diving into the retrofit. I never read where anyone had solved the issue though. Now that I've been down that road, I know what causes the problem (in my case anyway) and I think I have a solution other than having the base remachined accurately.

There won't be any servos on this X2. For my purposes, it is not worth the time to get an X2 up to the level I want it, because even if I make it into a 'good machine" it is still going to be too small and not rigid enough for upcoming projects.  I'm hoping the X3 is better quality.