Messages

1431

General Mach Discussion / Re: computer causing gorilla cnc glitch

« on: November 29, 2008, 10:32:17 AM »

thanks  I will add the charge pump  and I'm also going to try a pci lpt port add on , some say this cleans up the lpt port.
I tried 5 different computers and they all cause this whether they are new or old
I appreciate the help.

 

That would suggest to me your real problem lies outside the PC - something about the way your drive electronics are setup that causes an high noise sensitivity....

Regards,
Ray L.

1432

General Mach Discussion / Re: setting a permanent home point

« on: November 25, 2008, 12:20:50 AM »

That is the purpose of home switches.  Without home switches, you have to position the machine to your 'zero' point manually each time you turn it on, and zero the machine position DROs.

Regards,
Ray L.

1433

General Mach Discussion / Re: servo motor not getting up to speed

« on: November 24, 2008, 11:49:57 PM »

How far does the table move before reversing?  An encoder failure would most likely either run full speed in one direction, or just "dither" back and forth a very short distance (just a few encoder counts).  If it's moving any significant distance, the problem is much more likely to be either a failed drive, or a problem with the DIR signal.  I would first swap out the drive, and see if that fixes it.

Regards,
Ray L.

1434

General Mach Discussion / Re: Soft Limits

« on: November 24, 2008, 07:04:07 PM »

Okay, I'm back after a computer meltdown. If it isn't one thing it's another....
I have reread all the posts re: this subject several times now, and I still need some clarity. Firstly, unless I have completely misunderstood some of the posts, it seems that there is some disagreement about the Z axis and whether it is standard for the Z zero to be set at the high part of its range, and everything below that (closer to the table) is negative. Others seem to think that Z zero should be set at the work surface, and everything above that should be positive. In the case of the Z zero at the top, a soft limit above the Z zero position would be positive, but it would be negative if it is set below the low position. In the latter case (the Z zero is at the work surface), the soft limit would have to be negative if it is below the work surface. The problem as I see it with the first configuration is that you have to work with negatives, measuring down from your tool bit and then adding another negative number to that to get the cut depth you want. The problem with the second method is that if you want your tool to go home after doing a procedure, or to get ready for another procedure, it would travel at the height of, and/or end up at, the work surface, making it hard to remove the work and possibly damaging the surface of the material.
So, let's solve that first.
As to Hood's question about my machine orientation, the lower left corner of the XY axes is near the operator and on his left. As of yet, there are no limit or home switches -- this is why I want to get this soft limit thing correct.
Is it possible to avoid some of the issues mentioned above by having the soft limits be the home and positions away from home beyond which you don't want to go (that is, what I would consider the usable work surface), and the slow down 1/4 inch, say, before that? The only problem that I can see is that the machine slows down when it is working near the limits...is that a problem?
Thanks again, Bob

I think your mixing home positions, machine coordinates, and work coordinates all together.  The home position can be where you want it to be.  It is probably most often set to one corner of the X/Y travel, and, I think, *always* full up on Z.  Work coordinates are generally zeroed somewhere else that is on, or at least relative to, the actual workpiece.  It is conventional for Z=0 in work coordinates to be the top-most surface of the workpiece.  Moving Z in the minus direction always moves the tool downward.  If you have no home switches, then machine coordinates have relatively little meaning, and you can define machine zero to be wherever you like on a job-by-job basis, and set work coordinates to be the same.

Regards,
Ray L.

1435

General Mach Discussion / Re: Problem; rapid at end of op

« on: November 22, 2008, 10:36:24 PM »

Adam,

   You need to examine the G-code, and see what is causing those moves.  It is almost certainly in the G-code, not a Mach problem.

Regards,
Ray L.

1436

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

« on: November 22, 2008, 11:20:20 AM »

I appreciate the replies, but I still don;t think I have an answer.


I get the chassis grounding and protecting people from high voltage, etc.

I get that the DC common is 0v and should not be connected to earth ground. All of the 0v (common) wires from the Geckos go to com terminals on the BOB.

I have a 5v (to the BOB) and 12v (fans and relays) supply coming from an old PC power supply. Each is only two wires. I am not taking any power from the PC and it is connected by a shielded,  all wires connected parallel cable.

Here is the question as succinctly as I can put it:

Are there any earth (or otherwise) grounding requirements that must be done on the electronics side i.e BOB, indexer board, charge pump, spindle controller, PC, etc that I need to specifically address?

Sorry to be a pest, I just don't want to fry anything else due to my lack of electrical knowledge.

Just as for the power ground, all your power supply commons should be connected together at a single point.  You are probably accomplishing this, sort of, through the BOB, but that's really not ideal.  You should bring the commons from all supplies to a single point, and bring a dedicated wire from each device (BOB, drives, etc.) to that common point as well.  You can determine whether the mounting lugs on the BOB are tied to common by using an ohmeter.  Your supply common may, or may not, be bonded to the power ground.  I would suggest not.  Since it sounds like everything is mounted to a metal plate, that metal plate should be bonded to the supply common.

Regards,
Ray L.

1437

General Mach Discussion / Re: centering cross hairs on video camera

« on: November 20, 2008, 11:02:54 AM »

Rich -
 Yes - I've thought about this - AND - as far as I see it, the problem in machining the housing is that you could be off centre with it. My housing fits in the milling/drill chuck. So > I put a small drill in first, and drilled a target hole in the workpiece, then swapped the drill for the camera.

The picture I get is the target hole, but the cross hairs on the screen are  off to the left  (not a long way - but say 5mm - it is a bit hard to tell becasue I don't know the magnification).

If I spin the chuck manually with the camera in, the picture turns - not about the cross hairs - but about my target hole. Therefore my camera seems to be aligned with the spindle, but the cross hairs are not. If I move the camera, it won't be aligned with the spindle, it seems to me that it is the cross hairs I need to move - but how.

Jim

Jim,

The problem *is* absolutely that the camera is off-center relative to the spindle.  The fact that the cross-hairs rotate around the actual center point is proof of this.  The solution is as someone pointed out - you need to add three adjusting screws, that will allow you to move the camera to where the cross-hairs are aligned with the true center.  In fact, you need two sets of these screws, so you can not only get the cross-hairs centered over the spindle center, but also get the axis of the camera perfectly aligned with the axis of the spindle.  Otherwise, when you get the cross hairs centered, then move the head up or down, the cross-hairs will move off-center.  If you try this right now, I bet you'll find the distance by which the cross-hairs are off is a function of the head height, which, proves the camera axis is not aligned parallel to the spindle axis.

Regards,
Ray L.

1438

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

« on: November 19, 2008, 07:25:08 PM »

The most important thing is to HAVE a ground, and only one.  The body of the machine should be securely bonded, through a dedicated wire, to the power ground of your building.  In the US, this is the GROUND terminal present on any self-respecting outlet.  You want to have a single ground for the electronics, and connect everything to this point.  This can be a buss-bar, heavy terminal strip, a metal chassis, or something on that order - something with essentially zero resistance between the many connections.  NEVER ever daisy-chain grounds.  For shielded cables, ground the shield at only one end, usually the power source end.  So, for example, encoder cables should have the shield grounded at the end opposite the encoder, where the power supply is.  NEVER use a shield as a power or signal return.  Always provide a dedicated power or signal return wire, or you render the shield largely useless.  You never want to setup a situation where you can have current flowing through a shield.  You never want to have a situation where a signal wire can serve as a power return.

Regards,
Ray L.

1439

General Mach Discussion / Re: Mach XML Reader

« on: November 17, 2008, 10:43:10 AM »

Jason,

    Nice work!  I like it!

Regards,
Ray L.

1440

General Mach Discussion / Re: Z AXIS KNEE

« on: November 16, 2008, 01:20:17 PM »

I'm using a gecko 320. I have run it at 150ipm but the pulse rate is too high to be reliable so i keep it around 100ipm. It's only got a 250cpr encoder on it now but it's going to be a 120cpr encoder. The belt drive thru the original crank shaft is 2-1 reduction, then the gears are 2-1 reduction also.

What kind of motor?  My 850 oz-in peak servo will drive mine to 70+IPM, running through a 4.8:1 reducer.  I'm sure it will go somewhat faster (I currently have my SS limited to 128kHz step rate), but I doubt I'd make much over 100 at best.

Regards,
Ray L.