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Messages - garyhlucas

441
General Mach Discussion / Re: Maximum processing speed?
« on: February 10, 2015, 10:03:41 PM »
Think about this:  If acceleration is set for 281 in/sec/sec the equation is D=1/2AT^2 and V=AT so to get to 400ipm or 6.666 inches per second in 0.023 seconds in a distance of .079" and to stop will take another 0.079" and for a total move required of 0.158" in.  0.046 seconds to start and stop while reaching 400ipm.  Note that at a constant velocity of 400ipm the same distance 0.158" is traversed in half the time or 0.023 seconds.  This means that the best you could accomplish with moves of 0.158" starting and stopping is twice as long as the total distance at a constant 400 ipm.  Shorter moves make the time longer, longer moves reduce the time.


442
I can't help but be impressed with the Tormach machines and tooling. They are a bed mill design with a large Z axis running Mach 3. I have looked at them carefully at trade shows and the fit and finish looks very good. I also own a bunch of their TTS tooling for my homebuilt machine and inexpensive and works well.  I have their Aloris style tool post and tooling and it is really nice for the price too. I built my own machine from scratch and got some really good deals on precision ways, ballscrews, electrical parts, control cabinets, a PLC, and aluminum framing. I still spent almost 10K!

443
General Mach Discussion / Re: LTP cable overheating problem
« on: January 22, 2015, 08:17:05 PM »
You most likely have a ground loop because the sheild on the cable is connected at both ends. This also implies some device, possibly a motor is shorting to ground and the current is taking that path instead of the safety ground. Disconnecting the shield at one end may stop the heating. However it also could cause the PC or the machine to have a very unsafe voltage on them so proceed carefully!

444
G-Code, CAD, and CAM discussions / Re: Link to purchase cambam
« on: January 17, 2015, 08:29:39 PM »
Start by downloading the full version and you'll have 40 uses before you need to pay.  I finished building and upgrading my CNC before I paid for it, and I still had 14 uses left!

445
General Mach Discussion / Re: lack of power when using invertor ?
« on: January 17, 2015, 08:27:11 PM »
Fred,
If your motor is turning 500 rpm and the spindle is going 1200, then you have a large pulley on the motor and a smaller one on the spindle. So the motor is running at about 500/1400x50 = 17.85 Hz which greatly reduces motor torque, then you are gearing UP by 500/1400 = 35.7% of the motor torque to the spindle!  So there is nothing left. I don't know what the maximum spindle speed you want is, but this is a bad combination.

446
General Mach Discussion / Re: Steps to making mill bulletproof
« on: January 14, 2015, 07:56:37 AM »
A couple of other thoughts for you home builders:

If your wiring looks like a bowl of spaghetti you are bound to have noise problems
"I'll" neaten it up later" doesn't work, later you find out that some wires are too short and you won't rip them out and lengthen them.
Tie the wires down as you go, use cheap ties and cut them off when you add more wires, finish with good ones.
Once you strip off the shield twist pairs together as far you can. Twisting is an effective shield.
Wires that are not in cables that are pairs (to a limit switch for example) should be twisted when possible.
"Bury the grounds, and neutrals) my dad taught me.  Grounds are very important and never change, the same with neutrals.  So wire them first so that they are at the bottom of the wiring bundle, not on top of wires you may need to change.
Think about you wiring layout before you mount components. Always try to layout components for the least amount of wire and to minimize wires going in opposite directions in a bundle.
Draw a schematic or wiring diagram before you start.  You will be amazed at how quickly you will get confused if you don't, and how many wires there really are!
If want help, and you don't have a drawing you are pretty much on your own, and electricians bill by the hour!

447
General Mach Discussion / Re: Steps to making mill bulletproof
« on: January 13, 2015, 07:36:39 PM »
John,
No they are not crazy, they are just wrong.  Having been an industrial electrical contractor for about twenty years in my first career, and having built control panels for almost 50 years now I have never once found the need to install a ground rod at a machine of any kind. I have seen lots and lots of machines that have had noise problems and when you investigate closely it is never a surprise why that is the case.  In case of home built machines I see I am more amazed that they run all rather than whether they have an occasional problem!

Electronic engineers are a big part of the problem.  They just don't seem to grasp that the grounding done for shielding purposes is completely different than than the grounding done for safety purposes.  Grounding for shielding is all about making sure there is one and only one path from every point to ground.  Grounding for safety is all about making sure the voltage difference between any two metal parts on a machine is as small as possible, and you want to create as many paths to ground as you can.  In the case of shielding noise your are trying to keep out very small currents at possibly high frequencies.  In safety grounding you are trying conduct away what may be many thousands of amperes of current from a fault in motor, heater, etc.



So back to that ground rod.  It is driven into the earth. What is the resistance of that earth?  Well I can tell you that it is so high that it cannot conduct away a large current surge from from a faulted motor.  If the fault lasts the ground will be warm around the rod, and the rod will be at a voltage that will kill you, and yes I have actually seen this happen.  I figured it out when I kneeled down to look at something and the concrete was hot!  That rod is also a second path to ground, the other is through the safety ground wire that comes in with the power conductors.  Ohms law teaches that the current in a circuit is the same everywhere, while the voltage varies with the resistance.  So that means that leakage from motors, transformers, solenoids etc. cause all kinds of cray voltages to flow on the ground path, and you have two paths to complicate matters.

So a little checklist for you home builders:
Shielded wire on all sensors that connect to the CNC?
Shielded cables on motors that generate noise servos, steppers, VFD controlled?
All shields connected at only one point on the whole machine?
Ground wires from all electrical control devices installed and connected to just one point?
You checked with an ohm meter to make sure the shield isn't connected to the case of any device with a metal case mounted to the metal frame?
Power wires and control wires routed in separate raceways?
Control wires cross power wires at right angles and don't run parallel?
You are using a PC with a communications cable. Is the shield in that cable tied to chassis of the PC and then connected to ground on the card in the machine? OOPS that is a ground loop!

Let there be chips!

448
G-Code, CAD, and CAM discussions / Re: Pecking
« on: January 13, 2015, 07:01:51 PM »
I would think this happens because one flute of the drill is dragging on the way out.  Maybe the spindle isn't perfectly square to the Z axis.

449
General Mach Discussion / Re: Steps to making mill bulletproof
« on: January 12, 2015, 09:59:02 PM »
Damnit! I absolutely hate when I see advice to drive a ground rod to solve a noise problem on a machine. If that works it only proves that you have a problem you don't understand and are clueless about how to actual fix it!  Sorry for the harsh words but I have seen this kind of bad advice since the first days of PCs, computerized cash registers etc.  If you ever get this kind of advice from the manufacturer of any kind of electrical machine you should be very afraid working around it because it  very well could run amok and hurt you!
A 90 hr week I'm bit grumpy.

450
General Mach Discussion / Re: Control Box
« on: January 10, 2015, 06:38:33 PM »
Dave,
Lots of companies that do this out there. If you want build yourself you can get nearly everything you need from AutomationDirect.  Saddlebrook controls in SaddleBrook Nj is one of the few AD vars that they set up years ago and they can build the panel for you and even give you a UL label if you need it.