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Author Topic: Z axis loss of cutting depth after multiple Z movements  (Read 3907 times)

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Z axis loss of cutting depth after multiple Z movements
« on: December 13, 2017, 11:52:35 PM »
Using Mach3 and G540. V carve cutting depth set at i.5mm.  Series of text around a 475mm dia curve. At the end of the cut the tool is 2 mm above the material. Settings are from top of material.
Tried Z setting from top and bottom of material both of which show the same problem. Table is and material are perfectly flat. Tool is tight. No back lash. slides are clean ,lubricated and are not binding.
Have also a series of intermittent stops which seem to be getting worse. Suspect the G540 Bob is the cause. Have 4 Leadshine Microstep drivers DMA860H, power supply and ample wiring.
Was thinking of ditching the G540 and buying a ethernet BOB. The prices of the Smoothstepper are clearly excessive and beyond my means. The only BOB of reasonable price is the NVEM which claims mach3 compatibility but speaking to mach support they have never tested or approved this BOB.
Can anyone shed light on the Z axis problem and if the NVEM works with Mach 3. Is there a ethernet bob of reasonable price and proven use with Mach3










 











Re: Z axis loss of cutting depth after multiple Z movements
« Reply #1 on: December 14, 2017, 03:25:50 AM »
Hi,
even if you buy an Ethernet or a USB external controller like the ESS or the NVEM you'll still need your G540, it has your stepper drivers in it.
External motion controllers do not drive motors themselves.

The cheapest external controllers are the UC100 (don't buy a Chinese knockoff one from EBay) or  the PMDX-411. They are equivalent to one parallel port
and plug into USB on your PC. You could plug you G540 straight into it.

I use an Ethernet Smooth Stepper and have no problems recommending them, the equivalent of three parallel ports. PoKeys, PMDX and CNCDrive do good value
boards, all probably about the same price as the ESS.

While I understand you wishing to buy cheaply I think buying cheap Chinese is a mistake. That is probably a pretty contentious opinion but if you spend a few hours
reading on this forum you will see dozens if not hundreds of complaints about cheap Chinese gear. The evidence is pretty plain.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Z axis loss of cutting depth after multiple Z movements
« Reply #2 on: December 15, 2017, 05:56:33 AM »
Have also a series of intermittent stops which seem to be getting worse. Suspect the G540 Bob is the cause. Have 4 Leadshine Microstep drivers DMA860H, power supply and ample wiring.
Was thinking of ditching the G540 and buying a ethernet BOB. The prices of the Smoothstepper are clearly excessive and beyond my means.

Lets be very careful about the terminology we use. A BOB is a breakout board and a Smoothstepper is a motion control board. IIRC you still need breakout boards attached to the Smoothstepper to get where you are going.
A motion control board for less than $200 is a bargain. Just because it is out of your budget doesn't make it unreasonably priced. Not only are you paying for the hardware but you are also paying for ongoing support, improvements, and bug fixes.

Disclaimer, I have never used any of the Smooth Stepper stuff. I am using the stuff from Vital systems and if you think the Smooth Stepper is pricey, take a look at the Hiconn. The nice thing is that they now offer the Hiconn hobby version for much less but still "pricey" by your standards. By my standards they are a bargain because they work and have great support.

Lets also be careful about making assumptions about the equipment.I spent three day getting ready to call and scream at the guys from Vitals systems because I couldn't get my steppers to move but just as I was about to pickup the phone I took one more look and realized I had the damn step and direction wires backwards. It could just as easily be you and not the equipment.

If by intermittent stops you mean that the motor is stalling causing you to loose steps then most likely you are going too fast, have binding that you are not detecting, have something wired incorrectly, or just possibly you are using the rising edge vs the falling edge of the step signal. This of course depends on which way your drive like to see the signal. The G540 has an excellent reputation and I have had great luck with all of the Gecko stuff I have used.

Buying cheap almost always ends up costing me money in the long run so I just save up my pennies and buy what I need when I can afford it and if that takes quite a while, then so be it. Paying a lot for the sake of paying a lot is not what I mean by any means.


Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: Z axis loss of cutting depth after multiple Z movements
« Reply #3 on: December 15, 2017, 11:41:30 AM »
I doubt that the Gecko is the problem.  More likely culprits are, losing steps due to too much acceleration, coupler from motor to leadscrew slipping under stress or a piece of material in your collet not allowing the collet to fully close and moving the bit upwards under pressure.  The intermittent stops would be of concern to me as well.  If the computer (windows) is trying to check for something (java update, itunes, windows updates, screen saver...) there may be a loss of communication between Mach, the parallel port and the Gecko.  I'm sure you've already checked all of these things but I would check them again.

HTH

RT
Re: Z axis loss of cutting depth after multiple Z movements
« Reply #4 on: December 15, 2017, 04:39:35 PM »
Thanks for your advice. I am a long time retiree pensioner and have to watch the pennies. In looking at purchasing a new system the ethernet seems the way to go. It would seem to me that much of the systems are back in the dark ages only suitable for XP and parallel port and consequently are still reasonably priced. Have tried reducing acceleration, used new collets and double checked everything over and over again. Have also had help from a software design engineer to route out the problem. I see from Homann designs under EN-009 that I could use a MB - 026V BOB coupled to G251 Drivers. I have 4 Leadshine Drivers, power supply for the drivers and the BoB plus connectors and wiring.
This would seem to be the less expensive way to go albeit the use of XP and parallel port would be necessary.
I do not earn an income from CNC and use it to produce toys for disadvantaged children.
Is the setup on using the MB - 026V wired to Leadshine Microstep drivers a workable alternative. It seems to be a system without a motion controller.
David

Re: Z axis loss of cutting depth after multiple Z movements
« Reply #5 on: December 15, 2017, 05:41:49 PM »
Hi,
to be honest I think your G540 and Leadshine drivers are perfectly adequate.

The use of a good external controller which will get you away from the XP/parallel port bottleneck is the best use of your resources.

I use an Ethernet Smooth Stepper and two Homan Designs MB 026V boards. I have a very tight budget also and what I cant afford is to buy something
that doesn't work. The PMDX-424 is a highly practical board, it has its BoB interface builtin which includes it own power supply and has two port worth
of IO, so despite being $50 odd more than the ESS it probably works out cheaper in that it doesn't require the extras.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Z axis loss of cutting depth after multiple Z movements
« Reply #6 on: December 15, 2017, 06:47:55 PM »
Since you have the G540 you could take a look at the offerings from CNCdrive. Thier UC-100 is very reasonable.

In all honesty you should be able to run the G540 from the parallel port on an XP computer and get very good results. I ran my router with an old Dell PC, a inexpensive BOB and some Gecko drives and made nice parts until I took it apart to "make it better" It is still apart by the way but I digress. Cut the max speed and the Accel by 50% and try again. I feel that you are missing something very basic.

Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
Re: Z axis loss of cutting depth after multiple Z movements
« Reply #7 on: December 15, 2017, 07:58:41 PM »
To determine if you have a loose coupler put a witness mark each side of the coupler and the motor and lead screw where they meet.  If after running the program there is a shift you know that it is slipping.  Also mark where the bit is in the collet and measure the length from the tip to the collet to determine if there is any slippage there.

To determine if you are losing steps due to too much force run the program with no material being cut and see if the z is still 2mm above where it should be. If not then you have eliminated that.

Next search and replace all g0  commands with g1 f10 and run the program and see if the z is still off.  If so then your acceleration is too high.

That eliminates most of the possible mechanical problems.  This costs you nothing but your time.

HTH

RT

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Re: Z axis loss of cutting depth after multiple Z movements
« Reply #8 on: December 19, 2017, 05:03:19 AM »
The prices of the Smoothstepper are clearly excessive and beyond my means.
In that case you should reconsider whether playing CNC is for you.
Very bluntly, it is NOT a cheap hobby, and trying to go 'real cheap' via China will only bring on a premature heart attack.
And you can't run a 60' yacht for pennies either.

Cheers
Roger
Re: Z axis loss of cutting depth after multiple Z movements
« Reply #9 on: December 20, 2017, 07:17:58 PM »
The prices of the Smoothstepper are clearly excessive and beyond my means.
In that case you should reconsider whether playing CNC is for you.
Very bluntly, it is NOT a cheap hobby, and trying to go 'real cheap' via China will only bring on a premature heart attack.
And you can't run a 60' yacht for pennies either.

Cheers
Roger

Maybe you missed the part about being Retired and doing the work for Charity.

 Frankly I think he has everything he needs, and I am wondering if he tried the parallel port test that is in the Mach3 folder?  My old Lenovo T43  laptop is running my 6040 Chinese router fine on Windows XP but I have all the power saving, updating, wireless, screen savers and the like either off or disabled.  Good suggestions about acceleration and step adjustments.

I purchased the router from a USA based vender in Chicago that I have used in the past. Paid a lot more than eBay but I know its a decent machine.
« Last Edit: December 20, 2017, 07:19:40 PM by wmgeorge »
Retired Master Electrician, Commercial HVAC/R Service and lots of Hobbys.