Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Iawa on November 06, 2017, 12:39:02 PM
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Hi,
I've been having some calibration issues with my mach3 mill. I've set my steps using the step calibration feature and got that right but i went into the MDI panel to double check, triple check... I've been checking each axis numerous times to make sure its right.
for example i put in x1 and it moves exactly 1mm, then I'll move another 1mm - x2 and it will be out by .002mm and then another 1mm and it'll be bang on 1mm again.
i can deal with it being .002mm out but thats small movements (same as what i put above applies to movements of .1mm to 1mm)
I'll then do 2mm increments and it'll be bang on 1st time then .004 then .09 then bang on. the most its gone out is 0.1mm.
the machine will cut good circles and squares, apart from a very slight notch in corners for the circles.
If i run a long program, one being 3hours long for a small block it will cut perfectly for the roughing cuts to get the base shape, that being 1 hour and then the other 2hours being finishing, it will dive into the piece on the last 10,000 ish lines of code, right at the end . I know its not the code that's at fault because it never faults at the same line and i've had a few pieces finish without killing the material.
I'm still new to CNC and everything i know is from playing around, forum reading and youtube videos.
Im using Fusion 360 to design pieces and post to g-code and then use brackets to make small changes to the code.
The machine is a Bridgeport mill thats been converted to CNC with 3 nema-23 motors
The computer that is running it is a dell optiplex 780 series with a dual core CPU 2.93 GHz, 4GB RAM, An Nvidia GT 610 GPU 2GB DDR3 memory and its running Windows 7 Professional 32-Bit with some windows features disabled, such as mouse cursor shadows and unnecessary animations like window minimisation.
the version of mach3 is; R3.043.066
Many thanks,
Alex
(ps. the squares and circles as mentioned before are cut to the size specified and the right depth)
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Hi Alex,
Mach3 will only command a motion movement in multiples of your axis step size. Any discrepancy between a MDI commanded move and the actual DRO display are not cumulative and are not something to worry about.
Mach3 version .066 is not recommended by popular opinion, it is preferable to use version .062
Tweakie.
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Alex,
Calibrate an axis for the longest move possible and with any backlash removed prior to the calibration move.
That will provide you with most accurate steps per unit for the axis. How accurately the axis will move all along
the axis travel depends on the quality of axis components. Make sure you have tuned your axes.
it will dive into the piece on the last 10,000 ish lines of code,
Different kind of problem and there are a number of possible reasons.
You will need to do testing to find out why it is happening. Don't be surprised if you get a lot of different suggestions.
RICH
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Thanks for the tips Tweakie.CNC and RICH, i'll try out the older version today. And i'll go over the calibration again.
Alex
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Hi again,
I didn't know whether to make a different post or just post here, but i'll just post this here.
I did the driver test on my PC and its not a flat line but its not dropping below excellent, i'll attach an image to make it clearer.
i've read somewhere that changing the pc drivers from ACPI to Standard PC help improve the frequency but i have no idea how to change it on windows 7,
i've tried doing it the windows XP way but i can't see the Standard PC driver in the list.
Many thanks,
Alex
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Hi Alex,
I think that as long as the driver test does not show wild variations in the pulse timing then all is well and nothing needs changing.
Tweakie.
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Hi Tweakie.CNC,
Thanks for the quick response, i'll keep that in mind.
And thanks for your patience and time, one more question;
what would be the best learning source for mach3 and CNC in general?
I feel like im going to end up pestering forums while i learn and i don't want to be a burden
thanks,
Alex
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Hi,
CNC Programming Handbook by Peter Smid
is very widely regarded as the 'bible' of CNC. Its hardly an exciting read but it is thorough.
Some of the simpler Wizards in Mach generate code and is worth studying the code to see if you can understand it, Rectangular Pocketing, Rectangular Bolt Pattern,
Circular Pocketing etc.
Craig
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Thanks for the recommendation Craig, i'll look into it.
Alex
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what would be the best learning source for mach3 and CNC in general?
Hi Alex,
Nothing really beats hands-on practical experience.
A good CAD/CAM software (such as Vectric) then see what you can and can't do. Each time you run into a problem check the Mach3 manual, search the forum, ask the question. I have been using Mach2/3 for more than 10 years now and I am still learning.
Tweakie.
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Hi again,
Quick (hopefully easy) question;
How much am i looking at price-wise for a ball screw conversion for a bridgeport series 2 mill, and should i be sitting down before i'm given a rough estimate?
Im asking now because i've had to keep everything at a tight budget so far while i've been starting up and (knock on wood) my mill has been somewhat accurate considering its conventional with some years on the clocks (Mach3's backlash setting is a great addition) but i want to eliminate most, if not all the backlash and i've been told that ball screws are the way to go since they have a longer lifespan for wear and whatnot.
Again, thanks for your time and patience,
Alex
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Hi,
ballcrews are the right solution for backlash. Components for Bridgeports are readily available but they will cost many hundreds if not thousands of dollars
if you buy components specifically intended for Bridgeports.
You can buy cheaper secondhand off Ebay but will have to modify/machine to have them fit your machine. If you have a good lathe and the confidence to use it
it can be done.
Be aware of the difference between ROLLED ballscrews and GROUND ballscrews. Rolled screws a cheap and pretty damn good, say $200 for a largish one, the same size
but ground try $2000 or more....very very good but really expensive.
Craig
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Hi,
Thanks for the quick response Craig,
Sadly the lathe i use isn't the best, i couldn't trust myself to turn something of that importance or price on it.
i think a rolled ballscrew is my best option
Many thanks,
Alex
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Hi,
the only Bridgeport I've really had anything to do with is an Indian made copy of a series 1 I think. Its got a lot of backlash too, the yoke is badly worn.
The yoke is a big lump of brass with two machined ACME threads at right angles to each other for the X and Y lead screws. Its expensive to buy, really hard to
get at an replace. The separation between the axis screws is not that much greater than the diameter of the screws. To make a yoke with ball nuts (with their
much larger diameter) and so retain the existing screw locations is a challenge.
A conversion kit is despite the cost likely the best way to proceed.
A rolled screw will lose you considerable accuracy.
If you can't afford ground screws you might be better off buying another yoke and repairing what you have got. Even worn OEM lead screws are probably better
than rolled screws.
BoschRexroth do a line of ballscrews where they are rolled but subsequently ground. Still not the accuracy of C5 or better ground screws but better than C7 rolled
screws at an intermediate price.
Craig