[vkmaynard]

Not sure what mechanical issues I would have on the G0704. Everything is tight and appears to be properly adjusted.

There are probably tolerances on the lead screws that is causing calibration issues.. I doubt they are Haas quality items.

Currently at 8138 steps per inch.

Victor

[Topdecking]

So... do you have a question?

[waltpermenter]

nope a $1000 mill isn't going to be the same quality as a $50,000 Haas, why would you expect it to be.
walt

[vkmaynard]

Trying ot calibrate a G0704. All my cheap gauges vary in accuracy. I tried cutting a test 1x1 square. But that also gives a different answer. May the 0.25 end mill has a diameter issue.

Any great recommendations? I started at 8000 steps per inch. Now at 8170 after many hours of testing.

[Kenny Duval]

You will never get it right without accurate measuring tools. Address that issue first.

[joecnc2006]

Are you mapping your ballscrews with mach3 setup? I would not cut measure then adjust the settings, you have bit flex, cutting forces and Basklash etc. involved, use a dial indicator and move in one direction only to eliminate backlash in measurements.

Hoss has a video which shows how he did it on his Mini Mill. (HossMachine on Youtube) I always refer to his videos as he is a GURU.

[691175002]

You should never measure steps/inch off a cut, because endmills do not always cut their diameter. A 0.25" endmill might cut a slightly larger or smaller diameter depending on the rigidity of the tool, milling machine, feeds/speeds, wear, or it might not even be correctly ground to size. Understanding and compensating for these factors is part of being a machinist.


Most people measure steps per inch using a dial indicator but this has the disadvantage of only considering a very small portion of the screw.

I would recommend using at least a 4" gauge block, and even that is pretty short.


In the long run, I don't think steps per inch are a huge deal because even 0.010" of error across 12" of travel is very small compared to other errors such as backlash and machine flex.

I literally would not even be capable of measuring whether a 10" long bar was actually 10" long. I wouldn't have any way of verifying iftwo holes are exactly 8" center to center either. Worry about the errors that matter.

[109jb]

When checking the accuracy of your steps per inch setting you have to be moving in the same direction at both ends otherwise you are introducing the backlash into the measurement. For example, table moving right, stop, zero indicator, move table more to the right, take second reading. This needs to be done with measuring instruments and most common is a dial indicator and a gauge block. It can also be done over a shorter distance with a long travel dial indicator (1" or 2" travel). Trying to do it by cutting something with an end mill is pointless because end mills hardly ever cut EXACTLY on size and this will introduce another error.

From your description of being at 8138 steps per inch, it sounds like you are using 5mm ballscrews. Theoretically you should be at 8128 steps per inch using 1/8 microstepping and direct drive. This is an assumption since you gave no details of your setup. It would be nice to know if the motors are direct drive, the microstepping setting, the ballscrew lead, if you have double ball nuts or have replaced the balls to reduce backlash,...

If my assumptions above are correct (5mm screw, direct drive stepper, 1/8 microstepping), then the difference between 8170 and 8128 is 42 steps. 42 steps would equate to about 0.005". That little error is likely backlash, sticktion, etc. If you don't have proper measuring tools then your best bet is to just set the steps per inch to the ideal theoretical value and be done.

[vkmaynard]

Good suggestions. Theroticaally I have 5 in pitch ball screws with ballnut (see Automation Technologies). Not what is a double ball nut.

I am actually good with machines.

Just used to walking up and using them.

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[109jb]

If you have automation technologies ball screws then they are metric screws, not inch screws. Specifically they are 5 mm screw pitch so will move 5mm with one revolution. the screws are 1605 on x and y and 2005 on Z. The first 2 digits are the diameter (1605 and 2005), and the last 2 digits are the pitch in mm in both cases 05, or 5mm pitch. Based on where you are with your settings I assume direct drive steppers and 1/8 microstepping set up on the drive. the math is as follows.

(25.4mm/inch)/5mm = 5.08 rev/inch

5.08 rev/inch * 200 steps/rev * 8 microsteps/step = 8128 microsteps/inch

[vkmaynard]

109jb Thanks for the info. Automation Technologies said they were English. Your information confirms what I've seen. What realistic final accuracy? I used to machine precision scientific equipment before CNC. So used to high accuracy. First into to CNC was on a Tomah last year.

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[vkmaynard]

Is it possible for the axies have different steps?

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[Fastest1]

It is possible and will vary a few steps even if theoretically the same. Always best to check with an indicator to verify the distance traveled. Good to keep checking on a regular basis to keep accuracy in check.

[vkmaynard]

Looks like 8128 steps is exactly correct. Made the remote top in foam tonight. The PCB fit perfectly.

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