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Author Topic: Another lost steps post...  (Read 8786 times)

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Offline Sweep

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Re: Another lost steps post...
« Reply #10 on: May 24, 2010, 06:31:01 PM »
Appreciate your assistance Hood.
I will try this out tomorrow night, but according to my manual, and what I recall on the screen, the range of step pulse is only 1 to 5us ?

Offline Hood

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Re: Another lost steps post...
« Reply #11 on: May 24, 2010, 06:33:30 PM »
You can set it as high as 15 if I recall, if that doesnt help you may need to try Sherline Mode.
Hood

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Re: Another lost steps post...
« Reply #12 on: May 25, 2010, 12:43:46 PM »
No luck.
I have dropped the acceration right down, increased the step and direction pulse width from 5us to 20us, besides trying other settings in-between, I've tried changing from active high to active low on the step, but still i'm coming up short everytime by exactly the same amount. I even increased the acceleration to see if I could lose more distance but it performed the same.
I stripped off the X motor and counted the teeth on the timing pulleys and they are as expected 2.5:1 (12x30).
I measured the ballscrews with a rule and they are 5mm pitch and identified the ballscrew nuts as Warner RM1605 UF.
I have tried in Sherline mode (restating Mach3 as instructed) but nothing changes

 ???

Offline Hood

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Re: Another lost steps post...
« Reply #13 on: May 25, 2010, 02:04:30 PM »
What happens if you double or treble the distance?
Hood

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Re: Another lost steps post...
« Reply #14 on: May 25, 2010, 04:49:30 PM »
I have only tried the measurements over 12.7mm as my Imperial DTI is limited to around 1" range. I could experiment with larger distances but would have no way to accuratley measure them. For example at 127mm I wouldn't be able to get 0.030" accuracy. I suppose I could fasten my digital caliper to the table and have a go with that.

Offline Sweep

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Re: Another lost steps post...
« Reply #15 on: May 25, 2010, 05:11:03 PM »
ok, the results of tonight's futile experiments!

As mentioned earlier, I am pretty limited to the range of accurate measurement by the 1" capacity of my DTI.
Taking on board what Mr Hood said earlier and adapting it to my limited range I thought would smaller diatances result in smaller errors being recorded.

For anyone who hasn't picked it up, the reason for all the odd figures like 12.7 and 2.54 etc is because i'm operating in mm but have an imperial (inch) DTI.

So starting with the DTI zeroed I drove the table G0 X12.7 (1/2") and the result was 4thou short.
Then driving the table G0 X0 the DTI returned to zero, therefore the error is apparent in both directions.
Next I thought what about "electronic" backlash so I first drove the table from zero to G0 X-2.54 and the same 4 thou error appeared. Driving the table back to G0 X0 returned it to zero on the DTI.
Now the intresting bit. When I now drove G0 X12.7 the needle hit the 1/2" mark right in the middle. Brilliant.
When I drove the table back, i.e. introduced a direction change, to zero the 4thou error reappeared.
Next, because i had just sorted my nice big fat pro MPG I set it to single step mode with a step of 0.1mm (0.0039") and did the same experiment. This gave exactly the same results; take up the electronic backlash and the DTI would read true, change direction and i'd lose some distance, well if I moved 0.1mm (0.0039") whilst changing direction I would only move half that distance.
Now I know that i'm only losing, say, 2thou on the shortest of distances and twice that on long distances but I think we can see the problem.
Question is, is there a cure?

...Sweep

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Re: Another lost steps post...
« Reply #16 on: May 25, 2010, 05:16:35 PM »
oh, by the way, pushing the acceleration right up to 500mm/s^2, dropping the step pulse down to 5us still disn't cause a problem if i'd already taken out the 'electronic' backlash.
I was just playing with these silly high accelerations just to see what would happen and have returned them to a sensible figure.

Offline Hood

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Re: Another lost steps post...
« Reply #17 on: May 25, 2010, 05:32:37 PM »
Ok, make sure you move in one direction, zero the DRO and also zero your clock (DTI) and then still going the same direction move your 12.7mm.
What do you get in both DRO and on the Clock?
Next do a move back to zero, what do both say now?

Hood

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Re: Another lost steps post...
« Reply #18 on: May 26, 2010, 03:13:04 AM »
If I zero the DRO and DTI after a G0 X12.7 move, then do a G0 X-12.7 move the DRO will read 0.00 and the DTI will read -0.4996" (0.004" adrift by eye but probably will be 0.00039 due to my metric machine).

...Sweep
« Last Edit: May 26, 2010, 03:16:12 AM by Sweep »

Offline Hood

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Re: Another lost steps post...
« Reply #19 on: May 26, 2010, 03:16:03 AM »
What you need to do is keep moving in the same direction for this test. Move in a positive direction, zero the DRO and zero the DTI then move x12.7 thus still going positive.
Hood