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Author Topic: Trouble cutting accurate parts  (Read 15673 times)

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Offline wdp67

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Re: Trouble cutting accurate parts
« Reply #20 on: December 15, 2007, 12:37:55 PM »
I agree, I am sure that it is a mechanical problem, because like I said it does it when I switch directions manualy also. I just can not fugure out what to do about it.

Thanks
Walt

Offline Graham Waterworth

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Re: Trouble cutting accurate parts
« Reply #21 on: December 15, 2007, 01:41:45 PM »
If it is a mechanical problem then it would not show in the DRO's.

If you tell Mach to move 1.000" then the DRO will show 1.000", the only time this will be different is if you are using compensation of some kind.

Backlash compensation is applied on the start of the move and is not shown on the DRO's

Even on a servo system Mach has no idea if the mechanics are moving.  It just counts pulses out.

What is in your start up line on the config page?

Graham.
« Last Edit: December 15, 2007, 01:43:59 PM by Graham Waterworth »
Never give up, time will pass, the cloud will clear, the sun will shine once more.

Offline wdp67

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Re: Trouble cutting accurate parts
« Reply #22 on: December 15, 2007, 02:42:18 PM »
I never said it showed up in the DRO, I said the parts actually measure .010-.015 bigger than they are supposed to. At least thats what I thought I was talking about. :)

Walt

Offline bowber

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Re: Trouble cutting accurate parts
« Reply #23 on: December 15, 2007, 04:18:45 PM »
If I understand this correctly you move the table in say the Y+ direction and the DTI shows 1.000" you then stop and reverse the direction to move the table in the Y- direction and before it moves in the Y- direction the DTI shows 1.005" before reversing?
This happens on both stepper driven and manual driven lead screw?

This would indicate slop in the table slides to me, you'll never get any sort of consistant result if there is movement in the slides.
If it isn't the slides then I'm at a loss, I can imagine turning the lead screw manually with the handle could move the table a little but the stepper is attached to the table so it shouldn't be able to.

Steve

Offline wdp67

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Re: Trouble cutting accurate parts
« Reply #24 on: December 15, 2007, 05:17:58 PM »
Yea that is right. My mill is cnc'd as per fignoggle plans so I still have the manual capability. How would I fix the slop in the slide?

Thanks
Walt

Offline DAlgie

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Re: Trouble cutting accurate parts
« Reply #25 on: December 15, 2007, 05:48:29 PM »
I have to add, you are asking a $400 Harbor Freight mini mill, with the original Chinese leadscrews, NOT ballscrews, to be accurate within .005". That machine doesen't even have tapered gibs, it has setscrews that you load the parallel gib with, very flexible setup as the table loads go through these tiny setscrews. Maybe you need to map the leadscrews with Mach's mapping feature. Or spend the money and buy ballscrews for it.
    DaveA.
Re: Trouble cutting accurate parts
« Reply #26 on: September 11, 2010, 12:51:00 PM »
I have a question on Mach3. I don't know if it was ever addressed here or not, but let me try and explain my situation.
I have being running my CNC router for more than 2 years now.
I bought a dial gauge the other day and last night I put it on to check the setup.
I was very very close with my steps, but then I notice the following.  I have seen it also while cutting. I programmed the piece to be cut 2mm deep but Mach3 shows 1.985 mm for instance.

I then did the following, ONLY on Mach3.

On the TAB called MDI I enter a value...say Y6.5 to move my Y axis 6.5 mm.
Sometimes it does show 6.5 but but other times it differs.

The very next move say y6.66 show 6.6481.

Remember I get this only playing in Mach3...no machine attached.  

When I do it on the machine and I see this difference between what I asked and what the DRO shows, I also see this difference on the dial gauge...Dial gauge shows this 6.64mm movement for the 6.66 asked.






Offline Hood

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Re: Trouble cutting accurate parts
« Reply #27 on: September 11, 2010, 07:45:54 PM »
What are your steps per unit in motor tuning?
Hood

Offline alenz

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Re: Trouble cutting accurate parts
« Reply #28 on: September 11, 2010, 09:37:35 PM »
Woody, Hood will be able to answer your question definitely, however in the meanwhile you might like to play with a little excel sheet that shows the relationship between various parameters. Note in particular that it is possible to specify distances that require fractional steps :).
Al
Re: Trouble cutting accurate parts
« Reply #29 on: September 13, 2010, 03:17:04 PM »
Thank's Al and Hood.

Previously I calculated the steps as per my pinion sizes etc and got to 54 I think. I then used the Calibration in Mach to FINETUNE it.
Firtsly I draw a block in CAD say 500 x 500 then cut it say 1mm thick. I then measured the block and got maybe 501.6mm. I then used the calibration and told Mach to move x=500. Now I know I measured 501.6mm on my block that was suppose to be 500. So when Mach asked how far did it move I entered 501.6mm. Mach then re-calculated the steps and got maybe 53.923456783......lots of digits.

I brought it back to a full number of 54 tonight and did not see the problem yet....will have to do some more testing.