Cuts not repeatable, I'm losing steps

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lavrgs
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Re: Cuts not repeatable Pulley Confirm

Post by lavrgs »

lavrgs wrote: Mon Nov 15, 2021 4:26 pm Pulley confirmation; X 12 on Motor 26 on Ball screw Y 15 on Motor 30 on Ball Screw. So the X axis 10.7998 makes it bit of sense; 2.1667x5=10.8333. I will set my X turns ratio to 10.833333333.... The belt on the X axis was a bit tight so I loosened it so it wasn't in tension.
I will remove the backlash comp and do the test with engineering scale. With X Turns ratio set to 10.833333 it moved 12 inches based on a commanded X12. So by eyeball its very close....IMG_2255.jpg
I did the same test with 24 inch scale and had the same results- alignment to 0 and 24 in both directions was spot on
cnckeith
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Re: Cuts not repeatable

Post by cnckeith »

great, thats the way i do it. now you should be good to go.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
lavrgs
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Re: Cuts not repeatable

Post by lavrgs »

cnckeith wrote: Tue Nov 16, 2021 2:34 pm great, thats the way i do it. now you should be good to go.
I think I have a bigger problem...
viewtopic.php?f=60&t=6476
lavrgs
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Re: Cuts not repeatable < overall turns ratio not set correctly>

Post by lavrgs »

20211114_175540_HDR.jpg
After taking a closer look at what I am doing I'm seeing that I'm possibly removing too much material in one pass. I'm using a 2 flute 1/4 inch endmill running at 2500 rpm and taking 0.066 off the radius 8-(. I will try adding a couple more frame cuts to "sneak up" on the final diameter of 1.518. Hopefully that will help to keep my diameter more consistent. All my cuts have been climb cuts - should I consider using conventional and climb just on the last pass?
Currently the slot is cut with three frames; a center outside at 1.65 dia then an outer inside at 2.278 dia and the final outside at 1.518 dia. The 2.278 outside diameter has been consistent +/- 0.002 but the 1.518 dia has been consistently oversize and the X-Y measurements vary >0.010..i.e the circle is not round.
EDIT: Reducing the amount of material removed helped dramatically. My boss OD is now very close to nominal and +/- 0.001 different across X and Y.
I think I still have an issue that is backlash related. After the run the part I return back to 0,0 and measure the center diameter to see if I am still on center and it seems 0,0 has offset by double the backlash in X and Y.
martyscncgarage
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Re: Cuts not repeatable < overall turns ratio not set correctly>

Post by martyscncgarage »

I like and use Marc Leonard's (cncsnw) method of measuring backlash. Check out his website on the topic: http://www.cncsnw.com/Lashhowto.htm
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
lavrgs
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Re: Cuts not repeatable < overall turns ratio not set correctly>

Post by lavrgs »

martyscncgarage wrote: Wed Nov 17, 2021 4:16 pm I like and use Marc Leonard's (cncsnw) method of measuring backlash. Check out his website on the topic: http://www.cncsnw.com/Lashhowto.htm
Thanks Marty. I was able to measure the backlash and setup the compensation so that the travel returns to zero in both directions on the x and Y axes
lavrgs
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Re: Cuts not repeatable < overall turns ratio is not the problem, I'm losing steps

Post by lavrgs »

I found this topic on losing steps and it is more in line with the problems I am having.
https://centroidcncforum.com/viewtopic. ... s&start=10
lavrgs
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Re: Cuts not repeatable < overall turns ratio >>>not the problem, I' losing steps

Post by lavrgs »

I am trying to understand the changes proposed in the linked post above. Before I dive into the solution of cutting out the resistor in the DMM cable and hooking up wires to the DB25 connector I want to make sure I understand all the steps. The schematic
dontdoit.JPG
version S14989-ACORN_rev4, DMM DYN4 SERVO DRIVE states DO NOT CONNECT H6 WITH DYN4 DRIVE so I want to proceed with verified information. Is there a later or different version? Can the Acorn power supply provide the 5 VDC mentioned?
lavrgs
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Re: Cuts not repeatable < overall turns ratio >>>not the problem, I'm losing steps

Post by lavrgs »

I had a discussion with DMM and they relayed to me that "sometimes" Acorn boards do not work with their cables" and that it was an Acorn problem and that getting a new board solves the problem. What is the deal? Will I be able to use the DMM Cables do I return them and build my own ...? will I ever get to a point where I have a reliable accurate machine?
I was able to go in to create a report .However please note that the machine is not set up per my final desired config. For example there is no Z axis set up due to drive failure.
REPORThttps://drive.google.com/file/d/1GfhivO ... sp=sharing
kentonsj
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Re: Cuts not repeatable < overall turns ratio >>>not the problem, I'm losing steps

Post by kentonsj »

When I started my build, there was some discussion on the DYN4 connection details. I chose to go a different route given the inconsistent results that some seemed to have. I built a differential line driver converter (with input and help from this forum) that uses the signals from the DB25 and converts them to differential step and direction signals to run into the DYN4. I have run my router for about a year now and I've had zero lost step problems. I'm running at 400khz on the Acorn and with my setup, I can tell you that I routinely send 400khz to the DYN4 drives. To go this route, you would need to make new cables and have a signal converter. Your DB25 connectors could be reused, but for the differential wiring you need 8 conductors and I think the DMM cable has 7. There are some commercial signal converters out there, I haven't tried any of these personally.

https://cnc4pc.com/c72-differential-line-driver.html

I used this as an opportunity to consolidate the wiring with connectors on both ends. I'm still using the drive enable signal from the screw terminals. You can see my machine in this post:

https://centroidcncforum.com/viewtopic.php?f=57&t=6553

I want to be clear that I didn't even try my screw terminals or use a DMM cable, so I don't know if this differential driver is contributing to my success. I also took great care in running shielded wiring where possible, used all the power filters DMM recommended, and don't have my spindle VFD in the control cabinet. Your mileage may vary.
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