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Backlash / oblong holes

Discussion in 'CNC Mills/Routers' started by Rob J, Jul 16, 2021.

  1. Rob J

    Rob J New
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    Hello All,
    Until two weeks ago, I had ZERO experience operating a CnC. I had taken several projects in the past to a neighbor. When he was no longer available, I decided by my own machine. I bought my 1010 three weeks ago. After many days of building a cabinet for it and then building the machine, I got to work. My first few cuts/projects were awesome. Forgive the length of this first post as I'm unsure how much info to post and would rather err with more than less.

    I must admit to three significant oops to date that I expect are related to the issues I'm about to share. The oops were: forgetting to connect the probe ground wire two or three times (causing the machine to start the zero process only to have me cancel when it touched the plate and of course didn't stop...aaaaaaargh); forgetting to turn the router on prior to hitting start on a job (cancelled very quickly); and finally inputting the wrong depth on an end mill cut causing the machine to try to take out a much deeper chunk of wood than it should.

    All of those oops were cancelled quickly, but I'm guessing like with most precision instruments/tools, they may have led to the problem I'm about to describe. Don't worry, I've chastised myself repeatedly and will endeavor to not do any of them again. What I'm looking for here, is where to start with bringing my machine back into alignment. Forgive me if I don't use the proper jargon...I'm a newb, remember. Heck I'm even having problems figuring out how to post the pictures.

    As you'll note in the pictures (if you are able to view them), I'm experiencing all kinds of alignment problems. This project is going to eventually be a box comprised of three pieces of maple and walnut, CnC'd then laminated together. On the first attempt I used the CnC to shape the box exterior edges as well as the interior cut-outs. It worked but I decided I would use a saw to make the exterior cuts to save on CnC wear and tear. However, on the second attempt, the absence of the exterior shape made alignment curing lamination a royal pain in the arse, so I decided to try a third time, and added what I called a ledger grove at the bottom of each layer to help with alignment. I also thought I'd try to add a hole that would allow me to use a dowel for alignment. Basically, I was experimenting to figure out what I liked best.

    Problem 1. The hole, was supposed to be a .386" diameter circle, using a pocket tool path and a 1/4 end mill. The holes are oblong, not circular.
    Problem 2. The ledger cut at the bottom was supposed to be a profile tool path cut using a 1/4 end mill with 5 passes simply following a line at the bottom of the drawing. On both attempts there is very noticeable stair stepping or misshaped cuts near the ends (note there was a .5" ramp programmed in the toolpath). In addition on the second layer, the ledger cut extended to the right beyond it's programed length. I used the same dimension board and the same tool path command. Really not sure how the cu
    Problem 3. Lots of tool path marking (?). Basically I can see lines between the multiple passes.

    I have done a little reading and youtube watching. One item I planned on check was tram? Before I do that...any suggestions on openbuild specific items to check, tweak, turn, bash, etc...okay not bash.

    What else do you recommend?
     

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  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You have something loose in the system somewhere. Check to make sure the lock collars are fully tight against each end and there is no lengthwise play in the axis and check to see if there is any looseness in the flexible couplings where they connect to the lead screws or the motors.

    And you might cut way back on the depth of cut. Start shallow and work up once you're sure of what the system can handle.
     
  3. Giarc

    Giarc OpenBuilds Team
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    Once you get everything tight and calibrated, I would do roughing passes first, leaving 0.2 or 0.3 mm to be removed during a full depth finishing pass. When cutting woods or plastic I have found cutting at a depth of 1/2 the diameter of the end mill at 2500mm/min works well for me. Then I clean it up with the aforementioned full depth finishing pass.
     
  4. Rob J

    Rob J New
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    Thank you gents. I’ll start there in the morning.
     
  5. Rob J

    Rob J New
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    I believe I found my culprit. Everything I checked on the machine was still tight. However, I had recent tried rerouting my router power cord and I believe it was binding and resulted in a lack of free movement for the gantry. I will try some test runs today.
    Incidentally, I haven’t seen a training video that talks about how to generate tool paths for a full depth final pass. I’ve only watched a dozen videos so far so maybe I just haven’t gotten there yet. Do you have one you recommend?
     
    #5 Rob J, Jul 18, 2021
    Last edited: Jul 18, 2021
  6. Rob J

    Rob J New
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    The plot thickens. First, thank you for working with me as a newbie...if at the end of reading this your conclusion is all I'm dealing with is learning "feeds & speeds"...please tell me that...ultimately I want to make sure the machine is performing well and I'm the problem.

    I will try to give more information this time in the hopes you can help me dial my machine, process, or operator in (yes that was third person).

    Before I tell you about the changes I made in the tool paths and results. I did a test project before returning to the Ocarina box. The test used an 1/8" downcut and the results were extremely good in my opinion, so I'm mostly confident in the machine's capability, which I interpret to mean Giarc's recommendations are probably my biggest issues.

    Material for Ocarina project is Maple
    1. Alignment hole tool path (forgive me if there's a best way to provide this data): hole diameter .386, overall cut depth .83", tool .25" End Mill up cut (I adjusted the feed rate down from 160"/min to 100"/min), 10 passes (equates to .083"), offset pattern. Result is decidedly better, but still not a perfect circle.
    2. Alignment ledger line 2D profile toolpath: straight line, overall cut depth .83", tool .25" End Mill up cut (same adjusted feed rate down from 160"/min to 100"/min), I went with 9 passes to see if that made a difference (equates to .092"), machine vector was on the line, and included a .5" ramp. Result is better, but still a very small deviation approximately where the machine was ramping down...see the photo, if you look close it's down by the far end of the ruler.
    3. Additional issues/question. While cutting the Ocarina outline, I noticed the Do Separate Last Pass option, so I selected it but honestly could not figure out what it did. I noted burn lines on the wood where the tabs are on the first project attempt and this latest run. Is this an indicator of alignment issues or should I expect this normally? Here is the toolpath info: overall cut depth .83", tool .25" End Mill up cut (same 100"/min feed rate), 9 passes (equates to .092"), inside vector, separate last pass allowance set to .02", tabs length .17"/thickness .125", .5" ramps.
    image5.jpeg image55.jpeg image56.jpeg image6.jpeg
     
    #6 Rob J, Jul 18, 2021
    Last edited: Jul 19, 2021
  7. Giarc

    Giarc OpenBuilds Team
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    Have you calibrated the X,Y, and Z axis? There is a calibration wizard in Ope builds Control. I like to use as long of a measuring stick as I can.
     
  8. Rob J

    Rob J New
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    I used the calibration wizard and calibrated all three Axis. Z was good to go, but both X and Y were slightly off. I'm continuing to test. During one of my tests, I attempted to carve a new sign and had a curious result. On earlier carves using an 1/8" down cut, I selected Raster for pathing. The lettering came out wonderful...meaning curves were smooth. A recent attempt, also using Raster resulted in curves on the letters that had stair steps...almost like bitmap. When I went back into Aspire to check my work, I tried changing to Offset. The curves are smooth again. Any ideas what I might have changed to cause the problem? I don't mind using Offset, but sure would like to know what has changed.
    Thanks,
    Rob
     

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