Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: brixhamengineer on October 14, 2013, 09:51:46 AM

Title: Help for a new user - circles are not circles and its not backlash....
Post by: brixhamengineer on October 14, 2013, 09:51:46 AM
Hello, If I have posted this help request in the wrong place then I apologise, I am new to the forum. I have introduced myself though in the newcomers section.

I have a converted round column RF25 milling machine in the UK by Axminster tools. I have fitted new ball-screws to the X and Y axis (so eliminating backlash) and calibrated the three axis by DTI, cutting a part and checking measurements. I have adjusted the gibs for both X and Y again using DTI. I have checked the Z axis for slackness with the DTI.
 I have also tuned the motors to run the best I can and the conversion works very well.....as long as it doesn't include a circle. I have checked again both table security by dti and spindle movement.

Therefore I think it may be a setting problem, as when watching the Y axis motor, at the point the straight lines occur (along the X axis top and bottom) it slows down and whilst never stopping, slowly reverses before speeding up to produce a normal circle is produced again, until it is in the opposite position, where it again slows down before changing direction. At the same time the X axis keeps to the same speed for all the run.

I did find one suggestion where they said the acceleration for both X and Y should be the same. This seemed logical to me, as it was slowing down then speeding up again, so I made those changes. To find the problem still exists.  I did save the axis settings and did this procedure several times. It seems to me that both motors are working fine until the Y axis motor starts its slowing down etc.  I have also replaced the motor with one I have spare ready to make a 4th axis.......

Checking the internet and skimming this forum I cant find an answer to my particular problem. I know that a common reason for my circle problem is backlash and loose Gibb strips, plus possible play in the spindle.  I am used to the machine and adjusting it to eliminate play and it may be a red herring this slowing down of the Y axis motor but I have much to learn in regards to the software. Its frustrating as when cutting anything with no circle it performs brilliantly. I have thought of using it to change tool for a centre drill and spot where the circle should go, then boring on the lathe, or even using a boring bar (just thought of that Hmmm....) but that is not the answer. I want it working properly and I am doing something wrong.

Hope you can help...

Mike Freeman Brixham, UK
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: Hood on October 14, 2013, 04:51:54 PM
What do your circles look like?
Hood
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: Vogavt on October 14, 2013, 06:25:50 PM
What version of Mach3 are you using?

I know you stated that you've cut and measured items but do you have the backlash compensation on even though you're using new ball screws?
If it is on, are there still some legacy numbers there from prior to ball screw upgrade?

IIRC, some of the ball screws require an extra ball to ensure ALL of the slack is taken out, therefore minimizing backlash.


Might help to post your xml file.
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: brixhamengineer on October 15, 2013, 06:52:38 AM
Hello Vogavt,
 
Thanks for the reply, One question further before I go any  further, would a loose motor mount on the Y axis cause this oval circle?
I only ask because I have just tried to do a circle in MDF (less stress on the 3 axis) and still get the oval phenomenon? I am just having to go out and have no time, sorry.  I just spotted the bottom part on the mount has come apart leaving some movement?

Will look in later and give a better reply. I will have to weld now the bottom so in a sense I will answer myself but this may be a few days off.......If it can I will at least have a chance to rest my brain. I am failry convinced there is no backlash but have been wrong before.

Mike
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: Vogavt on October 15, 2013, 07:57:22 AM
I could certainly see where loose mounts could cause an issue. That very thing has happened to me before. Durin the change in direction the "slack" has to be taken out first in both directions.  We need to see a photo of how much oval you're talking about or at least measurements in the width versus length.
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: Jeff_Birt on October 15, 2013, 03:09:35 PM
Ballscrews do not mean you have no backlash.

Cutting something and measuring it is not a good method for deterring backlash or steps/unit. There are far too may factors at play.

To get the correct steps unit the best way is to calculate it based on your screw pitch, any other gear/belt reduction, stepper motor step angle and the stepper drive's microstep level. If you don't know these things then you have to measure it. Tell the machine to move a short distance, like 1" if it is close then move on, if it is too long/short adjust the steps/unit. Once you are close then set up a dial indicator and jog to preload it a small amount and take up any backlash. Now tell the machine to move a short distance the same direction you were jogging in, say 0.5", check your indicator to see how far you moved and adjust the steps/unit. There is a built in utility to make this easier on the Settings screen (as I recall).
 
To measure backlash you need to use a test indicator, jog the machine to preload the indicator 0.010" or so one direction and jog in 0.001" increments in the other direction. When the needle moves stop jogging. If you jogged three times and the needle moved 0.0005" then you have 0.0025" of backlash or slop in the system. Your motor mounts, stepper couplers, etc could all come into plate here.



Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: brixhamengineer on October 16, 2013, 04:53:53 PM
Thanks Jeff I will try what you say when next in the shop
Title:
Post by: Bodini on October 18, 2013, 03:22:57 PM
What does your gcode for the circles in question look like?
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: brixhamengineer on October 24, 2013, 06:10:46 AM
Sorry for the delay in responding (health issues) here is my code and also a picture of the results on a piece of aluminium. I hope someone can help. I have yet to try some of the suggestions above so the answer may already be there, but just in case.........

Code using CamBam

<?xml version="1.0" encoding="utf-8"?>
<CADFile xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Version="0.9.8.0" Name="two circles for trial">
  <layers>
    <layer name="Default" color="127,255,0">
      <ModificationCount>0</ModificationCount>
      <objects>
        <circle id="1" c="22,0,0" d="25">
          <ModificationCount>3</ModificationCount>
          <mat m="Identity" />
        </circle>
        <circle id="2" c="-31,0,0" d="50">
          <ModificationCount>3</ModificationCount>
          <mat m="Identity" />
        </circle>
      </objects>
    </layer>
  </layers>
  <MachiningOptions>
    <Stock>
      <PMin>0,0</PMin>
      <PMax>0,0</PMax>
      <Color>255,165,0</Color>
    </Stock>
    <ToolProfile>Unspecified</ToolProfile>
  </MachiningOptions>
  <parts>
    <part Name="Part1">
      <machineops>
        <profile>
          <WorkPlane state="Default">XY</WorkPlane>
          <OptimisationMode state="Default">Experimental</OptimisationMode>
          <RoughingFinishing state="Default">Roughing</RoughingFinishing>
          <ToolDiameter state="Default">6</ToolDiameter>
          <ToolNumber state="Value">6</ToolNumber>
          <ToolProfile state="Default">EndMill</ToolProfile>
          <PlungeFeedrate state="Default">300</PlungeFeedrate>
          <CutFeedrate state="Value">300</CutFeedrate>
          <MaxCrossoverDistance state="Default">0.7</MaxCrossoverDistance>
          <StartPoint state="Default">0,0,0</StartPoint>
          <CustomMOPHeader state="Default" />
          <CustomMOPFooter state="Default" />
          <Name>50mm</Name>
          <StockSurface state="Default">0</StockSurface>
          <RoughingClearance state="Default">0</RoughingClearance>
          <ClearancePlane state="Default">3</ClearancePlane>
          <SpindleDirection state="Default">CW</SpindleDirection>
          <SpindleSpeed state="Default">1000</SpindleSpeed>
          <SpindleRange state="Default">0</SpindleRange>
          <VelocityMode state="Default">Undefined</VelocityMode>
          <primitive>
            <prim>2</prim>
          </primitive>
          <TargetDepth state="Value">-2</TargetDepth>
          <DepthIncrement state="Default">0.4</DepthIncrement>
          <FinalDepthIncrement state="Default">0</FinalDepthIncrement>
          <CutOrdering state="Default">DepthFirst</CutOrdering>
          <CutWidth state="Value">3</CutWidth>
          <StepOver state="Default">0.4</StepOver>
          <StepoverFeedrate state="Default">Plunge Feedrate</StepoverFeedrate>
          <InsideOutside state="Default">Outside</InsideOutside>
          <MillingDirection state="Default">Conventional</MillingDirection>
          <CollisionDetection state="Default">True</CollisionDetection>
          <CornerOvercut state="Default">False</CornerOvercut>
          <LeadInMove state="Default" />
          <LeadOutMove state="Default" />
          <HoldingTabs state="Default">
            <TabMethod>None</TabMethod>
            <Width>3</Width>
            <Height>3</Height>
            <MinimumTabs>3</MinimumTabs>
            <MaximumTabs>6</MaximumTabs>
            <TabDistance>40</TabDistance>
            <SizeThreshold>4</SizeThreshold>
            <UseLeadIns>False</UseLeadIns>
            <TabStyle>Triangle</TabStyle>
          </HoldingTabs>
          <SideProfile state="Default" />
        </profile>
        <pocket>
          <WorkPlane state="Default">XY</WorkPlane>
          <OptimisationMode state="Default">Experimental</OptimisationMode>
          <RoughingFinishing state="Default">Roughing</RoughingFinishing>
          <ToolDiameter state="Default">6</ToolDiameter>
          <ToolNumber state="Value">6</ToolNumber>
          <ToolProfile state="Default">EndMill</ToolProfile>
          <PlungeFeedrate state="Default">300</PlungeFeedrate>
          <CutFeedrate state="Value">300</CutFeedrate>
          <MaxCrossoverDistance state="Default">0.7</MaxCrossoverDistance>
          <StartPoint state="Default">0,0,0</StartPoint>
          <CustomMOPHeader state="Default" />
          <CustomMOPFooter state="Value" />
          <Name>25mm</Name>
          <StockSurface state="Default">0</StockSurface>
          <RoughingClearance state="Default">0</RoughingClearance>
          <ClearancePlane state="Default">3</ClearancePlane>
          <SpindleDirection state="Default">CW</SpindleDirection>
          <SpindleSpeed state="Default">1000</SpindleSpeed>
          <SpindleRange state="Default">0</SpindleRange>
          <VelocityMode state="Default">Undefined</VelocityMode>
          <primitive>
            <prim>1</prim>
          </primitive>
          <TargetDepth state="Value">-3</TargetDepth>
          <DepthIncrement state="Default">0.4</DepthIncrement>
          <FinalDepthIncrement state="Default">0</FinalDepthIncrement>
          <CutOrdering state="Default">DepthFirst</CutOrdering>
          <StepOver state="Default">0.4</StepOver>
          <StepoverFeedrate state="Default">Plunge Feedrate</StepoverFeedrate>
          <MillingDirection state="Default">Conventional</MillingDirection>
          <CollisionDetection state="Default">True</CollisionDetection>
          <LeadInMove state="Default" />
          <LeadOutMove state="Default" />
          <RegionFillStyle state="Default">InsideOutsideOffsets</RegionFillStyle>
          <FinishStepover state="Default">0</FinishStepover>
          <FinishStepoverAtTargetDepth state="Default">False</FinishStepoverAtTargetDepth>
        </pocket>
      </machineops>
      <Stock>
        <PMin>0,0</PMin>
        <PMax>0,0</PMax>
        <Color>255,165,0</Color>
      </Stock>
      <ToolProfile>Unspecified</ToolProfile>
      <Nesting>
        <BasePoint>0,0</BasePoint>
        <NestMethod>None</NestMethod>
      </Nesting>
    </part>
  </parts>
  <ActiveLayer>Default</ActiveLayer>
  <ActivePart>Part1</ActivePart>
</CADFile>

picture of results (I have yet to repair the y axis bracket although I think it may have been there before?)

(http://)
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: Hood on October 24, 2013, 06:16:17 AM
You have backlash on the Y axis, likely the bracket but could also be due to other factors such as slackness in pulleys or bearings not properly adjusted.
Hood
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: brixhamengineer on October 24, 2013, 07:02:38 AM
Thanks Hood.

I accept what you say however the Y axis is a ball-screw and doesn't seem to have any backlash at all that I can find with the DTI? Also I found this info on the CamBan site which I am don't really understand and I have copied it below.  The circles are so far out that I would have thought they would have shown up on my backlash checks is that a fair comment? Any suggestions you have for testing/eliminating the Y axis problem would be appreciated as I cant see how (it being a ball screw) i can adjust it?

Info from CamBam

Crazy looking arcs (crop circles) or 'Radius to end of arc differes from radius to start' error when loading gcode into Mach3 or other CNC controller.

Gcode arcs specify a center point (I & J parameters), which can be absolute coordinates or relative to the first arc point. A problem will occur if CamBam and the controller are configured to use different arc center methods.

To change the arc center method in CamBam, select the Machining folder. Then change the ArcCenterMode property to Absolute or Incremental to match your controller configutation. Alternatively, change your controller software to match the CamBam setting.

For Mach3, it is sufficient to just select Mach3 in the Machining - PostProcessor property. Mach3 recognises non-standard gcodes G90.1 and G91.1 which are used to specify the arc center mode used in the gcode.

ArcCenterMode and PostProcessor properties are set per drawing. These can be set as the default for all new drawings by specifying a DrawingTemplate property in the system configuration settings.
Title: Re: Help for a new user - circles are not circles and its not backlash....
Post by: Hood on October 24, 2013, 07:19:18 AM
It is not crop circles, you would see them in the toolpath view and the cut path would be a mile out from what you are expecting.
I am not sure how you tested for backlash but you may not see backlash if you have no cutting forces present when checking, that is especially true for slack couplings, flexing or moving brackets etc.

Hood