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

What do your circles look like?
Hood

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.

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

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.

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.

Thanks Jeff I will try what you say when next in the shop

What does your gcode for the circles in question look like?

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?)

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