What's causing these hole location inconsistencies?

I have my work piece clamped onto a 90 degree fence. To make sure it was square I jogged the end mill from end to end while tightening. I’m not sure if it’s perfect but it seemed good.

I’m drilling holes on each corner of my work piece and getting major inaccuracies. I made an image to show just how significant. Any ideas what’s causing it?

You did not say what machine you have. If a belt machine check all your pulleys on the stepper motors to make sure they are tight. Check your belt tensions as well. You can run a calibration test making circles and squares of a certain size and check that they are indeed the size you expect. If the circles and squares are not consistent then it is likely a mechanical problem. If the circles and squares are consistent but the wrong size you can modify your gbrl settings to fix the steps per MM to fix that.

Lastly double check your measurements of the stock. Since your stock is 10" I bought both a 6" and a 12" digital caliper. The 12" one comes in handy on larger stock. The prices for digital 12" calipers is not that much. If you are using a digital caliper check that it is repeatable on measurements. The 6" one I have if the battery gets low it is inconsistent in measurement.

If you have a ball screw machine check your lubrication on the bearings and rails. A dry rail gets more resistance and is technically missing steps. Also check that all your bearing blocks on the ends of the ball screws are secure. If the bearing blocks are loose it introduces back lash and causes inaccurate cuts.

Are you measuring to the center of the holes?

If a belt-driven machine have you calibrated for belt-stretch?

You’ve entered your measurements with 3 decimal places. How are you measuring that accurately?
Also, it looks like you are measuring from the nearest edges, when it was all programmed from, I assume the lower left corner. What are these dimensions?


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I have a S3 XXL HDZ with dewalt router.

I measured with a caliper from inside the hole to the outside edge.

I did some testing and improved things by re-setting the fence. It seems when I clamped down the work piece it slightly shifted the fence and skewed things. There are only 2 bolts holding it in place.

I’m thinking maybe a 3D printed fence isn’t good for what I’m doing.

I have blanks I need to load into the CNC wasteboard, then I need to cut them out. I’ll use tape and glue if needed for now. Should I run a 90 degree line down the wasteboard with a thin bit then glue down the work piece alongside it (using it as a guide)?

Also feels like a retarded question, especially since I’ve been using the CNC for so long now… but I’m getting some problematic inaccuracies using the bitzero. I’m looking to test manually zeroing my work piece. For extremely good accuracy should I zero using the center of a vbit?

Edit: forgot to mention I checked my belts, they’re nice and tight

When you need to have a critical dimension and squareness referencing the fence you install on your spoil board plan to square it with the machine. A friend asked me to add juice grooves to some expensive cutting boards. I added a new sacrificial fence and machined the material support side in place. I only did one side, along the X axis so I did not over constrain the workpiece. It ensured it was parallel to the machine’s X axis. Using the Bit Zero to set zero at the lower left corner worked well and came out as square as my machine (3XXL).

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What bit are you using when using the BitZero? You can use any bit for probing Z, but a VBit is not the right bit to use for X & Y.

If you also have a BitSetter, then the best ‘bit’ to probe with is the dowels that came with the BitZero.

If he has a 3 then it is unlikely he has the bitzero V2 which comes with the probe pins. I originally had a V1 and it was used but I assume it did not some with the pins either since you have to pick the bit when you probe.

I bought some 1/4” steel pins and used that even with the V1 though.

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Just looks like your work piece was rotated ~0.75 degrees clockwise due to fence being out of square with machine.


I have multiple removable fences I have one on the far bottom of the wasteboard, one on the far left side, then another around the upper / center area. I think my main issue is that I was expecting to be able to install them in 2 minutes and get accurate square to the machine axis’.

First thing tomorrow I’ll try making a 90 degree indent in the wasteboard as a guide to line up the fence. If it’s not accurate enough, I think I might try one of those abs tubing fences. If that doesn’t work tape and glue will have to be the option.

With the bitzero the major inaccuracy that I know about is on the z-axis. Usually -0.035" compared to if I set the z-axis manually after the x,y,z corner probing cycle. I probe with either a 1/4 or 1/8 end mill. I would only use a vbit for manual setting if that’s a good idea.

I have this one here

Any ideas to make sure my fence is perfectly at 90 degrees? I need to be able to set it up quick. It needs to come on / off every couple of days. I have a threaded tnut wasteboard.

To make a right angle fence: Clamp a suitable sized piece of hardwood to where you want the fence to be. Mill indexing holes through the hardwood into your waste board. The holes should match the diameter of indexing pins/dowels that you purchase (eg hardwood dowels or steel rod). I would put two pins along X and two along Y. Pin it. Using the CNC, cut an X contour the depth of the hardwood, mill a relief hole at the corner, mill a Y contour the depth of the hardwood. This should give you a nice hardwood ‘carpenters square’ with two index holes in each leg which can be removed. When installed and pinned, it will be square to the machine ( you do not need the t nuts for this). This works for me but I do not require high precision. I am sure there are more qualified folks on here with a better way.


Also good to mill a shallow pocket on each leg at the corner to allow capacity for the bitzero in case your material is close in thickness or less than the thickness of the square.

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That seems like a great solution, I’ll make it today and see how it goes. I don’t need extreme accuracy, just “accurate to the eye of the client” type of results.

I ended up making a 90 degree score in the waste board using a 1/16" bit and clamping the 3d printed fence onto that line HARD. Since there are only 2 bolts in the design I added a couple of extra clamps just to stop shift and warpage when I apply the cams.

Ran a test piece and it’s perfectly accurate to the eye now. I should have taken time to fix it right away, I have 4 pieces that took around 10 hours of CNC work where the holes and border are slightly off now. Thankfully they aren’t going to a client but they are display pieces so I might need to remake them.

Did some tests on the X,Y for bitzero and it’s accurate. It’s just the Z axis which is off and that’s not a big deal.

Anyway, appreciate the help as always fellas. Really happy to have everything dialed in.

You said the Z is off. The Z-Plus and the HDZ have different pulses per MM. If you have a Z-Plus and tell the configuration it is an HDZ you get more steps per MM and the Z-Plus will carve deeper than it should if you have a Z-Plus and an HDZ. Same is true if you have an HDZ but tell the config it is a Z-Plus.

You can run the configuration to check your configuration.

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Hmm. I’m 99% sure my config is setup properly but I’ll double check. It’s the config in carbide motion right?

When I set cut depth to .25" on .25" stock it’s dead on at the end of the cut. It’s just the probe that’s inaccurate on Z for whatever reason. If I manually set the Z off the stock it makes the cuts perfectly.

I did crash into the probe about THREE times so I can’t really expect it to be perfect :sweat: 2x with a 1/8 end mill and 1x with a 1/4". I aim for a non-scarred location when I’m probing but it’s still inaccurate on Z lol. Every time I run a probing cycle now I trigger flashbacks of when I crashed it and freak out for a split second wondering if I remembered to attach the magnet to the collet :laughing:

I don’t usually probe just for Z but as I understand it when you don then entire Bitzero should be on the surface of the material, not resting over the corner. Have you tried it that way?

I assume by your description of looking for a non scarred pet you are only doing Z since when doing the corner probe you have no control over that.

I have crashed into my BitZero multiple times by forgetting to attach the lead. At least that is a slow crash but makes me slap my head anyway.

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Ohh yea didn’t consider running just the Z probe, I’ll try it out so see how accurate it is. Usually I do the corner probing (x y z).

No joke I start getting adrenaline when I press probe now. I was so intent on never crashing the CNC but screwed up 4 times (scuffed up the probe AND my bitzero :smile:). Bitzero was worse because the router was RUNNING. Thankfully only a 1/16 bit so minimal damage but it gave me a heart attack. Every screw up was because I was blasting music in headphones. I had to stop listening to music and just listen to self improvement content now since it’s less distracting.

I would share with you the video I did of using an SST dragknife and forgetting to turn off the router but it’s too embarrassing and NSFW.

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