Hi, I don’t enjoy calibrating the x-carve (who does) and changing the mill end to an engraving bit makes perfect sense to get that needle point accuracy, and the z-axis was always very fiddly, but there had to be a simpler method. Well this afternoon I found an answer that suits my needs and knocked up a simple adjustable bracket which bolts onto the back of the spindle mount.
The bracket comprises two main components, the attachment to the spindle mount and an adjustable piece which will hold a needle point for x and y axis calibration, and will also hold my digital/dial micrometer for the z-axis. You might wonder whether the mounting might limit the x axis travel but Ive been careful to make sure it doesn’t, i.e. if it were to cause a problem you’d already be beyond the safe limits of the machine anyway.
Parts: 5mm acrylic, 4 x M4 x 10mm machine bolts (acting as the guides), 1 x M6 x 15mm machine bolt (centre), 1 x M6 plastic knob.
Here are a couple of snaps:
Calibration bracket in the up position
Calibration bracket in the down position
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Interesting idea, can you show a couple more pictures with the needle and dial indicator in place? I’d also like to see how you attached it to the spindle mount.
I’m curious if a version of this can be made to fit on the back of the X-carriage somehow, near the center. It would completely remove it from the cut area and would still be easy to use if you can walk around your machine. Not much good if you can’t though.
Hi Robert, here are a couple of snaps with the digital dial indicator (I’m not an engineer so don’t know the correct terminology, sorry) and the sub-assembly which mounts it to the vertical plate.
Having looked at the the rear of the X-carraige I think it would be relatively simple to manufacture a modified bracket. The connector blocks could move, or you could mount them on a plate which would have a lateral mounting holes for the calibration bracket when needed. Let me know if you decide to build one; I may have a go myself.
I haven’t settled on a needle attachment yet (more accurately which needle device I’m going to use) but the mounting sub-assembly has been designed to allow it to be simply secured in place when complete.
Forgive my rush to get this in place, but I haven’t had time to polish the cut edges of the acrylic.
Here is a short video of the z-axis calibration in action. I sent a value of 20mm and the digital indicator read 19.90mm. I used the stepper motor calculation to determine the corrected setting and sent the same 20mm command again, which delivered the accuracy I was hoping for.
Z Axis Digital Calibration Test.mp4 (970.1 KB)
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Here’s a picture from the back side showing how it’s fixed to the spindle mount. The bolts are too long but I didn’t have any shorter to hand. That’s something I’ll address in time as I continue the modifications. The bolts replace the originals, going straight through, with a washer and a nyloc nut.
Did you glue two pieces of acrylic together for the dial indicator mount, or mill it from one piece? I really like the design, and it looks nice and processional with the curves and such. Once you get it perfected to your satisfaction, I hope you will consider sharing it as a project.
Scratch my idea for the rear mount, at least for Z axis calibration. The X-carriage tends not to go up and down unless there’s something drastically wrong. 
It would still work for X-Y, but in that case it would be better to just have a needle that is attached to the front of the X-carriage underneath one of the V-wheels that can be rotated out of the way when not in use. Your idea though, that kills two birds with one stone. 
The acrylic is fused together using a compound called (unimaginatively) Plastic Weld. It’s not a glue but actually breaks down the top molecular layer of each piece of acrylic forming a single piece of acrylic as it evaporates (quickly). The bond is extremely strong and ready to machine or bolt to in under a minute. You do need to set the surfaces correctly so that you have nicely smooth and flush surfaces adjacent to each other. You don’t need much compound as it’s the consistency of water and seeps very quickly into the joint. I use a syringe and needle that you might normally use for refilling ink jet printer cartridges.
You can see how I can mount other attachments now if needed. I’m thinking of a digital distance/travel indicator to replace the needle method; that’s if they make one (now to Google).
Here’s one final snap of the mounting plate without the dial indicator. The red bolts are left over from a motorcycle renovation.
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Hi Robert, I watched your video on calibration again this morning and thought it might be useful to create an online calculator to make the calculation part quicker and less taxing. I’d appreciate it if you could check it to make sure I have everything set correctly. Here’s a link:
Stepper Motor Calibration Calculator
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That looks good to me, thanks for making it! Can you post the link as a reply on the maintenance/troubleshooting thread so it’s there for everyone also?
Thanks for checking that for me Robert; I’ve put the link into a troubleshooting post as you suggested.
yeah i like that when is it going to be on the projects section of Inventables website?
with a small write-up?
Nice idea, Neat being in on the cutting edge of CNCing (new word).
I have my 611 mounted higher giving me more Z clearance but I see no reason I couldn’t use that.
Thanks for sharing.
Hi Evann, I have a couple of modifications to the design in mind but will look to write everything up and post it as a project over the coming weekend. I’m also working on a digital x/y calibration tool which uses sensors from an optical mouse hooked up to an arduino mini and a digital display. It will attach to the bracket designed above.
oh very nice i look forward to that
Hi Daniel, how much travel do you think you might need? This design gives 100mm z axis travel, which I’m extending to 120mm for the version which I’ll post to the project section of the forum. I’ll include all the design files in various formats which will hopefully allow you to modify it, if you do find it of some use. 5mm acrylic is has good structural integrity but I suspect that beyond 120mm, with the guide slots from this design lengthened, you may experience some undue flex under load. Not so much in the z axis but if you mount a tool for x/y axis calibration it may start to impact accuracy. Once I have mine in place I’ll give you an update. If 120mm is solid I’ll make a 150mm version and see what the results are.
Sometimes what I am carving is thick so the extra clearance is nice.
I am still finalizing the placement and anchoring of the machine so that I can pull the waste board for even more Z travel.
Presently installing NEMA 23s and then recalibrating.
I used a .25 smooth pin in the collet, a measured Mic standard and a 1" dial indicator. Got it to within .002 repeatable on all three axis.
Hope I do as well after the upgrade.
