Highest precision on Z axis down to 0.1mm

Hi everybody! This is my first post on this awesome forum, even if i got my x-carve since august. So first of all, nice to meet you all, and thanks for all the great tips! You’re a fantastic community, and i hope i’ll be soon posting my projects and helping others as well.

Now, straight to the point. I’m trying to achieve the highest possible precision on the z axis that this machine is capable of. This is because i need to mill some o-rings grooves for liquid blocking, and these grooves need to be extremely precise in depth. Say 1.4mm deep, not one tenth more, not less, or the liquid might come out.
Problem is, my x-carve cuts 0.3mm deeper on an average basis. This means that measuring the grooves with a caliper, i’m finding spots where it cut 1.56mm, others where it’s 1.65mm, or 1.82mm, or 1.59mm, bla bla bla…

I have read A LOT of posts here on the forum to check for solutions before posting, but as far as i could find, no post regarding z-axis inconsistencies or problems was about one tenth of a mm, but rather more about 1mm to 3mm inconsistencies. I apologize if this was actually talked about somewhere i couldn’t find.

My current setup:
I have a stock 1000mm x-carve, with dewalt 611 router, and a custom made z-plate.
Z-plate is aluminum, sanded down to a height of 9.98mm to 10.02mm (0.04mm is the highest tolerance i measured)
Stepper motors calibrated 3 times.
I squared the machine to the point it looses 0.5mm over a distance of 500mm on x and y axis. Couldn’t make it any better unfortunately, but my tests are on a far shorter length so for now it should be enough. (gotta fix this someday anyway)
Actual spoil board is an additional 3mm MDF board that i sanded down to about 0.05mm tolerance on its surface and set on top of the main spoil board.
I re-calculated and set the x and y steps/mm so it looses about 0.05mm over a distance of 500mm.
I didn’t re-calculate the steps/mm for the z axis since i still don’t own a gauge.

How i’ve run my tests:
I measured the cast acrylic pieces i’m testing with, and they are extremely inconsistent in height. What is supposed to be a 10.0mm piece, ranges from 8.9mm to 10.2mm. (btw where can i buy good precise acrylics in the EU??)
I tried with different cut settings (feed, plunge, depth), basically going down to half the stock Easel settings for cast acrylic, and down to 0.1mm with regards to depth per pass.
I run a lot of test cuts as close as i could to the clamps, so to minimize the spoil board and piece inconsistencies.
End mill is a 2mm, 2 flutes, 3mm shank hard steel from Proxxon, that i clamped using the 1/8’’ precision collet tightened to death :slight_smile:

Now, no matter what i try, i always get inconsistent depth cuts ranging from 0.15mm to 0.5mm deeper than what’s set in Easel. As i already wrote, the average inconsistence seems to be 0.3mm.

I know that the x-carve is capable of about 0.1mm tolerance, maybe a little less.
Next tests i’ve planned are to re-calibrate the z-probe, and buy a gauge so to re-calculate the steps/mm on the z-axis.

What in the world can i do other than this?
Oh i’m totally new to all of this, i’m learning a lot but still have a loooong way to go.
I’m sorry for such a long post but i thought it’d be better to give you as many details as i could.

Thanks a lot :slight_smile:

I agree. Just purchased a great caliper set (Amazon), “Peak Precision”. Includes the digital caliper with depth probe(already stabbed myself with the points, ouch), a 6" scale(with decimal equivalent scale on the back side), and a feeler gage set (.04mm-.63mm). Very high quality/heft. Replaced my old malleable plastic caliper.

Hi guys, thanks for your suggestions!

I’m using a digital caliper, i was thinking of getting a dial one, and now you’re giving me a reason to actually go for it.
I was still in the process of figuring out the correct groove dimensions for the o-rings i’m using. This was the goal of my tests. The o-rings are 2mm wide, hand-cut to length and at the moment i’m testing to seat them in a 3mm wide groove to allow for some squash, 1.4mm deep (i tried with a 1.5mm deep groove, it kept the liquid quite well mostly with the liquid actively flowing through, but when put to rest, it started flooding a very tiny bit all over the gap between the two pieces of acrylic).
Regarding your last question…my z-axis is 100% stock.

So you haven’t used the Xcarve to surface the board? You may want to try surfacing a board using the Xcarve which may help with your problem or give more evidence something else may be happening.

For better precision you are getting into the esoteric of design and micro stepping.

Do you have the upgraded gantry? Any flex in the gantry is going to impact your depth of cut as the bit deflects. Also make sure all your wheels are well adjusted, again so there is no wobble or flex.

Read this article on micro stepping vs gear reduction

So you may want to try reducing your micro stepping on the Z axis an see if this has any impact on precision. It is going to sound terrible when you do this by the way. “grind grind grind
Any positional issues due to micro stepping may be trivial compared to other flex issues, but it is something you can easily test out.

The stock design uses a belt and basic nuts, as opposed to anti backlash nuts. So backlash in the belt and nut could also be an issue.
There isn’t too much you can do about this beyond making sure the belt is tight.
You have a couple of options upgrade wise.
Maybe switch to an anti backlash nut? I don’t know what modification may need to be done to do this.
You could change the belt pulleys on the Z axis to add a gear ratio to give you more precision per step?
Or replace the Z axis with a balls screw drive from ebay or a c-beam setup?

But these are major hardware changes and there is no guarantee that they will result in a more consistent depth of cut. (especially if mechanical flexing in the gantry or other parts is responsible for the variability.)

My recommendation:
If you have not already do the upgrade to the new gantry rail and variable spacers - it is worth it.
Try setting up your carve on the edge, rather than the center of the X Carve, where it is less likely to flex - see if that helps.
Play with the micro stepping settings and make sure all your Z values are in single step increments - see if that has any impact.
After that…?

When I asked if I should concerned with a sag of.0015 to .002 I was told by a forum member said that if I am concerned about such a low value I shouldn’t be using the X-Carve.

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Kind of. I haven’t actually used the xcarve to surface the board, BUT i have used the xcarve to gently trace lines (using the end mill) to highlight areas with inconsistencies. Then i sanded the board with a 500 grain sandpaper.

You bet it! :slight_smile: Thanks for all your suggestions, i’ll give every one of them a shot and let you know.

I’m not using a pre-made o-ring, i’m using nitrile cord and cut it to size to fit in my design.
I can’t figure out what those 32s and 63s are on the first design you attached, can you explain?
The second design (the red one) looks interesting, i might give it a try!

Hi Clyde, actually i’m not concerned about a 0.002’’ (0.05mm) tolerance. I’m concerned about the double, so 0.1mm. I THINK that if i reached that kind of precision, my system could work.

So first things first, i need some very precise way of measuring the depth of my cuts. What’s the best method you know of? I’m concerned about using a good caliper to measure the depth, since the way of probing all calipers use (get the probe in the cut and lean the caliper’s body against the surface of the piece) doesn’t look very solid.

The 63 and 32 are denoting the surface finish, in microinches


Starrett micrometers: http://www.starrett.com/metrology/metrology-products/precision-measuring-tools/micrometers

Aah good to know, thanks!

Great tool! but that’s too much for me, other than this o-ring thing, i’m not going to need this kind of precision any time soon. I thought i could find a good depth micrometer for about 100€ or so. I was wrong :slight_smile:

Sorry if i’m sounding dumb, but are you saying that using the correct o-ring size and groove shape, the depth cut inconsistence i’m getting should not be an issue?

I’ll be trying to set a lower microstepping as per Aaron suggestion, i’ll let you know what comes out.
I should also be upgrading to the new wide makerslide so to stiffen the gantry and get less bit deflection, but shipping costs and customs to Italy are way too high.

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I purchased all of mine used at home yard sales and second hand stores. Some great bargains out there if you can take time to look. Hope it is the same in your area.

You have a point there. I’ll give this a shot and let you know. I have to find a cord of some material, can’t go for pre-made o-rings. Any suggestion?

Ouch. I’m afraid second hand tools of that kind (not “commercial” tools) are a no go for me.

Might be a dumb question but how are you completing the ring? Is that your weak point? Generally if you just butt ends up, it’s not going to seal well

I’m using Loctite 406 for sealing, butt ends one against the other, and honestly they look ok, but i might be wrong.
The spots where i got leaks from where not always close to the joint of the o-ring. I even tried placing to o-ring upside down to test for little inaccuracies of the joint, but that didn’t change anything. Leaks were from random spots across the whole o-ring length.
Do you have any hint on how to better make custom length o-rings?
Phil’s idea of trying with a softer material sounds promising enough, but i still have to figure out which material to go for.

I used a depth gauge to measure dept of holes. It’s a micrometer with a “t” for a base and different sized rods that goes down the hole. As far as checking groove depth thats a different story. The company I worked for had some special tools made just for that purpose.

Absolutely, no problem sharing! I’ll post a sketch as soon as i can. I was thinking about making a mold too, but i think it will be easier to just buy the right cord. I was looking at some silicone cords, i’ll post some links.

Yes, top quality and specialized tools would be the best, but they’re too expensive and hard to find for a hobbyist/craftsman like i want to be. I would definitely go for such tools if i ran a company!

Ok, so here we go. Sorry for the raw sketches. This is one of the tests i’ve run. I’ve threaded the two wide holes in the cover and let some fluid flow through to fill the pocket milled in the piece. The groove has the same outline of the pocket, and is offset by 1mm, and is approximately 3mm wide and 1.5mm deep. The o-ring i used has a 2mm diameter, shore a 70 (quite hard).
The holes on the cover and around the groove are threaded for M3 screws, and are needed to fix the cover onto the piece.

Cover (5mm acrylic) and actual piece (10mm acrylic):

Assembly view:

Pocket (for the liquid) and o-ring groove:

This is a terrible but quick sketch of the groove (this is NOT scaled properly, i’ve drawn this by hand :stuck_out_tongue: ):

I’ve searched high and low for softer o-ring cords, and this is the only affordable alternative i’ve found. It’s a shore 60 silicone cord. We were talking about trying a softer material, and something a little bit bigger then 2mm to compensate for my x-carve tolerance, so this might be it. https://www.polymax.co.uk/rubber-cords/silicone-cord/translucent-silicone-cord

I know shore 70 to shore 60 doesn’t change much, but it’s the only affordable alternative i’ve found so far. Some companies do sell a shore 40 silicone cord, but MUCH more expensive than the one i’ve linked.

Tomorrow i might be able to test for the microsteps setting of the g-shield, i’ll let you know. But still, the idea of trying a softer material and a bigger (maybe 2.5mm or 3mm?) diameter for the o-ring to compensate for the machine tolerance sounds best to me.

Indeed! i also thought of surfacing the acrylic before actually milling the pocket and the o-ring groove, but that would require a ton of extra time spent milling, and the loss of the transparent finish. I’ll give a look at that auto levelling thingie you mentioned. Thanks!

I have no psi info, and the nitrile cord i bought has no tech specs listed.
The screens you posted show shore 60 and 50 nitrile o-rings, but they’re pre-made o-rings, not cords that i can cut and bond on the spot. And by the way, i can’t find any shore 60 and 50 nitrile cords here in europe :frowning:

what do you mean?

Circumference = total length of slot for the O-ring :9