You are not alone, I’ve seen posts here from several people doing something similar and I remember particularly @Vince.Fab who did the same by filling the extrusion with sand I think. Some people reported using special sand with polymers. A quick search of the forum should identify several.
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I studied your build a lot, and it seems really only the big extrusions remain from the original machine. If you were to give your intuitive sense of what improved your machine the most (by whatever metric), what were your top three upgrades?
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Some folks are getting fantastic results from linear rails, but how much better? Can you get most of the effect ( or even a positive effect ) with harder wheels instead? Wheels would be a LOT cheaper and easier, if they gained most of the advantages. Nobody’s tried and measured, to my knowledge.
One of the advantages of linear rail is reduced risk of schmoo/chips binding the axis. Wheels would require some enclosure and wipers to take on the full advantage of linear rails - beyond the other aspects
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- Z axis with linear rails and ballscrew. Whether you’ll buy HDZ or decide to build your own, imho it’s a must if you’re planning on cutting aluminium efficiently.
- linear rails. I can’t imagine having any of my machines run on v-wheels anymore.
- making your machine heavier - fill the extrusions with sand, pebbles or steel and epoxy. Build a sturdy metal base for the machine and bolt it down to it. It’s incredibly important to have a very solid table. I wouldnt use wood ever again.
Also swap the original belts to the steel-core ones. Ohhh I can’t stress it enough what a difference it made for me when I was first cutting aluminium end-plates for my DIY cnc on the shapeoko.
Besides that, upgrading to the proximity sensors is a must.
All the above mods made the biggest impact to the quality of my cuts. If youre on a budget, replace the belts, z axis, limit switches, fill the extrusions and you’ll see a massive improvement. Adding linear rails is certainly worth the effort but so easy to screw something up.
Check this thread out. XZero CNC The machine doesn’t exist anymore, but pay attention to the components used to understand how important it is to use certain parts over the others.
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FWIW, I made similar deflection measurements with a HDZero (Luke’s project before joining Carbide, based on v-slot extrusions, linear rails, and ballscrews).
Over a 1.5m gantry (substantially larger than an XXL), I saw ~60 microns of deflection with a 5 lb weight. That’s 2.3 thou, or around 1/3rd of unllama’s measurements with half of the weight.
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You might want to consider applying the forces where they originate (at the end of the cutter) and measure the deflections there. My 2 cents on vibration damping (post 494).
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So if I understand your post there correctly, you don’t think increasing mass in the case of epoxy granite will help, but how do you feel about varying loss coefficient and damping effect? I’m kind of inclined to generally look at the vibrational world from a mass-spring-damper perspective, and I see the extrusion fills as touching on all three.
I’ll definitely be measuring at the cutting tip - Linear gantry deflection is preliminary but necessary. I would like to deconstruct the impact of individual modifications, and I view tip deflection largely as the end product of a combination of translational and rotational deflections (very roughly, gantry vs spindle/cutter/mount).
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Gameplan right now looks like:
| Configurations | Cost |
|---|---|
| Stock “sorta” tightened belts | $0 |
| Calibrated tightness belts | $0 |
| Center support | $2 |
| Steel belts | $10 |
| Harder V-Wheels | $50 |
| Filled Extrusions | $50 |
| HDZ | $400 |
| Linear Rail - X Axis | $150 |
| Linear Rail - Y Axis | $300 |
To be evaluated against:
| Metrics | Confidence I know WTF I’m doing | Corresp. Uncertainty |
|---|---|---|
| Gantry deflections | 100% | 0% |
| Bed weight deflections | 100% | 0% |
| Vibration characterization | 60% | 40% |
| Cutter deflections | 80% | 20% |
| Repeatability | 10% | 90% |
(^^^^ These need to all be 100% before I start the hard-to-reverse mods like V-wheels and filling extrusions)
"Value at Risk" - where am I losing out on the most if I deploy now
Hoping to see next week if I can finish up my vibration characterization metric/protocol, and I think cutter deflection is a matter of sitting down and doing it.
There’s another metric I’m trying to get my head around. Who’s got some ideas on how to evaluate “repeatability”, and what that means? Accuracy, precision, RTZ? Maybe I mill out and measure a circle-diamond-square? If we are to evaluate different homing switches in the future, how do we discern the improvement there?
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For repeatability, a good test ought to be milling a part such as a circle-diamond-square with a finishing pass, then milling it again, but afterwards, re-homing and then re-running the finishing pass — if the parts measure the same, then repeatability should be quite good — any difference should be attributable to either a deviation when homing, or other movement.
I suppose for best results do it 3 times:
- initial part
- initial part and a second finishing pass
- initial part, rehoming, then second finishing pass
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Do you intend to characterize vibration characteristics at machine resonances (too?)? Will you be limited to forcing frequencies below (and forces above) what people typically would/should experience because of measurement bandwidth limitations? Do you intend to measure and document cutting power and details of the cutting parameters (all of those in the SFPF calculator as well the spindle stick-out and test location X,Y, and Z)? Will you be recording audio, video, and calibrated sound pressure levels during your tests? Will you try to determine, address, and evaluate biggest “bang for the buck” modifications first?
As shown here, poor quality spindles can be another vibration source. It’s producer also has a series of videos on building a granite CNC machine,
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Just throwing this out there. Of all the mods ive done… the best one was tightening the nut behind the wheel.
The frequency and resonance bubble is super interesting once you dive in. Excited to see what kind of data you find
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The nut behind the wheel? The v-wheel nuts?
I think filling the Y extrusions might be OK since they don’t move. I don’t think increasing the mass of the X extrusion would be helpful since it’d take more energy to accelerate/decelerate it.
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increasing mass of a cnc helps a lot period! Your machine will be more stable. It might not make a difference when youre cutting wood but will make a difference when cutting metals. Like I’ve said before, my diy cnc was filled with steel and epoxy. Before that upgrade, when machine was making sudden direction changes (for instance during adaptive clearing) entire enclosure would shake like a jello. It was genuinely scary. Now after probably doubling or tripling it’s weight it’s stable as a rock. You want to have a heavy gantry, but need to find a point where it’s not too heavy to overpower your motors and cause them to stall.
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The nut driving the machine?
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Did increasing the mass help as much or more than the other (rather extensive) modifications that you’ve made? In your opinion what were your “biggest bang for the buck” modifications?
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From what I have read and heard, increasing weight has far more benefits than negatives. I think there would be a point where you increase weight too much and need bigger steppers or a more robust drive system.
I have been looking at filling all 3 of my extrusions with epoxy granite. If the stock steppers can’t handle it, I’ll upgrade them to bigger ones, I already run steel belts, but if they can’t handle it I will start looking at linear rails and ballscrews
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I expect this has been discussed before… why not use lead shot in the extrusions… ? It is a reversible modification and because the shot is loose, it further absorbs vibration to an extent. I used to use it in speaker stands back in the hi-fi days.
If you don’t like it just pour it back out… or if it is good just pour a thin epoxy in to solidify it.
It is also pretty cheap… and I guess most gun stores will have it to avoid shipping costs…
Something like this … or a bit more expensive on amazon…
https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwj_gYmn3enlAhWEn7MKHSAQBl0YABASGgJxbg&ohost=www.google.com&cid=CAESQeD28bUxmcuPxJGCwEaeieHVxfpv1kdcxgzYhF06rOVthfBuELR8uEO8IOr8PqvpeOPQLBL5lhcJADjhrgfS9u0Y&sig=AOD64_0DqzAonDZF_PpEEWEpgJ0DoA-HDQ&ctype=5&q=&ved=2ahUKEwiquv-m3enlAhUGVN8KHeZYAFoQwg96BAgLEAo&adurl=
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@gmack increasing mass certainly helped with the quality of a surface finish. To what extent however it’s hard to tell, because i did that at the same time when upgrading to linear rails and ball screws, so I can’t give you a definitive answer based on the so3 upgrades. That being said, increasing weight of my other cnc made an immense difference. Filling extrusions was such quick and inexpensive job that it’s a no brainer for me. 3d print end caps and fill the extrusions with sand from your local home improvement store and youre done. It’s less than $10 investment.
Now, best bung for the buck with a stock so3 imho were steel-core belts and proximity sensors. I never knew how tight should original belts really be, they would stretch and be difficult to calibrate. I’ve been calibrating, recalibrating, tensioning them and could never get them to work as precisely as expected. Swapping the belts fixed accuracy issues for me. Instalation was a breeze, because you can’t stretch them, they just fit how theyre meant to. Just used stock settings and every dimension was within 0.1mm or better (depending on a cutting strategy and tool path used). I do a lot of aluminium cutting so repeatability and precision is paramount to me. I could never work with the original limit switches. My work zero would shift sometimes even 0.5mm after homing the machine, which was insane!!! Luckily $15 switches from amazon and few minutes of soldering fixed that.
If youre asking about the best mods after the machine was completely rebuilt I cant give you that answer. Ballscrews and linear rails are simply staples of every cnc build in my opinion. They’re used on industrial machines for a reason. Even though the components I used are of a much lowered quality they still function in the same way. I’ve never lost any steps while using ball screws and didn’t have to deal with debris causing my motion system to affect cut quality. Ohh gosh, losing steps with belts even with light cuts in aluminium was something I could never get over. That combined with poor quality limit switches was a sign that I had to change something, hence the full machine rebuilt.
I’m not trying to completely bash so3, because it was a great machine to learn on and very capable out of the box. If I were planning on using it as a hobby and to make few parts for myself only I wouldnt modify it so extensively. Also people on this forum have far more ambitious projects than I’ve seen elsewhere. All the discussions about cutting techniques on desktop cnc’s is why I love visiting this place. Sorry for a lengthy answer.
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Awesome response in every way! 
Thank you! But, that’s the kind of thing that’s making it hard for me to shake my addiction to this forum! 
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