Building a CNC Mill/Router - Part 2

Filling my new CNC mill/router with sand and epoxy resin to create epoxy granite, which will increase it's weight and vibration damping!
CNC Part 1: • Building a CNC Mill/Ro...
Old CNC router video: • My CNC Router... FINALLY

[@lennart637]

I recommend to fill the legs with fine loose sand. It absorbs vibration much better

[@Supmah2007]

i think its gonna be hard to remove the epoxy sand mix

[@pedro_8240]

​@@Supmah2007 the legs are still hollow.

[@bj_]

Yea the whole point of using sand to dampen sound is that it converts vibrations into heat through friction, when you "stabilize" the sand with resin and remove the friction aspect, just creates a new medium for sound to travel through

[@TheRattleSnake3145]

Did you ram the sand down or just let is fall down?

[@lennart637]

@@TheRattleSnake3145 You want it loose

[@TaylorTheOtter]

As a piano tech, I'd say you did a great job eliminating the frequencies that cause the most trouble. In pianos, that is.

[@MuitoDaora]

Now he probably can reach all the gcode notes.

[@maximelebrun8569]

Haha, good point this would be an amazing piano now :D

[@purvel]

You know, fiddling with settings might actually eliminate any leftover problem frequencies! Maybe there are some sensors you can use to determine resonances, and software to compensate for it? If not, here's a great video idea :D

[@PiefacePete46]

@@purvel : There are companies out there specialising in eliminating resonance in machinery... witchcraft?

[@JamieBainbridge]

Next up, how to build an aluminium CNC piano

[@roflchopter11]

It's generally considered best practice to mix the epoxy parts before you mix it with a filler. That way you can be assured of good mixing.

[@simonrussell4986]

If I recall, New Yorkshire Workshop's CNC build featured concrete, so you're going in the right direction!

[@grahameida7163]

That was a great build !

[@stylerxxl1]

yea, i´m also waiting for part 3 ...

[@IonNight]

Print spacers in TPU to put between the 8080 extrusions and the legs to help blocking the resonance

[@jibkny]

Try steel or lead shot plus loose dried sand in the base. This should give you an acoustically dead stand, and make the tool bottom heavy. Right now you are top heavy and that will amplify any vibrations. You may also want to replace the uprights with square 80x80s. They will be easier to fill and give you a bit more contact area and stability at the corners. Lastly, you may want to use additional angle braces or plates to increase the rigidity of your extrusion joints

[@davidbradley6448]

Don't be disappointed Tom. Any added mass will help dampen frequencies in the range of your cutter speed rpm. Rubber or metalastic feet will also help. I think you should try it and see......fine tune the clearance on your axis guides. Loving the content.

[@redsquirrelftw]

I'm thinking bolting it down after might make a big difference too. Either to the floor, or to a concrete block if you don't want to make holes in the floor.

[@patriotic_salt]

Sound proofing material felt washers The main issue is hollow pieces but they are metal on metal which can transfer sound / vibration

[@Streamlines]

Do you really need to rigidly mount the frame to the feet? Maybe adding some rubber to the mounting-points could dampen the vibrations traveling from the main frame into the base/legs.

[@james2749]

I've been thinking about building a cnc with these extrusions too and I was thinking about filling them with some kind of damping material. Like greenglue or some liquid rubber type stuff that sets and becomes solid material that actually damps the vibrations rather than just adding mass

[@Zaldi_Txiki]

Mate, the idea of using sand it’s that stays loose (dat absorb vibration better) I made my farrier anvil stand and filled whit loose sand, that work perfectly

[@Zaldi_Txiki]

Its the principal on “dead blow hammers”

[@Cryptic_Orbit]

Just an idea to add to the masses, but a lot of machining tools have cast iron bases to absorb vibrations. I would think mounting the CNC on one of those plates would help with the vibrations in the legs, hope this helps!

[@Convolutedtubules]

80x80 extrusion on the gantry at 45°. Large 10mm or so triangular plates bolted on from the sides to further improve the rigidity of the gantry. I think some sand blasting media is more dense, especially if you mix different grain sizes. It can be packed more densely by tamping with a rod.

[@burnologist229]

If you want to eliminate the vibrations fill the table legs with a sand silicon mixture

[@oOWaschBaerOo]

you should also defenetly lube the bearings with lube recommended by the manufacturer, they usually come unlubed and just have a film of oil to protect them!, you have to clean off this oil and then lube them yourself

[@AJB2K3]

Flexible TPU washers between the legs and base.

[@fiskfisk33]

By epoxying the sand you took away the physical property that makes it dampening in the first place... Sand moving under vibration is what dissipates the energy. You didn't remove any ringing, you just added mass and so lowered its frequency.

[@MichaelScottPerkins]

If all you really care about is the "ringing"... for noise levels... or resonate frequencies... I'd say you could fill the legs with simple cotton balls or some kind of fiberous insulation. People who build skateboard ramps always glue sleeping bags or blankets to the underside of the skateboard ramps so that when the skaters ride on the ramps, the sound is "dead" and not like riding a skateboard inside an acoustic guitar.

[@jeroenvandend]

Make a wall brace and bolt it to a wall =D helped a lot with mine

[@pseudotasuki]

The sand might very well eliminate the need for threadlock.

[@deanpsomotragos8359]

you could truss the legs with braided cable

[@Levibetz]

I can't help but wonder if it would have been better to just have raw sand in there with no epoxy. There's not much that's less resonant than a bag of sand. Oh well, I'm sure it'll probably cut just fine regardless.

[@donniewatson9120]

Expandafoam would have been usable in the vertical beams.

[@patriotic_salt]

Sand bags .......vibrations when milling use modeling clay

[@hairygeeza]

Why not put a thick rubber gasket between the base plate and the legs that should stop the vibration transfer

[@spaaarky21]

Don't want to be negative but 8:40 really summarized why people are questioning this. A HUGE lead screw, big extrusions, filled with sand/epoxy and tested with a hammer in the very unscientific "ring test." 😂 Seriously. Build it and see how it performs before over "engineering" solutions to problems that might not even exist.

[@khardian2823]

so, you skipped your CNC machine's leg day?

[@dallebull]

Not filling the base is a mistake. Just play around with the epoxy/sand ratio until you get something pourable, just plain expoxy is better and stiffer than air. Never half ass the rigidity.

[@buildbotics]

I wonder which CNC controller you'll use.

[@Brandon-sc1fz]

I'm a consulting engineer for vibration related issues for a vast number of different products. Have specfically worked on mills and lathes. The lack of understanding in the comments is crazy. People stating something as fact and it being the farthest from the truth.

[@TimStation]

Would you agree with what I've done in the video? What else could be done to help with damping potential vibrations? Thanks!

[@Brandon-sc1fz]

Firstly, I'll commend you for taking on the task. Building a mill from scratch is no easy task. However. The downsides. The easy thing for me to say is there is a good reason lathes and mills are very very heavy and building one from aluminum extrusion is fighting a losing battle. Stiffness is the end all be all of what makes a good machine. So this in principle would mean you would end up with all very high mechanical natural frequencies. In the video it seems like you are insinuating lower natural frequencies are the goal. Shouldn't necessarily be the goal. The sand was likely a good addition. Additional weight can't hurt and it does add damping. Suggestions would be anything to increase stiffness. Cross bracing everywhere you can. I think the bolted connections in this design are the weakest point. Anything to stiffen those connections will substantially help. You're likely to not be machining steel on this. So keep doing what you're doing and should be alright.

[@ikbendusan]

@@Brandon-sc1fz there's a distinct lack of triangles in this design that could be addressed. perhaps tom can do some simulations in cad

[@oomwat6101]

Fill the legs with plaster of paris ;)

[@jakubzabocki6182]

Thats Very Very Cool i wonder what spindle motor will you use

[@mrDavo111]

Why not use those 3d printed spacers and fill the legs up with sand and no epoxy?

[@mrDavo111]

Further to my comment. Oil and sand is mentioned a lot online, but I think it's going to be a mess.

[@henzik]

Expansion foam in the legs maybe?

[@FaeTilgner]

Who knew filling a CNC mill/router with sand could turn it into a high-tech sandbox? 🏖️😂

[@schuylermontgomery3396]

Those custom-fit sand funnels are incredibly satisfying

[@ratgreen]

Your epoxy granite will have its own resonant frequency, because it is stiff. I think the whole point of the sand is that its lose and will move about and not resonate. Now you've just got 2 different materials with 2 different resonant frequencies, coupled together. Hopefully they overlap and still help a bit.

[@rob66181]

This is exactly the problem. You want sand as it has no resonance at all and is a great damper over basically all frequencies of interest. Also, sand fills the voids well but his cement will shrink a little as it sets and you lose the intimate sand to metal contact. All he has done is change the resonance by adding mass but has likely not introduced appreciable damping. I appreciate however that he has holes in the system and the sand would work it's way out eventually.

[@whirled_peas]

​@@rob66181 Added mass of different resonant frequencies is almost guaranteed to dampen vibrations.

[@wizrom3046]

Epoxy granite wont resonate it behaves like a piece of stone

[@ratgreen]

@@wizrom3046 Yes it does, most solid objects do. If you hang a rod of stone or concrete from a string, and tap it, it will ding. Thats it resonating.

[@wizrom3046]

@@ratgreen actually it doesnt. The epoxy is much less dense than the stone particles so the whole thing absorbs energy and is very low resonance.

[@Dia1Up]

Doesn't the fact sand moves help absorb vibrations? But won't the epoxy keep it from moving?

[@gedr7664]

hard to say - the increased density of the epoxy + sand will dampen the vibration amplitude and frequency of resonance on the other hand sand without epoxy could dissipate energy via friction overall I would say increased density has a greater effect

[@TheHanutaXD]

While I never build a CNC or anything that needed to have low ringing/high vibration resilience. My instinct would also be to use something that can move on its own and is only slightly coupled. Like Rubber or silicon. But then again, every build I have seen so far uses resin and sand/gravel. But all the other builds have their CNC standing on the ground or a very strong table. So I guess the feed are the biggest "problem".

[@BIGWUNuvDbunch]

Yeah the fact that the epoxy prevents dissipative losses means the sand is just ballast

[@wdwhitmer]

Both affect the vibrations in this dynamic system. The increased mass increases the inertial force and the sand increases the damping effect since it is not perfectly bound by the epoxy (both of which increase resistance to motion).

[@sweetnightmere]

i agree with you, to me thats one reason sound travels much longer distance in water then air

[@luisermert]

That Ballscrew is huge haha. Using huge ballscrews isn´t always good because it adds a lot of angular momentum to the axis, wich will impair acceleration a lot. 16mm Ballscrews are already way overkill for a hobby machine judging by the static and dynamic load they can take.

[@ripper132212]

yeah lol i've assembled a like 4m axis on a cnc machine and it aint have ballscrews that big

[@muzzarobbo]

yeah waaaayyy too big, if you want to reduce backlash you need a double nut as well, they preload the threads to provide greater axial stiffness.

[@ikbendusan]

@@muzzarobbo not entirely true; a ballscrew that uses "gothic arch type" ball tracks can be preloaded with a single nut. on a rolled screw this is the preferred method due to inconsistencies in the shape of the screw; a double nut on a rolled screw is more likely to bind up. if you want to use a double nut, the best thing would be to get a c5 or c3 precision ground ballscrew. the size of the ballscrew impacts acceleration but even a 60x60 mm 400 W servo should have no issues accelerating this ballscrew with 1 G of linear acceleration. the inertia of the system just needs to be close enough to the rotor inertia such that the servo control loop remains stable at those speeds

[@muzzarobbo]

i thought 4 point contact ballscrews like precision ground ones are quite expensive compared to cheap rolled ones? i use a double nut on rolled ballscrew with no binding issues@@ikbendusan

[@DarrinBaird]

Would loose sand dampen vibration better than the weight of the epoxy granite?

[@gedr7664]

imo increased density due to epoxy added has a greater effect than friction within loose sand.

[@yetanotherdan]

You're all going to give Tom a complex and his next video will be testing like 30 different materials for frequency and stiffness.

[@wdwhitmer]

The mass of the sand probably has more of an effect on damping than the loose sand itself. Additionally, loose sand would end up finding ways to get out and would make a mess.

[@DemsW]

@@yetanotherdan This reminds me of the whole marble machine madness for those that know.

[@whirled_peas]

@@ChrisValin-w6o not enough mass

[@dihler55]

MY only real concern right now would be that this is a little top heavy. Cool idea for a design though!!

[@DanT10]

Perhaps stiffen the frame with framing lumber like 2 by 6 or 2 by 8?

[@scratchbuiltdesigns]

Well done! I did exactly the same on a custom build that I currently assemble. Your problem is indeed the stand. The CNC should be heavy on the bottom and get lighter the higher you go. You have a very rigid machine now, on a flimsy undercariage. You will see how shaky it will become, once the machine is up and running and you do some highly dynamic stuff with repetitive direction changes, like boring or adaptive clearing. Maybe you have some possibility to attach the legs to the adjacent walls with some wooden spacers. This should fix it. But in any case, it is a great build 👍

[@patrickkawa6350]

I'd assume the dampening properties of the sand are cancelled out (or atleast reduced) by the expoxy holding all the grains together. The sand cant absorb the frequencies by moving around.

[@SamBarker]

Well if you ever give up KZbin, there’s hope as a percussionist

[@whatisjaspdoing]

Maybe diagonal steelwire or braces between the legs. It seems like you now have more weight on spaghetti legs. And I dont know what type of machine feet you have but stiff dampers could also maybe help further.

[@AJBtheSuede]

Good job! I think you'll find it helps a lot more than you think. Resonance or vibration is only part due to stiffness (lack of...), you also need to consider the accelerated mass. Doubling the tightly coupled mass of a beam lowers the resonance frequency, sure - but the important part is that the beam impact load moment of inertia goes up to a factor of mass increase squared. Doubling the mass means that the same impact force now gives four times lower beam displacement. This helps a lot on all vibrations and momentary impacts that are NOT perfectly synced to the resonance frequency. At (the now lower) resonance, the same amount of impact force has the same displacement as before though

[@roryoconnor4989]

You just described drum tuning in the most scientific way possible.

[@NainKaigo]

Excellent overview of the benefits related to increasing mass. It is my understanding that the stiffness of the overall system increases. I think he could have increased mass further if the mix was compacted in layers. The mixture didn't seem fluid enough to settle with just a few taps.

[@magnum_dingus]

For future reference, a bit of heat will soften threadlocker.

[@azfarazdiarfakhsyad9863]

the sand-epoxy dough looks edible enough, wonder how that taste like

[@jamiethacker675]

gritty

[@southerndime333]

cockles on a cold wet stoney brit beach

[@Sebastian-69420]

Looks like kinetic sand one had as a child

[@mark675]

It tastes like eating chips at the beach on a windy day

[@mavamaarten]

Probably tastes like cancer

[@TastelessChicken]

Tip for pouring from containers like the ones your epoxy came in: hold the bottle sideways, so the hole in the handle is "eye to the sky" This way you dont get the typical glug glug that slows down pouring and makes it more dificult to be precise.

[@theEduEnthusiast]

Tom! As a percussionist, I highly recommend using some drum mutes/dampening pads! You can grab a couple of snare mutes that are essentially like little sticky gel pads and slap them on the outside of the extrusions. Or you can fill the inside of the legs with loose sand which should do a better job of absorbing those frequencies. OR you can even encase the bottoms of the legs in a little bit of silicone (mold a foot around them and put a slightly more resilient rubber pad on the bottom underneath the silicone mold perpendicular to the end of the extrusion and the silicone, and epoxy the two together). Any/all of the above can help a lot with dampening the ringing if you’re not already adequately satisfied with how it currently is. Hope this helps!!

[@rider573]

Or Dynamat for car sound insulation on the legs might work.

[@PiefacePete46]

The objective is to remove chatter: Eliminating "ringing" created by tool cutting edges contacting the workpiece at a harmonic of the frames natural frequency is one reason to fill the extrusions. Another reason is to increase the overall mass of the machine... this alone can be a significant improvement. I guess that's why you don't see many portable Bridgeport mills! 😜 Really looking forward to the rest of the series; I don't think you are going to be disappointed with the finished machine.

[@nonchalanto]

It doesn’t sound the same at all! Sounds much better!

[@Fantic156]

Paving slabs, across the beam bottoms, heavy, stable and could be used as a shelf for stuff! Would probably benefit from bedding on closed cell foam/other stuff, and securing!

[@nagualdesign]

Good idea.

[@mythacat1]

The fact it still rings may be attributed to the hollows that still exist in the corners of the aluminium extrusions.

[@brock7074]

what a absolute waste of a $2000 piece of machinery.

[@cristiii7605]

I am guessing the Cnc wasnt as easy to build as expected

[@piberry6445]

Maybe try to Wrap a Rubber mat or Rubber Tape around the legs? The Rubber could absorb the virbrations and also isolate the Sound or reduce the frequency. I guess even normal Tape would Help notacibly.

[@Glocktopus42]

Where is part 3? I check back every week 😂

[@freescape08]

I feel like you're not taking this project as scientifically as the trebuchet. Small scale testing to prove concepts before a bunch of wasted manufacturing.

[@winnieman-fx1hu]

Use dry sand on the the vertical legs. its pretty much self compacting and should pour in like water if the sand it totally dry. iv had bags of kipn dried that were not dry before hahah

[@leightonfoster7525]

I think you are putting too much faith in the linear rails being straight, I would almost bet the extrusion is straighter reference edge. Even high quality rails are almost always bent from factory and you need to use the mounting screws to pull them in line. Really you should be setting the axis flat relative to the table, followed by setting the ballscrew flat to the rails. Unless you have checked them with a proper straight edge of course!

[@iteerrex8166]

The narrow legs, in fact all of it could’ve been filled with leveling cement. It’s very liquid and smooth, and much nicer to work with than epoxy.

[@tmoney1876]

I'm thinking about using high strength concrete...

[@philiprogers5772]

Ive used molten lead.

[@tmoney1876]

@@philiprogers5772 I'm too lazy to deal with epoxy. I can't imagine messing around with lead.

[@-vermin-]

@@philiprogers5772 That's going to play havoc with his 3D printed funnels :)

[@iteerrex8166]

@@-vermin- Lol, also I wonder if the expansion and contraction would cause deformities.

[@michawojtaszek2052]

The biggest mistake was mixing sand with epoxy. Loose sand acts like a dumper, it does not move like a single weight, but the movement of grains relative to each other dampens vibrations. Moreover, loose sand fills the empty spaces more tightly. In fact, you had to print the ends of the profiles (which you did anyway), paste them on epoxy, and pour loose sand between them. Now you just added masses to the profiles, which is of course positive, but not as good as it could be.

[@darkwinter7395]

Epoxy-granite acts differently - the epoxy absorbs the energy as the vibration waves travel between the sand grains and the epoxy.

[@Zeusbeer]

The natural frequncy of the central 2 beams in the bending mode is quite low still. You can help reduce ringing further by adding vertical (or triangular) support columns underneath the center 2 beams, supporting their centers from the floor. This should increase the lowest natural frequency of the center beams at least by a good amount (I am guessing 4 or 8 times), which should reduce ringing. This only helps the up and down bending vibration mode though. To also reduce the in and out of plane bending vibration node you could add 3 short support beams in between the beams on the platform, supporting the centers of the beams from the side.

[@nyeleskettes]

I would have only seal the ends with epoxi-sand and just fill the rest with normal sand.

[@dittilio]

I'd bolt the entire thing to the ground or a concrete block, with rubber gasket between aluminium and concrete. I'd also put lightly coupled (or gasketed) bracing between the middle of legs and the uprights, reducing the number of long lengths that can resonate.

[@ReevansElectro]

Loose sand absorbs vibration way better than epoxy sand combos.

[@H.D.83]

That's what I was thinking: you don't see deadblow hammers with epoxied shot in them

[@iteerrex8166]

Many likes the idea of lose sand, but I’m not sure how much that small amount of mass would dampen the high amplitudes of vibrations. If you look in the industry, dampening has never been used (as far as I know), only stiffening and mass in the body.

[@darksydedavid]

i thought the m in mill was a w and was spelled wii so i was thinking that he was gonna make his own wii sensor bar, but i still like this😅

[@casaxtreme2952]

I would suggest to further stiffen the lower structure (that can't be filled with sand), for example by simply introducing more cross beams or diagonal beams. This should greatly reduce vibrations in the system.

[@chrisadesigns]

The theory behind EG is to use different size aggregate, sand - 10mm pebbles, this breaks down the vibration a lot faster, stops the vibration from travelling because of all the different size objects to go around

[@ludviglindh4398]

Interesting that you filled up the rails with epoxy granite. I did something similar when I was putting together my own CNC router to cut down on the vibrations during milling. Instead of just the rails though, I made a mold for the whole base of the CNC and poured a mix of 20% epoxy and 80% sand into it. And it worked well. I basically wrapped an aluminium frame in epoxy-granite for my CNC machine. One thing you might want to think about is shaking out the air bubbles and gaps in the epoxy granite a bit more. I rigged up a DIY vibration table for this, attaching a cement vibrator to a plywood board, and let the mold vibrate for the entire curing time. I'd think filling in the gaps in the aluminum grid structure on your CNC with epoxy granite would make the vibration dampening even better. Just my two cents from building my own CNC machine with epoxy granite for the past year.

[@xyzspec82]

Where can i see your build? Made my CNC base out of structural concrete and i love it.😊

[@AirCrash1]

Do not constantly vibrate during the curing process this causes the sand to settle to the bottom of the mixture. This is a big no no when mixing regular cement. You can actually see it happen if you put a vibrator into the mixture and not by vibrating the entire structure. The mixture around the vibrator becomes watery if you leave the vibrator stationary.

[@jamiethacker675]

what about spray foam in the legs to deaden them?

[@TristanJCumpole]

Hi Tim. I've been considering epoxy granite for my CNC build, however I strongly believe that the Sikaflex 290DC deck caulking that we use at work for cruise liner Teak decking will be a good alternative choice. My reasoning is down to how these dampening materials work; converting vibration into heat through friction. Epoxy granite alters and shifts the resonant frequencies within the system to longer wavelengths which are less intrusive than the higher "ringing" plain Aluminium produces. Sound dampening materials in audio applications tend to use dense flexible materials such as rubber or polyurethanes which are very good at converting vibration to heat. Sikaflex polyurethane caulks are single component and much more convenient than mixing up dry aggregates and epoxy, which is an attractive benefit.

[@xero110]

How about filling the legs with lead shot?

[@leestons]

It might be 2030 by the time this is finished.

[@mark-]

Wrap the legs with a rubber material

[@1kreature]

There is always tradeoffs when designing such a machine. Take your gantry axis for example. You can use very low rails to increase rigidity but then often loose out on drive-stiffness by needing coupling over to the leadscrew (like you have). Alternative is using taller guiderails where the leadscrew can fit under and the coupling nut carrier can then interface directly with the axis for a stiffer drive position. In the end I do not know which is more rigid but I went for the second option on my machine based on simulations in the CAD.

[@randomginger11]

I don't think adding weight to the bottom of the base will help that much, since the main problem, it looks like, it the frame itself flexing (very slightly, which is what the vibrations are). Like others have suggested, I'd definitely say finding a way to fill the legs would be a massive improvement. Whether that means changing the legs to be the square tubes so they're easier to fill, filling them with loose sand rather than the epoxy mixture so that it's easier to fill, or something else. I work in custom automation, and for machines with something like an ultrasonic welds on it, which exerts tons of pressure (literally) and vibrates in the range of kHz, so frame rigidity is very important, I would think it would be a strange design choice if one of our designers made a big stout gantry and mounted it on less stout legs.

[@jamanjeval]

Here is what’s happening: filling the cores increased the mass and lower the resonant frequency. But to dampen the vibrations, you need to dissipate that energy somehow and for that, you need loose sand. I think you’ll be fine, but you could try filling the legs with loose sand and compare them to see how it changes. I did this awhile back with some speakers stands I have. I filled one with some very dry, fine Masons sand and compared the sound by swapping stands with one that wasn’t filled. I didn’t expect any difference, but it really sounded significantly better. So, I don’t know if it would make a difference in machining quality but it does make a difference. If nothing else, maybe it will help to make it quieter when operating. You should also try to use some strips of sound dampening mat, like they use for car audio. You don’t need much, just a strip on each extrusion. Just be sure to put it where you’ll never need to remove it because it really sticks.

[@eelcohoogendoorn8044]

The sand will help the most with the high frequencies represented by localized flexing of the walls. The lowest frequency modes represented by the whole thing going back and forth in bulk wont care as much about the epoxy fill; the high frequency modes would be the most annoying ones to deal with for the machining process though; there is a lot of energy injected into the system at your spindle rpm * number of cutting teeth; not really a whole lot in the lower audible range of a few 100hz where most of the leftover response seems to be. Thats just armchair philosophy though, don't have hands on experience. But it seems like a worthwhile upgrade to me.

[@n3ttx580]

I thought the reason for the sand was to bring down the centre of mass, and to make it heavier, so it wouldn't move. Dampening resonance might work aswell, but i don't know if this is the best way. I saw people hang lifting weights on steel wires on the bottom of it to damped vibrations.. the idea is that you have a dampening weight on a string, that can move freely and vibrate.

[@oBCHANo]

If you need to reduce vibrations then you just need more mass. So you could create a lower shelf and just add weight.

[@tummy_fritters]

Maybe adding strips of heavy rubber to the outside of the legs would dampen the vibration. Something like horse stall mats cut into strips and bolted to the extrusion?

[@h.y-chen]

maybe add between leg and main frame?

[@awatt]

Appropriate Barry Mounts would be my first choice.

[@ADBBuild]

I'm surprised you didn't use something to compact the sand. It doesn't seem like it "flows" very well. There are probably small voids lowering the density.

[@JilariousJamesGaming]

Great video Tom! Getting rid of all that vibration is indeed very important 👍

[@DUIofPhysics]

This sounds a bit out there, but take some 3M double sided adhesive tape (the really thin stuff) and tape thin aluminium plate over every exposed t-slot, this makes them all closed sections. 3M adhesive tape is shockingly strong in sheer (if you choose the right one) and changing the open sections to closed wall sections increases the Torsional rigidity of the beams, the tape also gives some dampening. This is something Alexander Slocum speaks about in one of his lectures. He's the writer of "Precision Machine Design" - which is basically the machine design engineer's bible. I think it's this lecture: kzbin.info/www/bejne/bqOuo4ipjc55hdEsi=mmLKntXZSzGy7-vk&t=700 (FOUND IT)

[@ChrisBLong]

You could add custom-designed tuned mass dampers to the outside of the legs if it turns out that you need to, that would make for another interesting video in its own right.

[@exol511]

I have done the same thing with my welded machine, but I compacted in the epoxy sand mix as I filled it and that made a noticeable difference. One tube I had to fill sideways and could not compact, which resulted in a noticeably less uniformly and densely damped tube (you could hear the difference when you hit it at different positions).

[@tanjiro3285]

Your videos are like asmr for engineers ❤

[@basarkuzucuoglu8174]

There is 4 ways to get rid of vibrations mechanically. 1)Dumping vibrations Vibrations partially turns into heat or another energy form. Filling with sand to body and adding rubber foots includes this approach. 2) Adding or substracting mass 3) Adding spring element (with dumping element) Firstly calculating (or FEA) the natural frequency helps a lot in the begining. Then you'll find some natural frequencies which is harmful to work with these frequencies. Accelerations of your cnc is limited by natural frequencies of machine's body structure. If accelerations matches with your cnc you have to move away these frequencies with adjusting accelerations, adding mass, spring or dumping elements can be added "with calculations". 4) Transmitting vibrations to more rigid mass Fixing the cnc to the floor helps to get rid of the vibrations because you will change the natural frequencies of the body. Bonus: Eleminating vibrations with stepper or servo motors and creating counter frequencies is the solution. Open loop (like input shaping) or closed loop systems available. Try use "klipper" with cnc for input shaping. (An accelerometer will help you to measure frequencies)

[@hamps856]

Could you not just pour raw sand in the vertical legs? And, for more rigidity, have bolts go all the way through the extrusions?? I have built a similar machine with 2 inch extrusions with no sand fill. It is accurate +/- .005".

[@The_Nonchalant_Shallot]

6:53 6:53 6:53 6:53 6:53 6:53 6:53 6:53 Buddy, you're a boy, make a big noise Playing in the street, gonna be a big man someday You got mud on your face, you big disgrace Kicking your can all over the place, singin' We will, we will rock you We will, we will rock you

[@hielkebrandsma182]

I really love your approach! But .. I would go for High-density polyurethane foam to create a sturdy base, and reduce the weight. I'm no scientist or expert, but this is what came to my mind. Maybe it won't win from the sand / epoxy mix. Another way to go, but ends op very heavy is to fill the profile with concrete. As this is not flexible, it could crack, so I think this is eventually a no-go. Keep up the good work Tom!

[@martinschwaikert5433]

Sorry to say so but all you did was increasing the weight (what helps) but you wanted something to absorb the resonance and not another solid that's having its own frequency. The result is within expectation. Next time you could either use sand without epoxy, or a soft, damping material like a 2K PUR filler. And, btw, use automatic connectors for item profiles. That's a big help

[@mrfochs]

While the way you mixed the epoxy was a great idea, I wonder if it would have been easier (and maybe cheaper) to fill the legs with bonded sand like Petrobond or even Kinetic Sand. There are also a few different kinds of casting sand (Sodium silicate sand) that can be poured easily and then cured to a "hardened state" with the addition of CO2. As for the legs, I think it is less about the weight and more about the long, hollow surfaces that allow for vibration. May want to look at car-deadening mats (like Dynamat) and paints (like Spectrum's Liquid Sound Deadner) that could be added to help lessen resonance.

[@injesusname3732]

Failed designed. Even if you replaced extrusions with solid steel, youll have the same problem. The bed and motor need contact with a heavy and dense mass. Youll be stuck cutting metals at 0.01 mm fpt. 2 posts for the motor, connected to horizontal posts with no direct underlying support 🤦‍♂if the goal was to create bell, this is perfect

[@darkmann12]

Feeling like the sand should have been loose