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

Those custom-fit sand funnels are incredibly satisfying

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

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.

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

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!!

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.

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.

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 👍

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

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.

The stuff in the middle of the beams is not as stiff as the aluminum, and it's close to the neutral axis. It isn't moving much, so to do much vibration damping it would need to really efficiently damp any motion that did get to it. The loss tangent should be high at relevant frequencies. Maybe RTV would've been a better binder than epoxy for this application. Something soft and goopy, bare minimum to hold in the sand--it wouldn't be load-bearing no matter what you did, so might as well maximize dissipation. In epoxy granite, the composite is load bearing and moreover in the good stuff the load paths are through the aggregate to such a high degree that its mechanical properties are more rock-like. That's hard to do. You need several aggregate sizes and powerful vibration to consolidate it.

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.

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

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

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

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

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.

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

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!

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.

cannot wait for part 3.... the structure is sturdy :)

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

Thank you! We make same frame. Waiting for Part 3!

Props for the £1 B&Q Orange Bucket!

Your videos are like asmr for engineers ❤

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

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

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.

Wow! You are so smart and strong! This machine will change the world!

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.

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

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

What a fitting video! Just yesterday I decided to fill the column of my milling machine to reduce vibration and increase weight. I used a product called "Durfill" by Durcrete which is a cement glue based engineering concrete for filling structures and building machine bases. It expands slightly when curing to fill gaps and self levels. It's less of a mess than dealing with epoxy resin.

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.

I think there’s a making of a drummer in you Tim!

Nice work Tim!

You can fill the smaller areas of extrusions by loading the epoxy granite into refillable caulking cartridges and pressure/squeezing it into the extrusion. If you want more rigidity, you can use steel rebar implanted into the epoxy granite.

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.

yea, i´m also waiting for part 3 ...

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).

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

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.

No rush but we need a part threeeeee!! I can’t wait I wanna copy this design a bit.

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.

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.

Thread locker. Every bolt, every time. Learned through hard experience!

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

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.

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!

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.

Perhaps you can try adding the material they use in deadening vibration in high end car sound systems. I think they sell that stuff in rolls and you might be able to attach it to the underside of your build-plate or other convenient areas.

I would think that Constraint Layer Dampening would work really well for damping the internal vibrations, easiest and most affordable way to do that would be the sound deadening used in cars. You'd want to get the stuff that has a goey viscoelastic layer on one side and a thick foil layer on the other side. It's incredible how effective it is at damping sound and ringing in solids. I have no idea if anyone has done that with a CNC machine but it should work! Also I would have left the sand dry and only added resin to the ends so it can't escape, seems like if you make the sand a solid structure then it's reduced its dampening effect and it's only lowering the resonant frequency, and hasn't increased the decay rate Good luck!

Currently working on a cnc build as well with an extrusion based table/enclosure. To cut down on vibrations and to make the table much stiffer im attaching mdf panels to the sides of the table. Also contemplating using some rubber like gasketing or some sort of putty between the mdf and extrusion. Regardless, stoked to see where this goes! Oh and also something worth checking out is services like jlcpcb, pcbway (pretty sure they do sponsorships) and rapid direct. If you have any weird brackets or mounts you wanna make, you can just shoot them some cad and some money and you'll get back freshly machined pieces. One other idea, where you have linear rails, you could just get a slab of mic-6 and mount your linear rails to that. Mic-6 is usually pretty darn flat and not too expensive. Anywho looking forward to the rest of your build!

Loose sand absorbs vibration way better than epoxy sand combos.

Удачи в проекте!!!

Maybe inserting rubber/elastic "cushins" between the bed and the legs could help isolating them from each other? Of course that means another cumbersome disassembly and reassembly... But if you still decide to do it, don't forget the screws connecting the two halves together would also need some mini-cushins!

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.

Tim, good job, I am keenly capturedin your videos about this as I only just finished my CNC mill (I wish I had a CNC to build the frame mounting parts as that would have eliminated my inaccuracies in making the fixtures and it would not have taken 6 years). You will definitely see an improvement in cut quality with your improvements, but making some chips will be the biggest tell. From the video it looks like rigidity from the grooves/T slot fixtures maybe your weakest point causing flex on the gantry and you may need to increase the gantry mounting strength with a drilled & bolted hole through Y axis mounting + to support this the gantry feet & fixturing could be bulked up. Love the videos.

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.

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.

This type must be very, very, very precision.

Where is part 3? I check back every week 😂

The sound definitely dissipates quicker now, you could even measure the damping by looking at the sound wave

Most builders fail to use rubber isolating pads for the feet of home-built machine tools. These pads help to reduce vibration.

It might be 2030 by the time this is finished.

B&q sell lead flashing for roofing that you could attach to the outside of the legs to damp them, a tight layer of some sort of tape, then wrap qith the lead flashing, then another tight layer of tape. Lead sheet is quite good for damping because it has high density, meaning the energy required to move it is high and it has a very small amount of area under the elastic deformation part of its stress-strain curve (this is a representation of the amount of energy able to be stored in its elastic deformation)

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

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

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

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

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.

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.

To be honest, I wouldn't worry too much about the resonancy, sound is just sound. I really think you're good on rigidity.

Following! :) Your videos are always top quality. I'm going to make a CNC lathe with filled welded tubes (80x80x5mm steel) but i'm thinking about using pure dry sand due to the huge epoxy cost. I'm wondering if there's much difference between dry sand vs epoxy-glued sand.

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.

Read up on input shaping. It is being used on 3D printers to avoid resonant frequencies.

Maybe try assembling the chassis with different types of material. Since materials vibrate at different frequencies. You could find a 2 or 3 materials to assemble that can cancel each others frequency out.

Flexible TPU washers between the legs and base.

You could have used iron filings or small ball bearings? If you Made an iron filing/ epoxy slurry you could have poured in like the sand. If doing the ball bearings you could drop in then pour the standard epoxy. With bearings you could possibly cap ends and pour in the bearing. That way you can recover and use again. Alternative solution for hollow sound is to use expanding foam to fill voids and damp the sound a little.

The point of the sand is to act as attenuation for the resonant frequencies of the extrusion, it's not really about the weight. The granules inside the cavity move around with the vibrations and dampen the effect by absorbing some of the energy. The same principal as a deadblow hammer (plastic mallet filled with lead shot).

Drill holes in the legs and cross beams and fill with straight epoxy. Gonna be TOP HEAVY and Wiggle. Should have filled them B4 reassembly... Cool Project to learn from. thank you

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.

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.

I am going to repost my previous comment from the previous video since I believe it could cause problems in the future for you: I am skeptical of that ball screw placement. Ideally, you'd want to position it in a location that wouldn't create torque on the gantry, which in a non-loaded situation would be in-between the two linear rails. You could also position it on the underside of the carriage in a spot that would oppose the torquing force produced during cutting.

You could pour lead into the extrusion. I’d imagine it’s way less messy than sand ;)

Merci! 👍💪✌

I would've sleeved the holes with tubes to seal the hollow and used loose sand.

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.

Definitely sounds better. Will it make a difference? No idea. But it does sound better.

This is awesome! Do you have a parts list?? Love your videos! Great inspiration as an ME student! Also it definitely is the fact that the legs aren’t full of sand. You could put some pads under the legs to act as dampers.

What you could do for the legs is use motor mix . It is much thinner than concrete but not as thin as straight epoxy so it would would flow into the legs much easer. But wouldn't flow out as long as you had end caps on the bottom. if you are worried about them ringing.

Pretty sure a lot of resonance would be removed by bolting a sheet of MDF or similar to one of the sides of the base, since MDF is elastic it's a great vibration sink.

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?

You could enclose the base by mountig steel plate on the legs, and then fill the void with epoxy granite. That will make the whole cnc a lot heavier but here heavy weight is your friend.

For an engineer, I would be embarrassed showing that drill 😂

There's no replacement for cast iron when it comes to reducing vibrations in heavy machinery, but for a "portable" machine I'm sure the sand idea will do just fine

Perhaps the ringing is coming from the contact between the heads of the fasteners and the inner surface of the t slot of the mating beam. I suggest testing various durometer rubber washers under the heads of the fasteners to dial in the perfect damping. (not "dampening" if you're going to use this in a video)

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)

You have to ask yourself a few questions if you want to go damping resonances. First one is which resonance will be a problem when running the machine. Next one is which mode of vibration were you hoping to dampen and will the method you chose do that. Increasing the mass will lower certain frequencies but to dampen a mode you have to actually get the vibration into the dampening material. Your structure has many modes of vibration, only a few will be dampened, many will just be at a lower frequency with more modes (higher order) at higher frequencies. Maybe a cad model will show you the frequencies if it can do modal analysis. Lowering some structural frequencies will likely bring unwanted modes down into your are of operation although it may also make some problem frequencies move down into a state where they aren’t a problem.