3 weeks later.. I measured the rigidity of the column again. Long story short: I expected some improvement due to the extra curing of the epoxy, but that didn't happen. The results are roughly the same as at the end of this video. So 40% improvement bij epoxy pouring seems the limit for this machine.

@HudsonPeter

5 ай бұрын

I wonder if the rigidity could have been further improved by placing rebar (steel or carbon fiber) into each of the four epoxy granite pours. Obviously epoxy granite has excellent compression strength, but when the column is under load one side is in compression and the other is in tension, so perhaps that could have increased the rigidity further. But nonetheless it's an improvement and and excellent video. Thank you for posting.

@Michel-Uphoff

5 ай бұрын

I think that could have improved rigidity further, but I suspect an important share of the remaining flexibility could be in the base.@@HudsonPeter

@TT-qo9dv

Ай бұрын

Thanks for the video 😊

@pentachronic

Ай бұрын

I wonder if 2 metal bar cross-members in an X shape in each of the cavities would have improved rigidity too along with your epoxy/sand pour ?

@Michel-Uphoff

Ай бұрын

@@pentachronic That could be right I think.

I just love your scientific approach, attention to detail as well as the combination of theory and practice. And that excel sheet…it’s a piece of art and a textbook example of how one should arrange their spreadsheets. I wish I had that touch to my own mediocre attempts in excel. 😊 Please keep posting. It’s always a joy to follow your work.

@Michel-Uphoff

6 ай бұрын

Thank you!

I find you learn way more during the process rather than the outcome .Good job.

numbers, sciences, not bed result - great video, thanks a lot!

Hi Michel, thanks for the great (as always) video! A potential way to add rigidity on top of the current construction would be prestressing the epoxy cast with say 4xM8 thread bars, each in a chamber with large washers (or other more efficient arrangement). Some plastic tubes can be placed to leave channels for inserting the rods before pouring the cast. Not only is steel stiffer, contributing to bending but also due to poisson effect the cast would expend, increasing the bound to Alu-walls, therefore the chance of composite action between walls and cast. Two cents from a structure engineer.

@Michel-Uphoff

3 ай бұрын

I think that would have made the column even more rigid, although I suspect that now the other parts of the mill flex the most, the base and the headstock for example. Anyway, drilling such long holes through that epoxy and sand is no longer feasible, I'm afraid.

Diagram @4:37 = pure gold! Thank you 🙏

I really like your approach to projects as you are able to quantify the improvements. If your sand was dry when you added the water to work out how much epoxy to use then it would account for your resin volume being too high. Dry sand absorbs a small amount of water. You would need to soak the sand in water before you start, drain off the excess and then add the water to see how much resin would be needed to fill the voids. The sand would need to be in the Saturated Surface Dry condition before you start.

@Michel-Uphoff

6 ай бұрын

I think I did it correctly. I calculated the volumes in the column very accurately and adjusted the amount of resin and sand in the epoxy concrete exactly accordingly. At 3,163 cm³ I was only 18 cc short. This is visible in the video, the column is completely filled except for a height of 2.5 millimeters. However, there is a thin layer pure resin at the top, but that's only 1.5 mm thick, and doesn't influence the rigidity at all.

@broglet2003

6 ай бұрын

@@Michel-Uphoff Thanks for replying. I certainly wasn't trying to poke holes in what you are doing, I was just musing as to why there was some excess resin on top. I didn't realise it was only 1.5mm. As you say, it is much better not to have too little resin or you risk having air gaps in your mix. A 1.5mm excess is probably as close as you can get without having too little. It will be interesting to see if you get any improvements in stiffness as the resin continues to cure. I look forward to your next video.

A good investigation. Bedankt Michel.

Another interesting video on improving your machinery Michel, Well done!! Although your disappointed with the initial results, I'm sure they'll prove beneficial overall, possibly with cutting speed/surface finish. Looking forward to seeing what the final outcome provides you with.

@Michel-Uphoff

6 ай бұрын

Hi Collin! I am only a little disappointed, until now. OK, a 40% increase in rigidity is nice, but I calculated 50% or even a little more. I will have to wait until the resin is fully cured. I did a hardness test yesterday with a sample of that epoxy concrete, and got Hv 17, while 23-29 should be achievable. So I still have to be patient.

Very interesting videos. I have often wondered - if you have a brick wall behind a milling machine - could you just bolt the column to the brickwork? An increase in rigidity for almost no cost? 🤔

@Michel-Uphoff

6 ай бұрын

Then, if it's a very good quality wall, preferable concrete, you would have to bolt the base also tight to the same wall somehow. Then it could work I think provided the temperature of the wall and mill doesn't change too much (difference in expansion coefficient). However it's something I will never attempt to do.

Did you vacuum degas your resin after mixing? It's hard to say for certain but around 6:20 it looks like there are air bubbles in your mix when pouring.

@Michel-Uphoff

6 ай бұрын

I considered that because I have a vacuum pump, but it turned out not to be necessary. This casting resin is very liquid and remains so for several hours. There was plenty of time for the bubbles to rise, which they did. After about an hour (during which I occasionally added a little epoxy concrete to compensate for the escaped air, as shown in the video), all the air had disappeared. Only after 3 hours did the resin become noticeably less fluid and no longer contained any air. I'm sure of that, because otherwise I would have had epoxy concrete left over, which wasn't the case.

I like this pure sand approach given the small volume, but I think the reasoning behind larger aggregate is cost considerations for larger castings. Epoxy gets expensive.

@Michel-Uphoff

6 ай бұрын

Yes that's true. This amount only cost 25 euros, but if you want to cast a complete bed for a large machine, that will be quite expensive. But then again, I would go for that extra cost, because the larger the aggregate, the weaker the concrete.

Hello Michael, i was wondering weather you considered using Industrial Grey cast Iron Chips (dust) instead of silica Sand? If Not, why? I am also researching on wheiging down and stiffening my Optimum bf20 mill column and bed and i really liked your Video!

@Michel-Uphoff

5 ай бұрын

No I didn't consider that. Could be a good choice I think! Does your mill has a hollow column also? First of all I would do the kind of measurements I did. The spring balance I used for this costs only a few dollars.

@alphatimo98

5 ай бұрын

@@Michel-Uphoff Yes, there is a Lot of free space in the column. In the base as well. I sadly am very disappointed in the stiffness of the column-bade joint of my mill, but i cant fit a more massive mill in my Workshop. Im Sure you know this Problem. The column tram is also very much Out of tolerable spec, maybe i can kill two birds with one Stone and rework the whole way the column is attached. I am Not quite Sure yet.

@Michel-Uphoff

5 ай бұрын

@@alphatimo98 Ok, that's the opposite of @cyberwendy, who wrote in a comment below that those Optimum milling machines are much more rigid than my Proxxon. So I now think that was an opinion and not so much an established fact. I'm actually very curious about what deflections you are dealing with. I have now taken a closer look at the Optimum and see that the column at the bottom is secured to the base with four tension bolts. And if I'm right, the vertical distance between those bolts in particular is quite limited. So it seems to me that this column can noticeably bend in the Y direction. Does extra tightening of those bolts help? What grade are those bolts? Is the part of the base where they are bolted into massive?

@alphatimo98

5 ай бұрын

Im certain my optimum is quite a bit more rigid than the proxxon, the weight and size of the Castings are obviously larger. However, coming from Industrial milling Machines such as FP1 etc. i did my apprenticeship with, these benchtop mills are sadly not comparable (without considerable upgrades at least). I have no experience with Proxxon, i based my assumtion on the physical size of the machine and your experiences with it. You are right, the four Bolts connecting the column are the weakspot. I have Not found a solution yet other than reinforcing this Joint by adding Metal bracing/ Polymer concrete to stiffen It. Checking the Grade of the Bolts is a great Idea, i can Imagine replacing them and adding preload will enhance the Connection. As far as i know, barely anything on this Model is "massive", apart from the wall thickness of the casting, which should suffice for tapping. But i was thinking, If i am disassembling the mill anyways and Handling Polymer concrete, i might as well fill in the hollow spaces on the Base, making it solid. I will try to Take measurements soon, my time in the Shop is quite Limited though unfortunately.

@Michel-Uphoff

5 ай бұрын

I don't think epoxy concrete is the solution to this problem. There is a lot more rigid material in your milling machine than in that extruded aluminum column of mine, and your machine will therefore intrinsically bend or twist a lot less. Your problem is mainly that weak design of the column-base connection and that problem remains manifest with a epoxy concrete filling.

Meten is weten . en gissen is missen ;-)

@Michel-Uphoff

6 ай бұрын

Zo is dat.

wondering why you picked super light silica sand as opposed to a denser material such as powdered lead, tungsten or even copper, which would have given a much greater final rigidity?

@Michel-Uphoff

6 ай бұрын

I do not think so. The epoxy resin is the weakest material. Silicon dioxide (silica) has a tensile strength of 15 kg/mm² (150 MPa) and the selected slow-setting resin ultimately reaches 9.5 kg/mm² (95 MPa). Lead is even weaker at 1.8 kg/mm2 (18 MPa), and I would need to buy 40 kg of it. With tungsten it becomes near impossible. The 80kg I would need would cost over $5,000. What I did consider is copper slag grit, but I couldn't easily get hold of it in such a small quantity.

@noviceartisan

6 ай бұрын

@@Michel-Uphoffthanks for the explanation, I don't have enough of a grasp of this end of physics to make these choices myself, I was considering doing similar with my MF70 column too, so was thinking a denser material would give less. I lack the understanding of why the tensile strength of the material would be the wiser choice over mass? As for copper, I'd think regular wire in a blender would become fine enough pretty quickly? Thanks 😊

@Michel-Uphoff

6 ай бұрын

​ @noviceartisan Extra mass is good to prevent resonances, but in itself it is not a good remedy against bending and torsion. For this you need strong, compression-resistant and tensile-resistant materials. Lead has a high density but deforms very easily and just like pure copper it has a low tensile strength. Silicon dioxide is less dense, but has a high compressive strength (~1400 MPa) and a reasonable (150 MPa) tensile strength. However, the mass of the aluminium column was 2,3 kg. Now it is almost 9 kg, so there's significant more mass and I think that will reduce the resonances considerably.

I'm curious as to why only using sand is superior to using a mix of sand and gravel? From all I've heard and read about epoxy concrete, a proper mix of aggregates gives the best strength and rigidity.

@Michel-Uphoff

2 ай бұрын

See the graph at 4:10. These measurements from AIMS material Science are, to my mind, very clear. I know that a mix of sizes is often presented as the most rigid, but nowhere is this substantiated with measurements. In many videos it is said that after the use of epoxy concrete the machine has become "more rigid", but there too nothing is measured and it is completely unknown how much stiffer the construction has become. Usually there is a lack of substantiation in these videos. I only knew of one video that actually tested whether the grain size and the mixture influences the strength, and there too the outcome was that a fine grain gives the best result. Unfortunately I can't find that video anymore. The finer the material, the stronger the epoxy concrete is my conclusion. And there is logic behind that, as I also mentioned in my video. See also: kzread.info/dash/bejne/ZpV2uKObltuyeto.html This Adam Bender did a great job and went further than most in comparising mixtures, arriving at a mixture of 80 wt% sand and 20 wt% epoxy, pretty much the same as what I found (78/22) to be the best solution.

maybe more rigid if you could have installed steel bars into the epoxy? pour lead instead of epoxy? at least your doing something!

@Michel-Uphoff

6 ай бұрын

Around 40 kg molten lead.. yikes. Besides, that would shrink too much and lead is very malleable.

If you want more ridged machine, better buy a ridged machine, these modifications lead to nothing in the end and create new problems. Increased weight, more stress on the base and bolts, and so on. A cheaper import mill, is right away more ridged.

@Andreas-Bauer21

6 ай бұрын

And may I assume you have heaps of experience with this?

@Cyberwendy

6 ай бұрын

@@Andreas-Bauer21 yes you may

@Andreas-Bauer21

6 ай бұрын

Yes, of course... But where are your videos?

@Michel-Uphoff

6 ай бұрын

For me at least it leads to a more rigid column, although I hope it increases to the expected 50% improvement in the coming weeks. More stress on the bolts due to 7 kg of epoxy concrete in a hollow column? I do not think so. The increased mass is actually an advantage, because there are clearly fewer resonances. Yes, imported mills are often heavier, but whether they are also more rigid remains to be seen, and the cheaper ones are certainly not more accurate.

@Cyberwendy

6 ай бұрын

@@Michel-Uphoff , I do understand what you are trying to do. But,.. don't forget, this Proxxon mill cost 2k, if you look what you can buy for Optimum mill for 2k, it just not to compare. You can ask Stefan Gotteswinter, here on youtube about accuracy, he used to use a Optimum mill before he switched to a Deckel mill. I did own a Proxxon mill, and i have a miniature 7 axis, Bridgeport style mill, made from solid steel, and i use a import X2 style mill. I have seen a Bridgeport mill shake as a leave in the wind, depending on what you do with it. But a Bridgeport mill owner would not think i pour it full with concrete, instead they thinking about a more ridged mill. So i know what i am talking off. Wish you success with your modifications, but i think it just not worth the effort, money and time. Nice video's you create, keep em coming.

Bela máquina,pena que não tenha aqui no meu país 🇧🇷