Is the surface of water ever "perfectly" flat?

atferrari

Joined Jan 6, 2004
4,764
Hola strantor,

Thinking of that .0001", not sure if relevant: the surface will reflect every time whatever vibration affects the tank containing the liquid. Easy to see when inside a partly filled ballast tank of a ship. Just anyone hitting main deck with a hammer, many many metters away you could see the concentric mini waves riding the surface.

BTW, many years ago I spent some three hours of my valuable time as a Supercargo in a terminal upriver, watching a group of three guys giving the finish to the concrete floor of a future cold storage chamber (allowing to drain liquids instead of absorbing them).

Using kind of big size squeegees, dry cement, careful watering and a well defined sequence they managed to create a smooth and bright surface on the cement that was still setting. Sure, nobody mentioned precision, but surface was much much smoother after this.
 

tcmtech

Joined Nov 4, 2013
2,867
I am not sure where this .0001" accuracy comes in at given the material that the overall machine is supposed to be made from plus the fact that no overall dimension is given for the .0001" reference. Is that .0001" in 1" or 1 foot or 5 feet" o_O

My point is hitting .0001" in any standard machining work even with very well kept precision built and massively rigid machines is hard. Doing it with DIY poured concrete and mixed metal framing plus wooden who knows what parts all for as cheap as possible is by a machinists standards somewhere between laughable and idiotic. Especially on a 5' x 5' homemade platform. :(

Thermal expansion, weight shifting, compound stresses and nearly everything else is going to keep such a contraption in a state of forever changing tolerances and reference points that nothing will ever have any repeatable accuracy or precision in the end.

To me the whole concept sounds like someone saying, Hey I can't afford or know how to build a rocket to go to the moon so I am going to build a bicycle and ride there instead and I want to make it affordable so others can do the same.
Sure it sounds dumb to anyone who knows where the moon is but to someone who doesn't hey why not.
From the unknowing perspective it looks more like this, The moon does not look that far away and it comes and goes behind the horizon every night and morning so I just need build a vehicle that can get me and others over the horizon and thus to the moon if we time it just right! ;)

So I say sure go for it! Achieving that .0001" tolerance on a 5' x 5' platform using concrete and mix and match metal wood and water for materials all put together on a cheap as possible budget's just over the horizon so peddle your heart out! :rolleyes:
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
tcmtech I think it would save you a lot of time writing these posts, and me and everybody else a lot of time reading them, if you just go ahead and write me off as an idiot not worth replying to.

You've somehow concluded that I've never touched a machine tool based on these retarded questions I'm asking. That isn't true. I have two lathes of my own and have been using mills at work for a few years. I'm not a machinist, but I'm not the uninitiate you think I am either. Here it is layed out: I know how far away the moon is and I'm still planning to pedal my bicycle there, and I am only interested in discussing pedaling methods and bike mods that might help me get as close as possible. Now, if you wish to civilly discuss the physics involved in pedalling to the moon, and any mechanical limitations of bicycles that might prove problematic, I am all ears.

I don't need anybody telling me it can't be done. It has been done, and it can be done again. Machine tools have been made successfully from ordinary concrete for nearly a century. Precision machine tools have been made in the absence of precision machine tools with which to make them, as evidenced by the existence of precision machine tools. I'm not convinced to the contrary by your compendium of machining knowledge.
 

tcmtech

Joined Nov 4, 2013
2,867
Machine tools have been made successfully from ordinary concrete for nearly a century. Precision machine tools have been made in the absence of precision machine tools with which to make them, as evidenced by the existence of precision machine tools.
I am a bit of a fan of old industrial and manufacturing equipment myself and have spent quite a bit of time reading about and looking at actual antique machines that were hand crafted well before modern tech was around and I have a huge appreciation for the insane amount of time, effort and detail that it took to build such equipment.

When you look at them they are massive in order to stay stable and accurate and were incredibly labor intensive to build and maintain hence the #1 reason they were never mass produced. They were never devices created by the common person out of odd bits and pieces to be easily replicated by any other average person. They were highly engineered devices for there day and even by today standards.

As far as my knowledge goes I consider it hard won from personal experiences. High precision and high accuracy come at a high price but if you think you can build a metal working machine that can hold a repeatable tolerance of .001" on a work area of several square feet all out of whatever you can find laying around for around $1000 I will pay for it myself!

By repeatable I mean it can make 10 fair sized items back to back without calibration and no two will be more than +- .001 off of each other in any machined tolerance all based off of one common reference point.

I'm not saying its impossible to build but give then specs you have said, the parts and materials list and the price range I say I have serious doubts and would love to be proven wrong! So build it and prove me wrong. I will be waiting. ;)
 
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shortbus

Joined Sep 30, 2009
10,045
As a retired die/mold maker machinist, precision costs money. There is no way around it. There is a magnitude of difference between accuracy of 0.001 and 0.0001. Go and look at the difference in price between a ball screw that guarantees movement of 0.001 per inch and one that gives 0.0001 per inch if you don't believe me.

Strantor we're not trying to discourage you on this project, just trying to put things in perspective. Even if you can get your base as accurate as you claim, how are you going to make the part or spindle move accurately? With it being in a circle belts or chains are the only way I can see. Both are plagued with inaccuracy and the problem of stretch over time. How will you allow for clamping the work to your to the concrete table? What about the coolant that is needed to allow the speeds a CNC operates at?

None of the standard metal cutting machines or operations has really changed that much since the days that machining first started, just the materials and methods used.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
By repeatable I mean it can make 10 fair sized items back to back without calibration and no two will be more than +- .001 off of each other in any machined tolerance all based off of one common reference point.

I'm not saying its impossible to build but give then specs you have said, the parts and materials list and the price range I say I have serious doubts and would love to be proven wrong! So build it and prove me wrong. I will be waiting. ;)
I appreciate your revised conversational approach. Really, Thank you.

I haven't put any "specs" in stone for anything. On the forum here I have provided numbers in places where numbers needed to be, in order to further the discussion. I realize that I left the door wide open for these numbers to be taken as bottom line requirements. The .001" (or .0001", or whatever I said) tolerance is a goal, not necessarily a requirement. I just want it to be competitive with what I've been looking at purchasing as a hobbyist machinist; like a common Bridgeport, including crummy asian ones and used ones; maybe even cummy asian used ones. The only bottom line requirement is that it can mill metal without self destructing. If it can do that, and produce parts with acceptable surface finish and at least enough accuracy that they are usable for their intended purposes, then I'm calling it a success. If the intended purpose of the produced parts demands a higher accuracy than what the machine is capable of, then I see that more as failure to select the right machine for the job than a failure of the machine. Unless of course it can't even make a straight line that passes hands-free visual inspection, then it's going to have to called a failure.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
As a retired die/mold maker machinist, precision costs money. There is no way around it. There is a magnitude of difference between accuracy of 0.001 and 0.0001. Go and look at the difference in price between a ball screw that guarantees movement of 0.001 per inch and one that gives 0.0001 per inch if you don't believe me.
Oh, I believe you. I have been on both sides of it.
I have been in the machine shop when the rookie engineer dropped off drawings showing unreasonable tolerances in every dimension, and the crotchety old lead machinist cut him down to size, making him justify the need for every specified tolerance on the drawing, one at a time, scratching this and that, until it was a buffet of red ink. He took it from something that would be in the realm of aerospace design to something that even I could make, on the bridgeport, with no DRO.
That experience had time to fade from memory; more recently, I was the rookie engineer. I sent off my design for an encoder bracket for bidding and was getting quotes over $4K. Then it dawned on me, duh! I revised the design to be something our in-house welder could cut out of plate, no tolerances stated, no machining required. Just a "make it as accurate as you can" - to a guy who uses a tape measure as a micrometer.
In both cases, the rookie engineer was happy with the end product.
Strantor we're not trying to discourage you on this project, just trying to put things in perspective. Even if you can get your base as accurate as you claim, how are you going to make the part or spindle move accurately? With it being in a circle belts or chains are the only way I can see. Both are plagued with inaccuracy and the problem of stretch over time.
Yes that came up, either in this thread or the last one, and I acknowledged that the belt was a terrible idea. I said I was going to hob the diameter of the ring and move it with a threaded rod. A huge worm gear like that can be made with a power drill and a threading tap. That should give it the needed resistance to forces generated by cutting, and even more accuracy/resolution than a lead screw of the same pitch in a linear machine, since the ratio of [#revolutions*pitch]:[distance traveled] will always be >1, where in a linear machine it's a fixed 1:1.

How will you allow for clamping the work to your to the concrete table?
I didn't really see this as being a snag. By the concrete table, I assume you're referring to the "table"/"bed" where the workpiece will be clamped in the finished machine, to begin cutting it? I was thinking about just embedding a grid of threaded inserts in the top of it. hold-downs could be bolted straight into the inserts, or notched removable plates/slats could be bolted down with a gap in between them, to form the traditional t-slot between them. I don't think the work-table would have to be perfectly straight, flat, or level for this to work. As long as the threaded inserts don't rip out, it should be fine. The workpiece can be held in a milling vice and adjusted true with the head, or if bolted down, it could be shimmed as needed true with the head. I guess the spindle would have to be trammed to the upper portion; hadn't really thought about that part. I will have to give it some thought.
What about the coolant that is needed to allow the speeds a CNC operates at?
What about it? do you see it being a problem for a concrete machine? You thinking about it causing the concrete to swell? That's a possibility. I guess it would need to be painted over with some of that garage floor coating.
 

wayneh

Joined Sep 9, 2010
17,496
atferrari touched on this in #41 and if it's already been brought up elsewhere, apologies.

The surface of a tub of water will also have significant imperfections - relative to the 0.0001" specification - due to varying air pressure above it. You would need a quiet and draft-free workspace above the water to have a chance at that level of precision. I'm thinking static might also distort the surface. A surfactant in the water might help.

I suppose the original question is moot at this point in the discussion?
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
I suppose the original question is moot at this point in the discussion?
Haha, yes I think so. I've filed the water idea under "bad ideas"
atferrari touched on this in #41 and if it's already been brought up elsewhere, apologies.

The surface of a tub of water will also have significant imperfections - relative to the 0.0001" specification - due to varying air pressure above it. You would need a quiet and draft-free workspace above the water to have a chance at that level of precision. I'm thinking static might also distort the surface. A surfactant in the water might help.
Agreed. I'm not sure if there's one place on earth still enough, stagnant enough, and static-free enough to get the surface of water to remain "perfectly" flat (if it ever was so) for long enough to use it as a casting surface
 

tcmtech

Joined Nov 4, 2013
2,867
I just want it to be competitive with what I've been looking at purchasing as a hobbyist machinist; like a common Bridgeport, including crummy asian ones and used ones; maybe even cummy asian used ones. The only bottom line requirement is that it can mill metal without self destructing. If it can do that, and produce parts with acceptable surface finish and at least enough accuracy that they are usable for their intended purposes, then I'm calling it a success.
Given that expectation I can say that I bought a brand new Smithy 1340I Mill/lathe combo unit a number of years ago and to be honest for the money spent it does a super job!

For normal farm and one off work where +- .010" is more than sufficient its plenty accurate and on the one in a hundred jobs I do with it that do require high precision and accuracy once everything is cleaned up lubed and tightened I can hit sub .001" tolerances without much trouble and even .0001" tolerances if I don't mind spending the time to sneak up on the final tolerances with fine grit sand paper and some direct hands on high precision polishing/detail work.

Price wise I spent just under $5000 on it and loaded it with every practical accessory I could buy for it at the time and since then my brother and I have probably spent a $1000 more on other new and second hand accessories and tooling for it as well including scrapping the Dc motor drive and replacing it with a normal three phase motor and VFD system.

Next major up date will likely be a home built CNC drive conversion for the XYZ and rotary table controls.
 

#12

Joined Nov 30, 2010
18,224
I cheat. My sister owns a machine shop. I just email a drawing and receive the parts in about a week. :p
 
Water can not be flat. The ocean is not flat it curves with the earth. So water in a small container like a glass of water is not flat either.
 
Hey i did some research for you and i suggest you to check this thread www . physicsforums . com/threads/a-perfectly-flat-bucket-of-water.690357/ hope i offered some help
 

theamber

Joined Jun 13, 2008
325
Actually if you look at it I cant think of any natural thing that would appear to the human eye flatter than water. Maybe the closets some quartz crystals So the world is not flat at all it is full of curves. To get water to be flat to 0.0001" could be possible in the right environment, since its molecules are much smaller than that even including its intermolecular space.
 

atferrari

Joined Jan 6, 2004
4,764
Actually if you look at it I cant think of any natural thing that would appear to the human eye flatter than water. Maybe the closets some quartz crystals So the world is not flat at all it is full of curves. To get water to be flat to 0.0001" could be possible in the right environment, since its molecules are much smaller than that even including its intermolecular space.
Appear yes, being, no... other than for an infinitesimal instant.

Go to the tank of your chocie and look to the surface of the liquid. Carefully.

No matter where in Earth.
 
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