Twenty-five years ago I got very interested in concrete and polymer-matrix machine tools, and studied the hell out of them for a while, but never did a darned thing about it. I'm wondering if there is enough interest among hobbyists to try to get a discussion group or something like that going.
There are a lot of routes that might be taken -- post-tensioned, ferrocement, polymer-modified, fiber-reinforced, not to mention polymer-matrix machines -- and there is room for a lot of experimentation on such things as aligning spindles, embedding bedways, and so on. A lot of the testing and experimenting can be done on the cheap. All it takes is time. I don't have the time to do it all myself but I'd like to see something come of it.
Is anyone interested? And for you guys who are more web-savvy than I am, suggestions for a way to upload and display photos and drawings?
I'm just looking for a show of hands to see how many might be interested.
There's been a HUGE thread on this very suject on CNCzone.com. Several thousand posts and a few actual machines built. I've only got a few minutes till the Marathon Lady leaves the dock. I'll search for the link tonight.
200 years ago lathe ways were made by mortaring iron strips into granite blocks. The closest I've come was welding a framework from steel channel and angle and shimming the pillow block bearings into alignment. As a long-time prototype machine builder I prefer a design and construction method that is easy to modify. Plastic castings don't have much tensile strength, especially where material has to be added and the reinforcing fibers don't cross the joint. Rapid prototyping resins were the worst, I've needed to cut away a large bonding surface and sculpt several batches of epoxy to build up a boss that would hold a new bearing.
My Picasa photo links have remained on one line since I started prefixing them with >. I don't know how you could post drawings except as graphic images, there isn't any common drawing package other than MS Paint. I draw machine parts with a Mentor Graphics circuit board layout program that theoretically writes and reads DXF, but I've been unable to open one from another CAD program with it.
Ha! That's interesting. The first reference on that page is to an article written by one of my old co-editors at _American Machinist_, Joe Jablonowski.
I've heard of that book and it's one I should get for my reference shelf -- as soon as I win the lottery . Thanks, Pete.
Right. The loads and their directions on standard machine tools, though, are well-defined and they have been dealt with effectively in concrete and polymer structures. Polymer is easier because it's ductile; reinforcing fiber begins to take up the tensile loads as they're applied, without destruction of the polymer.
Concrete is more difficult because it's brittle, as well as having almost no tensile strength. For that we have prestressing, post-tensioning, ferrocement, and modified concretes. They're still a challenge but there's a ton of experience with and information about structures built that way, much of which applies very nicely to basic machine tool structures. It's also worked well with some boat structures -- although it has enough problems that ferrocement boats have waned in popularity over the last few decades.
It's an intriguing idea. If others here who have more up-to-date exposure to the developments in the field it would be good to hear from them.
I'm interested. I have a CNC (woodworking) router which started life as a kit cheap enough that I could buy it, but which therefore has more flimsiness than I'd like - structurally similar to a (metalworking-type elderly) planer, and it might be that if I could find a planer that hadn't hit the junk bin, that would be the better starting point, but flinging something together from scratch has some appeal, if it can be done without breaking the bank, particularly considering that most planers have probably already been sent to China and melted down...
OTOH, Anyone with a planer (or shaper, for that matter) to part with in reach of SW Vermont, let's talk...
Ok, let's see what Karl comes up with from the CNC forum he mentioned. If they've worked out the details, that's a good place to begin.
Depending on the quality and stiffness of the guideways and so on, you may be able to reinforce the machine you have, possibly with concrete structure. Once you work out a way to reinforce it, its properties are pretty good. Ferrocement, for example, has about the same density, tensile strength, and compression strength as aluminum, with much better vibration damping properties.
Heck, I thought I'd get to see some pictures of fish. I walked across a nearby pond today, looking for bluegills frozen in the ice. I had my ice axe, but no luck.
I stopped in there and searched on "concrete"; 'found some comments, but nothing substantial.
Anyway, it all depends on whether enough people really want to get into it. There is plenty of information around to get one dabbling with the idea, but I'm wondering if people want to dig a little deeper.
Thanks, Karl. It took some time to go through all of those, which is why I'm slow getting back to you.
There are a few ideas in there but, frankly, those guys are mostly not up to speed with this material. The machine designer who complained about cracks in the polymer concrete reinforced it incorrectly. Most of the others are talking about making sheet metal structures and trying to beef them up with concrete. That's really not what I'm talking about. That's been done for decades (particularly by the Italians and the French), and the structural design issues they've had to face are much more complex than those posters are talking about. That kind of structure, while it sounds simple, is anything but.
I would have approached this as a long-term research project years ago, except that I don't want to spend that much of my spare time, and I see no money in it. No time, no money...I don't do those things anymore. I'd get involved now just for the hobbyist satisfaction of it IF there were at least a dozen other people who were serious about it and who would contribute. But I realize after reading those threads you linked to that even guys who are knowledgeable machinists may not understand stressed concrete and concrete composites enough to do serious things without a lot of study. Some boatbuilders know ferrocement, and some architects know FC plus post-tensioning. Civil engineers usually know general reinforcement and prestressing. Now I need to find a few of those who also are amateur machinists. d8-)
So, I'll put it back in the can for now. Maybe when I retire -- if I ever retire. Thanks again for your effort; it kept me from reinventing a wheel.
Yea, I know what you mean. its a bit like mining gold. You got to shovel a lot of ore to find that nugget. My hobby time has morfed from cutting metal to rebuilding old CNC iron to like new with a brand new control. Among all the idiots, there are a couple gems.
For example, I learned that my old wire EDM is the best possible candidate for upgrade to a new control and I found a guy that knows this machine like the back of his hand.
Say, I think the project after this is to build a four foot by ten foot Plasma, torch, router combination machine. I'm thinking weldament for the machine frame. Does this technology have any benefit for vibration dampening on this application?
Yes, concrete is a good vibration damper and you could make an effective and inexpensive router frame out of it. But it would take some real understanding of the material to avoid potential problems. And a good structure is not going to be light.
For something like that I'd look at prestressed concrete sections that are available commercially. If you wanted a perimeter frame, you could use small beams, which tie together with special mortar at the corners. Or, if you wanted a slab, you can buy hollow floor slabs. These things are heavily reinforced and prestressed so that they'll handle a lot of tension loads.
But after it was built, I don't think you could move it without wrecking it. That's one of the limitations. Small, squat machine tools are one thing. Larger structures are another.
Some of the first machine tool applications were oil-country-type lathes built by the Soviets back in the '40s, so big machines are entirely possible. In fact, that's a major attraction of concrete for machines. But you pretty much have to build them in place. Unlike cast iron or steel, they have to be built for the specific loads they're going to be subjected to. Put a forklift under a long span that's stressed for heavy loads from the top, and you can crack it.
Small machines, like a lathe chucker or a squat bridge-type mill, are an entirely different story. You can build them with ferrocement and they'll be capable of handling stresses in all directions. And they can be much lighter than girder-type structures. The material itself, loaded with a dense matrix of welded steel mesh, has an overall density similar to that of aluminum.
A big frame like your router idea is something for one's second or third project, IMO. It's a challenge unless you've been designing bridges all of your life.
Are you thinking of this as a manufacturing process or one that hobbyists could use to bootstrap a machine shop, like Gingery's cast aluminum tools?
I'll build things with whatever works, castings or welded steel or logs chainsawed flat or anchors drilled into a big flat rock. Assuming a hobbyist without FEA or the knowledge to apply it, I think metal bearings and support plates jigged in place and connected by the cast material might make sense. I would join the pieces with threaded rods so it could be disassembled for repair or improvement, and the casting wouldn't have to take much tension. Otherwise no matter how strong it is, it has to bond to the metal and they have very different thermal expansions. If the casting came out badly the metal could be reused. I have a vacuum oven to remove trapped bubbles but I don't suppose too many others do. I bought it cheap at an auction and spent most of a day chipping the old spilled resin out of the chamber and fixing leaks.
Nonmetallic castings seem to be used hesitantly in industry. My Powermate generator has one alternator bearing cast into the plastic end housing. DeWalt chose magnesium for the gear case on their high- end cordless drills, reportedly because they couldn't make a plastic one strong enough. I think that was in Design News. The Drill Doctor chuck is an example of a casting that isn't quite as satisfactory as a metal one. Polymer pistols have metal inserts cast in, I don't have one to decribe how, and the Segway which I've dis and reassembled many times has a very solid metal structure under the plastic.
Not the first, and not exactly the latter. I'm thinking more about building some simple machines that might be useful to someone who already has a couple of machine tools. Starting from scratch is interesting, and someone might want to build on these ideas to do it, but I think it's too many unknowns to deal with at once, for a beginning.
The machines I have in mind are things like a between-centers grinder and lapping machine; a speed lathe (that could be built up into an engine lathe); a sliding-head drillpress; a simple surface grinder; a benchtop mill; and a manual-feed gap-bed lathe. The latter few are a lot more complicated but they still can be simpler than a screw-cutting engine lathe.
That's the first thought of most people who have knowledge of machines and machine elements. I wouldn't want to foreclose options, but my own approach is to start with the structure and to figure out what means are practical to mount the guideways or rails, and the dynamic elements.
Using a metal structure to establish relationships among the elements is an attractive idea -- like a Glock pistol. As I mentioned, a few European builders have taken that approach. But the concrete is more than glue and mass. If you use it right, it's the structure itself.
Concrete has some properties that make it a challenge for machine structures. There is the obvious one that it has virtually no tensile strength. You deal with that by reinforcement, either by means of tensioned steel rods or fine fabric composites, such as ferrocement. When you get into machine tools, there are potential problems with loading it to avoid tension/compression cycling, and there is the problem, particularly for large machines, that it shrinks (slightly) for up to three years after casting. It's like dealing with a wood structure in some ways; you have to be mindful of expansions and contractions, preferred loading directions, and so on. You have to design around those issues or compensate for them somehow.
The upside is that it's so cheap and so versatile. And it's a great damping material that's also relatively stable, compared to most alternatives with comparable costs and versatility. The challenges can be solved with good engineering, mostly of the clever-hobbyist variety. That's what I find interesting about the whole idea. This project is more about making something with creative ideas than it is about building a machine shop -- although I would want to stick to useful machines for projects. I don't see it as a lab exercise, either.
I don't know about the effect of trapped bubbles in reinforced concrete. Considering the astonishing number of research papers on advanced concrete that are out there (from Europe and developing countries, as well as from the US), I'm sure someone has investigated it.
As for the thermal expansions, yes, and that's something that limits the approach of making a light structure out of steel and bonding it all together with concrete. Those differential expansions are not a problem in finely reinforced composites such as ferrocement. And they're well-known and characterized for pre-stressed and post-tensioned concrete.
When you use a material such as ferrocement, you can minimize the number of separate elements that have to be bolted or otherwise fastened together. Most of those machines I listed above can be built as more or less monolithic structures.
There are lots of ways to engineer a structure, and there are ways that are appropriate for volume manufacturing that can be done better in some other way by the one-at-a-time hobbyist. Monolithic ferrocement structures, or post-tensioned structures, are one-at-a-time deals. They can be better than anything made in production, like many other things we make in our shops.
The idea won't let me go; I've been thinking about it for roughly 30 years, during which time I've acquired a pretty good sense of concrete structures. Unfortunately, the time to do it has never magically appeared, and the incentive is purely one of personal satisfaction.
If a manufacturer could make a lot lighter frame work for say a lathe, it seems like it would be profitable. The do-it-your-selfer would buy some decent bags of redi-mix locally and pour/finish the machine in situ.
I don't think this is what you had in mind though :)
First, there's too much labor for it to be commercially viable. That is, except for the sheet-metal structures with the poured-in concrete. And the polymer/granite-aggregate machines you see promoted at shows are mostly viable for special, custom machines.
Second, "pouring" a machine is pretty limited, because it's not that simple to get the required tensile strength and resistance to cyclic loading. It can be done, and it doesn't require a lot of skill. But it does take some time and you have to know what you're trying to achieve.
Unfortunately, concrete is not cast iron. It requires some engineering for any kind of structure that needs to handle more than compressive loads.
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