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| AdeV:
Since it's only the weight you're after, and not the constructional qualities, why not just use a bag of sand? Seal the bottom as best you can, but leave a removable panel; pour sand in the top until desired weight is achieved - it'll find its own way past the internal structures obviously. Then, when you need to move the machine at a later date you can simply open the removable panel and let the sand out... The only thing you need to be sure of is that the sand is bone dry before you pour it in, wet sand will cause untold rustiness... |
| awemawson:
If it's a closed box structure i.e. No holes for stuff to flow out, dry sand or pea shingle will work just as effectively as concrete, and will settle into a dense packing over time. Also in extremiss it can be removed if you make a suitable plugged hole in the base. |
| PekkaNF:
--- Quote from: shipto on April 17, 2017, 05:36:02 PM --- --- Quote from: PK on April 17, 2017, 07:31:21 AM --- I like the idea of filling with concrete. Adding mass is one of the simplest things you can do to a small machine to improve it....... PK --- End quote --- I do too but Pekka disagrees and I see his point about shrinkage. However upon doing some extra reading it seems that most of the shrinkage comes from adding more water than is needed to make the concrete move better it seems that if the added water is calculated correctly then little shrinkage occurs but the mix is extremely thick. Will have to look into it a bit more. --- End quote --- The thing is that concrete shrinks for 400 years. First faster and then slower. Many factors affect on shrink rate and some you have influence and some not. Worst shape for concrete "filled machine" is a hollow thin steel section that you fill with concrete...some machine manufacturers tried this -70/80:s and failed. Concrete filling will shrink in time and delaminate from the skin...if you weld rebar to avoid that it will pull the skin out of alingnment. There are ways to reduce the shrink rate or compensate it, but it will not work in machine building scale. You can make a servisable machine if you know what you are doing. Basically you cast more or less square section, no voids in it, you may cast some features to it. You don't need rebar and other "iron" on it, unless you have hanging beam or such bad idea. And then let it cure and age some time - longer the better. Then use this cast as a sandwitch between steel members and have it on compression. You must use epoxy concrete, injection epoxy or grind the concrete surface flat prior mechanically mounting the steel sructure to it. Epoxy concrete works. And as Andrew et.al. said sand or such will dampen "ringing" pretty well too, it's cheap, reversible and has all good qualities to home build. Pekka |
| shipto:
What about a dry mix? www.precast.org Sent from my SM-N910F using Tapatalk |
| awemawson:
It will eventually harden from moisture in the air and you'll lose the advantage of being able to remove it. |
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