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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: I know this is hardly the best, but have a look... posted by Ortem on September 17, 2001 at 15:28:34:
OK, that's a lot of questions :-)To quote from Shannon Dickson's article "Bad Vibes" available online in Stereophile's archives: "The ubiquitous shelves made from medium-density fibreboard (MDF) benefit from uniformith and are fairly well damped, but are not particularly stiff." Stiffness in this context can be read as rigidity. Bear in mind that that statement is a comparative statement in relation to other materials used in racks such as steel and aluminium. MDF can vary considerably in terms of quality and density, but is relatively heavy in large pieces, and a 2" thickness is getting a lot thicker than the thickness in which it is normally used. Probably normal use is 1" thickness or less. so with a 2" thick platform you're at least doubling the weight, possibly more with a better grade of MDF which will be denser than lesser grades.
Your spans at 30" or more wide and close to 24" deep are getting wide also. I think the normal Flexy span is around 24" wide and probably 18-20" deep. There have been reports here of normal thickness MDF shelves in a Flexy sagging in normal use. Sagging is more likely with wider spans and the increased thickness adds more weight which may also increase the possibility of sagging. Bear in mind that the shelf is only supported by the nuts clamping it at the chosen height on the uprights. Effectively you've got a 6 point support on the full width shelves but, for practical purposes considering load bearing, each usable shelf area is only supported by 4 points with the weight of a component or TV acting together with the mass of the shelf between those 4 points. A fixed frame with cross members and the shelves resting directly on the cross members would provide considerably more support, especially if you introduced an extra strut midway across a span. That loses the Flexy construction simplicity, however.
As a comparison, I could see some sagging over time of the MDF shelves supplied with my old Lovan rack which supported a quite light Creek CDP and an 11 kg = around 25 lb integrated amplifier. Those shelves had a widest unsupported span of around 20" and a thickness of around 1 cm or a bit under half an inch. I don't think the Lovan shelves are the highest grade MDF. The Lovan frame includes a horizontal steel triangle support for the shelves but the shelf really only sits on 4 small rubber discs so it floats a bit above the triangular steel frame. Throwing away the rubber discs and resting the shelf directly on the frame helped by providing a lot more contact area for support, as did eventually replacing the original shelves with better quality MDF around 18 mm thick (almost doubling shelf thickness). Your 2" thick proposal is roughly equivalent to 3 thicknesses of the 18 mm MDF I used but the amount of support provided by the Flexy frame is considerably less than that provided by the Lovan frame after I removed the discs and rested the shelves directly on the hollow steel cross members. Your components are much heavier than mine.
Inserting a steel plate into the shelf construction would definitely increase rigidity and help avoid sagging. You might even be able to get away with 2 thinner sheets of MDF and reduce the overall thickness of the shelf as a result while ending up with a stronger product, but you will then have the problem of drilling the steel when you drill the shelf.
Reducing the number of uprights to 3 effectively reduces the number of support points per component to 3 and provides even less support. I don't think that is advisable. Adding more supports is possible but probably only between the front and back supports to a total of 9. You really can't stick more in running from left to right because they'll get in the way of access to the rear of the equipment at the back and access to the controls at the front, not to mention running directly in front of the screen. While that helps, it essentially leaves the widest unsupported spans, which could benefit most from assistance, the same as before.
I don't see a need to wrap the threads to protect the gear provided you have enough space between the uprights for the gear to sit comfortably. Just keep the free space to a minimum because that's increasing the span width and you want to minimise that as much as possible.
It's just that I think your design is really pushing the limits of what the Flexy is intended for, and that's physically smaller gear than your TV and lighter gear than 100 lb components.
Sorry I can't help with the questions on working metal - I've got no personal experience whatsoever. I had an aluminium fabricator do the construction work on my rack to my design and specifications.
David Aiken
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- Re: I know this is hardly the best, but have a look... - David Aiken 01:32:15 09/18/01 (0)
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