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Help: My Grace 902 rocks back and forth(does not sit firmly) when placed on my shelf! - Page 2

post #16 of 22
11/20/05 at 12:51pm
Thread Starter 
Quote:
Originally Posted by gerG
You likely have a long foot on the LR or RF, or a short foot on the LF or RR. Diagonal swapping will not change anything. First swap the LF for the LR and check for a change. If no change, swap the RF for RR. If it is the feet, one of these 2 swaps will isolate the culprit. (LR = left rear, RF = right front, etc.).

As for 3 point vs 4, maximum stability will be achieved when no part of the body overhangs a tipping axis. The tipping axes are defined by straight lines drawn from foot to foot. In the case of a rectangular shape, like the Grace, this means a foot at each corner will achieve maximum stability. Reducing to 3 feet will make the unit less stable. Try it, place 3 feet under there in any formation that you like. Now go around and press down on all 4 corners, one at a time. At least 1 corner will tip. For the same reason, cars have 4 wheels.

To achieve a stable platform with 3 feet, one could construct a triangular base large enough that no part of the component body overhangs a tip axis. If you draw this up on paper you will see that it is a poor use of space.

The only advantage of a 3 point mount is that all 3 points will touch, even with irregular surfaces, or poor manufacturing tolerances. Trading a solid 4 point for a tippy 3 point is not a trade that I would recommend.

I have seen a few products that are designed with a 3 point mount (most notably turntables). As indicated above, if the feet are moved far enough outboard the platform can be stable. This in not relevant to a rectangular component designed for a 4 point stance.


gerG
GerG

Then why are footers usually sold in sets of 3?

Thanks

Jay
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post #17 of 22
11/20/05 at 1:09pm
Quote:
Originally Posted by jaybar
GerG

Then why are footers usually sold in sets of 3?

Thanks

Jay
Not sure. My question would be, why would anybody buy them in sets of three? I certainly wouldn't.

My personal guess would be that if they sold them in fours, they would have to deal with exactly the sort of issue that started this discussion.


gerG
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post #18 of 22
11/20/05 at 1:30pm
Thread Starter 
Quote:
Originally Posted by gerG
Not sure. My question would be, why would anybody buy them in sets of three? I certainly wouldn't.

My personal guess would be that if they sold them in fours, they would have to deal with exactly the sort of issue that started this discussion.


gerG
GerG

I tried to change the feet as you suggested. No luck.

Its hard for me to tell, with my vision, but I could not see any gaps of light when I held a flat surface to the underside of the unit, so I doubt it is the chasis and yet it also happens on every other surface, so I am baffled.

The only way that all feet contact the surface is with 3 feet.

Jay
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post #19 of 22
11/20/05 at 1:31pm
Thread Starter 
BTW, has anyone used any after market power cords with the Grace m902?

Jay
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post #20 of 22
11/20/05 at 2:20pm
Quote:
Originally Posted by jaybar
GerG

I tried to change the feet as you suggested. No luck.

Its hard for me to tell, with my vision, but I could not see any gaps of light when I held a flat surface to the underside of the unit, so I doubt it is the chasis and yet it also happens on every other surface, so I am baffled.

The only way that all feet contact the surface is with 3 feet.

Jay
Dang, if you swapped the feet, and it always tips in the same direction (LF or RR off the ground) it indicates something on the base of the amp. If one of the holes is drilled at an angle, it will not allow the foot to screw in all the way, making that corner high relative to the others (one of mine has this issue, but it is slight). The last possibility is that the base is not flat. Either of these would require a return to Grace for resolution. If you have a Radio Shack around, I would suggest trying the large cushion feet that they sell. Try them in place of the factory screw in feet. You can experiment with 3 point, 4 point, or 5 point configurations. I always add one in the center. I tend to move my gear around a lot, so it is always good to prevent a scrape if one or 2 feet don't line up with another piece of gear.

I have used a variety of cords, but nothing more exotic than a Quail hospital grade cord.


gerG
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post #21 of 22
11/22/05 at 1:27am
Thread Starter 
Thanks everyone for responding.

Grace has identified the problem. In the assembly, some screws had the incorrect amount of tightening (torque) which caused the problem. I am being sent a new unit and will return mine. They have stellar customer support.

Jay
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post #22 of 22
2/28/11 at 6:25pm

I would simply buy some o-rings that fit nicely around the set screws. This way you can screw all of the feet down firmly, but not scratch the bottom surface. With the tension now on the o-rings you can adjust the tightness of each foot individually while keeping the set screw tight. O-rings will last a while as well if they of decent quality. 

 

I endedI ended up using some adhesive felt that worked out really well.  If you find the correct diameter you keep the sleek looks of your m902 / m903 and not worry about scratching the bottom chassis.


Edited by NA Blur - 3/9/11 at 8:37pm
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