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Posted by Eigenvector on July 3, 2007, 7:23 pm
> What you did so far sounds good.
>
> Are you saying your attic is sheetrocked?? So you have vertical sides,
> and *then* an A-frame?
> In my house, the A starts at the attic floor, with no over-head rafters.
>
> If the sheetrock is moving, that would indicate poor or non-existent
> bracing at various 90 corners, or where the A-frame commences. Bracing,
> gussetting, bracketing, or whatever one calls it would help.
> What you want to brace is not just between parallel rafters/joists (which
> can help), but the connection between the floor and any vertical members,
> and/or the angle between vertical members and the ensuing A-frame.
> IOW, you probably need to brace the house structure itself, on either
> side of the bag.
>
> Does your house creak/move in a strong wind? :)
>
> But before you do all this, as you suggested, hanging the bag higher would
> absolutely help, bec. a longer chain will inherently reduce lateral
> forces.
> In fact, the longer the chain, the better, in any circumstance. Perhaps
> even from the peak of the roof, where A-frame joists meet?
>
> A sufficiently long chain will allow positioning the height of the bag so
> that you strike the "center of percussion", which will also greatly
> reduce lateral forces, as will a longer/softer spring. This is the ideal
> positioning of a bag.
>
> The longer the chain is, that will position the center of percussion at
> the right height, the better--makes for a longer "softer" pendulum.
> A longer/softer spring will have the bag move more vertically, but also
> offers reduced lateral forces, *and* also reduced vertical forces.
>
> If you can't reach the peak or if that idea is just untenable, go as high
> as you can go, with some kind of simple box/truss above the rafters.
> You might consider bolting a set of rafters higher than the existing set,
> and using those to support the bag. This in itself would offer additional
> lateral bracing.
> And, there are ways to do this with just sheetrock screws, so that minimal
> damage/weakening occurs to the original beams, with plates. These are
> standard fare at HD, altho they may not fit exactly if certain angles are
> involved, but in principle you could use them.
>
> It's also possible to build, pretty simply, a 2x2 or 2x4 frame for the bag
> support, and have *that* attached to the joists with heavy springs, which
> would further reduce lateral stresses.
> But, I think a higher support point/longer chain/longer/softer spring
> offers the same force reduction, more simply.
>
> If you hang the bag higher etc, and the sheetrock *still* visibly moves,
> then I think you may have some issues with the house construction itself,
> and might want to consider some internal bracing at the sides/corners,
> regardless of the bag issue.
>
> email me if you want to fax me some sketches, which would help nail down a
> good solution.. Just remove the munge.
> --
> ------
> Mr. P.V.'d (formerly Droll Troll), Yonkers, NY
Whoops, sorry I credited your advice to MeatPlow. It was you who first
suggested the stringer bracing. Sorry about that, least I can do is give
credit where it is due.
As to your further suggestions, I'll have to work on them some other day, I
seem to have caught some loathsome plague or another and won't be doing
anything but popping Sudafed until it leave me alone.
But yeah my house could be better constructed, but its solid enough. I
suspect the placement of the bag might be exaggerating the problem, its
right on the end of the garage where there isn't a lot of framing or walls
to support the trusses.
>> So I posted a little bit ago about hanging a punching bag from the
>> rafters. I have the bag on a fixture mounted to 2 rafter beams (the
>> rafters are roof trusses, 2x6's). The bag is a 110lb bag, hanging from
>> an eyebolt . The issue that I'm seeing is that when I punch the bag, the
>> whole ceiling is moving. I don't mean shifting off its mounts of course,
>> but rather I can see the ceiling drywall moving back and forth and
>> rocking in tempo with the bag.
>>
>> It's not like I'm Rocky Balboa or someone, but I'm a pretty strong guy
>> and 110lbs is a lot of weight. So I'm looking for some advice/options
>> for my concerns. My concerns being that I'm afraid that if the ceiling
>> is moving enough for me to see, that means the whole structure is under
>> way more stress that it can take. But what to do about an object that
>> weighs that much but has to hang from 9 feet in the air. The rafters in
>> my house are at exactly the right height.
>>
>> Could I build up the rafters at the location where its suspended, add a
>> second 2x6, add a lot more cross bracing between the two rafters its hung
>> from, something like that. Admittedly I didn't do a lot of mod to the
>> hanging point, not knowing how it would respond I chose to take it slow
>> and see if this was feasible or not.
>>
>> Right now the eyebolt is hanging from 2 2x4's with a 1/2 plywood sheet on
>> top across 2 rafter beams. I believe MeatPlow offered that suggestion up
>> last time I posted this. Give a little more effort I could make a better
>> suspension jig, maybe 3 2x4's (hole for eyebolt in middle board), 1/2
>> plywood to tie them together on top.
>>
>> I don't know, what do you all think?
>>
>
>
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