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

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entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie,
all d'numbuhs

"Eigenvector" wrote in message
news
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?