[Ned Simmons]

On Sun, 3 Feb 2008 17:22:03 -0800 (PST), "
wrote:

whats better for strength? i have four fasteners to choose from:

8-32

10-24

10-32

1/4"-20

If diameter is fixed, whats stronger, more or less threads?

The load will be shear, i.e., it will try to shear the bolts off,
putting stress on them in that direction.

If the thread is in the shear plane, the screw with the largest root
diameter under the thread will be strongest. For a given OD, a finer
thread will have a larger root diameter. If the shear is carried by
the unthreaded portion of the screw, the thread pitch won't matter.

If the fasteners are torqued tightly enough that load is carried by
friction in the joint rather than shear, the fine thread again has the
advantage because its greater root diameter makes the bolt stronger in
tension, allowing it to apply more force to the joint.

Among your choices, the 1/4-20 is strongest; a 1/4-28 would be
stronger still.

--
Ned Simmons

[toolman946 via CraftKB.com]

If the fasteners are torqued tightly enough that load is carried by
friction in the joint rather than shear, the fine thread again has the
advantage because its greater root diameter makes the bolt stronger in
tension, allowing it to apply more force to the joint.

Among your choices, the 1/4-20 is strongest; a 1/4-28 would be
stronger still.

Well said. (I think he stole my answer!!! har har)

--
Message posted via http://www.craftkb.com

[Tim Wescott]

On Sun, 03 Feb 2008 22:42:47 -0500, Ned Simmons wrote:

On Sun, 3 Feb 2008 17:22:03 -0800 (PST), "
wrote:

whats better for strength? i have four fasteners to choose from:

8-32

10-24

10-32

1/4"-20

If diameter is fixed, whats stronger, more or less threads?

The load will be shear, i.e., it will try to shear the bolts off,
putting stress on them in that direction.

If the thread is in the shear plane, the screw with the largest root
diameter under the thread will be strongest. For a given OD, a finer
thread will have a larger root diameter. If the shear is carried by the
unthreaded portion of the screw, the thread pitch won't matter.

If the fasteners are torqued tightly enough that load is carried by
friction in the joint rather than shear, the fine thread again has the
advantage because its greater root diameter makes the bolt stronger in
tension, allowing it to apply more force to the joint.

Among your choices, the 1/4-20 is strongest; a 1/4-28 would be stronger
still.

Assuming that you have enough depth in the aluminum to fully engage the
threads, and that you're using a decent tap.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

[Stuart & Kathryn Fields]

"toolman946 via CraftKB.com" u40139@uwe wrote in message
news:7f362f74a04f5@uwe...

If the fasteners are torqued tightly enough that load is carried by
friction in the joint rather than shear, the fine thread again has the
advantage because its greater root diameter makes the bolt stronger in
tension, allowing it to apply more force to the joint.

Among your choices, the 1/4-20 is strongest; a 1/4-28 would be
stronger still.

Well said. (I think he stole my answer!!! har har)

--
Message posted via http://www.craftkb.com

Just a thought, we had a sailboat in the So. Pacific with an aluminum mast
and SS fittings. It seems that the combination created a small battery and
we would find a white powder around the joints. Cad plated bolts had less
corrosion and I guess, though we never tried it, titanium would have worked
better?

stu

[Rex]

Stuart & Kathryn Fields wrote:
"toolman946 via CraftKB.com" u40139@uwe wrote in message
news:7f362f74a04f5@uwe...
If the fasteners are torqued tightly enough that load is carried by
friction in the joint rather than shear, the fine thread again has the
advantage because its greater root diameter makes the bolt stronger in
tension, allowing it to apply more force to the joint.

Among your choices, the 1/4-20 is strongest; a 1/4-28 would be
stronger still.

Well said. (I think he stole my answer!!! har har)

--
Message posted via http://www.craftkb.com

Just a thought, we had a sailboat in the So. Pacific with an aluminum mast
and SS fittings. It seems that the combination created a small battery and
we would find a white powder around the joints. Cad plated bolts had less
corrosion and I guess, though we never tried it, titanium would have worked
better?

Always been my understanding that SS and aluminum were a no-no.
Galvanic action hastens corrosion.

[Jim Wilkins]

On Feb 4, 12:18*pm, Rex wrote:
...
Always been my understanding that SS and aluminum were a no-no.
Galvanic action hastens corrosion.

The 5-year-old homemade guy line pulleys on my antenna have aluminum
side plates, brass sheaves and ss axles. I took them apart Sunday for
cleaning and greasing and didn't see corrosion on any of the metals.
They are exposed to rain and wood smoke but no salt. Perhaps the
grease film protects the aluminum.

The rebuilt antenna's terminals are stainless, too, and the
connections have remained good enough that from NH I can receive good
NTSC TV from Rhode Island and watchable signals from Hartford.

Jim Wilkins

[Stuart & Kathryn Fields]

"Jim Wilkins" wrote in message
...
On Feb 4, 12:18 pm, Rex wrote:
...
Always been my understanding that SS and aluminum were a no-no.
Galvanic action hastens corrosion.

The 5-year-old homemade guy line pulleys on my antenna have aluminum
side plates, brass sheaves and ss axles. I took them apart Sunday for
cleaning and greasing and didn't see corrosion on any of the metals.
They are exposed to rain and wood smoke but no salt. Perhaps the
grease film protects the aluminum.

The rebuilt antenna's terminals are stainless, too, and the
connections have remained good enough that from NH I can receive good
NTSC TV from Rhode Island and watchable signals from Hartford.

Jim Wilkins

Jim: My experience was with a McGregor catamaran in the Marshall Islands.
We had an abundance of salt and warm air. It would only take one year for
the white powder to show around a SS bolt in the Aluminum Mast. If I
recall, there was some greasy like compound when applied to the bolt that
would slow the process.
Stu Fields