That is a good price of the rod but Enco doesn't sell acme wing nuts. You
would have to buy a regular acme hex nut and weld on some rod for handles.
Not exactly the strongest solution.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Richard J Kinch" wrote in message
. ..
Glenn Ashmore writes:

The 1 1/4" Acme
threaded rod for the top will cost about $12/foot and you will need
18"/stand. The wing nut is another $40.

$6/foot with free shipping from use-enco.com. Nuts are $4.29.

But you're right, the make-or-buy analysis sez "buy".

Glenn Ashmore writes:

That is a good price of the rod but Enco doesn't sell acme wing nuts.
You would have to buy a regular acme hex nut and weld on some rod for
handles.

I assume that would be the approach, if you're welding the stands
themselves.

Are the Brownells wing nuts a cast item, or welded, or what? Is this
something they make themselves or have made or is a more widely used
component?

The ones I have seen are cast wingnuts but I would guess that if you buy a
few thousand at the time the price goes down significantly. The $40 price
was from McMaster where you pay to get just one and get it today.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Richard J Kinch" wrote in message
. ..
Glenn Ashmore writes:

That is a good price of the rod but Enco doesn't sell acme wing nuts.
You would have to buy a regular acme hex nut and weld on some rod for
handles.

I assume that would be the approach, if you're welding the stands
themselves.

Are the Brownells wing nuts a cast item, or welded, or what? Is this
something they make themselves or have made or is a more widely used
component?

Glenn Ashmore wrote:
That is a good price of the rod but Enco doesn't sell acme wing nuts. You
would have to buy a regular acme hex nut and weld on some rod for handles.
Not exactly the strongest solution.

No, but look at the application. A 26' boat may weigh 5000 pounds, and
90% is carried by the keel on the ground. The other 500 pounds is
divided over the stands.

250 foot pounds of torque on a 1"-8 UNC thread will develop a thrust of
15000 pounds. I.e., enough to lift three of these bolts. Two pieces
of 1/4x1" flat bar welded to the sides of the nut to act as handles can
carry this much torque without the welds breaking. (Of course, a normal
human would have to put lengths of pipe over each handle to generate
this much torque...)

So while bar stock welded to a hex nut isn't the strongest solution,
it'll still be way, way stronger than needed.

I'll also suggest that there's no advantage to using acme thread in
this application. For a given size you get a coarser thread, which
means more movement per turn, but it's more costly and actually has
less strength since the threads are deeper.

Tim
(who's just designed a cradle for a 34' boat.)

wrote:

snip-de-dip)


I'll also suggest that there's no advantage to using acme thread in
this application. For a given size you get a coarser thread, which
means more movement per turn, but it's more costly and actually has
less strength since the threads are deeper.

Tim
(who's just designed a cradle for a 34' boat.)


But, but, but.....
In this application, the "bolt" is in compression, which puts the thread
in shear, which means that the broader thread base of the Acme is
WAAAAAYYYY stronger than a UNC thread.
Hence the fact that it is used in this application ;-)
Steve

Steve Baker wrote:
wrote:

snip-de-dip)


I'll also suggest that there's no advantage to using acme thread in
this application. For a given size you get a coarser thread, which
means more movement per turn, but it's more costly and actually has
less strength since the threads are deeper.

Tim
(who's just designed a cradle for a 34' boat.)


But, but, but.....
In this application, the "bolt" is in compression, which puts the thread
in shear, which means that the broader thread base of the Acme is
WAAAAAYYYY stronger than a UNC thread.
Hence the fact that it is used in this application ;-)
Steve

Hi Steve,

I'm going to argue the other way. The threads are in shear when the
"bolt" is in tension, as well. Just that the shear is going in the
other direction.

If you look at the cross section of a UNC thread you have a 60 degree
pyramid. The base of the pyramid for each adjacent thread comes pretty
close to meeting at the thread root. The root space is defined as 1/8
thread pitch wide, so 87.5% of the thread pitch is metal and bears this
shear load.

Acme threads are trapezoid sections with the base about 63% of the
thread pitch, so there's less area to bear the shear load. If they're
made from the same steel, the acme threaded rod will strip threads
under lower load than a UNC threaded rod.

The other problem in compression is buckling. For a given outside
diameter screw thread, the acme is cut deeper, so the acme screw acts
like a skinnier cylinder and buckles first.

Acme threads were designed for power transmission, e.g., vise screws,
screw jacks, machine tool feed screws, etc. Less of the torque you
apply is lost to friction so they're more efficient at transmitting
power.

I suspect they're used more frequently in boat stands because they're
off-the-shelf items over 1" in diameter while big UNC threaded rod is
harder to find. And since the space between threads is larger, they use
less steel, which make them cheaper in high volumes.

Tim

One thing to consider is that the standard Acme thread pattern is less
likely to freeze up than a standard NC thread after it has been in the
weather for a few months and rusted.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

wrote in message
oups.com...
Steve Baker wrote:
wrote:

snip-de-dip)


I'll also suggest that there's no advantage to using acme thread in
this application. For a given size you get a coarser thread, which
means more movement per turn, but it's more costly and actually has
less strength since the threads are deeper.

Tim
(who's just designed a cradle for a 34' boat.)


But, but, but.....
In this application, the "bolt" is in compression, which puts the thread
in shear, which means that the broader thread base of the Acme is
WAAAAAYYYY stronger than a UNC thread.
Hence the fact that it is used in this application ;-)
Steve

Hi Steve,

I'm going to argue the other way. The threads are in shear when the
"bolt" is in tension, as well. Just that the shear is going in the
other direction.

If you look at the cross section of a UNC thread you have a 60 degree
pyramid. The base of the pyramid for each adjacent thread comes pretty
close to meeting at the thread root. The root space is defined as 1/8
thread pitch wide, so 87.5% of the thread pitch is metal and bears this
shear load.

Acme threads are trapezoid sections with the base about 63% of the
thread pitch, so there's less area to bear the shear load. If they're
made from the same steel, the acme threaded rod will strip threads
under lower load than a UNC threaded rod.

The other problem in compression is buckling. For a given outside
diameter screw thread, the acme is cut deeper, so the acme screw acts
like a skinnier cylinder and buckles first.

Acme threads were designed for power transmission, e.g., vise screws,
screw jacks, machine tool feed screws, etc. Less of the torque you
apply is lost to friction so they're more efficient at transmitting
power.

I suspect they're used more frequently in boat stands because they're
off-the-shelf items over 1" in diameter while big UNC threaded rod is
harder to find. And since the space between threads is larger, they use
less steel, which make them cheaper in high volumes.

Tim

I'm going to argue the other way. The threads are in shear when the
"bolt" is in tension, as well. Just that the shear is going in the
other direction.

Why should thread shear strength matter? You just increase the number of
engaged threads to get the strength you need, for any thread type.

As regards buckling strength, you're correct that UNC beats Acme for a
given nominal size, but only slightly.

Stress area of a 1-1/4 Acme screw is 0.907 in^2.

Stress area of a 1-1/4-7 UNC bolt is 0.969 in^2.

(_Machinery's Handbook_, 26th.)