Good Morning All,
Doug, once again you are not examining the total joint situation. We
will get to that in a moment as there are other variables to consider.
You continue to make statements that may or may not be true, accurate
or repeatable. In reality, they represent your personal opinions, and
as I noted before, you are certainly free to do as you please. QSL?
Yet my PhD professor always cautioned, "beware the sample size of one!"
which I have always considered to be wise advice to follow.
Next, let's address how you conducted yourself with me. Where is there
any mandate that someone MUST reply to you within a specific time frame?
And look at the tone of your private email to me? What if I am traveling
or away, or gasp, have a life where forum email is not checked daily?
"Still waiting for your reply. You do have some answers don't you?"
The specific adjectives I used in my reply were ... rude and arrogant.
>From your past behavior, such as the "free climbing" discussion on this
same forum, you take the position you are 100% correct, and so therefore
everyone else is wrong. A review of the archives seems to confirm this.
Sorry my friend but your cyber-bullying is a waste of time on me. SK.
Now, let's move the focus back to the technical topic at hand ... and
from reading your other email on this, you don't seem to understand
how the typical worm-gear clamp actually works. This may help others
to understand how you reached your conclusions, which are incorrect.
A clamp is a form of a lever really, and there is a direct relationship
between the torque measured at the screw hex head and the band tension.
Torque is the measured friction between the screw threads and the band.
I can raise or lower that value by changing several of the parameters.
More friction between those two components, higher torque values.
Less friction between those two components, lower torque values.
We can also make the screw longer, or shorter with similar effect. And
we can mix the grade of materials of the components if/as needed.
Example, a 410 SS screw with a 201 SS band will have different torque
measurements that say a 305 SS screw used with a 301 SS band.
Or use a non-SS screw or housing, or a different housing design, or?
There are many many other variables that may impact performance.
We can by design change the plating, or add a chemical to the screw
surface. Any/all of this may impact the measured torque values.
This is also why manufacturers DO NOT advise adding anything such as
an extra lubricant. It will impact the torque measurements.
Don't believe me? Fine ... then consider this specific statement from
the NAS-1925 Rev 2, March 30, 2012 industry standard spec which reads:
(NAS = National Aerospace Standard)
"4.0 QUALITY ASSURANCE PROVISIONS
...
4.1.2 Test Condition. The adjusting screw shall not be worked,
manipulated or lubricated to increase the freedom of movement
prior to conducting tests, unless otherwise specified herein."
Now let's consider this statement:
"Take a look at a gear clamp. One band slides over the other
as the clamp is tightened or loosened. There is obviously friction
between the bands and as the clamp is tightened the friction increases."
Bands? There is only ONE band. B-)
I would suggest you take a closer look at a worm gear clamp. Other
than some exceptions, such as the LINED clamp or similar, and for
the typical clamp sourced from The Home Depot or an auto parts jobber
you will notice one end of the band goes into the housing, where it
engages with the screw and the install diameter can be adjusted,
along with the torque. The other band end is secured UNDER the housing,
so there is no obvious friction, as the band is not touching itself.
Then you stated:
"Many have tightened these clamps to the point where the slots become
distorted and the clamp strips. Now lubricate the clamp to reduce the
friction where the bands slide over each other. Voila, the clamp can
now be tightened further without self destructing especially on smaller
diameter tubing. Try it."
Again, there are no "bands", nor any major friction with THE band, and
again, you are simply trying to "lube around" the design limits.
Now let's look at another design variable, and one that I will point
out the clamp manufacturer has NO control over. And that would be the
joint itself and why I even attempted to help others on this topic.
If the smaller tubing still has movement inside the larger tubing, we
need to look at several factors.
1. Is the clamp tight enough? See the previous comments on torque, but
there is reason to not assume that a high torque value is a guarantee
that things are correct. So let's go a bit deeper on this.
2. Has the clamp 'bottomed out'? In other words are you at the stated
min diameter? When you reach the end of the notches on the band, guess
what happens? The torque goes HIGH, it has to as there is no movement.
3. Let's look at how the joint functions, and this can quickly become
more than a simple exercise. Narrow the scope down to yagi elements,
which we typically will cut "slots" in the tubing. This allows us to
compress the larger tube to hopefully provide us with a secure joint.
Sometimes we slot only one side, sometimes we slot both sides. Why does
that matter?
The worm gear clamp can only compress or reduce the diameter of the
larger tubing to the limits of the total open area of the "slots".
We can confirm this visually by simply looking at the slots. Are they
closed up, no visual gap? If so, adding more torque may not help!
The length of the slot(s) is also a factor. Not really simple is it?
Consider that tubing wall thickness varies, and worm gear clamps have
no magic properties to cover too wide a difference in tubing sizes.
So yes, we can have a clamp at the proper torque spec, and the smaller
tubing will still 'spin'.
The proper solution here is not to add a lubricant (see above), rather
consider making the slots wider, or using slots on both sides of the
larger tubing, or ???. Again, it can get rather complex very quickly.
4. This point may help to also explain the what many have commented
on as to the outer element tips and the clamps not securing the joint.
There are many valid reasons, so let's take a look at one more next.
For very small diameters, the clamp housing's dimension can begin to
represent a large portion of the overall circumference.
The clamp housing has a fixed radius. It cannot bend itself to 'fit'
around the tubing dimension.
Now the side profile of the clamp no longer represents a circle, like
the letter "o" ... instead, due to the housing, looks more like a "D".
That may or may not impact the joint performance. My point here is to
simply show perhaps, just perhaps, there is more going on that we might
think as to why does a worm gear clamp work, or not work at times?
As to personal application? For very small "tips" or similar, I tend
to use 2x Type M all SS ("micro") clamps which are spaced out across
long slots AND ensure the larger tubing slots are NOT being completely
compressed when the "micro" clamps are tightened.
For larger diameter tubing, I will use an all SS 5/8" HD bandwidth
clamp (ultimate torque is 150 inch-lbs!) again observing if the slots
have compressed, or use rivets or other hardware like 8-32, etc.
I hope someone will find practical use of these postings, that remains
my intention as to correcting some "ham lore" that was a bit incorrect.
73 and have a great week working on your towers and antennas!
Billy, AA4NU
----- Original Message -----
From: "Doug Renwick" <ve5ra@sasktel.net>
My problem with the torque method is so you torque the clamp to specs and
yet you can still turn the smaller element inside the larger. So torquing
in this application in meaningless. You tighten the clamp until the smaller
tubing does not turn, let it cycle overnight, check and retighten if
necessary. My elements don't fall apart and my temperature swings are from
minus 40C to plus 35C. Real world or simple method.
BTW this is what I e-mailed to Billy:
Still waiting for your reply. You do have some answers don't you?
After not receiving a response to any of my questions, I managed to inspire
Billy to try and answer one, however with a condescending tone.
Doug
I wasn't born in Saskatchewan, but I got here as soon as I could.
-----Original Message-----
Good Morning All,
And despite a rather rude comment from Doug sent to directly to
my email, here is a bit more information to HELP others perhaps.
Again, we are using clamp products in applications that may not
represent their common usage. So your mileage may vary, WFWL.
Our website shows only the more popular common designs, not the
special designs where the focus is on specific connection needs.
Doug's "simple" install method does not take into consideration
factors such as connection vibration nor repeated thermal cycling.
Let's say for example, you must hire a crane to lift and install
your new yagi. Once up there, you cannot reach the elements. If
something 'comes loose', it will be additional time and expense.
Now we have to make a critical decision:
A. Use the "simple" method outlined below that does not follow the
manufacturers instructions. It might work well, or it might not.
B. Use the method and torque settings from the manufacturer and
know you have followed the suggested install specifications.
Would that be over engineering, or simply using common sense given
risk of failure and related costs to repair the loose element(s)?
73 de Billy, AA4NU
----- Original Message -----
From: "Doug Renwick" <ve5ra@sasktel.net>
No one is pointing fingers. I don't know where you got that idea.
Just what were the original design requirements for this gear clamp?
And just what are the performance limitations for my real world method?
Doug
I wasn't born in Saskatchewan, but I got here as soon as I could.
-----Original Message-----
Good Morning Doug,
Not at all my friend. "WE" are using products for applications
that were not part of the original design requirements here.
Your 'real world' method has some performance limitations, but
then again you may do as you please, that's fine for you.
Just please don't go pointing fingers at manufacturers as to
poor products or weak design when used or installed improperly.
Have a great week there!
73 de Billy, AA4NU
----- Original Message -----
From: "Doug Renwick" <ve5ra@sasktel.net>
To: "Billy Cox" <aa4nu@comcast.net>, "George Dubovsky" <n4ua.va@gmail.com>
Here we go again; over engineering something so simple. Torque
specifications for a gear clamp used to secure one piece of tubing inside
another - really?
Here is how to do it in the real world.
Tighten the gear clamp only enough until the smaller tubing cannot be turned
inside the larger tubing. Lubricate the clamp so that the band will slide
and not strip or distort the slots in the band. Come back the next day and
test the joint. If you can twist the smaller tubing then tighten the clamp
more or restart with less joint compound. On small diameter tubing,
pre-form the clamp. Simple - right.
Doug
I wasn't born in Saskatchewan, but I got here as soon as I could.
-----Original Message-----
Well done Geo ... per an often shared motto on this forum,
simply do what the manufacturer states to do ... B-)
The smaller standard 5/16" bandwidth clamps (also known as
"micros" or SAE J1508 Type M) have low install torque values.
The common 1/2" and 9/16" bandwidths typically will have
install torque values which are much higher.
Some use a nut with nylock (t-bolts) or Belleville washers
(CT clamps) as ways to maintain constant tension.
Other clamp designs may have even higher values, but are not
always offered in the diameters we use for yagi elements.
LINED design clamps are mainly for very soft tubing or hose
material such as silicon, not much advantage otherwise.
I would suggest using an all stainless clamp, something in
the all 300 SS materials class should work well.
If you are in a more corrosive setting, say near salt water,
then the all 316 SS materials may provide better life.
Several years ago we added the install torque ratings to
help users properly tighten the various clamps designs:
http://idealtridon.com/aftermarket/
Perhaps a bit of general wide-stroke background might be
useful here? Three torque values you might consider are:
Free torque ... this is simply stated as the minimum amount
of effort to turn the screw. Typically a very low value.
Install torque ... this value is normally stated to be at
50 to 70% of the ultimate torque value.
Ultimate torque ... consider this as a "never exceed" type
of value. Go much past this, you are likely on your own.
Also these values, as noted are inch-lbs, NOT foot-lbs!
Additional lubrication is typically NOT suggested, as that
may distort the actual torque value being measured.
Size the clamp properly (band end should just be under the
screw cone area when tight) to help reduce snagging things.
One other suggestion, used by several OEMs is to slow down
the RPM rate as you approach getting the clamp "tight".
Hope this helps, and have a great week!
73 de Billy, AA4NU
(... also a Product Manager for Ideal-Tridon)
----- Original Message -----
From: "George Dubovsky" <n4ua.va@gmail.com>
I, too, have stripped hose clamps during installation, but it was my own
fault. Who knew the darn things had torque specs from the manufacturer...
;-) Now I use a torque wrench (a small one, calibrated in inch-pounds as
well as some weird Klingon standard - Newton something or the other), and I
tighten the large ones to 35-40 in-lbs and the skinny ones to 15 in-lbs,
and they don't strip.
Then I add the rivet!
73,
geo - n4ua
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