On 9/5/2011 10:12 PM, Grant Saviers wrote:
> 2.0 od into a 2.5 od with a nice slip fit means the 2.5 tube has 1/4
> wall thickness!
You would need slightly less than a 1/4" wall as that would give you
what is called an "interference fit" where the OD of the inner tube is
the same as the ID of the outer tube. For ease of fit and lack of
galling you would need at least 0.010 total or 0.005" clearance all the
way around and that might be a bit tight for a foot of overlap. Use lots
of noalox to prevent galling.
> If these are your parts (it seems unlikely), you need a
> .25 wall 2" od internal splice tube. 0.058 wall isn't anywhere near
> strong enough to splice 1/4" wall tube. If it really is 1/4" wall then
> buy a 2" fiberglass rod (McMaster) for internal reinforcement and sleeve
> the outside with 2.75" od by .120 wall. DX Eng can supply this tube.
> On-Line metals might have it.
>
> Regarding overlap, 4" would be about minimum each side, so you can bolt
> at 2" and 3" from the splice at 90 deg angles, with 1/4" SS bolts.
I think that 4" overlap with a 2.5" OD outer tube would be a bit on the
shy side. I use an absolute minimum of 4X the diameter of the larger
tube for a minimum overlap. I prefer at least 5 or 6X.
73
Roger (K8RI)
> Since the antenna has failed once, you might consider buying "yagi
> mech" stress analysis from DX Eng and checking all of the design for
> wind load and reinforce as needed. It is pretty easy to use and can do
> the calcs for sleeved sections, it assumes they are a snug slip fit as
> is the case with 0.058 and 0.120 wall thickness tube. FWIW 0.62" and
> 0.125" wall tubing usually won't telescope, unless the larger size has
> the 0.058 or 0.120 wall.
>
> Grant KZ1W
>
> On 9/5/2011 5:26 PM, Robert Chudek - K0RC wrote:
>> I am rebuilding an old Telrex 40m dipole that was damaged in a recent
>> windstorm. One side of the dipole buckled slightly from excess force. It
>> didn't break, rather it crumpled on the leeward side and the element was
>> about 20 degrees out of straight.
>>
>> Is there a formula for how far a smaller diameter tube (not pipe) should
>> be inserted into a larger tube and still retain the full strength of the
>> smaller tube?
>>
>> In my particular case, I have a 2.0" OD 6061-T6 tube, 0.058" wall
>> thickness that will slip into a 2.5" OD tube. The larger tube has the
>> proper wall thickness so the smaller tube is a "nice" slip fit.
>>
>> I am wondering if 4" is adequate, but that's just a SWAG.e
>>
>> 73 de Bob - KØRC in MN
>>
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