[TowerTalk] Imperial vs. metric tube size

[john at kk9a.com]

One nice thing about Imperial tubing is that it fits together nicely with
.009 (0,23mm) clearance and you can use a hose clamp to fasten the sections
together.  I suspect that you need a different method for fastening metric
tubing.  I do not believe that the tubing diameter is that critical, if you
wish to check there is a W6QHS element spreadsheet on the internet that can
calculate the resonant frequency of an element.

GL,
John KK9A

To:	towertalk at contesting.com
Subject:	[TowerTalk] Imperial vs. metric tube size
From:	HA3LN <list at ha3ln.hu>
Date:	Wed, 17 Sep 2014 00:30:56 +0200
Hi,

I'm wondering if I find a Yagi taper schedule (imperial) like this for 6el
20m
how I should "translate" them into European tube diameters?

...for example:
        1       0.875   0.75    0.625   0.5
0.00    48      24      44      36      65.73
90.00   48      24      44      36      58.70

1 inch (25.4mm) is easy, we have D25mm tube.
0.875 inch (22.225mm) is still OK, we have D22mm

But, what I should use in case of
0.75 inch (19.05mm), we have 18mm or 20mm diameter.
0.625 inch (15.875mm), we have 15mm and 16mm (I think this should go for
16mm).
1.25 inch (31.75mm), we have 30mm and 32mm. Should it be 32mm?

In general:
How critical the tube diameters are when I match them from the imperial
model to the metric? Can I maintain the same modeled performance if I have
~5% difference between metric and
imperial modeled diameters?
Is there any % tolerance?

I know re-modeling would be the best but I'm not an expert in that which I
could rely on...


Thanks a lot for your help in advance.


73!
Csaba  HA3LN