Horn Rounding Tool

[davec2]

There have been several posts lately with some magnificent examples of the ever popular banded horns.  In one post, we had a discussion about measuring things that were not round with calipers or a pi tape and about the difficulty of fitting bands.  This is a horn rounding tool I made up for two reasons.  First, I often find myself fitting a base plug in a horn that is not quite round but is not far enough out of round to warrent boiling, heating, etc.  I can use this tool to adjust the roundness of the end of the horn to fit and install the base plug.  Second, when fitting bands, it is usually not possible to round out the area where the band is to be applied by any of the usual methods.  Being able to make a part of the horn in the middle round is handy for measuring the diameter and for installing a turned band.  The tool can be used on any part of the horn.  It is machined out of aluminum and fitted with 12  1/4-20 thumbscrews.

The tool can be used on a cold horn or a softened / heated one.  As usual though, the tool must be used cautiously as it has all the power it needs to completely crush or crack a good horn.

[G. Elsenbeck]

I have to give you an 'A' for ingenuinity, but isn't a reason for heating the horn in the first place is so when a sizer is inserted into the horn it 'loses it's memory' after cooling? 
Although, like you said, if the horn isn't that too badly out of round then the memory may not that big a big deal.  However, after saying that and if you permit me to play devils advocate, won't the 'inside diameter' of the horn potentially  be a problem?  Aren't you going to want the horn wall thickness the same all around the horn or you won't end up with a perfect round on the inside?  This is where the base plug meets the horn and this is what ultimately needs to be 'rounded' in order to get a good fit and seal.
I would love to see this 'jig' work for all the horners of us, but I'm having a problem with all those thumbscrews.  I'm assuming once they are calibrated to give you a perfect circle, then leave the jig alone?  If the horns you have is too small for this jig then you need to recalibrate or make another, smaller jig?
Dave, I'm not trying to be a pain in the you know what, but as with things that are something new and 'unconventional'  full appreciation of the concept and understanding takes a bit.

Gary

[davec2]

Gary,

First of all, your questions are well founded, so please don't worry about being a pain.  I usually scrape the horn to an even wall thickness so, when I use the tool to force it round, it is round inside and out.  Also, I don't set the tool to make the horn perfectly round.  I just adjust the thumb screws while measuring with a micrometer until the horn is close enough to "round" to fit or install a base plug.  I do the same thing if I am working in the middle of a horn to measure for and fit a band.

Don't get me wrong here, I still boil / oil heat horns and use a sizer to make them round also, but, for me, this tool comes in handy for certain situations where I need to adjust the shape cold.

I made this thing one day when I had a horn that just would not stay very round.  I had a devil of a time trying to get the base plug in because it kept wanting to jump out of the end of the horn.  I made this tool, ran the thumb screws down on the high spots, forced the horn to a better round and easily installed the plug.  If I wasn't such a poor horner to start with, perhaps I would not have needed the additional help.  However, I almost never miss a chance to "over engineer" a problem.

dave C

[msw]

neat tool!  i've only made a few horns, and of those only one was way out0 of- round.  i tried boiling it, but that didn't work and i ended up just tinkering with the plug until it fit... a big pain in the neck..

i use water to boil the horn, but i've heard that boiling it in oil works better. 

any thoughts on this?

thanks!

[Ky-Flinter]

..... but i've heard that boiling it in oil works better. 

Hi ya msw. Welcome to ALR.

You heard right.  Water boils at 212 degrees, that's as hot as it gets.  With cooking oil you can get much hotter.  But be careful.  I "boil" my horn outside on a Coleman stove and use a candy thermometer to monitor the temp, around 350, works for me.  Don't leave the horn in very long, 15-20 seconds, or you'll cook the horn.  Not good.  I also wear heavy welding gloves.  Did I say be careful?

-Ron