Nelson's tube expander

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jscarmozza
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Nelson's tube expander

Post by jscarmozza » Mon Sep 23, 2019 6:57 pm

I was curious to see if the copper fire tube expander that Nelson describes in his book would work. So I made one from an Allen head cap screw and some soft nylon rod that I had laying around, then reamed a 5/8" hole in a piece of steel, annealed a piece of of 1/2" L copper water pipe and expanded the copper tube into the steel ring. To my surprise it worked! The copper tube was tight in the steel ring and because the nylon was an 1/8" longer than the steel ring it expanded the copper O.D. from 0.625" to 0.635" for about a 1/16" on each side of the ring. My question is: has anyone used this method to successfully install copper fire tubes in a model boiler, and if so, did the boiler function properly and with longevity?
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hoppercar
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Re: Nelson's tube expander

Post by hoppercar » Tue Sep 24, 2019 9:02 am

i have used expanders like this, they work quite well...i assume you annealed the tubing before trying to expand it. ...i usually use, commercially made tube rollers, but there are numerous materials that can be used as tube expanders, as long as there elastic enough to expand, when pressure is applied to them

Pontiacguy1
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Re: Nelson's tube expander

Post by Pontiacguy1 » Tue Sep 24, 2019 9:55 am

I've used an expander similar to what you describe, tube rollers, and also made swages to seat up tubes several times. All three methods work well, and if it will pass the hydro test then it will stay that way for the life of the tube, unless you do something like dry-firing the boiler. In any case, I always anneal the outer inch or so of each end of the tubes before putting them in, which you have done. Best way to do it in my opinion is to roll the tubes in, but if I was only doing one or two boilers then I wouldn't fool with buying a roller and maybe having to modify it to get it to work right. If you are only doing one boiler, then making a swage or using the tube expander like you made will work perfectly fine and give good results.

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Fender
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Re: Nelson's tube expander

Post by Fender » Tue Sep 24, 2019 10:34 am

In some fireboxes where there isn’t much space around the tubes due to the side sheets or crown sheet being close to the tubes, this may be the only style expander that will fit. One caution is to avoid expanding the tube too “deeply” where there is no tube sheet behind it, or the tube will bulge, or even split.
Dan Watson

rrnut-2
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Re: Nelson's tube expander

Post by rrnut-2 » Tue Sep 24, 2019 12:10 pm

I used Nelson's expander on my wife's Shay many years ago. Still running.

Jim B

jscarmozza
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Re: Nelson's tube expander

Post by jscarmozza » Tue Sep 24, 2019 1:54 pm

I'm neither a good enough welder or silver solderer to attempt boiler construction, but I was intrigued by this gadget and would have bet my next paycheck that it wouldn't work...as I said, I was surprised when it did! Thank you all for your replies.
John

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Fender
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Re: Nelson's tube expander

Post by Fender » Wed Sep 25, 2019 12:58 pm

Another situation where this type expander can be used to advantage is in a short firebox, where there isn’t much room between the tube sheet and the rear of the firebox. A conventional tube roller uses a tapered mandrel that sticks out several inches before the tube is expanded. On a small firebox, there might not be enough space to get the roller and mandrel in, and still be able to drive the mandrel, especially if it uses a morse taper.
Dan Watson

jscarmozza
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Re: Nelson's tube expander

Post by jscarmozza » Wed Sep 25, 2019 7:59 pm

Jim B. has a boiler that was made using this technique, and I've learned that someone at NJLS also built a boiler using this method, I'm going to chase that lead and see what I can learn.

Fender is right about not over expanding the tubes, Nelson warns about over doing it in his book; I was able to expand the O.D. of the copper tubing 0.010" where the expander extended beyond the steel sleeve without much effort. Over expanding beyond the tube sheet may set the stage for a shear failure in the fire tube at its interface with the tube sheet. I guess the question is what constitutes over doing it?

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Greg_Lewis
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Re: Nelson's tube expander

Post by Greg_Lewis » Fri Sep 27, 2019 11:18 am

According to the Elliott Co., a manufacturer of professional tube rolling equipment, the ideal expansion for copper tube is approximately an 8 to 10% reduction in wall thickness. It's a simple exercise in addition and subtraction and some measurements with a telescoping gage to determine how far to go.

By the way, back in 2003 I wrote up John Bailie's shop-made tube roller for Live Steam. This is a more conventional roller rather than the expander discussed here, but if anyone wants more info on it, send me a PM and I'll get it to you. I made a roller to his design and it worked fine for me.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
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