Notched Tubeholes

[chiptim]

I guess this question is aimed mainly at those of you with experience in copper boilermaking.

I'm currently reading Alec Farmers' book on boilermaking and in it he describes a method for ensuring good solder penetration on the smokebox tubeplate. The risk is that if the tubehole is too small, you won't get good penetration and may be unaware of this fact as once soldered in position as you can't then inspect the inside. The method described is to notch the hole with a triangular file down to the edge of the countersink or about 3/64". Two notches for a 1/2" hole, 3 for the superheater tubeholes.
I'm trying to gauge whether this is a technique worth employing and would be interested to hear if anybody has:

A)Successfully used this method?
B)Encountered problems trying this method?
C)Doesn't bother, instead ensuring the tubes are a good "drop-fit" in the tubeholes.

Regards Tim

[weldsol]

Hi Tim Iv'e done the notched tube using a triangle file and got a good fillet on both sides of the tube, although I didn't measure the notches just did them until they looked right.
Iv'e also done the drop in fit with a register pushed out on the tube using a small bar with a ball bearing, again this seemed to work ok.
I think either method worked but the notched tube was more predictable

Paul

[baggo]

Hi Tim,

this method is often quoted by the likes of Martin Evans, LBSC etc. I think it stems from the 'old' days when it was practice to make the tubes a tight fit in the holes. The nicks at least guaranteed that the solder went through to the other side and formed a fillet on both sides. There was no guarantee however that the solder would actually penetrate the joint and you could be left with a weak joint. Personally, I don't bother with the nicks and just make the tubes a 'loose' fit in the holes. So long as there is a small gap around the tube, the solder will flow through fine. At least you know then that the solder has actually flowed through the joint. Having said that, it won't do any harm to file the shallow nicks as well.

John

[maninshed]

Hi Tim.
When I built my boiler (holmside) I read as much as I could lay my sticky fingers on, including Alec Farmers brilliant book. In the end I made sure the holes in the tube plates were roughed up with a course file (not a smooth drilled or reamed hole) so the holes were afew thou over size. Some people recomend turning down the end of the tubes a little where they push through the tube plate to stop them dropping through while soldering, I wouldn't bother with that either. The key thing is to have some clearance so the solder can get through the whole circumferance of the joint. If I remember right Alec Farmer uses a jig to hold the tube plate horizontal, the tubes are then dropped through and squared up vertically to the tube plate, I had no problem using this method. The key things with silver soldering are clean joints, fluxing and enough heat.

[brozier]

Hi Tim,

I followed the Johnson-Mathey requirements for the Silver Solder I used for the tube joints (Silver-Flo 55) - JM recommend and I quote "The optimum joint gap for this filler metal at brazing temperature is normally 0.05-0.15mm."

This is quite loose fit I adjusted the drilled holes with a rat tail file which leaves a suitably rough finish.

You can see some pictures of my boiler making here

homepage.ntlworld.com/bryan.rozier/Spencer/boiler_making/Boiler_Making2.html#Drilling

There are some hints on Silver soldering here homepage.ntlworld.com/bryan.rozier//silver_soldering/Silver_Soldering.html

Shockingly this passed it's hydraulic test with no probs despite no Cadmium being used in the majority of the joints ;D

I'd suggest doing some test pieces like this

and



So you are confident of the penetration....

Cheers
Bryan

[havoc]

I have seen a boiler scrapped because they could not get the tubeplate tight because those notches continued to leak. Maybe the builder filed a bit too deep but I would not the risk at all.

[GWRdriver]

My first question is how, if the flues aren't a nice snug fit in the firebox tube plate, do you get the flues square to this plate, or square to their holes? Surely you don't just get them pointed in the general direction and then bend them to into place?? My preference is to make the flues snug and notch. I also take care to go easy with the file, this is not a situation where if some is good then more is better. I use a 3/16" diameter (approx) "rat-tailed" file rather than a triangular one and I go around and file little scoops, segments of a circle, here and there maybe 5 or 6 thou' deep and I've never had a flue leak. I also rock the file as it crosses an edge in order to break or chamfer the edges of the scoops so they flare a bit at the ends. I spend quite a bit of time in the assembly and prep stage to make sure the solder has a channel to follow anywhere it needs to go, because I hate re-heating!

[havoc]

Tubes are rarely square to the plates. Often they have a designed rise towards the smokebox.

[baggo]

Mar 25, 2009 2:08:30 GMT GWRdriver said:

My first question is how, if the flues aren't a nice snug fit in the firebox tube plate, do you get the flues square to this plate, or square to their holes? Surely you don't just get them pointed in the general direction and then bend them to into place??

I make a simple jig using a bit of angle clamped to the firebox and the smokebox tubeplate to hold the tubes in the correct alignment. The firebox ends of the tubes are turned down a few thou to stop them falling through the tubeplate.



John

[chiptim]

Many thanks for all your replies and photos. I think what has emerged is that the correct joint design is key. However bearing in mind the method used to create the joint i.e. drill hole then open it out with a round file, the clearance may be hard to determine making the notches a sensible addition (just in case you've underestimated the clearance) provided that the notches are correctly formed! The Alec Farmer book shows quite a large triangular file being used. I think I'll use a much finer file bearing in mind we only need a few thou for the solder to flow through.
Regards Tim.