Stove chimney measuring

[Rory_d]

Hi guys, 

 

I need to replace the flue pipe on my boatman stove. The boat was refitted out totally and the stove was moved. The angles are therefore incorrect to the new installation, plus the flue is old so needs redoing in time for my bss. I have got the new flue pipe ready but haven't got much hair left to pull out! 

 

Has anybody got any clever ideas how to measure the angles so I can cut and weld the new tube up. It needs 2 angles one bottom and one top. The stove and the collar are offset. 

 

Any ideas greatly welcomed! 

 

Here's a pic of the current one

[Richard10002]

Cant see too well, but is there a chance that it could go straight up, rather than needing the bend/s ..... maybe with a small move of the fire on the hearth?

[Rory_d]

It's got quite a big offset , if it goes straight the fire will almost be off the hearth. It definately needs a couple of angles putting in.

 

The picture is taken dead straight so you should hopefully be able to see the angle is miles off on the top and also the bottom.

[ditchcrawler]

I used 3 lengths of wood and made a template  stuck one bit in the top of the stove, one bit in the roof and then connected the two with a third length.

[Rory_d]

Just now, ditchcrawler said:

I used 3 lengths of wood and made a template  stuck one bit in the top of the stove, one bit in the roof and then connected the two with a third length.

That's what I was thinking of doing but wanted various opinions first 

[BEngo]

Ah, the compound flue angle problem.

 

I have done this twice: for my Squirrel  in the Saloon and for my Boatman in the back cabin. It was years ago, so I am a bit rusty, ( like the back flue).   It is easier to do than to describe, but here goes.

 

It depends on being able to find a vertical plane that passes through both the centre of the stove collar and the centre of the roof collar.  To do that, use a vertical board wedged between the floor and the roof, and sight across  it, moving the board around as required until you have found a spot where it lines up with both centres.

Measure the offsets from the board edge to where the flue will go.  Adjust the heights of the vertical flue sections at top and bottom so that the slanting section is parallel to the side, for appearance and neatness.

 

Once you have the offsets  use them to draw the whole thing full size.  If you can run to it  a large piece of thin ply is ideal, but you can get away with a big bench top and chalk or even some lining wallpaper, gluing two strips together if it is not wide enough.  Having drawn it,   either measure the angles and use a band saw to chop your tube to the right angles àor, on the drawing,  join the apexes  of each angle  together with a long line.

Lay  a plenty long enough piece of flue tube on the drawing to match the central section.  Use the long line to guide a big angle grinder and cut the pipe in one hit, keeping the disc vertical. Roll one section of pipe through 180 deg and tack.  Repeat at the other vertex.  Try the pipe  for fit and adjust the angles  if needed. Mark and  trim the vertical bits to length.  Weld up. 

 

 If your existing flue is OK for shape forget offsets, just take it out and draw round it, then proceed as above.

 

Buy your flue tube as rolled circular section from a steel stockist.  It is cheaper to buy 3×2m lengths this way than to buy 1 piece off a Chandler.  Steel stockists also do thicker walled tube which lasts longer than the chandlery stuff.

 

If you use a piece of ply to draw on  you could cut the pipe shape out of the ply, and use that as a check that you have the shape right.  It does make it a bit more difficult to do the actual cutting.

 

Once you have sorted it make a  dimensioned sketch of the pipe drawing  so you can easily  re-create the full size drawing.  Keep it safe.  It saves a lot of buggering about when you need a new flue tube.  I am on  my 4th Squirrel tube now and it took about two hours using my bandsaw to fabricate it at home and then minutes to fit it when we got it to Jarrah.

 

Another way is to cut 3 strips of say 6mm ply which are as wide as the outside diameter of the flue pipe and use these, clamped together at each angle,  to make up a pipe template then cut the pipe out as above.  If doing this you will need another pair of hands and several small G clamps.

 

N

 

 

[Tracy D'arth]

5 minutes ago, BEngo said:

The other way is to cut 3 strips of say 6mm ply which are as wide as the outside diameter of the flue pipe and use these, clamped together at each angle,  to make up a pipe template then cut the pipe out as above.  If doing this you will need another pair of hands and several small G clamps.

 

N

 

 

This is the way I do them. You only cut the pipe once at half the offset angle and turn one part 180 degrees.  I bolt the pieces of wood together so that they pivot, then you can get the angles right and tighten the bolts to lock it all together. 

Then you can fit it in the boat to see if its right.

Tack the pipe together and try it in the boat before welding it all round.

Keep all the pipe away from the boat linings so that the wood doesn't get too hot.

[Slow and Steady]

You just need to know the horizontal offset between the stove and roof hole, then ask you fabricator to make it. They'll know both angle joints have to be the same to keep the bottom and top sections vertical. The sharper the bends, the shorter the middle section will be. If you say plump for 30 degs, that will dictate the length of the middle section. How high up you want that shuffle is up to you. 

[Tacet]

I might drop two strings - one from the soffit to the centre of the flue collar on the stove and the second through the centre of the roof collar.  Some circular pieces of ply will help keep the strings centred.  Measure between the strings on the perpendicular and you have the offset.  Measure the height too. Then draw on CAD until it looks right.  Cut and weld to the CAD dimensions

 

It will be a lot easier if the bottom and top sections are to be parallel.  And also easier if you are happy for the flue to be offset in one plane only - more complicated if you want a swoopy compound flue.

 

If you want to mock-up before committing to steel, then maybe a length of upvc soil pipe would work?

 

 

[Rory_d]

Thankyou to everybody for your responses! Got it all sussed now!