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Help with forming holes in flue sheet

steamandsteel

Aluminum
Joined
Oct 21, 2017
Location
Wichita, KS
Hello,

I'm trying to figure out the best way to go about forming holes in a pair of flue sheets, for a small scale boiler.

I've got a CNC Plasma that can cut out the round pieces from plates, and the related mills, drills, and lathes for finishing work.

My question is - what would be the best way to form the holes in the sheets themselves? I've attached a few pictures for reference.



Thought #1 - The plasma can cut holes that are very square. However, they would still need to be cleaned up, and be approximately 1/64th oversize to allow the tubes to be expanded and rolled into place. A carbide burr could remove the hard layer from the plasma, but I would still need to ream/drill/bore out each hole to get an accurate and round hole.


Thought #2 - Cut out a stencil to lay on top of the two blank circles, which would let me center punch and drill to size. The only downside here is the amount of material that will have to removed for each hole, and the time it would take to do all of them.



I'm very curious to see what you all think.
 
I'd mark out and drill, ream etc etc, as they always were?? .......... .yes it's a lot of work, but tube sheets always were, and IME any shortcuts ''almost always'' lead to disappointment and possible failure of inspection and pressure testing.

All that HAZ? around all those holes? in boiler plate? ............cost you a fortune in tooling :eek:

It's really one of those jobs you need to do right first time, and not concern yourself too much with how long it takes etc etc

IIRC Youtube has several vids of big tube sheets being CNC drilled etc etc, an ideal job for CNC but if you haven't got that - dig out your mag glass and sharpen your centre punch and drills.
 
Small scale boiler.... What is the working pressure and function of it? If it's for heating liquid water and not producing steam and is operating under 100 psi with a temperature/pressure valve on it. I would plasma cut the flue tube holes oversize and weld it on the wet side (inside).

If it's for a micro steam plant you are asking for trouble. Think bomb.
 
I would print/draw the holdes/centers on a sheet of copy paper. Punch mark the holes through the paper on one part, then stack the two parts and drill through both at the same time.

Oh, and have a this-side-up mark so the holes would be exact one to the other.

an accurate and round hole.. needed then pre drill with a smaller drill and drill with the finish drill to be 2 or 3 tenths larger than the finish drill micrometer check.

Having a programable machine likely use a 1" end mill it likely a little slower that a deill but would give nice holes...

could put a bolt through the twe after first two holes to keep them the same..with no chattering.
 
I am an novice when it comes to machining, but I have put large number of holes in I-beam flanges.For that I used a mag drill and a Hougan? Rota-broacg. The holes are pretty accurate and since they work like a hole saw you are removing less material.

Maybe this is not the right application for what you need, but they much much better than a drill.
 
Set the square array up in your DRO (unless your mill is CNC too) and drill it. You can cut the holes with a center-cutting endmill (preferably after drilling to, say, 1/2"), and get very accurate sizing. The 8 remaining holes can be set up in another square array, skipping the unneeded positions.
 
Thanks for the great replies, everyone.

The tubes will not be welded. I plan to roll them into the sheets.

I'm thinking I'll cut out my two discs, weld them together with a few tacks on the edges to stop chatter, and then center punch my pattern.

Roto-Broach / annular cutters are a good idea.. also like the "this side up" idea for alignment. Fantastic. Thank you
 
Nothing about your response pertains to the OP's question. Really, when you're clueless about the subject, you don't need to reply.
:rolleyes5:


Small scale boiler.... What is the working pressure and function of it? If it's for heating liquid water and not producing steam and is operating under 100 psi with a temperature/pressure valve on it. I would plasma cut the flue tube holes oversize and weld it on the wet side (inside).

If it's for a micro steam plant you are asking for trouble. Think bomb.
 
I think you re using too many tubes ....larger tubes ,fewer ,simplify .And yes ,I ve made a few little boilers ( legal limit here is 14"dia ).....If the firebox heating surface is 85% of the heating system ,a lot of tubes dont make much difference to efficiency ......and Ive not bothered with tube expanding ......what I use is some 3" (actually 2 7/8") stay tube ,which is heavy wall ,close fit in the tube sheets ,and a weld all round the fire side .....Its quite likely you will end up with seal weld all round the rolled tubes anyway ,to stop leaks......The point of the staytube is that its similar wall to the shell ,so should last as long.....And ,just for good measure for the purists .....the shells come from salvaged air compressor tanks,older ones are made of proper boiler grade plate ,and have at least one inspection door.........And..I aint been kilt yet!
 
I have made quite a few 6" to 14" diameter boilers for live steam locomotives. Always have just rolled the tubes in, always use copper type K pipe. Usually just drill the holes with a annular cutter and insert the tubes, if too tight then just run a reamer through.
 
It depends, are you going to weld the flue,s or roll them? If you are going to weld who cares, if going to roll, better machine a good hole...Phil
 
When I finished the front tube sheet for my steam roller I hole sawed fifty holes one at a time. After I hole sawed each hole without moving the tube sheet I finished each hole by boring out with a single point tool in a adjustable boring head. I did this all on a Bridgeport milling machine.
The boiler shop installed the tube sheet and rolled and beaded the tubes. The shop said the holes were all on size and rolled perfectly. The tube sheet is .500" thick. WP 150 PSI
 
You not only expand the tubes ,but bead them over too_Otherwise they will not only leak ,but also the exposed edge will get burnt off very quickly.Without beading ,tubes dont have much holding ability ,and will work in the tube plates and come loose quite quickly.Consequently welding is a much quicker way of building a boiler,if you use steel tubes ......obviously if you use copper tubes ,welding is out. .There are all sorts of "bodges" to stop tube ends leaking ,such as driving expanding thimbles into them ,or even the old method of using wooden plugs.
 
Nothing about your response pertains to the OP's question. Really, when you're clueless about the subject, you don't need to reply.
:rolleyes5:

Actually his questions pertain more then most of the other answers. If this boiler will be used at at a live steam club or in public it probably needs to be inspected and insured. Part of that inspection may involve some basic plans showing the internal construction. I am sure there are standards for tube fit before swaging or welding that must be met. Does the welder have to be certified, and by who etc. I do not think a torch cut hole with no cleanup would be appropriate here.
Many hundreds of people have been killed by boiler explosions.
Bill D.
 
John K, great input.

I forgot to mention that they will be beaded as well. My plan is to use K Copper, but I've had trouble sourcing it. Who carries that wall thickness?
Interesting thoughts on the amount of tubes. On that center "stay tube", I'd venture a guess that it's the same steel as the shell? I'm shying away from using any steel tubes, as I know that proper boiler tubes are ultra-low carbon tubing, and I think only one outfit out of Germany makes that stuff. Something to do with the constant heating and cooling that would crack tubes with a higher carbon content (ie Steel pipe)

I've got a tapered tube roller/expander coming in the mail. The type with three rollers on a tapered mandrel. I figure I can make a beading tool to fit on my pneumatic scaler/hammer for beading the top lips.

This boiler is just for fun, not going to be fired at any shows, maybe just to run a small engine or two.

Bill D, great input. To all concerned, my plan is to drill and ream these sheets. I've got some 5/8" plate laying around, good & clean without rust. Would this be too thick to where the water inside could not cool the plates effectively? I'm familiar with why boilers are stayed in certain areas..

John, Shay, Phil, others:
The next issue I'm facing is fresh water supply to the boiler. I'm familiar with injectors, but have only ever worked with large (think 3.5") units. A quick browse on ebay shows smaller Penberthy units to be quite spendy for small scale steam. Is this something that can be made in a well-outfitted shop? Otherwise, how have you run water into a pressurized boiler? I've seen some manual and mechanical water pumps with a couple check valves on smaller hobby sized units.

Thank you everyone for the great replies so far. This has me "fired up"
 
I forgot to mention that they will be beaded as well. My plan is to use K Copper, but I've had trouble sourcing it. Who carries that wall thickness?

McMaster has copper in the right wall thickness, or used to.

Interesting thoughts on the amount of tubes. On that center "stay tube", I'd venture a guess that it's the same steel as the shell? I'm shying away from using any steel tubes, as I know that proper boiler tubes are ultra-low carbon tubing, and I think only one outfit out of Germany makes that stuff. Something to do with the constant heating and cooling that would crack tubes with a higher carbon content (ie Steel pipe)

Just weld in some proper stays. I'm assuming that this is a vertical boiler and intended to provide wet steam, if you want/need a superheater you might add another firetube or 2 of a bigger diameter.

I've got a tapered tube roller/expander coming in the mail. The type with three rollers on a tapered mandrel. I figure I can make a beading tool to fit on my pneumatic scaler/hammer for beading the top lips.

I'm not completely convinced of any advantage of beading. If you expand the tube the copper will have a little lip on the tubesheet - not anything you can feel but enough to retain it.


The next issue I'm facing is fresh water supply to the boiler. I'm familiar with injectors, but have only ever worked with large (think 3.5") units. A quick browse on ebay shows smaller Penberthy units to be quite spendy for small scale steam. Is this something that can be made in a well-outfitted shop? Otherwise, how have you run water into a pressurized boiler? I've seen some manual and mechanical water pumps with a couple check valves on smaller hobby sized units.

Thank you everyone for the great replies so far. This has me "fired up"

Small scale injectors are available. Take a look over at discoverlivesteam.com or search on ebay.com. The expensive ones are the ones made to scale but you can find $100 models that'll have the input that you want (something around a pint/minute at 60 psi steam). Here's a supplier selling what I think are English made injectors:

LIVE STEAM BOILER FEED INJECTORS
 
Small injectors are troublesome at best .....I use the brass pumps that come with the bucket type plumbers pressure leak testers.....generally antique ,never paid more than $4 for one ,and the pumps are always solid brass with a packing gland on the plunger ......driven from an eccentric on the engine ,and also easily set up for manual operation as well .....I was a bit lucky in getting a lifetime supply of of very nice little wooden handled steam valves the time I bought the boiler house at GMH Acacia Ridge.......if you want to play with a boiler ,I suggest the Sentinel Wagon type.....a single square section flue with crosstubes in the square pipe........the beauty of these is ease of manufacture.....Incidentally ,the Sentinel doesnt need a firebox door either ,stoking is done down the central flue........the system must have bee OK as Sentinel made its last steam wagons in 1952.....(OK,the purists will be pointing out Sentinel always spelled Wagon with two Gs.....Waggon.)
 
I have installed injectors on all of my steam locomotive boilers. The English injectors don't work worth a darn,they have too close of a range in pressure for them to work. I have several injectors including a 1/4" IPT on my 14" boiler that are made by Eccentric Engineer that work perfect and with a large range of pressure.
 








 
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