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Post by runner42 on Jan 2, 2021 4:01:24 GMT
Thanks for the replies. The second new year's resolution is don't put up with second best, so I am scrapping the smokebox tubeplate. It would have caused problems during assembly of the boiler because apart from the reduced circulation issue which I don't need, is the fact that the outer tubes are significantly misregistered with the firebox tubeplate and will be entering at an angle, not good. I have much better ligament distance so the BI is not going to get out is vernier and have something to say. The firebox tubeplate requires the flues to be opened up to 1" dia, but I shall await until I have the copper tubes to use as a gauge. Brian  firebox tubeplate by Brian Leach, on Flickr |
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Post by steamer5 on Jan 2, 2021 21:16:34 GMT
Hi Brian,
Good choice!
The plates are looking great. Hope you and the family are all safe.
Cheers Kerrin
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Post by coniston on Jan 4, 2021 23:20:58 GMT
Brian, definitely the right decision, better to scrap a bit of copper now than a part built boiler later. BTW dimension for bend in throatplate works out at 2.832" from the bottom corner where the 31/32 dimension is. Right angle triangle with 20 degree angle and 31/32" side, hypotenuse is (31/32) / Sin20 = 2.832" (if my trig is correct LoL).
Chris D
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Post by David on Jan 5, 2021 1:24:01 GMT
It's all looking very tidy so far!
The tubes in my boiler are banana shaped, so I don't think having slightly splayed tubes is that big a deal. Having them wider could only improve circulation at that end, surely.
I have no idea what effect the banana shape will have on gas flow. I can only hope the draft in the smokebox is strong enough to draw the gasses through the downward slope. Maybe slowing the gas down will allow more heat transfer?
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Post by runner42 on Jan 5, 2021 7:12:17 GMT
Brian, definitely the right decision, better to scrap a bit of copper now than a part built boiler later. BTW dimension for bend in throatplate works out at 2.832" from the bottom corner where the 31/32 dimension is. Right angle triangle with 20 degree angle and 31/32" side, hypotenuse is (31/32) / Sin20 = 2.832" (if my trig is correct LoL). Chris D Thanks Chris, I did realise that simple trigonometry for a right angled triangle applied here, however to undertake the calculation was unnecessary if the hypotenuse measurement was given instead of the 20 deg angle. In practical terms when making the throat plate it is more likely that linear measurements are used in preference to angles, because it is easier to apply. I suppose DY chose the dimensions based on the sanctity of round numbers, 20 deg is a nice round figure and 31/32" is a convenient fraction, but 2.832" is an odd ball decimal figure that can't be expressed even in 64ths , which wouldn't sit nicely with the propensity to use fractions instead of decimals. I just wonder whether or not it was important to have the bend at 20 deg or some angle slightly smaller or larger would make much difference? Brian |
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Post by coniston on Jan 5, 2021 19:53:58 GMT
Ok Brian I guessed I may be 'teaching granny to suck eggs' I know what you mean about DY drawings I have his for the A3 Doncaster and trying to work out some of the bits needs reference to more than one drawing which is really not very good for a 'professional' draughtsman. I would have got hauled over he coals by the Chief Draughtsman if I presented drawings like some of DY's. I suppose DY found it easier to use the 20 deg angle rather than having to work out the trig for himself, but that doesn't help the poor model engineer trying to make each part separately.
Like your thread, very interesting, keep it up
Chris D
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Post by runner42 on Jan 7, 2021 6:41:49 GMT
I have run into a major problem in sourcing 7/16" OD copper tubing, it is an odd size and probably only available in the UK. The nearest size that is readily available is 1/2" OD, which I cannot use with my existing smokebox and firebox tubeplates because there in insufficient space between the hole positions to drill out to 1/2" dia. This will mean that I have to scrap the tubeplates (second time for the smokebox tubeplate) and rearrange the tube layout to accommodate the larger size, it will probably require a reduction in the number of tubes. I am not sufficiently design savvy to establish the best possible layout, so I am hoping that readers will assist me in this regard. The area enclosed in red is the available footprint that can be used for an arrangement of 1/2" OD copper tubes and the spacing between the holes should be not less than 2.5 mm. The OD of the smokebox tubeplate is 5" and the material thickness is 3mm. The 4 off 1" dia flues' position cannot be altered. Those with CAD skills will be able to redraw the tubeplate and have a 1/2" dia hole that can moved around the area, then replicated to the max number that can be achieved. Brian  smokebox tubeplate drg by Brian Leach, on Flickr |
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Post by John Baguley on Jan 7, 2021 16:29:26 GMT
Is this any good Brian?
That gives eighteen ½" tubes with a ligament of near enough 3mm. I think you will be struggling to get any more tubes in even if you try and reduce the ligament to 2.5mm. You are only losing three tubes and you may actually get more free gas area due to the larger diameter.
John
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kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 575 
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Post by kipford on Jan 7, 2021 16:51:26 GMT
Just done some sums based on 20 swg tube 12 in long. 18 1/2" tubes compared to 21 7/16" tubes gives an increase in flow area of 17% but a decrease in surface area of just over 2%. So it looks likes John solution has potential.
Dave
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Post by runner42 on Jan 7, 2021 21:51:44 GMT
Is this any good Brian?
That gives eighteen ½" tubes with a ligament of near enough 3mm. I think you will be struggling to get any more tubes in even if you try and reduce the ligament to 2.5mm. You are only losing three tubes and you may actually get more free gas area due to the larger diameter.
John
Many thanks John, that is an excellent solution, not only providing the principle but a dimensional drawing. I'll use the drawing to add to the club's data package that is needed for the boiler certification. Because it meets the AMBSC Code Part 1 requirements the BI will have no problems with the change. Brian |
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Post by Deleted on Jan 7, 2021 22:28:33 GMT
Hi Brian...love the quality of your tube plates...I note that you followed AMBSC code with no longitudinal stays allowed. I thought that the tube plates needed to be thicker or have supporting strap doubler added in that area. Do I have this wrong or are you adding a doubler later?
Regards
Pete
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Post by Jim on Jan 8, 2021 1:19:40 GMT
I'm assuming Brian that your club boiler inspector approved your boiler drawings before you started work as the DY drawings may not comply with the current AMBSC code. The Perrier drawings for the Britannia certainly didn't.
Jim
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Post by runner42 on Jan 8, 2021 6:35:59 GMT
Hi Brian...love the quality of your tube plates...I note that you followed AMBSC code with no longitudinal stays allowed. I thought that the tube plates needed to be thicker or have supporting strap doubler added in that area. Do I have this wrong or are you adding a doubler later? Regards Pete Hi Pete longitudinal stays are allowed by the code, if you have a copy of the code type 2 are to be used, i.e. blind threaded nipple at one end and a threaded bush and lock nut at the other. Because the boiler length is 24" or 610 mm, to meet the not more than 100 times criterion (the length of the boiler between the smokebox tubeplate and the backhead shall not be more than 100 times the dia of the stay) means that the stay diameter is to be 6 mm or greater. There is a requirement that the stay must be hard drawn (un-annealed) and fitted after all silver soldering operations are complete. You understand the logic, silver soldering heat will soften the material and its ability to prevent bulging of the tubeplate and/or backhead is lost. 3 mm thick plate is used throughout and the BI inspector indicated that the WP could be raised from 90 psi to 100 psi. Brian |
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Post by runner42 on Jan 8, 2021 7:05:33 GMT
I'm assuming Brian that your club boiler inspector approved your boiler drawings before you started work as the DY drawings may not comply with the current AMBSC code. The Perrier drawings for the Britannia certainly didn't.
Jim
Jim I have provided the BI a copy of the modified boiler drawing which has been reviewed and commented on. The modification has replaced the girder stay with preferred conventional rod type stay used in other places on the boiler. The stay diameter and spacing meets the criteria of table 3.4.1A for a WP of 700 kPa a 6 mm dia stay and stay pitch of 27.5 mm. The double segment barrel has been replaced by a single tapered type. He has not provided approval of the drawing, but instead considered it to be WIP and be used as a basis of an iterative process as the build proceeds and comments/modifications are undertaken. A Black 5 boiler has already been built and approved and I am using the information and photographs established for that as a basis for my build. Brian  boiler drawing modified by Brian Leach, on Flickr PS of course the number and size of tubes will be updated to meet the requirements provided by John Baguley above. |
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44767
Statesman
Posts: 538
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Post by 44767 on Jan 10, 2021 12:48:13 GMT
The Don Young Black 5 boiler "steams like a witch" as it is. Although redesigning it for ½" tube would be alright, as long as you keep the ratios of total cross-sectional tube area to grate area within the guidelines, wouldn't it be better to use the 7/16th tube as per the drawing? It is available from MaccModels in the UK for a mere £7.60 for a 36" length (you can get two tubes out of this). Then you can use your existing tube plates.
Regards,
Mike
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Post by runner42 on Jan 10, 2021 22:12:52 GMT
The Don Young Black 5 boiler "steams like a witch" as it is. Although redesigning it for ½" tube would be alright, as long as you keep the ratios of total cross-sectional tube area to grate area within the guidelines, wouldn't it be better to use the 7/16th tube as per the drawing? It is available from MaccModels in the UK for a mere £7.60 for a 36" length (you can get two tubes out of this). Then you can use your existing tube plates. Regards, Mike Thanks Mike I have checked them out and the costs is more than you quoted, for a 36" length is £12.28. However I have messaged them for costs of 15" length tubes. Brian |
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44767
Statesman
Posts: 538
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Post by 44767 on Jan 10, 2021 22:42:57 GMT
Brian, Well this is what I get!  Cheers, Mike |
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Post by runner42 on Jan 10, 2021 23:20:41 GMT
Mike I got the same as you by going to their website, but my initial investigation was through eBay which shows a higher price. Thanks I shall ignore eBay and go through their own website.
PS it's even cheaper with VAT removed.
PPS But another anomaly postage costs are £25 through eBay but £55 through their website.
Brian
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Post by David on Jan 11, 2021 5:53:37 GMT
This will mean that I have to scrap the tubeplates (second time for the smokebox tubeplate) Admirable restraint for what must have been a very frustrating and expensive realisation! Good news you can get the 7/16" you need. |
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Post by runner42 on Jan 15, 2021 6:34:08 GMT
Roll out the barrel, let's have a barrel of fun. But not quite, not yet. The smokebox end of the barrel is 0.006" undersize and the smokebox tubeplate is 0.015" oversize. The latter maybe improved by judicial tapping of the flange on the smokebox tubeplate to bring it closer to size. The reason for the oversize is that I couldn't remove the steel flanging die if the tubeplate was too tightly peened. To show the affect of this error of dimensions I have pushed the smokebox tubeplate into the end of the barrel and show the amount of gap that will occur at the joining strip if nothing else is done. If the tapping of the smokebox flange doesn't improve matters I could take a few thou' off the smokebox tubeplate diameter or insert a very thin piece of copper to close the gap. Any suggestions? The 1 1/4" joining strip will be on the inside.  barrel by Brian Leach, on Flickr  barrel1 by Brian Leach, on Flickr  barrel2 by Brian Leach, on Flickr The smokebox tubeplate is the scrapped one so a bit of coaxing didn't go amiss. Brian |
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