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Member postings for Bob Worsley

Here is a list of all the postings Bob Worsley has made in our forums. Click on a thread name to jump to the thread.

Thread: Copper boiler plate flanging, or not?
09/07/2020 19:57:17

Just been given a large pile of MEs, and quickly scanning my way through them.

One from the 1980's I think had an article by Keith Wilson about how great silfos is to soldering up boilers.

Then I have just read Wardle's article in 1st Feb 1980 about a couple of silfos boilers that literally fell to pieces after about 1000 hours of steaming. I found that incredibly frightening.

The solder had been attacked by the sulpher in the coal causing it to turn to black mush. This is one of the reasons I hesitate about ME flanging plates, that the 5 thou gap might be 50 thou and I do have a bucket full of silfos (used to solder coax cables in the days before fibreoptics) and was tempted to use it. I still look at the reverse curve on a loco firebox and think, without rivets, how do you keep those pieces of copper at a 5 thou distance. Note, not more than 5 thou, or less than 5 thou, but at 5 thou. If bits of the gap are 5 thou then what percentage?

Yes, I worry, but my professional engineering was like that too, eliminate by design known possible failures.

09/07/2020 10:54:27

Thanks for the continued interest, or exasperation!

Oxy acetylene.

If you are skilled then, as people say, use it. If you are not skilled then steer well clear. After reading books and articles on the use of oxy then that is my conclusion. The problem is that the flame temperature is so hot, 3,300C, and the boiling point of copper is 2560C. So the chances of overheating rises to, what, 100%? Look at the tubeplates, the firebox one is hard to see with lots of very thin copper. Gas is 1900C so can't melt and the flame size spreads the heat so even oxidising is unlikely.

The snag with reading older books and articles is that things change. Silfos was recommended ears ago, now it isn't, with large warnings of sulphur effects in coal fired boilers if the temperature exceeds 200C.

Flanging

What troubles me is providing the guarantee that the flanged joint is consistently the required 5 thou. If you are making some steelwork then you use bluing paste to make sure that the whole area that needs to be in contact is in fact in contact. This is easy on the tubeplate, but that can be machined anyway, it is the firebox tubeplate and the springiness of the joint. This is why it is suggested you tack the joint with rivets, but then how do you know if you still have the 5 thou. At this point you have filled the joint with flux and any gaps are now invisible.

Solder is strong, far stronger in tension and shear than copper. This means that with a 3mm plate then the solder only has to be 0.5mm for the same strength. So the 6 or 8mm flange has plenty of redundancy, the snag is you have no idea how much of that redundancy you are using. Is the flange width so wide simply because they are so poor and the maximum redundancy is needed? My suggestion using thick plates might bring some clearer idea of how much is being used. Many years ago I found Frank Price's book Right First Time in the library, and bought a copy, and that has been a guiding principle ever since in design.

As mentioned, using a sandwich of formers seems a very good idea to improve the quality, however defined, of the flanges.

The last jobs I had to do that were completely new to me were felling trees. Standing at the bottom of a 90' tree smartened up you risk assessment. But even more so did the cutting of wind throw and hung up branches, they look small, lots of them, just hack away with the saw. One tree about 70' high and only 5" DBH I felled, oblivious to the squirrel damage, invisible, half way up that caused to tree to fold in half as it came down. If I hadn't obeyed the rule, watch it, then it would have hit me. Likewise with hung up branches, you wouldn't believe how much weight a 2" branch can support without breaking, cut it and twang. You hide behind the stem and cut from there. Similar situations is repairing valve audio amplifiers, 600V HT is nasty. Don't really want to have a boiler experience.

06/07/2020 20:05:52

Short delay while I bought and read Alec Farmer's book as suggested. Yet another person who is incapable of creating an index!

Thanks for the comments on wire drawing.

I see that it uses oxy acetylene for all soldering work. The other boiler books are all very wary of this, and some ME articles positively say no. Basically the flame is too hot, and can/will result in the alloy metals being boiled out. Possibly of more importance with cadmium alloys.

To reply, not answer, comments. Copper is a very good conductor of heat, and I don't have the expertise to say that heating the water will result in an x deg C temperature drop along the copper. Many experiences with a soldering iron and far thinner wire than a 3mm sheet of copper suggests this speed of conductivity is high. So I really don't see that using a 6mm tube plate without flanges is in any serious way different to a 3mm flanged plate. What about around the firebox? Again don't see that it is important, especially since the foundation ring could be 1/2" square copper. Also the firehole ring is a piece of far stiffer metal than the surround, don't get fracture failure around them.

The shell will expand. But all the descriptions of boiler testing are that the whole boiler can, probably will, move slightly as the pressure comes on. The metal will move until enough is there to take the stress, the strain in the metal is minimised. With firing of the boiler hopefully this movement won't reoccur, but if it does then the copper is as soft as it can be, and will adjust. Again, don't see this as a problem.

Other comments are that the instructions to solder a boiler very frequently say that it is the firebox plate where the leaks are. Could be for a number of reasons. 1 - There is very little metal left after the tube holes are cut, so could be partially melted or other nasties. 2 - It is always a tricky shape, not like the smokebox plate, so can't just stick in lathe and machine the flange. 3 - Because it is hand work to get the plate to match the firebox then who is going to claim their filing is within 5 thou over a distance of 10" and a complicated shape. 4 - And how are you going to justify that claim.

This is why using a thicker piece of metal, no hammering and banging, has got to be an improvement.

Thread: How to contact another person
02/07/2020 18:43:29

But there is an email account, no phone number?

02/07/2020 18:39:54

Oops, thought all that had been done.

02/07/2020 17:11:37

Wanted some Fowler Lion drawings, a reply but saying they can't directly contact me, and now I can't directly contact them.

Thought that once logged in all the contact details were there to be used?

Thread: ISO Container for Workshop
30/06/2020 11:21:53

Try looking regularly on

mod-sales.com

in their auction. Often have the ex-military workshops, toilet blocks etc which have 2" foam insulation around them. Most are only 15' or so long, check. There are a few of the curved top type, but inside heght less than 6', don't buy unless you are shorter.

I bought one of these years ago, got logburner in it and really comfy.

I have used Worcestercontainers to move several of my lumpy bits, nice helpful people.

Thread: Copper boiler plate flanging, or not?
29/06/2020 12:21:38

Re-starting model engineering and need a boiler.

Got and read the various ME books such as Tubal Cane, Martin Evans etc. First gripe, haven't they heard of indexes? What is wire drawing?

It is clear from these that the clearance between copper surfaces in the boiler are of critical importance when silver soldering, something like a few thou.

Never made a boiler but done some limited, evening class, copper bashing and seems to me that the hammering needed for a 3mm copper plate to flange it results in anything other than a few thou close fitting joint.

One example I am working on is a part complete Clayton by Robin Dyer. Nice and simple with just two plates, top and bottom. But they are both, particularly the firebox end, with the tube holes very close to the flange with consequent pulling of the metal and hammer damage.

Why not just use a piece of 5mm or 6mm copper plate and just bore the holes, turn to exact size on the lathe, and solder? Ok, the copper cost will be higher but in the whole model that isn't really very much, so ignore cost.

Yes, copper is sticky and not the easiest metal to drill. But use a lubricated step drill, I find these are amazingly useful drills and solve endless problems, probably the greatest one being the end result is circular! Or could bore the holes on a mill.

The soldered joint needs to be in shear, from books, so the wide plate joint will be in shear. In fact exactly like the foundation ring. The actual area of solder will be the same for plate and ring, so no hazard there.

Inspecting the joint is equally impossible for flange or plate, no extra hazard there.

The next model wants to be a traction engine with a loco type boiler. Here again I can't see why the plates need to be flanged, a solid 6mm plate will be just as good. Yes, there will be a reduction in the water space around the firebox, but just make it slightly smaller to maintain the 3/8" or whatever gap. There is the throatplate, double flanged, but could be two 6mm plates brazed, not soldered, together with one for the boiler, one for the firebox. Again, cost but seems a cheap solution to hammering and bashing a poor piece of copper sheet.

Any one already doing this?

Thanks.

Thread: milling machine which one ?
08/06/2020 15:04:25

The motor rating plate is the mechanical power out. Multiply by 1.2 for power factor and another 1.2 for efficiency to get power in.

Thread: What *should* a Warco Super Major Milling Machine be able to accomplish?
22/05/2020 10:33:34

Why practice being silly?

This is a home workshop forum, and the machines as used in such an environment. A column mill is the mill drill and similar mills, which took years before they bothered to put keyways or other anti rotation devices on the column.

Look at your wonderful Bridgeport, just how far is it from the tip of the cutter, through the head, down the column, into the knee then up to the vice? And how many joints and gaps are there? It isn't rigid. Do the finger and DTI test, but you won't, nobody ever does. Then you have the Senior mills, nice solid column but the table dovetails are square, as long as they are wide. This means that you can do nothing to stop the table twisting on the dovetails. This is not rigid.

Each machine has a limit to what it can do, to push that limit buy a Huron, for spotting holes and thin aluminium buy a Bridgeport. Most work is lightweight, works fine, unfortunately as a model engineer the work is far more diverse.

21/05/2020 16:16:21

Rigidity is what you want, and a Bridgeport or any column mill doesn't provide it.

Put the tool in the chuck, bring it up to the work but not touching, then get a DTI between the work and the cutter. Using finger pressure only push the cutter to and from the work and be amazed at how many thou movement you get. That is the play.

If you get 10 thou then buy a file, even a couple of thou is far too much. A real mill will only move a couple of tenths, that is what you need to get cutting.

Look at a real industrial mill, and the amount of cast iron in it.

Thread: Digital Phase converter...
14/12/2019 17:00:04

Interesting, not come across a digital phase converter before, but then I have three phase in the house.

As has been mentioned just seem to be a standard VFD with a voltage booster on the input. This is both a tribute to the amazing electrolytic capacitors now available, and a problem.

To step 220V up to 440V needs a capacitor, it is charged to peak volts on the negative half or the sine wave, and then lifted up to charge the output capacitor on the positive peak of the sine wave. This is identical to the dual voltage switch mode power supplies that have been around for years. The snag comes because the output capacitor is only charged once per cycle, so 50 times per second. And that charge is just a rapid dump of charge from the input capacitor to the output capacitor. If the VFD is running 5hp, then that is 3730W, divided by 0.9 pf divided by 0.9 efficiency giving 4600W. So this 4600W for one cycle needs to be dumped in the output cap in about 5ms to run the motor for the 20ms cycle. Simply put if the motor takes 10A then this current is 40A.

Certainly works the caps hard.

You can emulate this with a standard 400V 3ph VFD, the few I have seen all have terminals on the back to add in extra smoothing caps. Just make your own voltage doubler and attach the output cap to these terminals. It is seriously lethal, so perhaps not.

An induction motor will take an 8x overload to start. Don't forget that all that is limiting the current is the synchronous impedance of the motor. This is why a 5kW generator won't start a 3hp compressor. To some extent it is relying on the inertia of the rotor to keep turning to get the voltage regulator to crank up the excitation current.

If the rotary converter is noisy then switch the motor off as soon as the lathe is running, not then needed provided you check that there is enough running capacitance to keep the phases reasonably at 120 degrees.

Thread: Allchin 1.1.2" boiler
07/11/2019 18:42:46

That is exactly it. Perhaps it is time the drawings were updated to reflect modern construction methods?

Thread: Another unfortunate milestone reached?
07/11/2019 18:38:33

Received a flyer in my Machinery Market magazine today, a glossy advertising the shutting down and selling off of Electro Motion's largest sales building.

For sale are over 600 machines, from the photos mostly manual or early auto types.

Does this mean that manual machines are now scrap? If it hasn't got a colour screen and 15 software updates a month then no one wants it?

I remember visiting Nettlehams at Gainsborough about 20 years ago. They were in the same position, no one bought what they sold, place turned into a supermarket I think.

I have personally experienced the same with electronic test equipment. Analogue scopes, spectrum analysers, signal generators plus just about every other type of non-colour LCD screen equipment is scrap. I know, I scrapped about 70 Tektronix and HP analogue scopes few years back, worthless.

Is this good, or bad? That you now have trouble finding a machine that will do a serious job without needing software is an advance, or not? Is the thing to do to salt away old mills and lathes, a Parkson for £400 doesn't sound expensive, or big old Colchester lathes, radial arm drills, even trivial stuff like a drill grinder.

Feels to me that this isn't good. The lack of any software in a machine is good. Starting out don't you need simple, reliable and cheap tools?

Thread: Allchin 1.1.2" boiler
07/11/2019 10:42:59

No!

Do not confuse brazing with braze welding, or bronze welding.

Brazing uses what is in effect a piece of brass to join the parts, and it also requires a few thou gap for the spelter to run in by capillary action. Braze welding uses a different type of filler that will only form a fillet.

Added to that the throatplate joint will be made after other joints, tubes etc, so they also would need to be braze welded due to the far higher temperature this requires.

No one has picked up on my point about pinholes and the possibility of them opening up under steam pressure.

If the method of construction requires a change, then what is wrong with that? I would plan to use metric threads rather than inch, another change.

If you read the Haining book about boilers for ploughing engines then he talks about the Greenly method of boiler design, but that is thickness of metal, not that they think a line joint several inches long is good enough for 100psi.

06/11/2019 11:37:47

The Allchin barrel is made from a short piece of tube joined to a wrapped sheet that goes over the firebox. Figure 2.1 in the book shows the join between these two pieces. What I don't understand is that the throatplate just touches the underside of the barrel and is soldered there. There is no folded flange going inside the barrel to make a decent area to solder. The drawing just shows a line join between the throatplate and barrel.

I have done a search of the forum and can find no mention of this.

The figure 2.1 also shows the waisting of the firebox wrapper which is far more than the 1/32" on the drawing.

As far as I can see the throatplate needs flanging on the sides backwards into the firebox and forwards into the barrel. This makes for an interesting shape to the copper where the backwards flange meets up with the forwards flange. Must be possible, I imagine all loco type boilers have this double bend at this point, but can't find a photo of one in my limited collection of books.

The point is that at two points one either side, there seems to be a pinhole gap in the flange where it touches the wrapper and barrel. It also seems to be impossible to reinforce this point with some copper.

This raises the question that is 13SWG copper sufficiently strong that if this pin hole leaks then the copper has sufficient strength not to tear and cause the boiler to fail? I can find no intelligible information about how strong copper is in tension. If you had the 100PSI steam in the boiler and drilled a hole in the shell, would the steam just rush out or would the boiler explode? Is the tensile strength of the copper greater than the tearing force from the steam? What size hole would there have to be before the steam exceeded the strength of the copper?

Why wasn't the boiler made with the barrel split and folded down? But this also raises the question that the sides would need to be extended by a small amount. Instructions for other boilers say to rivet these extensions then solder. But again there are now four places where this strap butts up against the flanges at the front throatplate and rear backhead. Is this another source of weakness?

Reading scientific how to books (Materials and Techniques for Electron Tubes by Kohl) where they use silver soldering and the gap between the two pieces is given as 0.0015" to 0.010" (p382). This is not very much after walloping the copper to flange it. Ok, can clean up the front tube plate on a lathe, but all the others are just filed, 0.010" is a scratch. The scientific book specifically mentions solder dams where it can't flow past a scratch in the joint.

For example the wrapper side extension pieces. Do you put some flux in the between the side pieces and the reinforcing strap before riveting. Then what happens when it is heated up, has the flux dried? Is it hard and holding the pieces apart? Is assuming the flux will get inside the joint by placing on and around good enough? How do you know any solder has actually gone inside the joint? Don't forget we are looking at just 0.010" gap here.

The join between the barrel wrapper is made with a piece of 5/8" strip copper, this is 5/16" on each surface. Where is there any figures for the shear strength of copper and soldered joints that this is adequate. With the stresses on this joint from the model moving then this is needed? The steam pressure on this joint at 100PSI is 1104 pounds, or nearly 1000psi tensile.

Does this need to be addressed? Is is a problem? Tilting at windmills?

Thread: Graham Howard and Brunell Steam Model Engineering
28/04/2019 17:35:10

Wow, has Graham Howard of Brunell Steam Model Engineering been resurrected?

About seven years ago, I bought a complete set of everything for the Fowler ploughing engine from Graham Howard at Brunell, costing £2,300.

I assume this is the same one.

I am still waiting for most of the castings plus all the other odds and ends, strakes, rims etc to be delivered.

The said Graham Howard ignores phone calls, emails and posted letters. Just how do you communicate with someone like this.

It would be really nice, even now, to get my order completed.

Would Graham Howard of Brunell like to comment on this forum?

Thread: DRO using a wire
08/08/2014 20:35:15

Ah, it is nice to be remembered!

Yes, I still make a limited range of the draw wire sensors and displays, just the two axis now, run out of labels for the three axis.

Expensive! They were £390 for a two axis DRO when I started making them in 1992, and the price is still £390, gotta live.

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