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Member postings for Paul Kemp

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

Thread: Wohlhaupter UPA4 Boring and Facing Head Operation
12/07/2020 12:59:34


I don't have a 4 but do have a 3. Looking at all the info available the two are significantly different in operation. However there was one comment I heard or read last night after seeing your post and nosing around the web which referred to a built in design flaw that causes the internal gears to break! There was no real exact detail apart from saying one type of gear (unreliable one) is two part the better gears are single piece. Not sure if this is applicable to yours as the inference was more towards the 3. I could imagine though that if a gear has sheared the drive may be intermittent as the fracture slips and grips? There is a quite a good you tube video on operating the 4 by a French chap - unfortunately my French isn't up to the job of understanding but you may pick up a few points by watching.


Thread: Selling on behalf of executors in 1975
11/07/2020 22:05:06

Also be interesting to have a poll as to what people actually have now. I have the impression (which may be completely wrong) that the majority on here have newer 'import' style machinery rather than the ex industrial stuff mentioned?


Thread: Copper boiler plate flanging, or not?
09/07/2020 21:23:42


If you have a bucket load of silfos I think you should use it to make more buckets or use it on other less critical projects than a boiler. Following is taken from Silfos 5 product data sheet but the other grades have similar comments.

"Normally the corrosion resistance of Sil-Fos 5 is of the same order as copper, but under certain conditions it may corrode more rapidly. Sil-Fos 5 should not be used where the joints are exposed to sulfur compounds, especially in gasses or oils at temperatures above normal room temperature. As the corrosion by sulfur is cumulative, even very small percentages will eventually cause failure of the joint by disintegration. Exposure to pressured steam can also result in accelerated corrosion. "

Even if you use a sulfur free heat source to fire the thing it will still be exposed to pressurised steam. A decent solder will be fine with a conventionally designed joint, there have been thousands made that have performed perfectly well, this that I have seen that have leaked or had failed joints were down to the gaps being too small for the solder to properly penetrate forming a nice looking fillet on the outside but with nothing actually in the joint.


Edited By Paul Kemp on 09/07/2020 21:29:30

Thread: elliot omnimill convert to cnc?
09/07/2020 19:47:03

I would echo John's suggestion re the knee and torque required as the standard set up takes a bit of turning (I have a larger diameter hand wheel on mine) although with a ball screw I guess it may be less?

From memory top speed as standard on the vertical head is around the 2000 mark, well short of CNC speeds but I don't suppose the bearings would mind too much they are a decent size, check the specs maybe? They could perhaps be swapped reasonably easy to something better suited to the speeds.

Nice machine even in manual form though, I was taking 50 thou cuts with a 2" facemill in steel on mine last weekend for fun. I love it.


Thread: Copper boiler plate flanging, or not?
09/07/2020 19:39:28

On the acetylene question I have often heard tell of insurance exclusions but does anyone have any specific info to back this up? Not that I have acetylene at home or any real intent of doing so in future but out of interest I dug out my home policy and there is no specific or related exclusion that I can see? Interested to hear if anyone has a concrete example of this being the case?


06/07/2020 22:12:43
Posted by Bob Worsley on 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.


oxy acetylene; no real problem with this if you know how to apply the flame to the job, yes you could overheat either the parent metal or the filler but if used correctly you won't.

Diferential expansion is less about the speed of conduction and more about the absorption. A thicker section takes more heat (energy) to raise the temperature a given value in a given time than a thinner section. You don't need to be able to calculate it you can do an experiment with your soldering iron, a thermocouple and a stop watch.

Older copper boilers do develop leaks around the fire door ring / section and around the foundation ring. Agreed model boilers less likely to develop cracks in the backhead / inner firebox due to the malleability of the copper (although copper does work harden even in a boiler). Usual source of leaks in firebox tube plate, smokebox tube plate, firehole and foundation ring is joint failure.

Yes the shell will expand, but not as quickly as the firebox, only source of heat to the shell is by conduction through the water. The whole boiler will expand and yes both as a function of heat and pressure, my 4" scale TE boiler expands about 3/32" between 0 psi and 120 psi but that is steel and only an infestiminal amount is due to pressure, the rest is heat.

If the tube plate does get overheated in my experience as per cracking and quilting of the firebox sides and crown it is due to a boiler not having been maintained correctly and a layer of scale deposited which is a good insulator and stops the heat conducting to the water or the water level has been allowed to get too low!

I will claim to be able to file a piece of metal to within 5 thou, one of my first jobs as an apprentice was to make an engineer's square calibrated to a master, manufactured using only hand tools in fact the calibration was less than 2 thou and as to irregular shapes we had to produce other pieces that fitted inside each other supporting their own weight and with no light visible through the joins.

Dont get me wrong, there is absolutely nothing wrong with questioning a process that has always been done in a particular way as to whether that is the correct way. However there is usually an underlying reason why it has been done the same way for many years! Feel free to construct / redesign your own boiler in any way you wish, there is nothing stopping you. However to get it certified under either the MES boiler scheme or a commercial examination as it will not be to a published or established design you will be expected to present calculations to justify your method. I would suggest you run your ideas past whichever boiler inspector you intend to use for certification before and during construction to avoid any disappointment on completion.

All the best,


Thread: Which Milling machine and what is its footprint?
05/07/2020 13:29:04

I have two mills, one with a tilting column and one with a tilting head. The former I can only remember tilting the column once. The latter I tilt the head all the time, granted its bit bigger than your average hobby machine but in terms of say drilling steam passages in the cylinder of my 6" scale TE or drilling the stud holes in the saddle (radial) I would have needed a pretty massive tilting table and setting up for each hole would have been pretty time consuming! I don't find any particular problem tramming it back to vertical. If constrained by space (as I am at home) and if starting over I would definitely go for a tilting head over a tilting column.


Thread: Britannia Lathe
05/07/2020 13:04:12

En3 is not generally known for its machinability, you can get a good finish on it but you would have to be a bit more fussy in everything being 'right' than for En1pb as noted above. As to 3" protrusion from the chuck, that depends on the size of the bar. 3/8" bar or smaller sticking out 3" would tend to ride up, can be done but sharp tool and light cuts are the order of the day. A lump of 3" bar, fill your boots, take as big a cut as your motor will drive 3" from the chuck! It's not only the rigidity of the machine that determines what you can do, you also have to consider the work piece.

It's all part of the learning curve.


Thread: Copper boiler plate flanging, or not?
29/06/2020 13:37:53

Bob, main problem I see with your plan is as you identify cost but in more practical terms unequal expansion. Whilst it is true expansion is linear and to a degree not vastly important on thickness but over the area of the plate, when heating up (raising steam) the thinner sections will heat up quicker and thus expand quicker and when cooling down the thinner sections will lose heat faster and contract quicker. Whether this is a problem in very small boilers I am not sure but certainly in full size boilers by raising steam too fast (or forcing as is usually the term) considerable damage can be caused by the stresses to stays and plates. This is the reason on a full sized boiler steam is raised over many hours, often with a small warming fire being set the day before to bring the temperature up slowly and as evenly as possible. Whilst a flanged joint is double thickness at the joint it is a relatively small area of the whole (and the plates need to be joined somewhere somehow. The technique of thick plates is sort of the approach taken in a miniature steel boiler although there most of the plates will be a very similar thickness and the joint will be a full penetration weld with root and capping runs and may even be back gouged and capped on the inside as well depending on access and sequence of assembly. Foundation ring is usually the same section all the way round and is at the cooler end of the boiler (below the fire) anyway. Just my thoughts.

As Jason says it is normal to adjust the flange faces either by machining, filing or other hand work to maintain the requisite clearances for the solder. It can be a mistake to have clearances on say tubes too tight because the silver solder if the clearance is tight will not flow through the joint. Seen several loco boilers fail at the smokebox tube plate / tube joints where they have been built like this and there is only a fillet of solder outside the tube. The tubes being thinner than the shell and heating up quicker by being exposed to the "fire" want to grow quicker than the barrel which is heated by the water and the stress on the joints of the tubes to firebox and smokebox can be quite high.


Thread: WM250 Sticky Carriage
29/06/2020 00:41:00

Agree it may be the carriage pinion as above. However you say it's new? Is that brand new, straight from Warco? If so I would be on the phone to them. I also wouldn't put anything harsher than a fine stone to the bed, if it's got lumps on it big enough to warrant a file there is a serious quality problem!


Thread: The fit of tapers
28/06/2020 15:11:20

Just to throw a curved ball, the repeatability of how far a female taper seats up a male taper will also depend on the rigidity of the female component and the force used to push it up the taper. This property is used to good effect on large high power taper fit couplings that have no key but rely on the "push up" of the female over the male. The elastic properties of the material mean the greater the push up the greater the "grip". In your application the difference will probably be only microns but to gaurantee a consistent linear position a consistent seating force would be needed.


Thread: Wilesco D16 Steam plant
26/06/2020 21:28:05


i don't think the boilers are stainless, some of the blurb suggests polished nickel plating but looking at a video the bling looks like a cover especially round the whistle and safety valve. I don't have any Wilesco products so can't speak with any authority but I would expect the boiler to be copper under the skin. Was quite surprised by the quoted operating pressure of "about 1.5 bar" almost double what you would expect on a Mamod.


Thread: Brian's Horizontal Stirling Engine
26/06/2020 20:57:03

Excellent job. Posts like this where people get on and do something with no drawings and limited facilities I really enjoy. A bit of determination and inginuity goes a long way. Love it.


Thread: Brazing Oilite bearings
26/06/2020 20:42:15

Personally I would doubt you will get them clean enough but you never know till you try!


Thread: Wilesco D16 Steam plant
26/06/2020 20:39:55


If you are going to use a glass (Pyrex or similar) window you might want to ensure you use only demin or soft water or it will scale up and be pointless.

Was that the soft soldered boiler in the boat that exploded in the other thread?


Thread: Newly back to model engineering - Issue with Hobbymat BFE65
26/06/2020 13:13:35


I think the mill head has the same motor as the lathe. Check the motor fan cover, it may have been displaced in the move? That makes a dreadful racket! Just a thought.


Thread: vacuum brakes (again)
25/06/2020 20:32:19
Posted by Andrew Tinsley on 25/06/2020 20:04:24:


Leaving aside the physics of ejectors. I have carried out tests running ejectors on both compressed air and steam and within the limits of experimental error, steam and compressed air produce the same ultimate vacuum for a given pressure

The steam used was not super heated and a maximum pressure of both steam and compressed air was 80psi. with a minimum pressure of 15psi .I used 3 designs of ejector and all showed the same results on steam and compressed air. Although the efficiency varied between designs (The Doug Brown design was the best).

If you wish to dispute the results then you are welcome to carry out your own tests. I would be interested to see the results.


Can I ask how you measured the efficiency? I need to make a water lifter (same principle) so interested in the theory. From my brief research on model water lifters the parameters for cone angle and position seem to vary quite widely between 'designs'. I want to move the most water for the least steam consumption as that should result in the minimum temperature rise of the delivered water?



Thread: Safety valve spring length
25/06/2020 19:24:45

See similar post for Mamod SV, same principles apply. Spring rate is the important thing, 1/2" compressed for a 3/16" spring sounds reasonable you need to make sure it won't become coil bound before fully open though. Free length can be calculated by working out the area of the valves exposed to pressure with the valve closed and multiplying by lift pressure, this will give you the load the spring has to exerpt in the closed position. The Spring rate will be the increase in force per extension or compression of the spring being used (Hooke's Law) so if you know your compressed length you can work back to get your free length. Hope that makes some sense?


Thread: Mamod safety valve
25/06/2020 19:14:59

As Martin says but remember a safety valve has hysteresis. The force on the spring to get it to open initially is as stated but as it opens the spring compresses (closing force increases) and the area exposed to pressure increases (so opening force increases) so unless you choose a spring with the correct 'rate' the boiler pressure drops below the lifting pressure before the valve closes - wastes precious steam. To determine the rate you also need to estimate the lift and calculate the force from the steam pressure on the increased area - this isn't so easy as the steam is expanding at this point too where it is throttled by the valve so its a dynamic state rather than a steady state. Not so easy to calculate and the reason why on many miniatures the valve lifts at say 100psi but does not reseat itself until the pressure has dropped to say 80psi or less. One reason why you see people clouting model valves with shovels lol. 5 psi hystereresis is probably pretty good for model valves in general use although pop type valves can be tuned better.


Thread: vacuum brakes (again)
25/06/2020 13:25:43


Thanks for that, confirms my thoughts from looking at the valve drawing. Need to be careful "plonking" em on hard and fast with a Maisie though, not a massive amount of adhesion so with a train a recipe for flats on the wheels unless the stock is similarly fitted - in which case there would likely be a significant lag in application.


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