Member postings for Paul Kemp

Steve,

You were actually climb milling there mate. Climb milling basically means the cutter is dragging the work into itself. That's why with gib loose it jumped at the end and why you had all those scallops in the surface. Nothing wrong with climb milling on a well set up machine and it can actually give you a better finish and with some jobs it's hard to avoid but best to not take heavy cuts. With a slab mill on a horizontal mill it can spit the job out of the vice!  Just visualise the rotation of the cutter, if it's dragging the work towards it its climb milling, if it's pushing it away its "conventional".

Have a go the other way and see how that goes, you will be able to up your feed rate.

Paul.

Edited By Paul Kemp on 11/04/2020 23:23:38

Derek,

That's the spirit! Measuring the valves will be difficult as they have three flutes, easiest way would probably be taking a first guess undersize and drinking a hole in a piece of plate, then slowly keep opening it out. Can't remember if you have a lathe but if you do then bore out in small steps until the valve goes in and then you can measure the hole - will be close enough. Can you post a couple more pictures of the body and the underside showing how the spring is adjusted?

Paul.

That is a lovely bit of kit. I reckon finding a vertical head for it will be like looking for hens teeth though but with the twin over arm plenty of scope to make something up. You should be able to rip some metal off with that!

Paul.

Nothing wrong with cheap brazed carbide tools as long as you have a green grit wheel and can grind em (and the carbide doesn't chip). If you are getting a good finish on the larger diameter and a good finish facing it would seem unlikely it is the tool unless as others have said it is too high. Just for fun, try setting it 10 thou lower than you have it at the moment and see what happens. Failing that get yourself a bit of known free cutting (leaded) bar the same size and see what that does under the same conditions. Swap your carbide for a bit of HSS and see what that does.

For tools, whatever takes your fancy, I use a mix of insert tooling, brazed carbide and HSS, really depends what you are doing, what material you are machining and your ability to grind your own tools. All have merits, there isn't really a one size fits all answer!

Paul.

Derek,

As Micheal says the point of effort for the spring bar needs to be below the line of contact with the valve and seat. One of the points on the bar as indicated in Micheals drawing also needs to pivot. You will not find a pair of these valves that both lift at exactly the same time so small degree of articulation is required. The set up shown is similar if not identical to a set from a Burrel I repaired for a friend. Adjustment was a nightmare as the adjusting nut was inside the steam cavity. I ended up making a false housing for the valve assembly to bolt on to and set them up on air for the lift pressure. Air does not behave the same as steam but in terms of the actual pressure to get them to lift is close enough, it's the re seating that will not be the same as the air does not have the expansive property of steam. You say the fit of the valves in the body is "loose" what does loose actually mean? A couple of thou clearance, 5 thou or 20 thou? They should not be a tight or even a close sliding fit at normal temperature as you need to allow for some expansion, the last thing you want is for them to bind when they get hot and jam shut! Conversely they don't want to be so slack that you can throw them in from the other side of the room? Loose is a relative term here!

As Micheal also says the width of the seat wants to be fairly narrow I am not sure of the relative size of these parts but I would say 25thou contact would be more than plenty. If the body were machined to a sharp corner and then lapped in with fine time saver the resulting bevel of the seat should be plenty.

I would suggest for a start you make a dummy housing with an air connection, get a bit of weight on the spring (having lowered the point of contact for the bar by removing the solder) and see what happens and at what point they lift -! You need a decent gauge in the system! If it's any consolation this type of valve in miniature are really hard to set up and get working right, that's why lots of people hide a pop type valve inside a dummy representation! Also at the moment if they leak like a sieve they are as safe as you can be because you will never build up any pressure in your boiler under steam!

I am afraid this is a case of patience and perseverance and unlikely to be solved purely by having two new valves made. You will get there.

Paul.

Scaling speed is an age old thorny subject as speed is distance over time and time you can't really 'scale'. If you wanted a scale 60mph for a half size model and you scaled 60 by half and a minute by half it would be 30 miles in 30 minutes, which is.......... 60mph. RPM would be the same. You are straying into Einstien territory here!

Paul.

Derek,

Any chance you can post a picture or two of what you have and maybe a shot of the relevant part of the drawing? I am not familiar with the Alchin design. I would assume the "poppets'" have a stem with reliefs machine in to allow the passage of steam and guide the valve onto the seat but maybe not in your case!

Paul.

Iain,

Loving this thread and your approach. Keep it up, really interested to see the final result.

Paul.

Because it's like an iceberg it won't roll much and in any case it will have a weather limitation on it I would expect.

Paul.

Henry,

i bought a Noga style small mag base for my mill from RDG's stand at Ally Pally about 3 years ago. I turned up an adaptor to fit it that goes in the lug on the clock (it's a nothing special clock, only reads to a thou) but it does fine for general set ups squaring the vice on the Omnimill and I also use it on the lathes, it's become a sort of workshop go to where no fine accuracy is required. I wasn't expecting great things of it when I bought it but I have to say it's been great. I even use it as a quick and dirty tram of the mill vertical head by sticking it on the spindle. Very good value in my opinion, it's not a Rolls Royce of mag bases to be sure but it works plenty good enough for me.

Paul.

Peter,

No worries, just let me know if you don't get sorted. You won't be disappointed with the machine if it's a good one, wouldn't be without mine! Very versatile bit of kit that opens up many possibilities for the home workshop.

Paul.

Peter,

I have what I believe to be an ordinal copy kindly posted to me by a forum member that I would be happy to scan for you (in the fullness of time when I can sort out the scanner connection screwed by a new router!).

If you want to pm your email address Inwill see what I can do in the next couple of days.

Paul.

Doh, how else are they going to guard their stocks of toilet rolls? They don't call it the Wild West for nowt!

Paul.

Chris,

As others have said Gordon's work is a very good reference on these valves. Also if you can get a copy an article written by Ross Bishop in Australia. I designed a pair of valves for my traction engine with guts as per their advise and they took a little tuning, but work just fine.

The problem you describe is unlikely to be a high water level especially if all you see is steam coming from the valve, if it was picking up the water you would A, get very wet. B the water level would drop in the glass very quickly!

Sounds like the hysteresis of your valve is wrong. Basically to get the valve to open at a predetermined pressure is quite a simple task of balancing the force on the 'valve' (ball) exposed to the boiler pressure by the seat area against the static load of the spring at that point. However as soon as the valve opens you get a larger area presented to the steam pressure and you now also have a dynamic component due to the flow / velocity of the steam past the seat. Thus to get it to reseat quickly with minimal pressure loss you need a good spring rate (load / extension) and the correct annular area around the valve for the steam to escape.

To fix your valve you may need either a higher rate Spring, an increase in annular area or a combination of both. Making and tuning your own valves is not difficult just fiddly on adjustments (no point tuning on air as it doesn't react the same with steam) and it can be a challange to get the correct / ideal springs.

Paul.

Jens,

A little difficult to be definitive on the small amount of info provided. However assuming the port face is conventional with 2 inlets one either end and the exhaust in the middle (rather than some balanced type of valve that sends the exhaust through the valve and out the top) try measuring the recess in the valves (exhaust recess) and comparing the width of the recess to the distance between the inner edges of the cylinder ports, it should be the same or a little more (exhaust clearance or negative exhaust lap). If the distance is less (not uncommon on fast running engines) you will be developing compression in the ends of the cylinders because the exhaust will close before the piston reaches TDC. With a compound it may be designed as such to maintain a higher exhaust pressure from the HP to deliver to the LP, I would expect the LP valve cavity to have clearance though to get the spent steam out as easily as possible.

Hope that makes sense and gives you some ideas?

Paul.

There is a really good example (Einstien) who in his day was in the 3%. Trouble is he was subsequently shown to be right. So those that chose to follow and support the 97% were hoodwinked! Exactly why I would prefer to weigh up the balance of the evidence and form my own opinion even if I don't have the expertise to follow the detailed complexities. In my experience those that refuse to answer questions but evade or deflect or has often been the case on this difficult subject become aggressive or belittling are following the crowd or are politicians.

Paul.

Thanks for that, that gives me a reference against those credited in the IPCC report and some further info to look at. As regards your statement "that you are wrong" what pray am I wrong about? I have not made any reference to an opinion either for or against and in my first post clearly stated up til recently I have no opinion, that has not changed. I will form an opinion eventually based on looking at all the arguments on both sides. There I think lies the problem firstly with your 'assumption' that by asking questions I have committed to denying climate change! Secondly with your statement "I'm not going to argue the points of Science. I leave that to the Scientific experts" so it seems to me you are quite happy to accept a study proclaiming 97% of those experts are right (and I am sure the study is perfectly valid) without even examining any of the evidence they offer to support their conclusions!

Neil's link later to critical thinking is more the process I wish to adopt. There is no need to argue with the experts but a critical review and broad understanding of the reasons for their conclusions doesn't as the article states require a PHD in climate science. I am afraid I was born awkward and not prepared to accept the opinion of 97% of my neighbour's that if I go past the top of the hill out of our town I will fall off the edge of the world! The first two para's on Niel's link and particularly the second really highlight the situation for me.

There is a lot to be gained and lost on following the current course, I am not yet ready to jump on any bandwagon.

So I will repeat my last question to you in a different way, is there anything else that really convinced you in your opinion (evidence based and referenced and not presented in the media) apart from the consensus of the 97%?

Paul.

Well if you read what I said.......... In fact relatively recently spans back to the beginning of this year (ie not decades!) and doesn't amount to a few minutes or hours on google but includes abstracts and some full papers. If you do the same looking at both sides you will see why I am asking the question, I haven't professed to know the answer I am asking if there is anyone who does and has specific undisputed evidence. As you seem to, maybe you would care to share? Can you list the 96 percent who are sure or even the alleged 4% that are not? With your obviously superior knowledge can you point me to a piece of authoritive research that includes explanations of the questions I asked?

What hard evidence convinced you?

Paul.

Dave,

I have long held your logic and evidenced based responses in high regard but on this subject I think you are a little wide of the mark.

I like your analogy with smoking as like climate change the initial suppositions were based on suppositions, personal experiences and opinion, later supported by definitive research and evidence. My feeling is with climate change we are still well in the supposition stage. During that stage with smoking there was no real government intervention into the activity until much later when research supported, even then there was no appetite to ban the activity altogether just tax it to the hilt (maybe justifiably on the basis of covering the cost to the NHS while still allowing a degree of choice) but that is an argument for another day!

The question I pose is beyond the suggestion and supposition that CO2 is definitively the culprit in this is there any actual verifiable evidence to back that up that definitively justifies taxing carbon to the hilt? Looking at your link it is to BBC news who have seen the JP Morgan report, quoting sound bites that support the story, I didn't see the whole report reproduced in full to allow the reader to form an opinion either way? Unfortunately I don't think even BBC news is free from bias. Also it needs to be considered that JP Morgan is a business and likely to bend to public opinion to protect its interests.

I am afraid I am not so adept at links as yourself but see if you can get this to work;

https://www.climate.gov/news-features/climate-qa/why-did-earth’s-surface-temperature-stop-rising-past-decade

This is a supposedly (we have to trust it is anyway) independent source of information. It concentrates on explaining the 'recent' often quoted by sceptics, slow down in temperature rise. This was an anomaly from the IPCC model and I am particularly interested in the line the model was re-calibrated. I have seen the temperature graph in other papers over a longer time span with CO2 overlaid and shows CO2 levels lagging temperature. Has this been falsified by the researchers presenting or is it true? I don't know! However if it is true and valid information if CO2 is the cause how can temperature be affected by a CO2 level not yet achieved? Are these versions of CO2 versus temperature also 'recalibrated'?

As I stated before I don't deny climate is changing but do we really know the reason? What has caused it to change before when CO2 levels were relatively stable? The above example of a pause over a decade or a slowing of the rate of rise is but a nano second when examining the history of the earth so hardly representative overall of a trend. When Greenland was green CO2 was lower, so why was it green?

The use of renewable energy is also to be encouraged, sustainability is of course essential but the pace at which change is being driven may still be felt by you in your lifetime. From November 2019 to date there has been a significant target suggested in my industry that cannot be met currently in the 10 years allowed by existing proven technology without adopting bio fuel (already noted as being land wasteful) and as demand increases that will get more expensive. The costs will inevitably be passed down the line. I am just looking for reassurance the world is still flat and it's not going to turn out its round! Whether people like it or not the notion of cheap renewable energy is a myth. Recouping the capital invested in a wind farm for example is a long term return and maintaining / overhauling the equipment to keep it going is still not cheap! Those putting their money in to any energy project, sustainable or not will want their returns in spades! I suspect JPM will be keeping a foot in all camps although not so prepared to advertise some of them!

Paul.

Mine runs at 90psi too. Should be dictated by the pressure test cert but what if it's not got a cert! Another of the vagaries of model drawings! I seem to remember the only indication of WP on my Juliet drawings purchased 40 odd years ago and now too faded to read was a sketch of the pressure gauge with the needle at 90!

Paul.