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Member postings for duncan webster

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

Thread: Saving the Planet or is it ?
05/10/2021 12:50:34

Going back to SOD's latest (03/10), if I just take 3000 as the expansion ratio of a coal fired set, that is 3 stages of 14.4 ratio, so the IP entry is 208 psi. I do know this is a bit crude, but it shows that somewhere along the HP set the pressure has dropped from 3000 psi to 1000, and probably not very far along. It should therefore be possible to change the blading in the HP or even replace it complete to work on 'nuclear' steam. I will take some convincing that a single SMR boils more water than a big coal fired set, so the condensers and cooling towers should be re-useable.

Yes the power output of my conversion would be lower, and replacing the whole setup might be a bit more efficient, but the depreciation on the existing turbines, alternators, cooling towers etc is over, and they are not cheap.

Thread: Recommend a grade of steel
05/10/2021 11:39:59

pump area = 0.307, so load is 0.307*120=36.8 lbs, add 10% to allow for pressure drop in clacks and friction, say 40.5 lbs. Presuming the pin is in double shear the area is 2*0.25^2*pi/4 = 0.098, so the shear stress is 40.5/0.098 = 413 psi, which is quite low. Yield stress of even EN1A is 230 MPa, 33400 psi, and BS2573 would recommend 37% of this (as allowable shear stress, so you are well in. The bearing load is a different matter. The projected area is 3/16*1/4 = 0.047, and so the bearing pressure is 864 psi, which is on the high side, so bronze bearing and case hardened pin would be my choice. Good provision for lubrication as well. Avoid notches/sharp edges as much as possible, and if it has a thread on the end avoid case hardening that. There are a couple of ways of doing this. One is to apply the case compound before you cut the thread, allowing it to cool slowly, then cut the thread, then get it red hot and quench, the other (which I've never tried) is to copper plate the bit where the thread is going to be. Cooling a small part slowly is not that easy either, trial and error, if you can still machine it it's ok.

I know that silver steel is the go-to material for model engineers, but in well over 40 years in industry I've never seen it specified for a machine part, except for punches, dies, trigger blocks etc for which a very hard part is needed

Thread: Antikythera Mechanism
05/10/2021 00:15:48

Measure the chord from 41 to 79,and the offset to the middle hole 60, then you can work out the radius and the angle subtended, which then let's you work out how many holes in a full circle. Absolute dimensions don't matter as long as there is no distortion of the image.

I'd probably import the image into cad to do the measure but there might be a better way

Thread: Recommend a grade of steel
04/10/2021 21:17:05

Only if you divulge the load it is going to see. What is diameter of pump ram and boiler pressure, diameter of pin and length of bearing?

Thread: Tool Chest
03/10/2021 22:32:56

About 30 years ago I was working on a large construction site away from home and had to rent a flat during the week. No problem heating thought I, there's loads of wood from packaging, pallets etc being thrown out every day, so I arrange to fill the boot with wood and take it away. Why are they all smiling? Anyway, I sawed it into manageable pieces, and got a little blaze going with with twigs from the woodland, then apply some of my bigger bits. Fire went out almost immediately. Tried again, several times. Turned out all wood coming onto site had to be treated with something which when it got hot gassed off and put out the fire. Ah well, sawing it all up kept me warm for one night anyway.

Thread: Clock Stand with a difference
02/10/2021 13:04:43

To use Phil's method you'd have to move the cross slide in/out, so unless the cross slide is truly square to the axis it won't work. Many lathes are set to machine a very slight concave on facing. You could clamp a parallel to the base so you don't have this issue, but then you're reliant on the parallel. Of course you could do it twice, second time with parallel reversed, but it's getting to be a lot of work.

Thread: cutting spur gears on a mill
01/10/2021 14:07:20

But you must remember that the OP started from a position of knowing very little about gears, and judging by his latest post has not changed his position. Anyone who does know something is dismissed as an armchair engineer, and all the money spent by industry on machines to make properly shaped accurate gears has been wasted. Redefining accepted terminology is not really helpful

Thread: TIG welded copper boilers
29/09/2021 17:46:14
Posted by Phil H1 on 29/09/2021 17:05:03:

I am not a welder but I agree that It is about time we moved forwards on TIG. Just a quick google says that TIG has been around since the 1940s. So it might be new to the Victorians who first built steam locomotives but it is not a new process.

Phil H

Agreed, if you turn up with a commercially built boiler and a proper welder cert for the bloke who built it there should be no problem, time for some SFED guidance. If it's commercially built then whatever has replaced CE mark will require welder certs, so there should be no issue. It only costs pennies to photocopy the cert. Problem comes with home built.

The big railways used to weld repair copper fireboxes with oxy acetylene. That must have been heroic. I believe they had one bloke inside and another outside to get a balanced setup. Bags I be the outside man!

29/09/2021 15:42:28

Not wishing to stir up a hornet's nest, but I think anyone contemplating welding their own copper boiler should speak to their club's boiler inspector first. The SFED rules on testing say

An Inspector acting as a competent person who carries out an examination under the Written Scheme of Examination shall have such sound practical and theoretical knowledge and actual experience of the type of system which is to be examined as will enable defects or weaknesses to be detected which is the purpose of the examination to discover and their importance in relation to the integrity and safety of the system to be assessed

which implies that the inspector should know about copper welding and possible defects. Not all will. Don't get me wrong, welded boilers are fine as long as stuck together by someone who knows what he is doing.

Thread: Indexing Plate
29/09/2021 14:15:58

Arrange a second pin so that it is at half space, then use them alternately, no drilling needed

Thread: Saving the Planet or is it ?
29/09/2021 13:30:40

No reason why several SMRs cannot work in parallel to feed one big turbine. Plenty of cotton mills had more than one boiler feeding one engine.

The idea that we are going to build new coal fired stations is for the birds

29/09/2021 11:36:31

There are still several coal stations not demolished, but it would take government action to prevent their demolition. If mothballed they probably still have to pay business rates, and cannot be sold for housing. There are also lots of nuclear stations coming to the end of their lives, replacing the reactors with SMRs would give them another 40 years, and an income stream to pay for the decommissioning of the old reactors. With the current crop of politicians of all hues I'll not hold my breath

Thread: Hardening gauge plate (O1)
29/09/2021 00:27:58

They used some stuff called Ucon for quenching where I worked many years ago. It is water based with some organic compound dissolved in it. When it gets hot (close to the job you've jusr dunked) the organic comes out of solution and coats the job, so you get a sort of oil quench but no fire risk. Probably stunningly expensive and only available in 50 gallon drums

Thread: TIG welded copper boilers
28/09/2021 17:16:24

Most copper sheet/tube on sale to model engineers will be C106, which is claimed to be OK for welding

Thread: Hardening gauge plate (O1)
28/09/2021 13:20:02

This little book tells you all you ever needed to know about heat treatment

Tubal Cain

this is the real English TC, not the American pretender.

Thread: What do you think of this con
28/09/2021 13:10:04

Our local supermarket prices bags of onions etc as per kg, but loose items as each, and as there are no scales you can't compare. I think SWMBO would blow a gasket if I took my own weighing apparatus. Also watch out for giant boxes of washing powder being more expensive pro rata than small.

Thread: Chatter/finish problem
28/09/2021 13:04:58
Posted by Nigel McBurney 1 on 27/09/2021 19:24:02:

Have a look at the workholding ,is the bar held firmly in the chuck jaws? From the photo the new chuck appears to be a self centering 4 jaw chuck, not the best way to hold work, I would never dream of using this type of chuck they are ok for woodturners.........

Never understood 4 jaw self centering chucks. As they work on a scroll all 4 points of the jaws are unlikely to be truly on a circle, and not all round bar is perfectly round, so chuck is likely to just grip on 2 opposite jaws. That's why self centering chucks traditionally have 3 jaws, 3 points always define a circle, and will cope with slightly out of round bar

Thread: Saving the Planet or is it ?
28/09/2021 11:13:40

Why would we need to replace the turbines and generators. Might need to reblade the turbines, but generators, condensers, cooling towers should be reusable.

Nigel makes an excellent point about Tay bridge

28/09/2021 00:38:30
Posted by Kevan Shaw on 27/09/2021 22:47:06:


there are other options including underground gasification of the vast remaining deep coal reserves under the UK. Nuclear in its present form is not a good idea as evidenced by Three Mile Island, Chernobyl and Fukishima.

one point that is being roundly ignored is the inefficiency of power transmission. Between 40% and 60% power is lost between power generation and socket outlet. Big scale generation is not as efficient as it might seem. ........

Underground gasification produces just as much if not more CO2 than digging up the coal and burning it in a power station.

Burning coal kills a lot more people than nuclear per MWhr, mainly widely spread out due to pollution, and of course nuclear has a much lower CO2 emission. Very few people died as a direct result of Three Mile Island and Fukushima

according to Wikepedia

Although overall losses in the national grid are low, there are significant further losses in onward electricity distribution to the consumer, causing a total distribution loss of about 7.7%.[29] However losses differ significantly for customers connected at different voltages; connected at high voltage the total losses are about 2.6%, at medium voltage 6.4% and at low voltage 12.2%

I do wish people would check their facts.

The Vajont dam disaster in Italy killed at least 1,910 people, so even hydro power isn't completely safe. This is well worth a read deaths per TWhr, shows nuclear is actually relatively safe

27/09/2021 17:31:01
Posted by J Hancock on 27/09/2021 16:03:11:

Agreed, it couldn't happen to ' us' with a separate public water supply.

But , IF the aquifer that public water supply is being drawn from is 'contaminated' then , no potable water for anyone in that area.

Want to risk it ?

But large areas of the country don't get their water from aquifers, so why can't we get shale gas from there? We will need to burn gas for a long time yet even if the plan is to phase it out eventually, so we might as well use our own rather than import it. All depends on the pay back period for drilling the hole, but I bet that isn't all that many years. We could start by allowing people to fit energy efficient windows and insulation in listed buildings etc, which is banned at present according to the press

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