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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: Metric micrometer what t buy?
18/11/2019 00:33:09

Is it just me that finds metric micrometers a right royal pain. The number of times I've made something exactly 0.5mm wrong is legion. I now tend to use the digital caliper to get near then switch to the mic. Never had this issue with imperial.

Thread: What Did You Do Today 2019
17/11/2019 23:29:30

That's an easy way?? 5 minutes with a craft knife and a punch would have made 2 gaskets. But there again I am an old ****

Thread: 5 speed Hacksaw
11/11/2019 23:06:21

I do all my sawing mandraulically, it goes slow, very slow, very very......Ok you get the idea.

The worst ever was a 10" I beam for a house extension. I scrounged it for free, but it was too long

Thread: Black anodised steel????
11/11/2019 23:03:15

Parkerising is one method of bluing and applying rust resistance


If anyone has a recipe for the gloop you heat the component in I'd be interested. I've got one for bluing which sounds distinctly dodgy, boiling solutions at well above 100C

Edited By duncan webster on 11/11/2019 23:03:45

Thread: Suitable metal / enclosure for project
11/11/2019 00:22:51

Do you need to think about motor cooling air? If it's metal make sure it is earthed

Thread: How does someone gauge the power of a DC or AC motor?
08/11/2019 00:24:17

Speaking in complete ignorance (as usual) but 400 rpm sounds very slow for a 50 mm diamond grinding disc

I have a 100mm CBN disc and the manufacturer recommended 3000 rpm

Thread: injectors
05/11/2019 15:19:31

If it's time for silly questions, could you take the overflow from the injector back above the level of the tank so that it didn't drain the tank. I realise you wouldn't then be able to run water through the injector to cool it if it got too hot

Thread: Track laying
04/11/2019 22:36:10

Calcs have half the weight at mid span on one rail. I've no idea what defection is acceptable, but I feel that 20mm is far too much. It will be more when you allow for loco and truck, but not pro-rata as not all the weight is at the centre.

The yield stress of ordinary flat bar is 275 N/mm^2, I'd not go above half of that in service

If you double the depth you 1/4 the stress and 1/8 the deflection, but 2 flat bars spaced apart don't have all that much torsional rigidity. Our track is supported on 3" channel. Very much overkill, but it's the smallest channel readily available. Ex railway point rodding was good stuff for this application, but is as rare as rocking horse droppings nowadays. Hopefully someone with actual experience of a lighter track construction will chip in

Drilling holes won't make a lot of difference if they are on the centre line (Neutral axis), but it will be a difficult issue to make curves, the distance twixt holes on the outer rail will be greater than the inner..

Edited By duncan webster on 04/11/2019 22:37:18

04/11/2019 13:20:12

Super-elevation, raising the outside rail relative to the inside like a banked racetrack (eg Brooklands). This reduces the tendency of the loco to topple over on corners. The centripetal force required to make a mass go in a curve is mass * velocity squared / radius (F1 = M*V^2/R). The ^ sign means 'raised to the power of'. The force acting downwards on the mass is mass* gravity (F2 = M*g). If we add these forces together we get a resultant force Fr = sqrt(F1^2 + F2^2) and the angle of this force from vertical is arcTan(F1/F2). If you tip the track at this angle the passengers will not perceive any side force, like leaning a push bike on a corner. However if you come to a standstill there will be be a tendency to topple inwards, so it seems reasonable to use half this angle, then the perceived out-force when going at speed round the bend is the same as the perceived in-force when stationary.

Speed in metres per second, radius in metres mass in kg, although this actually cancels out. g is 9.81 m/s/s. If you really want to do it in mph and feet we need to introduce all sorts of silly factors.

If a 14st man sat in the middle of your proposed span the track would deflect 20mm, which I suggest is quite a lot, and the stress would be 266 N/mm^2 which is definitely a lot, and we've not allowed for the loco , truck and passengers yet. Here's screen dump of the sums


h     25.0 mm  
b     6.0 mm  
second moment of area     7812.5 Mm^4  
section modulus     625.0    
young’s mod     207000.0    
span 60 in 1524.0 mm  
load 98 lb 44.5 kg  
      436.5 N  
deflection     19.9 mm  
bending moment     166306.5 Nmm  
stress     266.1 N/mm^2  

Edited By duncan webster on 04/11/2019 13:20:53

Edited By duncan webster on 04/11/2019 13:22:30

Edited By duncan webster on 04/11/2019 13:23:59

04/11/2019 09:41:15

We have 30ft radius curves on 5"g, no trouble even with big locos, but we have gauge widening so it is 128mm on the curves, 127mm on the straights. You also will benefit from super-elevation. Depends how fast you are intending to run, but work out the ideal for running speed then halve it, because you are going to be stationary on it at some time.

The wheelbase * 20 figure should be fixed wheelbase I think, bogies/trucks don't count

Thread: Help with FML reading lamp please
04/11/2019 00:40:08
Posted by norman valentine on 03/11/2019 19:57:53:

Why bother with it? You can buy a ' sewing machine light' on Ebay for less than £5. They are fantastic value for money.

I'd be very careful buying a mains powered 'sewing machine light' from other than a European supplier. I bought one from China and fortunately opened it up before I plugged it in. Potential death trap, very skimpy insulation, not double insulated and non earthed metal bits.

If it is a 5v device driven off a wall wart It is probably OK, but check the wall wart is CE marked. If it is mains and comes with a non BS1363 plug don't touch it (literally). I've even been supplied with kit by a UK supplier which had a 3 pin plug with no fuse, hence non compliant

Thread: Boring bar toolpost.
04/11/2019 00:28:57

If you get chatter on a long boring bar try winding lead or solder wire round it loosely. It rattles about and damps out the vibration.

Thread: Cutting stainless steel rod. Bandsaw or chopsaw?
04/11/2019 00:23:32

When I was still being paid not to know what I was doing we did a series of tests to increase the life of band saw blades cutting Austenitic stainless, in particular heavy wall pipe. Using cutting lubricant, Rocol or Trefolex or similar, massively increased blade life. Running a bit slow helped, and keeping it cutting was essential. Once it rubs you've had it.

Thread: Additives to kerosene for degreasing?
30/10/2019 20:06:00

Gunk is £9.35 for 5l from Amazon, free delivery if you've got Amazon Prime. For smaller parts the dishwasher does a remarkable job, just wait till domestic authorities are out for the day

Thread: Stephensons Valve Gear
28/10/2019 16:57:43
Posted by SillyOldDuffer on 28/10/2019 12:16:40:

Not an engine builder myself, and am prepared to have my views questioned. But they might attract better answers!


For a Stephenson Gear, it might be worth using EN8 (a strong mild-steel) rather than EN1 to resist buckling.


buckling is governed by section shape/size and young's modulus, not by yield strength, and just to be pedantic (who me) I would call EN8 a carbon steel

Thread: Mills with tilting heads..?
28/10/2019 00:02:01

Friend of mine who has several Bridgeports reckons they can machine any angle apart from a right angle. When setting up, set it ever so slightly off square to the x axis, then you don't get trail marks when feeding in one direction. When I say ever so slightly I mean just that,

Thread: What to do with a stationary engine
27/10/2019 23:57:32

There was an old guy in our village back in the 60's who had ridden Scott Squirrels back in the 20's/30's. He had extensively modified his, one of the mods being water heated handlebars. He also claimed to have done 2 wheel drive on a solo and 2 wheel drive on a combination (easy by comparison) but I never saw any evidence. Probably helped that he had a business making oddball machinery for the textile industry, so plenty of machine tools. It's houses now.

Thread: Silicon piston ring
26/10/2019 21:58:39

if it's cold water then you don't need silicone, nitrile will do and is more easily acquired. For a dynamic application, especially if a completely tight seal is not needed, then 5% squeeze is enough. Any tolerance to increase this

Thread: Mastiff
25/10/2019 23:38:51

what are you going to use for a transmission. Electric?

Thread: portable LED floodlight , power source ?
24/10/2019 23:19:17

Glad it's fixed, but i'd take the old ones off the bonfire if I were you, one of those going off with a bang could take your eye out, and the contents are probably most unpleasant

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