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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: Pickle
21/07/2018 20:41:13

I find that citric works a lot better if you heat it up. For small items I pour some into a glass jug and microwave it, before putting the brass bit in. You still ned to use scotchbrite, but just to wipe away the deposit. As others have said a lot safer than sulphuric

Thread: Balancing full size locomotive wheels
21/07/2018 20:23:11

As a follow up to my article in ME 4586 I've written a second chapter, which goes into cross balancing and 3&4 cylinder locos. I bet you can't wait!

Thread: Solid fuel IC engines
21/07/2018 20:06:08

Or a coal fired Doodlebug


What the first link doesn't cover is coal fired gas turbines, on which a lot of sweat has been expended. What you do is replace the combustion chamber with a heat exchanger so that the hot gasses from the coal fire heat the pressurised air from the compressor. All very nice in theory, but ash deposits on the heat exchnger sounds like a bit of a problem to me. Challenge for the hot air engine men

Thread: Balancing full size locomotive wheels
21/07/2018 11:57:30

To partly answer SOD, a typical 5"g 0-6-0 might weigh say 150 lbs, so it's axle load is 50lbs. A fully loaded riding truck (5 off 12st men+truck) could be 1008 lbs on 4 axles, so 252 lbs axle load. Who cares what the loco axles are doing. The loco wheels are probaly bigger as well, certainly on heavier locos, which helps to reduce the wheel/rail contact stress. However, I at least find shuttling annoying, the connecting chain can be seen to got tight/slack at a fairly high frequency on some locos

20/07/2018 23:22:16
Posted by Paul Lousick on 20/07/2018 13:28:12:

Before computers, wheels only had a static balance using a pair of horizontal blades standing on edge. The sharp edge of the blade has little rolling friction. Not perfect but good enough for slow rotaing shafts and wheels.

I remember that car wheels where balanced by placing on a jig with a pivot point in the centre and a spirit level bubble used to check balance.


The GWR certainly had something better than knife edges, but I'm not sure how it worked.


It was definately pre computer, even the modern ones built by the model gas turbine lads don't always employ computers. I think you can do it with valve amplifiers and a cathode ray tube, they were a commercial product by the 1920's

Thread: DC motors
20/07/2018 08:51:50
Posted by Neil Wyatt on 19/07/2018 19:47:23:

If I recall correctly electric motors in parallel will tend to balance current to run at the same speed, with motors in series if one is stalled and the other is free the free one will overspeed.

OP says they are coupled together mechanically, so they have to rotate at same speed

Edited By duncan webster on 20/07/2018 08:52:17

19/07/2018 18:56:47

As they are mechanically coupled they must rotate at same speed, so I can't see any problem running them in series, provided they are the same type of motor. As someone above said, plenty of full size electric locomotives had motors in series for starting, then switched to parallel for higher speed.

Thread: How to machine an ellipse
18/07/2018 15:53:37
Posted by Bazyle on 18/07/2018 13:39:08:

If you are after a curve rather than a true ellipse have a think about a steam engine connecting rod. One end goes in a circle and the other end goes in a line. In between you get points following a curve (asymmetrical). A little ingenuity with a rotary table on a mill should achieve the required effect.

angularity of the con rod results in an asymmetric ellipse, sort of egg shape. If the con rod were long enough it might not matter.

Thread: Bushes Jim, but not as we know them.
17/07/2018 22:39:31

What you want is stump killer. The stuff I use is diluted with old engine oil, then drill some big holes say 1" diameter * 3" deep in the stump and fill them with the mix. However If you're goiung to build in brick or blocks with conventional footings you'll still need to dig through the root system to get proper footings

Edited By duncan webster on 17/07/2018 22:41:14

Thread: How to machine an ellipse
15/07/2018 22:16:40

If making a gland then the end radius and overall width are givens, and possibly do not approximate to a true ellipse. If you want a good approximation then proceed as follows

draw a box with the major length of the ellipse along x axis and the minor length along the y

from the end of x draw a line up at 60 degrees to the x axis o'clock)

from the top of the y draw a line at 15 degrees below the x axis (just before 9 o'clock)

from the intersection of these 2 lines draw a line down at 60 degrees below the x axis to intersect the y axis.

where this line crosses the x axis is the centre for the end radius

where it crosses the y axis is the centre for the top radius

all shown on picture.ellipse (small).jpg

Thread: Rear toolpost for parting tool
15/07/2018 21:53:23

I'm on the brink of making a rear toolpost for mine, but the brink is getting crowded. If you are using the tapered HSS blade, then as you grind the top to get back rake, the cutting edge gets thinner. Seems to me better to angle the whole blade then you only grind the front edge. However this is all theory as I haven't made one yet.

I think it is in accordance with GHT articles from the 70s/80s

Edited By duncan webster on 15/07/2018 21:53:48

Thread: New application of Mole Grips
13/07/2018 13:34:55
Posted by Martin Connelly on 13/07/2018 12:34:11:

This reminds me of a day in my youth when waiting at a bus stop to go to school. A bus went past with the driver wearing an open face crash helmet, goggles, scarf, heavy coat and thick gloves. He was driving a bus (a Leyland Atlantean) with absolutely no bodywork on it. This was in the late sixties or early seventies so he had no seatbelt and nothing around him to stop him from coming off the seat.

Martin C

Used to be a regular sight in the north west. Chassis made by Leyland in preston then delivered all over the country for coachbuilders to ply their trade. Probably less unsafe than riding a motorcycle, but that doesn't mean it's a good idea

Thread: Is this really a clock?
13/07/2018 11:59:35

According to the clock maker's definition, if it gives audible indication of hours it's a clock, if it just displays the time it's a timepiece. However, buried deep inside many microprocessors is a device which gives out a stream of pulses at millions per second and this also gets called a clock, even though it is hopefully silent

Thread: another mystery object
13/07/2018 11:49:15

Thanks for4 the replies chaps, I looked up the resistance/temperature chart for a PRT100 and then immersed the end of the probe in boiling water. It behaves as predicted. Now I know what it is I'll have to think of a use for it! Bit OTT for a workshop thermometer. Perhaps I'll have to fit a feed water heater to my loco then I'd have something to measure.

12/07/2018 15:42:32

Thanks Trevorh, to check your suggestion I connected it to a multimeter set on mV and plunged it into a nice hot cup of tea, no output. However if I set it on ohms it measures 110 at room temp and increases by a few ohms at tea temp.

Edited By duncan webster on 12/07/2018 15:42:55

12/07/2018 14:53:45

Anyone know what this is? I'm guessing it is some kind of temperature sensor. It has ND/LS/89 engraved on the side, I've tried Google, no joyimg_3317 (small).jpg

Thread: rail expansion
12/07/2018 14:50:01

img_3315 (small).jpgFollowing Brian's advice we've fitted fibreglass board spacer between ends of rails on worst affected spot, will keep an eye and do any more if successful. I've also made a sunhat for the signal which gets full sun, that was getting up to 50C+ as well. Note after you've cut the SS sheet with an angle grinder, wearing safety boots, overalls, goggles, gloves and making sure it's clamped down, don't then pick up the cut off pieces with bare hands, not unless you want a trip to A&Eimg_3314 (small).jpg

Thread: Political views within the forums
12/07/2018 14:15:26

most of the stuff being objected to is paranoid conspiracy theory, let's have no more

Thread: Advice regarding Meddings M10 Bench Drill please
10/07/2018 10:15:06

from the link it looks like a flat belt drive. If so you can use poly vee or toothed belts inside out. I suspect poly vee are cheaper.

Thread: How can I drill a deep, non-standard, small diameter, hole?
09/07/2018 17:52:16

Going back to SOD's original, I've often wondered how you strike a centre for a 0.3mm drill? Do centre drills go down that small?

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