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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: 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?

09/07/2018 16:49:51

and I thought I got easily distracted!

Just had a go with some indeterminate mild steel with my tangent turning tool. Found I needed to set the approach angle to deflect the swarf away from the tiny little bit left, otherwise the swarf wiped it out. As others have said, sharp, plenty of rake and bang on centre height. Reduced from 1/4 diameter in 2 passes.

Edited By duncan webster on 09/07/2018 16:50:21

09/07/2018 10:30:51

now I'm confused, I thought the problem was to drill a 0.3mm hole, in which case why are you turning silver steel down? If you are talking about drilling it, why use silver steel, EN1A would be plenty strong enough and drill/turn a lot more easily.

Thread: Aircraft General Discussion
08/07/2018 23:53:52

so how about a vee 20, not much use in an aeroplane I suspect


Thread: How can I drill a deep, non-standard, small diameter, hole?
08/07/2018 23:45:57

A different approach. Epoxy the carbon fibre through a small bead (jewellery type), then when the epoxy has setpass it up through the 2.5m hole and with the bob resting on a flat surface, arrange a pulley above, pass the fibre over the pulley to a small weight to keep it under tension and shift the bob around to get the thread central. Then fill the 2.5mm hole with potting resin. It's a bit permanent, but could always be drilled out

Thread: rail expansion
08/07/2018 18:57:13

We are on plastic sleepers. Using a thermocouple on the rails you can tell when the sun goes behind a cloud. Today was quite windy, but rail temp was ~38C, we've measured 50+ on windless days.

08/07/2018 16:53:33

We've been having trouble with our signals in this recent hot weather. The one which kept on having intermittent fault is the one exposed to full sun from about 1:00pm. Of course this doesn't happen when I'm there, so I have to rely on verbal reports. Why can't people write it down with all relevant info when it happens? Come Wednesday I check the gaps in the track circuiting, a bit small but definately there. Just to be safe I ran a saw down the gaps. We measured the temperature inside the signal box itself. Over 50C. This is pretty warm so I made a sunshade (baco foil and plywood as a trial). Signal now much cooler, but as soon as the sun came round, the problem came back. The gaps had closed up again, it looks as if that whole section of track is somehow ratcheting itself down the hill.

Has anyone else come across this, if so how did you cure it? We are going to experiment with insulation between the rail ends, and perhaps some kind of link between the rail and the bolted down sleepers to stop it moving at that one point.

Edited By duncan webster on 08/07/2018 16:54:18

Thread: Powered Bogies
08/07/2018 16:42:16
Posted by Perko7 on 08/07/2018 13:31:20:

Sorry to admit i'm no expert in these matters, my only knowledge is what i learnt doing engineering at uni too many years agofrown. There is a download on the SMEX site to calculate rolling resistance for a train based on various inputs, which can be used to estimate the power required to pull that train. As an example, a loco weighing 100kg towing a train consisting of 2 wagons each weighing 100kg, with each wagon carrying 6 adults weighing 80kg, at 10km/hr up a 1:50 grade would require a drawbar pull of about 27kg assuming relatively free-rolling wheelsets. The maximum drawbar pull available from our 100kg loco would be about 35kg so the train is within the loco haulage capacity. The power required to accelerate our train to that speed is a different calculation that is a bit more complex. Basically, more power = faster acceleration, up to the limit of our drawbar pull which is a function of loco weight and the adhesion factor for steel wheel on steel rail. I would look at what others have used in practice and found sufficient.

can you post a link to 'SMEX', google doesn't find it? The figures you quote seem a bit low but in the right ballpark. The gradient resistance for your 1260kg (100+2*100+12*80) train is 25.2 kg, leaving only 1.8 kg (1/700 of train mass) for rolling resistance. This is very low, you can't freewheel down a 1:700 slope, you can down 1:100. It makes very little difference as the gradient resistance dominates.

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