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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: 24v dc motor powering a drill press
22/03/2019 00:23:22
Posted by John Haine on 21/03/2019 22:21:34:

Puzzled. Plate says 24v 11 amps. 24x11=264watts, not 950! Something doesn't compute.

perhaps it's 110A, and motor is inefficient, 2640W in, 950 out. Must say I agree putting a 5400 rpm motor on instead of 1500 (probably) doesn't make sense

Edited By duncan webster on 22/03/2019 00:46:40

Thread: The Workshop Progress Thread 2019
21/03/2019 15:48:58

Not my idea, Mr Tredenick from Australia, as featured in MEW Feb 19. How to stop the jaw lifting on your Record drilling vice. Only took an hour or so

img_3538 (small).jpg

img_3539 (small).jpg

Edited By duncan webster on 21/03/2019 15:50:36

Thread: contact T Fletcher
21/03/2019 12:23:52

At the doncaster exhibition I took photos of a CNC rotary table made by a Mr T Fletcher. Unfortunately I didn't make a note of which club he was from. I'm now making one using the same keypad, display and box, so it would be useful to contact him to see how he arranged the insides.

Anyone recognise the photos or the name?

img_3148 (small).jpg

img_3147 (small).jpg

Thread: Milling curves
21/03/2019 00:33:57
Posted by Roy Garden on 21/03/2019 00:14:39:

1) I'm lazy and fairly inept, so that's a non starter.
2) Better but see 1)
3) Which one ?

as you only want a 1" radius a small one will do, but might be restrictive for future jobs. I have 4" and 6" and use the 4" most, but anything you can do on a 4" you can do on a 6". However I'm not sure how a 6" fits on your milling machine, others will advise.

21/03/2019 00:09:45

several suggestions

  1. If you only want 'approx', file it
  2. work out the required co-ordinates and plunge the cutter through multiple times, then smooth it off with a file
  3. buy a rotary table
Thread: How Are Letter / Hallmark Punches Made?
20/03/2019 23:58:10

At £10 for a set of 36 they ain't using files and gravers

set of stamps

Thread: Resilient motor mountings/bearings
19/03/2019 10:51:52

If you're ok with working with mains electricity, it is easy enough to rig up a system of buttons/relays to make it run without the centrifugal switch. Might not be worth the effort, but I could sketch out the circuit if it helped.

Thread: ER25 or MT2 Collets
18/03/2019 14:26:12

+1 for R8 then you can use R8 collets for big cutters and ER chuck and collets for little ones, perhaps using a smaller ER series as well. R8 are much less likely to get stuck, and is standard on Bridgeports so widely available

Edited By duncan webster on 18/03/2019 14:27:39

Thread: Potty:- Helping Dad Grasshopper Engine
17/03/2019 20:47:29

Stew, I've joined the Gadarene rush and sent you a pm

Thread: Its nearly there !
17/03/2019 18:22:40

Paint doesn't make it work any better, and it looks pretty good to me anyway.

Rather than a clutch have you considered a 3 phase motor? Much smoother running and much less troubled by stop/starts. Could easily be cheaper as well.

Edited By duncan webster on 17/03/2019 18:23:56

Thread: Steel identification
16/03/2019 21:22:46

What size do you need? Someone might have a bit kicking around. I'd be surprised if EN8 woudln't do, there's not that much difference

Thread: What is this grinder?
16/03/2019 15:42:02

That's just silly money, I thought I did well getting £70 for mine. At that price you could get a Worden, granted not built like a battleship, but more functionality

16/03/2019 00:31:29

It's exactly what it says it is, a sort of industrial Worden grinder. Most of them are 3 phase, and they are very heavy. I had one which I converted to single phase but it was too heavy to keep moving around. The original size wheels are as easily available as rocking horse droppings, but I've no doubt you could alter the nose arrangement.

Edited By duncan webster on 16/03/2019 00:31:43

Thread: KX1 CNC Mill Clearance Offer
15/03/2019 16:46:25

You happy men with your new milling machines will be in want of a stand for it, see ad I've just placed in classifieds

Thread: Tangential tools ?
15/03/2019 00:14:24
Posted by John Haine on 13/03/2019 09:47:10:
Posted by duncan webster on 12/03/2019 23:20:14:

........ I'm going to make one for my little Cowells in the fairly near future

..........

Duncan, this might be interesting if you haven't seen it - for the Unimat rather than Cowells but similar size.

Thanks John, that looks just the thing. I might even have a bit of cast iron lurking under the bench to make it out of, but I'll need to mout an expedition, workshop is a bit of a tip at the moment. The swing over the saddle on the Cowells is 2" (at least mine is), so I think I make it a tad shorter, but otherwise it's all there

Thanks again

Thread: What gas for a Centaur?
13/03/2019 14:22:51

There was an article in ME about running engines on gas not that long ago. I seem to remember that it's not as easy to get the mixture right as using petrol or coal gas. No doubt someone will come up with issue number

Thread: Model Turbines
13/03/2019 04:31:18

Martin and Turbine guy, I've pm'd you both

Thread: Tangential tools ?
12/03/2019 23:20:14

Well I must disagree, I wouldn't be without mine, it makes sharpening so much easier. However if starting again I'd make one, plenty of ideas on Google. I'm going to make one for my little Cowells in the fairly near future

Not the tools for loco wheel castings tho, I use brazed carbide for that, ground to he correct radius for the flange/tread interface

Thread: Model Turbines
12/03/2019 11:28:58

Mea culpa, I've got it wrong! If you are stuck with a low blade speed, there are advantages in the ejector idea, but you'd still be better off with steam only and very high speeds

Blade force is mass flow rate * change in whirl velocity, so increasing the mass flow rate for a given blade speed increases the blade force. If for steam only we have a mass flow of M kg/sec and a blade speed of B, the blade force is M * B * 2, and the power output is force * blade speed = M * B^2 * 2

Mixing in an equal mass of air, the mass flow is 2M, for the same blade speed, the blade force is 2M * B * 2, and the power is 2M * B^2 * 2, so there is an advantage.

You're still better off with higher blade speed tho as the change in whirl velocity increases as well.

11/03/2019 21:04:20

I'm not sure this ejector idea works. The force exerted on the blades is the momentum flow rate * the change in whirl speed (see below). For single stage impulse the change in whirl speed is roughly twice the blade speed (up to the limit of blade speed = half steam speed). The mix of air and steam from the ejector has the same momentum flux as the steam alone, so for a given blade speed the blade force is a constant. However, the power output of the turbine is blade force * blade speed, so the for a given blade speed the power is the same. However, if you can physically achieve it, you can have a much higher blade speed for steam alone, hence higher power.

Newton's second law, usually expressed as F=m*a can equally well be expressed as F = rate of change of momentum

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