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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: Tube Seam
16/02/2019 11:02:54

If you do have a go at a barrel with a seam then you'd be better with a butt strap rather than a joggled joint. Not only is it stronger it's also easier to make

Thread: How many threads please?
12/02/2019 23:46:14

All these rules for depth of thread are aimed at developing full strength, but you don't need anything like full strength on this application. Assuming 80 psi steam, you have 2.2 lbs force. The pitch diameter of the thread is near enough 11/64" and the thread length is 1/8" (again near enough), so the area of thread in shear is 11/64 * pi * 1/8 * 1/2 = 0.034, so the shear stress is 65 psi, which is not a lot. Go for it, use sealant and don't over-tighten

just for interest, a 1/4" bsw nut is only 0.2" thick, 0.8D, your 3mm is 0.63D

Edited By duncan webster on 12/02/2019 23:50:39

Thread: The Workshop Progress Thread 2019
11/02/2019 20:09:39

A bit of progress on motion plates, how can it take so long to drill and tap 12 holes? Not the easiest thing to hold together with the bits in the right place I supposemotion brackets assembled (small).jpg 

Edited By duncan webster on 11/02/2019 20:10:09

Thread: Thick walled copper tube
11/02/2019 19:59:12

If using an external feed I'd put it right next to the boiler under the cladding to keep it hot. I've seen at least one loco at our track with water droplets coming out of the blower as the feed pipe was running in fresh air. Two of my locos are done as suggested successfully

Thread: anyone recognise this milling machine
10/02/2019 21:45:09

Thanks chaps, I even managed to find a spec sheet in an old thread, so it's going on the classifieds in the next few minutes

10/02/2019 21:28:50

I'm going to advertise it on behalf of a friend who is having to give up due to ill health. It would be easier if I knew what it was. I know it's from Chester, but can't find a model number anywhere

milling mc (small).jpg

Thread: Every Tea Room needs a toaster topic...
09/02/2019 21:23:35

many moons ago I discovered that you could make toast on the wall mounted electric fire in my room, Clip the bread to a wire coat hanger and hang it from the front grill. Always tasted better somehow, but not much good for making toasties

Thread: Single phase verses 3 phase motor
09/02/2019 17:53:35

Wouldn't go back to single phase for all the tea in China. 1.5 HP single phase is going to be quite a lump as well, as Brian says you'll get S/H 3 phase if you search. Try Gavin Oseman who sometimes advertises on **LINK**. Never dealt with him but I know a man who has.

Thread: What is this electric clock mechanism
07/02/2019 10:08:04

Please don't debase it by fitting a quartz movement. I've got several slave clocks driven by home-brewed electronics. 555 is not go not accurate enough. The simplest is to use the crystal out of a quartz clock to give you a 1 second pulse and feed this to an arduino to further subdivide it to the (probably) 30 second pulse required, but if you're not into Arduino then you could use decade counter chips. You can also use decade counters from the mains, divide by 10, 10, 10 and 3. Arduino is simpler!

If you're interested send me a pm and I'll send further details

Thread: Pitched aluminium rings. Any ideas how to machine them?
05/02/2019 16:01:40

You could also use one of those pointy inserts, but for cutting ally I'd use HSS

Edited By duncan webster on 05/02/2019 16:03:35

Thread: Displacement lubricator - with or without valve ?
05/02/2019 15:57:30
Posted by norm norton on 05/02/2019 14:37:35:

The steam enters the oil chamber and condenses only when there has been a change in pressure, i.e. you start the engine. Then when the pressure drops some oil will be expelled into the steam line. If running at constant speed there will be no additional oil introduced. The volume of oil displaced each cycle also depends on the amount of (compressible) air in the reservoir at the start.

It just needs a reasonable one inch or more of small bore tube to tee off the steam line and possibly a jet of 0.010" or 0.020" in the line if it does empty the oil too quickly.

That's not how it works, steam enters all the time whilst there is steam in the feedpipe. It condenses and sinks to the bottom displacing oil back into the steampipe. I think you need to make sure there is no trapped air.

Thread: Pitched aluminium rings. Any ideas how to machine them?
04/02/2019 21:26:04

+1 for SOD method, but I'd have machined a groove with a parting tool so that the outer chamfer ran into fresh air rather than becoming a wider and wider cut.

Thread: Unused Xmas Gift
04/02/2019 14:47:53

If it's one of these 

I've got one fitted with a 2MT shank on my Centec, and it works a treat. I'm gentle with it, 0.03 depth of cut, 800 rpm and 8" per minute feed rate. Gives a very good finish on steel. The tips that came with it are absolute rubbish, not even flat on the back where they bolt up, but they work, I haven't chipped one yet. When I've used up the stock that came with it I'll buy some decent ones. Even with the small depth of cut it is shifting metal as quickly as a smaller cutter going more slowly. You do need cotton overalls and safety glasses, the chips are hot and fly everywhere

Edited By JasonB on 04/02/2019 14:57:08

Thread: Fitting a Reversing Switch to a Motor on a Myford Lathe
03/02/2019 00:18:00
Posted by Martin Cargill on 02/02/2019 19:45:36:

A couple of points regarding this.

Whilst its not the best idea to change the reversing switch on a single phase machine capacitor start machine while the lathe is running it won't do any harm because the start winding is switched out (by the centrifugal switch). Any time you change the switch it won't take effect until the motor is started again. N.B, three phase motors are different and reversing the switch will have immediate effect !!!

You can use a simple two pole on/off/on toggle switch as a reversing switch. You wire a pair of crossover wires between the two end pairs of contacts and then feed live and neutral to the middle pair. The feed to the capacitor and start winding goes onto either of the pairs of end contacts. Switching the switch from one end to the other will reverse the motor.

My own lathe does not have centrifugal switch built into the motor, instead it is supposed to use an external current sensing relay to switch out the start winding once the current drawn by the winding allows. Not having this fancy relay (they are still available but they seem to be used/available only in the U.S.A,) Instead I have an extra set of contacts on the back of the start button that power the start winding. Pushing the start button for a second or so holds the start winding energised during start up, once you release the button the start winding drops out leaving the main winding held on via the NVR contactor


That's pretty much what I did when the centrifugal switch died on a very old motor I had on my ML7. It was so old that in the 1990s there was no-one at the makers (Crompton Parkinson) who was working there when it was made. Despite this they sent me some capacitors to reduce the start current and a diagram of how to connect it as Martin has. Worked a treat, just need to use some intelligence, hold down the start button till it's got going. You don't get that sort of after sales from Banggood

02/02/2019 00:48:22

You can actually get a reversing NVR contactor, my 254S had one before I converted it to 3 phase, if you're interested I could photocopy the wiring diagram from the manual, but if you've already got a reversing NVR and a Dewhurst I'd use them

01/02/2019 12:53:20
Posted by Roderick Jenkins on 01/02/2019 08:25:24:
Posted by Mike Donnerstag 1 on 31/01/2019 20:09:25:

I assume a VFD with a new 3-phase motor would be around £400?? Also, do the VFDs all create that horrible high-pitched whine?


The whine is a function of the carrier frequency and can usually be adjusted by selecting the correct parameter on the VFD . This **LINK**

explains it better than I can.


Mine whines all the time and continues to do so for several seconds even after the power is switched off, which is what made me think it was a cooling fan. Eventually the noise reduces in frequency and stops, and I can feel the cooling draft tailing off at the same time, still sticking to my fan theory! The newer one on the milling machine doesn't, it is completely silent

Edited By duncan webster on 01/02/2019 12:53:58

31/01/2019 22:44:00

One of my vfds from about 15 years ago does have a whine, it's the cooling fan I think, but later one is silent. I think it's the MCB that trips under inrush current, you can get slow action ones that will cope. I have a normal 30A MCB supplying the workshop and a local distribution board with a 15A fuse for the VFD

3 phase is so much better, but If you do go down the route of reversing your single phase, don't use a Dewhurst switch to start/stop, keep the NVR and use the Dewhurst when it's stationary to change direction

Thread: Centec question
30/01/2019 00:33:56

Of course I do, just testing!

29/01/2019 23:16:28

If your motor is built into the cabinet I strongly advise you to stick with 3 phase motor, a single phase motor makes the cabinet vibrate like mad and you need ear defenders. Mine was transformed by fitting 3 phase. As others have said you'll get an inverter for less than the cost of a singe phase motor, provided tat is you can reconnect the existing 3 phase as star.

I have a stepper motor driving the table, with the inevitable Arduino really handy to be able to wind the feed rate up and down

Thread: superheaters
29/01/2019 19:35:54

Do you really mean 3mm OD? That is going to be very small ID. As for material, use what you can get, I doubt you'll have much choice

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