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Member postings for Robert Atkinson 2

Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Multiple vee-belt lathe drive
11/10/2018 13:29:12

I agree with Howard, not a problem. Hundreds of helicopters use multiple V belts to transmit power from the engine and act as clutches without significant issues. See https://www.atsb.gov.au/media/4120236/ai-2009-038_final.pdf for an interesting investigation (The R22 uses double V belts but otheres use multiple singles or polyvee. Theis service note even gives instructions for gluing down loost strands at the edge of the belt!
http://enstromhelicopter.com/wp-content/uploads/2012/03/SDB0117R2-Drive-Belt.pdf

Most main dealers would be trying to sell you an new alternator belt for you car if they saw that level of dmage.

Robert.

Thread: High Voltage influence on a remote control
07/10/2018 11:12:46

A 50Hz field should not affect a UHF receiver if it has any kind of tuned front end, which it should. It is possible that the 50Hz field is gettinng into the control wiring and causing issues.

It easy to find out if it's radio or wiring interference by halving the distance between the remote tranmitter and the tower for some tests. If it works at half the distance the problem is RF interference not 50Hz.

Robert G8RPI.

06/10/2018 19:50:08

Hi,
The field the chart you refer to is that generated by the 50Hz power. This is not what is causing the interference to the remote control which will operate on a much higher frequency. The interference will be caused either by arcing / corona on the line due to faulty insulation or, less likely, radio signal being transmitted on the lines.

The answer is to move the antenna (or receiver and antenna) closer further from the lines and closer to the transmitter. How yuo do this deends on the type of antenna. If it plugs into a coaxial connector you just need a coaxial extension cable with male and female connectors to match. If it's just a bit of wire it may be more difficult.

Moving the antenna 20 ft from he line will reduce the intereference by a factor of four.

Another option would be to use a directional antenna. A reflector plate behid the existing antenna mightt work but it depends on the frequency and the type of existing antenna. Do you have any information on or psctures of the receiver / antenna?

Robert.

Thread: Perforated copper sheet
04/10/2018 19:39:06

Look at a laser cutting firm like LaserMaster not only will they cut the holes in plain sheet they will cut the outline shape too. You could even try fancy hole shapes or patterns. Cost is generally quite reasonable.

https://www.lasermaster.co.uk/materials/brass-copper

Robert

Thread: Rocol RTD shelf life
04/10/2018 12:55:23

Some of the early explorers suffered from lead poisoning caused by the solder used to seal the tins. I have some ex US military MRE (Meals Ready to Eat) that I've had for over 20 years (traded a polo shirt for 3 boxes in the Jordanian desert) the outer boxes specifically said that they did not need refrigeration and had no expiry date....

Back on topic I've also had a plastic bottle of drilling fluid (not Rocol) split in storage and leave a sticky mess.

Robert.

Thread: Myford super 7 Positioning servo's on Spindle and main infeed
04/10/2018 12:27:48
Posted by Muzzer on 27/09/2018 12:33:58:
Posted by blowlamp on 25/09/2018 13:13:59:

Buy a kit from cncyourmyford.com

Martin.

Wow. £3300 plus painting and a lot of fitting. Pigs and lipstick come to mind. For that cost plus the cost of a Myford you could probably pick up a proper CNC machine and spend your time bringing it back to life, with some likelihood of ending up with a decent machine.

Murray

Plus stepper controller / drive x 2, power supply, case connectors and wiring. I'd have thought the bit's that are selling are the "easy" bits for the average model engineer, and the electrical bit's being more of a challenge.

Robert.

Thread: Help wanted in sourcing sewing machine motor capacitor
03/10/2018 22:57:42

If the OP's component is connected across the mains (L & N) then it should be a class X capacitor (this is what I think it is). If it's connected across the switch a snubber would be more appropriate.

Robert.

03/10/2018 20:17:05

The component Neil mentioned is called a Snubber. It limits the rate of change of voltage across a contact (or electronic switch like an SCR). While not a EMI suppressor per se, reducing the rate of change reduces the EMI.

Robert G8RPI.

Thread: How much do Colchester spares cost ?
03/10/2018 07:36:18

I know of a current large machine where a complete subsystem is supplied to the machine maker free of charge and the subsystem manufacturer makes profit purely on spares. There are no routine replacement or "wear-out" parts in the system. Hardly a model for making reliable machines. The accountants must love it.

Electronics has gone through a huge obsolescence period of the last several years. Banning lead, corporate takeovers and changes in packaging for has lead to devices that were common disappearing from stock virtually overnight. It's a big issue for industries with long product life cycles like defence and aerospace.

If you want expensive nuts try buying aircraft ones.

Robert.

Thread: Fly presses - weights and capacity
02/10/2018 21:54:46

Unless you have a very good reason to want a flypress I suggest you consider buying or making a hydraulic press. The only advantage of a flypress is speed and compared to a simpe frame an open working area. The downside is they are heavy take up a lot of space and are dangerous. If you don't crush a finger you will at least bang your head on the handle. A frame made of U section structural mild steel and a hydraulic jack is all you need. Compact, powerful, lighter (and can be dissasembled to move o store) make the cross mean movable and you can fit taller items in.

Robert.

Thread: More powerful batteries to make steam?
01/10/2018 12:39:21

Those sums look about right, a bit less than 4kWh or about 55 18V 4Ah batteries for the run.

What this does not include of course is the much larger amount of energy needed to raise the water to boiling point in the first place.

Robert.

01/10/2018 07:22:24
Posted by duncan webster on 30/09/2018 23:27:43:
Posted by Robert Atkinson 2 on 30/09/2018 22:22:05:
Posted by duncan webster on 30/09/2018 17:33:26:

AC still electrolyses the water, it just swaps the anode and catode around so you don't erode the anode.
It's not unsafe s long as the case is well grounded. Early designs of electric water heares and showers had a bare resistance element immesed in the water.

Robert.

I'm sure you're correct, but I'm confused (no change there then) If the water is still electrolysed by AC, then it is split into hydrogen and oxygen. This sounds like a recipe for a bomb unless there is a divider beween the anode and cathode extending below water level, which you cannot acheve with AC. According to

**LINK**

it is all down to current density, keep it low and the gasses recombine as they are created. I'm still not going to make such a boiler

Correct,

but electroplating / electrolytic corrosion happens at any current which is why AC is better for liquid resistance heating.

30/09/2018 22:22:05
Posted by duncan webster on 30/09/2018 17:33:26:

I think I might have been the gunner when SOD got shot down, but back in the 1920s/30s there was an article in ME about a mains heated boiler. Heat was generated by passing electricity through the water. They just connected neutral to the shell and had a big insulated electrode inside connected to live. You could actually make a safe version of this if you had a big enough transformer to get the volts down to something non lethal. You could then ground the neutral. This would generate enough steam for a little stationary engine. It has a built in safety feature, if you let the water run down, there is no path for the electricity, so it doesn't overheat. You have to use AC so you don't electrolyse the water

AC still electrolyses the water, it just swaps the anode and catode around so you don't erode the anode.
It's not unsafe s long as the case is well grounded. Early designs of electric water heares and showers had a bare resistance element immesed in the water.

Robert.

30/09/2018 09:15:35

A few calculations shows it's impractical.
Firstly the battery rating is misleading. 20V is the off load fully charged voltage, not the rate voltage which is 18V. (Dewalt tools in the USA are "20V" but the same tool in Europe is 18" due to consumer laws.) So using the correct rating 18V x 4Ah = 72Wh a watt is one joule per second so thats 72 x 3600 = 259.2kJ (about the same as 6g of coal) Specfic heat of water is 4.186j/g or 4.186kJ/l so our battery will raise 1 litre of water 61.9 degrees or from 20 to 81.9 degrees (at ses level ambint pressure)

Even if you start off at boiling, the heat of vaporization of water iss 2261kJ/kg so a fresh battery will boil away 115ml of water.

Robert.

Thread: Hut Consumer Unit & MCB Question
28/09/2018 18:22:21
Posted by Mark Rand on 27/09/2018 18:50:08:
Posted by Robert Atkinson 2 on 27/09/2018 17:50:01:
Posted by Bill Chugg on 27/09/2018 16:55:11:

My workshop was 5 metres from the house at my last property.

Electrician used 6mm SWA as supply as he said that was the minimum he could use to comply with the regulations.

Thats just wrong, 6mm SWA is rated for at least 50A. A workshop feed should not need more than 32A. 2.5mm would do for a short run and 4mm would be conservative. Too late now though.

Robert.

Sorry, but that isn't the case. It's rated at 50A current for a short length. You'd need 10mm^2 for 50A over 20 metres buried in earth. You have to plan on voltage drop as well.

I did 16mm^2 over 30m to the shed, with a 40A circuit to allow me to go to 63A if needed.

The current rating of a cable has NOTHING to do with it's length. The only consideration is temperature rise and subsequent insulation damage. You can run the same conductor size at higher current if the insulation is rated to a higher temperature. Voltage drop is another matter and a larger size may be required to keep this (and the related loop impedance) within limits. Note that having a low loop impedance can cause as much trouble as high. The Prospective Fault Current (PSC) goes up as impedance goes down and can force the use of proctive deivice with high interruting current ratings pushing you to more expensive industral switchgear. The feeder in question was only 5m long and while the OP did not say, I'd be suprised if the demand was for more than 32A. Additionally few homes in the UK have more than a 100A incoming feed (many are 60A) so even with diversity a workshop feed taking more than 32A leaves little for the rest of the house.

Robert.

27/09/2018 17:50:01
Posted by Bill Chugg on 27/09/2018 16:55:11:

My workshop was 5 metres from the house at my last property.

Electrician used 6mm SWA as supply as he said that was the minimum he could use to comply with the regulations.

Thats just wrong, 6mm SWA is rated for at least 50A. A workshop feed should not need more than 32A. 2.5mm would do for a short run and 4mm would be conservative. Too late now though.

Robert.

27/09/2018 17:29:18

My earlier post crossed with Martins.

The SY cable is not suitable for this application especially if buried. A 32A breaker will not protect this. You need to change the breaker in the house to a 16A one as soon s possible. (a 20A might do but but you would need to know the loop impedance. Change the hut one to 10 or 16A. Even SWA comes in different current ratings depending on the plastic used for the insuation. I disagree with the comment that cable size is not affected by MCB type (B,C or D), it does indirectly becaus it affects the loop impedance. The loop impedance must be low enough for the MCB to trip quickly with a short circuit. https://www.electricalsafetyfirst.org.uk/mediafile/100106752/master_EARTHFAULTLOOPtable.pdf
If you have a long cable and a C or D MCB you may have to go down in MCB rating or up in wire size.

Sounds like you need to get a electrician in, trouble is finding one that knos what they are doing but won't do more than is really needed.

Robert.

 

Edited By Robert Atkinson 2 on 27/09/2018 17:29:33

27/09/2018 12:58:27

The primary purpose of an MCB (or fuse) is to protect the wiring so it should be rated to the wiring. A 32A MCB is only appropriate to a ring main wired with 2.5mm Twin and earth cable or a spur wired with heavier cable. So if the 32A MCB in the hut only has one 2.5mm wire connected to its output it's oversized. If this is the case change it to a 16A MCB MAXIMUM. The size of the one in the house depends on the cable feeding the hut. It should be the same or larger rating than the largest in the hut without exceeding the cable rating. I'd hope the hut is fed with 3 core 2.5mm Steel Wire Armoured (SWA) cable. if so a 32A breaker is OK. If it's just a length of 2.5 twin and earth you need to change the breaker to a 16A and think about a new feeder.

You should really use a "C" rated MCB on a motor circuit but has been mentioned the earth impedance needs to be low enough to allow it to trip quickly in the case of a short circuit. This really needs a measurement.

The other easy and safe fix is to fit a 16A "B" MCB in the house and a 10A "B" or 6A "C" MCB in the hut.

Robert.

Thread: Identifying a model motor
26/09/2018 22:17:01

Posted by SillyOldDuffer on 25/09/2018 14:32:35:

<SNIP>

The green plate has been made from a fire-extinguisher label or perhaps a fire control lever from a console. The engraved letters probably spell out:

IN CASE OF FIRE
TURN HANDLE TO LEFT AND
PULL TO FULLEST EXTENT

For some reason thie instructions remind me of aircraft engines?

<SNIP>

Dave

Aircraft "fire" handles are normally two motion, Pulling shuts down the engine and closes fuel, oil, hyraulic and (on jets) bleed air valves at the firewall behind the engine. Turning operates the extinguisher(s). I also thought it was a aircraft placard.

Robert.

Thread: Myford ML2 re-commissioning
26/09/2018 22:12:30

So an update on the ML2. I finally had a company come back with an estimate for repairing the damaged spindle - £350 to £500. This is dressing journals, ceramic spraying, grinding journals, line boring headstock bushes and re-assembling. The bull gear and pulley would also need boring oversize. This is not a bad quote for the work involved, but more than I want to invest in this machine. While I was considering options a complete late headstock appeared on ebay see

**LINK**

Not the best picture but there are some differences in this headstock that I want to check out before detailing in a later post. I’m guessing some scraping or shimming may be required to get this aligned to my bed. I’d already ordered a 2MT alignment bar which will be invaluable for that. The bar was from an Indian seller on ebay (most seem to be from India for some reason) and seems to be pretty good quality. It arrived in a few days by Fedex so pretty good service.

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