Member postings for Robert Atkinson 2

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.

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.

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

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.

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.

It's very well made, not a toy originally. I suggest it was a war surplus item, probably aircraft. I don't recognise it specifically though. Anyone got any old Proops or "Service Trading Co." catalogues?

Robert.

Bandersnatch is totally correct, it's all about liability and total costs. Twenty or thirty pounds for a bottle of sealant (or lubricant) may sound a lot to a hobbyist but it's a fraction of the cost of re-working a batch of kit when it didn't go off, or a warranty claim, never mind being sued because a car, train or plane crashed because a screw came loose. It does happen, the 2011 crash of a P51 Mustang at the Reno air races killing 10 spectators and the owner/pilot was caused by the failure of locking on a small screw on a elevator trim tab (not loctite, an old "red fibre" insert captive lock nut that probably ha been on the aircraft sincei t was built). You don't want to be the company that saved £20 on loctite and killed people and / or caused millions in damage. I have a bin full of precision minature bearings for aircraft equipment whose lubication time expired 20 years ago and I rescued frm the skip. They are fine for hobby work but I would not put them in an aircraft.

Robert.

Edited By Robert Atkinson 2 on 24/09/2018 23:13:20

Edited By Robert Atkinson 2 on 24/09/2018 23:13:51

There starts the slippery slope of loosing independence. I see it in amateur radio publications, Dealers supply much of their income though advertising. Review equipment is often loaned and the editors don't want to publish bad reviews for fear of loosing the advertising.

Robert.

UK gun law is now totally weird. You may have something like a blank firer, certain airguns e.g. Brocock or military surplus tucked in a cupboard or box could get you locked up. An example is that it's illegal to own a realistic replica of say a vintage "cap and ball", even in plastic unless you are a member of a recognised re-enactment group, movie maker or similar (painting it orange make it OK) but you can own a REAL one if you are a collector. There is definition of a collector but just get a couple . You can even own a semi-automatic pistol if the ammunition is no longer made commercially. There are few restrictions on muzzle loading weapons either so you can happily make that miniature cannon. Power for it is UK as long as you have less than 10kg. Of couse take any of these out in public and you will get locked up. Then again people have been locked up in the UK for having a "rocket launcher" the disposable tube from a Light Anti-tank Weapon (LAW) which is probably less of a weapon than a piece of drain pipe. I've modified my daily carry Leatherman multi tool so the blades (which are accessible single handed without opening the body of the tool) no longer lock. carrying a locking knife (even a "Stanley" carpet knife) in public need a good reason. The authorities do monitor sales of some substances and equipment and that's not new. I personally have had direct experience of questions being asked. No problems because it was all legitimate. Even the new(ish) EPP licences don't apply to businesses or professionals.

Robert

Edited By Robert Atkinson 2 on 21/09/2018 13:03:10

It's a collection of bits, a tribrach, microscope tube with rack, bubble level and laser pointer. The collar holding the laser in is machined so not a complete bodge. I can see puutong a laser on a tribrach to level it but the microscope horizontal "translation" does not make much sense.

Robert.

To reverse a 3 phase motor you just need to swap two phases of the supply, any two, it doesn't matter which two wires you swap.

Robert.

Sodium nitrate isn't on the EPP list, see https://www.gov.uk/government/publications/licensing-for-home-users-of-explosives-precursors/licensing-for-home-users-of-poisons-and-explosive-precursors

So you can buy it OK . Try ebay.

Robert.

I agree flat stock would be best (no sharp edges) but there is another approach. Get someone to cut the strips from sheet and then cut the ends yourself with a chop saw. You can get a stand to hold an angle grinder for use a chop saw.

Robert.

Not heat related but many years ago a new employee from "down under" asked if I could look at his, then very expensive, 21" computer monitor which had "funny colours" I ased if he had brought it with hm and being told yes, told him to turn it upside down. He thought I was pulling his leg so I made a bet for a 6 pack of the "amber nectar". I won the bet. Electrons (in the CRT ) are affected by magnetic fields. A perfect CRT does not mind which way up it is, but many have small magets stuck to the neck for correction of errors. If setup in the southern hemisphere they can be the wrong way around magntically in the northern . Can also affect the adjusable convergence magnets but not so mus as they are a stronger field. I ended up turning the CRT through 180 degrees and reversing the scan coil connections. Even the EHT lead reached.

Robert G8RPI.

I just had a thought. The spindle from a roller bearing ML10 / Speed 10 could be ground for an over size (26mm) front bearing and a sleeve added for the rear. The shells would have to be bored or reamed oversize to match. The only question I have is the length of the shaft in a ML10, does anyone know?  How long is a ML7 spindle? it looks too long to me.
And of course where to get one for less than the £130 Myford want.

Robert.

Edited By Robert Atkinson 2 on 09/09/2018 19:21:26

So an update on my “new” lathe. I managed to get the chuck off without further drama. Took chuck off backplate and bolted a length of angle across backplate and a rubber strap wrench around the pulley. A small amount of heat from a hot airgun on the backplate and it loosened without any impacts. Change gear came off spindle end with a small 3-leg puller. Threaded collar came undone after application of penetrating oil. Bearing pinch bolts loosened and spindle is out. I can confirm the lathe is indeed a ML2 or short bed “Superior” model with bronze bearings. That is the end of the good news. The spindle and bearings are worn and scored. Rear bearing is worse as suspected because the gap in the housing was fully closed. It’s scored down to 0.2mm undersize. The front is 0.1mm under. So I’ve limited options,
1/ New spindle and bearings - not available.
2/ Repair old spindle and possibly re-bore bearings.
3/ Clean and lightly polish the old spindle, tighten the front bearing up (taking care not to crack the housing and accept it for how it is.
I’m tending towards 3/ but have asked one of the spindle plating/spraying and grinding companies for a rough idea of the cost of refinishing the spindle. I suspect it will be more than the lathe is worth. Being a parallel design with closed bearing blocks it does not really lend itself to other repair options like sleeves.

Ther are some photos in my album.

Robert.

Edited By Robert Atkinson 2 on 09/09/2018 18:48:15

You are considering a perfect inductance, which the motor is not. It has resistance and X resistance will dissipate A squared times X Watts of heat (real energy) where A is the measured current in "VA". The phase with respect to the supply voltage is irrelevant because the voltage developed cross the resistance is of course inphase wth the current. This is why the power companies ar concerned about VA and power factor the out of phase current causes heating in their equipment without doing any work. If you connect a 50mH choke across the mains it will draw about 15A but dissipate no power (if it is a perfect inductor). A real choke has resistance so it will get warm and that is wasted energy. For a motor the primary losses are resistive (unless it has really poor iron and bearings) so it's current that counts for heating.

Robert.

Edited By Robert Atkinson 2 on 07/09/2018 17:51:58

Remember that for heating, which is mainly resistive loss (I squared R), it is the VA that matters not the true power W.

Robert.

Posted by Joseph Noci 1 on 05/09/2018 14:53:43:

The videos..

I used AXI brushless motors for the tests - all the same size, 36mdiameter x 40mm long.

The slave motor was always a 990KV motor

I used a 900KV motor as driver in the 1st video 'Motor-1'

This did not work well, very jerky and intermittent.

I then used a 1200KV AXI motor as the drive motor - this was much better, but still not reliable startup. Motor-2.

Perhaps using a very small motor as the slave, say a 15mm or 20mm diameter motor, of around 800KV, and a larger ( similar to the ones I used) motor, of around 1200 to 2000KV might work? Bottom line is..Maybe, with a lot of fiddling and mucking about - Use two plain, small dc motors, of the old ferrite magnet variety - that should always work!

Joe

EDIT - just to say how I drove the drive motor:

The drive motor was driven in my lathe which has a tacho readout - I varied the spindle speed from 0 to 800 RPM.

Motor-1 Video - jerked all the way up to 500 RPM and then started to try turning.

Motor-2 Video - jerky up to approx 350RPM and then work turn well up to 450RPM or so, and then jerk again, and then smooth out at 700 RPM, with a few occasional jerks...

Edited By Joseph Noci 1 on 05/09/2018 14:56:50

This speed is too low for reliable operation of a drone type Brushless DC motors. They will not generate enough voltage. Using lower kVP motors will help.

Robert

Edited By Robert Atkinson 2 on 05/09/2018 19:18:24