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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: Home built trailer
14/08/2019 14:37:48

There is a photo of an unacceptable light arrangement (obscured with doors open) in the .Gov "pass the IVA test" page

About half way down, it's obviously a minature railway layout. Trailler looks professionally made, galvanised etc, but still a fail. Possibly modified from a drop down ramp to spit doors.

Robert G8RPI

Thread: Meter Probe
14/08/2019 12:23:15

The 4mm plugs with spring loaded sleeves are pretty useless and no longer common (or acceptable for new mains rated leads).

When teaching use of meters I had a "lesson" on digital accuracy. It involved a PP3 battery, AVO Model 8 analog meter (1%) and AVO DA116 digital meter (0.5% +1 count). Tne lesson was to measure the battery with both meters and discuss the results. The Model 8 read around 8.4V and the DA116 read 9.0V. Most students said the Model 8 was out of calibration and inaccurate (dispite having a in cal sticker) by 0.6V. A small percentage said the DA116 was faulty. - these had noticed that the PP3 was a rechargable with a nominal voltage of 8.4V. The DA116 had been deliberately adjusted to over-read. More digits does not mean more accuracy. The DA116 was only good to +_ 0.055V making the last digit virtually useless.

Robert G8RPI.

Thread: Small Volume PCB printers?
13/08/2019 19:00:44

You can also scan the PCB, clean up the image, print it onto transfer film in a laser printer, transfer to a clean copperclad board with an iron (don't let SWMBO see you and then etch in ferric chloride solution.

Robert G8RPI.

Thread: Meter Probe
12/08/2019 21:25:00

The old BT leads were only designed for low voltage use. You should really only use leads and probes with sleeved safety plugs. Buy them from a reptutable supplier like RS Farnel, CPC or electrical factor. If you are a business or employer of any sort you must use appropriate safety leads. For domestic mains on the "user" side of the socket they should be "CAT II" at least andfor house wiring work CAT III see

Robert G8RPI.

Thread: Boiler testers and material verification
07/08/2019 12:53:49

Certificates are only as good as the process and people behind them. I've been directly involved in an aircraft case that shows this I'm changing details due to confidentiality. We ordered some one way valves with male and female ports from an approved suppler who sourced them directly from the manufacturer. Normal flow direction is male to female but optionally it can be reversed, this adds a R to the part number. Valves arrived with all correct paper work and were installed on aircraft. They would not fit with the marked flow arrow in the correct direction. Turned out that the reverse flow valves had been supplied. They had the correct part number on valve (no R) but the marked flow arrow and actual operation was for the reverse flow type. Turned out to be marking error but neither the makers or distributors inspection picked it up. This type of thing could cause all sorts of issues as it is often hard to check non return valves when installed in applications like vent lines.
Liability in this case would have gone back to the manufacturer.

A material certificate is also of little value unless there is the quality process in place to support it along with proper stores controls etc. You might have bought the right material and then picked up the wrong bit by mistake.

Conservative design and hydrostatic testing are the best defence. The most useful high tech instrument for a boiler inspector is an ultrasonic thickness meter.

Robert G8RPI.

Thread: Home built trailer
06/08/2019 07:23:51

Since 2012 virtually all trailers need to be approved or inspected see

This ties in with new laws (draft in 2018) that will require registration of al trailers over 750kg.

Note that trailer laws generally don't apply to mobile plant. This can be useful for stationary engines if they are bolted down on a chassis with wheels. Used this clause about 15 years ago when putting a gas tubine airstart unit on a ex MOD Sankey landrover trailer chassis.

Robert G8RPI.

Thread: Dam Solution?
05/08/2019 12:50:55

KKKD Indeed the top of the "hump" in a syphon cannot be higher than the local air pressure can push the fluid for a simple fluid. One other issue is vapour pressure. Not a real issue with water but I once looked at control system for a project that was sucking solvent out of a tank to a higher level (pump at higher level) I said it would not work, they would just boil the solvent, but hey I'm just an electronics engineer so they didn't listen to me. Then the pump supplier came over from North America to discuss details, took one look at what they we doing and said "no we don't do pumps that defy the laws of physics".

Robert G8RPI.

Thread: Locking Levers
05/08/2019 12:33:27

The comments are very unfair to RS Components. The devil's in the detail.

The handles linked to in the original post at £12 are made from Stainless Steel. A more common glass filled nylon version is a more reasonable £2.60


Robert G8RPI.

Thread: Shot peening for metal improvement
05/08/2019 12:06:15

Not common



Robert G8RPI.

Thread: Tolerance for needle bearings?
05/08/2019 07:23:09

Cam followers are similar to the track rollers I liked to previously but typically have a slightly crowned otter surface


Have tried applying load to the sides and front edge of the seat to see if you are getting some kind of locking up? A load directly on the cross member with the nut will tell if it's the screw that the issue.

Do you have a proper thrust bearing at the bottom of the threaded rod?

If you can put an ammeter in series with the motor that will give you a direct indication of the motor torque and you can see the effect of putting the same load in different places.

Robert G8RPI.

Thread: Does anybody know what this is ?
03/08/2019 15:53:26

My pet peeve is people saying something is tested and working when there ar obviously crtitical parts missing or broken or/and they clearly have no idea what the thing is.

I concur that is a telephone magneto, used to generate the ringing current on old manual exchange sytems or simple point to point systems.

Robert G8RPI.

Thread: Automotive starter ring (ring gear)
03/08/2019 15:45:43

I'd use a angle grinder (or toolpost grinder) with a ttin cutting disk to take the teeth off. Tidy up with grinding disk before turning to size.
This could be done on the lathe or rotary table (with protection fom gringing dust) or a jury rig on an old wheel hub and grinder holder. The gear teeth may well be hardened.

Robert G8RPI.

Thread: Tolerance for needle bearings?
03/08/2019 15:35:35

I don't think two screws are automatically better and you would have to use toothed belts (or encoders and feedback if you are of an electronic bent) to keep them syncronised.. One thing to consider is rollers or bearings of some sort on the outside faces of the frame. unless the weight is exactly centered the moving part will try to tilt sideways and as there are just flat plate it will lock up. The don't have to take the same load as the main rollers.


Robert G8RPI

Edited By Robert Atkinson 2 on 03/08/2019 15:36:23

03/08/2019 15:28:59

For that application look at the track rollers I linked to in my earlier post

I also think you need two back braces either wire, rod or tube, one on each side to stop the frame twisting.
While I know Remap provide liability insurance, how do they deal with CE marking? As a powered lift for human this arguable comes under a whole raft of legislation. I'm not saying don't do it, just curious.

Robert G8RPI.

02/08/2019 12:54:08
Posted by Gary Wooding on 02/08/2019 08:28:21:

Thanks for the information guys. That all makes sense. The outer race will not be supported - it will just roll along a flat tube where it will have to withstand a radial thrust of about 100Kg. I considered case hardening the axles, but in light of Duncan's statement am having second thoughts.

If you are literally using the outer of a drawn cup needle roller bearing on a flat surface like a tyre you will have trouble. The walls are not designed to be run un-supported. Running them un-supported will either roll the outers oversize or cause them to fatigue and breakup depending on the material and hardness. Have you considered using bearings with machined rings or even better a track type bearing?


You might get away with it at light loads but 100kg is not light.

Robert G8RPI.

Thread: IC engine tractor conversion query
31/07/2019 19:31:01

Have you actually investigated the size of the motor in the tug? I looked at a baggage tug some years ago for a possible full size electric vehicle project. It was huge and very heavy for it's output. The tug was up for grabs and literally 1/4 of a mile away on the same industrial estate as my work but I still passed on it.

Robert G8RPI.

Thread: 3 phase - radio puzzle
31/07/2019 12:05:20
Posted by XD 351 on 30/07/2019 20:03:54:

I find it odd that the issue is still present on different bands and only on one radio , are any of the radios the same brand and model ? Does the offending radio do the same if you change bands and frequencies? Does the interference change pitch in tune with the vfd setting?

I’m asking this because i am curious as to where the signal is getting into the receiver , if you can tune it out it is via the antenna / tuning circuit and if not maybe via the IF or audio sections that may not be screened properly .

Either way you are producing some EMI which needs to be addressed .

I had a problem recently with a couple of dab radios , every time i would turn on my switchmode power supply they would go insane if they were any closer than a few metres away from it .


The issue is present on two different radios on different bands but only in one of two locations. The oddity is that it's the location remote from the VFD that has the problem. see my earlier posts.

Robert G8RPI.

Thread: Garryflex Blocks
31/07/2019 07:28:21

They start at £4 (plus VAT) from Farnell


I've used the Kellan ones for years. Mostly to clean copper clad circuit board material.

Postage free if you make the order up to £30 and they sell a wide range of products from tools to consumables as well as electronics. You don't need an account, just a credit card.

Robert G8RPI.

Thread: Is there a type of Sellotape/"sticky-backed-plastic" that forms a PERMANENT bond
30/07/2019 19:27:16

I use Kapton / Polyimide tape with silicone adhesive for this type of job. One possible issue for you is that while transparent it has an amber/copper/gold colour


Robert G8RPI.

Thread: 3 phase - radio puzzle
30/07/2019 18:49:41

Hi ,

The Ideal solution is a two stage block filter like this

But they are not cheap .As Geoff suggests a IEC mains input connector with built in filter is a lower cost ooption. It also has lower perfomance but one like this should cure your problem and provide a handy inlet connection.

I could dig out a used filter if you don't want to order one.
Is your VFD in any kind of enclosure?

Robert G8RPI.

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