Member postings for Robert Atkinson 2

If you are happy with the machine you have and don't intend putting any significant new software on it in the near future why not just replace the disk? If you fit a solid state (SSD) one you won't have to worry about mechanical failures. Most "retail pack" SSD's come with software to transfer your operating system, programs and data with minimal fuss.

Robert G8RPI.

Hi,

Sounds like a brake caliper piston seal e.g.
www.ebay.co.uk/itm/for-Vauxhall-Astra-Meriva-Rear-Brake-Caliper-Repair-seal-Kit-Lucas-36mm-3627/274056153625
Holden Astra down under.
Try talking to the ebay seller BigRed, I've found them very helpful.

Robert G8RPI

Hi,

Where you start looking is the details of the wavelength and power output of the laser(s) he is using. You cannot do anything without these details. I have 4 different pairs of laser safety glasses just for the lasers I play with at home and none of those are capable of cutting. well maybe a thin piece of paper if focused properly.

Robert G8RPI.

I second what Jeff says. You cannot go by the visual colour or density of plastic to determine light blocking. It is highly dependent on the base material, pigments and wavelengths that need to be blocked. For example black acrylic (Perspex) while appearing completely opaque to visible light will pass infra-red light with virtually no attenuation. Virtually all of the coloured plastic sold for filtering lights also pass IR light. If they didn't they would melt in front of the lamp. Conversely some grades of plastic which look crystal clear will totally block UV light. Then you have to make sure the laser can't burn through the plastic or degrade the dye(s) in the plastic. Overall solid metal is the safe option. Even then you have to make sure all the joints and seams are light tight. This is easier said than done. One check is to put a bright light under the cover. close it, and then inspect in a totally dark room for any leaks of light. Don't forget to wait in the dark for at least 10 minutes to let your eyes become sensitive. Some black anodised finishes are IR reflective too.
I've done laser safety design as part of my day job for instruments with high power UV lights and various lasers.

A related problem with some lasers like some blue or green ones is that the lightis generated by frequency doubling a infrared laser and with low quality ones they don't fit filters for the IR on the output so you can get dangerous levels of invisible IR light as well as the visible light.

You only get one pair of eyes

Robert G8RPI.

The KEDU NVR unit seems a good cost / safety compromise between a simple on/off switch and a full direct on line or contactor set-up. It is better than the "KJD" type NVR's with the flip-over E-stop that just presses the stop button. This is because the KEDU E-Stop is a separate switch so can still cut power even if the NVR contacts stick shut. If not using fully qualified industrial safety parts having a second means of stopping is good insurance

Robert G8RPI.

First, if you have data for the pressure gauge, check what it can withstand. It may be OK with 70 PSI. A restrictor will only help if there is sufficient air or other compressible fluid or resilient expansion between the gauge and restriction or in the gauge itself. If the gauge is mounted above the oil level then air in the pipework and gauge my provide this if the restrictor is at the engine end of the connection The ratio between the restrictor flow and compressible volume must be high enough that the oil pressure has reduced to below the maximum non-damage pressure rating of the gauge before enough has flowed through the restrictor to compress the volume of air to the limit. If the gauge and pipework can fill with oil and not drain you could use a small spring loaded accumulator (cylinder with a spring loaded piston designed for full compression of the spring at a bit more than the gauge max pressure rating) and restrictor.

Robert G8RPI.

I've personally seen a scrap dealer who had a cheque cashing kiosk right next to the payment desk. I'd hazard a guess the bank never saw any of the checks they took.

Robert G8RPI.

While most Hammod boxes are 6-32 UNC and tapped holes, not all are

https://www.hammfg.com/electronics/small-case/diecast/eddystone

6-32 is 3.5mm major diameter but coarser pitch than metric but a taptite will fit.......

Robert G8RPI

Hi Neil,

Diecast box screws, including Taptites are normally M3.5. This odd size appears to be for compatability with 4BA which was used on the original Eddystone boxes (and electical "back" boxes)

This rather than the tri-lobular form is likely why ir seemed small for a M4.

Robert G8RPI.

Great Post SOD

Re "Ought to be emphasised that the size of the boiler is all important. It limits their capacity to store energy. "

So true, this is where the 250 Bar/Litre "rule comes from. If the product of pressure and volume is less than 250 many of the regulations don't apply. 250l tank at 1 bar is same energy as a 1l at 250 bar.

Robert G8RPI

The problem is poor insulation and earthing of the Dewhurst switch. First thing is to check (or more likely provide) the earthing on the switch chassis and cover.
Theses old switches probably would not meet current safety standards. A modern cam switch (proper make and suppler, not junk off ebay or alibaba) in a proper enclosure would be a better choice.

Yes it is something you should be worried about.

Robert G8RPI.

When you are talking about ultra high vacuum (UHV) such as is used in semiconductor manufacturing and electron microscopes, pressure is no longer measured as a force. You are talking about how many molecules of gas are present. Measurement is usually electronic as in how much current will flow. The pressures are measured in Pascal and UHV is below 1x10^-7 Pascal or 0.0000001 Pa. One atmosphere is about 100,000 Pa (101325 standard sea level 1013.25 millibar) so that is 1x10^-12 Bar or 1.47^-11 PSI 0.00000000000147 PSI.

The pumps used look like multistage axial turbines running at very high speed but are actually sweeping individual molecules out of the UHV volume rather than pumping. They have to be "backed" by a high vacuum system of less than 100 Pascals (0.015 PSIA).

Robert G8RPI.

CMM is a coordinate measuring machine. A surface table with a touch probe and 3 axis measuring system

https://en.wikipedia.org/wiki/Coordinate-measuring_machine

The one in the skip even had the Rennishaw touch probe still fitted. )-:

Not on this planet. The maximum differential you can get with a vacuum is dictated by the local air pressure. This is variable but at sea level is about 1Bar, 14.7 PSI, or 30" of mercury. (Hg) The brake gauges are 21" of Hg not 21 PSI.
30" hg is 407" of water so that is the absolute maximum you can suck fresh water UP with a pump about 30 foot in practice.

Robert G8RPI

Edited By Robert Atkinson 2 on 06/10/2019 16:50:18

There would be a relative drop of 100 PSI but even with a full vacuum inside the boiler there is only atmospheric pressure, 1 Bar, outside. The pressures quoted for steam work are "Gauge" or relative to local air pressure. If you connected an absolute pressure gauge (which is referenced to zero or a vacuum) to the same point it would read 14-15 PSI higher depending on local air pressure.

Robert G8RPI.

As Dave says, maximum differential is less than 15 PSI (higer at sealevel on a nice day)

Tanks can implode see https://www.youtube.com/watch?v=Zz95_VvTxZM Anyone wo has see an old, non-protected TV tube smashed will testify to the forces involved with larker volumes.

Robert G8RPI.

If doing the immersion trick, white sprit is a lot safer than petrol.

Robert G8RPI.

I've used Motion Control Products professionally with no issues

https://www.motioncontrolproducts.com/

Head office is in Bournemouth

Robert G8RPI.

It's two things,

Health and Safety - no digging in skip in case you cut yourself. That I can sort of understand.

Controlled materail #most of the work material has to be traceable and there is a concern that somehow uncontrolled stock would get re-used either by us or someone making bogus parts. They won't even put off-cuts back in stock. If making some 0.51m parts from 1m length of stock 0.49m goes for scrap.

A couple of years ago there was a complete CMM in the skip.

They have recently agreed to put timber and office furniture in a bar for a week for staff to take but no electrical or mechanical equipment (H&S again). And they have donated some old commputer equipment to charitable causes. Our WEEE skip is huch high quality they don't charge to take it away.

What I find really frustrating is walking by the scrap skip at work and seeing off-cuts of new stock still marked with the material specification and not being able to to take any. I've stopped looking.