Member postings for Andrew Johnston

The problem with that is one is doomed to repeat all the mistakes that have already been made, and learnt from. Fine if one has time to waste, but not so good if the objective is make parts with the least fuss. All learning is a mix of theory and practice.

Andrew

I have the professional kit needed, but personally wouldn't mess about trying to repair the board. I'd rather make parts than repair electronics. Don't like doing it in the day job, let alone at home.

Wow, Electronics Weekly has gone downhill? There used to be two weekly electronics papers for the professional; Electronics Weekly and Electronics Times (?). I skimmed them for interesting components, and count the number of pages of job ads, to get an idea of the state of the jobs market. No point in actually applying for one of the jobs, as most didn't exist. They were simply listed to sucker you into going onto the books of one or other of the recruitment agencies. Cynical? Me? Never!

Andrew

Edited By Andrew Johnston on 15/02/2022 19:11:09

A resistor like that should be capable of dissipating several watts. They are designed to run hot, often a couple of hundred degrees, or more. I'm surprised it has failed in the way it has, with no heat discolouration. In my experience power components fail like that when short term grossly overloaded.

I would agree with Les regarding his diagnosis. I would also support his warning about debugging. Personally I'd use a high voltage differential probe with an oscilloscope rather than an isolation transformer, but that's my preference:

Good luck with trying to repair the board.

Andrew

Electronics has moved on from batteries and bulbs.

The board runs off AC mains, not a low voltage battery, so there needs to be input surge protection, rectification and filtering. It's also possible that the motor types are different.

Andrew

There is a picture of the board in the OPs album. It's a rather odd component, apparently on its own PCB. It's definitely flipped its lid. Looks a bit like a power resistor, but why 120V? Alternatively it could be a MOV. It would help to know if the OP is in the UK or the US?

Andrew

It can be a bit gummy. But if speeds and feeds are in the right ballpark it machines reasonably well. I use a lot of hot rolled rectangular section, for the following reasons:

1. I've got a lot of it, as it is cheaper to buy standard 6m lengths than just the amount needed

2. It's less likely to distort than cold drawn when machined

3. It seems less prone to rust compared to EN1A

4. It is easy to weld

Andrew

Not sure why that should be. For reference my hobby CNC mill has a 1.5hp induction motor driven by a VFD. At the speeds mentioned the VFD is running in constant power. With the speeds and feeds mentioned the mill certainly didn't sound laboured.

My CNC mill has the same horsepower as my Bridgeport. While the Bridgeport will happily drive a 1" diameter endmill I've learnt that the CNC mill is far happier running small cutters at high spindle speeds and feedrates. For general work I use 6mm and 10mm 3-flute cutters on the CNC mill.

Andrew

Just had a look at another job I did machining lever blanks from hot rolled steel plate with a 6mm 3-flute uncoated carbide cutter. I was running 3800rpm and 200mm/min with full width cut and 2.05mm stepdown.

Andrew

I'd be running 2500rpm and around 250mm/min. Flood coolant is essential.

Andrew

My Arc/TIG welder is by Esab, and was bought from a professional welding supplier. It was supplied with a 13A plug.

Andrew

Edited By Andrew Johnston on 13/02/2022 15:07:09

It means:

Conducted emissions: The internal electronics might cause current harmonics and poor power factor to be imposed on the mains supply in excess of the limits set for domestic equipment. In practical terms it is unlikely anyone will notice.

Radiated emissions: The plasma will generate RF interference that could be picked up on surrounding radios and TVs to the annoyance of the neighbours. Whether that will be a problem is ill defined. Depends upon how close people are, how the plasma cutter is used and the design of the equipment that could be prone to interference. I've done a fair amount of arc and TIG welding at home with industrial equipment and not had a problem so far. But the houses are fairly well spaced and I mostly operate weekdays when most neighbours are out at work.

Andrew

They do come in 1.2mm radius, but a bigger size than is common in the ME world:

CCMT 1.2 radius

Andrew

It's a coincidence. Hundreds of thousands of these automated calls are made using a sequence of numbers, irrespective of the numbers being valid or not. Only a tiny fraction of one percent of the calls will hit the mark, but it's enough to make money.

Andrew

Mathematically the number needed is the least common factor of 127 and a multiple of the metric pitch to make it an integer.

For 1.5mm pitch it is 2x1.5x127 = 381 = 15"

Andrew

Edited By Andrew Johnston on 10/02/2022 12:18:08

Wot? Not all electronics engineers are mechanically incompetent!

As stated above a combination of the overhang of the test piece and a carbide tool isn't going to tell you anything about the alignment of the lathe. I'd unbolt the stand and just let it sit on the floor. Then I'd turn a short length (~100mm) with a sharp (large rake angles) HSS tool and see what the results are. You might be surprised.

In 20 years of operating my lathe I've never felt the need to machine test bars. I just make parts, but what do I know. I'm just a dumb electronics guy!

Andrew

The test tells you nothing about the mill, as you don't know if the corners of the endmill are ground symmetrically.

Andrew

That was interesting and obviously works; but seems more of a faff than just withdrawing the tool and throwing the lathe into reverse? It wouldn't work for me anyway, as I removed my imperial thread dial indicator to fit an Ainjest unit.

Andrew

Don't know about standards, I just design, and make, what looks sensible for the pipe size I am using.

Andrew

Correct, it was done on the lathe. My mill didn't have enough headroom. The part has a cover on the end with a short 1/2" spigot. The OD of both part and cover are stock size. I can just feel a slight ridge between the cover and part. So I guess the runout of the hole is around 0.1mm or so.

Andrew

When I needed a 1/2" hole through 250mm of EN1A I centre drilled, started the hole with a 12mm stub drill, then a jobbers drill and finally an extra long jobbers drill. Lastly I reamed with a 1/2" long series reamer as I needed a good finish.

Andrew