Member postings for SillyOldDuffer

I find blades in a rear-tool post work best for me, but it's not really the cutter that makes the difference. Which tool is the wrong question, should be 'What's the best way to part-off?'

First secret is rigidity. Parting-off applies more force to the cutter, job, and lathe than most operations. They are all likely to bend, causing chatter and dig-ins. When a dig-in occurs, the forces involved make it likely be violent.

Second is the need for a steady feed at the right rate. Steady is vital, and most humans are wobbly. The tool has to cut continuously, not too deep or too shallow.

Third is making sure the cutter is aligned correctly, going straight in, not applying side-pressure because it's at a slight angle.

Fourth is making sure swarf doesn't collect in the slot and jamb the cutter. Cutting fluid in applied in quantity helps.

Example likely to fail:

• A small lathe, these are light and bendy
• protruding job, sticking out of the chuck, also bendy
• a long slim cutter in a towering tool post perched on the top-slide, perched on a cross-slide, perched on the saddle, gibs loose or unlocked. The whole arrangement is bendy, plus all the slides can twist
• Operator mounts the tool at a slight angle, causing heavy side pressure. Maybe gets the height wrong too - parting off is fussy!
• Operator moves the tool by hand. He is unsteady, and him varying the feed-rate causes the cutter to bounce. It often collides violently with the job rather than peeling metal off at a sensible rate
• Operator is low to lubricate and stop swarf jambing the cutter

Counter example likely to succeed:

• Heavy lathe - big lathes are far more rigid than small ones
• Job protrusion minimised
• Short deep cutter able to resist pressure, protruding just enough to make the cut.
• Cutter mounted on a hefty rear tool-post bolted directly to the saddle.
• Ideally run lathe in reverse. This pushes the rear toolpost and saddle down, rather than lifting them.
• Operator selects correct RPM and feed-rate and engages automatic feed. Automatic feed maintains a constant cutting force, and eliminates human error.
• Operator pays close attention to clearing swarf

Only real men can part-off on a mini-lathe. They're light and don't have a rear tool-post or automatic feed. The tools are small and bendy.

Myford size machines are much less challenging, They have more weight and probably have a rear tool-post and automatic drive. Parting off from the front is do-able, but more likely to go wrong. A rear tool-post is generally reliable.

Parting off on bigger than Myford is almost trivial. Lots more weight, and even the front tool-post is impressively rigid. Automatic drive etc available. With a rear tool-post, parting off is trivial.

My lathe is a WM280, rather heavier than a Super 7, but not massive.

I can part-off by hand using the front tool-post if I'm really careful, but failure is always an option Front-tool post with automatic feed is almost 100% reliable - mostly works, occasional grief. Rear tool-post is 100% reliable unless I do something stupid.

Dave

Ancient craft-skills are unlikely to have been applied to a Replica bell sold in 1985, and probably still available new!

I agree matching colour is difficult though. Repair Shop used to annoy me because it skipped over important details, but later programmes are more forthcoming. They would fix this with paint. They carefully prepare the surface, cleaning and making good, test various paint types to find the one that sticks best, and mix to get the correct colour, perhaps a range of near misses to improve blending. They make it look easy, but I think a good eye, steady hand, suitable brushes, experience and plenty of practice are needed. I noticed they often apply paint in much smaller quantities than I would, probably taking much longer to build up the effect than TV implies.

I'd be very surprised to find the bell is made of Bronze, because it's expensive. More likely to be Brass in a replica, maybe something even cheaper like plated steel.

Whatever, the patina will have been produced by dipping the item into a hot chemical mix, compounded to create the appearance of ancient Bronze in a few minutes.

Several mixes could do the necessary, but we've no idea what the chemicals used were. It makes a difference - all acids react with Copper to produce green salts, but the greens aren't the same. The green produced by Vinegar on Copper, an Acetate, isn't the same as the Verdigris produced on Copper roofs by Carbon Dioxide, which is mostly a Carbonate. Paint is much more controllable.

Dave

Agree, I think the PicPET chips are brilliant. For anyone interested, here's a PiCPET and Arduino Nano side by side.

The PICPET is ringed in red. There are only 8 pins, 3 of which aren't used. The main complication on a modern computer is the output is RS232 serial at 9600baud. In the good old days all computers had RS232, but this has been replaced by USB. To connect it to a new PC or Apple, it's necessary to spend a few pounds on an RS232 to USB converter. Also needed, a stable accurate 10MHz signal, ideally an OCXO. If you want to change what the chip does, PICPET is coded in PIC Assembler. Delightfully cheap and simple plus top performance.

In contrast, the Nano has 30 pins, and the chip has more memory and capabilities than the little PIC. USB is built in, and so is a 16MHz oscillator, unfortunately not very stable! Programmed in C from the Arduino IDE, and there are a multitude of plug-in modules, with software, available to simplify the electronics. You don't have to design and build your own Motor controller, Real Time Clock, Accelerometer and Sensor boards etc as well as write code. Precision Event Timing can be incorporated into a larger system. In my experimental pendulum, the same Arduino:

• runs two PETs, one measuring pendulum period, the other crystal frequency
• drives the pendulum, controlling when the impulse occurs
• reads temperature, pressure and humidity,
• counts pendulum time in seconds and microseconds, compensating for environmental changes s required
• displays Day/Month/Year/HH:MMS locally
• logs the all data to a remote PC and
• responds to commands sent from the PC, such as set current time

All this is more complicated and not so cheap. Also, I haven't got an Arduino PET to measure events as accurately as a PICPET.

Like everything else, the worst shortcoming of the PICPET is what it doesn't do. Monitoring a pendulum clock it's useful to log temperature, pressure and humidity as well as period because they can all influence the pendulum, and PICPET doesn't do that.

Back to obsessing about pendulum precision, after applying temperature compensation, a close look shows air-pressure needs attention too. Maybe humidity as well, certainly if the rod is made of wood. Anyone know what happens to a pendulum's period when water condenses on to a metal bob and rod? I guess it would shift the centre of mass slightly, causing a serious disturbance if condensed water collected on the bob base and then dripped off!

Dave

Bazyle's question first: does temperature alter the electronics? Potentially yes. Definitely is the electronic clock is based on the computer's oscillator, less so if the electronic clock is a Real Time module, or an OCXO, and not at all if the electronic clock is GPS based. So needs thought.

John's remarks above - my approach is very similar except I use an Arduino rather than a PIC.

Ages ago John drew my attention to the PICPET chips. These use a hardware counter/timer to get high accuracy, and the same technique can be implemented on Arduino (Atmel) and other microcontrollers. The only disadvantage of PICPET is the chip can't be programmed to do anything else: it can only be a Precision Event Timer.  Otherwise, they are the bees knees.

Arduino et al. can be programmed to do PET and other functions, but there are ifs and buts. PICPET can be plugged into an accurate 10MHz OCXO, but the Arduino has a 16Mhz uncompensated oscillator. An external clock can be connected to an Arduino pin to do PET, but it's limited to 6.4MHz tops. In practice I run it off a 5MHz OCXO, but this loses a lot of resolution compared with 10 and 16MHz.

My sub-miniature soldering skills aren't up to replacing an Arduino's onboard crystal with an accurate 16MHz source. What I have done is have the Arduino run two PETs off the onboard cytstal. The first measures the crystal frequency once per GPS second, which tells me the oscillators real frequency over the last delta. The second PET measures the pendulum relative to the crystal, whose actual frequency count during the last GPS second ago is known, and can be error corrected. I doubt the trick is better than an OCXO because the crystal may have drifted whilst being counted, but results are in the same ball-park.

The ATMega 16U4 and PIC chips are both 8 bit time predictable with support for counter/timer Input Capture. Other microcontrollers are more or less suitable. Not all support Input Capture. As far as I can tell the ESP8266 has no programmable hardware timer functions at all. The ST32 family (Nucleo) are promising, but the system clock doesn't run at a steady rate - the chip pulls fancy tricks to increase average speed, by running some instructions faster than others. I've not confirmed it's possible to drive an ST32 counter timer with an external clock and get reliable high accuracy timing.

The Raspberry Pi has a multi-user multi-tasking SOC. It pulls even more fancy tricks to increase average speed, and an operating system schedules work, not the programmer. Though possible to get close to real time performance, all processes are regularly or irregularly interrupted by the operating system, which makes accurate sub-second timing of external events difficult. On the other hand, PI supports Network Time Protocol, always within 100 mS of atomic time, usually within 20mS, and it's not difficult to GPS discipline a Pi to get better than 10mS accuracy. Though poor at measuring short external events, a GPS'd Pi is about as good as it gets for long term accuracy. Provided that is the network stays up! I intended to fixed my Pi's network problems by hardwiring it with Ethernet, but moving it closer to the router made WiFi reliable.

I found my 433MHz modules and remembered why they're so slow. I bought a cheap controller pair of the type used to open garage doors. They recognise 5 or 6 'commands', which can be encoded to send data, but the transmission rate is too slow for clock logging. I need to cough up for a proper telemetry pair, about £30. The first one I found only does 9600 baud without error checking. More research needed.

Dave

Edited By SillyOldDuffer on 04/08/2023 21:50:49

Perfectly reasonable Andy, and it's refreshing to find someone wanting to sensibly downsize their motor. More usual for testosterone fuelled folk to insist on upgrading a poor old Super Adept to 3HP and 6000 rpm,

I exaggerate slightly, but the notion more power must be better is very common. There's no need - painting a go-faster stripe on the stand massively improved my lathe!

Dave

Ah yes, I was a hippy too. Always started the day by sprinkling Cocaine on my breakfast grapefruit...

Just a guess about 'periodic reset' but there are two ways the antenna could be aligned.

One is by calculating the X,Y,Z angle the antenna has to be pointed to target planet earth. This requires knowing where the satellite is and its attitude. Both can be obtained from the telemetry. The calculation is probably too much work for Voyager's tiny computer, so better done back on earth. Having done the sums, the ground station sends a command to move the antenna. All that's needed is to send the right value, and minimum power is consumed making the adjustment by the antenna motors. (Voyager's battery is tiny too.)

Given Voyager's age I bet the command was sent manually, and someone fluffed. They will never hear the end of it!

The second method is for the satellite to adjust the antenna for maximum signal. At an agreed time, normal operation stops and the satellite listens continually for a powerful 'here I am' signal sent from earth. If nothing is heard, the antenna manoeuvres until the signal is received, and then the satellite fine adjusts for a maximum.

Not hearing earth during a 'periodic reset' probably causes the satellite to keep searching until it picks something up. Having to scan the antenna probably thrashes the battery, which might go flat before normal service is resumed.

Dave

Yes, hot rolled is about 20% to 30% weaker than cold rolled. Some example numbers:

Tensile Strength. Hot Rolled 67000psi, Cold Rolled 85000 psi
Yield Strength. Hot Rolled 45000psi, Cold Rolled 70000psi

So,probably better to machine hot-rolled for non-structural parts because the stock won't warp, and to machine cold-rolled whenever strength matters.

I mostly work with cold-rolled steel because starting with clean straight surfaces often saves a lot of time - I rarely have to machine an entire block. Warping is definitely a real problem, but I've only been caught once in 12 years. Took about 5 years before a length warped on me during a cut and it hasn't happened since. Could be the devil looks after his own!

Dave

A CE mark means the supplier asserts the item meets all the necessary legal requirements that apply before the item can be sold in the European Union. They mostly relate to safety, and most developed countries have similar or identical requirements. In practice, most UK manufacturers have continued to meet EU requirements and CE mark all their products. Two reasons:

• British products have to be CE marked before they can be sold in Europe or any other country that recognises the CE mark. Brexit does not alter the need for exports to be CE marked.
• Almost all the legal requirements needed to get a CE mark are enshrined in British Law, and nothing has been done to unpick them. Thus, UKCA and CE both require conformance to the same British legislation, which is still EU compatible. In most respects CE and UKCA are identical, except UKCA adds more bureaucracy, especially when products are sold in Europe and the mainland UK, and in Northern Ireland where special rules apply. Basically, it's necessary to satisfy UK law to get a UKCA mark, and because British law is the same as EU law, it might just as well be a CE.

To be sold outside the UK, boilers have to be CE marked.

Even though UKCA and CE are equivalent at the moment, UKCA isn't accepted abroad. The problem is UKCA could different to CE in future, and foreign purchasers aren't interested in working out what the differences might be. It's easier for them to demand CE, because then they only have to track one system.

I suspect after all the rah-rah-rah of leaving, the government is finding 'getting Brexit done' to be far more hard work than the optimists expected. Fairly easy to leave the EU and sort out a divorce settlement, but not to fix what happens next. It includes revising the entire body of British legislation. Not easy to unpick European requirements from British ones, especially as European and many British requirements are satisfactorily interrelated in complex ways, and shouldn't be changed unless there's a positive advantage.

Typical of how all governments work: they'd rather fix details when they're obviously broken than plunge into tricky new policy that requires making complex legislative changes on a grand scale. Extra painful for Conservative politicians who are against intervention on principle.

Could be done, but it requires MPs to work much harder on changing the law than they are. Instead, they passed the Great Repeal Bill in 2016, and empowered themselves to make changes later. Since then it's been found difficult and/or counter-productive to change anything. The devil is in the detail.

UKCA burdened British firms with a lot of extra bureaucracy for no practical benefit. Recognising that, government are backing away from it. Quite right.

Dave

I recommend starting by using the lathe to cut metal rather than measuring. Measuring is difficult and understanding the results more so. Getting either wrong can lead to unnecessary remedial work and making the lathe worse.

In contrast, cutting metal is relatively easy to do and it makes faults very obvious. Bent spindle, knackered bearings, head and tailstock misalignment, loose headstock, unacceptably worn bed, worn jaws, damaged chuck internals, cracked parts, broken keys, broken & maladjusted gibs, worn worms, backlash, broken shear pins, jambed collars, missing parts, blocked oil-ways, damaged nose thread etc. Running a lathe reveals problems that are hard to measure - like overheating bearings and horrible mechanical noises!

Many of these are cheap easy fixes, others difficult and expensive, possibly show-stoppers. Although she looks lovely, that lathe could be BER. (Beyond economic repair.) I advise putting the lathe 'as is' through it's paces to identify as many faults as possible before deciding what to do about them.

So don't start by laying a straight-edge on the bed and going immediately for an expensive regrind! Cutting metal highlights other issues, and the bed may not be worth fixing. A rust pit under the tailstock is unlikely to matter, whereas a deep hollow ground into the headstock end is trouble. But note it's possible to do good work on a rather badly worn lathe - how important the wear is depends on what the lathe is used for. Don't fixate on the bed or anything else: before spending money, cut metal and evaluate whatever it reveals.

With luck cutting metal will allow everything that matters to be fixed in short order. But cutting may only the first step. Although a good way of identifying lots of problems and giving a rough idea how serious they are, measuring is the next step, and essential for fine adjustments. For example if a DTI or micrometer shows the happily working lathe cuts a taper, measurement is needed to identify and correct the cause - might be bed-twist, which is fixed by "levelling", or the headstock needs realigning. Both are delicate adjustments.

I would only buy the lathe in it's present condition as an ornamental antique. It's obviously been beautifully cleaned up, but she's a very old lady, and condition as a working precision machine is unknown - could be anything between good or scrap. Unfortunately it's not difficult to tart lathes up, and anything of that age looking that gorgeous makes me suspicious. Appearance is secondary to me. Buying a second-hand lathe for work rather than decoration, I'd insist on seeing it run before buying it.

That said, lathes are fairly robust, and quite a few ancient survivors are in remarkably good condition. It depends on the machine's history - many were thrashed by men working hard to earn a crust and were scrapped decades ago. Others were used for light repair or prototyping work. A few sat on a bench, or in a crate, for 50 years. Lathes owned by hobbyists mostly have a very easy life. Not unusual for good lathes to end up rusting slowly away in a damp cellar, in which case the damage varies from fatal to cosmetic. When an item becomes BER depends on how much time and effort the owner wants to spend. In my case, not much, because I own tools to use them. But restoring old equipment is a respectable hobby in itself. Men cheerfully spend years bringing historic gear back to life. Heritage repair may not be for me, but I admire those who do it, and their results.

Regrinds - anyone able to name any firms doing this work at the moment? They seem to be disappearing.

Dave

Um, the cool kids are probably wrong. John mentioned the issue in his question - protocol overheads. Bluetooth, which is a form of Wifi, has number of protocols available (synchronous or asynchronous, with connection set-up, link management, acknowledge, error correction, retransmit, multiplexing, buffering, segmentation and polling etc. ) All good stuff, and quick, but not time deterministic. Wouldn't matter for nearest second clock purposes, but bad for sub-second timings.

I bought an ESP and some 433MHz modules ages ago for time trials but am miles away from doing them properly - dreadful slow progress elsewhere on my to-do list! From memory, I fired up a pair of 433MHz modules to check they worked and found they were very slow, probably limited by bandwidth and modulation method. If I can find them I'll measure what they can manage.

Dave

+1

Older guns contain powerful v-shaped leaf springs, not coils, and the spring pressure has to be released before the lock can be worked on. One way was to squeeze the V together with a clamp, either to remove and replace the spring entirely, or to work on the unpressured mechanism with the spring clamped down in place. Spring clamps are available for repairing spring powered clocks - same purpose, different shape. Car engines too, but constructed to clamp coil springs.

Dave

'Common Sense' has little to do with economic principles. For example, plenty of posts in this thread assume the cost of fossil fuel sourced energy will stay low forever! Alas, it is not so, unless magic can be made to work, or the people who believe such stuff know of an enormous new source. Or believe 'they' will find more oil, not realising that 'they' will have to be a fairy godmother.

Always better to tackle problems before they turn into a crisis. Denial and self-interest are strategies, but they're not smart. Today, Silly Old Grandad might safely rely on dying before big bills start arriving, but his children will have to deal with life no matter what the old man believed.

No politicians I'm aware of, of any political stamp, have provided guarantees that not making the necessary changes will be affordable for the individual on a limited budget. Worse, my understanding of the oil and gas problem is that individuals on a limited budget are going to suffer unless something is done. The issue is that fossil fuel energy is about to become irreversably expensive.

Given oil and gas are depleting, our job is to reduce the pain by finding alternatives to them. Pretending it's not happening will only cause more difficulties. Kicking the can down the road may be easy, but it's cowardly, and never ends well.

Regretfully true that: 'Until the necessary changes are viably affordable alternatives to the way we as individuals do things at present, then those necessary changes will not in most cases be made, and understandably so'. Slow movers always risk being left behind to sort themselves out. In 10 years time, perhaps sooner, I shall be a vulnerable pensioner. There won't be much help available for me if the whole country is struggling with an ongoing energy crisis. Therefore I'm against negligence.

Anyone study history? Today's high expectation levels are not justified by the history of human affairs. Human affairs are never stable in the long run. All previous civilisations have collapsed. Nations don't remain top dog forever. Wealth and liberty wax and wane. No society is immune to famine, disease and war. And on a personal level death is inevitable. Turns out large numbers of historic disasters were caused by avoidable human error. Not just the blunders of rulers, but whole populations choosing to believe in utter nonsense rather than deal with uncomfortable truths. I fear the same is happening to us. Too many heads in the sand.

Climate change and rising energy costs are manageable, but only if we get stuck in and deal with them. Faced with serious physical and practical problems, denial, wishful thinking, vested interests and conspiracy theories are, and always have been, pointless time-wasters. They have a rotten success record.

Dave

Edited By SillyOldDuffer on 03/08/2023 20:30:38

Can you explain please Nigel?

For all practical purposes Petroleum is a fossil fuel. Though it's possible to make petroleum from vegetable and animal sources, almost all petroleum is cracked and refined from Crude Oil, which most definitely is a fossil-fuel. Never mind politicians, campaigners, journalists and the General Public, the definition of petroleum comes from geologists (formation of rocks and minerals) and chemists (hydrocarbons).

Difficult to match the volume of petroleum currently made from crude oil by synthesising it. As reserves of crude-oil are depleted over the next 20 to 30 years, the cost of petroleum will rise sharply. Won't disappear entirely, just become too expensive for the ordinary motorist to burn in an engine.

Dave

Edited By SillyOldDuffer on 03/08/2023 13:53:22

Oeer, Mark! Am I doing it wrong again?

Do you mean 'HSS tool bits do not have to come out of toolpost whilst they are being sharpened'?

I thought 'HSS has to be removed from a 4-way tool-post for resharpening and then be re-shimmed to height.', that is blunt HSS always has to be removed and taken to a grinder for sharpening? In that case, quick removal of HSS tools for sharpening without disturbing the cartridge means a QCTP is faster than a 4-way, where shims have to be adjusted.

However, carbide inserts are different. They're replaced without disturbing the tool-holder, which means a 4-way tool-post with pre-shimmed carbide holders is pretty much as fast as a QCTP. Fast because only the insert changes, the tool post isn't touched, and no time is wasted at the grinder. To my mind carbide inserts do away with much of the need for a QCTP, unless that is, the workshop uses HSS most of the time.

Dave

I think Jason is on the ball. Jim's 0.055" is about right for a 0.64 x pitch depth of cut but that's only valid for a full-form thread cutter. I bet Jim has a partial form cutter. For these, depth needs to be more like that of a V cutter, where Whitworth depth of cut is 0.8 x pitch, roughly 0.068" (13 thou deeper than Jim)

Thread inserts are often 'Partial form', that is they don't finish the top of the thread. The advantage is the same insert can be used to cut different pitches, but for them 0.64p isn't deep enough unless the outside diameter is reduced to compensate. Or the insert is pushed a little deeper.

'Full form' inserts cut the thread correctly top and bottom, so 0.64 pitch is the correct depth for them. Unfortunately a full form insert only cuts one pitch, and owning a full set of them costs a bomb. A waste of money unless exact specification threads are essential.

Rather than do hard sums when using partial form inserts, I cut the thread to a middle depth, and then finish to fit by testing with a nut. I'm a metric shop, where full form is 0.625P and V form is 0.72p. I normally use partial form carbide inserts. For ordinary work I generally jump straight in by going 0.66 x pitch deep. If a close fit is needed, I only go in about 0.63 pitch and carefully fine tune to fit the nut from there. When using a V HSS cutter, I go straight to 0.72p, and don't worry about the result not being perfect metric - it only has to fit. Or I take a little off the rod diameter before starting, about 0.1xpitch, and then cut to theoretical depth.

if I have one the right size I always finish lathe cut threads with a die. Dies do a good job of getting the form correct.

Dave

Er no.

First, the profits made by energy producers during the recent price hikes, were and remain a scandal. Unfortunately, the government's decision to issue exploitation licences adds to their profits. Emptying the UK's North Sea oil reserves benefits producers, not retailers, and certainly not customers. The move is political, a temporary relief strongly related to a recent by-election result. It's designed to appeal to voters who don't believe in Climate Change or diminishing resources. They are of course wrong. If anyone likes the decision, I suggest they shine a bright light on it! I doubt they'll find any way in which the move benefits them personally. It won't make gas, petrol or electricity cheaper...

Second, outsourcing did not reduce the UK's carbon foot-print. Burning was transferred, not ended. The industrial products of outsourced burning are largely bought back by developed countries. We are still responsible. Rather than burning coal mined in Wales, to make steel, to build ships, we now buy ships built abroad from Chinese Steel made from coal mined in Australia. It doesn't matter where Carbon Dioxide is generated because we all live on the same planet.

Dave

The motor is more powerful than needed, but I'm not convinced it's worth changing it.

Deliberately putting a monster motor on a power tool seems stupid to me because it suggests the owner wants to force the pace. He assumes that the machine's safety factor will accommodate the abuse. Unfortunately overstressing the drive train, bearings and frame causes rapid wear, and the extra-power will cause more damage if there's a crash. As it takes time for trouble to appear, it may take a few years for the owner to realise he's blundered. In the meantime, ignorance is bliss!

But as the motor has already been fitted, and 1/3HP isn't outrageously over the top, I'd be inclined to live with it. The important thing is not to use the power by persistently driving the lathe hard. Driven sedately in the ordinary way, the motor will only deliver enough power to do the job - something under 100W rather than the >250W a 1/3HP motor could output if the operator pushed it.

Rather than relying on a small motor to reduce damage, the operator takes full responsibility and doesn't drive like a maniac. Most of us, I believe, learn fairly quickly that impatient gorilla tactics don't work well on hobby machines! Stripped gears, brushes burning out rapidly, fried electronics, smoking motors, knackered bearings, worn out nuts, poor finish and poor accuracy all suggest an excessively heavy-handed operator. Results and the life of the machine both improve if the operator backs off into the machine's comfort zone: patience rather than brute force. One of the reasons new professional machine tools are six to thirty times more expensive than hobby equivalents, is they are sized to work flat-out 24x7, and cope better with brutality. Used to the full, even they only last about 5 years before needing a major rebuild.  Used gently, they last for ever!

Dave

Edited By SillyOldDuffer on 02/08/2023 10:42:57

Naive question from me - what are metal-cutting chop saws for?

I own a mitre saw for woodwork, where it is extremely useful for quickly cutting largish sections of wood - up to about 2 by 4" Skirting, cabinet frames, pelmets, floorboards etc. Never done it, but I guess it would do plastic barge boards and soffits a treat. Not bad for PVC drainpipes. On the other hand it's not good for fine work like picture frames and PVC guttering didn't go well.

I imagine a metal chop-saw to be useful in much the same way. They're for cutting bigger box section, pipe, and sheet rapidly to size for structural work rather than making small numbers of precision parts. So not much use in my workshop, where a band-saw is about the right size for most work, and it runs quietly and doesn't make much mess. For larger lumps I've started using an angle grinder - outside only, because it's so noisy and messy.

The tools I buy are decided by the type of work I need to do, and at the moment I don't think a chop-saw is worth having. Maybe if I ran a busy workshop and got my metal from a shed full of chunky scrap. I'd definitely buy a chop-saw if I wanted to build a 40 metre antenna tower, where a few hundred cross-braces have to be cut to size. But I don't.

Am I right to think a chop-saw isn't for me?

Dave

It works either way round because the input is an alternating current. In terms of electrical function there is no difference between Live and Neutral, because they operate as a pair. But don't do it!

The important difference is safety.

Electricity suppliers make the system safer by ensuring that one wire is earthed, rendering it Neutral, that is at the same potential as anyone on the ground who touches it. No shock.

The other wire remains 'Live' and is dangerous. It coming loose and touching the metal chassis would turn the equipment into a widow-maker, except all exterior metalwork should be connected to earth, which instantly blows the fuse.

Fusing the neutral wire stops electrical fires, but it doesn't disconnect the live side, so the equipment is still a shock hazard. It fails dangerous. Then Mr Innocent opens the box and pokes around inside, wrongly assuming that the equipment has failed safe, and it isn't. To be safe the fuse must be fitted to the live wire, not the neutral.

General rule is to always unplug electrical equipment before going inside. Don't trust fuses at all! If essential to debug a live circuit, assume the worst and take every precaution. A few electricians are killed every year despite their training. Even when you understand, it's easy to make a mistake.

Dave