Member postings for Muzzer

Note that the LM2596 controller used on this module seems to be automotive rated ie -40...+125C case temperature rating. The pain threshold for most people is in the 50-55C region, so it may be fine as it is. Does a droplet of water on the device boil away after a few seconds?

In the limit, if it gets too hot it will simply inhibit the output until it cools down enough. Cooling the black resin surface won't make any noticeable difference - you'd need to be cooling the copper slug that's in contact with the board. Of course, these things are designed not to need much heatsinking....

Murray

Looks like an HSS tool. Pretty impressive but I'm not sure I would have the balls to use power feed myself. I always use power feed with my indexable tool to get consistent (and sufficient) feed but usually during parting there are one or two "events" that would finish off an HSS tool, as the swarf decides which way to exit the work zone.

Let us know how you get on!!

Murray

I input the measurements in inches if necessary but use metric units as the default thereafter, as my measurement instruments including my brain and machine scales work in mm. Things like threads can be displayed on final drawings as TPI etc if necessary. The power of CAD....

It's another old chestnut but I struggle with fractions, particularly when you actually have to work with digital values (eg "3 thou under 7/32" - what's that work out at??). Metric avoids all that.

Murray

Oh, dear! I see you are working in imperial units. That's the first thing that gets changed when I'm getting set up....

Merry

“Using cnc somehow suggests that your hobby is model making rather than model engineering, cnc is sort of.........................cheating?”

I consider myself more of an engineer than a craftsman and will never make models myself. Nothing against those who do (in fact I have considerable admiration for what they achieve) but I must say I’m struggling to discern the difference between a model maker and a model engineer - would one be insulted to be mistaken for the other?

Merry

The Bantam comes with a large T slot,as you may be aware. Didn't know the Student had this type of tollholder.

I don't have a DRO on my Bantam although I bought the components last year. I've been thinking about fitting scales to the saddle and cross slide but couldn't see how to justify one on the top slide. Do you have a fancy display unit that can account for the angle of the topslide or do you simply use it to measure linear movement regardless of the angle - and do you find that useful? My display which I bought in China for peanuts is really intended for use with milling and CMM machines and doesn't have any specific lathe functions.

For the moment I am making do with a butchered digital caliper on the tailstock but there are times I wish I had saddle and cross slide scales.

Murray

We're all different but when it comes to learning, personally I find that applying several different approaches at once gives the best rate of return ie working through the tutorials, checking out the Youtube videos and user forums, reading through a couple of "how to" books and getting your hands dirty - all at the same time. Trying to learn by only getting my hands dirty or by only trying the tutorials doesn't get me there as quickly.

For me this applies to most technical challenges, from new machines to new software languages - and CAD, CNC etc. To some extent I reckon the rate at which I can take this kind of stuff in has some bearing on the satisfaction I gain from it. Of course, the bottom line is getting something real out at the end.

Murray

It's human nature to dismiss anything we don't do ourselves and to be annoyed (partly with ourselves) when we come to suspect we were mistaken.

I may not be of watchmaker class myself but after the best part of 45 years of (both tutored and self-taught) manual and machine practice, I believve I have a reasonable level of machinist skills. I resisted looking into 3D CAD and CNC until the last year or so and now kick myself for being such a complete Luddite, despite the fact I like to think of myself as a technophile.

Engineering companies used to have vast drawing offices where parts were laboriously drawn up using slide rules and drawing boards (I know - I remember them well). The reason they have vanished is that a small handful of CAD engineers can do the same job much quicker and better - and print out automated part and assembly drawings, BOMs, GAs etc in minutes. What is wrong with that? I passed my BS308 test years ago but wouldn't dream of going back.

CNC isn't for mass production only. When you take into account that some one-off jobs require the work to be repositioned and moved from vise to rotary table etc many times, you are keeping yourself very busy - and working hard to avoid human error. Given the choice I don't see anything particularly admirable in persisting with manual methods unless you have an inverse snobbery complex going on. CNC's there if you want it and really the cost isn't the barrier.

Having said that, I don't think anyone here has actually suggested that beginners should shell out for big expensive CNC machinery, unless I've missed something. I think you'll find that most of the CNC users on this forum are actually pretty handy with traditional manual machining techniques but see CNC as another productivity tool (and possibly good clean fun - is that allowed??). Take a look at some of their photos if you need convincing.

Murray

Sorry, I misunderstood. I thought you were proposing to uprate the motor on a BP which sounded questionable.

Without seeing what your Aciera head looks like, I assume a vee or poly-vee belt would be more than man enough. I'm a VFD preacher myself and like you I'd take the chance to uprate the motor if you are going to the effort of changing belts and pulleys.

Murray

Saw THE Vulcan bomber pass overhead some time around the 5th or 6th Aug. Can't recall exactly where I was but it would have been somewhere in the Yorks / Lancs (Pennines) area. Very majestic and ominous.Presumably on a test run or heading to an air show.

Last saw one in the flesh at an air show just outside Doncaster in the mid to late eighties. Took off and immediately went into what looked like a vertical climb. You could almost feel the noise in your bowels. A phenomenon I'll never forget that!

Murray

I suppose the technical answer is rather academic. However, if we supposed that for some reason we needed to manufacture steam engines using modern technology, you'd be using processes such as robotic arc welding, CNC machine/cut/bend, robot painting etc. As for gears, injectors etc, they would be designed in CAD and made in CNC machines. There would be little need for laborious machine "fitting" because these days you take account of tolerances in the design process.

You can see a lot of this already in use in products like pressure vessels, pipework, food and drink containers, advertising (on vehicles and buildings) and modern engines and transmissions.

I don't think there is any doubt it could be done but for one-off models it would be utterly pointless. As Bill points out, there's no call for these manual skills these days, hence no general capability exists out there.

This whole range of crafts and skills are certainly pretty demanding and I am staggered at the amazing results that many MEs can produce. I can say without any doubt that I could never achieve anything like that myself. This is not purely down to a lack of interest on my part as opposed to a simple lack of capability to begin with!

Murray

Edited By Muzzer on 20/08/2014 04:26:33

If you have a quick sniff about on AliExpress, you can find all the constituent parts for making your own CNC laser cutter or engraver, if that's your thing.

Here's a randomly chosen store that stocks those types of parts - motors, lasers, mirrors etc. Of course, it's questionable whether you are actually "making" your own machine rather than simply assembling parts from a kit onto your own framework. I would challenge anyone to make their own CO2 laser tube, mind...

There is a Darwinian risk to this kind of activity, as you could potentially blind yourself. Rather like using a machine tool without a guard I suppose.

Murray

"I may just put a bigger motor on mine and raise the head. I had assumed the Bridgeports were much more powerful."

You may not benefit much from uprating the motor. They aren't rigid enough to be able to tolerate significantly higher loads, so the only way you'd get to use higher spindle power would be by increasing the spindle speed itself. However, although the bearings might tolerate that for a while, they're not designed as high speed machines (balance etc) and the std pulley ratios aren't conducive to achieving that either.

With a VFD you can operate a std motor at higher than standard speeds, albeit at lower power. However, you may struggle to get all that power through a small (= high speed) cutter anyway. High power will most likely be required for hogging (ie bigger cutters with lower speeds and higher loads), where rigidity will be the limitation.

There are quite a few BP-derived machines that are more rigid (larger!) and more powerful. However, you can achieve a pretty respectable metal removal rate with the right cutters, speeds and feeds on the std BP machine. Depends what you are trying to do.

Murray

I have no comprehension of this concept that engineering (model or otherwise) is an activity you turn to once you retire, with no previous experience or inclination. I suspect many MEs are more like me - for whom technology and engineering are a lifestyle and a passion. I've spent most of my life since primary school immersing myself in technology of almost any form, from cars, bikes. electronics, software, machine tools, welding, building, plumbing etc both professionally (getting paid to enjoy myself!) and in my own time. It's about fun and enjoyment surely, not ticking off the days and weeks.

I'm not shy of getting my hands dirty and putting sweat into what I do but I'm not about to make my own machine tools from scratch or cut and file parts from solid for no reason. That would be completely stupid and I like to think when I am tackling a job I'm doing it in a reasonably efficient way. As I see it, engineers can tackle jobs that they or others may never have tackled before.

I don't get paid badly but I won't splash out silly money on selfish indulgences like flashy cars or big tellys. I have family dependents, mortgage, retirement etc to think about. When I buy machine tools, I buy quality used examples that are fundamentally sound but may not be pretty, at a fraction of new cost and often requiring me to put in a fair bit of elbow grease to get working. As for CNC and CAD costs, you can do pretty well without spending much. It's simply a question of what you want to spend your time doing. I suspect I have a lot less free time than many of the retired hobbyists but I try to make it count. Standing at a machine turning a handle slowly is ok for the first few minutes but after a few hours the novelty has worn off.

I've been taking ME and/or MEW on and off for almost 40 years and have never made a model as such. I'm not unusual in that - and it's not about to change. However, as an (initially) amateur engineer, ME was THE place to learn about workshop practice and is still pretty relevant.

If today's young engineers (makers?) had exactly the same experiences as we did at their age, progress would grind to a halt. It'll never happen of course, which is why technology is unstoppable. It's pretty well impossible for us to comprehend where things will be in 50 years from now but I'd love to be around to see it. It's going to involve digital control, power electronics, software, CAD and all sorts - stuff our kids have known all their lives but which wasn't even a wild imagining when we were young. I expect that filing simple components from lumps of metal won't be illegal but will still be a minority sport.....

Merry

Ian, I'm not quite clear what you believe a PWM motor controller to be other than a voltage regulator, given that we aren't talking about any form of speed or position feedback. Without such feedback, the torque-speed characteristic inherent to the motor is fairly poor and can't easily be improved beyond voltage regulation. It'll be fine for driving a filing machine.

BTW, the datasheet I linked to is simply the PWM controller IC that is used in the original ebay purchase. For a brushed DC motor, you can't really drive or control it any more efficiently than this. The controller is already using PWM drive and there is also a flywheel diode in there, as well as various protection functions.

Murray

A variable voltage DC supply is not the best way of driving a brushed motor, far better for your purpose in this case is a variable pulse width controller. eBay has lots of them

The LM2596 actually is a PWM buck converter, so it wouldn't actually be a bad choice for controlling a small motor. The switching frequency is 150kHz (hence the tiny inductor which is the small grey cube). The main issue here is that the max output of 3A sounds rather puny.

On the other hand, the 8A units are rather crude in comparison - they don't even have any form of current limiting or voltage regulation. The lack of current limiting may not matter much if you can avoid wiring shorts and the speed regulation will be pretty poor when driving a brushed motor anyway, even if you had a regulated voltage. As suggested, you'd want to fit a flywheel diode for driving a motor with one of these. Even better get a proper motor speed controller....

Murray

One of the most "valuable" products of my Bantam was one of those wooden telescopic toilet roll holder spindles. Pretty much justified the presence of that particular half ton of cast iron in the garage!

Interesting. Psophometers are used in telecoms to detect audible noise on the supply rails because if there was noise, you'd hear it on your handset.

I've tested telecoms "rectifiers" (PSUs that generate the 24V / 48V bulk power) with psophometers but never realised they were also used for testing high current connections. That way you would be able to "hear" a dodgy connection.

You live and you learn...

Murray

The terminology is a bit confusing but:

• BLDC (brushless DC) drives and AC inverters all operate from a DC source internally and generate an AC voltage as seen by the (3-phase) motor. Inverters that operate from an AC source (mains) actually convert the AC to DC first.
• Most AC motors are induction (asynchronous) machines. The torque generated is proportional to the slip frequency ie the difference between the unloaded speed and the loaded speed. The more you load them, the slower they turn until they reach breakover torque. The nameplate tells you what the speed would be at rated torque.
• The unloaded speed for 50Hz machines would usually be 1500 or 3000 rpm depending on how many pole pairs it has. For 60Hz machines that would be 1800 or 3600rpm.
• BLDC aka AC brushless are synchronous machines and need to be driven by a drive waveform that is synchronised to the position of the rotor. You can drive some of them open loop but generally you need a position sensor to do it. The simplest position sensor is a Hall effect device or devices that responds to the passing magnetic rotor.
• AC synchronous machines are pretty much similar to BLDC but are generally driven by a sinusoidal current (BLDC require a "6-step" trapezoidal waveform). They give a more constant torque output than BLDC but unless you are doing something clever with the position signal, you also need a higher resolution absolute position sensor like a resolver or encoder.
• There are inverters that can drive synchronous machines as well as asynchronous but I doubt any of us would have the need for one.
• Most inverters drive the motors with a PWM (high frequency on-off voltage with variable duty cycle) voltage but the current is smoothed by the inductance of the motor. It's the current that ultimately generates torque, so the PWM shape of the drive voltage has little effect on the performance, even though it results in a higher voltage stress on the insulation and can induce some nasty currents in bearings etc.
• If you spin up a synchronous machine (careful!) and look at the back EMF with a scope, you will see that some are designed for a sinusoidal drive voltage and some for a trapezoidal voltage. So as well as needing a position sensor, you need to provide the correct waveform shape.
• Proper DC motors are a different beast.

Hope that helps.

Murray

Is the one top right "before" and bottom right "after'? What's wrong with them. And did you make the piston ring - that looks tricky.