Here is a list of all the postings SillyOldDuffer has made in our forums. Click on a thread name to jump to the thread.
|Thread: Belt grinder advice please.|
Basically the power needed to drive a machine tool is related to the metal being cut and how fast you want to remove it. A small motor can do the same amount of work as a big one, it just takes a lot longer!
How much work is required to remove a cubic millimetre of common metals:
Aluminium Alloys - 0.3 to 1J
It takes about 2 Joules to remove a cubic millimetre of mild-steel and a Joule is a Watt-second.
Grinding 100 cubic millimetres off a mild-steel bar would take a 500W belt grinder:
(2.0 * 100 ) / 500 = 0.4 seconds
A 2500W belt grinder could do the same job in:
(2.0 * 100) / 2500 = 0.08 seconds
Knife grinders work with hardened steel, say 8 Joules per cubic millimetre. Shaping the blade of a largish knife, which might include grinding fullers, means removing a lot of metal - perhaps half a blank. A 200x6x40mm blank might need 24000 cubic millimetres to be removed. On a 500W grinder:
(8.0*24000) / 500 = 384 seconds
(8.0*24000) / 2500 = 76.8 seconds
Makes sense for someone making lots of chef's knives out of old farrier rasps to own a powerful grinder. The same machine isn't an intelligent choice for someone doing occasional light work in brass and mild-steel, or someone who needs the grinder for sharpening rather than serious metal removal.
When buying tools I always ask myself what it's for. Usually there's a huge gap between what I want, (a pristine tool-room Dean, Smith and Grace), and what I need ( a mini-lathe ). 45 years ago an old chap bent my ear about the inexpensive Japanese socket set I'd just bought. He told me cheap rubbish like that is a waste of money because it won't last. 8 or 9 old-bangers later, the set is still in perfect condition today. Buying the quality socket set recommended by the old chap would have been a complete waste of money.
But I do recognise that pride of ownership is important to many. If spending time and money on good tools is your thing, go for it! But don't tell the wife or your accountant!
|Thread: DIY Bed Gap|
Well, it's Terry's lathe and he can do what he likes with it!
Bodge maybe, but it's an inexpensive modern machine unlikely to become a collectors item. It's just a tool.
Cutting off the section of prism Terry highlighted is unlikely to effect the rigidity of the bed much; I think on the 290 the rear V stops at the headstock anyway. The rear prism has no function at that point - the tailstock can't get anywhere near the proposed gap unless the saddle's been removed.
Jason mentioned the problem that would put me off most which is the difficulty of getting tools close to a large disc on these machines. On these machines the saddle design makes it awkward to approach an unusually large diameter object without overhanging the tool risking chatter and poor finish.
Why Terry's brake discs have such short lives only he can answer. Moving heavy loads in hilly terrain near salt water would do maximum damage. Friend of mine traced his problem to being a keen musician performing 2 or 3 times a week. With the band's heavy kit packed into his car his late night drive home included a long empty ring-road where he would hammer up to several roundabouts at 70mph (possibly faster, ahem) and then slam the brakes on just in case. His discs lasted a lot longer when he took to driving less enthusiastically!
|Thread: Cheap DRO for Mill|
Criticism of the display jumping as described is a little unfair in that it seems bad rather than being a real problem. The accuracy of most basic scales is typically 25 micron, or 0.025mm. So the display jumping 0.02mm as you creep up to a measure isn't surprising and despite appearances the result still isn't so dusty. 0.02mm is rather less than a thou. The easiest thing is to ignore display jumps unless you're doing something requiring special accuracy - a difference of 0.02mm is often small enough not to matter. If high-accuracy matters, double check that whatever scales and display you buy are actually better than 25 micron, many aren't. Also, unless you own a hot machine in good condition, it may not live up to the promise of a high end DRO display and expensive scales.
When my cheap scales die I'm going to open the wires up to see if they're shielded or not. I had suspicions about shielding when mine misbehaved but I couldn't recreate the fault by putting the wires near mains cabling. In my case the problem was a loose USB plug vibrating mechanically. However, a loose plug might not be properly shielded, explaining Ed's symptoms. Certainly we agree the USB side of these units isn't covered in glory!
Despite shortcomings, even a simple DRO is far better than driving a mill on the mechanical dials. The inexpensive Warco scales may not do PCD calculations or be highly accurate, but they eliminate operator mistakes caused by misreading the dials or forgetting to allow for backlash, and even the cheapest DRO can do Imperial and Metric.
Edited By SillyOldDuffer on 23/04/2019 17:30:54
|Thread: Safety of phone chargers|
Interesting, let's hope it's a rogue example.
What's your friend doing about it? Did he use a Registered Electrician or notify Building Control himself? Either way there's a complaints procedure.
Awkward questions may be asked if he doesn't have a certificate as a result of having a cowboy to do the work and not telling Building Control. 'By law, all homeowners and landlords must be able to prove that all electrical installation work meets Part P, or they will be committing a criminal offence.' Likewise, if your friend is a fraud victim, pretending to be a Registered Electrician could be embarrassing for the offender.
I'm not defending the current way of doing things. Shifting responsibility to the purchaser and supplier rather than having an Government Inspector on the job makes it too easy for shady types to get away with stuff. It also puts responsibilities on customers they may not be aware of, like only recruiting qualified people. Unfortunately it would require a major policy change to undo 40-odd years of deregulation and I don't think politicians of any flavour have it on the agenda, nor are they keen on funding enforcement.
We live in an imperfect world!
|Thread: Z Axis-Support|
Further to Simon's query about Nm, I did a bit of internet searching last night whilst watching telly and found a mix of struts being sold in Newtons (which I understand) and Nm (which I don't). If Nm is a typo, lots of people are doing it! No explanation for Nm as applied to struts, nor a clue by finding an example measured in both N and Nm.
Nm sort of makes sense as a measure of torque force, but as Simon said, the theory doesn't wash. In the non-torque sense a Newton Metre is a measure of work - a Joule - but that makes no sense at all. It's a mystery...
|Thread: Safety of phone chargers|
Warships are a real world example where a ring-main can be undesirable. Ships are compartmentalised by waterproof doors and bulkheads making wiring, piping and ventilation a challenge!
It's good when several compartments are serviced by a ring main because the lights stay on should the ring be cut in one of them by battle damage. Not good if damage or flooding shorts out a ring in one compartment because that removes power from all the others and causes chaos.
The account I read (long ago!) concluded ring circuits were to be avoided afloat, but it also criticised radial installations, for example because they imply complicated duplication and rerouteing switchgear. Anyone know what's recommended afloat today, perhaps they mix and match?
Thanks Phil, you spotted I was over-simplifying at best and disgracefully tongue-in-cheek at worst! Always good to be put right by someone who really knows what he's talking about!
|Thread: Z Axis-Support|
Offered as a suggestion!
I think the force needed to operate the strut is given as a torque measurement because they're most commonly sold to support car tail-gates or boot lids.
The diagram shows a tail-gate applying a weight to a gas strut. More force would be applied to a strut mounted in the blue position than one mounted in the red position. So choosing the right strut depends on the weight of the tailgate and the struts position along its length. As the tail-gate is hinged, a turning force is applied to the strut and, like a torque wrench, it's expressed in Newton metres.
I won't attempt the maths needed to translate 850Nm torque into the equivalent weight of an up down milling head. My maths is terrible at the best of times and I've got hay fever. 85 Newtons is roughly 85kgf, or 190lbf.
|Thread: Cross slide backlash|
Most lathes have a bit of backlash and it doesn't matter much. It has no effect whilst cutting pressure is applied.
The usual problem is when you reverse the tool out, have a think, and then go in for another cut forgetting the need to compensate for backlash. But provided you are in the habit of reversing out a little further than the backlash, then the dial will realign correctly before the tool reaches the job with the calibration still correct. Not difficult to do when the backlash is small, but easy to mess up when the backlash is very bad. How big is your backlash?
Beware of obsessively minimising backlash. Often done by tightening everything up beyond the point severe wear is caused. Sometimes it's best to leave well alone.
|Thread: Safety of phone chargers|
Two basic ways of wiring a house for electricity. You can either connect each socket individually back to the consumer unit where it is fused (star or radial) or you can connect several sockets in a loop connected at both ends back to the fuse box (a ring main).
There are advantages and disadvantages to both systems, but being a true-blue Englishman I shall claim the British ring main is for real men while radial systems are for girly girls and nervous colonials.
Not only is UK mains full throttle 240VAC but our domestic ring mains are typically good for at least 32A each. Pumping 32A or more into an electrical fault is a bit scary. The UK designers knew there might be a lot of heat if something went wrong and to minimise the fire risk they decided to fuse all the plugs in the system 13A, 5A, 3A or 1A depending on the appliance. The fuses aren't there to stop people being electrocuted or to protect the appliance, they are installed to stop the wiring catching fire and burning the building down.
Not all countries are happy with ring mains. A safety advantage of radial wiring is the lower current available at the socket (which is often fused) makes overloading of the wiring less likely, in consequence such systems don't require plugs to be fused. Not inferior or better, just a different approach.
Wherever you live appliances are mostly fused internally to protect themselves; these typically blow well before any fuse that might be in a plug. These appliances are suitable for both Ring and Radial systems.
A criticism of the ring-main approach might be it was designed at a time when people owned small numbers of power hungry domestic appliances: irons, kettles, immersion heaters, electric fires, and vacuum cleaners etc. In contrast most modern homes actually contain large numbers of small consumers - radios, TVs, computers, hifi, phones, clocks, printers, wifi, and rechargeable toothbrushes.
Which system best suits today's homes could be debated endlessly, I reckon its six of one and half a dozen of the other.
|Thread: How can I change colours in a jpeg?|
Another beginner mistake is trying to learn how to use complex software by reading the built-in help! The 'Help' provided with software varies considerably in quality, but it's quite common for the 'Help' to be Reference material rather than a User Guide. It's for checking points of detail and not for explaining fundamentals.
The effect is like trying to learn English with only a dictionary; very difficult! Wanting to ask the way to the Zoo, you start by reading that 'A' is the first letter of the alphabet, and is the 'low-back' vowel, formed with the widest opening of jaws, pharynx and lips. About 2000 words later (there are 12 definitions of 'A' ), you reach the first real word in English. In my dictionary, it's 'Aal', "a species of Morinda, whose roots yield a red-dye". Not only are you nowhere near 'zoo', by now you are thoroughly confused by a host of new words and abbreviations, like 'proclyptic' and OE.
Sometimes software 'Help' includes a comprehensive set of Tutorials, but - until the jargon is learned - it can be hard to find the particular tutorial you need.
If you have a particular task with GIMP or any other high software, the internet is your friend. If you search for 'gimp change colour tutorial', you should get several tutorials showing various ways in which the job could be done. There is more than one method, which is best for you depends on the nature of your image.
Usually a good idea for newcomers to follow tutorials exactly at first. If you try and adapt one to do your job without understanding it, you're liable to come unstuck. There is a lot to image processing.
My GIMP help works fine and it looks to cover beginner basics fairly well. Unfortunately I'm using version 2.99, which is the development release, and the help may be different to that provided with 2.10
Edited By SillyOldDuffer on 22/04/2019 12:20:41
|Thread: Safety of phone chargers|
I hate generalising because there are always exceptions, in this case if someone has picked up a cheap nasty example!
However, the few phone chargers I've opened up have all been fused internally without a conventional mains fuse in the 'plug'. With one exception, the fuses were soldered in and it wasn't immediately obvious which sub-miniature component it was. The sub-miniature fuses used may be more sensitive than usual mains types, the only one I was able to identify was rated 160mA, which makes a 3A fuse look like a monster.
Another generalisation is the design of these small power-supplies makes them unlikely to fail in a way capable of drawing a heavy fault current. Most of the components are delicate and fuse-like in themselves. Overstressed they either go open circuit or burn-out in a flash. An older transformer based wall-wart might be more hazardous, but the examples I've disembowelled have all had wired in fuses and sometimes a thermal cut-out as well.
These units aren't intended to be repaired when the fuse blows.
Little cause for concern if the charger came with a new phone, or is a genuine replacement. All bets are off if the charger was bought new for a quid from Flash Harry at a car-boot sale...
|Thread: How can I change colours in a jpeg?|
GIMP has a tool for doing this. From the menu bar click, Colours->Map->ColourExchange. It gives a dialogue like this:
The colour exchange dialogue lets you select a colour from the image (with the eye-dropper button) and then change it to another colour. The new colour can also be selected from the image, or it can be set manually to anything. The RGB threshold sliders control how close you have to be to the selected colour for the change to be made: this is necessary because many images are built of similar but different shades.
By default colour changes are applied to the whole picture but you can select a specific area to work on. Works fastest and best on images with a simple colour scheme - can be hard work on images packed with subtle shades.
Another possibility is to convert the image to greyscale and then 'Colourify' it. (Like tinting an old black and white photo)
Francis makes a good point about GIMP's steep learning curve. It's easy enough when you 'get it', but it's NOT like Photoshop or other picture editors. For example, the screenshot above shows GIMP uses 3 separate windows to do its stuff: this alone is enough to blow the mind of many a newcomer! It's done that way so power users can edit with more than one screen: typically a big screen is used to display the image and all the controls are out of the way on a smaller one. Great feature but it tends to stall the average Joe out for his first test drive.
Well worth persevering with if you want a high-end image editor and don't like Photoshop's license system.
Charles probably doesn't need to worry about absolute position. He's frame stacking on focus to increase depth of field rather than to improve signal-to-noise as the astronomers do.
Given an object like the head of a wasp, I guess Charles would start by focussing a highly magnifying camera lens on the very front of the insects head. As the camera is only in focus in that particular plane, most of the head will be more-or-less blurred, not a good photo. Moving the camera to focus on the middle part produces another image, again mostly blurred but now with the central plane in sharp focus. Repeating after moving the camera to focus on the rear of the head, and you get 3 mostly blurred photos, each of which is good at one point. Focus stacking creates a new picture by combining the in-focus parts of the three duds, essentially by ignoring anything in each image that's blurred.
Charles hasn't said what his lens is, but no doubt it's far more tightly focussed than would allow a good photo to be captured from only 3 images, hence he proposes to take 2 or 3 hundred. Provided he has a reasonably spaced sequence of images it should work without any need for CNC-level precision or accuracy. I don't think focus stacking needs to know how far the camera is moved, nor is it critical to move the camera exactly the same distance each time. A few missed steps resulting in duplicate images are unlikely to make much difference. The software cares little what the distance between frames actually is; whatever image it gets, blur is suppressed and focus retained.
What might cause trouble is moving the camera backwards and forwards during a run. As moving the camera along the rail alters the apparent size of the subject the focus stacking software likely compensates by resizing frames on the assumption camera movement is linear. Either forwards or backwards, but never a mixture.
The number of steps needed to get a good composite is related to the depth of focus of the lens. Too few steps and the composite will be inferior to the best possible, too many steps wastes time because adjacent photos don't differ enough in focus to matter, and they increase the risk of unwanted artefacts appearing due to computer processing.
Adrian is right to suspect the accuracy of micro-stepping, but my experience with a rotary table suggests it's much more reliable than 5 steps in 30! Provided the motor is lightly loaded and not driven too fast with an adequate driver, it should work well. I'll be surprised if Charles doesn't get good results - unless his stepper motor is tiny.
Any chance of sharing some pictures when it's working Charles? It's an interesting project. Macro-photography and frame stacking go together like bacon and eggs!
|Thread: How to level BOTH the Myford cabinet and the lathe bed?|
The main reason for levelling is to provide a known reference against which structures can be designed to transfer forces to ground without twisting, toppling, or otherwise stressing the construction.
For example, a brick tower is most stable when erected so that most of the forces (mainly weight) are kept vertical and transferred directly to ground. The easiest way to do this is to level the foundations and carefully align the walls as they go up with a plumb-bob. An arch-bridge is a different proposition because the forces have to travel safely sideways before they can go to ground at an angle making it harder to design a brick-arch than a tower. However, assuming a level is still the easiest way to calculate the forces involved and then to manage construction of the arch. Although it's possible to design and build at angles off vertical, it's simpler to do everything relative to a well-established real-world plane.
A secondary reason for levelling is to provide a reference against which adjustments are made.
As a Myford Lathe on a stand is both a structure and a precision instrument, levelling is done for both structural and adjustment reasons:
Levelling may not matter much - you might have a good floor and a decent stand from the get go, whilst Chinese lathes tend to have stiffer beds, and many industrial machines are massively rigid. Other lathes are more sensitive and I think this is why Myford owners worry more about levelling than others.
It's for tuning out errors that an engineering level is most useful, but as they only register on a surface that's already nearly level, using one might force the full 3-stage levelling treatment.
Once a machine has been set-up rigidly it's not necessary that it be level in operation. Plenty of lathes used on ships at sea...
Not sure if it will hold accuracy well enough for your purpose, but if you know backlash to be equivalent to 13 microsteps, then change the code to add 13 extra steps each time direction is reversed.
After making sure backlash is taken up at start, say the platform is moved forward by turning the screw 500 steps. No problem with backlash. Also, if the platform is advanced in the same direction by another 20 steps, there's no need to compensate for backlash because the screw is still engaged properly.
But when the direction is reversed backlash kicks in and the screw has to be turned 13 steps in the new direction to re-engage the screw; after that the normal move should work.
if ( directionChanged )
Adding a correction on each reversal might be 'good enough' but because the computer can't guarantee its exact position over time the platform may drift sufficiently away from it's calculated location to mess with the focus. If that happens either:
Assuming a digital camera such that you can see the platform is out of position because of backlash, it would be possible to combine the compensate on reverse method with a manual rewind to start as in 1, at any point the operator decides a reset is necessary.
|Thread: Cam Calc|
I'm committed to a social weekend unfortunately, but a quick look at the code suggests it might be fairly easy to convert into something that will work. No promises because there may be hidden complexities and I don't understand the maths but I'll see what can be done later. What platform are you on, Windows, or Linux?
PS Typical, no sooner do I press send than I see Roderick posting he's the original author and already has an Excel port - if you'd said Windows, that's probably what I'd have used!
Edited By SillyOldDuffer on 19/04/2019 16:15:18
Which Cam Calc do you mean Graham? A quick search on the web found one belonging to Westmer, previously available as a program, now only available as a programming service, POA.
There's another discussed on ModelEngineerMaker that looks to have gone through various implementations, some of which are certain dead-ends.
Or this web-based effort, which is hasn't been updated for 11 years and wants long obsolete versions of Internet Explorer or Firefox2. I tried it and it works OK up until it tries to load a Java applet, which it can't find. That's certainly because <APPLET> is itself obsolete and modern browsers only respond to it by throwing a warning message. The current HTML language reference says:
There is now very limited applet support in most modern browsers, as they no longer support the NPAPI plugin required for showing Java applets. This page exists as a reference only."
It might be possible to get it working on an up-to-date computer by loading Firefox53, how to installing older versions here. I wouldn't bother, could be a lot of computer hacking with no result. Though CADCALC should work OK if you can find a computer that hasn't been updated for a few years, this CADCALC really needs to be re-written.
|Thread: Cheap DRO for Mill|
What makes a difference to a DRO is the how well built and protected the scales and electronics are, and to a lesser extent the features offered. For high-precision work, different types of scale technology are available. A high-end DRO will be mains-powered, with well-sealed scales, smooth action, and bullet proof electronics.
In comparison, I bought a pair of Warco's cheapest and fitted them to my mill, an easy job. The scales are battery powered lasting 9-18 months and each scale has it's own readout unit, a simple plastic box with a magnet on the back, with a a small unlit LCD display. The display is inferior to the nice combined XYZ and keypad units that have to be bolted to the head. The scales are unshielded and must be vulnerable to coolant. Reset accuracy OK - within ±0.02mm. Perhaps because I don't often flood cool, the scales work fine: after 5 years an occasional wipe with a tissue has kept them in good order. The only fault was mounting the displays on the motor control box caused one of them mismeasure when the motor was turned off. This turned out to be due to contactor thump shaking a slightly loose USB connector: moving the displays fixed that, but note USB connectors aren't supposed to wobble! Otherwise the DROs turned out to be a bargain: they make a huge difference to milling.
However, despite satisfaction, when they fail, I'll go up market. Although they've been reliable, the vulnerability of the scales is a worry and I don't entirely trust them. (Causing time-wasting double checking). The batteries are a pain, and the display hard to read and inconvenient compared with a combined unit. Although the scales provide 'good-enough' accuracy for most of what I do, improved accuracy would save time when being spot on matters. I rarely work outside a 200x150mm footprint, and the DRO is accurate within that range. I'm not so sure it's good to ±0.02mm across the entire travel of the table, about 550mm.
As a hobbyist my experience with this DRO has given me confidence in the very basic breed. But they wouldn't do in a more demanding workshop. Chaps who need to crack on would be frustrated by the hard to read displays and tiny buttons. Keeping an eye out for misread measurements caused by mucky scales or dying batteries slows everything down. Having confidence about the accuracy of large movements might be vital. Most of this can be fixed by doubling or tripling the budget.
If you really need the very best, buy from a professional supplier. Not many do, the very best is very expensive.
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