17322 forum posts
'cause it's easier for them to set their compass to the radius
|not done it yet||20/02/2020 08:24:40|
|4170 forum posts|
No, not really. They only use a mm measuring stick in schools? Setting a compass doesn’t rally come in into use for determining the value of Pi - one of the first things for students to investigate and determine that Pi is a constant.
In real life we measure diameters, not radii. When did you last measure a radius? What are your drills marked in? Radii, or diameters? When did you last turn a bar to a radius? So it goes on - diameters are far more useful/important than radii.
Same as teaching subtraction in schools - a cluttered top line when so easily the number changing could be spread over both top and bottom lines of the sum. Different approach but the same outcome (with fewer mistakes, I would suggest).
They would need to find a centre first, so if drawing it they might as well draw a diameter.
It comes down to just using r^2 instead of (r^/2) ^2, which, of course, simplifies to D^2/4.
|Mike Poole||20/02/2020 08:32:21|
2446 forum posts
I’ll pop down the Workshop and bin my radius gauges now! Well perhaps not.
|47 forum posts|
Edited By Tricky on 20/02/2020 09:02:18
|Michael Gilligan||20/02/2020 08:59:36|
15029 forum posts
You’re right, Jason
But [despite protestations from ndiy] it’s even better than that ... it’s also purer
I didn’t attend ‘good’ schools, so I was not weaned on Euclid ... but in later life I have come to realise that study of his ‘Elements’ would have been time well-spent !
Like many others, I was taught geometry with barely a nod to this masterwork. [*]
[*] which, as recently posted on another thread, is available in English translation in a very accessible format:
Edited By Michael Gilligan on 20/02/2020 09:02:50
|Andrew Johnston||20/02/2020 09:45:19|
5203 forum posts
In Euclidian geometry the circle is defined by the distance known as the radius. So it's logical that properties of a circle, like circumference and area, are defined in terms of the radius.
The equation given by Nigel is only true if there is no pilot hole, which would seem unlikely, although it hasn't been explicitly stated.
|Neil Wyatt||20/02/2020 09:51:37|
17391 forum posts
I don't have a WM18 manual but one for a similar machine states very clearly:
"Never force the tool or attachment to do the work of a larger industrial tool. It is designed to do the job better and more safely at the rate for which it was intended."
|Howard Lewis||20/02/2020 11:26:20|
|2927 forum posts|
Putting aside the semantics of using radius as opposed to diameter in calculations, as a spectator, it seems to me that the lesson is that if you overload a machine of any sort, you damage it. How badly will depend on the safety factor, if any, designed into it.
The manufacturers of my small car specifically forbid fitting a tow bar, or any towing. So I don't.
Years ago we used to tow in Buses and Coaches with a Series 2 Land Rover. It regularly had gearbox problems, and failed a clutch. We had no alternative. Does anyone wonder why the failures happened?
As previously posted. "Know the limitations"
17322 forum posts
More like cm, don't think they have heard of mm
Strangely in woodwork I often use a roundover bit in a router and like most other bits the curve of the cutting edge in stated as the radius. Look at my recent CNC posts and you will see me frequently mention a corner radius cutter. In another thread we are talking about bending pipe to a tight radius, crests and valleys of a thread form are in radius and so on.
But I'm sure you are happy that the far eastern machines state their capacity as diameter unlike your old lathe that measures what it can turn in relation to radius.
Edited By JasonB on 20/02/2020 12:18:48
|5370 forum posts|
Got to say NDIY has a strange notion of what's taught in schools. Perhaps he remembers what he was taught and assumes that today's equivalent has been dumbed down. My granny thought anyone who couldn't name all the bays, capes and rivers around the british coastline was a hopeless thicko.
I happen to have a GCSE Maths Textbook and it doesn't support NDIY's simplistic view. It's about triangles based on chords leading into trigonometry in the widest sense. It describes 3 different ways of calculating pi, none of which are how it's computed today, but hey it's historically correct. Radius and diameter are described in a way making it fairly obvious they're both useful.
In respect of geometry, trigonometry, graphs, probability and algebra it seems GCSE covers much the same ground as my O-Level maths syllabus did. But a couple of differences leap out. First, GCSE puts more emphasis on practical applications, I remembering feeling O-Level maths was too theoretical and none of it was useful. Second, a fair amount of new ground has been added to GCSE - transformations, symmetry, and data, while others like Matrices, algorithms, critical path, and statistics have been extended.
Although there's a fair amount of common ground, I wouldn't be confident of passing GCSE Maths today without doing a fair bit of study. And at my age I'd rather sit on my fundament & tell youngsters how much harder I had it when I was their age. They nod politely, but know I'm hopelessly ignorant of their challenges and can't be trusted to remember a short shopping list, or who's birthday is next!
|Andrew Johnston||20/02/2020 13:39:19|
5203 forum posts
Hang on while I go and get my wind up handle. Does the syllabus cover non-Euclidian geometry then? You can't calculate pi, only approximate it, as it's an irrational number.
Wouldn't want to sit my school exams today, although I didn't exactly cover myself in glory at the time either. My secondary school assessed me in the stupid category.
|Andrew Johnston||20/02/2020 13:46:21|
5203 forum posts
I'd disagree with that. Sure if one runs a tool into a rotating chuck for instance then something is mostly likely going to break. But if I overload a machine tool simply by being over-ambitious with the cut then I expect the machine to survive without damage. By experiment I've proved that most of my machine tools will happily survive an overload without damage. The only exception is the horizontal mill; as I've never got close to overloading it.
|Howard Lewis||20/02/2020 15:12:46|
|2927 forum posts|
It has to be doubtful if any designer allows for a toolpost being run into a chuck. Few of us avoid that failure of care!
What do you expect to happen if you hang a 500 Kg load from a length of 2mm diameter mild steel wire?
Hooke's law will provide you with a beautiful example of a cup and cone fracture, because of an overload. in tension.
The fact remains, as I said earlier, if you overload something it is likely to suffer damage. The extent of the damage will depend upon the safety factor designed and built in.
An overloaded machine tool, will with luck, have the belts slip, if not, the overloaded motor will overheat and suffer damage to the insulation. How long before the motor fails depends upon how long it is allowed to overheat.
Increasing belt tension, to prevent slip, may damage bearings eventually.
If you lock a Myford by engaging back gear without freeing the bull wheel, when you hit the chuck key with a heavy hammer, you are very likely to break the chuck key, or teeth off the gear. You have overloaded things, and they break, because you have exceeded the load, shear, torsional, or tensile that the part was designed to withstand.
I ran my saddle into the headstock. The pinion engaging the rack, and the rack, were damaged. Simply because I overloaded things, Accidental or deliberate, damage ensued.
Many years ago a tower crane collapsed on the London North Circular Road. Like all tower cranes, it had been designed with a small safety factor . The loads imposed by high winds, and having been locked so that it could not "weather cock" to minimise side loading, resulted in loads in excess of the maximum allowed for by the safety factor.
Possibly if the safety factor had been greater, it might have sagged or bent, but not completely collapsed, killing people.
The C47 Dakota was designed with a large safety factor. During WW2 in the far east one was loaded with, supposedly Aluminium perforated runway strips. When it had struggled into the air and delivered the load, it was found to be Steel! A smaller safety factor would probably have meant the aircraft collapsing on the runway, and never even managing to get airborne, But that event must have surprised the designers!
You are experienced enough to know that beyond the yield point, the elongation is permanent. U T S is the abbreviation for Ultimate Tensile Strength. If you exceed it, it breaks!
So we should work within the limits of our material of machine, or suffer the consequences.
|Dave Halford||20/02/2020 15:29:43|
|616 forum posts|
Does it then go on to document those rates? It would be really useful if every machine was supplied with at least the max boundaries. Just saying capable of drilling16mm is no help if half the available speed range might burnout the motor. My old lathe has the dangerous threading speeds marked up on the gearbox as for backgear only.
The old iron is better argument is kind of pointless as there's not enough to go round so the newcomers have to buy Asian.
I do wonder how many Asian machines are out there, out of guarantee with overloaded electrics waiting for the shed roof felt to blow off just for the lack of guidance on speeds and feeds that could have been supplied with the machine when new.
17322 forum posts
Worth bearing in mind that many of these machines don't have the traditional V belt so may not slip as easily. Many have Poly flex or Poly vee belts which will grip for longer or like my previous Emco lathe and current X3 mill have a toothed timing type belt from the motor.
I seem to recall that this mill has already stripped a gear and we don't know if it has been regularly expected to drill holes larger than 16mm so this may simply have been the straw that broke the donkey rather than going bang the first time it was overloaded. Just have to hope the newly fitted Z-axis power feed was not being used to force the drill into the work which would remove all "feel" for the forces needed!
Edited By JasonB on 20/02/2020 16:04:33
|5370 forum posts|
Told to "Let the tool do the work" when I was at school. And we were beaten if caught misusing tools. Didn't make any difference, most men in a hurry will thrash the machine. And some folk are naturally heavy handed, insensitive to the sound of distressed mechanics, and unable to smell smoke. Damn the torpedoes, full speed ahead! Testosterone rules, KO.
|176 forum posts|
So many explanations of what went wrong and why it happened at what needs to be done to fix it.
Prevention is better than cure. Fit a an AMP meter to the DC motor leads in a position where you can see it easily..
Fit auxiliary cooling fan to the motor
Mark the Meter With Maximum Rated Amps of the motor.
Adjust the speed and feed to below the marked amps.
A KB Electronics AC to DC controller set up correctly with the "Locked Rotor Test" to Less than the rated motor AMPS will trip on excessive loading.
Either one will will help I prefer both "Belt and Braces" man myself
Edited By oldvelo on 21/02/2020 18:05:12
732 forum posts
Bugger, for some reason I have never recd email notification of replies to this. Poss because I forgot to check the box.
So appologies for not replying.
Yes an expensive lesson thats now fix. It was the motor and I suspect I had cooked it when I had a jam a couple of months ago and beoke the sacraficial cog between the motor and spindle and then the drilling opperation was the final straw. Warco had stock and got it next day. Cost £270!!!
Now I see that Ian was offering his grrrrrrrrrrrrrrr My loss
My pal also suggested I 3 phase it but that was after I had bought the motor
So Ian, in case there is a next time what motor did you use for the 3 phase conversion and was it a straight saw or did it need some fettling?
Email noitification box ticked
732 forum posts
I just saw the first page when I posted my reply but oh boy 3 pages
Skimming thro I would agree that it was my fault, impatient git that I am and the learn the hard/expensive way.
732 forum posts
One of the problems with the WM18 is the motor is emclosed in a fibre glass case with little ventilation. When I stipped the old motor down it was obvious it had overheated several times so some sot of aux fan would help. Have a few large computer fans lying around that I could use. Note sure where I would fit it ie above the motor and would it suck out heat or blow in cold air?
However I also understand that because I have fans does not mean I can, again, try to make the mill do what it was never inteneded to do.
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