Here is a list of all the postings Simon Williams 3 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Magnetic bases - stored on or off?|
+1 for Robert's explanation above.
As far as I can see, no-one has explained that the function of the on/off switch is to short-circuit the magnetic flux in the OFF position, and to remove that short circuit in the ON position. So the "switch" function is analagous to that of a parallel shunt in an electric current circuit. The magnetic flux never goes away, the off position of the "switch" just routes it internally so it doesn't pass through an external object. The switch routes the flux internally in the off position, and routes it externally via the pole pieces in the on position.
Of course the statement that the flux never goes away is a bit of an assumption, and this goes to the heart of the original question. Magnets not made with rare-earth compounds are prone to losing their flux intensity (de-magnetising) if they are left open circuit ("ON" in this application) and without a keeper (Old Mart's bit of steel stanchion). But that goes back to the dark ages, and any magnetic stand made in the last (say) 60 years is not going to be made of materials with such a significant design weakness.
And Robert is also right about the safety aspect of this. Getting your finger pinched in the (reducing) gap between the magnet and its attraction hurts. A lot. With modern rare earth magnets the attraction force at close range can be more than your skin can support, at which point it becomes an amputation. Ouch!
The mathematics of this are simple. For a simple magnetic circuit, the closing force (force of attraction) rises as the inverse cube of the separation. So magnetism is a short range force, and the cartoon characters being sucked onto a magnet over inter-stellar distances weren't paying attention in school physics lessons.
Rgds to all
Edit - to be fair to Neil his post (while I was typing mine) introduces the magnetic "shortcircuit" concept, so my apologies for saying no-one had explained... etc. As ever, someone was typing a more succinct and elegant answer while I was still en route.
Edited By Simon Williams 3 on 04/04/2021 00:25:59
|Thread: Problem with an Altivar 11 driving a 3 phase motor.|
Apologies to the OP for butting in, but :
Old Mart, could you possibly point me at the reference you found for a factory reset?
I have two of these units (Altivar 11) I bought from Germany, but they have been programmed and locked with remote software and I have failed to connect to them, let alone guess the password. I'd love to try a factory reset. Both of them work OK but not at the settings I want to use.
Many thanks in anticipation and excitement (it doesn't take much these days!)
Best rgds to everyone, hope your Easter Egg chocolate weekend goes well.
|Thread: Allchin TE model in the Times|
Nice looking model of an Allchin TE has made the cut in the "News in Pictures" section of todays Times.
Not too sure about the copyright implications of linking to it here, but it's easy to find though you may need to be a subscriber to access the inner workings of the paper.
|Thread: Myford Layhe|
If I may suggest -
Give some thought to the buyer's constraints on collection. Something of this ilk is actually pretty fragile (woe to the carrier who drops one of these!) and would normally be best served by "collection in person only"
But present constraints on travel and meeting etc curtail such. I have dipped out of several such transactions over the last few months for not being able to "collect in person". Quite apart from the restrictions (and cost) of travel I don't think I can justify the journey.
The restrictions relax shortly, but the idea of two people trying to load this into a van while maintaining the rigours of social distancing is a cartoon waiting to be writ.
There isn't really an easy answer at the moment, but hopefully these tribulations will pass ere long.
|Thread: Weller Soldering Iron tips|
If you append two zeros onto the number stamped on the end you get the nominal temperature in fahrenheit to which the temperature control operates.
So 7 - 700F = fairly normal for 60/40 solder or its more modern lead free equivalent
8 = 800F = blooming hot
|Thread: thresher belts|
FWIW twisting (crossing) the flat belt coming off a traction engine or a portable engine has nothing to do with reversing the drive, and everything to do with keeping the belt on the drum.
The friction face to face of the cross-over damps much of the vibration in the belt and helps control the amount it whangs up and down with the torque impulses from the engine. The engine, of course, runs equally well in either direction.
All the best,
|Thread: Advice and guidance for arthritic folk|
A fascinating chance observation about feline dysautonomia
In 1987 or thereabouts we lost two cats to what the vet determined was Key-Gaskel Syndrome. Both were DSH about 3 yrs old. If I've understood you correctly this is the same condition you have described above.
I put it down to overdosing them with an organo-phosphate based flea spray, but your comments lead me to wonder if that was not the explanation.
Whether it was or no, they didn't make it.
If you would like to know more PM me.
|Thread: 2-Part Covid Vaccinations|
It's a mistake that all the journalist make to assume that the statistical figures quoted mean anything useful when applied to one individual. It's a mistake to particularise from statistics.
Whether you (as an individual) contract the disease is controlled more by the "hands, face, space" concept, together with the local prevalence of infected and infectious candidates.
The 67% protection figure simply means that the number of infections in a sufficiently large sample group will reduce by 67%, it doesn't follow that any one person's chances of getting infected are reduced the same. Either you get it or you don't. It does however seem to mean that the whole group (i.e. a group of a statistically significant size) is protected to a large extent from acquiring a potentially fatal illness.
Remember that the vaccination program isn't about protecting individuals. It seems to be achieving that but it's incidental. The point of the vaccination program is to change the statistics of hospitalisation, severe illness, death. On a country wide scale - a statistical sample of about 65 million individuals - even quite low effectiveness percentages give wholesale benefit to the population.
Given enough vaccination recipients, the concept of herd immunity starts to affect the mathematics, and (hopefully) our present constraints on our way of living become irrelevant. The "R" index is controlled not by physical distancing (social distancing) and precautionary measures such as shielding, but by a natural mass immunity and the consequent reduction in the number of carriers (infectors).
But (unfortunately) no-one's told the virus to play fair. We could be here some while yet.
|Thread: What alternative size motor pulley?|
However there is a complication which confuses things, particularly with significant differences between driver and driver (correction driven) diameters.
The actual running ratio of flat pulleys is properly calculated using the effective neutral radius of the belt wrapped round the pulley. That means that the smaller pulley in the drive (the driven pulley in the second stage, the driver pulley in the first stage) is effectively BIGGER than it's outside diameter. The same is true of the bigger pulley, but this has a smaller effect.
In this example you got two corrections which must nearly cancel each other. But don't be too surprised if the calculated speed isn't spot on with the reality.
I'm sure I'm not alone in looking forward to seeing how the results turn out in due course. Do let us know.
Your comments about needing double pulleys for the first stage are right, at least to maintain approximately the same centre distance of the pulleys. But with flat belts this will make the whole arrangement bigger and bulkier.
Edit - typo in italics
Edited By Simon Williams 3 on 14/02/2021 15:43:12
Based on your declared pulley diameters the final spindle speed works out to be 605 RPM. Which begs the question of why 874 rpm was ever mooted, but it is what it is.
Still everything points to the choice of 2.25 ins dia as the motor driving pulley. Go for it!
No point in worrying about 840 or 874, I rather doubt if this exercise is that accurate!
On the basis of 1425 rpm in, step down is presently 1.75/8.25, so countershaft speed would be 302 rpm. There are several approximations in this calculation, so achieving 285 rpm as you have measured is within the realms of believability. Motor should be running a bit faster than the rated full load speed anyway.
To change the top speed, as discussed before the answer we've come up is go for the 2.25 inch option. By my arithmetic you should should end up with 600 x 2.25/1.75 = 771 rpm (ish).
But we still haven't understood why your present top speed is so far awry. If you could advise the outside dia's of the two pulleys making up the second stage drive we can follow the logic.
Sorry, hadn't seen you had added that info when I pressed the button to post.
Edited By Simon Williams 3 on 14/02/2021 15:02:13
I'm assuming there is another second stage step down (actually step up), and the OP is simply considering an alteration to the first stage drive from the motor to the countershaft.
I'm just wondering if one of these stages is actually slipping, hence my wondering if a flat belt is in the mix.
So a list of the pulley train diameters and a measurement of the input speed would allow us to model the behaviour and see if it makes sense.
Edited to add "Step up\"
Edited By Simon Williams 3 on 14/02/2021 14:23:35
As Hollowpoint says, 2.25 is the better option on the face of it. The arithmetic says 2.45 ins PCD is needed, so 3.25 is a step too far.
The arithmetic is simple enough - new pulley dia = 1.75 x 840/600 = 2.45
But I'm profoundly suspicious that all is not that simple for the speed to be that far off the mark. Lathes.co.uk says 874 rpm is the top speed, and 600 rpm is the next speed down. Seems a bit basic, but are we missing a trick here?
What speed is the input motor actually doing? If you can check the spindle speed can you check what the motor is doing?
Is this a flat belt final drive?
|Thread: Seized stopcock|
I hesitate to be the party pooper, but please take into account that introducing oil or penetrating oil into the public water supply (even if it is only your own individual supply) is illegal, and carries quite stiff penalties. It's not just jobsworth pedanticosity, even small quantities of hydrocarbons will taint your supply and you will taste them.
Materials in contact with drinking water must have passed through the Water Research Council approval program and be WRc approved.
There are food grade lubricants about - Rocol make one called Foodlube which can be bought in an toothpaste tube, but to the best of my knowledge it doesn't have WRc certification.
The materials used by the water companies have to be DWI (Drinking Water Inspectorate) approved, which is even more stringent to ensure that even small traces of deleterious substances are kept away from the public water supply.
Best answer by far is as suggested - get your local Water Supply Authority to check over their stopcock, so you or they can isolate your supply. Then remove and replace the offending consumer side valve.
You may have difficulty retaining command of whether a water meter is fitted or not, depending on the local policy.
|Thread: Noga Rotodrive|
I managed to coerce Santa Claus into putting a Rotodrive in my Christmas stocking. The little one (10.4 mm dia) is absolutely marvellous.
On the strength of this I have since bought the bigger one - the 20 mm dia version, which is less convincing and a countersink in a battery drill is better 'cos you can push harder.
So I have managed to convince myself that the bigger 30 mm Rotodrive is probably not worth the money, not for me anyway.
Best prices I found for genuine Noga stuff were from Farnell. There are clones, no idea if they are good, bad or indifferent, but some of the prices look a bit less exotic.
|Thread: Push broaches for square holes|
I've got a 1/4 sq push broach, and you're right they do cost north of £100 a kick. BUt if you would like to PM me with details of what you want done I'll consider doing same for a small fee to charity.
Quantity, material, length of hole, any orientation requirement, any thing else relevant. Can't remember the size of pilot hole offhand but approx 6.5 mm - it's slightly larger than the across flats dimension of the square hole. Broach cuts dead to size 0.250 across flats IIRR.
Where are you - I'm in W Glos UK. Forgive me if we don't meet up, present restictions as you know, but if you can post me the bits I'll make the hole and post 'em back
Best rgds Simon
|Thread: Parting 1 1/2 phosphor Bronze|
Well, someone is welcome to correct me if they'd like, but I think that ain't phozzy-bronze, which is a pretty pink colour because the addition of phosphorous reduces the oxygen content and leaves the bulk material near the colour of fresh copper.
It's not aluminium bronze, which is a pig to machine cos' it work hardens and grabs. It is a much lighter yellow.
That sexy sun tanned golden colour is a different relative of the bronze family, with all the potential delights of work-hardening characteristics.
My comments earlier were based on the supposition that the parting tool is the normal way up in the front tool post. Now we know it's upside-down in the rear post the logic is reversed. So the cutting edge is too low.
Another cause of the OP's symptoms could be that the tool is chipped, moving the actual cutting edge and making it less efficient. Either way all that heat is trying to tell us something.
Please forgive me if this sounds silly, but those circumstances say "tool above centre height" to me.
Probably need to use zero or very small top rake as well. If the tool grabs go slightly negative as for cutting brass. If it truly is phosphor bronze, and the set-up is stiff enough, you should be able to peel out a nice even spiral. I agree with the suggestion to go fairly slowly.
If things are getting hot that means there is rubbing not cutting going on. The majority of the heat should be carried away in the waste chip material.
What machine are you doing this on?
|Thread: HSS Tool Geometry|
Assuming we're talking HSS here, there is no such thing as a roughing tool, and of the two shapes shown in the original post the right hand one is a left hand tool. As has been said by others.
"No such thing as a roughing tool" is a sweeping statement, but on a small power lathe it is impossible to get enough power to the cutting edge to take advantage of shaping the tool cutting edge to cut freely and easily so as to maximise the metal removal rate. The best you can do is to remove metal efficiently, which means shearing it off the workpiece cleanly and quietly, without tearing. That's done with a finishing tool. The only difference between a roughing stage and finishing is freshly sharpening the tool, giving it a lick with a fine carborundum stone to make sure the edge is good. Putting a radius in contact with the cutting zone is generally counter productive. However you do need to take care setting the angle of the tool face so it takes a shearing cut off the remnant work (we're talking turning a cylindrical surface). Too long a shearing interface gives rise to chatter, so anything wegge shaped or cutting a chamfer is counter-productive.
Achieving a fine finish is partly about having something other than point contact between the cutting tool and the work, which is where the misconception about putting a radius on the tool originates. A radius on the end of the tool is there to extend the life of the tool, not to give a fine finish. It will give a better finish than a point tool (zero radius) but that is a red herring. Fine finish on a small lathe is about having a shearing action going on at the work/tool interface, and above all not letting the freshly sheared metal pressure weld either to the tool or the work piece it just left. That's partly (largely) why HSS tools like cutting lubricants.
For best efficiency with limited power at the cutting edge, the tool cutting force reaction should be at right angles to the tool travel. That isn't the case with a radius as the cutting interface, but it is exactly how the traditional knife edge tool operates.. If so, this has the result of no lateral force on the reduced diameter after the chip has left the work.
Carbide tools use a completely different process to cut metal, and by and large if you want a better surface finish change to a fresh tip, then go faster, deeper quicker till you find the sweet spot. That's because the cutting action is a hot form action away from the tip of the tool - the tip itself isn't shearing metal like a HSS tool does, it's causing a pressure zone.
All of this is covered in the books recommended. though Sparey (love him to bits) spends time discussing carbon steel tools, which is of his time. The recommendations he makes for those tools translate well to HSS
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