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Member postings for Billy Mills

Here is a list of all the postings Billy Mills has made in our forums. Click on a thread name to jump to the thread.

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Thread: Searching google
26/02/2011 16:30:16
If you google search help you get a very helpful selection of tips about searching e.g. a minus sign excludes whatever follows. Well worth looking at if you use search engines.
  
 Google guide lists all of the valid search options including filetype: (filespec) -which is a perfectly valid and safe option that can save a lot of time. There are a lot of options.
Regards,
 
Alan
 PS had the same attack of the smiles as the original post , perhaps it's a colon then brackets  eg   ?
 
Yes it is! 

Edited By Alan Gray 1 on 26/02/2011 16:37:05

Edited By Alan Gray 1 on 26/02/2011 16:37:48

Edited By Alan Gray 1 on 26/02/2011 16:39:47

Edited By Alan Gray 1 on 26/02/2011 16:41:08

Thread: mini electric motor
10/02/2011 12:49:15
Simular motors are used in electric flight, geared down 4:1 or so to drive a small prop. or as the muscle in very small servos.
 
Regards
Alan
Thread: pcb guillotine
10/02/2011 12:39:40
The Proxxon saws all have a dust extraction port for a domestic vac cleaner for dust extraction ( the circular and bandsaw models) and have good solid carbide and tipped carbide saw blades available. They are good for G10/ FR4 and PTFE substrates , SRBP laminates are also no problem. The small table saw is an entry level product with a fixed height blade, the larger table saw is a very potent small circular saw which is a very useful machine- would not be without one!
 
The scribe and snap method is just about OK for SRBP but stronger laminates tend to delaminate unless the scores go deep at which point you are almost through.
Liked the scoring jig!
 
Regards,
Alan.
Thread: Harrisons gearing and friction.
28/01/2011 10:27:08
Had a glance at Stuart's book on Sunday, ordered it that night , arrived Tuesday. It is the first detailed account of a John Harrison clock that I have seen, Stuart also gives a great deal of background detail and a concise history of early timekeeping. Some of John Harrison's thoughts and ambitions are quoted which helps form a much better picture of his genius.
 
A very good book.
 
Regards,
Alan.
Thread: Backlash - Steppers, Toothed Belts & Ballscrews
27/01/2011 20:00:41
Well how long is a bit of string? or how much money have you got?. Ballscrews generally have less backlash and can wear at a lower rate but it depends on their construction i.e. cost. Cheaper rolled screws are formed by rollers under extreme presssure, More expensive screws are ground and more accurate. If you don't keep the junk out of the nut it can wear although they don't seem to jam. The manufacturer can then fit different size balls to tighten it back up if local screw wear has not happened.
 
The Acme thread is a lot less efficient -harder to turn - but the nut should be adjustable to remove the backlash. Real issue is that after some time the screw wears in the most used parts then you can't have uniform nut tightness along the whole thread. A CNC machine tends to have a lot more action on the leadscrews than a manual machine so some sort of pressurised central lubrication system is very desirable -even essential with acme screws.
 
Many commercial machines use belts to connect the screw to motor, the belts are not a problem, with home use you may not need to ever change the belt. Some designers use the belt drive to change the torque/ speed/ step size or to tuck the motor underneath.
 
Oldhams can wear, the bellows coupler can be better long term. The coupler tends to be longer than the belt solution so the motor sticks out more. Some use rigid or no couplers, nipping the stepper flange bolts up last and praying that the screw and motor end up on the same axis.
 
Software can compensate the average backlash, a good test is a nest of circles stepped by 0.1" in alternate cutting directions or a square at 45 degrees to the X axis.
 
So how much backlash ? Well the stiffness of the machine is another big limiting factor. Given perfect ways and gibbs with great screws, if the machine is bendy then climb milling may end up badly.
 
You could fit the drives to the existing screws and add one shot oiling and linish the gibs then see how it runs. If or when screw wear is an issue then you can always fit ballscrews.
 
Regards,
Alan.
Thread: Cutting steel plate
27/01/2011 14:57:46
The Rage saw is great, for those wondering how it works there are bumps behind the carbide tips that limit the depth of cut so that the tips can always cut their way out as opposed to kickback.
 
This kind of blade is mentioned in the "technical" bit on www.atkinson-walker-saws.co.uk with a few other details. They make blades for all kinds of uses.
 
regards
Alan
Thread: Toolpost Grinding
27/01/2011 11:24:23
Perhaps a reversing switch might be handy!
 
Regards,
Alan.
Thread: Aircraft General Discussion
27/01/2011 11:22:28
Ady
Don't think you mentioned the scrapping of the Canadian Avro Arrow. Very much the same story as TSR2, very advanced, very high performance and chopped up including the jigs. Subsequent US purchase to fill the void? Nimrod chopped up - When's the AWACS coming then ?
 
Regards,
Alan.
Thread: Electric Motor Noise
27/01/2011 11:13:03
Steve, it was a bit more expensive than a Revox which was a domestic machine. That suddenly triggered an interesting memory. The Alistair Cooke "Letter from America" was sent over on 1/4" tape that was then replayed on a rack mounted Revox which had been used for a very long time, the capstan had worn down so the program would run a bit slow and over-run it's slot. So they told Cooke to slightly shorten the item as he was over-running, when the tape was replayed on the worn Revox it fitted fine.
 
The external rotor was good on radiated field but the main advantage was the flywheel effect from the largest possible diameter rotor (compaired with the internal rotor) to reduce flutter.
 
The mystery machine was a Stellavox Sp7 from Neuchatel. Like the Nagra 3 & 4 it was used for film sound recording and was also battery powered. The quality of the recordings was better than "Studio" recorders of that time because of clever design. These machines recorded a "pilot" tone from a generator attatched to the camera film transport. For 25 frames/sec it was 50Hz, for the US , 24 frames/sec and 60Hz. The pilot tone was recorded on two narrow tracks over the top of the full width audio track. One track was in antiphase and carefully amplitude balenced. So when you played back the recording with a full width head you only heard the program, the pilot balenced out completly . In the Transfer Suite the pilot head nulled out the program and replayed the pilot signal to lip sync the audio to the film. Simples! even a meercat could have done it!
 
The Stellavox had a very low rotor inertia because it was ironless- nearly all copper windings in epoxy. Unlike every other machine of that time you could run and turn corners whilst recording without any wow being recorded because the servo bandwidth was very high, the motor speed would vary to exactly compensate the motion of the machine around the capstan axis- but you can only do that when the tacho marks are extreemly accurate because the accuracy substitutes for the flywheel inertia that every other machine uses. If you ever use a magnetic recorder again try rotating the machine while replaying some music.
 
Sorry guys- way off three phase topic but hope you found it interesting as a different motor application!
 
Regards,
Alan.
24/01/2011 17:44:52
Well perhaps a small fryer would be handy for tempering......
Hope that your earplugs hold up until you can get a decent UK made motor.
 
Had a call the other day about my encounter with a motor with a static shaft and spinning rotor. Well I didn't say that it was 3 phase! It was an ironless PM motor in a professional tape recorder ( no, not a Nagra but close). The rotor was an epoxy casting containing skewed copper windings with a multipole commutator on top. There were optical tacho markings on the top which was read through multiple sensors to average out errors. The shaft was about 1/2" and was the direct drive for tape transport. It had a fast servo to set the variable speed with some precision, the opto tacho signal was limited then fed to a weise discriminator then to a DC power amplifier that drove the motor which was over 90% efficient. Very nice Swiss engineering, state of the art at the time.
 
It was a VERY expensive item 40 years ago . Just before letting a well known reviewer have this latest kit I did a quick test. The speed meter indicated that the motor was up to speed and locked but the tape did not move. The rotor was at speed but the epoxy casting and the shaft had divorced and were going their own ways. So even something as simple as a motor can sometimes do the unexpected.
Regards,
Alan.
Thread: DRO switch
22/01/2011 14:22:20
Another way would be to use a multiway connector on the display and matching connectors on the machines so you could have the display in just the right spot for each machine. If everything is grounded down there is no static risk in swaping the display over but keep the ground on the display.
Regards
Alan.
Thread: Metric or Imperial, Fractions or Decimals
22/01/2011 13:54:25
Terry
Have you gone mad? Pi has NEVER been exactly 22/7 since Archemedies time...it is more like 3.141592653589.......... If you must use approximations 355/113 is a lot better. And you such a stickler for accuracy and precision?
Regards
Alan.
Now wait for the explosion.........
Thread: Electric Motor Noise
22/01/2011 13:23:33
I purchased a machine from a gentleman who worked for a well known safe maker. He was very good at breaking into safes, the Company concerned rated their safes internally by how long someone in the know took to open it up. Their old style safes made in the UK took so long to break that the law would arrive before the safe was open. They closed their manufacturing in the UK, but sold Indian made safes under their label. They tested the new product. It took ten seconds to open so they had tested the safe and put the same reasuring tested by ......... sticker on the safe.
Sometimes qualitative assurances are not the same as quantitative.
Regards,
Alan.
Thread: Harrisons gearing and friction.
22/01/2011 10:32:41
It would not be too innapropriate to use ball bearings in a clock. There is a sample copy of the BHI Journal on the BHI website which discusses this application. About 20 years ago I was given a Devon Clock Co "Sea Clock" kit. which is very loosly based on H1. It has two compound pendula on two shafts connected by toothed quadrants and sittting in a total of four ball races. After assembly it would only run for around 30 swings before stopping. That was because the grease had not been flushed from the bearings. After trying IPA and meths with the bearings in place, I dismantled the clock then ran the races in white spirit which finally removed the grease.
Like the original, this deviant clock has the escape wheel mounted between the ends of the shafts. A pallet arm on each shaft alternatly locks on the escape wheel. This arrangement is very tricky to set up and somewhat counter-intuative. If both arms loose lock then the scape wheel spins up to very high speed then chops off two grasshopper's legs!
The clock is a very poor timekeeper however although it does use pendulum oscillators you can pick up the whole clock and rock it around without missing a beat. The poor timekeeping is due to a lot of different factors. The Q of the resonator is very low, there is loads of friction in the oscillator which causes each beat to roam over a considerable range. The saving grace -like some other clocks- is that the variations average to a mean rate that is not too far out over a day.
Regards,
Alan
21/01/2011 21:27:58
Harrison used four anti-friction devices for diffferent applications. These were:-
1 Use of loaded wheel material--oily woods in segmented wheels with radial grain
2 Anti friction wheels- pairs of plain edged wheels seperated horizontally with the shaft sitting on top of both wheels
3 Anti friction arms- two long arms ( about 12") with radiused ends, shaft sits in the notch between two arms, counterbalenced and sprung to allow arms to oscillate over a small angle- used on H1 on the axles of the inertial arms.
4 "Rollers".
The idea of the wheels (2 + 3) is to reduce friction by using mechanical advantage. Imagine that you have a 1/16" shaft resting on a 3" plain wheel with plain bearings with some friction u. When you turn the shaft 1 turn the bearing shaft rotates by 1/48th turn so the friction is u/48, a large amount. However there are two plain wheels at each end of a horizontal shaft so the overall reduction is u/12 but still a great advantage and totally in keeping with the concept of no lubrication. So the principle emerges that you get a friction reduction of vr/4 with four wheels where vr is the velocity ratio i.e. the ratio of the shaft to wheel.
You stop axial movement on the main shaft by turning a short taper to reduce the diameter to the wheel contact section so the shaft is centred between the cones, the turned down diameter in contact with the wheels being the smallest that you can get away with!
The only currently made anti-friction wheel device that I know of is the prop balencer made by SLEC. The same idea can be used for loco wheels or motor rotors. There is a single wheel bearing on a tumbling barrel in the Stott Park Mill.
The roller bearing is very different to the anti-friction wheels, in the roller bearing the details of the roller constraint set the frictional losses however lateral shaft constraint can follow the concept of cones as above.
Regards,
Alan


Thread: Parting off on Myford lathes
18/01/2011 02:16:13
Yes but what about the parting off on bendy lathes with top slides?
Perhaps we could get back to the shear plane sometime?
All of this persecution is just too complex.
Alan.
 

Thread: Electric Motor Noise
18/01/2011 02:08:14
I would readily agree that the bearings are the most likely problem but it is surely better to listen to the bearings- at both ends- with a stick of wood to hear the sound of the fault. If the bearings are noisy( and maybe the shaft will move axialy) then the noise is a grinding sound- but nearly all ball  bearings will make some noise of this kind. If there is a buzz involved then loose lams or windings may be involved.
 
I have seen cages rocking on shafts and 1 case of a rotor rotating at normal speed with a completly stationary shaft on a very expensive swiss machine so I do not rule out anything without hearing what the symptoms are before dis-assembly.
Other encounters have been untied/unvarnished windings and foreign ferrous objects - like the e clip that the service person dropped or the tiny rare earth magnet that dropped out of a reed  door switch that ended up inside the ali cased motor on the lam stack and made an extreeeemly loud noise. Always the first clue is the nature of the sound but I now never try to underestimate human activity- it delays finding the solution.
 
Steve's sperical integration is not so great, you need a chamber, the gear and a lot of time to integrate  positions, hardly at home stuff. I will stick with my wooden stick and personal aural analyzers or Spectran if I want pretty pictures.
 
regards,
Alan.
17/01/2011 20:17:57
Think that the conclusion should be after the test and examination. If the windings or laminations are the source then 20p's worth of  the right varnish in the right place should fix it without complications. The bearings are best tested on load but if they are rattling around new then the remedy is obvious. Either way around you have to take the motor apart and be carefull...
 
Regards,
Alan.
Thread: Parting off on Myford lathes
17/01/2011 19:30:18
Gentlemen
 Everyone has different experiences and equipment and therefore opinions. Lets ask what is happening under normal conditions. The tip of the parting tool is fed into the rotating workpiece so that the tip penetrates into the rotating cylinder. The material above the tip is compressed beyond it's yield point and is detatched. You could say that the rotation of the workpiece and the presence of the tip steadily working toward the centre of rotation propagates a spiral crack.
 
The forces involved in making the material detatch are very high and act vertically downwards on the tool for front mounting.  If the cutting edge becomes rounded then the forces increase. If the tool is forced into the workpiece then the amount of work needed to remove the material above the tip increases rapidly. The amount of force acting on the immersed tip of the tool is not far short of destructive for the tool.
 
So we can suggest several failure modes. With zero clearance we could have chip jamming causing the swarf to jam the tool into the sides of the cut. We could see a detatched wedge of material of larger than normal thickness combining with another part detatched chip wedging against the tool causing an impulse to the tool with an elastic rebound causing a dig in where the tool breaks. There is also the chance that the tool+toolholder+mounting+slack slide system has a resonance. Once the mean free length of the chips times the surface speed hits the resonance then the tool starts oscillating, heats, blunts and digs in. 
This latter concept does fit the noise before dig in experience.
It would not be too dificult to fit sensors to a machine to find out why although we may already have all of the clues needed!
 
Regards
Alan.
 

Edited By Alan Gray 1 on 17/01/2011 19:59:45

Thread: Electric Motor Noise
17/01/2011 18:26:45
Peter,
Would suggest the large wooden stick to the ear method. With the far end pressed firmly against the bearing covers you can listen to the noise from the bearings at each end. Be careful that the stick does not slip, don't use a screwdriver!
 
Apart from the bearings the other sources of noise are likely to be poorly clamped laminations or poorly varnished windings both of which will buzz at a multiple of 50Hz. A special air drying varnish is used to secure windings and laminations which does not damage the enamel insulation on the windings.
 
A slightly more scientific method would be to use a spectrum analyser. Fortunatly there are some very good freeware downloads that run a fast Fourier transform on a PC soundcard to give a realtime spectral display. Spectran from www.weaksignals.com is an easy program to use with a modern electret mic in the mic input.
 
Bearing noise will be broadbandish, winding or lamination noise a multiple of 50Hz, a periodic rotational noise will be slightly lower in frequency than the mains because of "slip". Bet you can't resist making silly noises and looking at the spectra!
 
Regards,
Alan
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