By continuing to use this site, you agree to our use of cookies. Find out more

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.

<< First < Prev 10 11 12 13 14 15 16 17 18 19 Next > Last >>
Thread: Surface Roughness Measurement
04/11/2010 20:05:02
The paste layer may be limited by particle size and compressability then. So any old paste is a no go. The case for lapping the heatsink seems stronger still, if you ensure that any high spots are lapped off with a non-embeding abrasive then the surface defects should be pits rather than peaks and fill in with paste.But how flat is the module?
 
Your original question on surface roughness remains interesting. How do you depict a three dimensional surface in a single number? the answer has to be an "engineering approximation " that is very measuring method dependant- just as hardness testing methods are- but more so because of modality. SEM on E-bay? For heatsinking we want the plateau to valleys area ratio with no mountain ranges at all! 
Regards,
Alan.
 
 
Thread: Metric vs Imperial - Practical or Traditional?
04/11/2010 01:55:07
Chris ---- Deep significance--- the great numerator in the Sky has given you 60 posts TWICE at two different times . Is that a hidden message that there is life beyond 10? i.e. should we count on ten fingers then multiply by 6 toes to get base 60 i.e. SIX times better than decimal could ever do?
 
There is hope for the Human race after all. Except when it gets cold with snow on the ground and you might have to take both socks off. Below 32 degrees F we might have to revert to thumbs and fingers base ( at least in the UK )
 
Regards,
Alan.
04/11/2010 01:47:24
SI rationalised physical units, it was not part of any conspiracy. The Arabs gave us base 60- hence 360 degrees as an angular measure and 60 divisions of the hour and min.
 
The time units go straight into frequency units and are deeply ingraned so don't see that ever changing. The general public don't need to know about the Cs resonance definition to catch a train or a TV show. It works fine and is built into every clock dial and gearing ( ok wheels then)
 
The Earth's orbital period is not up for  change so our day  week month and year are unlikely to change. Every earth society is based upon agricultural annual cycles to ensure food supply. That sets the midwinter festival, harvests and sowings at set times independant of your number of fingers.
 
Model engineers will continue to arge the merits of linear measurement systems while everyone else just gets on with it in rods poles  perches chains or metres.
 
Regards,
Alan.
Thread: Mistakes in Van Rennes article
04/11/2010 01:12:53
I cannot see how David can produce as many pages every month without the odd problem. There is  the dilemma of people- who are not natural writers- describing their ideas. Do you edit the article back into "house style" or let the writer ramble?  What do you do with drawings that miss out important details, have missing views or are inconsistent? How do you cope with howling errors without upsetting the writer? How do you do it all seamlessly, be all things to all men ( and women) , put it to bed every time without fail and keep smiling  while readers love to spot and spotlight the errors and omissions.
 
 David, you win my admiration for being able to do this and more on a long term basis. Steve does have a very good point however, a peer review panel is a feature of nearly all technical and scientific journals. To have several different people looking at  new material might just cost a few subs but would be a way of ensuring that the error count could be  reduced. With email the whole process of review and correction could be quick and painless. There are a lot of talented specialists on this forum,  they are just waiting for the call to arms.
Regards,
Alan.

Edited By Kelvin Barber on 04/11/2010 08:34:37

Thread: Surface Roughness Measurement
04/11/2010 00:13:15
Andrew
Why worry about surface irregularities of  fractions of a uM when you might have 35uM of much higher thermal resistance in the way? The surface finish is far less significant than flatness over the area of contact. Some semiconductors are best lapped against the heatsink. Many other power modules are on sheared integral heatsinks which are far from flat. 
It is always worth testing with blue to see how much contact area you actually have. You can use the regular irregularities to dither the binary  blue/no blue by getting the thinnest coat posible then looking at the blue /silver graduation.
 
 There is one common app where the power density is much higher, CPU's . The interesting detail is that there is a mounting pressure advisory from the manufacturer which few motherboard mounts can attain long term. Some CPU's dissipate 150 W from a 10mm x 10mm area, the ordinary blown finned al heatsink + smear of grease can give 0.1C/W, better with a silver loaded grease. Think that I would worry about the device contact over the very large area and how it will be maintained.

regards,
Alan

Edited By Alan Gray 1 on 04/11/2010 00:16:21

Thread: increasing milling machine speeds.
03/11/2010 23:38:04
Dave,
You don't say what size cutters you want to use. If you are  around or under 1/8" then speeds of 5,000-20,000 might be needed depending on what you are cutting. That is why some mills have seperate high speed heads for vertical milling to replace the standard spindle. 
 
The forces are very much lower with small diameter cutters but the bearings of standard mills are not normally rated for anything like the speeds needed for small cutters.  One option is to get a high speed  Kress  head and mount that in place of the vertical head. The mountings can be a lot lighter than for full size cutters.
 
Regards,
Alan.
Thread: heat treatment oven
03/11/2010 23:19:32
Second Keith's suggestion, for around £30 you can get a temp controller which will display and control the temp. Some models will also control the temp profile against time.
Regards, 
Alan.
Thread: Warco WM180 motor control
29/10/2010 15:57:08
John
 
Don't know your machine but wonder if there is an opto tacho connected to the corner connector. Would suspect that a dirty or failed slot sensor could produce the fault. With no tacho signal the controller would run above the set min speed. Would never rush in to modify stuff without understanding what we are dealing with.
 
Regards
Alan
Thread: Electronics in retro fit of CNC control on X3 Mill
28/10/2010 15:11:25
Had a quick look at the part 3 article on Arc's site. There were two 7490 decade counters in the original design which was pictured in the article. You could use one of the switches ( that were not in the circuit) to get 1, 10 or 100 to 1 reduction in the jog rate. Those are the two larger IC's on veroboard.The 100:1 was found to be not very useful so was left out.
 
There is another, smaller IC  ( LS7184)  which is an interfacing device, it converts the two quadriture signals ( A & B) from the encoder into clock and direction signals. This IC also multiplies the clock rate by four. Most serious of all is that the divider will never work at all. The diagram shows the clock is not connected to the divider ( pin1 BD in) at all!
 
Regards
Alan

Edited By Alan Gray 1 on 28/10/2010 15:13:25

Thread: Dynamo/generator.
28/10/2010 14:41:48
Here's a twist in the story. The Dynamotor did not normally have an output shaft and is truly obsolete, it is heavy, the brushes wear out, it is noisy electrically-needs "hash"filters and takes up a lot of space.
 
You might find a motor with two sets of brushes - one at each end and two commutators. It is a servomotor with built in tacho generator. One set of windings are low resistance for the motor, the other windings are much thinner wire wound in the same slots. Sometimes the larger versions use seperate short slots for the tacho rotor windings.
 
The integral tacho provides a direct voltage proportional to rotor speed with polarity indicating direction of rotation. When used with a good bipolar servo amp you can get a very high performance servo loop.
Regards,
Alan. 
Thread: Electronics in retro fit of CNC control on X3 Mill
27/10/2010 14:22:47
CPC have always stocked active and passive parts, their origins - as with RS- were in the Radio/TV servicing trade. They have very good prices on connectors and made up leads, CAT 5 leads are a fantastic bargan from them as are very many other bits. Use them a lot.
 
Would not argue with John S about the origins of the controller however  Steve is looking for a simple way of testing his work so the rotary encoder is a simple way of getting there. Decent encoders are a bit pricy but you could rig up a trial with an old scroll wheel mouse and a D type flip flop.
Regards,
Alan.
26/10/2010 21:11:35
Think that the other IC  provides  gates. The basic idea of the controller is very simple, there is a rotary encoder which generates pulses when turned, the 7490 decade counter is used to reduce the pulse rate from the encoder. So it is a bit like putting a reduction gear between the knob and encoder.
 
Any division will aid slow adjustment, 4,8,16,32 are all very easy and cheap to arrange. But the whole thing needs redesign to bring it up to date. Tried looking for the article on the Arc site but the PDF's don't seem to want to open.
regards,Alan.
Thread: Dynamo/generator.
26/10/2010 20:37:36
Paul,
You have a rotary convertor, around WW2 vintage. It was used to generate the voltages needed for valved electronic equipment in a car, lorry or tank.  From the voltages  would suggest a transmitter or radar equipment. It is a 12V motor with extra windings and commutators-but no drive shaft.  As the motor spins the secondary windings see a changing magnetic field that induces the higher voltage in the secondary coils. Millions of these things were made in WW2. With the advent of  transistors rotary convertors became obsolete.
regards,
Alan
Thread: N.V.R. switch
25/10/2010 23:22:11
A common China type NVR fitted to many machines has two push on connectors for mains in and two identical connectors for mains out. If the connections are reversed then the coil will be on all the time and will burn out. A buzz from the NVR when off is a good clue!
 
For this type, the coil is wired to the output terminals so you can check in and out by measuring the resistance between the terminals. Had a brand new belt sander from a well knowen supplier that had this problem.
Regards,
Alan.
Thread: Drill Sharpening Jigs - Advice please.
24/10/2010 21:44:55
Had a look for  John's Christen machine, found the spares and operating instructions at :-
www.christendrillgrinder.com/manualNOV2009.pdf. It is not vastly more complex than many T & C grinders but has a 20x microscope for aligning the drill. The operating instructions and the parts drawings might give the keen all they need!
 
One of the interesting details is that this is a 0.5-6mm drill sharpner i.e. it works in the range where the simpler adaptors fall off. But £9,000 buys you a lifetime supply of drills and some!
 
Regards,
Alan.
24/10/2010 15:26:51
The Tormek jig and their grinderwould take you into £400 region depending on the grinder chosen. That is a lot of drills. Having said that, I am a great fan of Tormek, their slow wet grinder is the fastest way of getting brilliantly sharp edges on edge tools time and time again. The grinder is a large wide stone wheel running around 90-120 rpm, the stone is immersed in a water bath at the botom. The bare stone is about 220 grit but with a re-grading stone you can convert the grade to 1000 grit.
 
There is a round bar mounted parallel with the stone axis along which all of the jigs are mounted so it is easy to remount a tool for resharpening. The stone is dressed with a diamond tool referenced to the bar. All of the jigs from Tormek are very well designed and easy to use alloy castings while their use is described in a book and DVD with current updates on the website! The system includes  leather honing wheels as well.  Jet make simular parts at lower prices.
 
Don't have the drill jig but can say that wet grinding is very effective and completly avoids the risk of destroying edge temper. The other key detail is that the edges have much greater smoothness than from a 36 or 60 grit dry wheel so cut  with less force and better surface finish.
Regards,
Alan
Thread: Midlands Model Engineering Show at Warwick
22/10/2010 01:19:57
I would love to see  larger shows with more small stands as well as the larger ones. However it is a chicken and egg affair, high stand prices stop smaller people who often have the interesting bits.
 
Many locations are grossly overcharging, one London location doubled their two day hire rates from one year to the next. So the show went from two days to one day to never again.  All shows have best days and dull days, Fridays and Saturdays are generally good, Sundays around 30-40% of Saturdays, Monday and Tuesday are time to be elsewhere.
 
My experience in a related market is that the traders are too worried to speak out against rising costs,when they have had a few bad shows they pull out or show wherever else they can. The traders will not admit that they had a bad time for fear of not being offered a stand next time so the whole structure can fall apart very easily because people don't speak out.
 
Anyway it was great being a buyer for a change, there were some good bits to be had  and it is always nice to actually see the stuff in the metal instead of pictures. Meeting Sir John and Adam Stevenson was great as was looking at the work of real craftsmen.Good show but concerned about the future.
 
Alan.
19/10/2010 20:50:29
One exhibitor told me that his 10'x10' stand cost him £1500 for the 5 days, this is around the same rate as we pay for the NEC!. So if you have a normal retail margin you have to take £4500 to break even on the stand alone, add in 5 days stay with food, staff and travel costs and you might begin to understand why some exhibitors are no show at all. We did not show at WEC, we are in a different but simular business.
 
We also show in Chicago, Holland and Germany. The cost of a stand in these places is ONE THIRD of UK costs. At the NEC we pay £50 for a two day 250W electric supply- we get free electricity in the USA, Holland and Germany. Sales are 130-210% GREATER in these countries than in the best UK shows. The facilities for visitors and exhibitors are better too.
 
The out of UK shows  are attracting more exhibitors and visitors, when there is more to see more go to show and more go to see. In the UK we are up to our normal business practice of  stuffing ourselves.
 
Alan.
 
Thread: Testing Stepper Motors/Drivers
14/10/2010 20:32:57
Joe
You probably can use your audio oscillator, you just need a simple interface. Any small npn transistor emitter to ground. Audio osc to base, collector to STEP input - might need a pull up - say 1K ohm from STEP to +5V. Set the oscillator for 100Hz, 1V or so output. It probably has a source impedance that will limit the base current to a safe value. If you are worried then stick a 1Kohm in series with the base.  The pulse shape will probably be quite quick enough for a stepper driver without squaring up. 
Regards,
Alan.
Thread: A strange fluid
11/10/2010 19:31:53
Howard
Think you have been slightly lead astray. The gap is small so that the fluid breaks down and allows current to flow into the workpiece. That detatches a small sphere of the job which is in the gap. If you don't flush out the "swarf" it accumulates. You can't have the flow on then off! the flow is continuous. When the spark passes through the dielectric it vaporises the fluid then the vapour channel collapses when the current stops. If you get it working nicely there are hundreds of  thousands of sparks per second.  Each spark is around a micro-second. It makes a nice fizzing sound.  There  is a fair bit of dielectric flow with some jobs however flushing removes the conductive material from the gap, it is more important with deeper jobs.
 
It is common to rough out with a high current then finish cut more slowly at a lower current. If the machine ( and the Operator) is up to it the finish can be  very good. Electrode wear is down to the material that the electrode is made of (- Copper , Copper -tungsten or graphite are common) and the type of pulsing used, Graphite can have much lower wear rates than metalic electrodes and machines beautifully. Don't think ringing has anything to do with it. The physics happen when the channel ionises, not after. EDM is very inneficient in energy terms, the dielectric can get very hot however it does stuff that might otherwise be impossible.
Regards
Alan.

Edited By Alan Gray 1 on 11/10/2010 19:33:35

<< First < Prev 10 11 12 13 14 15 16 17 18 19 Next > Last >>
Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts
Support Our Partners
cowells
Sarik
MERIDIENNE EXHIBITIONS LTD
Shopping Partners
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate