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Member postings for Martin W

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

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Thread: Stepper Motor General/Basic Question
25/04/2010 13:14:07
Peter
 
Stepper motors are exactly what it says on the tin. They actually revolve in a fixed number of steps per revolution which makes them ideal for shaft position controls and things like print head drivers where repeatability of shaft or linear position is important/critical and they then can actively hold this stationary position. I personally would not use one for a shaft drive unless you want these very particular features. That said this effect can be smoothed out a bit by choosing a stepper motor that has a high number of steps per revolution but the effect is still present.
 
If it is just to turn a shaft at an approximate speed then I would favour a brushless DC motor similar to those used in models with the relevant controller, in fact Sieg have moved to a brushless motor for their new release of their mini lathe replacing the brushed motor they used to employ.
 
I totally agree with Les regarding the driver issues.
 
Good luck
 
Martin
Thread: Clarke CL300 Speed control
25/04/2010 01:12:18
Hi
 
Anthony & Peter you right and there is no probably about it. The speed control system forms a closed loop feedback system and as the motor speed falls under load the control system senses this and ups the voltage. hence current/power, to the motor in order to restore the speed.
 
Using just a variac and rectifier only controls the voltage, and pretty crudely at that, which means there is no feedback and the lower the speed is set the less torque the motor will develop. The result is that at low speeds the motor becomes increasingly sensitive to load and will slow with load and eventually stall.
 
The speed control boards are relatively sophisticated electronic units and are designed to minimise speed change with load variations. They are, or should be, tailored to the motor characteristics so that speed remains constant regardless of load up to a preset threshold at which point they should limit the power being applied to the motor.
 
Cheers
 
Martin
Thread: 2 questions - threading silver steel; tightening bar in the chuck
16/04/2010 15:57:20
Hi AES
 
Re the private mail I sent to you. To read this 'log on' to this site in the normal way and then in the 'My Account' box on the top left of the page click on the 'My Messages' line and this will open your Mail Inbox. You should then be able to read the PM I sent re the above topics.
 
Hope this helps, this type of PM messaging allows members to contact each other without having to put their personal email address onto to a site for all the world to see, most open forums have this type of messaging service.
 
 I would advise that you NEVER put your personal email address on any open sites like forums because then it is open to abuse from malicious 'nere do wells' whose IQ is  inversely proportional to the amount of time they have on their hands. Once you have read my PM then you can, should you wish, email me at the address supplied or PM me back on this site by clicking on the 'message member' located in the grey bar, directly under one of my posts.
 
Cheers
 
Martin
16/04/2010 00:56:39
Hi AES
 
Sent private mail re tool post problems, if you feel this could help drop me an email at address supplied.
 
Are you using the supplied brazed carbide tipped tools, assuming any were supplied? If so see if you can get hold of some HSS tools and try them, often these will perform better than the carbide tipped varieties that are supplied as standard. Secondly the hss tools can be readily sharpened, if somewhat crudely, on a standard grinding wheel (MGJ I know not the best way but when the devil drives and needs must etc etc. ).
 
Regards
 
Martin

Edited By Martin W on 16/04/2010 01:12:44

15/04/2010 12:19:23
A quick addition to my previous post. The RDG stock number for the quick change tool post is 725MYFORD and while I said it was a Dixon style the larger version they sell is compatible with Dixon type assemblies (so they say).
 
I had to make a plate to fit this tool post onto the top slide and increase the locking stud diameter from 10mm to 7/16ins to match the through hole on the tool post  but with 10mm thread top and bottom to mate with the top slide and to keep the locking system the same. I had already dispensed with the supplied locking handle, bruised palms, and replaced this with a 10mm nut with existing thick washer. The stud was made from EN1 steel and works fine which supports what mgj says above.
 
The only other thing I did was to make new height adjusters for the tool holders to bring their adjustment to mid range for the tooling I am using.
 
As I said before this has made a massive improvement in the performance of my DB7V.
 
Cheers
 
Martin
15/04/2010 11:12:26
Hi AES
 
Your comment about tool deflection interested me as I wonder whether this is associated with tool post stud flexing or elsewhere. I assume that the current tool post stud is 10mm and can be tightened down fairly securely. If this is the case then, unless the tool holder assembly bottom surface or top slide surface are not true, the stud only pulls these mating surfaces together and it is these surfaces which then take the brunt of the load.
 
I would be inclined to check if there is any movement elsewhere in the system starting with the setting of all of the gib strips. I too have a chinaman lathe, supplied by Chester UK, and it suffered very slightly from tool deflection, under heavy loading in my case, but after a good clean, lubrication and adjustment of the gib strips all is well and I can take relatively large cuts as well as parting off steel bars greater than 25mm dia without any problems.
 
While it won't necessarily help you I ordered a Dixon type quick change tool post from RDG and fitted this to my lathe. The increase in stability was massive partly due I suspect to a stiffer tool holding assembly and the greater mass near/supporting the tool. Another point is to keep your tool overhang to the minimum for the task in hand as this helps to stiffen things up and helps to prevent tip deflection.
 
If I am teaching my gran how to suck eggs then I apologise. The lathe I have got is the Chester Model DB7V so you can compare this with you machine for size and functionality.
 
 
Cheers
 
 
 
Martin
Thread: collets
05/04/2010 14:47:40
John
 
This may be a stupid question but why not take 2 thou off the male ferrule rather than opening the female part of the ferrule. It would be easier and could be done using very fine emery paper followed by metal polish for a fine finish .
 
Cheers
 
Martin W
Thread: Lament for a lost grease.
21/03/2010 11:31:00
Steve
 
I completely agree with what you say about some of the older greases. I was going to say something similar about the moly grease being 'greasier'   but decided to rationalise my reasons for using it. Seriously though I find that the moly based grease just seems to make things slide/move more smoothly than ordinary unloaded grease especially after a little while when it has really got to all the contact surfaces.
 
I now wait for this post to explode into a frenzy of advice of which grease to use where and why and how and when etc..
 
That said in my youth I used to work part time in a garage, when cars had a chassis and engines came with side valves as standard and points were cleaned and reset etc. We were instructed to use a graphite based grease on the sparking plug threads. It was soon found that if there was a trace of grease left on the plug body the spark would track down this rather than the plug gap. It caused several engines to sound pretty rough until the cause was found  !
 
Enough ramblings for now from an oldun.
 
Cheers
 
Martin W

Edited By Martin W on 21/03/2010 11:33:00

21/03/2010 01:29:24
Hi
 
Steve under the Castrol link above there is in the Classic Grease selection a calcium based grease under the heading CL Grease. Whether this is the same or not as the Morris grease you refer to I have no idea but for the die hards Castrol are still in the market for a calcium grease.
 
I must admit that I prefer to use greases with molybdenum additive for no other reason than they offer that extra protection. Still as they say it's a personal choice in non critical applications.
 
Cheers
 
Martin W
Thread: Hallam Engine
10/03/2010 16:20:38
Alan
 
Not sure if it has been covered or not but it could be that the coil is failing. While it gives a good spark at atmospheric pressure when the ambient pressure is increased i.e. in the cylinder at near TDC, the voltage required to generate the spark increases significantly.
 
Stirring me grey matter from 50 or so years ago when points and coil was the standard car ignition I seem to remember that this increase in voltage can cause an ignition coil to fail internally and stop it generating a spark. I believe that this can also be applied to the spark plug itself where the actual spark then doesn't go across the plug tip but arcs over elsewhere in the body of the plug. Another possibility is that the capacitor might be failing of have a poor electrical contact with the earth of the coil, again a faulty capacitor can cause a loss of spark.
 
Then we had a piece equipment in which you could mount the spark plug and observe the spark gap while increasing the pressure. Frequently it was seen that some coils and plugs we tested would perform brilliantly at atmospheric pressure but quickly lost spark as the pressure increased. 
 
I expect you will have covered much of this in your own investigation and there will be other ideas out there which will be worth looking at.
 
Might be worth while swapping things about if you have some spare bits.
 
 
Cheers
 
Martin W

Edited By Martin W on 10/03/2010 16:26:22

Thread: What type of STEEL?
07/03/2010 20:49:57
Hi Circlip
 
Missed  the link in your post on the previous page OOPS. Still never mind  eh! Some else might only read the later posts and pick it up!!!
 
 
Cheers
07/03/2010 16:39:34
Hi
 
I hope this post will help with the original query regarding steels etc without getting into the esoterics of composition and off beat applications.  The following reference gives both the EN (emergency number) plus the BS number series of various steels plus notes on their cutting and application characteristics.
 
 
I have found this quite useful reference especially as I am a relative newbie to the hobby. This site covers a wide range of materials plus a lot of other useful, well to me it is, data.
 
I hope this will help James, who like myself, and others find the array of available materials somewhat confusing.
 
Also to muddy the waters further standardisation has now re-introduced the EN prefix as the European Numbering plus a range of numbers and suffixes. However this numbering system has a raft of numbers after the EN prefix so it is easily distinguished from the Emergency Numbering prefix introduced sometime in the 1930/40s. 
Cheers
 
 
Martin W

Edited By Martin W on 07/03/2010 16:49:32

Edited By Martin W on 07/03/2010 16:55:08

Thread: Hallam Engine
28/02/2010 16:53:36
Hi
 
I make this contribution with little or no detailed knowledge of this type of engine but have a question having had a look at the photos that Alan supplied. The question is, and it will have probably been looked at anyway, can the fuel tank breathe adequately and if not could it be starving the engine of fuel so it can' rev correctly??
 
As I say this question is based on observations from the photos so I would appreciate it if the more knowledgeable didn't launch into a tirade regarding my lack of understanding etc!!!!
 
Cheers
 
Martin W

Edited By Martin W on 28/02/2010 16:54:12

Thread: Lower Price Optical Rev Counter Accuracy
23/02/2010 13:45:38
Hi Frank
 
Yes you are right about the 50Hz, afraid I had my wrong head on and was thinking in 'lectronics' terms of accuracy . Tomorrow, all being well, my new mill arrives and I can then start getting to grips with things.
 
Cheers
 
Martin W
23/02/2010 11:19:45
Hi Frank & Les
 
I am glad you spotted my deliberate mistake. It was late at night and I claim that I was not thinking clearly. Of course you are right a standard fluoro will flash at 100Hz and not at 50Hz. Retired and brain dead that's me. But with Les's help it seems that there is an easy way to calibrate, well fairly accurately, an optical tacho without too much effort which was the aim of my post.
 
I am fairly certain that the instantaneous mains frequency will vary depending on time of day but over a 24hr period is very accurate, hence bog standard mains clocks are relatively accurate. Therefore the readings Les has got look very good and reflect what can be expected when making spot measurements.
 
Les you realise that now everybody that has an optical tacho and access to these forums will be looking at the mains frequency and complaining when they feel it has drifted too far from 50Hz.
 
Good spot and great solution.
 
Cheers
 
Martin W
23/02/2010 00:21:22
Hi
 
A way of checking the tacho at the high end is to increase the number of counting marks on the shaft. Put one on and note indicated speed reading and then add another and repeat and so on. While it will not give a calibration for the tacho it will, providing enough marks can be put on the shaft or encoder disc, give an idea of where the tacho starts to lose its ability read the shaft speed. On the high speed motor, 25000rpm unit you have, three distinct marks should give you a reading about 90,000 rpm; this assumes that the measurement you made earlier of 30,000 rpm is about correct.
 
As I said it won't calibrate it but should give an idea if its up to the task.
 
 Taking up Meyrick's point regarding the mains frequency. It is possible to strobe against the mains especially if you have a standard fluorescent lamp in the workshop. If so set your machine to 1000 rpm and then looking at the chuck see if you can see a set of ghost jaws revolving slowly, if not move the speed control until they appear; hopefully. If you can see them then adjust the speed control until they appear to be stationary, to all intents the chuck should now be revolving at 1000. Now measure the rpm of the chuck using the optical tacho and with luck it should be in this area.
 
Ideally this should be done at 3000rpm but that's not an option so using each jaw effectively reduces this by a factor of three to 1000 rpm. The above assumes that you have a three jaw chuck fitted and that you are on standard UK mains power.
 
 
Hope this helps
 
Martin W
22/02/2010 18:26:12
Windy
 
My guess is that the optical rev counter will be more accurate that a mechanical one, even the cheap ones should measure against crystal oscillator circuit which is inherently accurate and the mechanical ones tend to be analogue with things like hairsprings, magnets and aluminium discs.
 
However at very high speeds it will depend on the sensor response but again I would be surprised if the elctronic unit couldn't handle 70,000 rpm. This is only about 1667Hz (cycles/per sec  in old money) which is very low frequency for electronics these days.
 
I think your own tests at low revs indicate that the electronic unit is more accurate than the mechanical unit and it reflects the sort of error you are getting between the two systems when measured against a stop watch.
 
Cheers
 
Martin W
Thread: Hot air and stirling engines
18/02/2010 19:14:11
I don't know whether somebody has done something but now the posts are OK and terminating before the 'ads' column.
 
ED done anything???
 
 
Martin W
18/02/2010 17:13:25
ED
 
Whats up with this thread, and some others??? I am having trouble with the posts going under the 'Ads' on the right hand side!!! This does not happen on all pages of this thread so I don't believe its my system. This page seems the worst so far, anybody else suffering from this on this thread???
 
Sorry to the contributors for straying off topic but it is annoying and needs sorting.
 
Cheers.
 
Martin W
Thread: Perpetual Motion
15/02/2010 10:45:48
Neil
 
Maxwell's Demon is alive and well, if my understanding of extreme cooling is correct. To get extremely low temps, a few milli kelvin above absolute zero, a magnetic or optical well/trap is created in which a few, relatively speaking, atoms are contained. The shape of the trap allows the more energetic atoms to climb the walls and then with the help of a finely tuned laser they are removed from the trap, the demon has opened the door to the high energy atoms, and hence energy has been removed from the group.
 
Continued removal of the higher energy atoms causes the cooling of the contained atoms as a cloud. Certainly not perpetual motion in any shape or form but Maxwell might have been interested!!
 
Cheers
 
 
Martin W
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