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Member postings for John Haine

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

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Thread: This months MEW are 3 CNC features two too many
17/05/2011 20:44:14
David,
 
Just to redress the balance...
 
More CNC please! In particular (as I have converted my S7 then found that using it wasn't as straightforward as you might think) articles on setting up the machine, calibration, detailed screw-cutting etc.
 
Shame we don't have any articles yet on 3D printing machines - there are at least 2 different self-build versions out there. One could add a polymer print head to a CNC mill and use it to make plastic components.
 
One day when i have time I might start contributing some articles, probably on CNC!
 
I still read every issue cover to cover as there is always something to learn from the ways people have solved problems, even if I do wonder how many times you can tread old ground.
 
John.
Thread: "An Accurate CNC 4th Axis"...?
29/04/2011 11:47:06
My own experience of measuring repeatability and accuracy of my CNC converted super-7 cross-slide bears this out. i am using 8 "microsteps / step" and certainly don't obtain the predicted accuracy or resolution, and the repeatability depends on the applied load. Seeking advice on the Mach forum it was pointed out that stepper motor accuracy is poorly specified for microstepping, since it is achieved by applying linearly interpolated current values to the windings between full steps and the torque/current curve is probably non-linear so there is, even in the best case, a non-linear relationship between demanded and actual position. This will be made worse by the effect of cutting torque and variable friction since I suspect that the full holding torque of the motor probably isn't available. I've seen adverts for specially made steppers with a linear microstep characteristic in the US "digital machinist" magazine to improve performance, but no idea how much these are or whether available over here.
 
The main reason for microstepping seems to be to allow better driving of the motor at higher speeds without exciting resonances. For accurate positioning looks like it's better to have a large mechanical reduction (worm/wheel) and rely on whole steps.
Thread: Amolco milling attachment
25/04/2011 09:48:58
Did you sort this Alan? Trick is to insert the clamp bolt from the "wrong" side against a thin plate in the slot. Tightening the bolt gently forces the slot to open and the foot slides off.
Thread: Epoxy Bearing Materials and Method
20/04/2011 21:47:12
Remarkably little content for a file of over 40 Mbyte! What there is is interesting and innocuous, I have re-saved it as a PDF which reduced the file size by a factor of about 100! As it's a PDF I can't post it so have emailed it to Dave Clark as editor.
 
(By the way, WHEN will we able to upload other file types than jpegs? All the other engineering forums allow it.)
 
John
Thread: Thread tool form
13/04/2011 21:54:51
The book on threadcutting in the lathe by Martin Cleeve has an excellent and simple design for a lathe tool grinding jig which will ensure correct angles.
Thread: Suggestions please.
28/03/2011 23:05:22
I doubt that there is any simple way of checking it that will be any more accurate than the Quorn was in making it! I must say though that Ramon's & Terry's idea with the scanner is inspired....having spent quite a long time adapting the bits of an Aldi microscope with CCD camera and a cheap Proxxon XY table into a travelling video microscope last year, I wish that I'd thought of this first!
Thread: Tony Jeffree's Grinder letter in MEW175
16/03/2011 17:18:06
Well, I've got a Quorn which I inherited from my father - it was his big ME project in his retirement (though he built a lot of other great stuff). It isn't an exhibition quality version but is workmanlike. Some of the things in the original design you don't need - for example the 2 tpi thread for elevating the wheelhead, you can get away with a lockable collar on the column to stop it sliding down once adjusted. As a matter of fact I can't understand why the design didn't just have a vertical leadscrew and dispense with the fine adjustment. Equally, having ball handles looks nice but isn't very practical - those resettable lever-operated screws would be much more practical for anyone starting one today I think.
 
The unit was built with the 3C collet arbor for cutters as designed. These are too small really and the collets not readily available. MT2 collets are an alternative, but there isn't enough meat in the original design for MT3 or R8 (I have the latter in my VMB). So I have designed and built an alternative workhead that takes R8 collets so I can use the same ones as the mill.
 
The original design is not very good for lathe tool grinding, so having recently made a tangential tool holder I've made a simple holder for square toolbits that mounts instead of the workhead - makes life much easier.
 
The Quorn as designed is not in my view good for flute sharpening, it doesn't give well-controlled axial movement of the mandrel while you spiral the cutter against the wheel. I've tried making air bearings without success, also a plain polished bronze sleeve. I even started to make a new TCG design but have given up! My conclusion, inspired by a Quorn that is regularly exhibited, is that you need a system that allows the tool to rotate freely against the tooth rest whilst being positively moved axially by a lever feed - that's my next move (so to speak), to add something like this to the Quorn.
 
Setting the workhead up is a bit of a pain using setting pins and the like, but I have a little optical gadget that I use for setting a cutter in the collet which is very quick.
 
The Quorn isn't so good with big wheels so is distinctly for finish grinding rather than rough shaping - so you need another grinder with some sort of accurate-ish rest for this.
 
I often wonder why some enterprising company doesn't supply a simple bench grinder with a conventional wheel at one end with a decent rest; and a cup wheel at the other with a simple angled table with guides, a bit like Harold Hall's design. This would be just the job for most people on its own (as they could make gadgets for cutter sharpening just as Harold shows), and ideal for rough tool shaping for finishing on a TCG.
 
I will try to get round to posting some photos of my mods.
 
John.
Thread: Hipp Pendulum Clock
11/03/2011 13:18:24
Er, the Eureka is a balance wheel clock and doesn't use the Hipp toggle principle - see http://www.hvtesla.com/masters/po36_toggle.html for a description of how that works.
Thread: VFD Drives
03/03/2011 22:51:14
It depends what you mean by significant! They will have to meet the EMC directive conditions, but like most modern electronics don't expect to be able to use a portable radio in the same room! I find for example that a cellphone FM radio or an iPod radio is totally blotted out next to my laptop. On the other hand our kitchen radio works fine on FM and DAB with a wire antenna with two or three computers going in the house and my CNC setup going in the workshop.
Thread: Metric screw cutting
21/02/2011 13:06:08
Richard,
 
When I get home I will copy for you the threading table for the Super 7 without gearbox which gives approximate gears for metric pitches without using the "metric conversion" set (50:127). If you do the sums you find that the errors are insignificant over the length of a normal nut, in many cases probably less than the error in the leadscrew pitch itself. Have you got an email address?
 
John.
Thread: mini electric motor
10/02/2011 13:22:43
Phones are extremely price sensitive but also extremely power sensitive - anything to reduce current is highly desirable. Motors are much more efficient than oscillating or linear magnetic displacers, and given the enormous volumes of cellphones (1.6 billion last year - I think only electric motors, ironically, are made in larger numbers) it was well worth developing very small motors for the purpose.
Thread: MT2 collet slipping
08/02/2011 18:03:02
Just a point about comparing collets. I mainly use R8 collets directly in the bore of my VMB (never seen an R8 collet chuck as such!). Though the drive to the collet is via a key, the cutter is held in the collet itself without any other aid such as you might find in an Autolock chuck. And the taper on R8 is significantly greater which means that the mechanical advantage is less than the rather gradual taper on a Morse collet. I have never had a cutter move in R8, and as the system is widely used on machines like Bridgeports I would guess that few other people have either. So what's the difference between holding say a 3/8 cutter in a Morse collet or an R8 collet? And I should add that the R8 collets I bought were J&L's cheapest so they can't be much better made than the standard MT2 drawbar types.
 
As for drawbars, AFAIK there is little difference in Young's modulus between different grades of steel, though they have different hardnesses and yield strengths. So whether you use HTS or studding won't make much difference as long as you don't approach the elastic limit of the material, and if you do then probably the collet will stick immovably! When I bought my VMB there was a choice of MT3 or R8 nose, but Myford strongly recommended R8 because of the danger of MT3 sticking.
07/02/2011 17:46:17
I have heard of Myford pattern collets slipping when used in a milling machine as well.
 
Two thoughts. One, don't take such challenging cuts! You might also try a very slight amount of lubrication on the taper, it may be that slight roughness between the taper and the collet is preventing it exerting maximum clamping force because friction prevents it pulling in completely. I have also seen that Morse tapers can get stuck if over-tightened - a bit of lube would help prevent that but also perhaps make it happen! Possibly worth a try though.
Thread: Dividing plate
02/02/2011 19:49:17
64?
Thread: Single phase or Inverter
30/01/2011 22:18:56
Um, I don't think fluorescent tubes have capacitors do they? Inductors, yes.
 
Thread: Boring deep holes
30/01/2011 14:09:20
I'd make a boring bar. I've made a few of these, they are very easy, using both HSS and carbide inserts. HSS is easier, just drill and ream a hole for the bit and drill and thread another hole at right-angles for the locking screw. For a flat-bottomed hole the toolbit will have to be at 45 degrees so it slightly projects from the bar, and it may be difficult to get the hole completely flat-bottomed. I have found big reamers to be a bit problematic to handle, and you would anyway need a machine reamer to get a blind hole parallel.

Thread: Diamond tool holder.
30/01/2011 11:00:24
After further experience and thought...
 
I discovered that I was cutting too fast - hangover from tipped tools! Slowing the lathe down solved the finish problem, can now get near-mirror finish, excellent. This is without feeding the tool "backwards" on the finish cut or raising it slightly.
 
Small problem with cutting edge getting deformed - Chris at Ally Pally suggested that this was due to unsufficient tip rounding, so need to hone a bit more off the HSS steel square blank to improve that.
 
I was also wondering what the actual cutting angles were and how to set up the angles on a conventional grinder that holds the tool bit "flat" rather than "diagonally" on its edge against a cup wheel (think of a Worden), so did a bit of geometry. You need to know by how much the tool should be angled in the horizontal and vertical planes to give the equivalent "diamond" angle. There is a simple formula as it turns out. If the "diagonal" angle is d, (d=30 degrees in the usual tool), the H and V angles should be arctan[tan(d)/1.4142] .
 
For 30 degree diagonal angle H and V work out to 22.2 degrees. With 12 degrees cant forwards and sideways on the tool the side and front rake then work out at 10.2 degrees.....seems to me this might be a bit much for some materials, but the formula lets you work out alternatives. For brass for example you would want H and V to be 12 degrees to give a flat-topped tool when held in the tool holder (i.e. zero rake). The end face of the bit will then be angled at 16.7 degrees along the diagonal. Or, for 8 degrees top and side rake, H and V need to be 20 degrees, giving a "diamond" angle of 27 degrees.
 
I hope someone else finds this information useful.

Edited By John Haine on 30/01/2011 11:01:02

Thread: Varibale Speed for Drill Press (Induction motor?)
18/01/2011 15:36:24
Almost certainly the fan uses a "torque motor" which is made having a higher resistance rotor than a standard induction motor.  These will slow down according to the stator current (less = lower) but correspondingly are rather inefficient and get rather warm.  All induction motors run asynchronously*, the rotor going slower than the stator fields, but torque motors are very asynchronous.  Standard induction motors just stall if you try to operate them in this mode, and then get very hot. 
 
Torque motors are used where you need very simple speed control but efficiency isn't important; or when you just want to exert a constant torque at variable speed.  I used to have an audio tape deck with such motors driving the reels - normally the takeup reel exerted just enough torque to roll up the tape; whilst the feed reel was actually driven backwards by the unrolling tape and the torque kept it tensioned.  Fast forward or rewind involved increasing the appropriate motor current to drive the reels fast.
 
*unless they are "synchronous induction motors" in which case they start like induction motors but when close to synchronous speed the rotor locks into synch with the stator field operating as a reluctance motor.  Ordinary induction motors with "squirrel cage" rotors can't run synchronously.
Thread: Parting off on Myford lathes
16/01/2011 16:18:11
I use a rear toolpost of the type Kirjeng sell.  Blade is ground with a small hollow in the top surface made with a rat-tail diamond file.  I follow the advice of GH Thomas, run the lathe reasonably fast so the cut per rev is under better control.  I always use power feed (now the lathe is CNC'd there's no alternative).  Never have a problem.  Also have Q-cut tool which is good but now seldom used, but was used in the Dickson toolholder on topslide.  Again used power feed but less good 'cos being a carbide tip the edge is lee keen so needs more cutting pressure.
Thread: steam turbine and generator
12/01/2011 22:16:28
Another issue is that generators are intrinsically AC machines, even though they may have a commutator, so you have to consider core losses.  At 60,000 rpm a dynamo would be working at 1000 Hz where ordinary laminated motor cores would be rather lossy.  Best would be either ferrite or even (assuming neodymium magnets) no cores at all?  Also use a diode rectifier rather than attempting a commutator. 
 
You could also think about a Tesla turbine which uses plain discs rather than blades - much easier to make.  Very exaggerated claims are made for them (as for everything to do with Tesla [oh dear, I can feel the flames already]) but worth looking at.  Goole will lead you to more sites about Tesla than you want.  Wikipedia has a reasonable page -
 
 
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