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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.

<< First < Prev 273 274 275 276 277 278 279 Next > Last >>
Thread: B & Q Steel stock
05/11/2009 09:53:02
I was really excited that they have a store in Cambridge, until I realised it was in Ontario!
Thread: TA8435H stepper driver
04/11/2009 18:52:25
Hmm.
 
That page links to this:
 
 
which describes the unit with the connections including the usual enable/direction/step inputs.  Also describes use of Mach 3 and the unit comes with a copy of Mach 3!  Obviously expect you to use the normal E-stop via a break-out board.
 
John.
Thread: "Precision" or "does NOT do what it says on the tin"
04/11/2009 16:19:42
I think one lesson here is to ask suppliers of all this low-cost tooling for a SPEC before buying.  First, you can then check that the spec meets your needs; and also whether the kit meets the spec.  The first might save you hassle buying something unsuitable; the second gives you easy comeback at the supplier.
 
Talking of PGMS by the way, I bought a length of 1" centreless ground PGMS from a supplier at a MEX a few years ago....it measured 1" diameter OK, but it wasn't round at all as I found when I tried to mount it running true in the 4Jaw! 
 
John.
Thread: TA8435H stepper driver
04/11/2009 09:18:50
Ken, these are just the driver ICs, looking at the data sheet.  You would normally connect the limit switch to the software that drives the drivers, for example to the Estop input if using Mach 3.  Info on the IC is available at:
 
 
John.
Thread: where can i buy a bell punch?
02/11/2009 21:23:40
Do you really need one?  Seems to me that to be accurate you have to face off the end anyway otherwise the cone will not centre properly anyway.  If you have to face it you may as well centre drill it!  There must be a reason why the things aren't made anymore, maybe this is it!  IMHO, a vee-block on a flat surface and a scribing block is just as good and much more versatile.
 
John.
Thread: Work positioning in the 4 jaw chuck
01/11/2009 11:23:58
For a job like this I'd face both ends; centre-punch where you want the hole axis; open the jaws of the 4-jaw too wide; clamp the billet with one end against the flat face of the jaws and the other with a centre in the tailstock with its point in the centre-pop mark so the pressure of the tailstock holds the billet.  The carefully run the jaws up to the billet and tighten them progressively being careful not to shift the billet.  Job done, quite accurate enough I'd think for a job like this, no need to use a DTI.
 
John.
Thread: Visiting UK
24/10/2009 11:03:00
If you are interested in clocks and instruments, two not to be missed are the old Royal Observatory at Greenwich (take in the rest of the National Maritime Museum as well) where they have Harrison's clocks;
 
http://www.nmm.ac.uk/
 
and the Whipple Museum in Cambridge
 
http://www.hps.cam.ac.uk/whipple/
 
(the latter possibly not worth a trip to Cambridge on its own but there's lots of other stuff there including the Corpus Clock
 
http://www.chronophage.co.uk/
 
Depending on the breadth of your engineering interests there is Bletchley Park
 
http://www.bletchleypark.org.uk/
 
 
How long are you in the UK....?
 
 
John
 
Thread: Depth of cut
23/10/2009 10:24:36
Eric, I have a Myford VMB with a fixed table, dovetail-slide head and movable quill.  The quill only has a "drill type" downfeed (for drilling!) so accurate vertical feed has to be applied via the feed screw.  It works fine.  Whether the same will work for other mills I don't know
Thread: Milling Machine Low Speed Torque
16/10/2009 20:27:34
Peter,
 
Going back to your original question about improved drive electronics, you could look at "Pentapower" units from KB Electronics (http://www.kbelectronics.com/).  I got one of these with a DC quarter-horse motor from Model Motors Direct (not used yet but may be fitted to my CNC mill conversion).  I gather this has compensation for motor speed reduction with load so could solve your problem.  The one I have is the KBWM240.
 
Cheers, John.
 
 
Thread: Clarke milling attachment
16/10/2009 20:14:54
Frankly, I would just get an X1 mill and not bother with trying to add an attachment to an older lathe.  The X1 with the long table from Arc Euro Trade is quite a nice machine and will take much bigger workpieces than a lathe saddle, and as you say the price is at least in the same ballpark.  I just bought an X1 for conversion to CNC because I didn't want to risk messing up my Myford VMB (and the latter is also a very heavy machine to work on), and I think that though it has a few limitations it's a nice bit of kit.
 
John.
Thread: Electric motors
16/10/2009 20:04:00
Mike, I used to have an Amolco imperial head that I paired up with a metric Amolco XY table.  I replaced the vertical feedscrew with a new one made from M12 stainless studding, with a new nut turned up from brass bar.  Also added ball thrust races to the bearing which made it a lot freer.  It worked well, though I never got round to re-doing the graduations which were still "imperial" based and didn't work so well with a 1.5 mm pitch screw.  Anyway, the maths was easier than using the imperial screw!
 
John.
Thread: Rear mounting parting-off tools
16/10/2009 19:54:54
Um, I don't get Clive's argument here.  Yes, if you are pushing the tool in and the cutting forces pull the tool into the work then any backlash in the feedscrew & nut means that there is nothing resisting the pull.  But equally if you are pulling the tool in and the cutting force is also pulling the tool in, then again any backlash also means that there is nothing to resist it.
Thread: Wilf Baker's variable feed for mill
16/10/2009 19:42:28
Fred,
 
I know what you mean - couple of times I've thought I made a posting but found it vanished - frustrating.  The big diode in the MFA circuit is to protect against connecting the supply up backwards as it is in series with the main supply.  There is also another diode across the motor connections to avoid the spikes, no need for another one.
 
You can cut Veroboard tracks using an ordinary drill, probably 5 or 6 mm should do the job, hold it and rotate in your fingers with the point located in the hole where you want the cut until all the track has gone around the hole - make sure it has all gone, sometimes there are very narrow bits at the side to get you very confused! (I'm betraying my misspent youth as an electronics student here.)
 
Actually there is very little difference between the MFA controller and Wilf's circuit, except for the series diode which is the main thing limiting the MFA's current capability.  You could take it out (it's the fat black cylinder with a silver band next to the speed control potentiometer, not to be confused with the thin black cylinder next door but at right angles to it) and replace it with a wire link with no problem as long as you were careful about connecting the supply up the right way.  The current capability according to the specs of the MOSFET would then be 10 amps or more.  However I'd try it under load first - if the diode goes you can always replace it with some wire.  I don't really know why they used such a wimpy diode in the first place.
 
If you don't want to fiddle round with the motor internal wiring the way to float the speed control circuit is as follows.  First, you'll have to avoid using the PC power supply because the negative side is inevitably earthed and make your own.  (Or use a car battery.)
 
Next you'll need a mains transformer and rectifier as in Wilf's circuit, together with the 10000 uF capacitor, the 180 ohm 1W resistor and the 12V zener diode.  Basically you wire up the circuit as shown in his diagram but everything to the left of the zener, and the BUZ11 and 10A diode, is replaced by the MFA board.  Connect the reversing switch to the "-" output on the MFA board instead of pin 2 of the BUZ11.
 
Now the important bit.  Normally you would connect the negative side of the electronics - i.e. the "-" side of the bridge rectifier - to ground.  However to avoid the problems that you have had you SHOULD NOT do this but  leave it floating.  Connect the outputs of the reversing switch to the motor - i.e. one to the wire from the motor and the other to the motor case (and hence to earth).  What will now happen is that the secondary winding of the transformer will be floating at around plus or minus 12 volts relative to earth depending on the reversing switch setting, but that shouldn't matter because the winding is insulated from the transformer core and the mains.  It isn't wonderful electrical engineering but it'll work!  You will have to be careful not to accidentally earth the negative side of the circuit when you assemble everything into the box.
 
I hope these thoughts are helpful.
 
Cheers, John.
 
 
 
16/10/2009 09:41:50
...and after all, all this is working off 12 volts!
15/10/2009 09:25:48
Just to add a further comment - I've looked at Wilf's article and from the schematic it's clear that he expects a floating motor as well since the speed control method is identical to the MFA device  - though with his circuit it could work with all the controller floating on the isolation of the mains transformer windings.
15/10/2009 09:16:25
I have one of the speed controls awaiting inclusion in a powered down-feed for my mill.  Tracing the circuit, it works as follows.  The positive power input terminal goes through a diode (for reverse-connection protection) and feeds one side of the motor (marked "+" on the output terminals).  The "-" motor connection goes direct to the drain of a power MOSFET (effectively a switch).  The source of the power MOSFET (i.e. the other side of the switch) goes to the negative power terminal.  The MOSFET is gated by a little timer circuit that switches it on and off at around 1200 Hz with variable pulse-width to control the motor speed.  Thus, the motor output is floating.
 
Running off a PC power supply, the negative side of the +12v output is almost certainly earthed (i.e. connected to mains earth) as this is normal practice.  One side of the motor will also be earthed because it is connected to the motor case and through that to the machine (assuming that this is earthed for safety!).  So connecting the motor to the speed controller will either connect the motor winding to the + output and the - output to ground; or short the + output direct to ground.  (That's assuming there is a reversing switch between the controller and motor.)
 
In the first case the PSU will drive the motor through the diode; but the MOSFET is just shorted out (which won't damage it).  However the 12V ouput from a PC PSU doesn't have a very high current capability so I wouldn't be surprised if the start current of the motor just causes it to trip; then perhaps reset; then trip again.  Result would be intermittent and slow motor movement, and the speed controller will have no effect since its controlling MOSFET is shorted out.  In the second case the PSU output will just be shorted via the diode - depending on the current rating of the latter it may or may not have blown.  So all this may not have damaged the speed controller if you're lucky.
 
Making the arrangement work needs a motor with a floating winding, which is true of most small DC motors.  You might be able to modify a wiper motor, depending on how it's made.  Make sure it's a permanent magnet type.  Alternatively there are loads of PM motors with gearboxes around on the web which ought to have enough (geared) torque to drive a mill table (though not necessarily very fast). 
 
Summary: speed control may be blown; motor with floating winding needed; PC PSU may not have enough current for wiper motor.
 
Hope this is helpful,
 
John.
Thread: Rear mounting parting-off tools
13/10/2009 15:24:11
The explanations of the better performance of the rear tool that I used to read had more to do with effects of a headstock bearing with a little radial play rather than tool deflection.  Reasoning went that cutting with a front mounted tool would cause the mandrel / work to lift and move slightly forward, suddenly increasing the effective feed depth and causing the tool to dig in.  I don't know if this is real, but that's what a couple of explanations I've seen say.  In the same lathe, a rear tool would cause the mandrel to press down harder on its bearing which means that it wouldn't move radially.  Now that most peopla are using better lathes maybe this is no longer true...
10/10/2009 10:47:43
I have a KitQcut and a rear-mount parting tool on my Super 7, the latter being one of the commercial versions bought from Kirjeng.  I have made a little scoop in the "top" face of the blade, using a diamond needle file, which seems to help make the swarf curl in on itself away from the edges of the cut.  I find both tools excellent and normally part off at the lowest non-bgc speed with slow power feed and a steady flow of cutting oil from a brush.  Never had a dig-in (fingers crossed for next time!). 
 
The KitQcut gets used when I want to use the topslide to accurately set the length I'm parting off, otherwise I normally
 
On a previous lathe, on the other hand, a **** 220 which had rather inadequate roller bearings in the headstock, I never ever got an HSS tool to part properly, and only the KitQcut would do it. 
 
John.
Thread: Just starting
08/10/2009 10:53:27
John, many thanks for this information.
 
John Haine.
 
05/10/2009 22:24:42
Can I ask a question?  The most convenient place for the PC in my workshop is the opposite side from the lathe, and running a ribbon cable across to the motor drivers on the side of the lathe will not be very neat.  It would be easier to run a USB cable, but as I'm not aware of any USB "breakout boards" I would need a USB - Centronics adapter.  Has anyone any experience of using one of these with Mach3 please?  Are they fully compatible of do they only do what's needed for a printer?
 
Thanks,
 
John.
<< First < Prev 273 274 275 276 277 278 279 Next > Last >>
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