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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.

Thread: VFD Question
08/01/2020 16:03:06
Posted by norm norton on 08/01/2020 15:52:14:

Ahh.. Thank you Martin and Andrew - got that.

So I (and perhaps two others in the world) have been misunderstanding the output from the workshop VFDs that we use. It is 240v phase-to-phase, and if there was a neutral it would be about 133v on each phase to neutral.

I guess the rules of physics say that one cannot phase shift 240v AC by 120 degrees and again by another 120 degrees, otherwise we would get 415v quite easily.

Norm

You can shift it using a resistor-capacitor circuit, but inefficiently (because of the resistors). To get high efficiency you need at least two power feeds with a phase difference. There's something for example called a Scott transformer that will generate two phases at 90 degrees given a 3 phase supply, or vice-versa.

08/01/2020 15:58:09

To save Andrew doing it. It a simple VFD the mains is full-wave rectified and charges a big capacitor up to 230 x sqrt2 = 325 V. It then has 3 high-voltage push-pull output stages run off this voltage to drive the 3 outputs. Each one is driven by a variable mark/space PWM signal at perhaps a few kHz. At 50:50 m/s the effective average output of one of these is 162.5 V, and it can be varied down to 0 V and up to 325 V. In effect this is +/- 162.5 V relative to an average of zero. If you vary the m/s ratio in a sinusoidal manner with time at 50 Hz you can generate what appears to a motor as a 50 Hz sine wave with a peak voltage of 162.5 V.

Now there are 3 output stages and they are driven to generate waveforms 120 degrees out of phase. If you connect a motor winding between two of these outputs it sees a voltage of 162.5 x sqrt(3) = 281 V peak or 199 V rms. This is not too much lower than the winding would see if it was connected between a line and neutral of a standard 3 phase supply so it will run with nearly the same current and power as normal.

You can also play games where the waveform is not sinusoidal but the peak is "flatter", which will increase the rms voltage and current to compensate for the lower peak voltage. There's nothing particularly sacrosanct about sine waves.

08/01/2020 12:58:55

Talking nonsense IMHO.

Thread: Watch servicing
07/01/2020 10:24:03
Posted by Steve Crow on 06/01/2020 19:28:54:

These symbols of obscene wealth provide employment for many artisans and ensure that knowledge is passed on.

Hmm. I'm not sure there are that many artisans involved or that the knowledge of making obscene bling is worth passing on!

06/01/2020 17:50:46

You're right, they are utterly disgusting at almost every level.

06/01/2020 13:40:24

Pictures Dave? Was that million?

05/01/2020 21:05:26

Very interesting transcript of the George Daniels lecture by Roger Smith in the January Horological Journal. He speaks about how to design and make reliable mechanical watches that do not need frequent servicing. You can hear a podcast of the lecture here.

05/01/2020 14:23:21

There are definitely issues with the supply of parts for mechanical watches and it is clear that groups such as Swatch seek to control the servicing of their movements to increase overall margin.

However...if there is going to be anyone around to service mechanical clocks and watches in the future they will need to be able to earn not just a living wage but something in line with the level of knowledge and skill required. If you grudge them that then buy a Swatch quartz and throw it away when it breaks.

Thread: Benbox 1310
05/01/2020 09:44:09

GRBL is as said in Emgee's link a G code parser and machine controller that runs on many platforms including in this case an Arduino. This is the same basic functionality as for example Mach 3, but the latter has lots of additional bells and whistles such as wizards. It would take G code for example from F360 though you might need to find an appropriate "post processor" for this machine.

I think I would have two concerns about using it as supplied for your application. First, the feed seems to be by standard screws whereas your friend's CNC probably has ballscrews. This means that either you need to have backlash compensation (BC); or carefully generate your G code to only have unidirectional moves to a desired coordinate; or correct any backlash in the machine. From a quick look, there seems to be a BC option in GRBL but it may need a higher spec Arduino (Mega?) than this machine has. Now Mach 3 does have BC but in my experience though it works well if the basic backlash is small (my Novamill has about 0.01mm), but can't properly cope with the level seen on ordinary feedscrews (such as my Super 7 leadscrew). (Or it may be possible to get F360 to allow for backlash.) But you may need to at least fit low backlash nuts (e.g. using a plastic material moulded to the screw) or even ballscrews.

The other thing is that the version of this machine I looks at seems to use just a DC motor with a collet chuck attached as the spindle. This won't have wonderful bearings and may not run quite true, not so helpful if you are using small drills and want accurate positioning. You could upgrade the spindle of course.

It also looks a trifle dear - there are other similar machines that have a larger working area for similar or lower cost. Search eBay for "3020 CNC".

Thread: Amolco Mill
04/01/2020 09:43:42

There are a couple of problems with the Weldon style holders. For one, they still have quite a long projection from the nose. The other is that though the imperial sizes have a 3/8 BSW drawbar the metric ones have M10, and IIRC I found that the spindle bore didn't accommodate the larger size (I may misremember). I did make some holders myself, using some very short MT2 centres I picked up surplus that weren't hardened. Faced off the end so there was just enough meat for a grub screw, drilled and tapped a 3/8 BSW hole in the small end, drilled and bored for the cutter.

Given that screwed shank end mills seem to be a thing of the past (neither Arc nor MSC list them as far as I can see), and the ones that came with the mill are probably blunt, I would suggest that you do not invest in an an Auto/Posi-loc chuck. Do try the collets you have, making sure they are really tightened, and buy some new cutters, maybe just 3 or 4 sizes to start. You will see a lot of postings here about MT2 tapers getting stuck, but a benefit of the Myford style collet is that the closer nut extracts the collet when it is loosened, as long as the collet is properly fitted into the closer using the tube. So they don't get stuck. If you decide to buy a collet chuck, ER is the way to go these days, and get a ball bearing nut so you can really tighten it.

I replaced my Amolco with a VMB with an R8 spindle. Almost always for milling I use R8 collets direct in the spindle, so get maximum daylight and rigidity. As long as you tighten the Myford collets properly you should find the same.

Thread: TiN coated twist drills
03/01/2020 21:34:39

+1 for cobalt drills

I bought one of these sets to drill an extra dowel hole in by Dickson toolholder block - went through it without drama. Highly recommended.

Thread: Amolco Mill
03/01/2020 21:28:59

An Amolco was my first mill, made of one of the original heads and a base made by a company in Baldock that bought the designs from Mole later on. The base was a nice bit of engineering, the head not so good, the vertical key combined with the split casting wasn't clever at maintaining alignment when you applied downfeed. Its other big problem was the limited daylight between spindle and work, especially when you fitted a vice.

I did buy a Posilock chuck for it at considerable expense and in retrospect wish I'd just bought MT2 finger collets for use with a drawbar, because of that lack of daylight. The machine is also not all that rigid, having a lot of overhang and having to have the head a couple of inches higher because of the chuck doesn't help.

I don't know why you assume the cutters will move in the Myford collets, they shouldn't if properly tightened and you don't get too ambitious with cuts (which on a machine with limited power and rigidity isn't advisable anyway). Sharp cutters help too.

If you have the Myford collets that have a closer nut then treasure them. The collet closer tube is vital - it allows you to close down the collet so the nut will locate in the groove just behind the nose, so that as well as tightening the collet it will also extract it. If this isn't obvious then say and I'll post some photos. Before you spend money on a posiloc type chuck I suggest you try using the collets you have, possibly with some new sharp cutters. If you do decide to get a collet chuck then most people on here seem to find ER types very satisfactory and much cheaper.

Going back to that keyed column, it's very important that when you apply some down feed you then re-tighten the clamp otherwise the head gets deflected sideways by cutting force.

I made a significant modification to my column to get more daylight. This involved three things.

  1. I fitted a new, longer key (a piece of key steel IIRC) to allow more travel.
  2. Also then needed a longer leadscrew, which I wanted anyway as I'd bought a metric base and wanted metric downfeed. Also needed of course a new feednut.
  3. I made a new fitting for the top of the column which added 50mm or so to its height and held a plate for the feedscrew bearings. The head didn't actually run on the extension, it just allowed the head to make use of all the existing column.

Had I kept the mill I think I would have changed the motor to 3-phase with a VFD, but I was finding it a bit too small for what I needed at the time.

Thread: First mill
31/12/2019 22:35:50

If you go for R8, use R8 collets direct in the spindle.

Thread: What Did You Do Today 2019
31/12/2019 22:02:04

I've posted a couple of photos of my clock project, and today finally after nearly 360 days since acquiring some of the bones of a Synchronome I installed the clock in its new case on our kitchen wall.

img_20191231_182057399_hdr.jpg

Not a wonderful photo I'm afraid. The clock keeps the gravity arm and the basic chassis, but the arm is reset by a cam driven by a stepper motor. Pendulum is sensed by an opto interrupter (you can just see a little white blob which is the mounting for it below the pendulum). Swings are counted by an Arduino Nano which drives the stepper. Most of the dial is used but driven by another stepper rather than the original electromagnet. I had to make a new pendulum using a carbon fibre rod and cast iron bob since the original was missing - also a new pallet.

Pendulum is impulsed every 40 swings = 80 seconds rather than the original 30 since it doesn't have to drive a count wheel, and the dial impulsed once every 9 seconds. Main reason to use stepper motors was to make the clock much quieter than the standard 'Nome.

The case is made from Valchromat, a sort of engineered MDF using Melamine resin - woodword is not my forte but it's turned out OK. Though I have the original case it's not in great condition and anyway I wanted more space to reduce pendulum air loss.

Before installing in the case the clock was keeping pretty good time over quite a long period, but I anticipate quite a lot of regulation as its new home is warmer and the pendulum amplitude will be a bit less. Now I can think about the next project!

Thread: Shaper in action
31/12/2019 07:51:49

Or scale scale models...

Thread: Opening a Port
31/12/2019 07:50:02

Unless you can clamp it to the mill table don't even think of using an endmill or slot drill, it will be uncontrollable.

A rotary burr or grinding point may work.

Inlet ports on exhaust?

Thread: Warco WM18 lead screws upgrade
27/12/2019 08:11:26

I have a ballscrew on my Super 7 CNC conversion. If you push the slide without the stepper attached the screw is happily turned by the nut.

Thread: Stanley Blade Lathe Finishing Tool
26/12/2019 10:30:53

Ideal application for the Turnado?

Thread: Archiving old data
26/12/2019 09:41:40
Posted by Andrew Evans on 25/12/2019 23:28:17:

.....

The BBC had a project in 1981 called the Doomesday Project to record census data and general information about life in Britain - the data was stored on Laser Disks. I understand there is only a single, working Laser Disk player in existence now that is capable of reading this and this is used as a classic example if digital obsolescence. So it can be a hardware problem as well as a software one.

.....

A great example of a failure to think the problem through. When laser disks became obsolescent there should have been a plan in place to transfer the data to the next mass storage technology - preferably in the cloud. As always, this isn't a technology problem, it's a process and system failure. I've recently been reading up on Bletchley Park again, and what comes through from a couple of the better books is that, whilst the technology was key, it would not have worked without a carefully constructed and maintained process to industrialise codebreaking.

Thread: Making a superglue chuck adapter for brass wheel
25/12/2019 22:22:51

One technique that seems to work quite well to stick flat parts down on a CNC mill, and also for wood routing, is this. Stick Good quality blue masking tape firmly to each surface. Apply superglue to one surface in dots, press the other surface firmly down on it. After cutting, peel the part off the tape - it's surprising how firmly the tape sticks over a large area, but it comes off quite easily when done. May work for turing too, maybe worth a try.

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