Member postings for John Haine

Gardening shops often sell packets of aluminium strips about 1. X 3 cm used for bending into clips for greenhouse glass. They are 0.5 mm thick and just the job for packing jobs of this sort.

Neighbours may complain a bit?

I have a Tesa mechanical micro which used to work very well and would read to a micron, but I dropped it and the readout was ruined! So I bought a Mitutoyo digital mike which I hardly ever use because it's not absolute. Every time I switch it on I have to wind it right back to closed to zero it which takes forever. So last year I spent £27 on a s/h Mitutoyo mechanical micrometer, 25 mm, and it's just great! So spend a little time on eBay looking for one like this, or Tesa, or M&W.

Well, I can only say that I'm amazed at the large number of responses and the ideas here! The "Acute" system looks interesting too - the pantograph-like arrangement to allow a tool to slide at a set angle anywhere on the rest plate is brilliant.

As well as a Quorn (inherited) for which I've made a new workhead to take R8 collets, I have adapted an Axminster grinding reat for shaping tangential tools - I'll take some photos of these and post them. But I still find the Quorn tedious to set up and fussy about wheels, so it gets little use. I'm thinking about a fixture to grind the end teeth of whatever we are supposed to call end mills and slot drills these days, which will be quick to set up and preferably can stay on the grinder for most of the time, along the lines of Harold's gadget. As I have a couple of angle plates and a Myford swivelling vertical slide that never get used, they may play a role!

One thought: most of us have a tool with a driven spindle and adjustable slide rest in the form of a lathe. Conventional wisdom is "never grind on the lathe" because you get abrasive dust all over the slides. But I'm wondering if the same is true if you use a diamond wheel, especially one of the electroplated ones? These seem to last a long time and most/all of the "swarf" will be metal dust. Obviously it will be hard metal dust but generally easier to pick up with a magnet. Any views on this?

For those of us interested in making our own version of the EMG12, or doing a similar job in a different way, maybe we should have a separate thread? Post your ideas and gadgets here!

Schottky diode overkill surely? They have two benefits. One, the forward voltage is lower than standard junction diode, but only by quarter volt or so. But this will make very little difference in this circuit as Trevor's oscillograms show.

Second, when they go reverse biased they turn off very quickly compared to junction diodes as the stored free charge is small. This is very useful in a high frequency rectifier, where combined with the low forward drop it gives good efficiency. But in this circuit the diode is reverse biased most of the time and turns on only to clamp the inductive kick.

I reckon an ordinary 1n4148 would do the job perfectly fine, the main thing is to protect the MOSFET against avalanche.

Does anyone have some metrinch holes to spare please?

The tip is tungsten carbide and can be ground to a sort of point for steel I understand. I think some sort of 4 facet grind would work. I can't remember where I saw this but could be useful if you have something too hard for a normal drill.

http://www.maplin.co.uk/p/mfa-panel-mounted-speed-regulator-module-rn41u

An almost identical circuit ready made on a pcb. Does the world really need another 555 speed controller?

Musing on how this works and noting the comments made about the "striations" on the ground faces, I had a close look at one of the photos.

I've superimposed some arrows that indicate ground lines visible on 3 of the 4 teeth (and probably on the 4th but there isn't much reflected light). They are in virtually the same position on each primary clearance and also line up on the secondary clearance. I would guess that these are due to a slight prominence of a diamond on the wheel surface? It indicates I think that the action of turning the cam advances the cutter directly onto the wheel surface, so small irregularities in the wheel get transferred "negatively" onto the tool. This of course doesn't matter at all since its only the end of the teeth that cut, but it helps to explain the action of the machine.

By contrast, on a grinder of the Quorn / Clarkson type, the face is ground by stroking it across the wheel until it sparks out. Any prominence on the wheel effectively acts like a little "flycutter" and you can get almost a mirror surface. It's maybe because people got hung up on designing TCGs that would hold the tool to permit this kind of action that it took so long for this new design to appear.

Edited By John Haine on 01/06/2015 21:55:36

Well this has been a very interesting learning experience! It's 45-odd years since I did courses in electrical machines in my degree and even then I regarded them as a bit of an irrelevance to electronics. So I did a bit of digging and analysis and found that the reason the polarity matters is because the windings in a 3 phase motor are magnetically coupled (as the test method described indicates). If you reverse one winding then it turns out that the resulting 3-phase impedance is serious imbalanced, and at least one impedance seen by the supply is much lower than normal which explains the high phase current.

Edited By John Haine on 01/06/2015 21:34:33

4 slots much better.

There is absolutely no reason to check the polarity! As long as the windings are connected in a delta the motor will rotate one way or the other. If it's wrong just swap two of the wires round.

To get more height, I bought a Myford VMB, the later version that was taller. They come up second hand from time to time. I've found it generally very good.

Zapp Automation?

Given the attraction of building tool & cutter grinders I'm not surprised at the level of interest in this machine. What's interesting to me is how it turns conventional wisdom on its head. Conceptually it's like those rather duff drill grinders where you stick the drill in a collet, thrust it into a plastic housing against a grinding wheel and rotate the collet against a cunning cam to shape the end of the drill. The difference is that this works, and on cutters that are supposed to be much more "difficult" than drills.

I've got a Quorn which my father built. It took him months of his retirement and he made a load of the accessories in the book, but once built he almost never used it! I find it so fiddly to set up that I hardly ever use it either and I keep on trying to work out easier ways of sharpening end mills! So when I saw this my first thought was, how does it work, and how could I make one? I don't think I'd buy one myself but I might join an ME club that had one!

now if it had another couple of ports at angles that did 4 facet drill grinding too....!

But I hope this is really successful and good on Ketan for taking the risk to import it.

Moglice?

People have had success casting delrin (I think) around the screw but I can't remember where I saw the technique described.

eBay is your friend. It's worth what someone will pay.

One of Guy Lautard's Machinist's Bedside Readers has an article about case hardening. Fill the hole in the bottom of a small clay flowerpot with fireclay; put bonemeal in tha pot converging the item you want to harden; stick another clay pot over the top with clay and seal that one too. Then heat to red in a fire for a few hours, it will smell ghastly. Then drop the whole red hot assembly in a bucket of water and fish out your hardened item. Recommended.

Well this sounds an interesting unit! Also from what people say it does a better job than a Quorn which people tend to regard as the gold standard I'm ME. how hard could it be to design and make a unit based on the same principles?