Member postings for David Littlewood

Graham,

Yes, I realise I could have fixed it to the column - the only reason I did not do this is that I didn't think of it at the time! As far as the length is concerned, once I was fixing it to the base then I needed the backing and cover, and the marginal cost of increasing the scale length is quite small.

I haven't quite worked out how rotating the column would allow you to do a longer machining run without resetting; surely that is governed by the table travel. I could still tilt the head to use as a horizontal borer without rotating the column - not that I ever have. Perhaps I've just not been as adventurous as you have been!

David

Graham,

When I first read this, I thought "that's a good idea". Then, on thinking about it, I decided that since I fitted a DRO system a few years ago, the ease with which I can go to a specified position - either setting in advance and locking the Y axis, or even while cutting in the Y direction - is so reliable it would not serve much purpose. It does however look extremely well done, like all your other work, and I'm sure if I had no DRO I would be looking at copying it!

David

In the time I have had the FB2 (almost 30 years) I have never needed to swivel the column. Not even once. If I ever did, for some exceptional purpose, it would only take a few minutes to remove the Z axis scale. On the other hand, the Z-axis scale is used about half the time I'm using the machine (i.e. almost always for milling, hardly ever when drilling). Seems a fairly clear winner to me, but YMMV.

David

Ian,

For real precision setting there is nothing which matches a DRO. That gives an absolute - and very precise - indication of the head position. It's a little trikier fitting one on the Z-axis, but it just needs a bit of imagination and some alloy brackets. Here is the one on my FB2:

The Machine-DRO kit that I bought came with a generous supply of alloy bits to make brackets.

The stick-slip issue still occurs, but at least you know that whatever the display says is accurate, you just have to learn to manage it (or cure it - must try some of the suggestions above!).

David

Edited By David Littlewood on 12/03/2013 14:51:43

Just out of interest, I got out my power meter and plugged my larger VFD through it. The latter is a Newton Tesla one which drives the 3 HP (2.25 kW) motor on my M300 lathe.

At rest, i.e. with the motor off, the quiescent state showed a PF of about 0.4. At slow speed it drew 300 W resistive, and showed a PF of 0.6; mid-speed was 1000 W and 0.66 (total VA of 1500 W), and at top speed (2500) it drew about 2000 W and a PF of 0.70. The lathe was unloaded at each setting, but of course the headstock gears do take up a lot of power, especially at the high speeds. (Incidentally, if you've never run a large lathe at 2500 rpm or more, it's pretty scary!).

Not sure what this proves, just interesting. It does rather show that the previous suggestion (that inverters do not draw much reactive flow - VARs - they do.

Incidentally, my textbook on Electric Power Systems (B M Weedy) speaks of reactive power quite consistently when discussing the subject. High voltage power transmission systems are a complex subject which I don't pretend to understand, but it appears that the voltage drop in the lines is largely determined by the reactive power; this causes increased line current, and hence much increased I^2R losses, as I suggested above.

David

Edited By David Littlewood on 10/03/2013 15:22:53

Russell,

Well, you were the one who said that "the out of phase current doesn't go back again".

David

Russel,

Sorry to disagree with you, but the out-of-phase current flows in both directions, so it does go backwards and forwards along the transmission cables, causing losses.

David

I always understood the reason why larger customers are charged for "reactive power" (by whatever name - I believe it may be called VARs, for Volts-Amps-Reactive) is that the out-of-phase current still has to be trasmitted from the generator to the customer, and back again; this gives rise to transmission losses just as does all other current. Also, if there is too much of it, it can destabilise the system, and require the purchase and fitting of expensive power factor correction equipment in the distribution system.

David

David,

You should easily be able to hold a ruler to the nose thread and count how many crests there are in an inch; 8 and 12 tpi are pretty different.

Some threads are a bit too close to each other for such crude tricks to work. For future work you will find it invaluable to have a thread gauge - only a few quid, and should allow you to identify most threads. I suspect many of us have found it paid for itself in allowing us, over the years, to identify many of those bolts one finds lying in the road!

David

Edited By David Littlewood on 05/03/2013 16:24:04

David,

To add to the advice already given, it is always helpful in such a case to prepare in advance a dummy of the lathe spindle nose; you can then use this to check the progress of the female thread. It is a lot easier to cut an accurate male thread than the female equivalent, and having the dummy will avoid the need to take the backplate off to test it, with all the risks of misalignment when returning it to the lathe.

I'm not familiar with the lathe this is for; if it has a parallel portion at the bearing end (as the 7 series does) then cut this first - on the outside, of course, on your backplate.

David

Edited By David Littlewood on 05/03/2013 15:46:26

These people also do a large range of brass angle, and other small sections: **LINK**

David

Sid,

Many thanks for posting that link: as I imagine many others did, I went out with my binoculars several times on Friday night, only to see an unrelieved bank of dense cloud every time. I don't imagine, even if it had been clear, that I would have had as good a view of it as the one in that recording.

David

The sealing of bids and the anonymity or otherwise of the bidders don't have to go together; it is perfectly reasonable to have sealed bids, but the names of the bidders could still be published.

David

Baldric,

I think there must be some confusion of nomenclature here. To use this type of attachment, you must* remove the cross-slide leadscrew as its position needs to be controlled by the taper bar. As Brian said, if you don't, there will be a massive smash up. You apply progressive cuts with the topslide, not the cross-slide. The Boxford attaachment is slightly different in that it looks to replace the cross-slide altogether (which of course automatically removes the cross-slide leadscrew from the equation).

On another note, most makers, and users, seem to assume that the taper guide bar and the slider which travels on it need to be dovetailed. This is quite unecessary; a rectangular bar is perfectly sufficient, as the rigid coupling with the cross-slide prevents any vertical movement. This is much easier to make in the home workshop. The Hemingway kit works on this basis (at least mine did, but that was 20 years ago).

*The only exception to this is if you have the type with a telescopic cross-slide leadscrew, as in the case of the one for the Harrison M300. If you have one of these - lucky you - then you need to follow its own instructions.

David

Edited By David Littlewood on 13/02/2013 12:51:38

I don't think Andy's example is a case of automatic incremental bidding at all. Here, a***p had put in a bid at 2232 on 07/02; on 09/02 at 1442 another bidder, _***p put in a bid of somewhere above £106. The a***p, on noticing he had been outbid, started putting in sequential bids, trying to find the second guy's bid and slightly outbid him. He gave up at £104, or ran out of time as the auction ended, and this set the final price of £106. Note that it is always the second highest bidder that sets the price in an eBay auction (unless there is only one bidder!). The creeping barrage approach of a***p is the hallmark of a novice, and he probably can't understand why he hardly ever wins anything - he might have been prepared to bid a lot more, but it may be that the auction ended before he got there.

If a***p had put in a bid of £104, after a previous higher bid had been made by _***p, his automatic bids (if shown, which they were not here) would have been at the same time, and presumably _***p's automatic responses would have shown as well. It also looks like _***p is also a novice; if he had put in his maximum bid of £106 (or more) in the last 5 seconds, it is unlikely a***p would have had time to put in another bid, and he would have won for £51 instead of £106.

There is nothing at all wrong with the eBay bidding syestem; it is rather that people expect it to be like a traditional manually operated auction, which it isn't. The process is set out clearly, and if someone doesn't understand it, that's their problem. It is, or would be if everyone used the best approach, more closely akin to a sealed bid process - everyone decides what they think a thing is worth, they put it in a sealed envelope, and at the end the one quoting the highest price wins. The difference here (and it favours the buyer) is that the highest bidder does not pay his bid price, he pays one bidding increment more than the second bidder.

David

Edited By David Littlewood on 13/02/2013 12:35:47

I bought a set about 30 years ago and have never used them, I guess, if the need arises, then you need one, depends what you do. It's usually a lot easier to make the hole a standard reamer size and make the shaft to fit, but I suppose some refurb jobs might be different.

David

Terry,

Be aware that there is a 45 day time limit for raising a dispute with eBay. I just got caught out on that: 3 weeks for post office to deliver, seller ignored my email saying I wished to return for 3 weeks, then I spent another couple of weeks arguing when she refused to refund.

You do of course have the option of suing in the County Court, its a very simple on-line procedure to start it. Note the Distance Selling Regulations 2000 only apply (for eBay deals) to Buy it Now transactions, not to auctions, but there are other laws that should help you if the item was defective.

David

Thanks Michael and Neil.

David

I wish you guys wouldn't give the game away like that! I've been relying on the stupid bidding practices of others for years!

David

Martin,

I agree the ball turning article was particularly interesting, but it was also the most frustrating, in that there was insufficient explanation or constructional detail. The function of some of the parts was quite difficult to fathom, at least I found them so.

David