Member postings for Andrew Johnston

That's interesting, a thread I started last night seems to have disappeared. I'm not that bothered as it had answered the question I had and I wasn't expecting any replies. Which was what happens in a post if one uses a picture from an album and then deletes that picture from the album. But having had a post edited recently it would have been courteous to have had confirmation that the post had been deleted.

Andrew

Clive: Thanks for the exposition. When I was looking for a DRO I considered a 3rd axis. But I ended up buying a professional DRO (Newall) and the 3rd axis was a significant increase in cost. That's important when spending ones redundancy payment!

I must do simple machining as I don't miss a 3rd axis readout or a quill scale. I've never needed to drill a blind hole to an accuracy better than that obtainable by visually setting the quill stop. Likewise it's fairly rare that I need to pocket out or mill down to a specific depth with any degree of accuracy. When milling the quill is fully up, locked and never moved. These valve chests were milled to a specific depth (although not strictly necessary as the valve floats vertically):

The valve chest cover face was already machined and set parallel to the table in X and Y. I then touched the tool on the cover surface, as indicated by a fag paper. Set the Z dial to zero and job done. The cylinder is being machined imperial but my Bridgeport is metric. On the drawing it is simple to dual dimension and a few seconds with a calculator gives the number of complete turns and remainder. I machined down in steps, keeping count of turns. Before the last full pass I extracted the cutter and did a sanity check on the number of full turns, as well as blowing the swarf away with a bendy straw. Easy then to do the final full pass and partial pass, leaving about 4 thou for a slow finishing pass. Endmills with radiused corners give a really nice finish. I can't get into measure it but probably better than a micron Ra.

Andrew

Dunno quite how we got here from an M300. My only excuse is that my Bridgeport and M300 are next to each other.

Such as?

Andrew

Can't say I've ever missed not having the carriage graduated on my M300. Generally if I need accurate lengths it's often a small spigot or hole only at one end, and I just use the top slide dial. On the rare occasions where I need an accurate length on a long bar I simply measure, put back in the lathe, touch off and use the top slide to remove the amount I need. For the rear axle on my traction engine I didn't even measuring, just machined by eye to a scribed line created on the job:

Personally I wouldn't bother with a DRO. On the Bridgeport a 2-axis DRO is the best bit of kit I ever bought, but on my lathe it wouldn't be useful.

Andrew

I'd agree with Clive, a lot of trouble for a bodge result. I've got RH and LH boring bars but I've never needed a LH knife tool. If I did I'd just use one of the boring bars, or grind a piece of HSS.

Andrew

I'm with Henry. For rough alignment (and castings) I simply align by eye on the tool. If I need better accuracy I'll use a feeler gauge between tool and work. For yet better accuracy I use a DTI on the top of the work (easy to read) and adjust the jaw at the top, spin 180° and adjust again, and the same for the other pair of jaws. I only use one chuck key; I wouldn't be able to access the bottom jaw, my chuck is fairly large, work is normally heavy and the workshop gorilla does things up tight such that I couldn't loosen a jaw single handed.

For the few times that I need to pick up on a centre pop (which happens to be the current job) I use a wobbler:

Andrew

No, the fact that you do it at all. I've been operating under the illusion that private messages were just that, private.

Andrew

That is deeply concerning................

Andrew

Probably not, it might be like asking Gavin Williamson to mark his own homework.

Andrew

Oh dear, as an undesirable I'd better leave now before I get banned by SoD for pointing out defects in his posts.

Andrew

That's a nicely made spindle and some pretty impressive traverse rates. I love the power drawbar. Really must get mine fitted. It's been on the sitting room floor for too long. My only disappointment is that what he's got is quick change tooling, not an ATC (automatic tool changer). That's a whole different ball game. I did look at the Tormach ATC, but it's expensive (~$5000) and offers no real advantage, to me at least. Of course in the professional world they're indisensable.

Andrew

For those seriously interested in electronics there's a new book out called the X-Chapters. It's a companion volume to the Art of Electronics (edition 3), which is the best book bar none on real world electronics, and is by the same authors.

The book goes into much greater detail on passive components, transistors and opamps. It even discusses the capacitance voltage coefficient for ceramic capacitors versus dielectric type. There's more detail on opamp internal design and characteristics than even the professional is likely to need. It also covers switchmode supplies and some power electronics, although for me at least, those sections are a bit low level compared to the other areas.

There is also a wonderful comparison of a genuine Apple wallwart and a fake import. That should serve as a dire warning to those who buy grey imports to 'save' money.

The book is not cheap, and you really need AoE3 to get the most out of it. It's mostly at the professional level but for the keen amateur it's a most interesting, and challenging, book.

One caveat, it's printed on tissue paper so thin you can see what's printed on the other side of the page. That's a real disappointment, CUP must be going down the pan.

Andrew

CUP = Cambridge University Press

That's because high speed is a misnomer. It's not necessarily about higher spindle speeds or feedrates. What they try and do is keep the cutter engagement constant so feeds and speeds can be maximised. The outcome is the the overall machining time is reduced - hence high speed. In contrast a simple 2D path might use a given stepover, but depending upon the geometry may decide to do a full width cut over a short period. In that case the speeds and feeds (and DOC) are determined by the full width cut, not the majority of the machining. So overall time might be slower. Another bonus of constant engagement is less chance of chatter due to short term large engagements.

Andrew

Surely that should be full power not torque.

Although I've got a varispeed head on the Bridgeport I've never missed infinitely variable speed on my other machine tools. As long as one is in the right ball park it's fine. The exact speed isn't critical. What's the betting someone will pop up and mention chatter?

Andrew

The steam flows from the regulator chest (bypassing the regulator) through passageways in the cylinder to the back of the valve. As per the red wire:

In the CAD model the valve is shown closed. When open the steam flows through the valve to the downward facing union to a pipe. The pipe then connects to a flange on the cylinder rear face and a hole that goes into the LP valve chest, again follow the red wire:

Although not shown in the CAD model the valve is spring loaded shut. On the fullsize engine the pipe from the valve outlet to the LP valve chest is 3/4" OD, which has a small area compared to the normal flow through the valve passageways.

The singling valve is operated by a push button on the regulator assembly; the brass knob in this picture:

Again, although I haven't made it yet the push button is spring loaded against the rod bushing top right, on the spectacle plate. In use it is intended that the valve is used with quick 'blips' of the operating button, usually with the regulator closed. If nothing else the passageways are not large enough for sustained running of the LP cylinder at nominally full steam pressure.

Andrew

The fine detail:

What surprises me is that the flutes seem somewhat longer than quoted.

Andrew

Better make sure you sit down before looking at a 0.5mm cutter then!

Andrew

This has been discussed at length recently on the TractionTalk forum:

**LINK**

Although I believe you have to be a member to be able to read posts. In summary it's not simple (pardon the pun) as every manufacturer did something different, often on different engines.

My simple understanding is as follows. A starting valve allows boiler pressure steam, from before the regulator, to be applied to the low pressure cylinder. On a DCC engine this allows it to be started when the HP cylinder is on dead centre. External starting valves are quite small with restricted pipes so wouldn't be able to run the LP cylinder at full power for sustained periods.

As you say a simpling valve is internal to the cylinder and connects the HP exhaust to the chimney. For running as two singles in parallel one needs both a starting valve and simpling valve to be operated.

On my SCC there's a starting valve, although I prefer to call it a singling valve as if the engine is on dead centre applying steam pressure to the LP cylinder won't help to start the engine. I'm told that this valve (and presumably a proper starting valve) is used in quick bursts to provide some torque for manoeuvring in tight spaces. Note that the valve bypasses the regulator so the valve can be used with the regulator closed. Presumably something one would do if space was limited.

This is a sectional CAD model of my design of singling valve for the Burrell, based on full size:

Hope that at least helps in part.

Andrew

Job done:

Followed by a clear up of the lathe, mill and floor. It's amazing how much swarf was created.

Andrew

Pictures would be most interesting. I do still have my Britan. It gets used regularly, mainly for knocking out custom studs, bolts and nuts for my traction engines. So I'm not really challenging the machine, but I sure wouldn't want to make the parts without it. Of course building two engines means lots parts. So far I've made at least 300 1/4" BSF full nuts and 50 or so locknuts.

Andrew