Member postings for Andrew Johnston

David: Thanks for the information, but I think I'll be coward and stick to stopping the spindle to change parts. I was using a secondary split bush to hold the parts, which tends to fall out if the spindle is still spinning. I can always include the time to stop and start the spindle in my quotes.

Regards,

Andrew

I don't remember trying wood, but we did set paper, and cigarette cards, alight with magnifying glasses, even in the UK.

Andrew

There is still quite a high technical content in the RSGB magazine (Radcom), including in recent years some very interesting work on software radios, albeit not in great mathematical detail.

Software radio is an area where you really need to understand the theory in detail in order to have any hope whatsoever of putting it into practice.

Regards,

Andrew

Thought I'd better add a PS:   RSGB = Radio Society of Great Britain

Edited By Andrew Johnston on 09/02/2013 10:57:12

Edited By Andrew Johnston on 09/02/2013 10:58:34

I've never had a problem with cutters slipping in ER collets, albeit on a smaller scale (ER20). The torques recommended for ER collets are quite high, see here:

**LINK**

Regards,

Andrew

Dave,

Thanks for the confirmation that I've understood your advice. I've got quite a lot of tools ready ground by the previous owner(s). I've also got a few 5/16" tool blanks, and I've bought a few more for stock.

I didn't have any problem drilling 20mm deep with a 3mm drill in one go; may be I was lucky. Then again Delrin is one of the easiest plastics to machine. I did open the collets a few times before stopping the spindle, by accident. All these jobs involve pushing the part up against the backstop before closing the collet; I didn't fancy doing that with the spindle running. I'm rather attached to my hands, and I'd like to keep it that way!

Regards,

Andrew

False - Andrew

Rod,

Thanks for the information. In my limited experience of flycutting it didn't live up to expectations, probably due to vibration and tool resonance arising from the initial impact of the tool. I'll agree that 10 thou per rev is a respectable feedrate. I'll use a value like that milling plastics, but for milling metal the values tend to be lower, albeit with much bigger DOC.

I have recently bought an 80mm diameter insert milling cutter, which I hope will speed up the milling of the cylinder blocks and other castings for my traction engines. It will be interesting to see what feeds and speeds it will cope with. Substantial I hope, as it'll have 5hp behind it.

Regards,

Andrew

Seems a bit odd? I've used my pin chuck to drill several hundred 0.7mm holes 8mm deep in brass, on a Bridgeport mill, without breaking a drill.

I also found that, by just touching the small drill on the surface before commencing drilling proper, I didn't need to centre or spot drill first.

Andrew

Hi Dave,

Fun indeed, and being paid for it! I have been very pleased with the way the Britan has helped me do the tasks outlined. They may be simple, but they're a PITA to do on my conventional lathe, particularly for multiple parts.

By not using a centre drill presumably that implies that the twist drill will start true by itself? I didn't try that, although on my conventional lathe it doesn't work.

I assume by 'opp' it you mean doing one operation with one tool on all parts before moving on to the next? If so, that's what I've been doing, as I judged it to be the quickest for these particular jobs, particularly as swapping parts in the collet is so quick. It's the first time I've used lever operated dead length collets, quite a revelation. Some of the operations have been done on the conventional lathe as I judged that to be quicker than setting up the Britan.

It's good to have finally used the Britan for some real work. To paraphrase, it may be a small step for me but a giant leap in my potential capabilities. I've got the metal in stock so I'm looking foward to knocking out studs, nuts and washers for my traction engines.

Regards,

Andrew

......we'll let all his tyres down.

Andrew

Another first for me, machine tapping on a lathe. I've machine tapped thousands of holes on vertical and CNC mills, but never done so on a lathe; before now. Here's a picture of the setup:

The tap is M3, spiral flute, in a holder with a one way clutch. In other words the holder will drive the tap until it pulls out and disengages the drive, but in reverse it always drives the tap. After a tentative start on slow speeds, 56 and 112rpm, I finally settled on 562rpm for the tapping. The procedure was to start the lathe in reverse, ie, conventional direction for a normal lathe. Feed the tap in up to the preset stop on the tailstock. After another couple of turns the tap holder disengages and the tap spins with the spindle, then knock the spindle into reverse, just hit the reversing lever, no need to stop the lathe. The tap holder engages and reverses the tap out. Job done, takes much longer to write about it than to do it.

It took me less than 45 minutes to thread 32 parts this afternoon, including making a split brass bush to hold the tap, the initial tentative experiments and a few tests with an M3 bolt to make sure that I really was cutting a thread.

The more I play with the Britan the more I like it!

Regards,

Andrew

Rod,

I though that the analogy between flycutting and milling was a good one, but may be not? I'm curious as to what conditions you're using for flycutting in terms of speeds, feeds and depth of cut. I assume that by 'tooth loading' you mean chip load, ie, feed per tooth?

Regards,

Andrew

Use an Eclipse pin chuck, mine will easily hold a No.80 drill, the smallest I have:

I bought mine on Ebay, but they are available commercially.

Regards,

Andrew

Thanks for all the information. I've got boxes of standard length lefthand centre drills, so I'll probably follow Keith's suggestion and use an extension. Taking the idea a step further, if I used a short split sleeve to mount the drill I could use the drill in a collet rather than a drill chuck which would mean that the overall lengths would be similar.

Plenty to think about!

Regards,

Andrew

I also use Alibre. When I bought my copy I went for the top of the range, as I needed the sheet metal facility, but as Jason says there are cheaper versions available. The software does have some irritating features and limitations, but that is true of all CAD software. I've just finished a project where an outside company designed an injection moulded case using Solidworks. They spent most of the meetings thumping the computer and cursing the software. One big limitation of Alibre is that it is not good at free form surfaces, but that is unlikely to be a problem for steam engines.

Here's an assembly of parts for the motion work on my traction engine. So far it has proved that the paper drawings are a complete fantasy, almost none of the parts fitted together as drawn. And the valve gear appears to be wrong too.

On the assembly I can rotate the crankshaft and see how all the parts move in sympathy. PM me an email address if you want a PDF of the above which you can pan, zoom and rotate.

Dimensions are inherent to the creation of the 3D model. Alibre is also parametric, which means that the dimesions can be equations. I am designing the traction engine in imperial so I can enter 7/32 in the dimension box instead of working out the decimal equivalent. I have had to make changes in the design as some material is only available in metric sizes. So if I need to take 6mm off a dimension I could type, for instance, 7/8-6/25.4 in the dimension box. Finally for a square I could dimension one side with a number and it would be allocated a name, say D1. Then for the second side I enter D1 as the dimension instead of a number. Then, if I change the size of the first side, the second side changes automatically.

Using a 3D CAD system requires a very different mindset to a 2D CAD system. If you can think in 3D and see how parts are built up from simple 3D shapes it helps enormously.

Regards,

Andrew

David,

Thanks for the hint. I can find left hand stub drills with no problem, but nothing for left hand long series centre drills. Any ideas?

Regards,

Andrew

I can't dance to save my life; that probably explains why I had a few 'issues' pulling levers in the wrong order. Fortunately none of them resulted in clean underwear being required.

Regards,

Andrew

The shutters are useful on the descent off tow to prevent engine cooling, but the golden rule is to make sure that they're open before take off, otherwise it gets stinky pretty quickly (burnt oil), followed by an overheated engine.

Andrew

Aluminium pistons are commonly used in model traction engines. I'm planning to use aluminium pistons in my 4" scale compound traction engines, with cast iron rings. I haven't heard of corrosion problems.

Andrew

Finally the Britan is paying its way. As part of a set of plastic production jigs I am making for a client I needed 33 spacers, each 80.65 ±0.05mm long, with a 5.8mm hole in each end for a threaded metal insert.

It's long been a PITA facing items to an accurate length on my conventional lathe; face off, take the part out, measure it, put it back, take a bit more off and so on. Things are not helped by having a Burnerd multisize collet chuck, which is not dead length, on my conventional lathe. Due to the design of the jig it is important that the spacers are consistent on length as it controls how the internal parts clamp together. Here are the finished spacers:

The plastic (delrin) is nominally 12mm diameter, in practise it is 12.4mm. I don't have a collet for the Britan of that size, so I made an aluminium split collet to fit a 15mm Britan collet:

One end of each spacer was cleaned up on my conventional lathe. I then fitted the backstop to the Britan and using the adjustment screw crept up on the correct length for the spacer. Once set up it only took about 15 seconds per spacer to face off to the correct length:

I then used a centre drill (left hand) to centre each end:

And a 5.8mm drill, also lefthand, to drill the holes:

The centre and drill were separate operations, as I haven't worked out yet how to cope with the very different lengths of the centre drill and jobbers drill when they are mounted together. I'm really pleased with the operation of the Britan, it made what is normally a tedious and long winded job very simple. Doesn't happen often, but definitely one of my better buys.

I quoted a fixed price to make the jigs, so I'm feeling rather smug that these parts took a lot less time than I budgeted. Tomorrow I'll make up a simple adaptor to fit the threaded inserts, while ensuring that they go in square.

Regards,

Andrew