Member postings for Andrew Johnston

Plenty of suppliers for machined BA and small metric nuts but not so for BSF. I've been caught by a supplier advertising machined BA nuts sending cold formed BSF nuts. I wanted the old style thicker nuts, so I made my own, 1/4" BSF full and lock and 5/16" BSF full:

Andrew

In addition 48V is a standard industrial distribution voltage within automation cabinets and the like, as well as for power over Ethernet units. The problem with 60V is that it is at the SELV voltage, so regulations get rather more onerous.

Andrew

I'm embarrassed to say about 10 years. But in my defence I'd note the following:

• I'm building two engines, so everything in the picture is doubled
• There are quite a few parts made but not yet installed, like hollow pistons, eccentrics and brake handles
• All the parts exist in 3D CAD for several reasons; some imperial materials are no longer available, I've made a number of design changes for increased authenticity, I've redesigned a lot of items as the original drawings are poor and riddled with errors
• I have an out of control garden
• I've got sailplanes and aeroplanes to fly
• Until recently I've been working full time

That's probably enough excuses to disguise my indolence.

Andrew

Miniature pinking shears?

Andrew

It's a rare workshop day when I don't make a mistake. Likewise it's a rare day at the gliding club when I don't get a rollocking for something or other!

Andrew

What's the problem? According to the experts all you need to do is press the button marked 'GO'!

How would I do it, assuming rotational symmetry? For a start I wouldn't split the big end at this stage, and I'd leave the material over length. I'd drill and/or ream the little end. I'd also drill a hole in the big end, but of a size and in a position that will disappear when the big end is opened out. I'd set the work co-ordinates to zero in X & Y on the little end bush. Then mount the work with bolts and washers in the little and big ends. If one is particular about accuracy you could bush the little end or provide a tapped spigot. Machine the profile (except the outer end of the big end, so to speak) and then relieve and flute one side. Turn over and relieve and flute t'other side. I'd clean up the outer edge of the big end, and drill and start the tap, for the big end bolts while the stock is still rectangular; makes life easier.

Once all that's done I'd split the big end, clean up as required and bore the big end hole.

Andrew

Depends if the electrics/electronics work and you have a 3-phase supply. If neither then bin the lot and take note of Muzzer. If yes to both I'd be inclined to play before stripping out.

Andrew

Edited By Andrew Johnston on 14/05/2019 15:18:13

I've done it the other way round, importing a new mill from the US. I used ACC Shipping in Gravesend:

**LINK**

Going t'other way may be different but the following points may be useful:

I don't think ACC do pallets and boxes

Normally the supplier needs to provide a description and nominal value - ACC can say what they need

They will pick up from the supplier, ie, you, and take it to the docks.

A small item will be LCL (less than a container load) so ACC will combine it with other items to minimise cost by ensuring that the container is full

They organise the ship

Into the UK they looked after all the customs forms, duties and VAT - I then paid them

They organised shipping from the UK port to me - don't know if they do the same overseas

Best thing is to give them a call; I found them pretty helpful to a novice.

Andrew

For material up to the thickness mentioned I use a power guillotine.

Andrew

Errr, I think so? Burrell called them anchors, which is something of a misnomer as they're designed to get you out of a sticky situation rather than keep you in it.

Andrew

You're a better man than me; I couldn't even close a 3/16" rivet with a hammer. Well, not strictly true. I can hammer the rivet end flat with a hammer, as I'm doing at the moment with the strakes. But no way could I form the domed head with a hammer. I got so far, but couldn't force the head that last little bit. So I resorted to the flypress. Much less drama and less chance of hammer blows in the wrong place, followed by naughty words.

Andrew

Wot Jason said.

If there's trouble with vegetables I'd better not mention traction engine spuds!

Andrew

The bolt might be in tension but the threads themselves will be in shear. For many materials the shear strength is greater than the tensile strength. That's why a bolt shank will break before stripping the thread.

Andrew

Many full size engines have the cylinder fixing holes drilled right through the boiler shell. The only difference being the holes are not tapped; carrot bolts are used instead of studs.

Andrew

A further variation concerns the cross slide feed. On smaller, cheaper, lathes the cross slide screw is disconnected and the slide driven by the taper attachment. Feed is put on using the top slide set parallel, or close to parallel, to the cross slide. On larger, mostly industrial lathes, the cross slide screw is telescopic so feed can be applied with the cross slide handle as normal while still allowing the cross slide to move in sympathy with the taper attachment.

Apparently the taper attachment for my lathe (Harrison M300) is of the latter type. I don't have a taper attachment; if one came up at an advantageous price I'd buy it, but I'm not desperate to buy at any price. If I need to cut long taper I use the hydraulic copy unit. if the taper really needs to be accurate I'll use the cylindrical grinder. The swivel table on the cylindrical grinder is marked in degrees.

Andrew

Over the recent Bank holiday weekend I assembled enough of one engine to have it sitting on it's own wheels:

After I'd recovered my jaw from where it hit the floor my reaction was bleep bleep that's seriously BIG! Where on earth am I going to put the second engine? It's just as well I moved the parts out of the kitchen, the assembled engine won't go through the door. Fortunately I got the specification for the front door correct when it was replaced a few years back, there's an inch or two of clearance.

Andrew

Current sensors are fairly good straight out of the box. You need a burden resistor on the secondary, usually tens or hundreds of ohms. The secondary has many turns, often 1000, and the primary one turn, ie, a wire through the hole in the middle. The manufacturer wil often give a formula for the voltage across a given resistor for a given primary current.

However, there's a caveat. Last year at work we had a need to measure a three phase supply, so we used three cheap, made in China, current transformers. The client complained about non-linearity at low currents. The transformers were rated at 20A and sure enough at less than 200mA or so they went non-linear. A lot of effort went into measuring the effect and correcting same in software. Then we bought exactly the same part (same company name and part number) but made in India. They were linear down to the limits of our measurements, a few milliamps. Go figure!

Andrew

If I recall correctly differential probes have been discussed before, quite possibly wih SoD. This is what I use:

It's not isolated and doesn't need to be. However, it's not really the best probe for the measurement specified as it uses an input divide ratio of 100:1 or 1000:1. That's fine if you're measuring mains size voltages, but not helpful if one is trying to measure small voltages riding on a large common-mode voltage.

Andrew

For free form shapes I hand grind, possibly against a template, and finish with diamond hones. If the profile is important I'll machine it and finish with diamond hones.

Andrew

Oh dear, I use an ISO68 hydraulic oil in the geared headstock of my lathe; although that is as recommended by the manufacturer. I use an ISO68 slideway oil on the slideways, feedscrews and change gears. The change gears are totally enclosed so they're not going to get dusty. The quickchange gearbox uses an ISO220 straight oil.

It's interesting to note that the ISO68 slideway oil doesn't work too well on my repetition lathe; too much drag makes the slides difficult to operate. All by hand lever of course. Instead I use an ISO32 hydraulic oil.

Andrew