Member postings for Andrew Johnston

Depends on the size and shape of material, but I use one the following options:

Hacksaw, with or without a scribed line depending on shape

Bandsaw

Parting tool

For sheet material a power guillotine

For lumps that are too big for the bandsaw a slitting saw in a horizontal mill

Andrew

In short I don't sweat it. There are draws in the workshop for tooling, but tools are also stored on shelves in the workshop and a significant number of taps & dies, cutters and reamers are in the dining room. I know where the most commonly used tools are. If I need an odd one I'll have a ferret round and see what I can find. If nothing surfaces I'll either buy something or change the design to use a tool I do have.

Andrew

Can't remember precisely, but I started with a centre lathe and vertical mill bought from the same dealer. After that I think it went roughly like this:

Surface grinder and donkey saw

DRO for vertical mill

Pillar drill

Horizontal mill

Tool and cutter grinder

Shaper

4-axis CNC mill

Cylindrical grinder

Professional quality machine vice

Box and pan folder

Power guillotine

Repetition lathe

Instrument makers lathe

Horizontal bandsaw

Everything, apart from the CNC mill, machine vice and DRO, is secondhand.

Accessories and tooling have been bought (all secondhand) as available from all types of sources.

Andrew

Edit: Forgot to mention the welding gear (oxy-acetylene and TIG) but can't remember where they fitted in. I bought a propane burner relatively recently.

Edited By Andrew Johnston on 01/06/2020 21:03:04

They're available and called logic analysers They concentrate on displaying time relationships between channels and are less concerned with voltage levels. They usually display a channel as 0 and 1 based on the levels of a selected logic family. Relatively cheap ones are available, although I can't remember the details. On the other hand fancy ones (32 channels and upwards with bandwidths into the GHz) can approach £100k. The better ones can morph a number of channels into one line with a binary or hex equivalent of the channels. When looking at address and data buses that's often more useful than displaying individual lines.

Andrew

I've no idea what the question regarding hand turning was about, but it can't have been important.

To complete the picture the drive pulley on the crankshaft for the governor is also crowned:

SInce this pulley only has one flange the crowning was machined using a hydraulic copy attachment and a marked out and hand filed pattern; the one bottom right:

Does this count as hand turning?

Andrew

Repeatability and accuracy are not the same thing. Generally the former is easier to achieve than the latter.

Andrew

What do you mean by hand turn?

Andrew

I made these governor pulleys by forming the groove with a HSS parting style tool. I then tilted the top slide a couple of degrees each way and machined a small taper each side. Final shaping was done with needle files. The exact shape of the crowning isn't critical as long as it has a bigger diameter in the middle and is a smooth curve:

Andrew

+1 for Weller. I've got a dual 80W iron with digital temperature control. I use it for components down to 0402 (1mm x 0.5mm) and fine pitch ICs.

I've still got my 15W Antex iron. I really liked it and used it for many years for home electronics. I bought the Weller for professional use. My Antex iron has a small (~4mm diameter black power lead) and was bought from an old school TV and radio repair shop in Bedford in 1971.

Andrew

The corollary of no specification is that it doesn't matter what you buy - anything will do.

I chose to buy the following, all from Ebay at a total cost of less than £150 including delivery of the 3ft x 2 ft surface plate from Nottingham to Cambridge for £40:

The vernier height gauge is dual scale and was made by Etalon and the surface plate is Crown Windley.

Andrew

Because it's not a parting tool, but is intended for profiling and grooving. At least that's what I use mine for:

Dunno why he feels the need to part off so far from the chuck. Well I have an idea, but this is a public forum.

Andrew

I'm making progress on the piston rod glands, just the CNC profiling left to do. Given the recent post about inconsistent micrometer readings, and the dismissal of micrometers and comments on fitting, I thought I'd expand on how I machined the glands. First, the front face was cleaned up and the hole bored and reamed:

Next, using a split bush, the boss was brought to the correct diameter and length and the back of the flange cleaned up. The width of the flange is not critical, so I didn't measure it but just took enough off to clean up the surface. The nominal width of the flange is 3/16" and the flange was made from 5mm plate so there's some meat to play with anyway. The length of the boss is also not critical so it was measured with a rule.

For the diameter of the boss I first measured the recess in the cylinder cover. The recesses were 'bored' out with a 7/8" endmill but have come out a bit oversize, measured as 0.892". I turned the boss to 0.891" using a micrometer and the lathe cross slide dial, with the number noted. A sanity check with the cylinder cover confirmed that the boss fitted with slight play, as I wanted. The bosses on the remaining three glands were turned to the same diameter using the same cross slide dial number, and sanity checked with the micrometer. All four bosses are within a thou of each other with no great effort on my part, other than remembering a number.

Finally the centre of each hole in the boss was picked up on the vertical mill and holes for the studs drilled using the DRO to position them relative to the central hole:

The holes for the 1/4" studs were drilled 6.5mm. So in theory there should be 3 thou radial clearance, although bronze has a nasty habit of closing up slightly on drilled/reamed holes. Here's the cylinder cover and glands assembled:

All glands fit in each location with the piston rod running smoothly in all cases. So basically the glands are interchangeable and I don't need to mark each one for a specific location.

It took longer to write about than do. My point is that with some thought and proper measurements it is possible to make parts that fit without each part being specific to one location or needing post-machining fitting. Which is good for a lazy bones like me.

Andrew

Do NOT wear gloves when operating machinery. If they get caught on something you'll be dragged in before you know it. I use brushes and scrapers for cleaning up swarf and rarely have problems as I don't touch the swarf.

Andrew

Here's a better picture of the wheelhead weight on my MG12:

The MG9 seems to have a coolant tank at the back, looking at the newly refurbished casting. Does it have a separate coolant tank and pump as seen on tbe right in the above picture. On the MG12 the tank at the back of the machine is divided into 2 compartments, and is basically a settling tank. The two bent plugs top right are for draining the settling tank.

Andrew

This morning I flew the tug albeit by itself - no glider on the back. It's been nearly six months since I've flown power and if it goes over six months I'm supposed to fly with an instructor. Which would be difficult while maintaining social distancing. To start with I thought I'd spend a few minutes just flying around before attempting a landing. I went to have a look at my bungalow. Then I noticed a red light on the panel, oeeeeer. Darn alternator isn't working. I start the engine with the alternator offline, and having forgotten to connect it and flattened the battery in the past I'm paranoid about putting it online. Looked at the breaker and it's in, trip it and reset, still got a red light. Work through all the other breakers and find a new one on the other side of the panel labelled 'charge'. Press it and whoopee the red light goes out and the ammeter indicates the battery is charging. But the darn breaker won't stay in, took five goes before I got it to stay in. Fortunately it stayed in while I did four circuits and landings. Report the new breaker issue to the Chief Tug Pilot and he says he'll investigate, and find out when and why it was fitted. I'm now happy to start towing again.

This afternoon I did some more silver soldering, on the valve rod glands:

This evening I started machining the previous silver soldered parts. The sequence will be:

In the 3-jaw chuck face one side of the flange and bore/ream the hole.

Use a split mandrel to machine the other side of the flange, bring the boss to thickness and to the correct diameter, using a micrometer.

On the mill centre on the hole and offset to drill the holes for the studs.

Finally mill the outside profile.

Andrew

Some interesting results, and as you're discovering the biggest problem is interpreting said results.

As for filtering it's a case of what they didn't say in Star Trek:

It's filtering Jim, but not as we know it.

Filtering in the mathematical sense is a convolution in the time domain, which conveniently transforms to a multiplication in the frequency domain. The Fourier transform exhibits linearity, so for two time series x(t) and y(t) we can say:

x(t) + y(t) <=> X(f) + Y(f)

So the subtraction in the frequency domain is the same as subraction in the time domain, if a bit more convenient in the frequency domain. In a sense it's a filter in that one is saying I don't want that frequency and removing it by subtraction. But of course the 'filter' characteristic would change with each FFT unless the unwanted frequency stayed exactly the same.

Feel free to have a beer after that!

Andrew

That's good; it's saved me writing out the mathematics of the Discrete Fourier Transform to demonstrate the relationship between the x-axis in time and frequency domains. The original FFT algorithm by Cooley and Tukey reduced the number of operations for an N length transform from ~N^2 to ~Nlog2(N), where N is a power of 2. Note that these operations are complex as the Fourier transform uses complex numbers. So each complex multiply is four real multiplies and two additions.

Andrew

Looks like it's long been obsolete. A search only finds archived datasheets and brokers who may, or may not, have a link to some in stock. But you won't be able to buy one off!

It was made by Sprague who sold out to Allegro Microsystems, I think. Farnell have loads of Allegro sensors listed so I expect one will be suitable.

Andrew

Ok, thanks. Seems a bit rude to me, even if I agree with the underlying point. But what do I know!

Andrew

The tension weight is a hefty lump of steel, well over 100lbs. I think there's a chain up to the wheelhead slide and a folded steel cover attached to the back of the cabinet. Since the operating thread is fine pitch you don't really notice the thunking great weight when operating. If it helps I can take a better picture.

Andrew