Member postings for Andrew Johnston

Given it's US made I'd bet it's 8-32 UNC.

Andrew

Silver steel is designed for water quench, while gauge plate is designed for oil quench. I don't do enough to justify buying the special oil, so I quench both silver steel and gauge plate in brine. The addition of salt makes the quench slightly less violent. When quenching you need to agitate the work; don't just dunk it in and leave it. And I mean agitate, move it like your life depends on it. To get full hardness the metal needs to cool very quickly, before the atoms realise what is going on and re-arrange themselves. If you don't agitate the hot metal forms a blanket of steam around itself, which acts as an insulator and reduces the cooling rate.

Andrew

Sheet and plate are one of the few forms of material that have gone exclusively metric. The hornplates on my traction engines were specified as 1/4" plate, but I had to use 6mm. I'd second the advice from Jon and keep the outside frame dimension the same. That's what I did on my traction engines, so all I had to adjust was the width of a couple of castings. I also slightly altered the crankshaft bearing housings to keep the crankshaft and valve gear in the same place relative to the engine centre line..

Andrew

+1 for M-Machine; they're one of my suppliers. Only use Ebay if you know what you're doing and are prepared for the metal quality to be poor, which may not matter for temporary fixtures.

I've had poor finishes like those shown. It's all down to the cutting tool, material and cutting parameters, especially feed rate. What it isn't down to is the rigidity of the machine. I got my poor finishes on a Bridgeport. While that isn't the most rigid of mills, it's much bigger and heavier than a SX2!

Andrew

Postscript: Get some bright steel flat (EN32B) or, if you want a slightly increased challenge and to save money, get some black (hot rolled) flat. Thickness and width aren't critical, but may be 6 to 8mm thick and whatever width will be useful. Note that bright flat will be to size, black is usually slightly over to allow for removal of the black mill scale. Learn to get a good finish on low carbon steel before worrying about testing the mill with more difficult materials like  gauge plate or stainless steel.

Edited By Andrew Johnston on 16/05/2020 09:51:27

More likely that the slides moved under the influence of the cutter. If the two flutes are not cutting evenly, which they won't do on a casting, the cutter can easily drag the table. Been there, done that.

Andrew

Edited By Andrew Johnston on 15/05/2020 20:43:14

I very much doubt the problem is anything to do with resonance. Chatter is all to do with the cutting process, not the resonant frequencies of the machine tool. Chatter does not imply resonance of the tool or workpiece, but unstable cutting conditions.

I'd agree with JasonB. The cutter looks blunt to me. A shallow cut with conventional milling on unknown material with a blunt cutter will almost certainly lead to rubbing and then cutting, and back to rubbing. A slow feedrate will make matters worse.

Andrew

I'd agree with Paul; a copper boiler is a bad idea, for the reasons given.

What pressure are you planning to run at? The equations in K N Harris's book make some assumptions about safety factors and I'm not sure if they take into account the loss of strength with temperature. Whichever way you look at it this is going to be a big boiler, so you need your figures to be checked by a club inspector, or more likely a professional insurance company.

While I am making as much of my 4" Burrells as I can, I know my limitations and bought professionally made steel boilers.

Andrew

My imperial lathe is calibrated in thou off the diameter. I wouldn't have it any other way. One measures diameter so it makes sense to be able to directly set the remaining material to be removed.

Andrew

I'm a cynical old barsteward, but I wasn't overly impressed with the video. Obviously one can't cover all aspects, but a run in the lowest and highest speeds would have been good, along with some proper cuts.

I had a quick play with my Harrison M300 this evening. At 800rpm it's definitely noiser in reverse. But at 400rpm there's no difference and it was much quieter than the video. The speed in the video doesn't seem that high to me. When cutting there were horrible noises, although it's not clear if that's the lathe or poor material, tooling or technique.

Personally I'd either get someone to have a proper look, or walk away. The only upside is that on Shetland a boat anchor may possibly be of some use.

Andrew

I can tell you that. This is a picture of the part I showed previously, but taken as near along the straight top edge as I could:

The cut was done on a CNC mill using an Arc carbide premium cutter. The curve looks to me to be pretty darn close to a perfect quarter circle, as it should be. So the premium cutters are correctly ground, the budget ones are not. I definitely won't be ordering any budget cutters.

Andrew

Must be cabin fever setting in but I'm confused. Is the lathe motor single phase or 3-phase? And is it 2-speed or not? While 2-speed single phase motors are not unknown they're pretty rare.

A 2-speed 3-phase motor is N or 2N poles; it doesn't have to be 2 and 4. Poles are not switched in or out but are connected in different orders to switch number of poles. Having unconnected windings would really mess up the magnetic performance of the motor. Whether you can switch poles on the fly depends upon the motor design.

I have a 2-speed motor on my horizontal mill. It needs to be turned off to change speeds. There are two controls that need to be moved, one on the electrical cabinet and one on the column of the mill. As well as switching poles the poles are also configured as star in high speed and delta in low speed, so that low speed is not half power.

My repetition lathe also has a 2-speed motor; it operates in star for both high and low speeds. There are two coaxial electrical switches on the headstock, one for changing speed range and one for forward/reverse. These can be operated while the motor is running, either individually or together. So you can go almost instantly from high speed forward to low speed reverse.for instance. Although you do get a 'thunk' from,the motor.

Andrew

Just looking at the cutter one can see that the end is not a full semi-circle. All my ballnose cutters are semi-circular as far as I can tell. I use them a lot on the CNC mill and the parts wouldn't be right if the cutter wasn't semi-circular. All my cutters are professional quality; including the Arc premium range.

The filleted profile on this part was CNC machined with an Arc premium range 5mm ballnose cutter:

I wouldn't have machined the slot with a ballnose cutter, but would have gone in sideways with an endmill.

Andrew

Superficially the bed and tailstock look like a Harrison M300. But there are huge differences everywhere else. I doubt that Harrison M300 parts will fit, and they go for silly money anyway. Given that the seller hasn't sold much recently, what he has sold is a right mixture, and he can't be a*sed to write even a basic description I wouldn't touch it with a barge pole.

Andrew

I suspect that box shifters have been around since time immemorial, although Clive Sinclair certainly let the customer do the quality assurance. I never succumbed to the original audio, radio and calculator kits. I let my school mates do that! The first calculator I bought was a Sinclair Oxford, sold ready made. I had a friend who bought the ZX80, ZX81, Spectrum and worst of all the QL. The computers were definitely let the customer do the QA; the repair 'organisation' was a man in a shed in his back garden in Cambridge.

When I was in the university engineering labs at Cambridge there was a debate as to whether Sinclair was a technical genius or a marketing genius. I'm inclined to the latter view. He spotted gaps in the market, filled them, and made a fortune. He made several fortunes over the years, only to lose them at later dates with disasters such as the universal miniature TV set and the QL computer.

I've met Clive Sinclair a few times as he joined college at the same time as me, to do a Ph.D. in business studies. So he was around at some of the parties and dinners. Sharp guy, but with a scattergun approach. Later, when I was learning to power fly, I also met his chief designer, Jim Westwood. He had a fancy aeroplane with a wobbly prop. He was a great chap and we did a couple of flights together - one to the Shuttleworth collection at Old Warden for tea and cakes. Jim is a clever designer. The Sinclair products were very innovative, especially given the cost constraints. Pity about the QA and marketing though.

Andrew

My reply rather assumed a solidstate polyfuse rather than a mechanical one. A picture of the offending component would help identification.

Andrew

Mine are cast iron since I bought castings, and it's prototypical. The front cover is just a flat plate, so if I hadn't bought a casting I would have used some hot rolled plate as it distorts less than cold drawn, and seems less prone to corrosion. For the rear cover anything other than a casting would have been a right pain:

The expansion rates of low carbon steel and cast iron are pretty similar.

Andrew

As per the manual I use an ISO220 oil in the screwcutting gearbox on my lathe and an ISO68 hydraulic oil for the headstock. For slideways I use an ISO68 slideway oil. A slideway oil is stringy but not sticky; it's designed to minimise stiction.

Andrew

Better learn to draw file then.

Andrew

If you're sure it's a thermal fuse and not for limiting in rush current then yes they can age with time and more importantly number of cycles. Same as an ordinary single blow fuse. Like ordinary fuses they're not particularly accurate and operation is, to some extent, dependent upon ambient temperature.

Andrew

Oh dear, and I've just done it on some hot rolled plate.

Andrew