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Member postings for John Olsen

Here is a list of all the postings John Olsen has made in our forums. Click on a thread name to jump to the thread.

Thread: Coronavirus
26/03/2020 02:34:26

I'm not sure that a microwave will have much effect on any viruses (or bacteria for that matter) lurking on incoming mail. Microwaves only heat things that contain water and are of a reasonable size. (A significant portion of a wavelength.) I think you will find that if you manage to trap a household fly in the microwave, it will buzz around inside with a great lack of concern while the oven runs. Ironing the mail with an iron hot enough to almost scorch the paper would have a better effect.


21/03/2020 08:54:52

Here's a light hearted approach to isolation by Colin Furze:

Colins isolation chamber


Thread: Sanitizer
19/03/2020 03:35:10

But of course the Coronavirus is not a bacterium. It is not alive in the usual sense, it is just a little package with some RNA inside. It does not need nourishment, and probably not even oxygen but has to survive undamaged long enough to find a host cell that it can take over.

So to get rid of the little suckers we need to disrupt them, and it seems like soap and water is actually the best way. Quite likely ultraviolet light would do the trick too, which would not be good for your skin but would be a good way to disinfect surfaces.


Thread: Motorcycle General Discussion
18/03/2020 01:00:07

Turning a silk purse into a sows ear?


Thread: Acetal or phosphur bronze
17/03/2020 00:00:46

Acetal would be fine in this sort of service, or you could consider going the whole hog and doing the mod on the Arc Euro site:

Arc Euro thrust bearing mod



Thread: Shaper Vice?
11/03/2020 02:35:02

I just took a look at my shapers to see what is what. The 18 inch Alba has the arrangement that puts the screw under tension. The 10 inch Alba does not, the screw will be under compression. Those are both original vices. The Ammco shaper does not have an original vice, but I have the drawings and that would put the screw under compression.

I think the main feature of a shaper vice is that they are usually low profile.

I don't think that the cutting forces on a shaper are any higher than with anything else, the only point you should watch is when the cutting force is along the vice jaws, when it may move the job. A piece of paper between the jaws and the job is enough to prevent this.


Thread: ML7 Main Shaft Slipping?
09/03/2020 21:03:53

Ok, Swarf mostly is probably right, the little toothed segment that should be engaged when you are not using back gear is probably not engaged. You need an allen key with a very short leg to work it. When you are in backgear it is in the out position and for normal work it slides in to engage with the gear.

However, another thing that can happen is that the aluminium pulley comes loose on the bronze sleeve that is part of the small gear. If this is happening you will be able to see that the pulley moves relative to that gear when you put a load on it. The only way to fix that is to dismantle the whole shaft and use loctite to improve the fit. I had to do this to mine, it has given no trouble since. You don't want any loctite getting inside the bronze sleeve locking that to the spindle of course.


Thread: Should my pistons be round
29/02/2020 09:54:25

No, they are slightly oval, by maybe about a thou per inch of diameter or so. When hot, they expand differently because of the gudgeon pin bosses, so are more round at working temperature. Pistons for small model ic and steam engines are mostly machined round, but the IC ones probably bed in slightly oval.

The Honda suffered from rules essentially designed to prevent four strokes from competing. It was an attempt to get the effect of an eight cylinder while only allowed four by the rules. The shape of the pistons made for difficulty in sealing. Meanwhile, the two strokes were effectively supercharged.


Thread: Mag Base
29/02/2020 02:38:04

The older types of permanent magnet do indeed tend to lose their suck over time. There are people who will remagnetise them which will make them as good as new. The basic idea is to apply a very strong magnetic field, for example by placing a few turns of heavy wire around the magnet and then applying a pulse of current from a large battery or a bank of capacitors. The field does not need to be applied for long.

The generator is a different kettle of fish to the magneto or the permanent magnet alternator. The generator does not have a permanent magnet in it, it relies on residual magnetism to get it started when it begins turning. If it has been standing around long enough to lose the residual magnetism it may need a pulse of current from a battery through the field to get it going. That can also be done in the reverse direction if you are changing the polarity of the system.

If the magnetic base is the type with a "switch" to turn it on and off, leaving it in the switched off position will effectively be putting a keeper across the poles. The same applies to magnetic chucks. If there is no control, clamping it onto a piece of steel when not in use will help.


Thread: Upgrading to Stephenson Gear
24/02/2020 03:14:03

If you were not using any lead the two eccentrics would be 180 degrees apart. They both have lead applies, but since one is for reverse the lead is in the opposite direction. For a first approximation, you can regard each one as if it was for a single eccentric gear for that direction of rotation. I suspect that the way it got invented was when someone realised that by connecting the two parts of a gab gear with a curved slot you could avoid a lot of mechanical clunkiness, and that the subtleties of early cutoff came later.

The two types of expansion link are launch type, with the eccentric straps connected below the slot, and locomotive type, with the eccentric straps connected to the ends of the slot. There are also differences with the way the weigh shaft attaches, it may be attached at one end of the link, or in the middle. If it attaches at one end, that should ideally be the reverse gear end.

There are some subtleties to the whole thing. When in mid gear, the link kind of sums the motion from the two eccentrics, and the result is that the valve moves by about the amount of the lap, not doing much. A bit towards one or the other direction, It will actually admit steam, but for a shorter proportion of the stroke, giving early cutoff. This is a useful feature, although not all that important on a model engine not working for its living.

Whether the eccentric rods are crossed or uncrossed is another subtlety. If they are uncrossed when the valve is at maximum upwards travel, the total valve travel (when in mid gear) will be more than if they are crossed when the valve is at maximum upwards travel. This can also be used to change the characteristics when early cutoff is being used. Again, probably not a great concern on a model engine.

If you can get hold of the Dockstadter valve gear design programme, it is a great help in figuring out what is happening.


Thread: manual for ajax shaper
09/02/2020 00:28:02

The fastest speed may only come into its own when you are using very short strokes.


Thread: Unimat 3 Drive Pulley
31/01/2020 06:01:00

The O ring used for the fine feed should stretch over the main pulley easy enough, that is how I have always done it. Like the main drive belt, they don't last all that long anyway. I've changed the main drive on mine to toothed belt drive, a great improvement, but I've never improved the fine feed belt.


Thread: Bending Stainless
30/01/2020 22:50:45

I have tried to silver solder stainless, with the right flux it can be done but I would not recommend it. TIG welding is the way to go with stainless, it is easy to do and provided there is no gap, you often don't even need filler. I found when making tanks for my steam launch that flanges are not needed, in fact they are a liability, and a corner will weld very nicely.

If your piece is shaped like I think it is, I would look for piece of tube the right size and the length you want the flange, and cut a piece of flat to match. Then I would Tig weld around the edge.


Thread: Glue du jour
22/01/2020 05:31:23

My understanding is that if Loctite is still runny, it is still good. So if you can still get it out of the bottle it should be OK. (Maybe not if you are working on life critical stuff! )

It can go off in the bottle, especially if you do things like clearing the nozzle with a metal pin. Metal ions will catalyze the reaction.


Thread: New legislation that could affect us all.
09/01/2020 20:36:12

We have got into the habit of always closing the lid down properly ever since we saw a video somewhere of a rat climbing up out of a toilet. They are out there in the sewers and apparently the u bend is no obstacle to a determined rat.


Thread: VFD Question
08/01/2020 10:20:53

Hi Gerard,

The usual VFD can only provide a maximum phase to phase voltage the same as the input AC Voltage. So it will run a delta connected 240 Volt motor at full power. The same motor if Star connected would run off the usual 415 V supply. This supply would provide 240 Volts between phase and neutral. Most motors come star connected for 415, and it is usual to have to restrap them to delta connected to run off a VFD, at least the type of VFD that is designed for 240V input. (There are VFD's that will take three phase input, these are not usually of much interest to amateurs since we usually don't have three phase power.)

There are VFDs that will take a 240V supply and provide the correct output for a 415 V star connected motor, probably by using a voltage doubling rectifier. I have no experience with these, but they have been on the market for a while, so presumably work OK.

Incidently you can run a motor on a lower voltage than the plate rating when necessary. I have a shaper with a Delta connected 460 Volt motor. This makes it impossible to lower the voltage rating, since if I star connected it the required Voltage would go up, to over 600 Volts. But it actually runs fine from a VFD , even the the voltage is effectively half what it should be. This limits the maximum power to about half the nameplate rating too, but since it is a three horsepower motor, half that will shift metal quite fast enough for most purpose.

So normal 3 phase is 240 phase to neutral, 415 phase to phase, but the three phase from a VFD is 240V phase to phase, and there is no neutral. (The neutral from the incoming mains is not a neutral for the output side.)


Thread: The Engineers Emporium - Red Wing hit and miss engine
02/01/2020 23:11:05

I got my Red Wing castings direct from PM Research in Wellsville, a little country town in upstate New York. I'm planning to install the minimag magneto as described on RCDons site. Anyone thinking of doing this should contact the minmag people, they were out of stock when I ordered mine and had been thinking of dropping the kit due to lack of demand.


Thread: Eccentrics
25/12/2019 04:23:21

The ideal lead on the eccentrics will depend on the lap of the associated valve. If you are sufficiently curious, you could measure all the relevant parts and do a diagram or better yet, use the Dockstater software to see what the events are like.


Thread: Castings, creating a datum before milling
23/12/2019 04:26:47

Nick, To drill gunmetal with less risk of grabbing, it would be worthwhile to stone the rake off the cutting edges of the drill. This can be done by hand with a small stone. To be clear, this is not done on the end facets of the drill, it is done on the flute so that where the drill is cutting it has zero or negative rake, rather than the positive rake that the flute gives as it reaches the cutting edge.

A drill treated this way is not as good for cutting steel as it used to be, but if you can manage it, it can be good to have a few treated this way for brass and gunmetal.


Thread: Three phase Variac Internal wiring
15/12/2019 19:55:34

Robert, I don't think that connection with the two in series will work properly, at least not if you put any load on it. The impedence of the one with the load on will be lower than the other, so the voltage will vary with the load. The two cores would need to be magnetically coupled for it to work well.

We once had a number of VHF receivers that were burning out lots of mains transformers, a little 25 VA affair. By testing (with a Variac!) we found that they had too few turns on the primary, and were only good for about 180V input. The magnetising current below that was very small, only 20mA or so, but there is is very pronounced knee in the curve when you reach saturation. We successfully rewound one with about 20% more turns and that gave no further trouble, but of course that was an unauthorised modification and we could not persuade the powers that be to let us fix the rest, so we just had to keep on changing the transformers at frequent intervals.


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