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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: Battery charger problem
03/10/2019 01:15:26

A lithium battery that has gone below 3.7 volts per cell is probably not going to recover. Some of the chargers sold for charging them for model aircraft have a setting that will attempt to recover a cell that has been over discharged, I think by gently charging them at a low constant current until the cell comes up into the normal range. (3.7V is flat, 4.2 V is fully charged.) This sometimes works, but not all that often.

NiCd cells can suffer from whiskering, tiny crystals of nickel that short them out. A pulse of a good high current will sometimes fuse the whisker, after which they will take a charge again, although probably not improved by the experience. So far as I know there is no similar effect with lithium cells and as has been commented, they do not react well to overcharging.


Thread: Red Wing build article
02/10/2019 00:01:16

I'm currently building one, and a Minimag to go with it, the same as in the RCDON build log referred to by MichaelR above. I'm about 9/10 of the way through both builds. I picked up my set of castings at the factory when I was in the USA last year, and started machining them about last Christmas. Not very fast working, but my main project is getting my steam launch finished.

I'd be happy to discuss the Red Wing. The casting are all of excellent quality and I am very pleased with it.


Thread: cutter slippage using ER series collets
29/09/2019 02:25:59

Well, I hadn't heard of ball bearing nuts, so I did a google, and found an interesting video showing the difference.


So now I guess I will have to buy a new nut for my ER32 set!


Thread: Petrol Gen for 7 1/4 locomotive
16/09/2019 02:39:07

If you want to be a bit different you could have a three phase motor, which would be smaller than a single phase of the same power. You would supply it with a VFD (AC motor control) which would be supplied from the Generator. The downside of this sort of arrangement is that everything is high voltage. The nice side is that everything is available off the shelf.


Thread: To Pin or Not To Pin
11/09/2019 06:59:42

I've just received the latest "Funnel" magazine from the Steam boat association and there is some discussion there about pinned and loctited crankshafts for the Leak compound engine. Apparently the published build instructions from Camden press suggest doing it that way, and apparently quite a lot of people have had trouble with cranks made that way. I didn't have the Camden book when I built mine, just the original Model Engineer articles, so I went for a crank locally cast in SG iron, which is also what the Funnel now suggests as a solution. It is interesting that the pinned and loctited ones should give trouble, since in a steam launch there should not generally be a lot of shock loading, unless you are in the habit of running hard aground. I would have thought that a locomotive would be more demanding.

Press fits with no keys work fine on many motorcycle crankshafts, but getting the right degree of interference could be a bit of a challenge in the home workshop


Thread: Just bought an ML7, what should i do first?
11/09/2019 06:17:59

Ok, just been out to check what my one has. The spindle has a 65 tooth bull wheel, that's the one with the little dog to engage and disengage it. The other one on the spindle has 30 teeth. The ones on the back gear shaft seem to be the 21 and 56 combination, assuming I counted correctly which is a bit harder with that one. It is a bit oily under there! My ML7 is early fifties vintage.

Is it the one on the spindle that is broken, or the back one? Mine has one tooth missing on the spindle one. I have the spare but have not yet got around to putting it in, and it actually works fine for the odd time I have needed back gear. NDIY is right that you can do a fix in a number of ways that will be quite satisfactory, they are not all that heavily loaded.

The usual cause of broken teeth on these gears is using the back gear to stop the spindle rotating so you can get a stuck chuck off. This is not what you should do!

The 65 tooth gear means that you cannot use a simple detent on the bullgear to do simple dividing, unless all you ever need is either 13 or 5 divisions.


10/09/2019 06:44:06

You can get a new back gear easy enough from RDG, mine was about NZ$60 if I recall correctly. Change wheels are not a problem until you want to cut threads, so long as you have enough to give you a useful fine feed. The price sounds pretty good considering the prices sometimes asked for Myfords here in NZ, even if you do have to do a bit of work. Don't rush into doing any major work. until you have had a bit of a play with it.

So whereabouts in NZ are you? I'm in Cambridge (NZ) myself.


Thread: Hello
02/09/2019 23:24:29

AS Bill says, there is a little sliding catch on the bull wheel which is held in place with an allan screw. To engage it, you need to loosen the allan screw, slide the catch inwards to engage with the gear teeth on the smaller wheel, then tighten the screw again. You need an Allan key with a very short leg for this, eg cut away most of the smaller leg of the Allan key so it will reach in Ok


Thread: Lathe rigidity
02/09/2019 06:23:40

You could make a split lap to polish the shaft. The lap needs to be made of something softish, brass or aluminium for instance, bored to an easy fit on the shaft, and then split with a saw cut and drilled and tapped for a screw that can be used to close it up slightly. Then you can lap the spindle, using a bit of fine valve grinding paste. You can work the lap by hand since the lathe will be out of action. This is quite a slow way of removing material so gives quite good control. The spindle wants a good clean afterwards of course.


Thread: Trip to New Zealand
27/08/2019 04:11:41

Since other people might also be interested here are a few suggestions:

Most cities have a model railway club with a track.

Auckland has the Museum of Transport and Technology (MOTAT) which has a beam pumping engine and plenty of other stuff to see from trams to aircraft.

Glenbrook Vintage Railway is not far out of Auckland, they have their own dedicated branch line and run steam locos. Would pay to check when they run first.

Whanganui has a working river paddle steamer, the Waimarie. Again it would pay to check when they run.

There is a good steam museum at Tokomaru near Palmerston North, however it has only just been bought by new owners and I am not sure what the situation is with visiting yet.

Near Christchurch there are two places, Ferrymead heritage park and Mcleans island "Steam Scene." I haven't been to either for a long time but I believe they are both worth a look.

At Ashburton there is the Plains railway, they have a beautiful Rogers 2-4-2 of 1877 vintage among other things.

There is a gas works museum in Dunedin.

On Lake Wanaka is the twin screw steamer Earnslaw, well worth a trip both for the scenery and the ship. The Earnslaw runs daily.

I don't know how you plan to travel within NZ, but many tourist find that a self contained campervan is a good way to go. Being a relatively sparsely populated country, public transport is not all that prolific although there are plenty of flights between the main centres. I think sometimes people book two separate campervans, one in each island, since it saves the cost of crossing the strait with one. We drive on the left here, same as the UK. Apart from near the cities, there is very little motorway and most main roads are only one lane each way. You generally don't need to plan to drive very far in any one day.



Thread: Unimat milling tables
25/08/2019 02:00:20

Just checked the dimensions given by Emgee above against my own Unimat 3 milling table. That table would work on my Unimat 3, even though the mounting holes are a slightly different spacing. It would work because the cross slide of the Unimat 3 has a T slot, so the slightly different hole spacing would not matter. The table mounts either across or along using two of the holes.

There does seem to be a difference in the T slots. Mine are 4mm where the ones given by Emgee are 3mm, eg both the length of the stem of the T and the thickness of the top of the T. So my T nuts would not fit into Emgee's T slots. This would only matter if you already have the same T nuts as me.


Thread: Anyone good at fault finding with amplifiers here?
18/08/2019 01:34:19

I haven't attempted to fix a direct coupled amp like this for a while now, but anyway...Because they are direct coupled and have DC feedback as well as AC, faults can manifest themselves in subtle ways. With one I worked on, replacing a cooked output transistor just lead to the immediate demise of the replacement. I ended up checking the transistors one by one with the power off to localise the culprit. That was one that had been built from a kitset by a learner, so I had to check everything. You can sometimes check them OK in circuit, but sometimes it is better to take them out so you can be certain.

Other than that I tend to agree with Simon's reasoning up above. Bear in mind that something like a leaky capacitor could put the circuit out of balance enough to possibly take out one of transistors in the early stages, so there may be more than one fault.

Also unplugging the preamp does not do anything with respect to C204 being possibly faulty. If C201 was leaky unplugging the preamp would help.


Thread: What 3 Words
16/08/2019 22:04:30

It's all fun and games until they turn the servers off...

Thread: Myford ML7 - Size of Mandrel Through Drilling?
11/08/2019 04:35:25

Mine, of about 1953 vintage, measures at .590 inch. That's using a digital caliper, maybe + or _ a thou or so on that. It is of course too small, but anything will always end up too small because the jobs expand to exceed the capacity of the lathe.


Thread: Dam Solution?
08/08/2019 23:40:02

Properly built earth dams are actually very good, and there does not appear to be anything wrong with the basic construction of the dam itself here. Earth dams have the advantage of being able to absorb a bit of movement in the underlying material, whether from natural faults of mining subsidence. However they are vulnerable if water is able to overtop them, and the situation with this dam where the spillway concrete had failed would have much the same effect. Water running over the dam is quite capable of eroding the dam quite quickly and catastrophically.

At Oroville, the failed emergency spillway was not built over the dam itself, so there was natural rock under the vanished concrete. There was some concern about the nature of the rock and its ability to withstand the erosion from the overflowing water for very long, and of course if they had not spilled water fast enough the dam might have overtopped at the earth dam itself, which would be bad news. They did have the advantage of being able to pass as much water as possible through the hydro electric plant there. But mainly they had to keep using the emergency spillway despite the damage it was doing to itself and the surroundings.


07/08/2019 05:32:37

Going right back to Neil's original suggestion, I wonder if he has really thought it through? So OK, we know now that a big enough siphon pipe could shift enough water to help...but how does he plan to get the siphon started? I don't think any of us have a thumb big enough to block the end of the immersed pipe, nor would sucking on the bottom end be much fun. So it seems to me that getting the siphon started is going to need a big pump. So since you are going to need a pump anyway, why bother trying to set up a siphon?


04/08/2019 01:10:42

I can't see why anyone should have the slightest difficulty in understanding how a siphon works. Atmospheric pressure can support a column of water about thirty feet high, which is why a pump can only lift water from that far below itself. Really the pump just removes the air from the pipe, and the atmospheric pressure pushes the water up the pipe.

So OK, we want to do without the pump and start a siphon. For the siphon to work, the low end must be below the level of the water in the reservoir. The highest point must not be too high above the reservoir, eg about 30 feet for water, or 29.6 inches if you are siphoning mercury. You can start the siphon by filling the entire length of the tube with the working fluid. With a hose, this can be done by immersing the whole length, then blocking one end and transferring that end to the low point, then unblocking it.

If you were to measure the absolute pressures along the tube, you would find that at the inlet, the pressure was about 14.7 psi. At the highest point it would be less, a minimum of zero psi. So there is a pressure gradient causing the water to flow towards that point. From the high point to the outlet, it is downhill, so the well known tendency of water to flow downhill accounts for the flow there.

Overall, you can calculate the flow on the basis of the difference in height between the two ends and the resistance of the total length of tube. A siphon will not work if there is a vacuum above the fluid in the top reservoir. It will also not work if the whole system is in free fall. You can still use capillary forces in these situations, but that is a different can of worms.

Do not try to siphon petrol by sucking on the hose. You are likely to get lungful of petrol vapour, which can cause your lungs to go into spasm and can be fatal quite quickly. One guy was found lying dead beside the car with the siphon still running onto the ground. The same would apply to any other volatile liquid.


Thread: 316 Stainless
04/08/2019 00:31:53

Stainless steel is a relatively poor conductor of heat. You need to keep the speed down to control the heat build up. This is a particular problem with drilling, where you need to withdraw the drill frequently. It is a good idea to use coolant, even if all you can do is squirt it on from a plastic bottle.


Thread: Myford 7 Capacity Check
02/08/2019 22:37:25

Bear in mind that you can't usually get right to the maximum size since you have to be able to hold the job somehow. So it is generally better to have something with a bit to spare.

However...if it is only going to be one or two parts of a job that won't fit the machine, sometimes it is better to just find someone cooperative to help with those bits. Usually best to make a start on the bits you can do, then when people ask how you are going to do the big bits , say you are hoping that something will turn up. People are more likely to offer to help if they can see you are making a good start. This worked for me with my compound launch engine, where some of the bits were too big for my ML7. Speaking of which, by the time you have a face plate on there is not much gap left on the Myford anyway.


Thread: IC engine tractor conversion query
01/08/2019 05:43:49

Husqvarna do an electric ride on mower, as well as their robotic ones where you don't even need to be there at all. The ride on one is about NZ$7500 which would translate to about 300 to 4000 GBP I guess.


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