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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: Marking out fluid
26/07/2010 08:01:51
While the DRO does a nice job for coordinate drilling, I quite often do a cheap and nasty but quite effective trick. Draw what you want up in a suitable CAD program, print it out, then stick it onto the job.  (Often with double sided tape.) Centre pop through where the holes are supposed to go and Bob is your uncle. Accuracy will of course depend on your printer. I have a little laser printer which does about 300 dots per inch, so the accuracy limit is about 3 thou or so. Not as good as the coordinate drilling, but much better than I would expect to acheive with conventional marking out, and plenty good enough for a lot of work. It is only possible of course where the job is flat
 
John
Thread: New lathe advice
26/07/2010 07:50:18
I don't have advice on the machine itself, those are all good brands, but you are getting into the size range where they tend to come with three phase motors. My advice on that side of things would be to get it with the three phase motor and get a suitable speed controller to run it from single phase if that is what you have available. This is better than trying to shoehorn in a single phase motor that may not fit well in the available space. You will probably get a suitable controller cheaper than you would get a single phase motor too, and the speed control itself is a great thing to have. Also bear in mind that there is a company advertising in ME that has a controller that will work on single phase 230 Volts in and provide 415 Volt three phase out for the motor, so even if the motor cannot be reconnected from star to delta you can still get a controller that will do the job.
Thread: The HobbyMat BFE 65 again
12/07/2010 10:57:14
Cpacitors should measure open circuit, although witb an analog meter you can often see a kick of the needle when first connected to the meter, as the capacitor charges up.
 
Windings should show continuity end to end. You are not very likely to be able to detect any shorted turns with a meter. The normal resistance will tend to be fairly low, a few ohms sometimes, and any change due to shorted turns is minimal. However a sudden stop while running sounds more like either a winding has gone open, or the capacitor has gone short. I suppose a winding could have gone down to ground but you would expect a fuse to go then.
 
Usually shorted turns in the motor would be accompanied by heat, smoke, and smell. The motor would often still run, albeit poorly.
 
Some motors kindly provide a one time thermal overload buried in the winding, which stops it setting fire to things but of course is not designed to be replaced.
 
regards
John
Thread: MEW Archive
12/07/2010 10:43:37
"but i'm using vista"
 
Well, there is your problem right there....
Thread: Douglas engine......again
12/07/2010 10:37:13
Most of the older floats that I have seen were made from very thin brass pressed and soldered. Think in terms of shim stock, and not too much solder.  Petrol is less dense than water so if it won't float in water it is certainly no go in petrol.
 
Modern ones are often plastic, and not always very suitable plastic either. One of the Universities here looked into methanol fuels back in the seventies, and checked out the effect on carburators. Turned out some of the plastic bits would not stand up long term to petrol, let alone methanol. My memory of Amal carbs is from the seventies, when, shall we say, they were not what they had once been. The concentric had a float that was too small, so it would fail to close the needle valve properly, It is somewhat disconcerting to look down and see a little jet of petrol flowing out the overflow and onto ones boot. The cure was a viton tip needle valve, but even that was not 100% reliable.
 
There was someone, I think in ME a few years back, who said he was idly wondering about floats, and though of polystyrene foam, so dropped a chunk into some petrol. He said he had never seen anything disappear so fast....
Thread: Need for recomandations on cut off or parting tool
12/07/2010 10:16:13
My two cents worth would be that the parting tool should be as narrow as is reasonable for the depth of cut. This keeps the forces low, which with our amateur machines is quite important. It follows that you will be limited in the diameter you can part off. On my Unimat three I use a little tool ground from square HSS, it will do up to about 1/2 inch diameter. On my Myford I get good results with a tool about 3/32 wide, and it seems to not make much difference if I use the rear tool post or the quickchange one on the front.
 
The other thing, as always, is to have it really sharp. 
Thread: Lathe Drive Motors, 1ph or 3ph?
08/07/2010 01:59:45
The power meter will measure the actual power used, to a pretty good sort of accuracy. The three phase motor is likely to be a bit more efficient. But there won't be enough in it for you to notice any difference. Of course there is a bit more capital outlay for three phase, the motor might be a little cheaper but you will have to buy the controller.
 
There is a maximum recommended speed for the Myford Spindles, I can't recall the exact figures although something like 2000 rpm for the Super 7 sounds familiar. The ML 7 is not rated to go as fast.
 
About thirty years ago I was involved with motor speed controllers at University, and did a project involving the design of an invertor. They had looked into the characteristics of the motors then on the market, and found that they were as supplied adequately balanced for running at up to 10,000 rpm. (eg three times normal speed for a two pole motor.) However, eddy current losses made it undesirable to go quite that fast. They did find that running at twice the normal frequency was no problem. Of course for best results you would want to set up the voltage/ frequency curve to double the voltage at double the frequency, and that is not normally feasible for us amateurs.  It does then give you twice the normal rated power out of the motor, without significant increase in losses. That was with good quality motors, I don't know how the Chinese stuff would fare.
 
If you do have the need for something to go fast, and here I am thinking more of tiny milling cutters rather than lathes, most controllers will let you program the maximum frequency up much higher. Since you can't also increase the voltage, the torque will fall off, but this is not likely to matter if you are trying to use a very small milling cutter.  There will be a limit to the speed for your mill spindle bearings too, but this is likely to be higher than for the plain bearings in a Myford lathe.
 
Most controllers won't give instant reverse, they have an acceleration/deceleration curve. (also programmable.) If you reverse too fast with a screw on chuck it will give you a nice surprise, so don't do this with a three phase motor on real three phase supply with a reversing switch. Also bear in mind that the turning loads will try to unscrew the chuck, so if you are using an upside down tool be careful.
 
regards
John
Thread: Shaper Tools
06/07/2010 07:37:48
One trick that can help with a machine where the table slide is a bit "tired". Set things up for the height you want, set the front leg down and lock it, then wind the handle as if to lower the table. Of course the leg prevent you, but it will bring the back of hte table down as far as possible and make sure that the leg is in good contact. While still pushing down, lock the table height screws. (There will normally be some way of clamping the table height .)
 
Incidently if a shaper does not have a support leg it would be a really good idea to give it one, where possible. Some of the hand shapers of course cannot have one fitted.
 
James, I would love that PDF...I have a paper one but the PDF would be nice to have too. You can get me at: mjolnir at paradise dot net dot nz.
 
regards
 
John
Thread: Lathe Drive Motors, 1ph or 3ph?
06/07/2010 07:30:36
Paul, take a look at the terminals as many motors have provision for changing them from star to delta built in. The give away is if they have six terminals. When it is strapped in star, three of these will be linked together, and you should find that there are actually three links provided, even though there are only two gaps to cross. That lets you rearrange the connections into delta, eg the three straps join the ends of a paif of coils each. If you are lucky there may even be a little diagram of how to do it. I could provide a picture of how it is done on the one I just did, but others may differ.
 
If there are only three terminals, then the star point is buried in the windings. A motor rewinder could do it, and you could yourself if you were very careful. But it is not so easy, you have to find the join, separate the three windings, and then provide each one with a safe terminal.
 
regards 
John
05/07/2010 02:07:12
I see this thread has been idle for a while, but I would like to add a couple of thoughts.
 
Firstly the comment about "never have to change a belt again" with a speed controller is not necessarily true. If you need to do heavy turning at low speeds then it still pays to change the belt or to use back gear.  If you are ripping something down to size and want to maximise metal removal rate, then you want the motor running at maximum power, which will of course be with the speed set to the highest. Then adjust the belt and back gear to give the correct cutting speed. While a Myford is only a light lathe, it can remove metal at a significant rate when set up correctly, and you can save quite a bit of time. I'm not going to quote actual depths of feed etc since that is going to vary a lot with the circumstances, and obviously some sensitivity needs to be used.
 
The main advantage of the 3 phase motor  would be with the speed control. I find it good for screwcutting, slow when it matters then a quick reverse back to the start.
 
Secondly, I've just done the conversion to poly V belts as described by Neil Hemingway back in 1983 on my ML7. The description was for a Super 7, but the idea can be adapted for the ML7 without too much trouble. I have found this very worthwhile. The poly-V belt does not slip as readily as a V belt, and runs much quieter. The pulleys also don't get hot, as they did with the ordinary V belt.
 
Incidently I have a Unimat 3 as well, which I converted to toothed belt drive about 25 years back.  The use of the toothed belts does not seem to lead to any patterning on the job. Any patterns I have ever noticed are due to the tool getting dull and chattering beginning. These small lathes will teach you to notice the difference between a sharp and a dull tool!
 
regards
John
 
 
Thread: Shaper Tools
04/07/2010 22:55:35
Hi Again,
 
OK, for Cornish Jack, the book I referred to is :

"The Shaping Machine" by Ian Bradley, pulblished 1973 by Model and Allied Publications
ISBN 0852423233
 
It may have been reprinted by one of their successors. Anyway, that book is a good run down  on shapers in general, and  has information on most of the more common British shapers. There is not a great deal on information on the Perfecto, but there is some. Somebody somewhere must have a copy of a Perfecto manual, assuming such a thing ever existed. Sometimes there was none, it was assumed that if you bought such a machine you knew what to do with it.
 
Bradley also shows the bicycle crank tool holder referred to above. 
 
For hand shapers sharp tooling is of great importance. The acid test is to see if you can take a scraping off your thumbnail with the edge. Not using the shaper,  just take the sharpened tool in one hand and see if you can take a scraping off the surface of a thumbnail. If you cannot, the tool is blunt, no matter how good it looks.
 
regards
John
04/07/2010 10:42:18
Hi Martyn,
 
The swan necked tool dates back to the days when such tools were also common on lathes. They should not generally be necessary. However, there is a case for keeping the cutting edge as far back as possible relative to the clapper box. One type of tool holder sold for the purpose has a round hole at the end. A roundheaded bolt with a slot across it goes through the hole, with a nut on the front, eg where you stand with the machine hurling hot chips at you So the tool is behind the main bar of the toolholder. Any flex thus tends to take the tool out of the job. If the tool is in front of the holder, the opposite would apply.
 
I have actually managed to buy a couple of such holders, one that is too big for any of my machines and one that I use reasonably often. They can be made, and a good starting point for a smaller shaper (6 to 10 inches) is to take a steel crank from a bicycle. Make a bolt with a slot in it for the tool and you are away. These holders do need a good long piece of high speed steel, you can't use up those little left over bits.
 
Standard lathe tool holders tend to have too much rake and also put the tool too far forward. Still, the ones that came with my 10 inch Alba have worked OK. You tend not to want very much rake on a shaper.
 
As you have decided, rigidity is all important. Apart from the clapper box area, check the ram itself for wear.
 
I beleive there there is some information on the Perfecto in the old book. (MAP? Argus ?Nexus? I can't remember which it was) If my copy comes to light I will try to post more details on it.
 
regards
John
 
 
Thread: Vice for Boxford 8" shaper
04/07/2010 10:20:23
Hi Guys,
 
Shapers are often missing their vices. This is due to the fact that a shaper vice  is a good substantial device, ideal for use on the milling machine that quite likely replaced the shaper. A good milling vice will do instead, although shaper vices tend to be a lower profile for a given size than a milling vice. This only matters when you need to do bigger jobs, in which case you should think about attaching it directly to the table.
 
TerryD, if you are getting substantial forces when you are shaping you are doing it wrong. This is a single point tool remember, the forces should be of about the same order of magnitude as you get on a lathe. The original vice for my 6" Ammco shaper was held down by a single bolt in the middle, through the table. (I don't have one, but have the castings to make two of them and a set of drawings.) The original vice for my ten inch Alba is held down by two bolts, and has a swivel which is also only secured by two bolts. It is only when we get to my 18 inch Alba that we find a vice with four bolts on both the swivel and the table mounting, but then that is a substantial bit of kit. It takes a bit of thought to get it on and off the table.
 
Where the vice needs to be substantial is that at times you will find you must cut parallel with the line of the vice jaws. This tends to move the job in the jaws, and of course the tool may pick up the end of the job, leading to mayhem. So for this situation, the job wants to be clamped really firmly, preferably with a bit of paper each side to improve the grip. This is one reason why thinking about attaching the job directly to the table is a smart thing to do. Another good plan is to see if you can provide a positive stop at the downstream end of the job. Generally if the job starts to move you will see it happen, and the machine will probably manage about three strokes before you get to the power switch. If you are lucky you will only break the tool and spoil the workpiece. Still, similar things can happen on milling machines and in lathes too.
 
The tilting table is a nice feature, but the downside is that having tilted it you now have to get it back in true again for the next job. So it is a bit like offsetting the tailstock on your lathe, or tilting the head on your mill drill. The one on my ten inch Alba will tilt, but I don't recall ever having used the feature in over ten years. But now if I could get hold of a slotter attachment for one of my machines....
 
regards
John
Thread: Stirling engines
04/07/2010 09:50:38
Well, here in NZ the authorities would not be very interested unless you were doing copies for hire or sale, or were doing it on such a scale as to impinge on someones business. But it would be a bit "in your face" to offer to make copies on the Model Engineers own web site wouldn't it.
 
One aspect of this in the past has also been that due to the various changes over the years, not to mention the bombing of the office during the Blitz, the Model Engineer itself has not always had a complete set of back issues available.
 
regards
John
 
 
Thread: Stirling cycle model - help
04/07/2010 07:09:11
Hi Robert,
 
See my reply underthe other thread.
 
regards
John
Thread: The story behind logging in...
04/07/2010 07:07:36
Hi Guys,

Well, I have been using forums of various sorts since about the early 1990's, including some of the old dial up Bulletin boards. So this is not as bad as some I have seen. However, could somebody please do something about the timeout. It seems to take no time at all for the system to decide you should be logged out, which is annoying when you have been working on a learned and erudite post for the benefit of the other readers. (Well, I would like to think so anyway.) Ok, I am working around this by using notepad, which avoids any problems from Word, but it should not really be necessary.

regards
John
Thread: Stirling engines
04/07/2010 06:51:14
Hi Robert,

Slight correction, that would be 2-15 December 1988, not 98. It often pays to quote volume and issue number as well as the date if you can. (vol 161 no 3838)

Anyway, the engine is a demonstration Stirling engine by Peter Meede in Germany. There is an article starting on page 699 of that issue, and concluding in part 2 in issue 3840 vol 162 dated 6-19 January 1989.
The second issue has the drawings, in metric. Looks quite buildable from the information given, although this is not a detailed construction series. The burner is a glass Pelikan ink bottle, which might be a bit hard to source these days. But I suspect any nice looking glass bottle of about the right size could be used.

I guess it is obvious that I have copies of the magazines, and could arrange copies, provided that does not offend any Editors who may be watching. However, I live in the Antipodes, so possibly somebody a bit closer may be able to come up with a copy for you. Many clubs have extensive collections of ME, some going back to issue 1. My own collection only goes back to the forties. (no I am not that old myself)

For those who are wondering, the engine looks very nice, a somewhat futuristic style in brass. I can see why it would attract as a project. I'm no expert on hot air engines, having built just one (Rider-Ericsson) but this certainly looks like reasonable project with no really tricky stuff involved.

regards
John
Thread: ED Racer 'times two'
04/07/2010 06:19:22
Hi Ramon,

No, the second AM15 crankcase was actually broken in that area. My thoughts on cleaning it up as a boy was that I would fit it with an RC style carburettor, and some of my first attempts on my Dads ML7 were making such things. Lack of radio control gear, or any money to buy it with, tended to render such thoughts moot. But that would be the sort of thing to do. Any slight restriction of the intake area would not be a big deal at this point in time.

The Ohlsson and Rice and the ED comp special are both older than me, or close to it. The Ohlsson and Rice would be about 1950 vintage, they had just started making the glowplug version, by leaving off the contract breaker. I think the Comp special is 1949, if I am interpreting the serial number correctly. I picked up the Ohlsson and Rice as an old second hand engine, and built a 1939 design of model aircraft for it...a Powerhouse, which I beleive is still a well known model. Seven feet wingspan. I still have the model, although it currently lacks covering. So that would have been built around 1964 or 65. Still have the lathe too. The last of the scars on my wrist from when the AM15 nearly got away seem to have faded over the last few years.

Now back in those days, as a teenage boy, I was able to go to the chemists and buy ether and even amyl nitrate no problems. My Dad went with me the first time so they knew what it was for, but after that I could just walk in and buy ether by the pint. I bet it would be harder to get that sort of stuff now.

So how did you manage to end up with the three bosses for the cylinder mounting screws the opposite way around on the two engines? I guess it does not matter, so long as you put the liner in to match. Going by my engine, the correct one has one boss to the rear and two either side to the front. Mine has the cylinder fins anodised red.

regards
John
Thread: Measuring tool accuracy
04/07/2010 05:50:43
Hi Guys,

I suppose we all know that the digital calipers, or any of that style, eg dial or Vernier, have inherent limitations due to the force not necessarily being in line with the measurement. Eg if you just slide the slide along using the grippy bit on the plastic, or the little wheels if fitted, then the force is being applied about an inch and a half away from the point being measured. This can cause an error. For instance, I have an M30 nut lying around on the desk here which measures 1.799" across one pair of flats if I apply the force out on the end of the anvils, so that it is directly in line with the measurement point. If I just push the slide along while holding the instrument in my hand the measurement can go as low as 1.795" with what seems like reasonable pressure. If I push harder it will go a thou or two lower. This sort of error is inherent to the design, and can be avoided for outside measurements by applying the force directly. It is not so easy to do that for inside measurements, which is one reason they tend to be a bit harder to get consistent.

Watch out when working with cast iron, as the measurement face, which is the plastic area with the numbers printed on it, can get contaminated with graphite. Since the measurement is done by capacitance, this can cause everything to go a bit haywire. I have found that wiping them with meths is a good cure, it doesn't seem to attack the plastic.

There are several sorts of errors with digital instruments in general:

Linearity error in the actual scale

Absolute error

temperature dependent error

Inherent digital uncertainty of plus or minus 1 count.

The first two are pretty much taken care of by the manufacturing process, and will depend on the accuracy with which the pattern is printed on the little printed circuit board behind the plastic face. Since this sort of stuff is done on a vast scale with high quality machines, there is little excuse for much error, and it seems that even the cheap ones are actually quite good. Temperature dependent errors will depend on the material that the scale is made from, and I suspect here that the stainless steel ones are probably more stable than the plastic ones.

The digital uncertainty you just have to live with, or else buy a more expensive instrument with more digits. But really these devices have enough digits for the purpose, due to the inherent limitations of the caliper design. Plus their versatility makes them so useful. A micrometer will do one thing extremely well, over a limited range. A digital caliper will do inside an outside measurements, steps, and hole depth, will work in metric or imperial, and will zero to a set point so you can work down to size. For this sort of veratility I think we can forgive a slight loss in accuracy, especially since they are generally good enough for much of what we do.

Incidently I have a very handy little four inch or 100mm digital caliper which is really useful in confined spaces, like under the milling head or checking a job in the lathe. Highly recommended if you see them about. The local importer was sent a batch by accident, put them out on special, and was surprised at how the word got around. they sold out in no time at all.

regards
John
Thread: ED Racer 'times two'
03/07/2010 06:26:41
Hi Ramon,
 
This is all very familiar since I have had an ED Racer since about 1964. I think yours look much nicer than the real thing, much better finish.  My first engine was an AM15, which I also still have. I also have most of another one, which I need to make a crankshaft, conrod and piston for. It does still have the contrapiston. It will also need a bit of cleverness on the crankcase, since the intake stub has been busted down to the level of the spraybar holes. Don't blame me, I didn't do it! I think it is actually what was left after various people scavenged the parts they needed.
 
Other interesting old engines I have here are:
ED Comp Special (2cc) 
Ohlsson and Rice .29 glow engine (about 1950 vintage,  based on their previous spark engine)
OS Max 3 .15
 
and I also just recently found out that the casting that has been sitting around for years is the crankcase for a Sparey 5cc Diesel.
 
 So one day I an have to get into this sort of stuff and fix up the AM 15 and build the Sparey. I'd like to know more about the process of lapping pistons to a good fit.
 
regards
John
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