Member postings for John Purdy

Noel

I just had a look through my old Reeves catalogues and they list cast frames as an alternative to bar material in their catalogues 1977 through 1993 ( the last one I have ) for the 3 1/2 " gauge Titfield Thunderbolt (Lion ). Don't show cast frames for Virginia though.

John

Edited By John Purdy on 04/06/2023 17:48:34

I just ran Llofty's link to Marv's HTML version using the parameters for my 6 spoke flywheel. Like Lofty I find it gives an incorrect number and angular position for the outer row of holes. It gives 10 vice the 12 it should be. After looking at the results I can see where the error is. My flywheel has the angle from the spoke centre line to the centre of the first hole as 11 degrees. If the centre line of a spoke is made the 0 degree datum then this gives the first hole at 11 degrees, the second at 11 + 38 (49 degrees ) ( since 11+38+11=60, the angle between spokes ), then the third hole should be 11+38+11+11=71 degrees with each succeeding hole being +38, +22, +38 etc. to give 12 holes.
The output of Marv's HTML program however gives the holes at 11, 49, 87, 125, etc. The first two holes are correct but the remaining are arrived at by just adding the 38 degrees between holes ignoring the every other 22 degree spacing between holes either side of a spoke.

From Martin's results with the Zip version it looks like it give the correct output for the outer holes ie. 7, 7+46=53 +14 (2 x 7 )=67 +46=113 +14=127 etc. for 12 holes. So there appears to be a problem with the HTML version. Are there any other errors in it's calculations I wonder ???

John

Thanks everyone for your replies. Rather than fabricate it, I have a spare brass casting for a depressed centre disk flywheel that I cast for another project that I want to use, but I want to make it a 6 spoke style rather than disk, hence my query.

Jason your link to the one on MEM looks like it will do what I want, but Marv's programme won't run, gives an error msg."written for a 16 bit system, won't run on a 64 bit system".

Paul, yours looks like it will be good if I decide to do curved spokes.

Still don't know if my recollection of an article in one of the mags.is real or if I am dreaming!

Thanks again, this has given me enough to work with.

John

I need to make a 6 spoke flywheel from the solid for a small hot air engine. In the back of my mine I seem to remember an article(s ) in one of the magazines on using a rotary table on the mill to carve out the spokes. I have gone through all the indexes I have but nothing jumps out at me. Rather than re-invent the wheel (pun intended ) does anyone know where the article(s ) might be?

I have MEs from '79 and EIM from day one plus "Live Steam" and "Modeltec" from the '70s and '80s.
Thanks.
John

Scott
To answer your last question the distance between the bearing inner faces and the crank webs should be the same plus a small clearance. On my engine, built in the late '70s, I'd estimate that it is a couple of thou. On the plans that came with my casting set there are some build notes and with reference to this it states "The shaft should turn without binding in the bearings but with practically no end play".

In my book, which is "Building a Steam Engine from Castings" by Edgar Westbury, not Andrew Smith, the crank webs are shown as 5/8" wide the same as the drawings. Check the distance between the mounting hole for the bearings in the base casting and the distance between the mounting holes in the bearings and the inner faces of the bearings. They should be the same as the width of the crank web plus a few thou. On my drawings, and in the book, the distance between the holes in the base casting is 1 1/4" and the distance from the mounting hole in the bearing to the inner face is 5/16" so when mounted on the base casting the gap between the inner bearing faces is 5/8", same as the crank width. Obviously there also has to be a small clearance as stated above so the crank can turn freely.
Check these dimensions on your plans, an in the book, and see how they add up.

I'm not sure this has answered your question but I hope it helps.
John

Edited By John Purdy on 21/04/2023 18:44:54

The advice in my copy of "Machine Tool Operation" by Henry Burghardt, 1936 edition, (first published 1919 ) basically echos the advice it the South Bend book. Here is the relevant pages giving the rational. It starts about half way down the first page.

This book came from my first high school in 1959 when it ceased being a "technical school".

Edited By John Purdy on 20/04/2023 18:06:23

Edited By John Purdy on 20/04/2023 18:18:51

Edited By John Purdy on 20/04/2023 18:19:34

Alan

I've sent you a PM.

John

Richard

If you have access to it Andrew Smith in his description of building the Stuart "Cygnet" (5A ) details a method of machining of the double one piece eccentric in the Apr '82 issue of Engineering in Miniature, page 377-378. I've sent you a PM.

John

Edited By John Purdy on 07/04/2023 17:56:31

I'm not sure how they happened, but I just noticed there are a couple of errors in the above schematics. The "6" on the line between the 4.7K resistor and the base of the transistor shouldn't be there, and the 22k resistor should be 33K. The corrected schematic is here. These values give an square wave output on pin 3 of the 555 timer chip of 5 Hz at a duty cycle of 11%.

John

Ian

Good to hear your engine is running well. For general info here are the circuits I have used. The top one is the engine simulator for testing on the bench. A 555 timer configured in astable mode to simulate the points on the running engine switching the transistor/coil to fire the plug.

The lower one is the transistor/coil assembly as installed on the engine. The transistor is not critical, any low power NPN transistor will do. It's only switching 6 volts at less than a milliamp at a very low frequency. I'm not sure the 1K resistor connected to the coil is necessary but was connected to the coil when I tested it so just left it. With the points open the transistor base is high turning it on, holding the coil IB terminal low. When the points close the transistor is turned off setting the IB terminal high energizing the coil. When the points open the plug fires.

John

I have not yet had a chance to run the Red Wing but I have run the Wyvern with no problems. I only run the coil on 6 volts (a 6V 4 Ahr gel cell ). The Wyvern points are cam operated and are open ( coil energized ) for 160 deg. of crank rotation, which gives a duty cycle of about 22%. With the way the Red Wing points are configured however they are open (coil energized ) most of the time and are only closed for 45 deg. of crank rotation, which gives a duty cycle of about 87.5%. I had previously experimented with the coil on the bench in both configurations and had not noticed any over heating. I just tried it again on the bench, in the configuration with the points open (coil energized ) and after 3 minutes the coil was becoming too hot to touch, that was on 6 volts and the coil was drawing 3.6A. I can see now that the way the Red Wing points are configured keeps the coil energized for too long causing it to overheat. It would be even more so when run on 12 volts. Two possible ways around this would be to one: modify the timing gear, replacing the insulating ring and the copper contact with a brass ring with a short insulating section to give a duty cycle in the neighborhood of 10%. Or two, to do something like Ian did to invert the output of the points.
I decided to try the latter and used a single NPN transistor to invert the output of the points. This worked well so I then bread boarded a 555 timer chip to give a 5Hz pulse with a 10% duty cycle to simulate the points with the engine running at 600 RPM (probably fast for a hit and miss engine ). Using these pulses to switch the transistor and the coil resulted in the coil sparking at a freq of 5 Hz and drawing current for only 10% of the time. After running for 30 minutes the coil was just warm to the touch. In the vehicle these coil are mounted directly on the head and according to my son are too hot to touch when the car has been run for awhile so are designed to run hot.
Here's a shot of the scope screen showing the output of the pulse generator (top trace ) and the output of the transistor connected to the IB input of the coil ( bottom trace ).

Thanks everybody. Although it's not quite as I remember it I think the one in MEW #107 is the one. Don't know how I missed it as I did use the key word "storage" in my searches. Getting old I guess!  I'm getting tired of digging them out of the back of the drawer in the lathe cabinet and then having to brush the swarf out of all the teeth!  

Thanks again to everyone.
John

Edited By John Purdy on 13/03/2023 23:10:57

I recall an article, in one of the model engineering mags, on making a holder for storing change wheels. It was wood and held the gears in order, vertically in slots. I have searched all the indexes I have using all the key words I can think of to no avail. Does any one recall the article and where it was? I have a feeling it would have been in the last 10 -15 years.
John

Brian

I have sent you a PM.

John

I do as Andrew, and use a dial indicator in the collet/chuck on the fixed jaw. I have made a couple of extra posts for the indicator so it always fits whatever I have in the spindle ( well almost always! ). I snug down one bolt fairly tight and leave the other slightly loose, then tap the end of the vice one way or the other while running the table back and forth till I get the min reading end to end, then tighten down both bolts and recheck.  It only takes a minute, two at the most, to get the 6" jaw within a thou end to end.

John

Edited By John Purdy on 12/03/2023 17:31:03

Edited By John Purdy on 12/03/2023 17:32:14

The $57 quoted by my son is for an after market coil and that may be his dealer price. I don't know what one from a Nissan dealer would be but I imagine more. So an auto wrecker might be better.

John

Ian and Hopper
I just talked to my son and he thinks the coil came from a 2004 Nissan Pathfinder. He thinks they are common to a number of models and will check and let me know. I also use one in my Wyvern engine and it runs very well on 6 volts. As I said previously they were expensive, $280 here in Canada, but he says the price has dropped considerably and are now about $57 but should be available from a wreckers for less. Here is how I hook them up (excuse the quality, it's just a shot from my notebook ). As can be seen there are two ways of hooking it up. One where the spark occurs on points closing and one where it occurs on points opening. I used the circuit where the spark occurs on point closing and arranged the timing appropriately. I had to do it this way with the Red Wing as the points are not isolated but one side of the points is connected to the engine frame, hence spark plug ground. I had measured current draw on 6 volts at about 4 amps.

Just got an e-mail from my son, here is the data on the coil. Any of these models with a 3.5L engine uses this coil.

Here are some pictures of the coil. I cut the tower for the plug connection back and solder the ignition wire to the exposed HV connection. The three connection pins accept standard 1/8" quick disconnect push on connectors.

You can see the pins labled IB G + in this last picture as per the schematics above.

If using one and experimenting with it on the bench be very careful as they can produce a lethal voltage especially if run on 12 volts.

John

Edited By John Purdy on 02/03/2023 03:27:27

Bob

I found a similar tool in an old (1990 ) Lee Valley catalogue. They call it a "blind nailer" or an "invisible nailer".

I just checked the lee Valley site and they don't appear to list it any more.

John

Edited By John Purdy on 18/02/2023 17:49:49

I've just moved the coils down so the gap between the armature on the end of the pendulum rod and the coils is 3/8" instead of the 1/16" previously but kept the same lateral distance from BDC as before. The impulses are now at 32 second intervals vice the 3 1/2 minutes previously and the "twang" is gone. Which seems to indicate that the magnetic flux was much stronger than necessary at the closer distance.

John

Steve

I've also done my radial dials in a similar manner to both Bernard and Hopper. A lathe tool ground to a 40 deg included angle with a very small flat on the tip, on its side and moved across the dial with the cross or top slide depending if the face is flat or angled. Indexing done with change wheels and an indent. The smallest I've done is 1/2" dia/ 25 divisions, (no numbers as I had none small enough ) which was for a ball turning tool. Here's my indexing set up for a 50 division dial.

I wrap a string around the chuck connected to a weight  via a small pulley  fastened under the shelf above and behind the lathe to take up the backlash in the gears.

Edited By John Purdy on 01/02/2023 18:31:57