Member postings for Norman Lorton

If you want something that looks authentic measuring about 3" you could try making this:

http://www.modelsteamenginesuk.com/acatalog/Electrical_Generation.html

I have some limited knowledge of dynamos from older motorcycles. The Lucas and Miller dynamos are 3" diameter by 6" long and much smaller than car versions and so might be better for your model. You could hide them in a larger casing that replicated the traditional showmans dynamo frame.

They will produce 12v and 60 watts or more at 3,000 RPM. There are earlier (1930 - 1950) types with three wires and inbuilt regulators that I suspect are direction sensitive - these are not so useful. The post 1950 type usually have two connections: 1) an output (output can be configured positive or negative by quickly polarising the residual magnetism and reversing the field wiring), and 2) a field energising connection. Both grounds (earths) for these connections are common and connected to the main body. The field energising input must be fed the correct variable voltage to regulate the output. Nowadays we use small electronic regulators.

Many electrical generating devices (e.g. a magneto) are optimised for direction of rotation but it is the view that this type of electromechanically regulated dynamo will work in either direction, however the field windings will have to be switched internally.

The dynamos and regulators are commonly available from several supplies to the classic motorcycle market. They would be able to tell you which direction of rotation it is set for. You also find them on eBay.

Mmm, tumbler. Must have had idle thoughts.

The issues of the best/easiest way to cut metric/BA have been discussed many times in this forum, but when I was asking the same questions as Ron a short while ago many people kindly answered, and so I am happy to repeat the perceived understanding on the topic in my own words. Incidentally, it is difficult to find threads of interest using the search window at the top of this page. I find it much better to go to Google and use a few choice words. The view that I feel most experienced users will express is as follows:-

1. If you do not have a gearbox then you have the fun of changing endless gears to obtain mostly any thread pitch you like and to reasonable precisions. You can use tiny 127 tooth gears, or bigger 63 tooth ones, or the Myford ingredient of mixing in 21 tooth gears. But you also have the fun of changing all these gears again every time you want a fine feed!

2. The delight of a gearbox is quickly selecting any imperial thread and being able to swap to a whole range of fine feeds in ten seconds. But without something else you cannot select metric/BA pitches.

3. To obtain metric/BA pitches, on a gearbox fitted lathe, Myford advised using the Metric Quadrant (that has slots) and a whole new range of loose gears. Once you have spent a lot of money obtaining these (if you can find a quadrant) you are back to all the fun of adding and removing gears every time, and you have lost the fine feed facility when the metric gear set is fitted. Some users estimate a 20-30 minute swap time! The benefit, however, is very precise metric pitches.

4.The easy way, on a gearbox fitted Myford, to get a good approximation to the metric/BA pitches is to swap the idler gear (normally 24T) for either a 20, 21, 25, 30, 33 or 34 gear. The last two have to be purchased specially and the the others are readily available. You then select the gearbox setting that gives the nearest approximation to your desired pitch, by looking it up in a table that someone has worked out. Typical pitch errors are 0.05 to 0.5% with the worst being 0.86%, but perfectly useable if up to ten threads are being engaged. The big benefit is that you can still instantly swap to fine feed, and the idler gear swap takes around 30 seconds.

Norm.

Rufus, Ron mentions that he has a gearbox so he does not want to go changing the wheels driving that box.

Ron, the JohnF link above points to a thread that I started when I had the same question. All you need to do is have few different idler gears, for example sizes 20,21, 24, 25, 30, 33 and 34. The idler gear is fixed by screw to the one that meshes with the Tufnol gears for forward/reverse feed.

The 33 and 34 gears are unusual sizes and you can (usually) buy them from John Corden's link above. The other sizes are available from several Myford parts suppliers. John Stevenson should also suppy a chart detailing which idler gear works with what gearbox setting to obtain a close approximation to the BA or metric pitch desired. If you send a 'Message member' directly to me, quoting your email address, I will happily supply a copy of a spreadsheet (chart) that I worked out for the various settings and errors.

Norm.

There is a nice article in another magazine this month by Ian Jefferson describing the cutting and fitting of steel tyres. He describes the standard practice of heat shrinking for the final fitting from 300-400 degC and the use of 6 to 8 riveted pins for security.

What is not mentioned, and what occurs to me, is whether there is any experience with the use of appropriate loctite. You would have to machine a location shoulder and suitable gap for the loctite, and would finish off with the same rivet security.

I have seen loctite hold onto main bearings in a racing motorcycle engine with a loose journal so I cannot see that the expected pressures, vibration and temperature will be a problem; there is a massive surface area as well.

Norm.

Edited By Norman Lorton on 15/04/2013 12:22:54

Apologies to Harold for making a blind assumption on how he worked. Clearly the exact Myford gears and quadrant are needed for precise work and gears. I am intrigued by the open thinking behind imperial pitch threads on metric dimensioned items. It is that quality that creates new ideas but I guess it should cause puzzlement for a future engineer who measures a piece of his machinery and studies all the thread charts looking for the right one!

Thanks also to John (who I guess is credited with the tumbler gear change idea?) for leading me to the simple solution I sought. I have myself drawn up a spreadsheet calculating all the metric pitches to be obtained from the Myford gearbox using tumblers from 20 to 35. One error I avoided was not assuming that the Fine Feed numbers printed on the case are accurate: e.g the first and last, 0.0139 and 0.0020, are actually 0.013889 and 0.001984 respectively (shown to 6 DP).

Picking all the best fits from the table, but trying to restrict the number of tumbler alternatives, I drew up a table of tumbler gears and box settings. What interested me was the errors resulting. I reproduce the table and leave others to debate which errors are acceptable and for which tasks.

Pitch Gear Actual Error %

BA

0 1.00 34 0.9995 -0.05%

1 0.90 34 0.8996 -0.04%

2 0.81 20 0.8141 0.51%

3 0.73 25 0.7350 0.68%

4 0.66 30 0.6615 0.23%

5 0.59 21 0.5849 -0.86%

6 0.53 20 0.5292 -0.15%

7 0.48 20 0.4811 0.23%

8 0.43 33 0.4312 0.28%

9 0.39 30 0.3920 0.51%

10 0.35 24 0.3528 0.80%

11 0.31 21 0.3087 -0.42%

12 0.28 24 0.2822 0.79%

Metric Fine

2 0.40 34 0.3998 -0.05%

2.2, 2.5 0.45 24 0.4536 0.80%

3 0.50 34 0.4998 -0.04%

3.5 0.60 25 0.6013 0.22%

4 0.70 25 0.6963 -0.53%

4.5 0.75 34 0.7497 -0.04%

5 0.80 24 0.7938 -0.77%

6 1.00 34 0.9995 -0.05%

8 1.25 33 1.2473 -0.22%

10 1.50 34 1.4993 -0.05%

12 1.75 33 1.7463 -0.21%

16 2.00 34 1.9991 -0.04%

18, 20 2.50 33 2.4946 -0.22%

24, 27 3.00 34 2.9986 -0.05%

I came to the same view as John in that if you have gears 20,21,24,25 and 30 then only 33 and 34 need to be purchased. I have not shown the box settings but I will be most happy to share the spreadsheet for private use with anyone who emails me directly. I have now ordered the gears from metoolsonline.com who are the only source I can find for the 33 gear and thus provide a very valuable service, and at a reasonable price. I have not yet seen their choice of gear set from their table and will be interested to see if it offers anything I have missed with reduced error.

Norm.

Edited By Norman Lorton on 04/12/2012 11:04:14

As I am the culprit who raised the question, never mind this thread drifting away, I have found the discussion very interesting and helpful!

Two readers have kindly sent me their calculations, one by spreadsheets and the other a calculated table with %errors. It is apparent that all the metric and BA threads can be obtained with just a swap to a set of tumblers betwen 20-34 although with just 34 and 26 a good number are solved. It is just a case of the acceptable error.

Surely this important story has been covered in ME or MEW before; do any contributors with good memories know? I do wonder because Harold Hall decribes on his website his construction of a Metric Quadrant implying that this was his method for cutting metric threads. However, there appear to be no Mertic Quadrants for sale, and 'new Myford' do not list them, suggesting that they are not in demand.

Norm

Thank you Gentlemen for the helpful and quick replies,

I now have a bit of reading to catch up on:

1. lathes.co.uk/latheparts/page14 'NthreadsP and BoxfthreadP screwcutting programs'

2. MEW 177 D A G Brown 'Metric Screwcutting'

3. MEW 39 D Dew 'Metric Pitches on an English lathe'

If anyone has tried making a spreadsheet to tabulate the outcomes from the Myford gearbox, from possible gear inputs, I would love to hear. That would have helped me find what John Stevenson kindly pointed out, and feel less of a twit for missing the obvious!

Ok, I have answered part of my question. I find that the ME home Page Google search works vastly better than the 'Keyword in a Thread in All Topics' search on this page. Perhaps I am doing it wrongly? If you try searching "myford Gearbox" or "myford metric" from both searches you may see what I mean.

From the Google ME search I found the intriguing 'Lady Engineer' thread from 04/09/2011 that had a very helpful reply from John Stevenson and that has pointed me to the metoolsonline site and the 33/34 gear pair with a table. Super. But, I see that the metric approximations claimed include pitches 0.45, 0.75. and 0.90 mm which do not seem very useful to me. I need 0.5, 0.7 and 0.8 mm pitches to cover 3,4 and 5 mm threads respectively and I presume so does everyone else?

Totally agree with John's view that the "quick change gearbox" is nothing of the sort if you need to swap to the metric quadrant.

Last thought - does anyone know whether the tumbler only gear swap enables the production of any BA threads? If I built a spreadsheet I could answer this myself perhaps. I guess there must be a copy out there.

I am planning to fit a Myford Quick Change Gearbox to my 1965 era Super 7. Rather than try and obtain all the Metric and BA gears and use the metric quadrant, I was looking for an approximation gear set. Searching the web I see that John Stevenson is quoted as having described a scheme using a 31 or a 34 gear in place of the 24 tumbler. But I cannot find any more information. I would love to see tables of threads produced and errors, maybe the construction of an excel spreadsheet, and perhaps obtain the two gears.

I am sure this has been discussed endlessly on this site and others but the search here won't find anything, and neither will Google. If I could I would email John Stevenson directly because he seems such a helpful chap.