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Member postings for Marcus Bowman

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

Thread: Aluminium Grades
16/01/2017 17:36:07

I agree with the initial comment on knowing what the part is for, and then selecting an appropriate material. Material selection is about the most important initial step in any job, and in terms of value, a good choice can make a decent job, while a poor choice makes it difficult to get a decent finish, or sufficient strength, etc.

I also agree that grade 6082/HE30 has good machining properties, as does the tooling plate.

I believe the 7000 series grades have better machining characteristics, and are significantly stronger, but at much greater cost. The tooling plate, which I use from time to time, machines nicely, but unless you specifically need guaranteed flat plate, the cost would be hard to justify, as it is very expensive.

So 6082 is the best compromise for the everyday jobs, in my book.

The results depend on speeds and feeds, as with almost any material. Running with a broad cut of 38mm, 0.5mm deep at 500mm/minute is fairly spectacular on a small mill, but although the finish is not bad, machining dry with a carbide cutter designed for aluminium is likely to produce thin hairy slivers which will attempt to weld themselves back onto the job. Running a little slower or less deep gives a finish like chrome plating.

Marcus

Thread: Boxford
04/01/2017 23:00:18

I second Brian Hutchings earlier reply re: belt. I have an AUD with the underdrive (motor in the cabinet), and I renewed the belt years ago. Cut it off, then fit a T-belt. The links are easy to assemble, and it can all be done without dismantling anything. Take care when oiling the backgear reservoir. Over-enthusiastic oiling with attendant spillage will shed oil onto the belt and it will slip. Other than that, I have had 20 years out of the current belt, and it looks as good as new.

You might also want to squeeze a rag into the gap at the headstock end of the bed, between the vee and the sheet metal cover at the rear of the headstock. Oil or coolant will run along the bed, and through that gap, then drip down onto the belt. My last rag lasted about 15 years, before I changed it.

Marcus

Thread: Stuart 10V - Advice for Novice.
18/12/2016 09:45:50

Harold Hall's articles provided good guidance on how to tackle the job, so they might be your first port of call. As I recall, there have been other similar series in ME over the years.

The book 'Building a vertical steam engine from castings' by Andrew Smith is still available, I think. That deals specifically with the Stuart 10V, and although it was written in 1977, it gives good advice.

I have built a 10V and the only real challenge was in converting the drawings to metric units.

The 10V is an ideal project and leads to a very satisfying model.

Marcus

Thread: Cable size for Oxford welder
24/07/2016 17:12:15

In practical terms:

I have owned an Oxford welder for more than 40 years, and I can tell you that it will require a heavier-than-domestic wiring feed, and appropriate trips (see Nick_G's post).

In a previous workshop, I began with a 16 amp industrial-style socket wired into its own fuse at the fusebox, but had endless trouble with the earth arrangements, so abandoned that temporarily many years ago. Using the welder via a 13A domestic plug into a good quality 13 amp socket for short welds the socket face plate soon had burn marks on it, and it got very hot if welding over a metre or so at a time. You can't really run more than about 110 amps with this setup. The 2.5mm2 wiring leading to the socket also got hot, which is a potentially serious problem.

So I would caution you not to begin by using a domestic wiring arrangement with this welder, but to install a proper high capacity fuse, thicker wiring and an industrial plug. Domestic wiring is a definite fire hazard.

I also have a large capacity fire extinguisher in the workshop, but that would not be much good if the wiring in the walls overheats.

One other problem is that when the welder is switched on there is a significant surge which can trip a domestically-rated fuse. The more often the fuse trips, the more prone it is to tripping. It's a cycle of despair relieved only by taking note of the differences between types and ratings of breakers (see Nick_G's post).

I'm hoping to add a different type of welder shortly, but it is clear that any welder capable of welding anything other than thin sheet (car body thickness) will draw more current than can safely be delivered via 13 amp domestic fuses and cables. The specs on many models make this clear, and I note that at least one manufacturer will not supply a 13A plug for their more capable welders.

Having said all that, the Oxford is a robust welder capable of heavy duty. I have not had a moment's bother with mine, despite miles of welding.

Marcus

Thread: Spindle Encoder / Leadscrew stepper threading leadscrew idea
13/07/2016 07:41:15

I assume the 'learned discussions' were printed in the journal the month before the article was published...

More seriously;

One difference between a one-pulse-per-rev system and a system which uses one index pulse plus a train of intermediate pulses is that while the 1ppr system calculates the stepper pulse rate needed for the next whole revolution, the multiple ppr system is capable of reducing ongoing and cumulative errors caused by variations between the theoretical pulse train and the actual motion of the work, in each revolution. So it produces a better match between prediction and actuality over the course of a single revolution, in an open loop system. Not quite responding before it happens, but certainly closer to continuous correction.

I agree with the earlier comment about power and electronic motor speed. As far as I can see, the typical variable speed control boards for low powered lathes and mills also use a single pulse per rev and have a visible variation in speed under varying load, especially at low rpm. That is bound to lead to variations in pitch and in cutting performance.

If there is a small range of optimum cutting speeds for a given material and diameter of work, why do we slow down for thread cutting? That seems illogical. I get better results when cutting at closer to theoretical optimum speeds. I suspect the low speed is to allow for operator thinking time, to allow for disengagement of the leadscrew half-nuts. I've had better results using higher speeds but arranging the direction of feed so that rapid disengagement is not required; or by using mechanical auto-disengagement or trip-switch electrical shut-off to cater for the fact that my own internal processing speed is very slow. An automated system, whether CNC or not, copes with this quite nicely. But I would not expect to have to make big compromises on the integrity of the pitch.

Marcus

Thread: Knurling Tools
12/07/2016 07:57:25

I agree that knurling is a displacement operation and that flow plays an essential part. So we can't really say we are "cutting" a knurl. Calculations would be based around pitch and pitch circle diameter, and have their place, but only when calculating using PCD, as when calculating gear dimensions. It think speed of engagement and squeezing/crushing the depth is also essential, as is copious coolant and continuous cleaning/removal of slivers or swarf.

That being said, I am far from convinced that most combinations of knurls and workpiece diameters give really cleanly defined knurls on the work. I much prefer to CUT knurls. For me, the most convenient way depends on where the work is, and what the previous operation was. Sometimes that's in the lathe, but mostly it is on the CNC mill, where all manner of patterns are easily achievable.

I have sets of good quality knurls in two-wheel squeeze-type holders (as in the illustration in a previous post), and they generally work well. Narrow knurls do tend to have the disadvantage that a greater amount of sideways traverse is required for a given breadth of knurling, so it is more likely that the knurl will tend to wander a little, producing a slightly drunken finish. Any slight out-of-square alignment of the arms or the tool tends to make that worse.

Marcus

Thread: Spindle Encoder / Leadscrew stepper threading leadscrew idea
12/07/2016 07:43:34

Sounds like the well-established electtronic leadscrew project (ELS):

**LINK**

for which there is a large Yahoo group.

There is also a version based around an Arduino; and there are youTube videos of that.

Thread: Boxford as a wood lathe?
06/07/2016 08:09:51

No-one has mentioned decent dust extraction as being a solution to most of the problems of dust and debris. A powerful extractor designed for wood dust transforms the experience by removing much (but not quite all) of the dust. The challenge is in arranging the nozzel near enought eh surface of the work, and making it traverse with the toolpost/carriage. I use an 2HP Axminster unit which operates on the "vacuum" principle. I have also used an earlier unit based on lower suction at the nozzle, but intaking larger volumes of air. The vacuum does the job for my kind of work, but must have a small nozzle positioned close to the work surface. That just leaves a bit of dust, which, while requiring clean up is not a great problem. Cleaning the bed of the usual oily film before turning wood is essential. Cleanu up of chuck etc is important, but no worse than when turning cast iron etc.

The comments on speed etc are valid, especially for small diameter work.

A lathe is a lathe, and I never could really understand how a woodturner could claim a wood lathe was better for tunring wood. To me (and I own a wood turning lathe too) the engineer's lathe has proper precise control of carriage and cross-slide, meaning one can turn wood precisely parallel and to size. Sure; it shrinks and moves later, but that's the wood, not the lathe. My wood lathe says under the bench, out of the way.

Boxford made two wood turning tool rests(short one and long one) to fit the old bench lathes (AUD, BUD etc) but ther are designed to fit the old-style rest-holding arrangements which use a tapered plug. It is easy to make a simple adapter to allow those rests to fit onto a plain surface or a tee slot etc. I suggest second-hand dealers (see G & M Tools, for example). It is also relatively easy to adapt other rests, and I often use a rest from a Record wood lathe to give me an extended rest which sits out a distance from the normal rest position, for larger jobs.

One other word of caution. It is worth pointing out the dangers of wood dust from some species of trees, as well as the general danger to the respiratory system from small wood dust particles. I have found this is not to be underestimated. The same is true for other materials, of course, but the species-related dangers are both real and well documented. Real woodworkers cheerfully ignore dust masks, goggles and ear muffs - but they are all dead, blind or deaf, so I guess they knew best.

Marcus

Thread: Question on gas bottles
25/05/2016 22:54:07

Calor bottles are paid for by a deposit, but the amount you get back reduces sharply as time goes on. After 3 years there is no residual return value. No problem filling any Calor bottle though. I've never been asked for ID or proof of purchase.

Marcus

25/05/2016 22:51:47

Or there's Hobby Weld, who sell bottles and gas. One payment for the bottle, then you just pay for the refill each time. Argon; Argon-CO2 mix; oxygen; etc. Lots of stockists.

Marcus

Thread: GUY MARTIN
04/04/2016 23:03:54

Didn't BSA own Triumph at that time, which would technically make both engines BSA.

It was a great programme, although stretched out a bit. But it held the interest of myself and my 25 year old daughter who still remembers, vividly, being taken to a real Wall of Death when she was around 5 years old (at Flook airfield, at the Cumbria Steam rally). I recall being taken to a Wall of Death at a visiting fair, by my Dad when I was in my early teens. Unforgettable.

And yes; the cyclist's performance was most impressive.

Marcus

Thread: merlins band clock
17/03/2016 23:13:58

Ok. If the workpiece is flat, and mounted on a faceplate, you could use a vee tool attached to the vertical slide, but swivel the slide for the angled strokes. You could also use a spindle and an engraving tool (or something like a Dremel or Proxxon drill as the spindle).

For curved arabic figures, I wonder if you could use the same principle as a taper turning attachment, where both the cross-slide and vertical slide are freed from their feedscrews, and follow the guidance of a template, rather like an engraving machine (but turned through 90 degrees so that the template is vertical to match the vertical face of the faceplate. That would require a pointer attached to the vertical slide, aligned with the tool or spindle.

I tend to think an engraving machine (commercial or home-made) would be more efficient. That has the additional benefit that the template can be larger than the engraved numeral, so errors are reduced.

If the bands are already formed, I'm not sure I can see an easy way to do this in the lathe for the arabic numerals.

This is an interesting problem!

Marcus

Thread: Model Engineer Editorial direction
17/03/2016 20:51:24
So "Model" Engineering would appear to be a hobby practiced almost exclusively by a very (very) small proportion of the middle-aged to old (predominately retired) male population of the UK

I suspect that this is the same demographic for a wide range of hobby interests. It certainly matches several other areas of my own interests. Same grey hair (or none...)

Marcus

17/03/2016 20:00:36

To quote Ajohnw:

To be honest I am surprised these magazines have not gone entirely web based even allowing single editions to be purchased.

************************

That would be the least acceptable format, for me. I spend a lot of time at the computer, but I am about to cancel the only web-delivered engineering magazine to which I subscribe. Web delivery just cannot compete with print. I can read a printed magazine over my meal, or in bed, or take it to the workshop, and I can delve into a huge collection of back issues, but I have found I hate reading technical magazines only on-screen. That came as a surprise to me, but there it is. Print is still king, for me.

Marcus

Thread: merlins band clock
15/03/2016 20:17:45

I have not engraved the bands for that clock, but have done some other dials, including dials like lathe feedscrew dials, which are orientated the same way, and I am familiar with the Merlin clock project. What's your specific question?

I have also dome some etching, although if I was making the bands I would engrave them by choice, as I think this gives a crisper finish to the sides and corners.

I would not make the bands the way that process is described in the book (page 50) but would either make the band from a strip and turn it, or, for preference, turn the band out of tube. I'm not sure if there is a convenient size of tube, but that would be the easiest way. Without removing the tube from the chuck, I would transfer the chuck to the CNC mill. Sorry if that's not your cup of tea, but it is the easiest way for me. That allows the engraving to follow the surface of the band, round the bend, so to speak. I have engraved plain flat dials mounted on a faceplate in the chuck, using a vee tool, but even if the bands remained in the chuck on the lathe, the problem would be the diagonal movements. Not impossible, I think, but very tricky to co-ordinate.

I believe a conventional manual engraving machine can engrave around a band, without much trouble, but I have no direct experience of that.

Marcus

Thread: Model Engineer Editorial direction
15/03/2016 19:59:58

Picking up the points by Harry and Daniel, perhaps there is another aspect of all of this we should perhaps think about.

When you know something, or you have developed a skill, continued practice takes you through a cycle where you begin as a beginner and are a bit lost. Then you get into it a bit and find you can see what this new world is all about. Then you begin to increase your skills and knowledge, until one day you discover that, in the case of, say, a model engineer, you have the confidence to be able to tackle most things in the workshop (I didn't say anything about the standard of the result...).

You begin to develop insights, and a deeper understanding until, finally, you become a Zen master.

Without the detail, this roughly follows a well-known description of the learning process.

But I would say that at each stage ME, MEW and EIM are a crucial aid to learning.

The small dissatisfactions with the magazines may simply be a reflection of the feeling that you are having to look down, from the Zen position, and see little new or challenging. There are, though, those occasional nuggets which provide a different view of this world, and introduce some new knowledge or techniques. For there is no Zen, really, just a continued journey.

Oh; and it is accepted practice for those who achieve enlightenment (at any level of the process) to return their knowledge to those who might benefit from it. None of us know, or will ever know, everything, and we all benefit from the knowledge and skills of others. For me, the Master in the early days was GH Thomas, and there have been two or three others over the course of many years. I have learned a lot from them; and would not have known any of it if they had not shared it in the magazines.

I said earlier, as did others, that I had been reading old copies of ME form the halcyon days of the 30s to 60s. Halcyon? Actually, no; I really don't think so. So much has changed that most of what is written in those early volumes seems somewhat lacking compared to what we have seen in, say, the last 5 years of current magazines. The technology has changed; the equipment in a typical workshop has changed dramatically; and the standard of today's average and best quality models is light years ahead of what was going on then.

All of that takes us much, much further and makes us much more capable. And it was all because of the magazines. So; while I might be disappointed in some of the content, some of the months, I know that over a period of time I will be able to look back and be satisfied that I learned something. In fact I will be glad. So I won't be failing to renew my subs.

Marcus

14/03/2016 23:14:09

There are some interesting thoughts here...

Like J I too have been wading through a huge collection of early MEs, from the late 30s to the early 60s. I received all the copies after that, as a subscriber. I have every MEW, as a subscriber, and I have all the EIMs too. I also used to subscribe to Don Young's much missed Locomotives Large and Small which ran some absolutely excellent constructional series, all with full good quality drawings.

The UK has the world's most highly developed magazine market, and I too am amazed at the content of some magazines. There is a problem, though, both for the readers and for the editors. I believe the long-term reader of almost any magazine will meet the same problems.

1. The content does repeat itself, with the same topics being repeated at intervals, and, in many cases, with old articles being reprinted.

2. As readers, we change over the course of a lifetime's subscription.

We can see the same phenomena in television and radio; and in most of the media in fact. TV channels run the same old repeats endlessly, and tackle the same basic topics time after time, because they are short of good content. I got bored of most of it a long time ago.

Problem 1 is a reflection of the plain fact that there is a high churn factor, with many subscribers being new readers, new to the hobby. Magazines need those new subscribers just to survive. But it does mean there is an unceasing demand for articles for beginners. It also means the same topics can be revisited at intervals. The challenge is to present those topics in new ways, and to avoid boring the older more experienced readers. That's a tricky challenge, and I'm not sure there is really an answer to it. It does depend to a large extent on the skill of the contributors, and on the editor winkling out interesting contributions from those who might have something appealing to say.

Problem 2 is an inevitable consequence of our own experience, our increasing skills and changing understanding of what the hobby means to us. Given enough time, it seems inevitable that we find less that appeals in any magazine. And yet, we live in interesting times, with advances in technology and new accessible ways of doing things, so there is always something to learn.

It's interesting looking at the output from the current fad - the Maker movement. I subscribe to some of the electronic newsletters and websites which proudly proclaim themselves as being in the vanguard of this new movement. What's depressing is that although there is some really smart computer programming going on, and some tolerable electronics, the standard of 99% of constructed items is very poor. None of these people have ever heard of ME, MEW or EIM. I do wonder, though, if the long-term trend will be for Model Engineering to be subsumed within the Maker movement, as interest in steam railways gently declines.

There is, too, the strong trend, common to many other constructional hobbies, to move towards ready-made items or to assembly of substantially pre-made sub-assemblies. That approach has almost completely taken over in aeromodelling and has made significant inroads in model boats. Of what interest would that approach be to those of us who have been in Model Engineering for a long time?

I don't think there are any easy answers. In fact, I don't think there are any easy questions about this topic. And it is too easy to say that if you don't like what you read in the magazines you should write an article yourself. Still; I do think it would be a shame if the more experienced folks disengaged form the model engineering magazines, because they are an important part of the overall infrastructure which supports model engineering.

It's interesting that this website and forums are part of the magazines' efforts to promote themselves by helping us to be an online community. I think it's a very valuable thing. Given that one can now find a huge amount of ME-related and workshop-related user content on sites like youTube etc, I do hope the printed magazines can survive as part of the mix. I subscribe to a digital-only version of another magazine from far away, and I must say I hate reading only on the screen. I prefer the physical copy I can read anywhere. The other valuable thing about the magazine is that the content is vetted before acceptance, unlike some of the rubbish on youTube and other websites, much of which is either boring or just plain wrong.

I think that's more than my tuppence-worth...

Marcus

Thread: tailstock tapping jig
08/02/2016 15:37:37

Buy a ready-made 2MT or 3MT taper with a large diameter blank end. Drill it right through along its axis, with a decent hole (maybe 10mm diameter). Get a good Jacobs chuck and turn an arbor to a sliding fit in the hole, and with a taper on the front to suit the chuck. Now you have a sliding, guided, version of Simon's method. Hand-hold tightly as you feed the tap into the work, then you can continue that way, forward and reverse in stages, or leave the lathe chuck stationary and turn the tailstock-mounted chuck by hand. Works a treat. Wouldn't be without mine. There's a photo in a recent ME. Photos also on page 59 of the Crowwood Screwcutting book. I can post a photo if you need one.

There is also a popular ready-made item which consists of a small chuck and body on a sliding bar which can be gripped in a chuck in a tailstock or drilling machine. Unfortunately, the range of grippable sizes is small, and the body is smaller than the body of a Jacobs chuck, so its not as easy to grip or turn.

Hemingway also sell a nice kit for a floating reamer holder and that can be adapted for taps. I made one and although it is a substantial item it does what it claims, and copes with minor axial misalignment, preserving the tap.

Marcus

Thread: Tapping Cast Iron
26/01/2016 10:27:12

Yes; ground thread HSS Dormer E500 series taps get my vote, but be prepared for severe financial pain in the larger sizes.

On a rainy day, if you are not using them, you can pull them out at tea time and just wonder at their beauty.

Above M10, I would suggest "progressive" "geometric" taps like the Dormer E105 series, but they are even more expensive. They make tapping large diameter threads a very low torque process.

I have quite a few Presto taps, bought locally many years ago. Again, they are ground thread HSS.

For less frequently used imperial, ME and MME sizes I have found Tracy Tools taps pretty good.

Sadly; despite what we all would wish, quality costs. But it can be a good investment.

One other thing: in general, I would recommend Trefolex tapping compound. In fact I don't think I have tapped a hole without it in over 50 years. Eases the process, lowers the effort, and protects the tap too.

It's wet here this morning; and its nearly tea break time; so I'm off to polish the contents of the tap drawer with a soft cloth. I think of it as cherishing my investments...

Marcus

25/01/2016 23:05:00

Interestingly, Whitworth is still a commonly used threadform for threads in cast iron, because of its relatively coarse pitch compared to its diameter; and because of its nicely rounded root and crest profile which means there are no sharp corners to act as stress risers, and no sharp vee points to crumble. Whitworth is still used in the metric zone for that specific purpose. Compared to, say, M6 x 1, 1/4 Whitworth is 20TPI and has a pitch of 1.27mm, so it is significantly more coarse than the nearest readily available ISO metric thread. 5/16 Whitworth has a pitch of 1.41mm which is greater than an M8 x 1.25 thread. If you prefer to stay with metric, on the basis that the taps will be more useful for other jobs, I would be inclined to choose M8 x 1.25 instead of M6 x 1 in cast iron. It probably depends on the amount of metal left around the threaded hole, because too little leaves the uncomfortable prospect of cracks in the main casting; so M8 might be too large for your tailstock.

Marcus

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