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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: Arduino Pendulum Clock Design - Comments Welcome
14/09/2020 23:31:42

I have had a test rig sitting on my bench for a while. It is a half-second pendulum suspended on a carbon fibre rod, and has a samarium-cobalt magnet attached under the pendulum. It originated with a series in ME by Dick Stephen. I built the rig because here were problems with the timing circuit and I thought I could do the job another way, using a microprocessor. There is a flat coil (no centre iron) which acts both as detector and as impulser (at least that's he theory). The original used two concentric coils, one for sense and the other for impulse, but I think more than one coil is unnecessary.

The pendulum will auto-start if timed pulses are applied to the coil.

The problem is that because the magnetic field is doughnut-shaped, the pendulum will tend to move in a slightly circular or elliptical path. Restraining the pendulum will mean frictional forces probably at the sides of the ball bearing at the top of the pendulum shaft. I am uncertain whether the fore-and-aft tendency is a result of the magnetic field, or simply created by minor random sideways forces - despite careful leveling of the rig, a rigid bench, and a concrete floor.

One of the problems with this kind of system, as Dick Stephen found, is that regular pulses tend to produce over-swinging, taking the pendulum far from any intended isochronous arc. Yes; we are trying to create a stable oscillator, but it must be resonant at the pendulum's natural frequency.

I don't think that a plan to apply regular pulses to the pendulum is necessarily a good way to ensure the pendulum swings at its own natural (resonant) frequency, and my plan is to use a statistical approach to try to identify what that frequency is, then try to maintain it. That means the adjustment of the frequency of swing will be by altering the effective length of the pendulum, which is what you would do on a mechanical clock, rather than attempting to drive the pendulum at a particular frequency to force it to time.

This is not a particularly urgent project. It has been maturing on the far end of the bench since 2007, and gets attention as the muse comes upon me.

It will be interesting to see your own results.


Thread: Claude Reeves 4 Legged Gravity Escapement Regulator
14/09/2020 22:43:16

A handsome job.

I must say I find your last photo, showing the blue hands against the polished brass very attractive indeed.

The case turned out well too.


Thread: Is a hand scraper pulled or pushed?
24/08/2020 08:02:23

Also +1 for the Sandvick.

I used to use a quality HSS scraper, but pushed the boat out one Christmas and ordered the Sandvick from Greenwood. Much better results than with the HSS scraper. The longer shaft helps, I find, and the blade is wickedly sharp (and has 4 cutting edges). A joy; in frequent use.


Thread: Free or inexpensive 2D cad for clock wheels
30/06/2020 20:08:34

Not free, but well worth a look. Takes a bit of getting into, but very capable indeed.


Thread: Reaming - depth of cut
06/11/2019 23:01:53

I use the rule:

Up to 8mm diameter hole, drill 0.2mm undersize.

Above 8mm drill 0.3mm undersize.

Dormer recommend the following allowances:

Below 4mm: 0.1mm

Over 4 to 11mm: 0.2mm

Over 11 to 39: 0.3mm

Over 39 to 50: 0.4mm (Good luck with a reamer as large as 50mm)

The larger the drill, the larger the allowance, and I have seen charts suggesting between 2% and 3% undersize.

I agree it is best to drill smaller then bore to the undersized size, then ream, but I seldom bother under 8mm.

I also agree that a floating reamer holder is best. I use one made from the Hemingway kit. Works well.

Lots of neat cutting oil too.

Don't let the flutes get packed, so retract and clean at intervals.


Thread: John Wildings great wheel skeleton clock
13/08/2019 17:41:40


That's good progress, and its nice to see the dial too, as that, together with the frames, gives a real sense of what the finished clock will look like.

I look forward to reading about, and seeing, progress.

Can I suggest you start a new thread for this clock? I think it would be very useful to have the posts accessible to anyone coming to the forum looking for info on the Strutt, or even just inspiration for a project. That post with the photos would be a good start, perhaps even with a sentence or two about the source of the design. I don't know how you would transfer that post to a new thread, but just starting a new one and re-posting the photos there would do, I think.


24/07/2019 22:42:36

Ah yes; time. That's an ongoing challenge, I find.
I have a skeleton movement n the bench just now, but it awaits one brass part, which is the little nut (the front collet) at the end of the minute hand shaft. I changed the design of that part of the assembly, so the nut will allow me to test my changes. It's only a very minor change, so I'd be surprised if it doesn't work. I have the base and legs ready, so assembly can begin soon, I hope. Assembly doesn't take long; its the parts for the movement which take the time. I have the drawings for a significantly amended part of the daisy wheel arrangement, so that will be the next stage, for the next movement. That's a bit away yet, though.
The Congreve movement needs the dials finished, and one finial turned. The clock stands on its own feet, but I intend to make a base for it to stand upon, although I have not yet decided on the material. Wood might be traditional, but I'm tempted by stone or even by Corian. I have used Corian (or one of the look-alike materials) for some clock legs, and it can look really good as faux-marble. Thicker sheets need to be built up in layers, though. There were some interesting photos of the Congreves built by the Sydney Clock Club in Australia, in the BHI Journal, some years ago. Their bases were made of Corian, and they looked very attractive.
So there is progress, but, as usual, it has been interrupted a little by other things which seemed more important at the time (and were supposed to be over quickly, but aren't).


21/07/2019 19:19:37


I'm pleased to hear of your progress, and I hope you will be providing updates (and photos?) as you go along. The Strutt is, to my mind, not only an interesting clock but one which will provide a really satisfying project. 'Half way through' means you are close to being nearly there...

I'm glad to hear you joined the BHI, and you will now have access to their new online library of back issues which are an absolute goldmine of good information. Mind you; I do appreciate the monthly physical copies of the Journal; thin but beautifully produced and full of interesting articles.


Thread: DIY Epoxy Frame based CNC MILL
29/01/2019 07:32:05


You said:

The sand used was washed silica as used by the building trade. one part sand to 3 parts granite aggregate with a maximum screen of 8mm. and a minimum of dust. These materials are both easy to obtain.

I'm off to mix some cement for a small foundation for a wall, this morning, and I wonder

(a) whether you needed to exclude moisture by using kiln dried sand?

(b) why exclude dust? I have used 'granolithic' as a screed, and that is mostly aggregate, with some cement. The aggregate is described as '6mm to dust' and the dust contributes to the strength, possibly because, like a larger mixed aggregate, the different grain sizes of the sand and aggregate lock well together, and provide strength. Would that not work in the same way with the epoxy mix?

(c) Experience tells me that if I lay a screed on a floor, then work it to a fine flat finish using a float, I need to take care not to over-work the screed, because the more I press it, the greater the tendency for the larger particles to work their way to the top as the smaller particles are forced downwards into the spaces between the larger particles. That can spoil the finish, as well as (I suspect) producing a kind of layering effect, with smaller particles tending to be more concentrated further down the mix. I note that you tamped in layers. Did that help the produce a more uniform distribution of particles? Might be rather difficult to tell, of course, but I shall spend the rest of the day pondering... Perhaps someone has done tests and reported results in one of the many papers on the subject?

Great progress, though. And I agree with your thinking re: concrete reinforcement bars ('rebar' in the UK) and 'inexactly placed' reinforcement.


Thread: Is it just me?
21/01/2019 22:34:15

I, too, have had many sites fail to reply to my messages. I took my business elsewhere. I will admit that is sometimes a case of biting off my nose to spite my face, but I resent the time wasted on writing in the first place, then waiting, chasing it all up, etc.

What's worse, though is major suppliers who invite 'reviews' and comments on their products via an automated system on their website. I have found at least one major supplier, which I use quite often, and who is well known to us all, simply ignores any comments or reviews which have any negative comments. So much for "Be first to review this product'. More time wasted trying to give genuine balanced comments.


Thread: L.A.Van Royen Twist Drills and their Grinding
08/01/2019 19:38:33

I emailed the Secretary, Norman Billingham, via the website. Norman gave me instructions as to how to pay via bank transfer. The book arrived shortly thereafter. I recognise the text as being based on earlier papers, but the book comes with a CD which contains an accompanying program which has not been available before (or at least for some considerable time). Nicely bound and presented hardback, whcih I am pleased to have in my collection. Did I say you need to love maths? The book takes a different tack to analysing the geometry than the Van Royen article, but geometry has moved on since Euclid and Van Royen.

I have a fairly sizeable collection of different types of device for sharpening drills, and the Van Royen article allowed me to appreciate the geometry of the devices, especially the differences between those which require a drill projection proportional to the diameter, and those which have a fixed projection (like the difference between the Reliance and the Picador sharpeners), as well as admire the way the drill jigs have simplified or transformed the way the drill is presented to the wheel, as is common with many present-day designs.

The Van Royen geometric explanation has been repeated and cited by many writers in ME and related places, over the years. Duplex (Ian Bradley) for example, cited the analysis when he presented the reworked Potts design in ME Nov 1963 onwards (issues 3237, 3239, 3240, 3241, 3242, 3244, 3245, 3246) - ME Plan WE19). Also of interest is Ian Bradley's HoneDrill in ME Nov 1961 Vol 125 beginning with issue 3151) (a nice example of which can be seen on GadgetBuilder's site). Bardley was half of the Duplex team.

There are others of interest, such as the design for sharpening small drills, by 'Inchometer' in ME Oct 25th 1934 pp397; and the Lammas design for a four facet sharpener in ME 5 Dec 1986 and 2 Jan 1987 (although that does not deal with the geometry of conical tips, of course).

There are lots more, but the further away one gets from the Van Royen work, the more tenuous the link becomes.

You might also be interested in the article by Mazoff, freely available on the web. Not a geometric analysis in the style of Van Royen, but some interesting assertions nevertheless.

What I would like to know is: if Van Royen produced an analysis, who devised the original geometry to enable the first accurate tips to be manufactured?


Thread: RDG or Myford ER32 collet set?
06/01/2019 22:22:33

+1 for Vertex. Mine have served me well.


Thread: L.A.Van Royen Twist Drills and their Grinding
06/01/2019 22:20:29

Once you have digested the Van Royen article, you might like the book by Professor J. Hugel, which the SMEE are currently selling. It was mentioned in ME a few issues ago. It is a much more mathematical analysis but also contains a CD with a useful Excel spreadsheet.

It's entitled: Twist Drills - Geometry and Performance

If you are mathematically inclined, it is well worth reading.


Thread: DIY Epoxy Frame based CNC MILL
06/01/2019 10:46:32


Talking of tolerances, what type of leadscrews will you be fitting, and what type of belts to drive the axes (unless they will be driven directly)? I assume ballscrews, but wonder what class/tolerance and arrangements for controlling backlash. The same is true of belts, which vary in the extent to which they introduce errors in positioning.

I know on my own mill, belt design has advanced in the last 10 years, and modern profiles are much better at transferring motion with reduced error.


06/01/2019 09:44:32


Looking at the first photo in your post dated

06/01/2019 08:20:45

I would suggest that when you have removed the second side, you clean the mould carefully then pour clear resin into it; polish the finished article, and mount it for display in your workshop. 'Tis a thing of beauty.


Thread: Drill sharpener
28/12/2018 07:13:46

I have a piece of worktop on which is mounted a Reliance and a side-facing grinder which carries a type 6 cup wheel. It's my go-to grinder for drills from 3 - 6mm, and sometimes larger. I fitted a steel flat at the side of the 'foot', so that I can slide the Reliance in or out a little to accommodate drills longer than the jig's range of adjustment, while maintaining alignment. Works very well indeed. I have some 'Picador'-style jigs too, but they came along later, so the Reliance is still my favourite. The advantage of the Picador is that the drill projection is a constant distance, while the Reliance projection varies with the diameter of the drill (hence the need for adjustment of the foot, for much larger or much smaller drills).


27/12/2018 23:08:37

I have one of these Sealey units, and although I have many other designs of jig, find the Sealey very handy and quick to use. It gives a reasonable finish, and the geometry seems to work. I agree with your investigation which reveals the wheel might be in a better position along the shaft, because I had the same thought in relation to the split points. I find that the wheel is inclined to grind too much, and give a point which is gashed down the centre, leaving two peaks, which is not correct at all. The problem seems to be that the wheel needs to be shifted along the shaft. I made some measurements, and made a spacer, but I have not got around to fine tuning the setup (too many more urgent jobs). It's something I will return to, shortly, in the light of your own investigations.

I can't comment on the clones, but the Sealey is a useful device, and well enough made.

I use a T&C grinder for forming 4-facet points on larger drills, and they work well. However; the convenience of the Sealey and my other sharpeners means it is easier and quicker to sharpen a standard conical grind drill, especially since they usually go blunt just when you need them quickly.

If I was to choose the ideal setup, I would sharpen my drills from 3 to 6mm using a swing-style sharpener (Reliance or Picador) and the Sealey from 6 to 13mm. T&C grinder above 13mm.


Thread: DIY Epoxy Frame based CNC MILL
15/12/2018 17:52:53

All the same, this is fascinating stuff, and just shows what can be done with oodles of skill and good planning. I look forward to the next instalment.

As for threaded rod; yes; I agree about the price. However; although I buy the occasional length in B&Q, I have a friend who uses it in quantity for a commercial product. Think of the cheapest price you have ever seen, then divide by 3. That's what he pays. It beggars belief that at that price it can still be manufactured at a profit.


Thread: Optical Centre Punch any good?
13/12/2018 23:33:18

I have the same kind as John. Works well. I made some punches with finer points to use in it, as I am used to using a 'pricker' punch. I generally try to avoid having to centre punch anything, but when I need it, the OCP is within arm's length on the corner of the shelf above the bench. I wouldn't be without it.


Thread: Hemingway Hacksaw
21/11/2018 23:24:08

Picking up on Neil's point about starting with a mill. I often use my mill for turning, using a tool held in the vice, the work in the chuck, and the Z axis moving the work past the tool. The too need to be centred on the work using the Y axis feed, whcih is then locked. X axis is the 'cut' depth.

It's fine for short work. And if, like me, your mill is CNC, it's a joy to do repetition work that way.

Longer work is difficult, of course, because you not only need the space for the work, but for the distance you will feed it downwards.

Like Neil, I have sometimes reflected that the Maker community has a slightly different set of needs and priorities as far as workshop equipment is concerned.


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