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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: Cutting a large round hole
21/11/2018 23:02:22

Bosch make hole saws with fine pitch teeth, specially for cutting holes in thin sheet metal. Not cheap, though.


Thread: Cox Per Wee or Tee Dee
04/11/2018 19:39:59


The book doesn't have an ISBN. It is:

Model Engine Plan Book, by The Motor Boys International.

It was originally published by the AMA (American: Academy of Model Aeronautics) and profits were invested in the AMA's Junior Program. I have checked the AMA's site and it is no longer available (and hasn't been for some years, I think).

If you have not already done so, you should check out the site at: **LINK**

There is also a thread on this forum which discusses obtaining a copy of the book as a PDF file:


but you will see that was written in 2014, and I can find no way of obtaining the book as a file. I believe the work was not made available before the death of Ron Chernich in March 2014. The Model Engine News site which hosts the Motor Boys pages has not been updated since then. It is still a great site if you love model aero engines.


29/10/2018 22:56:30

I agree with the comments re: choosing a first engine carefully.

Ron Chernich's site used to sell a book of plans, which I have, replicating some of the engines from the past. Sadly, the book is no longer available. Plans for the MATE were printed in Model Engineer, some long time ago, and that was designed for beginners. It depended on an aluminium extrusion, no longer available, but I am sure there was an article about making it from a block of aluminium.

Neil mentioned the Sparey engines, and they are not a bad place to begin.

There are also plans and build instructions for a series of splendid looking engines in the Super Tigre series, available free, here: (its the third DVD you want). OK; not quite truly free at the moment, but archived at low cost. This is not a beginner's project, though - not at all. Gorgeous though.

Thread: Taper turning
29/10/2018 22:23:26

Maybe the manufacturer of the lathe recognises the faffing about you need to do to offset the tailstock or use an offset centre etc, and just expects you to buy their taper-turning attachment which bolts to the back of the bed (usually) and controls the cross-slide movement as the carriage moves to the left. Its an expensive way of doing it, but it gives good results and usually allows easier adjustments to create a 'matching' taper.

Thread: Steel for machining
04/10/2018 22:25:54

The ideal material for a real machine tool would be Meehanite, which dampens vibration, but I imagine that might be a tad expensive. In that case, spheroidal cast iron ('ductile' iron) would still give good results. I have no experience of specifying grades, but this site gives advice:


and I guess a foundry would advise. There seem to be plenty of companies advertising that they either cast from patterns, or sell large section bar. West Yorkshire Steel, for example, sell bar. I have no connection with them.

Thread: G-Code editor with back plotting
02/10/2018 22:50:44

Taking a different approach, you could use LinuxCNC on a basic Linux machine, and simply run it unconnected, or run it in demo mode. The main window has a decent backplot display.

One thing, though: each implementation of G Code is in some way specific to the system it runs on. So Mach3 has one set of G Codes, Fanuc has another, and LinuxCNC has yet another. The issue is not with the basic core of codes, which they all recognise and interpret in much the same way, but the enhancements and the differences in syntax and program structure. Subroutines, for example, are structured differently and occupy a different position within different flavours of G Code. Mach 3 has no real flow control codes for logic, whereas LinuxCNC has many; and so on. So you would need a backplotter which suits the variant of G Code you want to use.


Thread: Once a fitter.....always a fitter....
23/09/2018 23:09:02

Anyone who has a pedigree starting with Airfix and Keil-Kraft is welcome here...

The GT40 is a nice car, but I always preferred the Lola Mk6, which indirectly gave rise to the GT40. I used to have a slot car of the Lola, back in the day.

Thread: Why did the tap stick?
23/09/2018 19:18:53

Serial taps are a good idea, but I would offer the observation that coated serial taps I have bought recently are definitely not as sharp as uncoated HSS taps. In fact, they cut as though they are slightly dull. One might argue that the coating does dull the cutting edges. So that might give rise to the same problem.

My coated serial taps have been consigned to the wish-I-hadn't-bothered bin. My uncoated serial taps continue to give sterling service.

23/09/2018 19:14:57

I tend to think SillyOldDuffer has a point.

Chris stated he thought the steel might be EN8. But suppose it was, say, EN24 or EN24T. All three may well work harden to some extent, and certainly may be sticky enough during tapping to cause some problems. I have used EN24T a little, and have cut sizeable threads using the lathe. It machines fine. But I would not be surprised if it was not so easily tapped. Cutting in a lathe is a rather different action, because the chips are quickly separated from the work, and there is more power applied. When tapping, especially on the tapered section, the same section of thread is being repeatedly cut just a little deeper, so if there is any suspicion of dullness in the tap, there will be much repeated rubbing, at least to some extent, and that may well induce a degree of work hardening. By the time you have the whole of the taper section (typically 6 threads or so) in contact with that rubbed surface, you are bound to have a fair degree of resistance. EN24T comes hardened and tempered, but it is usually further hardened by heat once it has been machined. EN8 is not hardened as supplied, but, again, it is hardened by heat.

SillyOldDuffer's question is interesting, though. How can we prove, or disprove, this?

22/09/2018 22:36:43

Did you use a tap lubricant? I find Trefolex paste is best, but Dormer tapping fluid is fairly good. Or just cutting oil. I agree with Bazyle re: withdrawing more frequently to clear the flutes, as well as the obvious slight reverse turn every 1 to 1.5 turns.

If the tap is blunt, you would need to take some care to preserve the hook angle when resharpening. I see lots of youTube videos showing how to sharpen taps, but I have yet to see one that does it properly.

In my experience, EN8 should tap without the difficulty you describe.

Thread: Jones and Shipman 540
22/09/2018 22:29:31

I have a 540 which was converted to single phase by changing the main motor and the pump motor. That happened before I bought it. Works well, and its a tool I would not want to be without. If I had realised how it would transform my work, I would have bought one years ago.

Thread: John Wildings great wheel skeleton clock
20/09/2018 08:29:50


The Strutt is an interesting clock. I have the Bill Smith book on that one, and I have seen several completed clocks, some original and some made from the Smith instructions. Smith's book refers to the photos of a Strutt in Royer-Collard's book "Skeleton Clocks", but I see better photos of a wider range of Strutt & Wigston epicyclic clocks in Derek Roberts' book "British Skeleton Clocks" (Wigston was an engineer, and business partner of Strutt, so I imagine Strutt was the designer, but commercial manufacture was arranged by Wigston). I have seen instances of completed Strutts at verious ME exhibitions, and I think I recall seeing one a couple of years ago in the collection of the Worshipful Company of Clockmakers, held in the Science Museum. The interesting part of the machining of the Strutt is the cutting of the internal teeth of what Smith terms the ring gear.

I built a Wilding 16th Century one-handed clock with a verge and foliot escapement, as it was serialised in the Horological Journal in the late 1970s. I can still remember quite clearly the moment I got it to run, so I can imagine your ow joy with your current clock. I have a Widling Congereve almost clomplete, on the bench at the moment. I have built a number of skeleton clocks which originated from a Wilding design and are based on a pigeon timing clock. My plan was to start with the Wilding modifications and make some changes as I went through a series of those. The clock features a daisy wheel mechanism in place of the conventional motion work. After the first one, which was fairly close to the Wilding design, I made some significant departures from that design, so that the whole motion work is now quite different (although still based on the daisy wheel). The clocks also feature a prominent platform escapement, so I have had to learn how to deal with issues concerning springs and rating. Other parts of the original design have now been progressively modified, so that the whole thing is now rather different. That was the idea behind the 'series' of clocks, and although it has quickly taken me in directions I had not anticipated, I have enjoyed the journey. Along the way, I have been unable to avoid a constant stream of repairs to (mostly) longcase and wall-hanging clocks, and cuckoo clocks (which I find bring a smile...), all of which brought valuable (and sometimes hard-won) experience. And I have a design for a wall-hanging clock which I am almost ready to start making. That's if I can get the next 3 skeletons off the bench, and get the Congreve finished, polished and into its Perspex case. Interestingly, Wilding recommends polishing the pinion leaves, in the Congreve book (and others) but it is a technique explained in a number of general clockmaking and repairing books, so I am surprised it is not in the Great Wheel book. Polish; harden; re-polish (or at least clean after hardening).

I can recommend membership of the British Horological Institute, and its journal, as well as branch meetings of like-minded souls who are a constant source of good advice. They run good courses as well, at their headquarters. There is also a distance learning course which can be done at your own pace.


18/09/2018 22:34:19

Glad to hear your clock is up and running sweetly now. You can count that a success.

What’s the next project...?


Thread: Stuart Steam fan from the USA
13/09/2018 22:06:25

Hi Bill,

That'll be Marblehead as in magnificent yachts, I presume?

Nice Stuart loco top right.


Thread: John Wildings great wheel skeleton clock
10/09/2018 23:12:10

Another thought about sticky teeth (more straws to grasp at):

When the clock stops, is it possible to apply just enough additional (small amount only, of) pressure to move the teeth past the sticking point? If so, you may just be able to see a polished high spot around the tip of the wheel. Burnish that, or scrape and burnish. I have a daisy wheel mechanism I make quite often for the motion work on skeleton clocks, and I know that spotting high points in this way can help. It is quite tricky, though. And almost impossible if you have carefully burnished the acting faces of the teeth. Felt tip pens are sometimes useful here. You would expect the ink to be rubbed off each tooth in the same way, so any obvious differences indicate a problem. One thing worth saying is that one turn of the pinion or one turn of the wheel is unlikely to give you all the meshing combinations of leaves and teeth, so many turns may be required before the troublesome combination occurs.

Second thought is that it might be worth making sure all is ok with the barrel and spring. Springs sometimes rub inside the barrel, and that can make the clock stop once the initial kick from the spring has passed, and the spring is exerting a lower torque. Rubbing would tend to leave a scrape in one barrel end. If it is a strong spring, you may find the problem is with the barrel pivots binding under power.

Is the motion work behaving, or is there friction in the hands or pipe assembly? There are lots of parts in close proximity there, so there is lots of scope for friction.


10/09/2018 22:38:32

I would hesitate and have a cup of tea before removing metal from the (steel?) pinion. It may be that the pinions were supplied with a final polish, but, if not, I would certainly polish the leaves using a piece of approximately-shaped wood and some fine abrasive powder. Wilding recommends ~"coarse oilstone dust" in one of his other books. I think a more modern way would be a finer grade of diamond paste. Rub along the gaps between the teeth. Once satisfied, move to a finer grade. JW recommends Solvol Autosol, and that's as good as any for a final polish once any marks have been removed.

I might also try my luck with the arbor suspended in vee blocks and a DTI with an elephant's foot against the tips of the leaves, to see if you can measure any eccentricity. I suppose you could do this in-situ, if you can secure the frame and the DTI so that they do not move relative to one another. You could repeat this with the mating wheel. I understand that clockmakers of yore used a 'topping tool' to ensure the tips of the teeth were all at the same distance from the centre of the wheel.

Forgive me if I grasp at a few more straws:

I assume you burnished the pivots at the ends of the arbors. Those need to be well-finished and burnished to harden the surface. The shoulders where the pivots step back up to the full diameter of the arbor should be finely finished, and undercut if possible. A watchmaker would polish the faces of those shoulders. The inner edges of the bearing holes in the plates should have a really tiny chamfer. The idea is that the pivot shoulder cannot seize against the corner of the hole. The bearing holes themselves should have their inner surfaces burnished, to harden them and reduce friction. I know you probably did all that, but those are sources of additional friction.

You say the train runs freely under finger-power. How freely? It should coast for a long time, if there is nothing to impede its progress. What happens if you tilt the clock while the train is spinning freely? Same if you tilt it the other way?


09/09/2018 23:05:27

I have not made one of these clocks, but can offer some suggestions arising from experience with other clocks.

I suppose you have tried testing the gear train with the clock assembled, but without the barrel or the escapement?

That way, you can apply gentle pressure and see and feel what is going on under gentle power but without the force applied by the spring. It's also quicker than waiting a week for the clock to stop.

As Neil says, it is a good idea to mark the offending teeth of pinion and wheel if you can identify them when the sticking occurs. Try it a few times. If it is always the same teeth, they can be given individual inspection and attention.

Is there an eccentricity caused by the seating on the wheel collet? It is always a good idea to finish turn the collet after it has been secured to the abor, before attaching the wheel.

If you know which tooth of the wheel is definitely causing the problem, I would recommend burnishing the face of the tooth before reaching for the file. Next in line would be the tip of a triangular scraper, followed by the burnisher, before reaching for the file.

Did you make the little depthing tool to J.W.'s design? It's quite handy. Not big enough for the great wheel, of course.

Neil is also right about the changes in meshing when the gears and arbors are under load. Skinny arbors tend to deflect under load.


Thread: Removing and re-chucking a part whilst thread cutting on Myford Super 7
02/09/2018 22:53:59

That's quite a short thread, but it looks as though you have 3 fully formed turns, so I would use thread wires to measure the pitch diameter, because that's the crucial dimension for fit. You do need a minimum of 3 threads to be able to position the wires. With care, that method should avoid the need for re-chucking. You should, in any case, be able to get a good indication of the required depth of cut by consulting tables. That might not get you exactly there, but you should get a good indication of depth, so that you can judge when to use the thread wires to work out the final cut(s). Thread wires are a bit fiddly to position, but worth the effort for a thread like this.

I guess the thread is too large for you to have a tap so that you can make a female thread to act as a gauge.

With that short a right-hand thread, I would turn it from the flange outwards, to minimise the need for a groove at the inner end of the thread. If you use the tool right way up, mounted at the rear of the thread; reverse the rotation, and feed the tool towards the tailstock, life becomes much less stressful. Grind the tool so that the point is close to the chuck end of the tool when it is in its mounted position, and you should be able to start it right up against the flange. Let it cut a vee groove for clearance, before engaging the half-nuts.

I like the nice crisp slot.


Thread: Is there a new standard for taps?
02/09/2018 22:33:54

Some years ago I bought a pair of Dormer M12 x 1 serial taps. At that time, it was difficult to find a stockist, and they cost around £35 per tap. They were for a specific job I repeat regularly, so I had to bit the bullet on the price. The tailstock drill chuck grips them more securely than smaller non-serial taps, simply because the turning forces involved are smaller, despite the larger thread diameter.

More recently, I bought some sets of serial taps in more common metric sizes, at much more reasonable cost. However; they are TiN coated and distinctly less sharp than the original Dormer uncoated HSS taps. That was a surprise, and largely negated any advantage in the small thread sizes (M6 and M8).

Surprisingly, Dormer serial taps are even more difficult to obtain nowadays, although I also suspect the price may be even more difficult to justify. Sorry - Dormer Pramet, as it now is.

Like JasonB, I favour spiral flute taps, and it is a joy to use them in a tapping head on the drill press.

I have always used Trefolex paste when tapping, but I recently bought a bottle of Dormer tapping fluid. 'Twas a waste of money; its not as effective as Trefolex, so I will be happy to switch back in a few years, once the fluid is finished.


Thread: Mercer British
01/08/2018 07:45:14

Can you post a photo of the instrument and the damaged/missing part?

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