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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: 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.


Thread: High tensile steel
21/11/2018 23:17:09

EN24T turns to a nice finish, using conventional tooling. I use tipped tools. The T stands for 'tempered'. So this is a relatively strong steel which can be hardened if necessary. I have made some parts which are subject to considerable stress in a full size hydraulic tube expander, from EN24T. They were hardened afterwards (not by me) and have outlasted the original parts.


Thread: How to fit a taper pin?
21/11/2018 23:13:11

A handy device for doing this in a more controlled, and better supported, way is to mount the chuck on a long parallel shank. Make a fitting to suit your tailstock, and drill and ream it right through to suit the shank of the chuck. That lets the chuck and shank slide while being guided. I made one for my lathe, from a blank 2MT arbor, and it gets lots of use. You could also look at the Hemingway floating reamer attachment.


Thread: Machine/hand reamers?
21/11/2018 23:05:04

Hemingway do a nice kit for a floating reamer holder. I made one a while ago.


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.

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