Member postings for Martin Johnson 1

The only problem with the single post type tools in this thread is that all the tension is on one bolt and a fairly small length of T slot. Rear parting is less prone to "dig ins" - but not immune. I will leave you all to work out what is going to happen if you do get a dig in.................

GHT thought that one through with a "toe" on his rear tool post and two bolts to hold it down.

Martin

I really would not go to the trouble of re-inforcing mesh. Put in 100 mm gravel, well tamped down. Put in 50 mm sand, well tamped down and raked level. Place 1 damp proof membrane over it and up the sides of any formwork or earth (if below ground level. Put in 100 mm of C20 concrete tamp down, strickle and allow to go "green" and then trowel off. Seal with proprietary sealer PVA or similar when dry.

At 3 m width, you might need a screed rail down the centre line to make strickling the concrete easier. Plus profile boards around the edges, of course.

That spec has supported my 1/2 ton lathe (Kerry AG) (plus a lot of metal in the cabinets below) plus a Tom Senior M1 and loads of junk in two workshops now for a total of around 30 years.

Martin

Do you mean that, in your experience, a 14 year old beginner with an Instrument Maker Grandad should shoot the silly old duffer before starting work on an ME article chosen at random? I'd worry that might lead to a 7½" scale Hackfly, converted to metric, and fitted with a home made soft-soldered stainless steel boiler.

And now I think you are being a very silly old duffer! I chose the project based on what I read, which was that Rob Roy is a beginners engine. I had enough common sense at 14 to see me through and Grandad to guide gently. I think I had a pair of goggles once I got a grinder. I also had a flat cap to keep my hair ( I had some then!) out of the way.

An ML7 is not a massively powerful nor dangerous machine unless you are terminally stupid with it. - I did find out what happens if you leave a chuck key in and I haven't done it again...........

But seriously - the lad is 17. He is either going to take to it or not. And lectures on this that and the other will not help. Advice, sure, but gently does it.

Martin

I started at 14 with a very grotty ML4. Fortunately, I had an instrument maker grandad who was there to get me out of trouble. I started straight in on a Rob Roy and finished when well into my 20's - but school, uni and lumpy jumpers tend to get in the way. That was nearly 50 years ago now.

Best advice - lend him a heap of ME's & MEW's and let him get on with it. Help him out of the hole when he gets in there.

But all this talk of safety rules and a course of instruction - forget it.

Martin

Aside from the basic horsepower question in replacing 3 phase with single phase, there are some other issues to consider:

Starting torque - not great with single phase, but very good with a 3 phase started directly on line. Spinning up the drive train, spindle, faceplate? etc. on a Harrison takes some grunt. Can be got round with a clutch, but maybe a VFD would be an easier route? The catering equipment you have seen started on single phase motors probably didn't have the mass of a Harrison to spin up?

Starts per hour - the high current at start up heats up the motor, so the more starts per hour you make, the hotter it gets. Can be significant when you are making a tricky component. You can either fit an oversize motor - go up at least one rating on the power, or try and find a specialist motor designed for such abuse (alternatively search for rocking horse poo).

Hope that explains some of the issues.

Martin

I have a series of articles starting in ME 4584 that describe computer techniques I have developed over the last couple of years. The aim is to improve the THERMAL DESIGN of small steam boilers. The calculation is not concerned with strength considerations, which are well covered elsewhere.

The program is in .xls format and it can be found at the following link:

**LINK**

along with a detailed report on how the calculations are undertaken.

I would also be pleased to receive comments on the techniques. The program as presently constructed is completely free to use and if you want to develop it further, nobody will be more pleased than me.

Many thanks to Neil Wyatt who has uploaded the files onto this site.

Martin

Edited By Martin Johnson 1 on 30/05/2018 09:07:24

I agree with Jason B. Start from the position - " Where will I store it? How will I tansport it? Am I fit enough to manhandle it?" There is also the important question "Can I afford it?"

When you have answered those questions, the rest will fall into place.

Martin

Back in the day (about 50 years now) I had an ML2 driven direct from a 1450 rpm motor by flat belt onto the headstock. Absolutely dire!

I built a countershaft unit hinged at the back of the bed with motor hanging off the rear, V belt drive up to countershaft. I modified the lathe to V belt pulleys by turning the cast iron flat belt pulleys off to leave a parallel sleeve, then loctited a multi step picador pulley onto the remaining sleeve. It worked OK. I later grafted a clutch onto the countershaft which saved a lot of motor stop / starting.

If I was doing the job today, I would use Poly V belts, J section, you would only need 4 groove pulleys and they could easily be turned into the existing cast iron pulley. You will need to beg / borrow / steal another lathe to the turning though.

A little warning - my ML2 had the cross slide feed screw graduated at 80 thou., but the screw was actually 12 tpi giving 83 thou advance per turn. This caused quite a few scrappers until I worked out what was happening and made a 12.5 TPI screw and tap. In hindsight, I should have made it 20 TPI, and re-made the micrometer collar with 50 divisions.

Hope that helps.

Martin

Just been to look out the good pot of case hardening compound. It is Blackgates own brew, and the tin says it contains Ferrocyanide. Can't remember just when I bought it, but less than 10 years ago for sure, probably more like 5 years.

Apologies for claiming it was Kasenit, but it does handle just like Kasenit.

Martin

Peter,

Please enable your profile and I can P.M. you some contact details - or P.M me with an e-mail address.

Martin

You could try the Scottish Model Engineering Trust at Methven, near Perth. There is also Angus Model Road and Rail, based in Montrose (I can get you details), and Edinburgh M.E. club.

Hope to meet you soon!

Martin

Deepest Strathspey

I had some cheap(ish) nondescript case hardening powder from one of the well known ME suppliers. I could not get any case hardening with it. I even tried making a box out of large screwed pipe fittings, filling with item + powder, heat ad nauseam, then dunk - but still no joy.

Purchased proper Kasenit and had no further problems. This needs heat to bright red, dip in and it forms a sort of crust over the item. Heat a bit more, then dunk. Repeat as required.

You get what you pay for I suppose - Caveat emptor.

Martin

The mains voltage is the same, the oven is the same, the potatoes might even be the same. However, the thermostat is a cheap piece of Chinese junk that will drift off specification quite quickly, and that is probably your (well, her's actually) problem. They are quite cheap to replace, especially if you go for non OEM spares.

Martin

Neil Wyatt said:

"Steam is about 3% efficient but many of the inefficiencies are getting heat into the water from the coal."

Actually, not so. A model boiler is a bit less efficient than full size, but still up in the 60% range. The real fly in the ointment is the small difference in steam enthalpy between inlet and exhaust of the engine unit. That is where the second law really kicks in. In short, you are throwing away most of the energy in the steam you are creating.

Martin

Hi Andrew,

I have only recently found this thread on your musings about injectors and applaud your inquisitive approach. It might already be known, but the only way you will really understand is to question things and work it out.

Way back you asked about the reason for a particular divergent angle on the steam cone. The answer is to be found in the simple truth:

"Accelerating fluid flow is easy, Decelerating fluid flow is damned difficult."

I have spent a working life in fluid dynamics finding that one out.

More specifically, in a conical diffuser once you reach a certain cone angle you will get flow separation - the boundary layer start to detach at some point downstream of the throat. This is precisely the same effect that causes a wing to stall at too steep an incidence. Initially you will get instability (buffeting) followed by complete BL detachment (stall). Obviously, in a cone of fixed angle you don't have the option of pushing the stick forward to get out of it. What you can do is keep the cone angle below about 10 - 12 degree included angle. Less than this angle and you will get a reasonably controlled (and hence efficient) reduction in flow velocity, turning the velocity energy back into pressure energy. There are charts published of loss coefficients Vs. geometry which show the detail of this effect.

I quite liked your explanation of why a steam nozzle must be convergent - divergent to extend the choking point. You are actually using Bernoulli's theorem to drop the exit static pressure at the throat, hence increasing the p1/p2 ratio which extends the sub-sonic flow regime. Not my specialism, but I hope this provides an alternative way of looking at it.

I have recently been looking at draughting, which is another application of the jet pump (and another area that everybody knows everything about because Kank and Snart said so in 1834). Anyway, one of the more reliable papers indicated that for good cavitation performance the area for the entrained fluid inlet was critical, which translates to radial gap between steam cone and mixing cone, plus axial standoff between same. This makes sense because the lowest pressure area is exactly there. You are trying to entrain water into a jet of steam moving at silly velocity and if you drop the static pressure below vapour pressure, cavitation (and hence loss of performance) will follow. This also explains why lifting injectors or hot water injectors are a *** to design because these areas will be critical.

By the way, I think you need to uplift your design water flow. You have not allowed for cylinder condensation which is likely to put up the water demand by another 50% or so, even allowing for steam jacketed cylinders. See the paper by Bill Hall "Measuring Steam Engine Performance"

Keep up the good work and the analytical approach. I copped out on injector building, there is a unit by Terry Baxter's old firm (He of "Injector Man" fame in another place) which is the vicar's knickers. Works beautifully and is encased in a lost wax casting which is a dead ringer for a Gresham & Craven vertical injector as used on tractions.

Best Wishes,

Martin

Chris,

As noted by others you need a specific flux for stainless, which should make your problems surmountable.

As to whether you need superheaters - yes you do. If you look at Bill Hall's tests at:

https://www.advanced-steam.org/wp-content/uploads/2017/08/Measuring-Steam-Engine-Performance.pdf

Fig. 5 in particular shows that superheat can change the steam demand from the engine over a range of about 2:1. Would you be quite so relaxed about putting in half the grate area, half the tubes and half a firebox? I rather doubt it!

Personally, I would not recommend a concentric superheater, but I see the manufacturing simplicity of such a beast. As Duncan says, a good dose of radiant heat from the firebox will also help matters along.

Martin

Thanks for the link Thor - they look like pretty high torques to get on the C spanner as supplied! Certainly a bit more than these arthritic hands can cope with these days.

Jason, Yes I am up to speed with locking the collet into the closing nut.

Thanks to you both.

Martin

Interesting! I have just gone down the ER route having previously used a similar tapered collet system but with only 3 slits down the collets. I also have a pucker Clarkson for the (increasingly rare) threaded enders.

Anyway, first trial with the ER25 set showed the cutter was pulling out on a modest cut with a freshly sharpened 16mm end mill on 6082T6 ally. Maybe I need to be a bit more ham fisted in the spanner department? Even so, it took a fair bit of getting out again. The ER25 set was from Chronos, fresh from China.

The bearing collet nut sounds interesting - are they on e-bay or similar? Should I bet putting little grease round the inside of the closing nut as an interim step?

Martin

If you don't mind joining tractiontalkforum.com, there is some interesting work going on there on 3D pattern printing for models and full size.

Martin

Martin,

If you have one of the Chinese DRO units, (mine is badged Sinpo) then hole PCD's are "interesting" and the Chinglish instructions are not a lot of help either. My experience is largely as you describe. I find the hole centre has to be 0,0, but I can see no reason why this has to be. Most times I can get it all to work, but sometimes it just seems to throw a fit and direct me to very strange places on the work - cannot work out why yet.

The moral of all this, run round the PCD with a pointer before you drill (or just mark the surface with a centre drill). Fortunately as with all things digital it is either right or very wrong, so easy to tell.

Martin