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Member postings for Martin Johnson 1

Here is a list of all the postings Martin Johnson 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Castings, creating a datum before milling
20/12/2019 16:45:52

As Jason says, it all rather depends. First step is always to knock the lumps off with a file. A good next step is to mark the castings out, with (say) the base underside surface and shaft centreline. Also mark out the base in relation to it's axial position with the bearings and spot where the holding down holes will come. You will soon see where there is not enough metal (happens on commercial castings too often) and too much metal, and can adjust your marking out accordingly to get the best shot at the casting.

I would then probably go for a preliminary cut on the under foot and the long side of the foot - not to size at first, just to give you square edges.

On complex stuff it can be like knitting with fog to get a start. A dodge then is to cut card templates to actual size and sight them against the casting to get the best shot.

Hope that helps,

Martin

Thread: Kerry 1124 lathe - some healing required
02/12/2019 08:24:12

On the Kerry, that damage does make a difference. It is a wedge type gib strip held endways by the mangled screw you can see in the photo and another at t'uther end. Someone has then drilled in a roll pin to hold it as a repair, but the gib strip cannot now be adjusted.

Three ways out as I see it:

  • Get the base casting built up with weld and machine back to original. Could be tricky to machine the weld back and blend well enough for a machine slide.
  • Shorten the base and re- drill for the gib strip screw. Will leave you with a little less support, but probably fine.
  • Make a pattern up and get a new base cast. You might be very lucky and find a foundry that would work from the knackered base if you build it up with isopon or similar, but they are a rare thing these days.

The upper top slide casting is easy, you can hack that out of continuous cast bar - don't ask me how I know that.

I checked in my instruction book for metric screwcutting charts, but it refers to a different style of box. I think you will have to try it out and count input turns Vs. leadscrew turns and then work it out from scratch. You could try asking Tony Griffiths - you never know your luck.

As to cross slide screw - bite the bullet and put a digi readout on that and the long axis.

By the way, you got an absolute bargain when you bought the lathe.

Martin

01/12/2019 11:43:34

I also have an 11 x 24 Kerry, imperial model with the angled tailstock handle - you'll know what I mean if you have one. I think you will be very lucky to find spares, but they will be worth the effort of making. You will end up with a very good lathe. If you need any photos taking I will be pleased to oblige, just P.M. me.

It sounds as though you have an unusual beast, the Kerry I have has 9 headstock speeds selected by 2 knobs with 3 positions.

My only quibble is that it doesn't cut 19 tpi (3/8 & 1/4" BSP)- but that won't bother you in metric! Changewheels on mine are 18 dp, but I don't know what the train would be on a metric model. My Tony Griffiths instruction book lists translation wheels for my imperial machine but nothing else. The book is worth getting anyway, as it has a lot of cross sectional drawings, which are useful if you need to make parts.

Martin

Thread: Rake angle on Cutting Tools.....memory tips???
21/11/2019 16:37:54

If the O.P. is working in industry trying to make a profit or bonus by turning things out as quickly as possible, then rake angles, clearances etc. all matter.

If as I suspect he is working in a home shop. They really don't. I turn just about any material with the same set of tools - all ground by eye with a bit of clearance on the front and whichever side face is cutting. Put a few degrees of rake on the top and that does the job. Only exception is some brass which is better without the rake on the top - even then, most of the time I can't be arsed to change the tool.

My qualifications for such a gung ho approach? 50 years model engineering, 40 years as a chartered mechanical engineer.

Martin

Thread: piston rings
12/11/2019 17:25:41

Another vote for adjusting the bore size to suit a commercial piston ring. My traction engine runs on a chain saw ring (High pressure) a Ural motorbike ring (low pressure) and I have just built a much modified Southworth steam pump that runs on a petrol strimmer ring.

Have a trawl round e-bay to see what you can find. If you go for non OEM parts, they can be dirt cheap - probably cheaper than the cast iron bar to make a ring.

For steam work, you can close a ring up slightly if you need to. Make a hollow ring to hold it in, cook the whole lot up to dull red and you will find the gap will close up nicely. A bit like the old trick of springing them open and heat treating, but in reverse!

Martin

Thread: Holbrook Model B No.8 Lathe
21/10/2019 16:41:37

If you have access to another lathe, the job is fairly simple. Some of the well known traders sell backplate and faceplate generic castings. It will help if the Holbrook spindle is available (i.e. dismantled) for fitting the threads and registers on your casting.

If you don't have access to another lathe, you really need to start with at least something that already fits on the nose - this can be a faceplate or a catchplate for between centres work. Have you tried the usual 2nd machinery dealers for something?

Assuming your Holbrook is now armed with a faceplate / catchplate the routine is drill, tap and screw your chuck backplate with boss pointing toward tailstock onto the facaplate. Now machine the thread and register - you will have to unscrew the whole lot to check thread fits and registers - a pain, but possible. Once you have a thread and register done, remove the backplate, screw it onto the spindle nose and machine the face and spigot for the chuck.

I hope that all makes sense.

Martin

Thread: Boiler build abandoned !
28/09/2019 09:39:50

Chris,

I know how much scrapping a boiler hurts, as I got myself into exactly the same situation with a Rob Roy boiler, more years ago than I care to remember. Just like you, the shell went quite well as did the tubes. But the stays.................

Well, I pickled, chased the leaks around using an oxy acetylene set at work to get inside the box. Created more leaks in diffferent placed, pickled, chased the leaks around a bit more ............. and so on ad infinitum. Until in the end, I was concerned about the safety of it all just like you.

I just hope knowing you are not alone will set things in perspective. You are not the first and I very much doubt you will be the last bulder to get into a similar situation.

The fact is, that commercial boilers represent a bargain when you look at cost of materials and the amount of fiddly work involved.

Best Wishes,

Martin

Thread: Building a 4" traction engine
05/09/2019 16:25:48

Forgot to mention - choosing a club:

For a larger scale model, you are probably going to have a steel boiler. At scales up to 4" or so, you can get that tested by a club. For 6" models and beyond you will be paying for a commercial inspector. If you are getting club inspections, be sure the club has experience of steel boiler inspection and know what to look for. Not all clubs have that experience, and you need that peace of mind.

Martin

05/09/2019 16:16:07

Hello Karl,

Glad to hear you are hale and hearty! Also nice to know you have the room and facilities, so my advice would be to crack on with a big 'un - given the way things are going, it will be easier to sell when that day (hopefully far away) comes.

Aside from the Burrells (various including GMT, agricultural, SCC, showmans, road, crane in 2, 3, 4, 6 & 8" scales) I would have a look at the McLarens (3, 4 & 6" scale of a big engine), Garrett agricultural 4" scale, Garrett tractor in 6" scale, Foster 4" scale (available in compound and single guises - the single is an easy(ish!) build but not very close to scale), Fowler singles in 2, 3 & 4" scales - a nice close scale model, Fowler compound in 4 1/2" scale - a nice model, but Plastow drawings again.

Given your easy access to HGV vehicles etc., I would consider the 8" GMT - there is a build thread on Traction Talk, or a 4" McLaren - they have an excellent reputation. If you want to go silly, have you considered a 9" scale Foden lorry? or 6" Foden lorry if you want to fairly sensible - they go like the clappers.

As to casting purchase, I do not like to tie large sums of money up (nor does SWMBO) so I tend to buy castings in batches and split the build into phases accordingly.

Martin

05/09/2019 08:35:26

I always advise prospective builders of larger scale traction engines to consider how you will transport it, where you will store it, and how you will manhandle it. There are huge (expensive) implications for what vehicle you drive or are likely to drive. A part built 4" scale engine is about the same footprint as a lathe - so could you easily cram another lathe in your workshop - it's a rare workshop if you can! Finally, how fit (and old) are you? - Don't answer in public on this forum! The fact is you will be shifting best part of 1/2 ton of machinery around on a regular basis so is that going to be feasible 10 years from now?

As to the models you mention, a few comments:

The Plastow drawings have a "reputation" of the wrong sort, being difficult to read and having their fair share of inaccuracies.

The Plastow 4 1/2" scale Burrell is of the 7 HP engine (I think), so makes up into quite a large model, roughly 6 feet long. These days, a copper boiler for this engine would not really be considered, purely on cost. So a steel boiler is probably the way to go - and that has implications for storage and long term care.

There are plenty of examples of this model around, so you will be one of the crowd. However, plenty of build advice and tips on where the drawing errors are will be available.

I assume you are considering the EKP 4" scale Burrell Gold Medal Tractor. I have not heard about EKP's drawings, but generally the GMT is a very detailed and good model. I have not seen the 4" scale model around, so they are not that common. It is to a slightly smaller scale and is a smaller prototype than the Plastow, so will be significantly smaller and lighter. I believe it to be considerably more detailed and closer to prototype than the Plastow.

Plenty to think about!

Martin

Thread: Grinding cup wheel help
31/08/2019 09:07:45

Since you are only generating a straight line for the edge of the tool, why do you need a cup wheel? Grinding on the periphery of a 5 or 6" disk wheel will give a perfectly adequate tool for cutting acme (or most other thread forms), albeit with a slightly hollow clearance face.

I have both types of wheel on my homespun cutter grinder, but the periphery is the "go to" option when possible.

Martin

Thread: Boiler testing pump - plans ?
24/08/2019 16:38:16

Another vote for buy it finished. By the time you have bought the brass, stainless steel, silver solder, balls, fasteners, the tank etc. etc. you will save money by buying it finished. I have been using a bought one for a couple of years now and it is so much more convenient and works very well. You can also use it to top up pressurised central heating systems.

Martin

Thread: Backplate debacle
24/08/2019 16:33:58

Several points worth flagging up on this saga:

1) "1/4 to 1/2 thou undersize" for what is probably about a 4" register, that is pretty fine tolerances anyway.

2) Another piece of received wisdom is that lathe tools have to be at centre height. If you are trying to take wee shaving cuts and the tool is actually a shade OVER center height, then the tool won't cut. So you put on a bit more and try again. Then, the tool finally gets "in" and takes off a load more than you bargained for. Moral - keep tools a shade BELOW centre height - especially on fine finishing work.

3) Funny stuff is cast iron. The finish straight off the tool (HSS at any rate) will be "whiskery", which gives a false over size reading on a mic or calipers. Before measureing take the whiskers off with a bit of wet & dry paper.

4) Another way to rescue such a situation is to let in and loctite 4 plugs, say about 20 mm diameter for your example, equispaced at 90 degrees and straddling the register. Then machine the plugs back to (hopefully) finish at size. Assemble it and hope you are long gone by the time someone else finds out your rescue bodge. Seen it done in my working days to rescue a very urgent part.

5) I agree with the others - no need to resort to bodges in this case. Crack on and well done.

Hope that helps,

Martin

Thread: Different ways of boring a hole
14/07/2019 17:11:33

I don't think anybody has mentioned that a hole bored on the lathe by rotatin the work depends on the accuracy of the lathe to maintain it's parallelism - if the lathe is "out" then the hole will be tapered. I know this because I have a lathe that is slightly out.

However, if you rotate the cutter the hole will be parallel, but not necessarily at a perfect right angle to the table. I know this because I have a mill that is "out" as well.

Tool deflection is another matter that will also cause inaccuracy.

To answer the OP's question. I have recently bored the pump cylinder for a Southworth steam pump. (65 mm end to end and 23 mm bore). I did it on the lathe cross slide with a between centre boring bar. Actually, it is a boring bar I grip in the four jaw chuck at one end and on centre at the other. By gently adjusting the chuck jaws and using a DTI against the tool tip, you can put on a fine cut in a very controlled manner to finish at a precise diameter.

Hope that helps,

Martin

Thread: "The Unique"
03/06/2019 16:34:45

I have one that I bought at a club sale for half a crown. That gives you some idea of when that was.

It has done sterling service over the years, setting up lathes and truing up work. With the arrival of a pucker dial gauge (for a lot more than 2/6), it is now still used on a crude stand for setting lathe tool height - on centre is centre of the scale, so easy to see if you are high or low. I ground the rounded "stylus" flat for this job.

Highly recommended for those on a tight budget.

Martin

Thread: Beginners question (sorry) - why I am breaking my small centre drills?
25/05/2019 09:41:58

I am glad others have noticed that some of the "Colonial" centre drills are dire. If you put a colonial against a good brand, the differences are striking. Buy cheap and buy twice!

Martin

Thread: Getting rid of the garage door...........
25/05/2019 09:33:32

I agree with all the above construction ideas. But keep a double width door somewhere - you never know what machines you might want to get in or out. Bargains pop up unexpectedly, house moves can be forced upon you and how are you going to get that milling machine out? Or you might decide to build a 4" scale traction engine, or take up motorbike restoration.

Plan for the unexpected.

Martin

Thread: Model Turbines
18/05/2019 20:27:48

If it makes Turbine Guy feel better, my old company that I trained with (W.H. Allen & Co, Bedford - see **LINK**) used to have an air turbine testing rig that was used for developing blading on steam turbines. So there is every good reason for using air as a convenient medium for development purposes.

Martin

Thread: Romulus Boiler Details
18/05/2019 20:10:08

As part of my continuing analysis of model locomotive boilers, I am trying to use some test results on a Roger Marsh Romulus to check my prediction software.

Can anybody help me with some leading dimensions of the boiler, please? I am trying to get the following (rather formidable), but any help would be greatly appreciated.

BOILER INTERNAL DIMENSIONS

Grate width & length

Firebox wall area

Length between tubeplates

Number & diameter & thickness of firetubes

Number & diameter & thickness of superheater flues

Outside, Inside diameter of superheater element, & how many elements to a flue.

Length of superheater element & length inside firebox (if applicable)

Boiler Outside Dimensions

Overall length of boiler shell

Diameter of boiler shell

Thickness of lagging (if any)

Many thanks in advance,

Martin

Thread: Steel boiler storage.
11/05/2019 11:47:11

A couple of points:

Burning a candle in a boiler for storage - so that hydrocarbon fuel will produce CO2 and H2O, which will condense and combine with the CO2 to make carbonic acid, and then lay in the nooks and crannies - Doh!

Filling to the brim. Does nothing to address crevice corrosion - in fact encourages it. You will find plenty of crevices around all fittings, around the foundation ring weld and around stays - none of which can be cover welded from the inside of the vessel. Maybe if you are filling to the brim with an inhibitor laden water.

For my boiler, anything over a couple of weeks it is always dry - blow down hot and let the residual heat do the rest. For over winter, take the plugs out as well. My boiler is stored inside in a heated room. For less than a couple of weeks (between rallies) then store well filled. I use boiler treatment anyway which will scavenge most of the oxygen out.

Martin

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