Member postings for Jim Nic

I scaled up this Mogens Kilde designed Double Diagonal engine by two by simply doubling the drawing dimensions and found that while most aspects looked OK at twice design size, the fasteners most definitely did not. Bigger - yes, but not twice as big. I actually used BA fastenings instead of the metric called for on the drawings and just chose sizes I thought would look right and took the view that for an air powered model whatever I chose would would be strong enough.

Jim

Edited By Jim Nic on 25/03/2019 22:04:23

I’ve not been well for a couple of months so there has been less progress on the Overcrank engine than normal.

This is the first engine I have built without the benefit of a build log or construction notes for guidance. My plan was to make the crankshaft next but luckily I had a close look at the drawings before I did and found that the valve eccentrics and crank centre bearing were on the shaft between the 2 throws.

The bearing could have been made as a split shell but I couldn’t see how to make the eccentric sheaves work with a join in them. So the only way seemed to me to make them as normal

and assemble them on the crankshaft before assembling and pinning the journals.

Happy days, the valves seem to move as they should so now it's back to the plan and build the crankshaft.

Jim

Jason

Firstly thanks for your consideration for the needs of your "customers".

My difficulty is sometimes visualising the shape of the part from the drawing so the addition of an occasional 3D image is welcome. The rendering of the intended result is also useful so I know where I am headed.

My preference of your options would be 1 or 2. Dimensioned in metric, on uncluttered A4 sheets in PDF format.

Jim

The vid worked for me Ron. All you have to do now is work out how to turn the web address of it into a clickable link

Jim

Nice looking result Mike, well done.

Jim

I would be very wary of cheap or free bits of metal. For use on our hobby machines free cutting metals are the best materials to start with then harder and tougher types can be utilisd when experience is built up.

Regardless of experience and machine it is always best to know what metal you are dealing with, there are some very tough machining resistant steels about.

Best, in my opinion, to bite the bullet and purchase known materials from known sources.

Jim

Thanks Jeff and George.

I blacked the parts by heating to red and then dunking (a technical term) in engine oil till cooled. Best done in the open as lots of smoke results and probably a fire risk. As you probably are aware used car engine oil is carcinogenic, although I'm not sure how much you have to drink before there is a real risk, so I use clean oil. It works for me and a part I blacked 8 years ago still retains its colour so I'm happy to use the process.

Jim

A small thing, but a win's a win.

Since I got my Rotary Table about 6 years ago I've been meaning to make a couple of clamping blocks for it. As a break from my current engine project, today I got them done.

Jim

I would welcome an artillery build log. Although artillery is not my thing I am always interested in how others approach modelling problems and engineered models of any subject are interesting to me.

Jim

Actually yesterday, I received the laser cut return connecting rods in stainless steel for my Overcrank Engine. These rods are in effect the crosshead but they work around the crankshaft thus shortening the engine. They were produced for me by Model Engineers Laser from a paper drawing.

I could have made them myself but producing 4 seemed like a chore so I took the easy route.

I understand that Malcolm at Model Engineers Laser runs it as a retirement project and he tells me that unfortunately his service will no longer be available after the end of 2020. That is a great pity as his service is excellent in all respects and he is willing to work from a paper drawing.

Jim

Yesterday I managed to break the mounting spigot of my DTI.

Today I spent some time on t'internetty trying to find a replacement spare. After a fruitless hour or so I got fed up and made one.

On the left the broken cast ali original, on the right the replacement from a bit of steel out of the bits and bobs drawer.

That should keep me going for a year or two.

Jim

One step forward and 2 steps back on the Overcrank. I made the base, just a piece of ali sheet with 6 round holes for the crank bearing supports and 4 elongated holes for the cylinder block. What could possibly go wrong?

When I offered up the cylinder to the base I found out. The holes in the cylinder base were incorrectly positioned and although I could have used them the cylinder would have been 90 deg out and pointing acrtoss the base instead of along it. The correct positions are marked out in the picture below.

"Oh, pooh sticks." I said, and went for a lie down while I considered whether to scrap the base or the cylinder block. After a while when calm was restored I came up with a simple plan and plugged the M4 holes in the cylinder base and redrilled them in the correct place.

After that I made the crankshaft bearing supports. Here is the base with one shaped support and 1 blank (the third is set up on the milling machine).

For some time now I have been muttering within earshot of the Domestic Authority that I could do with somebody to talk to while I'm busy making important stuff in my "playroom" as she calls it. I have let it be known that a dog would probably fit the bill despite her lifelong objection to domestic animals making a mess in her nice clean house.

Well to day she gave in and came home with my new pet. Meet Doug:

I'm not sure she is taking this matter seriously.

Jim

Not bad indeed Eric. A very attractive flywheel and the rest of the engine looks good too. As you say, all that's left to do is get it running and post a video.

Jim

Really nice result George. If Robbo is right and the domestic authority insists on replacing it with a new one, give me a call and I'll be round smartish to collect it.

Jim

I'm not a fan of hot air engines, but I have to admire the workmanship and appearance of the finished article.

Nice one Jason.

Jim

Not sure what you used when you say "retainer". Loctite is best at fixing shafts and bearings into holes and when correctly used for that purpose is difficult to shift.

I often use the adhesive method for workholding and use cyanoacrylate - instant glue. Ensure your surfaces are clean, and oil free, apply the glue sparingly and with pressure. I usually leave the assembly for at least 12 hours before machining.

To disassemble, moderate heat with a paint stripper gun and a light tap usually does the trick.

Jim

And all this time I thought your Horwich Crab was a bit bigger than that

Jim

Not a lot to show on the Overcrank since my last post on 12 Sep but here is a "family shot" of the components of the largely completed cylinder block.

And the assembled bits.

I'm not quite sure how best to proceed so to give me some thinking time I will make the aluminium sheet base and then probably the 3 main bearing supports.

Jim

My 8 year old WM240 does an indicated 1200 forward and 600 in reverse. I agree that there's probably nowt wrong with yours.

Jim

Other than an old bicycle lamp, what did you have in mind to use it for?

Jim