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Drawing boo-boos, faults and known problems and ways to over come them

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Jo:
Looking through our list of headings I noticed that we do not have a thread for capturing errors on drawings or known problems with designs :o.

So to start this thread I would like to identify the problems with my Arnold Throp Cross compound engine. The drawings are excellent, I know of only one fault that is the governor Housing Cover which shows that the spigot should be 11/16", whilst this is consistent with the casting it is wrong :ShakeHead: it needs to be 18.2mm.

You should also be aware of the problems with the castings. Originally the patterns were made in wood but Arnold was inundated with demand that these soon wore out :disappointed:. When the design was passed to Southworth Engines, Peter Southworth decided to make a casting from the original wood patterns in aluminum, the result is that you have to be really careful when you look at the raw casting and make sure that you put your datums in the right position. You can get the measurements out of the castings, if you are careful.

It is still a wonderful engine and well worth building. I will be documenting its build  8).

Jo

Maryak:
I have built 2 engines from plans for which I paid money. In both cases the plans have been wrong in a major way.

1st up was the steam chest on the mill engine, if you had put the studs and their associated holes as per plan you would:

1. Drill into the exhaust passage, be unable to fit the stud and if you had bought the casting set, both the cylinder and the steam chest would be stuffed.

2nd was the location of the head bolts to engine body on a small 2 stroke aero diesel.

If you had drilled the engine body as per plan for the bolts; lo and behold you could not fit the transfer port cover plate between the bolts and at the same time cover the transfer port in the body. Again if you had bought castings, the body casting would be stuffed.

My solution is to re-draw the plans and usually these errors come to light as you draw, as you build, as you draw.

We all make mistakes, some, (like myself), more than others but I have difficulty in accepting such errors when I have paid money. If castings are involved, the acceptance of errors in either the casting or the plan is outside my tolerance level.


Best Regards
Bob

Bogstandard:
Jo,

I have been mentioning this for a few years now. Especially concerning Stuart castings.

Over the years, the castings have got smaller and smaller, I suspect that they have been using finished castings for making the moulds rather than making new larger casting patterns. Hopefully now that they have been taken over, new casting patterns will be made, but beware, they have also taken over a lot of stock, so it might be a few years before the new ones get into circulation.

I would warn anyone to check, and then double check that they can get the part out of the casting before starting to cut metal. I have had a few castings through my shop where new machinists have started to cut, and ended up with a hole half way in mid air, and I have had to rescue the castings for them.

Just as a matter of interest, I have attached as a word doc. an easy to understand rough shrinkage guide to show how much a casting can shrink when it is cast.


John

Peewee:
HI All,
I was Chatting to the new owners of Stuart yesterday at the Midlands show.  They had some of the older engines on display that they hope to bring back in to circulation.  he said that they were making some new patterns for these as well as using some of the originals.  the first re releases should be next year, he was keen to point out that they feel as a foundry they are in the best possible position to correct the castings.  He also went on to say that the show visitors had helped them look at the areas of most interest.  including the 4 stroke petrol. 
An assumption here is, if concentrating on the re-releases they, like Bogs said may be running the old stock down.

Jasonb:
Seeing as Bridport have been casting for Stuarts for a number of years I wonder how much of that stock originated from them anyway?

J

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