Author Topic: Drawing boo-boos, faults and known problems and ways to over come them  (Read 4776 times)

Online Jo

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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
« Last Edit: October 20, 2012, 06:58:56 PM by Jo »
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Offline Maryak

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #1 on: October 21, 2012, 12:10:17 AM »
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
Если вы у Тетушки были яйца, она была бы Дядюшкой

Bogstandard

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #2 on: October 21, 2012, 08:50:50 AM »
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

Offline Peewee

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #3 on: October 21, 2012, 09:11:56 AM »
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.
Ian
Still sane?  definitely not but enjoying life more

Offline Jasonb

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #4 on: October 21, 2012, 10:13:57 AM »
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

Offline Peewee

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #5 on: October 21, 2012, 02:42:15 PM »
very true
Ian
Still sane?  definitely not but enjoying life more

Offline AlasdairM

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #6 on: October 23, 2012, 06:16:44 PM »
I may be mistaken, but I believe that whilst Bridport did originally supply Stuart with their castings, some 5 or so years ago this ceased - this may be (and this is my total conjecture here) why the quality dropped off?

I gathered the above info. from chatting to one of the "stall-holders" at MMEX last week, and also from a discussion with Andy himself on the Stuart stand.

Regards, A
New to model engineering but loving it!

Online Jo

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #7 on: November 25, 2012, 05:10:36 PM »
Double Tandem compound:

IMHO the author of the drawings for this engine never actually built it. You need to make the assumption that the single compound is ok, Stan Bray built one in ME and identified the problems with that, but all the bits that relate to the double should be approached  :Director: with caution.

The GA is not to scale :ShakeHead:. This is what you may wish to refer to as you notice many DTC specific parts have not been drawn up, but be careful. Many of the glands use 8BA studs but there is not enough space on them for the nuts. The same problem exists with the steam and exhaust ports which show 10 BA but there is only space for 12 BA nuts.

The DTC does not require bent connecting rods, they can be straight but the lengths must be reduced to take it into account (or you can reduce the valve rod length to compensate).

Jo

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Offline gbritnell

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #8 on: November 25, 2012, 05:28:56 PM »
Over the years I have built many models, engines and otherwise. I have built from castings, Stuart, Reeves etc. and also just from plans. I have gotten to the point where I always double check dimensions before cutting metal. I can excuse some mistakes as I have made them myself. What I can't excuse is a drawing for a part that has been around for years and has never been corrected. When an engine for example is designed, drawn up and built, it should have any errors corrected so it just makes you wonder if a particular engine was ever built from the drawings or if the author really cared enough to correct them after finding them.
In the not to distant past I built some engines from kits and the disclaimer on some of the drawings was "I'm not a draftsman so the drawings might not be totally correct".  :shrug: or the note 'fit at assembly' used too many times.
One glaring error can be found with the Holt drawings. The carburetor as drawn won't work, period. The fellows that have used it have made modifications to it just to get it to operate. Some builders have even switched to propane or model airplane type carbs out of frustration. Deplorable!!
gbritnell
« Last Edit: November 25, 2012, 05:32:43 PM by gbritnell »
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Offline Dave Sohlstrom

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #9 on: November 25, 2012, 09:15:22 PM »
On the Holt drawings I have. The cylinder spacing is 1.5" on the crank case, cam and crank shaft but the cylinder heads and cylinders are 1.625" in diameter so will not fit the crank case. I found this when a drew up the parts in 3D CAD and built an assembly.

Dave

Offline Mosey

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #10 on: January 04, 2013, 11:49:51 PM »
In the plans for the Silver Bullet there are several parts that need what I  call "revisions", . They concern the water pump and the starter hub, at least.

I will say that the castings are quite nice, and ample to make the engine without question. Of course, Bob made the engine himself and we have seen it run very well.
When I get to it, I will publish my corrections for the plans, and if anyone needs them sooner, I will gladly share my thoughts.

Imagine if you will, that I am a beginner on my 2nd engine, working on a challenging project, and not knowing how engines are really machined.

Mosey

Online b.lindsey

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Re: Drawing boo-boos, faults and known problems and ways to over come them
« Reply #11 on: January 05, 2013, 12:10:55 AM »
While the 1/4 scale Rider-Ericsson castings fro.m Myers are good and of ample size, the drawings overall leave some things to be desired. Mainly a good update, but a couple of things were just wrong as noted in the build log IIRC. One in particular was the spacing of the displacer yoke where it attaches to the actuator arm. Moral of the story...study plans carefully before cutting metal.
Bill