Woodpecker build advice please

[arc]

Hello All,
First post although I've been here a while. I really enjoy viewing the projects/builds and admire the talented folks here.I've built about three steam engines so far, and now I'm trying a 'hit n miss'. It's a Woodpecker casting kit obtained from Mini-steam.I have a question to ask of some of you that may have built one of these engines.I refer you to the pic showing the placement of the holes that need to be drilled in the bosses.They are for the cam lever and governor lock. Notice the peck marks that I made are not near the center of the bosses but this is exactly where the plans have them to be.I'm wondering if I can place them more centered or is this not advisable?
Andy

 

[Blogwitch]

Andy,

Normal model engine castings are not critical works of art, unless you really pay lots of pennies for them, so as you have shown, holes can look to be way off the "intended" target.

It also depends where you have set your original datum points that you are working from.

Maybe you have used the crank centre, or it could be the bottom of the base, preferably, you use two datum points to work from if possible, so wherever you have worked from, everything else should go from that (those) datum point(s). It is up to you to make sure that you have measured correctly and put the drilling points in the right place. Double and triple check your working out from the plans, and if they are right, then go for it.

Some people would go the whole hog and after the holes are drilled, they would then dress the castings so it looks like the holes are in the exact centre, or you could do what most people do, just accept that the castings are slightly out from the drawings and leave them as they are.


John

 

[arc]

Hi John,
Thank you for the reply. I did use the crank center as my datum, and that point was located from the base and so as to be directly above the reinforcement webbing of the crank saddle. I probably am expecting too much accuracy of the casting. It looks like I might have to 'live with' it.
Thanks again,Andy

 

[gbritnell]

Hi Andy,
I also built the Woodpecker engine from the castings that Ministeam supplied. First off in all fairness Ministeam didn't make the patterns and coreboxes for the engine, they acquired them and are marketing them.
That being said I had the same issues as you when locating the other holes. Coming from a casting background I laid out all of the holes prior to machining and adjusted the locations to best fit the bosses. That doesn't mean I changed the dimensions I only moved them all together from the drawing dimensions.
As John stated when working with castings you have to make adjustments but it doesn't affect the overall machining or operation of the part.
More than likely the original bosses were put on the pattern using the proper shrink and they produced a casting like you have but nobody went back to make the necessary adjustments to make them spot on because they worked.
I've gone back through my pictures of when I was building the engine and I don't have any of just the machined base but these 2 will show how the rocker stud isn't centered on the boss, just like yours.
gbritnell

 

[arc]

gbritnell
That sure does look just like what I'm running into. You and John have set my mind at ease about this. Well I guess that I'll proceed on with my winter project. You guys are a great help. BTW nice looking machine work on your WP
Regards, Andy