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Machining Castings

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James B11/07/2009 22:11:12
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101 forum posts
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Hi, 

Have been working on a Stuart 10H, in particular the soleplate.  When machining the castings, there seems to be hardspots in the casting - some areas cut nicely but others don't. 

For example, when I tried to machine the top of the crank bearings, I used a brand new end mill, and also tried a new slot drill. It was rigidly set up on my Mill, and I checked the speeds to use (around 500 rpm for 7/16 cutter?). I took the lightest of cuts first of all, but both cutters were blunted almost straightaway, and it just sounded wrong - cutters rubbing / squealing. After abandoning the job, I tried to file the casting roughly down to size, but it was like filing hardened steel.
 

Am I doing something wrong? Should I be preparing the casting in some way before machining? Do castings vary, i.e. could there be hardspots in it?

Any help gratefully received...! 
Charlie,12/07/2009 00:32:44
76 forum posts
1 photos
Hi James,
                  Your problem with the aparently hard casting might be that your first cut is not deep enough,In a manner of speaking you need to get under the crust,
Richmond12/07/2009 00:37:51
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64 articles
Hi,
 
Charlie is right, cast iron castings need ( usually ) approx 1/16 cuts to remove the crust.
 
However, Stuarts castings are usually quite good with regard to chilled / crusty spots. If this problem persists I suggest you contact them and ask them to replace the casting.... they have done this for me in the past
 
Rgds
David Clark 112/07/2009 00:38:07
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3357 forum posts
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Hi There
I have just machined one with no problems.
No hard spots at all.
Try putting a small chamfer on the cutting edge.
regards David
 
JasonB12/07/2009 07:25:06
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25215 forum posts
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The tops of the bearing brackets are probably the most likely part to get chilled as they are thin they will cool faster than the rest of the casting, though Stuarts Castings are usually good.
 
Another option is to anneal the casting, if you have an open fire or wood burner put the casting in there for a few hours and then leave it to cool in the ashes overnight.
 
A carbide tipped tool in a flycutter may get teh skin off if you can't get through it with a deeper cut using a milling cutter.
 
Jason
David Clark 112/07/2009 08:51:26
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3357 forum posts
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10 articles
Hi There
You can't take 1/16 of the Stuart bed plate castings or engine base.
There is barely 10 thou on each face.
I will put some photos in a gallery a bit later today.
I have started a Stuart 10H and 10V recently and am photographing it as I go.
It will appear in Model Engineer over the next few months as a beginners series.
regards David
 

 
James B12/07/2009 11:43:10
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101 forum posts
14 photos
Thanks all for your advice, I will give this a try, going deeper with the first cut. With the chamfer on the cutter, do you mean the actual cutting edge of the slot drill / end mill, or around the 'circumference' of the cutter?
 
I look forward to the series on the 10H / 10V - will be interesting to see how certain operations are approached, compared to how I have done.
 
Thanks again.
Circlip13/07/2009 12:33:04
1723 forum posts
Yes James, the circumferential corner. Although you end up with an internal chamfer between the vertical and horizontal faces, it is kinder on the cutter.
 
     Regards   Ian.
David Clark 113/07/2009 21:47:02
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Hi There
I have posted some photos of machining Stuart 10V and 10H parts.
 
regards David
 
James B14/07/2009 17:20:20
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101 forum posts
14 photos
Thanks David,
 
I would be interested in seeing the soleplate setup as well (for the 10H) as this seems to be the part with the most setup requirements (at least on my equipment).
 
Thanks.
 
James
David Clark 114/07/2009 22:09:52
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3357 forum posts
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Hi There
The 10H bottom was done exactly the same as the 10V.
Just make sure you remove any flash from inside the casting and it should be fine.
 
regards David
James B15/07/2009 09:23:00
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101 forum posts
14 photos
Hi David,

Sorry, by soleplate, I was referring to the part that sits on top of the base, which provides a mounting for the cylinder and crank bearings..?

Thanks

James 
David Clark 115/07/2009 09:38:56
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3357 forum posts
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10 articles
Hi There
Have not done that part yet.
I have done the underside but that was with a file.
 
Although I machined the underside on a previous engine, I thought I would use file and wet and dry to see what results I got and they were excellent.
 
I might have photographs of the last time I machined one.
I will see if I can find them.
 
regards david
 
David Clark 115/07/2009 11:28:31
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3357 forum posts
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10 articles
Hi There
More photos added.
Some of these were taken several years ago with a low resolution camera.
regards david
 

 

 

Edited By David Clark 1 on 15/07/2009 11:32:11

James B16/07/2009 13:15:01
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101 forum posts
14 photos
Hi David,
 
Thanks for the photos, these have helped a lot. I am looking forward to the series in the magazine - just useful to see methods used in tacking different operations, which can be applied to other projects.
 
Thanks again.
 
James
JasonB18/07/2009 19:34:30
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25215 forum posts
3105 photos
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I was speaking to someone today who machines  a lot of Stuart models and he said that all the 10 H & V base plates he has done recently are chilled and he anneals them before doing any work on them as a matter of course.
 
He is just completing the Major beam and said every casting was chilled and he has spent over £200 on tooling thats be blunted on this model alone.
 
So it does not look like you are doing anything wrong James
 
Jason
Tel18/07/2009 20:52:03
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157 forum posts
28 photos
Despite their reputation, Stuart castings can be pretty variable. My 10V castings (1980) were beautiful to work while the Stuart Beam (1990) were, to be frank, 'orrible. The cylinder casting, for example, was good one and and like trying to cut diamonds on t'other.
Albert19/07/2009 16:13:30
6 forum posts
Hello all,
  If I get a suspect hard casting I give the part a going over with my hand 4" grinder to remove the skin,and run a milling cutter at less than 100rpm.
  If possible I will use a fly cutter with a carbide tip rather than a milling cutter.
Albert
mike robinson 224/07/2009 14:26:10
38 forum posts
32 photos
All
I have started on a Stuart No9 and had trouble with 2 castings, the steam chest cover plate which hard pearlitic? corners and the bed which had the same problems around the mounting lugs. Its just rapid cooling of the casting in the smaller areas. The 8 hard spots ruined 2 HSS mills and took the tip right off a carbide insert tool. I cooked it in a multi fuel stove (wood) at cherry red for 5 hours and in the morning it was still warm to touch. Even so it was still impossible to cut. Having given up I ordered replacement castings from Stuarts and I was delighted when they shipped the replacements without charge. Thats good service. 
Mike  

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