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Cast Iron cutting depth

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Sam Longley 118/01/2016 18:21:39
857 forum posts
30 photos

I know that when one machines cast iron they have to get below the case hardened skin.

However, I am about to start machining a cast iron Stuart 10V & the feet of the stand seem liable to cracking off

So the question is :- How deep does the first cut have to be to get beneath the skin & how deep can one go with a small item like the 10V stand before one is likely to snap the legs off

Rik Shaw18/01/2016 18:48:39
1449 forum posts
396 photos

You first sentence assumes that iron castings have a tough skin. Not necessarily. If you are unlucky you may experience "chilling" (extreme hardness) in your casting in which case you have the option to return the casting to the supplier and ask for a replacement.

If you have any doubts simply run a rough file across the feet. If the file does not skid of then the casting might be perfectly OK. Rather than look for imagined problems I would simply attempt to machine the casting normally. I would think that a first cut of 1/16" deep should do the trick - material allowing that is.


Martin Connelly18/01/2016 18:53:01
1844 forum posts
195 photos

You can remove the skin with a belt sander or a grinder with a gentle touch if you have one then minimum machining to get the surface flat. If you have a carbide cutter this will tackle the skin better than hss. The depth of cut will depend on how flat the surface is to start with. The skin may be 0.5mm thick but have a height variation of 1mm depending on how well the casting has gone.

It is often only the edge that causes a problem, once past that the machining goes easily. Once you have experience you will not worry too much about it in the future. If you have a fly cutter and a lathe do you have a carbide tipped lathe tool you can put in the fly cutter? Otherwise a carbide end mill or slot mill will do the work but may take more passes.


Neil Wyatt18/01/2016 19:01:37
18721 forum posts
727 photos
80 articles

Just enough that the cutter cuts, rather than rubs over the surface.

If you are doing them in the lathe bear in mind the diameter is quite large, so don't over do the rpm and take care not to feed the tool across too fast.

Relax and take your time and it will be a relaxing exercise, not a nerve-wracking one.


JasonB18/01/2016 19:12:37
21280 forum posts
2415 photos
1 articles

As Stuarts Castings are quite tight on material I would be carefull about taking too big an initial cut as you may not have 1/16" material to remove in total

If you are using your new carbide tools then they won't be bothered by any skin and should also cope with any possible chilled extremities

Contary to what Neil says I would say that the bits on a 10V are quite small and I find the variable speed lathes are better run slightly faster with a shallower cut than slowly with a deep cut. I'd be going about 4-500rpm with 0.5-0.7mm depth of cut (subjext to how much metal needs removing as above)

Edited By JasonB on 18/01/2016 19:18:05

KWIL18/01/2016 19:25:51
3410 forum posts
66 photos

If it is chilled more than a very small amount send it back. The Foundry is at fault, too much hurry to get the cast out of the sand without allowing it to cool whilst still thoroughly covered.

David Clark 118/01/2016 19:30:17
3357 forum posts
112 photos
10 articles

No more than 10 thou on a Stuart casting. They are very close to size. Use an end mill with a 45 degree chamfer on the teeth. This will spread the load and protect the bottom edge of the cutter from any hard spots. You can put the chamfer on by hand, they don't need to be exact.

Edited By David Clark 1 on 18/01/2016 19:32:32

mechman4819/01/2016 09:51:29
2930 forum posts
460 photos

I have a Stuart 10v to start this year; having read most of other posters methods of machining the stand, all seem to set it up on the lathe, has anyone machined the stand on a mill, as I see it providing the casting flash is taken off & the stand is set up vertically, cross braced, & fastened to a decent angle plate it would be just as easily machined on the mill, has any one done it this way, the only point of concern I see is to ensure that the stand is set up vertically in both X & Y axes so once the feet have been machined the cylinder top face will be machined parallel to the feet, or vice versa, the same would apply to the box bed & sole plate, if so any one have pics of their set up ?


Edited By mechman48 on 19/01/2016 09:55:23

JA19/01/2016 10:35:01
1214 forum posts
73 photos

Slightly off topic - Before taking any cuts or trying to clean surfaces check all the casting dimensions against the drawing. That will tell you how much material you can play with. More importantly it will tell you where the casting has deviated from the designer's intent, that is undersize. Then you do have to do some thinking. I have a set of model castings supplied by a reputable firm that are undersize. I have put them aside for present but will make the model once I have redrawn it. I doubt if you will have such a problem with Stuart castings.


Donald Mitchell19/01/2016 12:30:53
90 forum posts
3 photos

Sam, there is a (very long winded) build diary of a Stuart 10V on YouTube. So far he is up to about part 54. Very slow going but maybe some good information for you on the builid of this engine.

Donald Mitchell
Bonnie Scotland
JasonB19/01/2016 13:20:39
21280 forum posts
2415 photos
1 articles

I would prefer to do the "A" frame on a lathe so you can bore the trunk guide with power feed, unless you have a mill with auto quill feed. Even teh much larger Tidman that I have just completed I still did the feet and cylinder mounting flange on the lathe

mechman4819/01/2016 17:09:16
2930 forum posts
460 photos

Watched Tinker Johns video on his S10V build; as you say long winded but confirms my original question. I did notice one of his videos where he tried the lathe method & the stand flew out of the lathe, not much to grip on the cylinder mounting flange & obviously too much of a cut put on. IIRC I did see another version where the builder had made a plug to fit the bore & had a drawbar pulling it back into the chuck face, so there is more than one way to skin the proverbial...

Sam Longley 119/01/2016 17:38:10
857 forum posts
30 photos
Posted by Donald Mitchell on 19/01/2016 12:30:53:

Sam, there is a (very long winded) build diary of a Stuart 10V on YouTube. So far he is up to about part 54. Very slow going but maybe some good information for you on the builid of this engine.

Donald Mitchell
Bonnie Scotland

Yes - Thanks- I have seen the video & whilst it is very good the chap does go on a bit--- as do a few others-- Just wish they would get on with the machining

But informative all the same

I also have the book by Andrew Smith on building the 10V which, having bought at the show, I have not read yet

Edited By Sam Longley 1 on 19/01/2016 17:50:29

Bruce Edney19/01/2016 19:02:29
161 forum posts
53 photos

Harold Hall as a series on his web site for building one of these here


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