Help with milling.

[Woz]

I'm hoping a member can provide me with some advice.  I'm starting on the bogstandard scrap box engine using an old widow sashweight for the block.  Being new to engine building I've never milled cast iron before.  My problem is that at the end of a cut the edge of the block is breaking off.
I'm using a 32 mm face mill with carbide tips.  Am I taking to big a cut (1.5 mm) or is the cast iron suspect? 

On the subject of carbide tips how much do the points wear before they need turning? 


Woz

[bogstandard]

Woz.

Cast iron has a very granular structure, and taking a cut of 1.5mm is more like hitting the edges with a hammer than shaving the granules off. I always use either a flycutter or a very sharp endmill, with a finishing cut of about 0.1mm.

As for the sash weight cast iron, I use it all the time for things like cylinders and blocks and have no problems at all with it. Just cut off the end with all the dross in it (usually about 3" long and the end opposite the hanging loop) and you end up with a very useable 12"+ length of well matured cast iron. The hardest part is the initial hard skin removal, and I normally do that on the lathe by taking a deep cut to get 'under the skin' and taking it off in one hit.

With regards to carbide tips, it is like asking how long is a piece of string. I have used some very good quality tips for turning that would need replacing in next to no time when cutting some materials, but would last for months when cutting free cutting mild steel. What really knocks them about is interupted cuts, that can take them out in seconds.

The plans only make suggestions, there is a chap making one at the moment using a brass block.

http://www.homemodelenginemachinist.com/index.php?topic=4294.0

John

[Woz]

John,

Thanks for the advice.  Looks like I'll have to stop being so enthusiastic with the mill.

Woz

[poodge]

Hi Woz(and John ).
I used a piece of said sash weight material for the block,and found it cut best with an HSS fly-cutter.If you don't have one,they are cheap to buy,or you can make your own.I don't believe carbide inserts are all that good at cutting finely grained material like cast iron.
I get rid of most of the hard skin and sand by running it against a belt sander.This makes an unholy mess,but reduces the amount of sharpening required.Try to make sure the final pass is a light cut,with a sharp tool,and slow speed.You'll be surprised by the smoothness of that piece of cast iron junk
regards.Hans.

[derekwarner_decoy]

Hi PD's ......'junk cast iron?'......I am sure others will support that Rolls Royce cast engine blocks & burried them in the ground for 10 years prior to machining

So from this I conclude stabilisation in the ground for an engine block possibly transdended neutral carbon from the ground   .......or did the window sill cast iron sash weight improve with age from the atmosphere ......

I suggest these are both true statements..... or ........was my teacher ....   ...I think not ....Derek

[poodge]

Derek,I'm not implying that cast iron is "junk",merely that it was bought as "junk",making it nice 'n cheap
I used to work at a tramcar restoration outfit,and when they received new wheels from the foundry,they were chucked outside in the weather to rust.Apparently this "ages" the iron,and relieves any stress in the casting.No doubt Rolls-Royce was using the same process.
Hence,cast iron which is in some cases likely to be a hundred years or more old,will be nicely seasoned.
I can't remember if it was John"bogs" that showed the trick of breaking your sash weight on concrete.If it's a slightly matte grey,all is well.If you can see shiny bits,be prepared for some problems.That's sand you can see sparkling .