Milling cast iron in the lathe

[jgb7573]

I'm in the process of machining a base for a stationary engine. I've got it mounted on the vertical slide and am using a 3/8" end mill in the three jaw. I'm machining the edge to get it square (or rectangular, since that's the shape it's meant to be), and made of cast iron.

My problem is that the corners of this base seem to be hard. Very hard. Just the first 1/8" or so in from the corner, then the rest of the edge machines fine. But those corners! I've done for one cutter, trying progressively lower speeds and feeds but with no success. Before I gather up the courage for another go, does anyone out there have any better ideas than me for dealing with things like this?

I'm using a 3/8" end mill, 210 rpm, depth of cut 10 thou and a slow feed.

Thanks,

John

[mmaidnz]

Could you start in the middle and work towards the corners?
With castings it can be a lottery how many hard spots you get.If possible ,I also grind the roughest bits away with an angle grinder.Then you need the first cut to be as much as your mill can handle,to get under the "skin"of the casting.

[mutley]

Hi John
You've got hard spots in your castings normaly caused by rapid cooling out of the mould. I have known some people have sucess by heat treating the castings first but ultimately you may need to get yourself a carbide cutter to have any real sucess.
Andy

[Jo]

It may be worth starting with a hand file on the corner to get under the skin to avoid too much damage to your cutter.

Jo

[SteveW]

John,

I had exactly the same problem a while back. As a big fan of fly cutting I was using a bought (Chronos) fly cutter that came will HSS tools. The tool was gone before I'd completed a pass.

I asked on the previous incarnation of this group about the viability of using a TCT tool and everyone said it would fail, "TCT won't stand the shock loads of fly cutting". Shortly afterwards I was at a stand and three quid away from buying a right-facing TCT tool that would fit the holder.

Back home I fitted the new tool and have never looked back. The nice thing about fly cutting is you can avoid having to manage the multi-passes with a narrow tool. Also, using a diamond lap you can restore the cutting edge to a TCT lathe tool and thus re-life it.

[houstonceng]

Steve

I use a 3/8" LH Facing tool with TCT in my flycutter and, as the well known soap advert (and LBSC) said, "Since then I have used no other".

Doesn't seem to mind the "impacts".

BTW. The tool that is usally meant to be in a lathe toolpost cutting towards the tailstock is a LH tool (OK. I know Chronos and others list them as RH - but they're not.)

You need a LH tool because the Fly-cutter is designed to rotate CW (as per normal drilling).

[SteveW]

Andy,

I confirm that my TCT fly cutting tool is for cutting towards the tail stock.

When I announced my breakthrough with TCT and debunked the "it'll just break" issue someone did provide a lot of detail on their development and that I was OK to abuse it thus.

[jgb7573]

Thanks for all the suggestions guys. Since theedge of the base I'm machining requires profiling (for some reason it has quite a fancy shape) I want to stick to an end mill. Given my 3/8" one is NBG any more, I've ordered a solid carbide one and will give that a try when it arrives (this weekend if it gets here on time - after we've moved house if it doesn't). Nearly twice the price of an HSS one, but if it works...

Sounds like flycutting is going to help on other parts of the base though - and I have a 'cuts towards the tailstock' inserted tip tool to try.

[Shawki Shlemon]

Hans have a look at my thread on boring cylinders between centres which include some photos and may be it will be of some help to you .Good luck.

[SteveW]

John,

A point on TCT end mills: I met an old chap while viewing the JB Tools stand and I asked him if they were any good. He said he bought one or two of their TCT end mills each visit and they lasted him all year. I've been buying odd ones ever since and yep, they were cheap and very useful.

The only down side is they're mostly straight shank types, some double ended. With this in mind (straight shank tooling) I bought an ER32/R8 chuck and later an ER32 chuck for the lathe. This gives me collets for 2-20mm. This gets around the slight disadvantages associated with using cutting tools in the lathe chuck.

[chameleonrob]

stevew said:

A point on TCT end mills: I met an old chap while viewing the JB Tools stand and I asked him if they were any good. He said he bought one or two of their TCT end mills each visit and they lasted him all year. I've been buying odd ones ever since and yep, they were cheap and very useful.

they're even better if you can't resharpen HSS cutters, altough they can be fragile. I've got a couple which I'm trying.

rob

[jgb7573]

Success!

I took the base down to the club on Friday night, and someone said why not anneal it? Having nothing much to lose and no carbide end mill yet, we fired up the forge, brought the base to red, covered it with hot coals and kept it there for 20 minutes or so and then just left it in the fire to cool down. When I retrieved it the next morning it was nearly cool enough to hold and filthy. So out came the gloves and wire brush.

There was a bit of distortion which I eased a bit by clamping between two metal plates over night on Saturday. I'm not convinced it did a lot of good, but I was told to try it. In the end I had to clean up top and bottom again on the faceplate because it wasn't quite as flat as before, and then it was time to try milling. And the results were good! Although the corners were still tougher than the rest of the edge, at least an ordinary end mill now coped with them OK, and machining is now possible.

So if I hit something like this again, at least I know something to try.

Thanks for your suggestions guys. I should also now have a carbide end mill and I like new toys!

[lancelot]

Finally got time on the keyboard again...will have to make time to do some work in the ''SHED'' myself...All the castings I have worked on with the exception of the ''Peter Southworth'' ones were ''Stuart and Turner''...now they had a very limited allowance for machining in most cases, so all my tooling was Tugsten burrs or cutters, skin was tested for hard spots with a file and where necessary eased on the linisher or by the dremel and tugsten burrs or files...end mills were a heavy duty 3/8 tugsten and a 3/4''... the idea of ''Heat Treating'' the castings although it usually works most of the time, unless there is a large allowance for machining if it twists...the casting is going to be useless.
Peter Southworths castings were a different ball game...as I did not have to strictly adhere to a ''finished'' size for the ''footprint'' of each base casting I was able to be a little more liberal with the machining leaving the ''drawings'' for a while and working freelance so to speak...but everything fitted together just so...
All the best for now,
John.

[dscott]

For roughing out on the mill or lathe, I have used a boring tool held in the 3 jaw chuck. later going on to a carbide one and the latest being a replacible tiped one, held in the 4 jaw you then have it adjustable and can open out holes in frames etc. They give a lovely finish.

David.