Why Am I Unable To Plunge Cut A Bronze Casting

Sorry, a Sherline? You should have a rigid machine when using carbide. Any unwanted movement and carbide is not forgiving, it will break, especially a 1/8” end mill. Maybe try Cobalt instead…Dave
 
I have had some PM research cast iron that was impossible to drill. Try moving the table at the same time you are starting the plug cut. It may allow the tool to start to cut. Once at one end move back the other way as you do the plunge. This may also break through the skin of the casting which is harder than the rest of the metal.
 
I remember milling a steam chest that had a pocket about .25 square and .100 deep. Or was that the valve itself. Maybe that was it.
 
I wonder if it's possible to find out from PM research what type of bronze they would be using for said casting? If they know and would tell you, there might be some peculiarities about machining it. As others have said and I agree, there are a number of different types that go under the bronze heading. The only one I know for sure to have worked with is 660, and it was a pleasure. I would be interested to know what this troublesome one is.

-frank
 
You said you did drill a small pilot hole so the material is machinable. I would drill the pilot hole ( if possible ) the depth of the flat bottom hole
you want and then plunge. Maybe drill 7/64" and leave a little side clean up.
Art
 
I will post a picture of the part and the mess I have made, once I have taken the photo.

Although Sherline's aren't super rigid, they are fast (2700 rpm) so I am hoping that speed plus carbide will help. Of course, I might just melt the bronze and break the tool!

I have sent an email to PM to ask about the type of bronze they use and what they recommend. I am sure they will answer.

Overall, I am really frustrated with this model. It's not PM research's fault, but my own ignorance. I am going to spend the next couple of workshop times filing the rough castings and pondering if this is just a bridge too far.

Cheers,

Tom
 
tom, Doe it seem like the same as the stuff on #7. The other thing is to watch once it starts it may and take off and want to go quick. Another can you use a bigger end mill to cut the center of the box and then the smaller one to finish it off.
Ken
 
Ken,

It seems like the same stuff, but I never tried to plunge mill on the other engine cylinders (just regular milling, boring and drilling). And when I did regular side/surface milling on this part it seemed to go okay. I agree that it can be grabby (but much less than brass). Definitely don't want to down-mill it, particularly with mini machines like Sherline. The part just doesn't seem that hard, but man is it giving me fits.

I am loathe to dull my other end mills, so I am going to wait for the new tooling.

I hope your progress on #7 is going better.

Cheers,

Tom
 
Right now I am waiting for some hard 5-40 screws that I can put in the lathe and make me 6 of the things to locate where to drill the holes in the new casting so that they exactly match the cylinders. So I started making me an additional tool holder for my QCTP, But had to do the chores first, Mow yard etc, now down with the back spasms and shooting pain. will try to get back at it tomorrow. Oh, are you still wanting socket head cap screws for your #7, Found a place to order them, Stainless and not real expensive. Let me know and I will send you the link.

Ken
 
Take one of your "dull" endmills, and stone or use a diamond file some negative rake on the cutting edge. At this point you have everything to gain.
 
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