Help with countersink

[gumba]

I'm trying to countersink a 7/8" diameter hole in the back of this wheel hub in the slanted section. It will be approximately .200 deep from the high spot. I used a 2 flute hss center cutting end mill. I tried plunging first, not much luck. Then coming in from the side taking a .025 pass. Though at this point I believe I already ruined the end mill. I've got 10 counter bores to do. I'm brushing on cutting oil as I go. I'm a hobbyist using a PM30LV mill.

My questions before I order another end mill.
What is the best approach, plunging or from the side?
Should I be using a low or high speed.
Would a colbalt end mill be better than the hss?
thanks,
Harold

[flyinchips]

I'm willing to bet that your problem is lack of support, not how the material is approached by the tool. That thing looks like a nightmare to hold without vibration. You need a hold it better than what I see in the photos. You might have to build a fixture to do your one off job. It takes time, but in the end you'll get the job done without broken tools.

[ad64075]

It looks like your thru holes are welded. Please tell me you are not trying to cut thru the weld???

First, you should pilot the hole with the maximum size drill possible. This will help relieve tool pressure on your countersink tool.

Secondly, run your countersink tool at a very low rpm. This will reduce or eliminate any vibrations and therefore eliminate the need for fixturing. Assuming your material is normalized cast iron, around 25 sfm or 109 rpm should be good.

Lastly, HSS or M42 won't matter much for 40 or 50 holes. You're not asking much from the tool.

Good Luck!

[RICHARD ZASTROW]

Is that a build-up of weld? If it is, that could contribute to your problem.

Dick Z

[gumba]

I'm not trying to cut through the welds. I'm drilling new stud holes in the angle section of the hub. I drilled a 9/16's dia. hole for the stud first. I'm trying to counterbore the angled part of the hub to get a flat surface for the stud head. The hub will be solidly bolted to the table, not the 3 jaw chuck. The chuck couldn't hold it, which I think was part of the problem. As well as trying to plunge instead of coming in from the side.

[H.A.S.]

I would come in from the side and use low RPMs. When milling castings, it's best to get under that scale as much as possible in the first pass.

[Valimarsbro]

carbide endmill and helical interpolation is all what will work. and make the thru hole while you are at it. email me at trblancha@gmail.com and will give you advice and a program free. if your mill wont do 3 axis? have other solutions depending on tolerance.........