Best strategy for milling top of large steel piece

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rronald

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I'm cutting a plinth for a solid lathe toolpost to replace my compound (at least for most of the time).

It's a big chunk- 6"x6"x2.5" of A36 steel. About 25 lbs.

I started with a HSS 4 flute cutter to take enough off the sides to square everything up. Didn't work too well (my speeds and feeds were too aggressive and I don't think that my mill is rigid enough for side cutting 60 mm high). But, I had a fairly short 12mm carbide roughing bit that goes thru it like butter. That bit is too short (about 25mm of cut), but I've got some longer roughers on the way. So I feel like I have a good strategy for the sides.

Top (and bottom) are giving me trouble. I've been trying to use a fly cutter with a carbide insert and it sounds horrendous. Finish isn't bad, but I'm afraid to remove more than about 10 to 15 thousandths per pass. Plus, it throws chips all over the place. Mostly in my direction .... regardless of where I choose to stand.

I've got another 1/8" of material to remove from the height. Is there a better strategy for the job....one that wouldn't sound like the mill is beating itself to death....and would be less vigorous in throwing "needles of death"?

Perhaps a smaller diameter cutter that traded off more DOC for less WOC? I have a 1-1/4" 3-insert indexable end mill that I could try.
 
A bandsaw would be the first step in this case. Cut out as much as possible way quicker. Then a face mill would be my next choice. If no facemill I would use the largest endmill. Once semi flat then I would fly cut the surface taking less than .005. Most likely .001 or .002 going for surface finish here.
Once you have one side to your liking then flip and repeat the process. After them two sides are where you need them flip it 90*. Rinse and repeat.
In my experience taking more than .010 off on a fly cutter is using the wrong tool for the job.
 
I would also advise moderate to low DOC on flycutting for best results .
Sawing and drilling are the fastest methods for material removal. Generally, facemills of larger diameter are next fastest , then endmills , then flycutters in that order
 
A cold saw would be even better if one is available. Tolerances of .001" to .002" are achievable on production runs of hundreds of pieces. If you're really careful and patient .0005" isn't out of the realm of possibility. In many cases the cuts are more accurate than most mills can achieve. A new one will cost a mere $8,000.00 to $12,000.00. Or you can resurrect one from near death at 1/10th the price.
 
Flycutting steel is horrendous unless you have a 5 ton machine to do it with. Large cobalt or carbide endmill is probably best
This type of job is what large horizontal mills really excelled at in the old days- that, or a big shaper
 
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Carbide inserts with generous radii can be employed, although interrupted cuts can be hard on carbide. If the DOC’s are kept reasonable it can work
 
I usually skip the fly cutter and just use an endmill. My mill isn't trammed perfectly but the steps barely catches a nail. Use the magic sanding block to finish the part.
 
Why are you doing that on a mill? That's a lathe job.

Every single mechanic around here has a lathe and not all of them have mills exactly because of that. Most jobs are just facing off stuff and that, not cutting complex features. And that is not only done easier on a lathe; it's just a lot cheaper, too.
 
Yes I agree but not everyone has a lathe that can accommodate that size of a workpiece,
 
I'd vote for lathe first (if the piece fits). If not, mill it close to size with the end of your rougher. Roughers typically leave a pretty good finish on the face. Flycut for a final finish.

GsT
 
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