Wall finish with reduced shank end mill

cosmos_275 · Jul 9, 2018

I'm making a part with a 2" tall wall and I'm using a 3/8" maritool reduced shank end mill to finish it. The finish looks good, but I can feel small edges left by each pass with my fingernail. I can get them out with the buffer, but I'm trying to figure out how to use this thing.

I'm taking 5mm pass depths, leaving .005" from the rougher. RPM is 3000, feed is 800 mm/min (31 IPM, chipload is 3.5 thou). I bumped it up to .010" stock left and 7mm depth passes, but that didn't help. The LOC on the tool is 3/4". Seems taking more would be more deflection, so more edges. Any advice is appreciated. Material is 7075. Thanks

doug925 · Jul 9, 2018

1) leave less for finishing
2) semi finish the corners first, then finish mill the entire ID
3) shorten the projection of the tool in the toolholder
4) grind off the sharp edge where the flutes meet the reduced shank

If all else remains the same, try spring passes at different depths.

Bobw · Jul 9, 2018

Is it the top of the flutes, or the bottom of the flutes causing the ridges??

I'm assuming this is a square corner endmill? I'd toss some small rads or chamfers on the
corners for starters.. Hard to tell without seeing it and feeling it myself.

DMF_TomB · Jul 9, 2018

CosmosK said:
I'm making a part with a 2" tall wall and I'm using a 3/8" maritool reduced shank end mill to finish it. The finish looks good, but I can feel small edges left by each pass with my fingernail. I can get them out with the buffer, but I'm trying to figure out how to use this thing.

I'm taking 5mm pass depths, leaving .005" from the rougher. RPM is 3000, feed is 800 mm/min (31 IPM, chipload is 3.5 thou). I bumped it up to .010" stock left and 7mm depth passes, but that didn't help. The LOC on the tool is 3/4". Seems taking more would be more deflection, so more edges. Any advice is appreciated. Material is 7075. Thanks

.
if you use toy size tooling you will get toy size problems.

riabma77 · Jul 9, 2018

In my experience (plastic and aluminum), those reduced shanks aren't good finishers.

Why don't you use a regular end mill with 2" LOC? I would go with a 1/2" or 12 mm diameter.

Destiny Viper (in inches) or Fraisa (in metric), are my favorite finishers.

cosmos_275 · Jul 9, 2018

Thanks for the help.

I think the wall itself is part of the problem being thin.

I think it's the top cutting edge making the ridges. I will try grinding them down.

BALNH · Jul 9, 2018

Don’t use a sidelock holder as any runout will be noticeable between depth cuts. Use a nice quality hydraulic em holder or collet chuck. Unless you are burying the tool in corners, I would use more of the flute length .5-.625 dp depth cuts. Leave less material for smaller finish pass and add spring pass at every depth.

Mike1974 · Jul 9, 2018

DMF_TomB said:
.
if you use toy size tooling you will get toy size problems.

Or maybe since you always bring up making your 10000000000 ton castings you are compensating??

To the op, nothing to offer that hasn't been said...

cosmos_275 · Jul 9, 2018

BALNH said:
Don’t use a sidelock holder as any runout will be noticeable between depth cuts. Use a nice quality hydraulic em holder or collet chuck. Unless you are burying the tool in corners, I would use more of the flute length .5-.625 dp depth cuts. Leave less material for smaller finish pass and add spring pass at every depth.

"spring pass" is new to me, sorry for the ignorance. I suppose that means run it twice, once for deflection? I reordered the leave material behind it (wall is just over 1/4" thick) and that did not help. Thanks

mhajicek · Jul 9, 2018

Yes, that is what "spring pass" means. I always run two or three passes for critical dimensions. Contrary to what some say it does remove material; a spring pass can shave tenths off of 17-4 H900.

Rick Finsta · Jul 9, 2018

Yes, that is a spring pass. I found using that exact same tool to finish a 2.75" deep 6061 wall of about the same thickness I needed to take spring passes, at different depths than the first passes, as mentioned earlier. Everything cleaned up nicely. I found I had to really give that cutter a chip load using an ER32 9mm collet to keep it from chattering at longer stickouts. If the internal radii allow I would use a larger diameter cutter with longer flutes, but of course that is dependent on the geometry you need to achieve.

cosmos_275 · Jul 9, 2018

The spring pass helped on the thicker of the two walls, although I didn't vary the pass depths. I will try that next time along with breaking the upper cutting edge. Thanks all.

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