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View Full Version : A return to HSS, figuring out angles again.



Deus Machina
09-16-2011, 02:08 AM
Alright, went outside and made an acceptable-for-its-use test bar from 01 drill rod to tram up my mill.

The carbide wouldn't cut well or leave a good finish, so I pulled out the old HSS bit I used to rough aluminum and plastics with, and it goes through like butter. Of course the actual finish is awful, but that comes later.

So, I've decided that until I can scrounge some better stuff off eBay and estate sales, to heck with carbide.

Now I just need to relearn how to grind the HSS, and for some reason I just can't find any material-specific info. So, what have you guys found to leave nice finishes on the basic stuff? Oil-hardening drill rod, mild steel, iron (always had a problem with those), stainless, brass?

I'm not too worried about roughing; unless the material is weird, my old extreme positive rake works well. And aluminum is pretty forgiving. But I've just never used much steel or brass before now, or never had an occasion to need a good finish on it.

Any tips?

Paul Alciatore
09-16-2011, 02:34 AM
Tips:

Steel: rake is usually best between 5 and 10 degrees.

Brass: less rake, 0 to 5 degrees, depending on the alloy. This is to prevent the tool from digging in.

Be sure to have a clearance angle on any tool.

DEAD SHARP is best. Use some oil or cutting fluid on the wheel to get a better finish on the tool while grinding it if you finish it there.

I use a small belt sander for the final touch-up on my HSS tools. Again, I use a bit of oil or cutting fluid on the belt to finish it up. After that I use a fine Arkansas stone, again oiled, to do a final polish. This stone can be used to touch up a slightly worn tool for several times before it needs to be completely reground.

Oh, and cutting fluid or oil will help with the finish when cutting most steels. Not sure about brass, but it certainly won't hurt there.

RussZHC
09-16-2011, 02:38 AM
As a noob, I have actually played around w this...if you want "definitive" answers look in the older books, Machinery Handbook, HTRAL, Lathe Operations etc., for HSS and angles all are pretty much the same. I just start by trying to imitate those drawings and then adjust until it does what I think it should be doing.

From my own, somewhat limited experience...for finish the "shear" type tool continues to work well (I don't think I have the angles quite exactly right yet...I have to locate it a touch low compared to other bits), nose radius plays a big role as that changes (or need for change of radius varies with feed and speed), brass seems to like more speed all around and definitely a sharper "point" but also seems more sensitive to keeping all the edges "razor" sharp (I hone more frequently and the polish helps ?)...
Sometimes odd events occur but I am not sure whether is material (no specifics of steels, it's bought at near scrape rates), fluke (the chance right combo of feeds, speeds and material...)
I've got one that I use to "rip" off rust layers, some heavy interrupted materials (rusty hex) and if I keep that one honed but without changing the angles much, in some steels you get a quite good finish as well...I got sort of an intermediate finish bit that I can move both directions with that I use mostly for getting near exact size and then use that shear tool for the last little increment
As Paul said, keeping things honed helps tool life A LOT, I have had only one "regrind" as what I had just was not working but I often finish the day by touching up on an oil stone any edges I used that session.

Oh, and I have gotten in the "bad" habit of using just a regular cheap grey wheel for grinding bits [bought and set up both a white oxide stone and a harder Norton synthetic (?) blue wheel and should be using them but too lazy to pull out that other, smaller, grinder ...except when I need a sharp, right angle corner as the grey wheels don't hold square corners well, or at least mine don't]

Dr Stan
09-16-2011, 08:58 AM
"How to Run a Lathe" by South Bend Lathe Works has a section on HSS tools. IMHO this is a "must have" reference book for everyone running a manual lathe.

Carld
09-16-2011, 11:50 AM
Using HSS I use 0 back rake and 5 to 10 deg side rake for steel for rough cutting and finish work but when I need a very fine finish near a ground look I use a shear cutting tool.

If you don't know what a shear cutting tool is ask me.

Tony
09-16-2011, 11:53 AM
If you don't know what a shear cutting tool is ask me.

That would make a great tshirt.

rythmnbls
09-16-2011, 12:05 PM
+1 on the shear cutting tool, the finishes are amazing.

Pic of some 4340 machined with such a tool

http://i87.photobucket.com/albums/k142/madluther/gtba/newshaft2.jpg

The only downside of the shear tool is, if the ultra fine swarf it can create gets into your skin, its very irritating.

Steve.

dp
09-16-2011, 12:22 PM
I'm not certain this falls under a shear cutting tool but i know it will take the toenails off a flea and leave a near perfect finish both on my shaper and on my lathe. It is the finishing cutter I refer to, second image down.

http://www.artfulbodger.net/docs/shaper/cutters/index.html

It will create a swarf curl as long as your cut, though.

vpt
09-16-2011, 01:47 PM
I spent a good amount of a day trying out different grinds mostly on brass. The shear left a nice finish even on my little atlas.

http://img243.imageshack.us/img243/7471/lathewood018.jpg

dp
09-16-2011, 01:52 PM
I just remembered Evan has some negative rake inserts that leave a mirror behind. I tried to find the thread but my Google foo has failed me.

EddyCurr
09-16-2011, 02:21 PM
I just remembered Evan has some negative rake inserts that leave a mirror behind.
I tried to find the thread but my Google foo has failed me.Is the thread you have in mind?


Machining dead soft aluminum against conventional wisdom (http://bbs.homeshopmachinist.net/showthread.php?p=460714) 2009.08.09

.

dp
09-16-2011, 02:28 PM
Is the thread you have in mind?


Machining dead soft aluminum against conventional wisdom (http://bbs.homeshopmachinist.net/showthread.php?p=460714) 2009.08.09

.

That's the one. Too bad it got bogged down in debate over angles. Whoops - never mind - it was a different thread that got bogged down over angles.

vpt
09-16-2011, 03:21 PM
Thats pretty neat!