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L6steel
05-02-2004, 01:13 AM
I bought a huge lot of hss endmills. Most are sharp and ready to go but I still would like to know how to sharpen them. Do you need a special tool? I have a belt grinder that I can put different grit belts on. Is it just a matter of keeping the mills square to the grinding surface? Thanks up front!!
Michael

CCWKen
05-02-2004, 01:51 AM
Belt Grinder? You mean belt sander?
Nope; That ain't gonna do it. Unless you have $500-$3000 to invest in a tool grinder, send them out. Even if you have the tool, it's easy to make scrap out of your end mills.

L6steel
05-02-2004, 07:01 AM
Belt sander, belt grinder, we call em grinders cause that's what we grind our knife blades and such with.
Why do you need a tool grinder to sharpen HSS end mills?
Don't mean to be stubborn, I'm just curious.

SGW
05-02-2004, 08:07 AM
You need to grind all the flutes equally, I'd say to within less than a thousandth of an inch variation, preferably better. Both on the ends and along the sides. You need to get the relief angles consistent, including along spiral paths. Maybe you can do that freehand -- I sure can't.

ibewgypsie
05-02-2004, 08:29 AM
I bought 30 pounds of endmills off ebay.

Most were useless. 1 3/4 mills.. Won't fit anything I have in the way of a kwik switch collet.

Some were sharpened like I have never saw any. they had straight lines of edge on them. I mean they were still sloping but not in the curvature that they once had.

Mostly, that money spent on surplus mills was wasted. It don't take many 1 1/2 mills to make 30 pounds.

David

Rustybolt
05-02-2004, 09:24 AM
<font face="Verdana, Arial" size="2">Originally posted by L6steel:
Belt sander, belt grinder, we call em grinders cause that's what we grind our knife blades and such with.
Why do you need a tool grinder to sharpen HSS end mills?
Don't mean to be stubborn, I'm just curious.</font>

I'll probobly get slammed for this, but accuracy is a problem with belt sanders.Because the belts are flexible it'd impossible too get an acurate cutting edge. No matter how tight you make the belt, it wants to ride up in front of the cutting edge.You want a setup thats as rigid as possible, with repeatability. The finish on the cutter is going to be the finish on the work.

G.A. Ewen
05-02-2004, 11:19 AM
Sharpening the ends is no great problem even with crude equipment. If you want to sharpen the flutes (which will reduce the size) that is a job for a precision tool grinder.

http://img4.photobucket.com/albums/0603/GAEWEN/4244e8a9.jpg

http://img4.photobucket.com/albums/0603/GAEWEN/066d2b88.jpg

L6steel
05-02-2004, 01:34 PM
Ahhhhhh, thanks guys!!!!
This place is fascinating!!!
Thanks for the pictures GA, I've never seen a tool grinder before. Now that I know what it is I'll start lookin for one.
Rusty, no slam here, you're exactly right!
That very thing drives me nuts when I'm doing certain tasks involved in folder making. Anything that you want ground exactly square is almost impossible on a belt grinder. I should have remembered that and seen that I would have gotten the same results with endmills.

spope14
05-02-2004, 01:55 PM
I have seen people sharpen end mills using a lathe tool post grinder and an indicator for the leveling of the ends. Even saw a rig with a Dremmel tool on a lathe. Worked fairly well.

I do have two "KO Lee" grinders, and they were a bit each, though one was actually given flat out to me with all the attachments. The other paid for itself in the first two years with sharpening student end mills.

I tend to use the pink 60J (i believe J) wheels - cup wheels, and a norbide to do general dressing (diamond dress when necessary).

I also have a new grinding rig given to me personally but ued in the school shop - SPG I believe is the brand name (will correct tomorrow if necessary). Actual cost of this rig is about 1K, and attachments are about $500.00. Wheels are for HSS or diamond (different wheels), and the AlOx wheels run about $26.00 each. I have done enough drills and reamers and countersinks to pay for this one if purchased about 20 times. It also sharpens end mills, and the beauty of this one is that they actually recommend NOT dressing but on extreme circumstances (which I found out after burning through 2 wheels, and ordering four more).

I do end mills for local HSM's and drills for local HSM's and shops in the area as a PR thing for the shop, and for the shops at min charge - usually tooling or material trade offs.

The key to all of this is accuracy. You can grind end mills or drills believe it or not on a hand pedestal grinder (ends on end mills)., but quality and tool life reuse will suffer. I have some end mills about 12 years old now, 3/4 size probably about .720 to .714 diameter (I retire when the rake starts to become neutral or negative on the flutes). I also do indicate each set-up for accuracy between flutes of ends to within .0003 or better, least chatter from cutting edges occur, or poor surface finish and uneven tool life occur (one tooth taking all the pressure, then dulling, and tearing occurs).

It is a skill, but a very fun and exacting skill to tool grind as I have found, and if you can ever get your hands on a small tool grinder - multi use (they sell these things at good prices used or new), it will be great.

Randy
05-02-2004, 03:42 PM
Typically the corners break down first, so just grinding the end back a bit is often enough. As GA said, that's not too difficult. In a pinch, you can do a passable, if half-assed job by off-hand grinding, at least with a 2-flute cutter. It's much like off-hand drill sharpening, but perhaps easier since you don't have to master that spiral hand motion. You need to maintain a 5* clearance angle, and a 2* center angle that's opposite that of a drill. I.e. the cutter is slightly longer at the points than the center. (Just maintain the original angles.) And as already stated, you need to keep the tips at the same length, though I think a thousandth or two is a reasonable target for most work. End mills don't drift from unequal tip lengths as badly as drills do. It's pretty hard to keep the proper geometry at the center of the cutter by off-hand grinding, so you may not want to plunge with a hand sharpened end mill. (Actually, with a 3-flute cutter only one flute is center cutting, so you might get away with it there.)

As I said, off-hand will work in a pinch, but you can buy, or make, a fixture for grinding the end at a reasonable price. Here's the fixture I made:
http://img7.photobucket.com/albums/v21/rykrisp/End_Mill_Fixture.jpg

Here's a similar item on e-bay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11805&item=3812750277& rd=1&ssPageName=WDVW (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11805&item=3812750277&rd=1&ssPageName=WDVW)
Most industrial tool suppliers sell them. Mount one on the milling machine table with a small grinder on the spindle head (I've used my tool post grinder) and you've got a servicable end mill sharpening setup. HSM magazine has had a couple of construction articles over the years.

Grinding the sides of an end mill is a whole 'nuther kettle of fish, but plenty of HSM's do that too. You need to do that if an edge is nicked, or you want to re-size a cutter. One of the projects on my to-do list is an air-bearing sharpening fixture that
was written up in HSM many years ago. Grinding bull-nose or ball-end cutters is more advanced yet. (Though I've turned a lot of flat end mills into non-critical bull-nose mills off-hand. That's a good way to use cutters with broken down tips.)

[This message has been edited by Randy (edited 05-02-2004).]

Joel
05-02-2004, 03:50 PM
Mill cutters have to be precisely ground to work worth a squat.
You aren't likely to find a grinder like GA's, its a one off he made himself. If you are good, you can hand grind the end (as was said) on a bench grinder. Carefully true up the wheel first though.



[This message has been edited by Joel (edited 05-02-2004).]

ibewgypsie
05-02-2004, 03:59 PM
I got a full plate right now,

Would it be pretty easy to write Gcode to turn a mill in a indexer according to sideways movements? A cnc sharpener?

It'd require a different program for each spiral different type mill.

Since helical milling is normal in most cnc programs that looks like it'd work to me.

David.

CCWKen
05-02-2004, 06:33 PM
Wow GA! I like the grinder setup. I know what I'm going to do with the saw I picked up at the salvage yard. http://bbs.homeshopmachinist.net//biggrin.gif

I knew it had a use when I saw it. (pun) I just couldn't pass up the nice compound table and figured some day I'd find a use.

Thanks for posting the picture!

Ken

DR
05-02-2004, 08:46 PM
"Would it be pretty easy to write Gcode to turn a mill in a indexer according to sideways movements? A cnc sharpener?"

Have you guys noticed that for the last few years most better quality end mills have the pitch of the helix stamped on the shank along with the size, etc. This implies a good deal of the sharpening now is done on CNC machines. I know some of the better sharpening shops even re-flute the end mills as part of their regular sharpening procedure.

sidneyt
05-02-2004, 10:48 PM
If you are a beginner HSM I doubt is worth the trouble or expense to sharpen your own end mills unless they are very expensive to begin with. When you can buy end mills for less than $10 each (most of mine cost less than $5) it really doesn't make a lot of sense to even get them resharpened. I save my old end mills for some future use.

I was interested at one time in building a Quorn grinder that can be used to resharpen end mills (an other tools) but the cost and time to make a Quorn just doesn't quite compute for me. I think I would rather spend my time making other stuff like model engines. You can buy a tool grinder like the one that HF sells for $600, but I wonder how long it would take to pay for itself at the rate I use end mills, reamers and other tools that I might sharpen with it.

Why don't you try sharpening a couple of your new end mills you just purchased using your belt grinder and report back to the group. I would be interested to hear how it works.

Gerryrig
05-03-2004, 12:26 AM
For HSS end mills, I true up the end. Then reshape the end using a Dremmel cut off wheel. I find this easier under a magnifier light. Next chuck it in the mill and touch it down lightly onto a diamond hone to true up the cutting edges and then finish up the cutting edges with a diamond file or oil stone under the magnifier. Takes about 20 min or less. Most work fine. If not, redo the mill step and touch up once more.
Gerry