breaking woodruff cutters

A fella needs a couple woodruff keys cut on a shaft for his combine. Its NOT
an option to break my only import Enco grade cutter on Saturday afternoon.
I have broken many cutters in the past and I wonder if I need a better
technique. My problem has allways been with the cutter catching at nearly
full depth and then snapping right off. I do this in the old manual
bridgeport, lock the gibs on the X axis and feed extremely slow on the Y by
hand. Low RPM, maybe 200, don't remember for sure. Squirt bottle oil
coolant/lubricant.
Should I maybe run the RPMs up? Do somethig other than just plunge in? Not
buy that el cheapo import tooling? (won't help for today)
Reply to
Karl Townsend
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let me know if you need a big woodruff key cutter that cuts 5/8" keyways.
i
Reply to
Ignoramus5411
Do you have chatter before it breaks? The cutters do have a relatively thin shaft and if the cutter is near the end of cutting, it has a lot of teeth cutting at the same time. You could move back/forth a bit along X to to reduce cutting forces. It isn't that tragic if the key doesn't have full contact on the round side. The flat side is important.
Nick
Reply to
Nick Müller
Use an endmill and a square key?
ED
Reply to
ED
this will be plan "B" if i break one. But, this can be total PITA for the mechanic installing as the key can slide and pinch when you can't go to the end of the shaft.
Karl
Reply to
Karl Townsend
Keywords:
I'm no expert, but I'd up the speed a bit and use lots of lube. It might also help if you use a regular end mill to clear out some of the metal to be removed first.
Good luck!
Doug White
Reply to
Doug White
What is the size of your cutter? That is going to determine your speed along with the material your cutting. You could rough out the hole with an endmill going below a bit the depth your planning with the Woodruff cutter. Then at full depth you won't have everything engaged. Is the cutter sticking out of the collet the absolute min? Everything as ridgid as possible? And have you got the backlash in the right direction. My former job was with a self taught everything and he hadn't a clue about backlash and also a cabinet full of broken endmills. It won't hurt to blow out the chips and use oil of course. My first thought though is backlash problem and then some lack of ridgidity. Of course cheap Chinese Army cutters don't help anyone but the Chinese
Reply to
Dr. Butter
What is the size of your cutter? That is going to determine your speed along with the material your cutting. You could rough out the hole with an endmill going below a bit the depth your planning with the Woodruff cutter. Then at full depth you won't have everything engaged. Is the cutter sticking out of the collet the absolute min? Everything as ridgid as possible? And have you got the backlash in the right direction. My former job was with a self taught everything and he hadn't a clue about backlash and also a cabinet full of broken endmills. It won't hurt to blow out the chips and use oil of course. My first thought though is backlash problem and then some lack of ridgidity. Of course cheap Chinese Army cutters don't help anyone but the Chinese
Reply to
Dr. Butter
Just plunge in to full depth? Are you kidding? Maybe you can do this with the largest sizes, but the 1/4" size is really fragile with that thin "neck". You have to make several passes at slowly increasing depth. With a cutter of about 3/8 to 1/2" diameter, you certainly don't want to cut any more than .050", and most likely .025" deep per pass. You can run the cutter a bit faster, depending on the workpiece material. Most shafts are fairly mild steel, and a cutter SFPM of 60 - 80 is good. That works out to about 600 RPM for a 3/8" cutter, 500 RPM for 1/2" and 300-400 for 3/4" diameter. Not
Better tooling always helps, but HSS is mostly HSS. If you overload even a VERY high-quality US brand-name cutter, it will snap just about the same point as a cheap one.
If you use horizontal mill cutters on a 1.25" arbor held at both ends in a real horizontal mill, THEN you can cut key slots all day at full depth. But, that has almost NOTHING to do with the typical small-size Woodruff keyseat cutters with those tiny necks.
Jon
Reply to
Jon Elson
The problem is most likely that the cutter is too sharp.
I suffered this same problem many years ago.
The steel you are going to cut is most like mild, as in 1018, or 8620 and is easy to cut, but however this is even more hazaderous to a sharp cutter as the cutter will tend to grab, and especially when the deeper you cut the more teeth you have involved causing more pressure on the neck of the shank.
My suggestion is that that you use a fine grit stone, and lightly hone the cuting edge of the teeth removing the wire edge of the teeth.
Think about it, even an old cutter that is just about worn out will still cut and not break.
Oldtime
Reply to
Oldtime
Easy way to do this is to use a fine grit abrasive bristle brush in your drill press. Most hardware stores have these. The fine grit ones generally have blue nylon bristles. Be careful not to "over hone" as these work quickly.
I oticed that this was how one of the computer drill sharpeners was honing/deburring the drill bits after sharpening.
for an example see:
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There are many other brads available.
Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.
John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).
Reply to
F. George McDuffee
...
The job didn't happen. He may be back in a rush on Monday, may have went elsewhere.
I totally agree that its the cutter catching and shallow passes would solve the problem. If I did this, how the heck to you get the proper shape? The customer expects a slot just the size of the cutter, not a slot even 0.100" oversize in length. It would take a CNC to make shallow cuts and end up with the proper shape. Or, am I missing something?
Karl
Reply to
Karl Townsend
Only if the cutter's diameter (or radius) is smaller than the radius required by Sir Woodruff. :-)
Na, if you do have a DRO (or know how to use the sin-key on your pocket-calculator) you can make a bolt-circle with lots of bolts (so you get a very small error).
Nick
Reply to
Nick Müller
Well I don't know what's proper just what's worked for me.
First things first is that I've never done this on a Bridgeport or any other type of vertical mill. Never having used one I can't really say much except that they look a little on the light side for the heavy cut needed by a woodruff key cutter. Most of them have been cut in my Abene mill. I can't remember how many but I also cut a few with the old Aircraft Machinery mill my former employer had (before they got the Abene) and possibly a couple of larger sizes cut on a Cinci #3 horizontal mill.
Me I go much slower like in 120rpm or less. I actually use the power feed on my Abene mill till the cutter starts complaining (usually about 3/4 depth) and then proceed by hand. Very slow feed at that point with pauses to allow the cutter to catch up when needed. I use sound, feel, and visual clues as to how fast the cutter wants to feed. One important point (which I'm sure you already do) is to lock any unused axis when doing this.
I can't remember ever breaking a woodruff key cutter. Nearly all of the cutters I've used where old (many pretty dull) and all good quality.
Reply to
Wayne Cook
This pops up an idea! It might help to clamp the shaft in the vice and mill in such a way, that the cutter is _pulling_ on the shaft, not pushing. This way, it's harder for the cutter to catch up.
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Reply to
Nick Müller
The only thing I have to add: Even though you have locked the unused axis, the cutter can pull against the backlash of the active axis. So, when I do things like that, I tighten the active axis drag as much as I can to minimize the pull.
Pete Stanaitis -----------------
J>
Reply to
spaco

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