Woodruff Cutter Feeds and Speeds

maikol2346 · Feb 28, 2020

Hello,

I am attempting to cut a 5/8" slot on A36 steel using a woodruff cutter in a HAAS Mini Mill. As of right now the feedrate is about 3.4 in/min, however when the cutter goes in it sounds like an earthquake and quite frankly feels too aggressive. The cutter broke after the 5th part.

The RPM is about 530 and I'm using a #305 Woodruff KSC Shank HSS RH STAG from Keo Cutters, Inc. The cutter diameter itself is 5/8" by 3/32" width and it has 8 teeth.

How much slower should I go if slower at all? I have tried searching charts online and calculators but they all give me significantly higher numbers, and the cut already feels very aggressive.

P.S.: While doing the cut, the load on the cutter is about 20% and then spikes to ~40%. For the first few parts the cutter was fine but now it broke.

Big B · Feb 28, 2020

535 RPM's sounds kind of fast to me.

13engines · Feb 28, 2020

My little helper is telling me 778 rpm at 3.62 ipm. That setting didn't seem to matter whether cutting an 1/8 deep or 3/16.

First you want to be climb cutting, and on these types of cutters, the truer you can make them run the better. I'd try this speed and feed and start the depth of 0.100 and keep adding on until it starts to sound scary again. then back off a little. Lack of machine/spindle/setup rigidity and high runout will kill these somewhat fragile cutters. You got the staggered tooth which is a good choice.

rogertoolmaker · Feb 28, 2020

Speeds & feeds

maikol2346 said:
Hello,

I am attempting to cut a 5/8" slot on A36 steel using a woodruff cutter in a HAAS Mini Mill. As of right now the feedrate is about 3.4 in/min, however when the cutter goes in it sounds like an earthquake and quite frankly feels too aggressive. The cutter broke after the 5th part.

The RPM is about 530 and I'm using a #305 Woodruff KSC Shank HSS RH STAG from Keo Cutters, Inc. The cutter diameter itself is 5/8" by 3/32" width and it has 8 teeth.

How much slower should I go if slower at all? I have tried searching charts online and calculators but they all give me significantly higher numbers, and the cut already feels very aggressive.

P.S.: While doing the cut, the load on the cutter is about 20% and then spikes to ~40%. For the first few parts the cutter was fine but now it broke.

RPM = 4 X Cutting Speed / dia.
Cutting Speed for low carbon steel = 60
RPM = 4 X 60 /.625 = 384 Cutter RPM for a high speed steel cutter.
It would help if you could slow down a bit.
FEED. This is not the place to be aggressive. Take it easy when feeding for a woodruff key. By time you finish the keyway you'll have a forth of the cutter diameter doing the cut. I have the same advice in feeding; Slow down a bit and lock the table in position.

Roger

Illinoyance · Feb 28, 2020

My understanding is that OP is milling a slot in a part, not a keyway. If that is the case he would be better using a short endmill. Woodruff cutters usually have a slender neck between the cutter and the shank, making them somewhat fragile. Correct me if I misinterpreted how OP is using the cutter.

Matt_Maguire · Feb 28, 2020

Are you cutting a keyway (long) or a woodruff keyseat? The neck dia of that cutter is around .200” & won’t take any more torque than a 3/16” end mill will with 3/16” depth engagement… Your speed for HSS is fine.

If it’s a keyway (long) then you have only 1 ¼ to 1 ¾ teeth engaged per revolution as you travel with that cutter (start with estimate of .0025” per rev feedrate like a flycutter). Stagger tooth cutters work better.

If it’s a true woodruff keyseat then you have a plunge cut that starts with 1 tooth and moves to 2 ½ to 4 depending on the tooth count. Then (old timey) we’d set the feedrate to .002” for half the depth and the rest at .001” per rev feedrate.

This is something you could actually feel with something like a manual bridgeport (after enough oh-shits). At least some could...

Good luck,
Matt

Ox · Feb 29, 2020

IM/HO you can toss the S&F charts when it comes to woodruffs.

Start slow and feed slower, and go from there.
No race was run by trying to git aggressive with a woodruff!

-------------------

Think Snow Eh!
Ox

guest · Mar 1, 2020

I have a 304 part that has a boss that gets an undercut with a Woodruff cutter. The cutter is a KEO 708. 1" cutting diameter, 7/32" face width.

I just looked at the program, I am running that cutter 250 rpm and 2.5" feed

.

Ox · Mar 1, 2020

You are finishing all surfaces with the KEO?

----------------

Think Snow Eh!
Ox

guest · Mar 1, 2020

Ox said:
You are finishing all surfaces with the KEO?

No, the floor and the boss are finished before the KEO. The boss is a trapezoid shape with radiused corners, the KEO profiles the same rad on each side, blends to the floor, and mills out the slot.

You can't really see it in the pic, but there is a 30 degree angle on the underside, one side only, that gets cut with another KEO- a dovetail.

This is the sister part, same thing but dash opposite on that feature.

Ox · Mar 1, 2020

Well, the pic sure looks like a perfect match in Z, but maybe it's not that perfect in another light?

---------------

Think Snow Eh!
Ox

maikol2346 · Mar 1, 2020

Sorry for the late reply y'all! Thank you all for the help. So to clarify things a bit, here is a picture of the slot I am machining:

The top part in the picture is the one with the slot being made by the cutter, the bottom part goes into the top part. I brought down the feed rate to 3 in/min and it sounds far less aggressive but I can still see peak loads of about 40%. I'll try some of the recommended RPMs and feeds and keep you all updated!

guest · Mar 1, 2020

Ox said:
Well, the pic sure looks like a perfect match in Z, but maybe it's not that perfect in another light?

Haha, is it ever?

They blend pretty good- I blue up the floor and bring the KEO down until it just takes the dykem, but doesn't scratch the part.

The only mismatch is inside the boss. If the light is right you can see it, but you can't feel it. If you look close at the first pic, you can see what looks like a shadow outline of the top of the boss. That shadow is a couple tenths mismatch to the floor.

guest · Mar 1, 2020

maikol2346 said:
...I brought down the feed rate to 3 in/min and it sounds far less aggressive but I can still see peak loads of about 40%. I'll try some of the recommended RPMs and feeds and keep you all updated!

Remember, the feedrate commanded is the center of the spindle. You are profiling a radius- the outside of the cutter is feeding a lot faster than the center, and the tool has a good portion of it's diameter in the cut.

So go easy on the feedrate. These cutters are not the ones to set speed records with...

Mtndew · Mar 2, 2020

maikol2346 said:
Sorry for the late reply y'all! Thank you all for the help. So to clarify things a bit, here is a picture of the slot I am machining:

View attachment 280542

The top part in the picture is the one with the slot being made by the cutter, the bottom part goes into the top part. I brought down the feed rate to 3 in/min and it sounds far less aggressive but I can still see peak loads of about 40%. I'll try some of the recommended RPMs and feeds and keep you all updated!

Are you cutting around the perimeter of that slot or are you plunging the slot?
Also, you're on a Mini-Mill, I'm surprised this little cutter hasn't pegged the load meter to 100% so don't worry too much about being at 40%.

maikol2346 · Mar 2, 2020

It plunges right into the slot. I'm trying to extend cutter life as much as possible.

G00 Proto · Mar 2, 2020

There is tremendous load on a cutter going into a full radius like that. Use a much smaller key seat cutter and program it like a CNC not a manual mill. Then you will never have a problem. I'm not even going to suggest feeds and speeds for doing what you are trying, because it will never work out well.

Another thing to note on the MiniMill, is that it is belt driven. They do not like to cut with large cutter turning slow. In my opinion (after doing so for many years), the spindle is slowing down and speeding up constantly as the little sewing machine motor tries to keep up. It probably sounded like whoooan ha whoooooan ha whooooan ha just before it snapped the cutter. I try and use small cutters going quickly vs large cutters going slow.

guest · Mar 2, 2020

G00 Proto said:
There is tremendous load on a cutter going into a full radius like that.

Big time.

I'd cut the groove on the lathe first, then take it to the mill to make the opening. Maybe go to a #304 keycutter to profile, 1/2" dia instead of the 5/8"...

Mtndew · Mar 3, 2020

maikol2346 said:
It plunges right into the slot. I'm trying to extend cutter life as much as possible.

Either get a smaller cutter like mentioned above, or get a carbide one where you can kick up the R's a bit to get farther into your "torque" range.

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