View Full Version : end mill in a slot

01-05-2003, 12:11 PM
I recall reading somewhere that if, when you are using an end mill to mill a slot, you let the mill exit the slot it will chip a tooth. Is this true or an old wife's tale? I'm too cheap to experiment;-)

Big Dipper
01-05-2003, 01:45 PM
Need a whole lot more of specifics. I suppose it is possible, but under anything close to a normal circumstance, that will not be a problem.

John Foster
01-05-2003, 04:19 PM
The problem arises because when exiting a slot you are conventional milling on one side and climb milling on the other side. This means that one side of the cutter will working against the direction of feed while the other is working with the direction of feed. When you get to just the right spot one tooth grabs and pulls the backlash out of the table resulting in a large tooth load for the next tooth, which usually breaks the cutter. How do you cure it, zero backlash if you are lucky or you cheat and snug the table lock down just enought to prevent it but not so much as to strip a gear! Are there any other solutions? I agree, this is not a good practice, but what are the other options?

[This message has been edited by John Foster (edited 01-06-2003).]

Big Dipper
01-05-2003, 07:31 PM
I'm not a big fan of the "snug the table lock to prevent grabbing" philosophy. There is usually another way. Would need more specifics for a proper answer, but...why not mill the slot starting at the edge and feed into the part? at least for roughing it out. A light finish cut, even if cutting on both side shouldn't break the end mill.

01-05-2003, 08:41 PM
Just feed slowly as you exit -- so you're taking small chips -- and you should be okay.
I imagine a relatively large end mill might be more of a problem than a smaller one, as a larger end mill will be generating more force for the suddenly-pull-out-the-backlash problem. With small end mills I've never had a problem.

01-06-2003, 05:06 PM
In 8 years of machining I've never had it happen. I was, however, running REALLY big machines so a 3/4" end mill could never jerk an 8'X 15' boring mill table weighing 4 tons or more. However I've never had that problem on my little 6-1/2" X 24" Rockwell horizontal mill at home either! Old wives tale I believe.
Regards, Ken

01-06-2003, 10:45 PM
Old wives tale not! Yep, end mills will "grab" when exiting a slot. Not too much of a problem if you snug down the gib a little and feed it out slow. Usually the end mill won't break when it grabs, but it'll give you a scare. Depends on how heavy you're cutting too. Bigger is badder.

John Foster
01-08-2003, 06:58 PM
Two flute are the worst were as 4 or more aren't as much of a problem as they have more teeth "in the cut" to help keep this from happening.

Al Messer
01-08-2003, 10:18 PM
There are some three fluted ones on the market made 'specially for slotting that don't grab as badly as the even fluted ones in my own experience, which only goes up to 3/8" slots (at the present).

02-15-2003, 12:24 PM
You have to go slow when exiting a slot due to one side pushing out and the other side pulling in and pinching. It's like driving a wedge in next to the end mill. http://hotrodders.com/photos/00003338/flute_breakage.jpg


[This message has been edited by Kevin45 (edited 02-15-2003).]

02-15-2003, 10:40 PM
Another option to avoid the problem is to use an end mill that is slightly smaller than the slot, so it is only cutting on one side at a time. Admittedly, this means another pass, but if you want a good finish on both sides of the slot, this is the only way to do it, or so I've been told. that said, knowing the capabilities of this group, you'll get another few workable options before the day is out!
Richard Medway in Los angeles

02-16-2003, 12:56 AM
double post

[This message has been edited by wierdscience (edited 02-16-2003).]

02-16-2003, 12:58 AM
Nope never happened to me the two forces involved counter act each other.It does however do lots of damage to cut back through the chips.Also if you want to eliminate the problem enter at the end of the slot,clear your chips and reverse your feed.

02-16-2003, 05:50 AM

Yeah, but a real man would fire up that horizontal mill with a side cutting slitting saw and do it right the first time.

Not that I am saying that horizontal mills are overlooked, but this is great place to use one - if you have one, that is. Just wait, they will be popular again - once they are scarce as hen's teeth. http://bbs.homeshopmachinist.net//biggrin.gif

02-16-2003, 11:04 PM
Thrud, I will have you know that I am in fact a real man and I already have two horizonal mills ,including a nice (little used) K&T "H"I picked up three weeks ago for $200.00 bucks including the illusive vertical head!YE-HA! baby YE-HA! http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif SOMETIMES ITS NICE TO GRUNT! ARRRRGG!!HRRRGGG!

[This message has been edited by wierdscience (edited 02-16-2003).]

02-17-2003, 01:28 AM
I r jealous, not just of the K&T with vertical head but that you have space for the pig! Lucky bugger!

02-17-2003, 08:53 PM
I didn't have space,I have it under a tarp!This summer I have got to build a new building I got ten pounds of sausage in a five pound casing,but hey when you find one of these at that price you got to buy it!! http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif Heck the other is a Cinn.the big one with the dovetail overarm and the NT50 spindle it makes the other one look small.

[This message has been edited by wierdscience (edited 02-17-2003).]