# A Tip for Slotting on the Mill



## BobWarfield (Feb 11, 2008)

I just cut the slots on the supports for my disc sander table:







I was reminded of a "trick" I use that seems to work really well: I avoid plunging the cutter straight down. Instead, I lower it slightly and then start cranking the X or Y (Y in the photo) in the direction I want to cut. At the same time, I turn the quill handwheel so the cutter is both lowering and moving along the slot. This seems to let me cut radically faster and more smoothly. Someone here probably knows the reason, but I just picked it up watching CNC machines which never seem to go straight in--they'll spiral or do some other manuever to get to depth. 

You'd be amazed at how much faster you can go this way. I was doing a couple other things when cutting that slot. First I had put a good shot of Tap Magic, my preferred aluminum lube. Second, while cutting, once I got to desired depth and had a hand free, I hit the trailing edge of the cutter with a continuous shot of compressed air to keep the chips moving. Lastly, I left about 1/8" on each end of the desired slot until the end. When the cutter was all the way through and cutting full thickness, I picked up the ends.

This process seems to work pretty well for me. The pros probably have further refinements. I would have preferred a 2-flute, but the 4 was all I had in 3/8".

Best,

BW


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## deere_x475guy (Feb 11, 2008)

Bob thanks for the tip. I have some pocket milling I am planning on doing this weekend. I will skip the drill first thing and try your method.


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## zeusrekning (Feb 11, 2008)

Bob next time try moving X and Y proportionally while plunging in Z.


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## deere_x475guy (Feb 11, 2008)

zeusrekning  said:
			
		

> Bob next time try moving X and Y proportionally while plunging in Z.



LOL....Bob does have a powered x axis I believe...))

Hmm...I could use my power down feed and power x feed and just hand feed the y....

Naw...I would screw that up for sure..


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## raym 11 (Feb 11, 2008)

somebody said a two flute end mill works best for slotting.

raym


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## BobWarfield (Feb 11, 2008)

2 flutes are recommended for aluminum as they clear the chips better. In this case the 4 flute worked fine.

Best,

BW


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## raym 11 (Feb 12, 2008)

Thanks Bob, I didn't know why the two flute was preferred but that makes a lot of sense.
raym

by the way, what is that little icon for that shows up to the right of the post? Looks like a pencil on a tablet.


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## tattoomike68 (Feb 12, 2008)

raym 11  said:
			
		

> by the way, what is that little icon for that shows up to the right of the post? Looks like a pencil on a tablet.



It lets you edit your post.


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## Circlip (Feb 12, 2008)

Raym 11, a two flute is called a slot drill and is used for.... slotting, cos the teeth are of unequal widths it allows you to plunge into the job. Bob only got away with using an END mill by moving in two directions at once simultaneously. If you look at the business end of an end mill you will see a domed depression which if you try to "drill" with will stop cutting and KICK the job,(you only do it once.) The other multi-flute cutter to use safely for drilling is the three flute, again the cutting end is shaped to DRILL. C'mon Bob, we're supposed to be teaching the kids safe ways to do things.  : ;D


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## Bernd (Feb 12, 2008)

Let's see, move the "Y" axis with one arm, the "Z" axis with other arm, while blowing air to clear chips.
You do have three arms!!!!   

Nice trick Bob. I'll have to give that a try.

Ok, for those two lipped end mills or slot drills. I remember them from work but have not seen them in any of the catalogs. I know the wood workers use them in the routers and I'm sure they would work in the milling machine, minus the ball bearing on the bottom anyway.

Bernd


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## shred (Feb 12, 2008)

4-flute mills plunge just fine, if and only if, they have teeth that go all the way across the end.


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## BobWarfield (Feb 12, 2008)

Circlip  said:
			
		

> Raym 11, a two flute is called a slot drill and is used for.... slotting, cos the teeth are of unequal widths it allows you to plunge into the job. Bob only got away with using an END mill by moving in two directions at once simultaneously. If you look at the business end of an end mill you will see a domed depression which if you try to "drill" with will stop cutting and KICK the job,(you only do it once.) The other multi-flute cutter to use safely for drilling is the three flute, again the cutting end is shaped to DRILL. C'mon Bob, we're supposed to be teaching the kids safe ways to do things.  : ;D



Circlip, you must be from across the pond, judging from your "slotting drill" terminology. That term seems to have fallen into disuses here. As Bernd said, they don't seem to be in the catalogs. I couldn't find a slotting drill on either Hanita or Niagara's web sites, but they had lots of end mills. Why? Because you can get all the flutes you want cutting in the center. Oddly enough, they're called "center cutting". There are endless videos of CNC machines with varying numbers of flutes cutting this way. As I said, that's how I got the idea to ramp the cut (which is what the CNC'ers call it). If you do have an end mill that is not center cutting, then the technique I describe is even more important. The one I used was a center cutting mill as that's all I buy. 

I tried a plunge with a 4 flute that didn't center cut once. It was frustrating, not scary. It creates a little mountain in the center of the hole and you go no deeper than that mountain allows once it fills the hole in the center of the end mill.

In retrospect, the reason this cuts so much better is obvious from the geometry of the cutter. The center, even if it has teeth, does not move as quickly as the OD of the end mill. Using the technique I've suggested simply causes most of the cutting action to happen at the OD where the cutter is moving faster, is likely sharper, and where there is more clearance to get rid of the chips.

I will also say that an awful lot of machines, including myself, have had success using end mills to drill holes straight down. They often cut better than a drill bit, and can save a tool change. Again, you must have a center cutting end mill, but it's worth a try sometime to see how you like it.

So why not always use as many flutes as possible? A couple of reasons. The most important is chip evacuation. Recutting chips is bad for tool life, surface finish, and accuracy. Aluminum can be especially problematic, so we often prefer fewer flutes as I mentioned. 2 flutes are common, but there are 3 flutes too. That brings me to the second decision criteria around number of flutes and that would be chipload. It's literaly your depth of cut on each tooth of the cutter. For a given feedrate and spindle rpm, chipload goes down as you increase the number of flutes. This is because you have less of a revolution = less time to feed = less distance fed for each tooth. So running more teeth is a little less aggressive cut, all other things being equal. In other words, as long as I could evac chips, running 4 flutes instead of 2 at the same speeds and feeds was an easier cut. 

Recall I was concerned with chip evacuation, hence the steady air stream and Tap Magic (more a lube to prevent build up on the teeth than a coolant).


Cheers!

BW


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## raym 11 (Feb 12, 2008)

Sometimes, when slotting alum or brass I start with a drill one imperial size under nominal and then chuck up a two flute and having at it. 

Any thoughts on side milling? One idea is to use a four flute because it is stiffer and you have a flute opposite the cutting force to counteract it. 

Ray M


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## Circlip (Feb 13, 2008)

Yep, you're right about the side of the pond I'm at Bob, we tend to be at least ten years behind in our home workshop technology, slot drills (two flute) and end mills (four flute) are still the norm from our model engineering suppliers. Slot/end mill drills (three flute) are freely available over here but like most tool types used in our workshops which are hand down from industry, I sometimes envy the fact that you still have a working manufacturing industry and the norm over there for home use is an active surplus market supply. I know that you are emulating CNC movements, but I can still perceive the smack at the back of my head by my late mentors of toolmaking if i did it on my own machinery. The hallowed ground of CLIMB milling would only be tentatively carried out on new machinery, but this is the norm in todays industry with ballscrews, they would be amazed.Differant tooling over there but I can afford to waste the extra few minutes on a toolchange cos it's a hobby. 
  Best wishes Ian


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## steammadman (Feb 13, 2008)

:you guys certainly have some "queer" ways over there,
   A "SLOT" DRILL IS FOR CUTTING SLOTS
   AN "END MILL" IS FOR NUMEROUS OTHER USES.

   it may say newbie against my name, but at 70+, and with 
   60 years experience i think i have done almost every "job"
   in the book.
    BEEN THERE GOT THE TEE SHIRT, "AND WORN IT OUT"


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## BobWarfield (Feb 13, 2008)

steammadman  said:
			
		

> :you guys certainly have some "queer" ways over there,
> A "SLOT" DRILL IS FOR CUTTING SLOTS
> AN "END MILL" IS FOR NUMEROUS OTHER USES.
> 
> ...



Steam, at this stage in your career I certainly wouldn't want to have to be the one to try to change your methods!

Stick to what works for you, but be aware there are other proven approaches available that work well for others too. Those with additional time and flexibility will get the most benefit of learning from trying both ways to see what may work well for them.

Cheers,

BW


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## Don Huseman (Mar 1, 2008)

El gringo
I noticed the cat in your avatar. My father had a Babbitt bearing shop and the cat they had was named Babbitt. Well the cat would **** in the Babbitt chips they would lay out on the floor at night waiting for the night Babbitt melter to melt the scrap Babbitt and cat ****. The smell would make your eyes water it was so bad. some times the Babbitt guy would put the scrap Babbitt with the extra into a hot pot and the "**** would hit the fan" as it formed a steam explosion. Babbit the cat got fired form the company and was replace with Lead Ass the new cat.


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## raym 11 (Mar 1, 2008)

Don, that is one of the funniest cat stories I've seen .

The pictured cat is called Slack and its almost identical running mate is called Slack. Their tails get stepped on anound the lathe and mill at times 

Sounds like they need new names that are more in line with model engine building. 

Any ideas out there? (they are female siblings)

T-head Tom....Dee Burr...Feed & Speed........
Whoops this is needing a new topic ???
Ray


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