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Is this going to wreck my mill?

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Cannonmn

Stainless
Joined
Jun 25, 2016
We used a shell mill on a very long NMTB 50 arbor to side- mill a feature on mild steel. Feed was set very conservatively. What I’d like to know is whether the moment aka leverage exerted on the spindle bearings might cause damage. This is a large OKK mill that I’d describe as robustly-built. I think if I feel the need to do this again, I’ll hand-feed the work, I’m nervous about the possibility of bearing damage.

https://youtu.be/rQSUIjUt2rY
 
Boy, are you gonna catch heat over those gloves....

The long snout on that tool sure isn't helping the bearings, but I doubt it will hurt with a low feed....unless you are doing 5 million cuts or something.
 
I didn't watch all of the video. You can't shorten it any? It was complaining a little but no it shouldn't tear up the bearings no harder than you're pushing it. That machine looks to be a good hunk of old iron. You'll trash the cutter, holder or the part first. If I had a bunch to do I'd find a different way to do that operation if possible. That's taking forever. My 2 cents

Brent
 
Agree with Brent. That machine wasn't even registering that cut. It's made to be pushed WAY harder than that. It could do that day in and day out with no problemo. Generally with long cutters like that it's better to plunge cut - that directs the force more or less straight into the bearings rather than side loading them. If you need to, step over a little at a time, then plunge to depth; step over, plunge to depth, etc. until finished. You can then take a light cut along the bottom if necessary and another light plunge to finish the radiused portion as well if needed. You'll generally get a lot less chatter that way too.
 
If that mill has an NMTB50 taper spindle, it probably isn't going to notice that cut. (I'm not familiar with that brand/model of mill, so basing that on experience with other 50 taper machines.) If you were removing more than 1 cubic inch per minute, it might have to pay a little attention. If the motor is 5HP or under, the motor will probably max out before you have any concern over spindle bearings (assuming you aren't slamming a 12" diameter fly cutter into the work or something like that). But that was a tiny cut at conservative speeds/feeds.
 
eKretz said:
Agree with Brent. That machine wasn't even registering that cut. It's made to be pushed WAY harder than that. It could do that day in and day out with no problemo. Generally with long cutters like that it's better to plunge cut - that directs the force more or less straight into the bearings rather than side loading them. If you need to, step over a little at a time, then plunge to depth; step over, plunge to depth, etc. until finished. You can then take a light cut along the bottom if necessary and another light plunge to finish the radiused portion as well if needed. You'll generally get a lot less chatter that way too.
Click to expand...

Thanks EK. Being a relative newbie, “registering” in this context is new to me, kindly ‘splain?
 
Thx, will tell the apprentice no gloves around rotating stuff. I’ll post a pic of the OKK older Japanese mill, my favorite mill in the shop. It is 10 hp. Never have found a manual for that MH 3V-II Model but there’s a metal lube chart on the side, the important part of the manual for me.
 

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Cannonmn said:
Thx, will tell the apprentice no gloves around rotating stuff. I’ll post a pic of the OKK older Japanese mill, my favorite mill in the shop. It is 10 hp. Never have found a manual for that MH 3V-II Model but there’s a metal lube chart on the side, the important part of the manual for me.
Click to expand...

Lose the long sleeves too. I got pulled into a lathe with a tee shirt. 28 stitches and only around because I grabbed the tool post and it pulled every thread of that shirt off. Learn from the mistakes of others, it's cheaper and less pain.
 
Hi Cannonmn:
When a cutter like that starts to scream and chatter, you want to turn the speed DOWN...not up.
Also, you want the cutter hanging out as little as possible and the workpiece hanging out as little as possible.

If I was making that piece, I'd do your second cut first. and then reach in with a tee slot cutter using the same setup...even if I had to make a single point flycutter with a stubby boring bar and a round HSS drill blank for it.
I'd never do it in two separate setups as you guys have done

I'd find a way to clamp the part so it wasn't hanging out in space like your second cut shows...even if you had to C-clamp a pair of scrap blocks to the sides of it while it was set up in your second cut orientation, just to keep the part from vibrating and screaming.

Last, I agree with other posters: this kind of job isn't going to make a mill like that even breathe hard...you're never going to hurt it with cuts like these.
Now if your first cutter had snagged on the corners of the workpiece and jammed and ripped all the teeth off, I'd be a bit more concerned.
Long reach cutters have a tendency to do that...they're pretty floppy compared to a stubby.
I think the stiffness decreases as the cube of the length (engineers correct me if I'm wrong) so stubbier is always better than longer, if you can find a way.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
Looking at it, I'm guessing this was a one-off. He probably used what he had on hand. There's no sense ordering an expensive cutter for one job when what is on hand will work. If he had a lot to do then it would make sense.
 
implmex said:
Hi Cannonmn:
When a cutter like that starts to scream and chatter, you want to turn the speed DOWN...not up.
Also, you want the cutter hanging out as little as possible and the workpiece hanging out as little as possible.

If I was making that piece, I'd do your second cut first. and then reach in with a tee slot cutter using the same setup...even if I had to make a single point flycutter with a stubby boring bar and a round HSS drill blank for it.
I'd never do it in two separate setups as you guys have done

I'd find a way to clamp the part so it wasn't hanging out in space like your second cut shows...even if you had to C-clamp a pair of scrap blocks to the sides of it while it was set up in your second cut orientation, just to keep the part from vibrating and screaming.

Last, I agree with other posters: this kind of job isn't going to make a mill like that even breathe hard...you're never going to hurt it with cuts like these.
Now if your first cutter had snagged on the corners of the workpiece and jammed and ripped all the teeth off, I'd be a bit more concerned.
Long reach cutters have a tendency to do that...they're pretty floppy compared to a stubby.
I think the stiffness decreases as the cube of the length (engineers correct me if I'm wrong) so stubbier is always better than longer, if you can find a way.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
Click to expand...

In a case like that where all the force is near the end of the tool, yes. For a distributed load like an endmill side-cutting with the whole flute maximum deflection would actually be the fourth power of length for any given chip load (if the flutes were straight but they are generally twisty so it gets a lot more complicated).
 
That was a nothing cut for 50 taper.

Lots of 50 taper CNC's have 50-75 HP spindles. My Cat50 Kitamura has 35 horseponies and 10K RPM. It's milled RC60 tool steel for the past 15 years and the spindle's like new still. Whisper quiet at 10K RPM. When you get after something with 50 taper it's a "holy shit" kind of experience. When I have pushed things hard the thing that always fails is the tooling.

I scrapped out a mid 80's Okuma 1000mm HMC awhile back for another company. It had a 4000 RPM geared Cat50 spindle with a 75HP motor. All this thing did was hogouts in big chunks of 4340. I never heard it run, but the guys were sad to see it go. They said they would bury an 8" face mill and when it got in the cut full width, the roar of the chips smashing the walls was deafening. They never stalled the spindle and it wasn't for lack of trying.
 
Hi eKretz:
You wrote:
"There's no sense ordering an expensive cutter for one job "
Yeah, I don't disagree at all if you're gonna spend a pile on a single use cutter.

But I was thinking of a simple 2 flute flycutter, or even that shell mill on a stubby but skinnier arbor so it could be run one time as if it were a tee slot cutter.
Not many seem to think of rolling their own anymore...or at least it sometimes seems that way.

I could make a flycutter to do that job in less time than they spent just screwing around in the video and I wouldn't have to hang it a mile out of the spindle.
A lathe, a mill,and a bench grinder will do it just fine, with a scrap bar of something and a cut off drill blank, hand ground on both ends and then centered with a clock.
Looks like someone spent a good bit of time somewhere making that home made arbor for the shell mill they've got, so a simple flycutter should be duck soup to make.

No need even for that Monoset you have that I'm still envious about:D.

Note I'm not concerned at all about the spindle bearings, but it offends my eye to see a cutter hanging out so far when it doesn't need to.
All that hopping and squealing and chattering makes me nauseous.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
implmex said:
Hi eKretz:
You wrote:
"There's no sense ordering an expensive cutter for one job "
Yeah, I don't disagree at all if you're gonna spend a pile on a single use cutter.

But I was thinking of a simple 2 flute flycutter, or even that shell mill on a stubby but skinnier arbor so it could be run one time as if it were a tee slot cutter.
Not many seem to think of rolling their own anymore...or at least it sometimes seems that way.

I could make a flycutter to do that job in less time than they spent just screwing around in the video and I wouldn't have to hang it a mile out of the spindle.
A lathe, a mill,and a bench grinder will do it just fine, with a scrap bar of something and a cut off drill blank, hand ground on both ends and then centered with a clock.
Looks like someone spent a good bit of time somewhere making that home made arbor for the shell mill they've got, so a simple flycutter should be duck soup to make.

No need even for that Monoset you have that I'm still envious about:D.

Note I'm not concerned at all about the spindle bearings, but it offends my eye to see a cutter hanging out so far when it doesn't need to.
All that hopping and squealing and chattering makes me nauseous.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
Click to expand...

Well, to be fair it really shouldn't have taken that long. They went about it all wrong trying to cut in from the side. Using a plunge cut methodology there would have been none of that chatter, or a whole heck of a lot less of it. And not to put too fine a point on it, but I think you're a *smidge* more experienced than those fellas. I'm not sure they would be capable of rolling their own. Otherwise, your point is valid... :cheers:
 
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