Endmill holders

[RSG]

Further to my quest for accuracy on the milling machine. Would an end mill holder in an R8 configuration be more accurate than a plain R8 collet?

[NP317]

End mill holders might be more accurate than R-8 collets. But it depends on the accuracy of the "slip fit" hole for the cutter.

ER-32 collets (or other sizes) might be more accurate than R-8 collets. R-8 collets close at the taper end only,
while ER collets close radially along their entire length.
Food for thought.
~RN

[SteveM]

R-8 collets close at the taper end only...

While they only close at the end, if they are gripping something that is the diameter the collet is sized for, the sides of the collet hole will be parallel and it will grip across its entire length.

That, of course, is if everything is perfect.

If the tool is oversize, it will grip more at the inner end, and if undersize, more at the outer end.

Also, the grip length on a collet like R8 or 5C is shorter than the grip length on an ER (an ER-32 is about an inch long).

What the end mill holders bring to the party is the setscrew on the side that, when screwed in, holds the end mill by the flat on the Weldon shank, preventing the end mill from walking out of the collet, which it can do because the flutes on the end mill are spiral in the direction that causes pulling forces.

When you install a tool with a Weldon shank, you put it in with the flat in the area of the setscrew, screw in the setscrew until it is on the flat, pull the tool out so that the screw is against the side of the Weldon flat and then tighten it. That provides a positive stop to prevent the tool from pulling out (and rotating).

Steve

[pete]

More or less accurate? That depends on just how accurate the hole is bored and ground at the factory in an end mill holder just as NP317 mentioned. There is usually less than .0005" or so of slip fit clearance in the hole just to allow the endmill to fit since a .500" shank tool isn't going to fit in a .500" hole. Mine are close enough you can feel the air trying to compress as the endmills shank is inserted into the holder.Tightening that set screw does push the endmills shank against the holes far wall. So unless the endmill holder was slightly ground to compensate for that and I'm not sure if any are or not, then you'll still have a few 10ths of runout plus whatever your spindle taper and bearings have as well. An endmill holder does move the tools cutting flutes farther away from the mills spindle bearings so that may or may not be important to you. On average if everything else is equal then a R8 collet would cut a bit more accurate and should be capable of taking larger cuts just because the end mill is closer to those bearings. Lot's of end mills do come with that Weldon flat ground on the end mills shank today, but there's still some that don't since shrink fit tool holders don't need it. Without that flat then an end mill holder can't be used. I've got other cutting tools with plain shanks so those get used in an ER collet. In hindsite I sort of wish I'd bought good R8 collets first. My best guess is an ER collet properly tourqued would hold an end mill more firmly than an R8 would but maybe a bit less than an endmill holder. ER's still have the possible runout in the chuck itself, the collet, plus the spindles taper and bearings. R8 collets remove one of those possible errors. R8 endmill holders would magnify any errors just because of there longer length.

I hope you don't mind a bit of advise that cost me a lot to learn RSG.I've said on this forum more than a few times that I've long since quit trying to buy tooling at the cheapest price. For me it just hasn't worked out that well.I also no longer buy any tooling that doesn't have some type of written specification about it's maximum allowable inaccuracy. Without that and if you did find a measureable high runout then you really have nothing to say it's defective. At that point I guess it depends on your tooling supplier if they will replace it or not.There no longer in business, but the tool dealer I bought a lathe from wouldn't replace it since there was no test certificate stating just what was allowed and what wasn't. That was a very tough and expensive lesson. The same can happen with tooling and they can or could say you bought a R8 collet or whatever and that's exactly what you got. For R8 collets that specified accuracy will most likely come at a higher price.For the cheaper tooling that has no specifications you may or may not get lucky. I can say I've read multiple threads over the years of people finding the cheaper R8, ER, end mill holders etc having large runouts for some but not all of them. Others say what they bought was just fine. Going by that it almost seems more luck than anything else. There's no way to tell who's actualy done some proper runout tests or not though. Me? I've learned to trust nothing and I do check what I've bought. So far when I do buy good tooling everything has fallen within the allowable numbers so I have gotten what I paid for. But even the best tooling manufacturers have the odd bad one get past there quality control. So I figure it pays to double check. But I also think tool and work holding are your basics and the finished part especially with work holding is only as good as your tooling and set up is. I finally bought Bison ER collets and end mill holders and I'm more than satisfied with what I got. But there not exactly cheap. Depending on your part shape those endmill holders can sometimes help give you enough tool extension to get the tool down past a higher area of the part without buying extended length endmills that aren't as rigid under cutting conditions. Other times the enlarged end can be in the way. Some tooling like slitting saws, even the good ones seem to come with there own runout problems and seem to cut far more on one side than the other even while held in a low runout collet. You can hear that happening real well as the tools cutting. Yet I've got a couple that don't do that at all.

Something to think about though. Very low runout numbers with collets for tool holding do make things easier. But since there's lots of other factors throughout the machine that affect the parts dimensions it's still cut, measure, cut to what the measurements say and remeasure to be sure. But my logic says good work can still be done with less than perfect collets. The higher runout does cause them to be harder on tooling since one side is doing more work than the rest of course. And everything still depends on just what accuracy your parts require. Ultra small diameter end mills especially carbide need the lowest runout you can afford to buy. But compensating for the machine, tool, work holding etc is still part of of the whole job. And from my reading the exact same thing is still done by tweaking the cutting program on super rigid high HP and accuracy CNC machines for multiple parts as what we have to do manualy with less than perfect machines and tooling.

[GlennW]

No amount of measuring and compensating will correct finish deficiencies caused by runout though.

Precision grinding will give you an education there in a hurry!

[pete]

100% right you are Glenn.

[RSG]

Thanks for the comments. I doubt I will persue Endmill holders. Likely go for a few high end R8 collets in the the sizes I use most.

@Pete, I would say I hit that curve a few years ago. It took me several years to understand the importance of buying the best I could afford. The first place I learned it was with my metrology. Now I only buy equipment/tooling with the spec sheets you mention. I'm still dealing with past purchases I guess when it comes to my collets.

For many years the level of accuracy I was able to achieve with my equipment was satisfactory but once I understood the next level of accuracy it became my quest to achieve it. With the ever increasing complexity of the reels I design I have come to understand the more accurate I can make the parts the better everything fits, to the point were it doesn't mater what components I grab during assembly they all fit their respective position perfectly. All my other equipment has been tweaked and tooling upgraded to produce the most accurate parts I can, the runout of my mill is the last piece of the puzzle to correct. I am confident I will be successful, just a matter of time. One thing I can tell you is I would not be this far without the help of the members here on the board.

RSG

[pete]

Yeah that metrolgy hurts to buy for sure. If you can't consistantly measure what your making you can't hope to make interchangable parts without taking a lot more time. Cutting tools were the tough one for me to accept the cost difference is more than worth it.

If all you've got left to sort out is the runout that's at least easy to figure out where the problem areas are. If the bearings and spindle taper are good then it's the collets. But even buying just under Hardinge quality usually isn't too bad for the more than common R8 taper collets. They also do wear with a lot of use so that could be a partial part of the problem.

[ctwo]

every legacy name brand end mill holder I've bought has excessive runout, according to the gospel I've read. I should take careful measurements to be sure, and I should probably know what the gospel really is. No more than a couple, two (2), tenths, at the shank,or 1" out? EM holder specs of my vintage seemed to spec just under a thou. Maybe I missed something? The discussion always seems vague to me.

[spro]

This type end mill holder has its place. The end mill wont creep out, if set per above information. I knew from the start that the tool could not be concentric as a collet but doesn't require huge tightening either. End mills are consumable elements and one answer is to grind another flat opposite the other. This would balance wear of the leading edges.

[BadDog]

Odd that this has popped back up now. My local friend who was a lifetime machinist has helped me in many ways, but one of the first things he prevailed on me to accept is working as close to the bearing as possible. To paraphrase my understanding, he firmly believes in using collets if possible (and quill retracted), which is most work. Then EM holders for roughing, or in some cases if you need clearance to reach past things. And that approach has always worked for me, with the only problems coming early on when I didn't know to tighten it adequately.

But last weekend I got an expanded education. I had a casting for an in-line exhaust brake going on a Cummins 6BT. I won't bore with the details, but it needed a moderate amount of material removed at one end to adapt it to my buddies setup. I have NEVER seen an EM pull out like that. I took everything out and cleaned it well (brake cleaner, no oil!), tightened it till I felt it "lock", but nothing I could do would keep it from pulling that EM down in the collet. It was a carbide 1/2" 3 flute rougher, and I tried 3 different examples, all "not new" but still sharp enough for roughers (and has worked fine in structural steel since then, where they get used most). I don't have a 1/2" EM holder, so my only recourse (since I didn't want to use my sharp finishing end mills) was to take my time (for a change). That was the most aggravating work I've done in my shop in a long time.

So at the very least a few main stream EM holders will finally be moving into my shop for the first time soon. Or maybe I'll get a set, depending on options that present. All I've got now are really nice EM holders for 3/16" and 1/4" EMs, but their main purpose is really just to offset from the spindle nose when working past obstructions. Whatever caused such a pull out fest, I don't ever want to be forced to nurse along a project like that again. What I expected to have done in less than 10 minutes took over an hour between fighting a difficult setup and the darn EM pulling out any time I took more than about 0.100 DOC with about 0.200 width of cut on a 1/2" roughing carbide EM in what otherwise seemed to be maybe nodular? Boring head had no problem with the recess to locate the pipe for welding, but those roughing EMs sure didn't like it.

[SteveM]

all "not new" but still sharp enough for roughers

At first glance, i would think that a sharper one would have MORE pulling force, rather than less.

A dull one is going to be pushing material, where a sharp one is going to me digging in.

Steve