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Buckshot
08-05-2008, 01:22 AM
I have a set of R8 collets x 32nds, and a set of ER40 collets and R8 collet chuck. Do I REALLY need to invest in setscrew endmill holders? If so, whycome?

Rick

John Stevenson
08-05-2008, 03:18 AM
Wouldn't have thought so.
I have just the standard R8 collets in metic and imperial and a R8 to ER32 chuck and collets and that does me for all my work.

In fact I don't own any end mill holders only a couple on INT 40 for the big mill but they never get used.

Personally I have never liked the idea of just one screw on a flat holding a cutter.

.

BadDog
08-05-2008, 03:31 AM
Do some searching, the answer to what you ask is akin to a religious argument and has played out many times.

I also see no reason for EM holders, and generally use only collets. I've even had screw ups so bad that it visibly (dramatically!) lifted a 9x42 Bridgeport table and knee, breaking a carbide EM, and it never moved in the collet. I know it didn't move because it was a TiN coated 1/2" bit and the coating was just at the edge of the collet both before and after the event.

For me, the only time I look for an EM holder is when I need clearance from the quill/spindle. Sometimes you need that EM out from the spindle just to get where it needs to be. Far from ideal in many ways, but there are EM holders that will give you more range.

Others will swear that disaster looms for any so foolish as to put an EM within 5" of a collet. Me, I haven't seen it. I say keep your collets clean and properly tightened, save the EM Holder money for other tools...

oldtiffie
08-05-2008, 03:46 AM
I second John Stevenson's answer.

I have never had anything shift in an ER collet. I have an MT3/ER-32 and a MT3/ER-16 set.

If the end mill cutter "walks down" the/its spiral from the collet, there is something drastically wrong.

In my opinion a set/grub-screw is a poor excuse for a driver/key.

Peter N
08-05-2008, 04:39 AM
I third Sir Johns answer.

The Mazak FJV-20 machining centre in my business partners toolroom uses ER32 collets, and with 20Hp on the spindle it tends to cut a bit more agressively then most home shop machines :D

Peter

Evan
08-05-2008, 05:24 AM
And I concur as well. I use R-8 collets for all my work, including for drill bits that will fit properly.

SGW
08-05-2008, 07:29 AM
I've never had a problem with holding an end mill in an R8 collet. I've got top-quality Hardinge collets. If I had collets that cost $3.99 for a complete set by 64ths, its might be a different story.

I have a couple of end mill holders that I use occasionally only to get more clearance. Depending on its design, your ER collet holder may achieve that same purpose for you.

In your situation, I think I'd wait until I ran into a situation where I said, "Self, for this job I NEED an end mill holder" before I went out and bought one.

ahidley
08-05-2008, 07:35 AM
As stated by SGW, they give you alittle more reach

JCHannum
08-05-2008, 08:22 AM
The choice is personal, or job dependant, the EM holder providing extended reach when that is needed.

I will contest John's statement regarding the holding power of an EM holder. The setscrew holder is intended to be used with endmills having Weldon flats, and when those end mills are installed properly in a properly designed holder, holding power is superior to an R8 collet and accuracy is comparable.

The Weldon flats may not be as prevalent across the ocean as the Clarkson system is not often encountered here, but it is a very secure method of end mill retention.

lazlo
08-05-2008, 09:35 AM
I have just the standard R8 collets in metic and imperial and a R8 to ER32 chuck and collets and that does me for all my work.

Same here, I use an R8 collet set and an ER40 chuck and that covers all my needs. I just nabbed a 1" APKT insert facemill that will be an interesting test of the holding power of the "25 - 26mm" ER40 collet.

If that doesn't work, I've got 3/4", 7/8", 1" ETM R8 endmill holders that I occasionally use for my big corncob roughers.

TexasTurnado
08-05-2008, 09:52 AM
This discussion is pretty lop sided so far, so let me try to balance it a little:)

I use the em holders quite a bit. As stated, they give the extra reach sometimes needed to clear clamps, etc. They also come in large sizes (1, 1 1/4, 1 1/2) which I use to hold carbide face mills with straight shanks and screw machine drills over 1 inch. In general, the em holders have a smaller dia head than collet holders and give a little more clearance in some applications. I also use the face mill holders for large carbide face mills.

OTOH, since getting a er-16 collet extension, I have the extra reach for small size em's, etc so I don't use the smaller ones as much. Plus the er collets can be used for drills when needed.

sidneyt
08-05-2008, 11:14 AM
I use end mill holders for some of the same reasons stated by others: to get the tool in the position I want it for certain jobs. However, since I have recently purchased an ER 32 holder and collets, that may change. I have also used R8 collets for holding primarily end mills. I have a modest collection in 1/8" increments, but I have rarely ever used anything other than the 3/8', 1/2", 5/8" and 3/4" sizes. Which gets me to the question of why buy a set of R8 collets in 1/32" increments? The ER collets should be much superior in holding tools that require any variation in size.

Mcruff
08-05-2008, 11:23 AM
I can pull an endmill out of the best R8 collets made and have done so in our ER collets at work also.
The main thing here is useage. When using a hog mill (like pictured) and taking a very heavy cut (.375 DOC or deeper) I do use an endmill holder. Only because prolonged useage and heavy cuts will pull them slowly out of the collet no matter what. A Weldon style tool holder with a set screw will not do this if the endmill is installed correctly.
http://www.use-enco.com/ProductImages/0188616-11.jpg

Collets will do probably 75% of the work but an endmill holder is very, very useful in 1", 3/4" and 1/2" diameter sizes. I have a 1/2" and 3/4" I use in my garage shop, at work we have several other sizes that get used alot.

If someone has never pulled an endmill from a collet they are obviously not pushing the cutter to its limits or trying to make money with it. Collets simply won't consistently hold a large endmill 5/8" or larger in diameter when worked hard. Light cuts they work great and will hold fine.

pcarpenter
08-05-2008, 11:29 AM
Mcruff-- I think the issue is the particular mill you have pictured...

If I am seeing it correctly, the helix angle and cutting resistance wants to pull the mill out of the collet.

Paul

dockrat
08-05-2008, 11:30 AM
Which gets me to the question of why buy a set of R8 collets in 1/32" increments?

Well for one thing, like Evan, I use my R8 collets for drill bits also. I can get way more clearance that way. Especially when I have work clamped to my 10" rotab and taking into account that I loose about 3 inches of vertical travel in my head because it hits the ceiling before toping out. ( I need a new shop!!!)

JCHannum
08-05-2008, 11:37 AM
Mcruff-- I think the issue is the particular mill you have pictured...

If I am seeing it correctly, the helix angle and cutting resistance wants to pull the mill out of the collet.

Paul
That is the issue with all end mills unless they have a reverse helix to force the EM into the collet. With a heavy cut, they will try to pull the EM out with mixed success depending how hard one cranks on the collet.

Mcruff
08-05-2008, 12:01 PM
The Helix on most endmills with a few exceptions is pretty much the same. The helix on the pictured hog mill is the same as a standard 2 or 4 flute endmill. If you really paid attention to my post you would realize I said depth of cut is 3/8" or better. Typically with these endmills you will take at least a 1/4" depth of cut the full width of the endmill or close to it. I have buried a 1" diameter cutter an inch deep and taken the full width pass all at once. You're never gonna get close with a conventional endmill. The more load you put on a cutter the more apt you are to pulling the endmill from the collet, thats just a simple fact.
I am not trying to be a butt head about this I am not a hobbiest at machining, it is my daily job and has been for more than 25 years, I have quite a bit of experience at what I do and am quite good at it.
I'm just offering a bit of info about the endmill holders and there use, there definitely better than collets but like I said, depending on there use are not always needed and I would not buy a full set of them just a few random ones for heavy cutting.

lazlo
08-05-2008, 12:06 PM
Mcruff-- I think the issue is the particular mill you have pictured...

If I am seeing it correctly, the helix angle and cutting resistance wants to pull the mill out of the collet.

Paul, that's a classic corn-cob rougher:


If that doesn't work, I've got 3/4", 7/8", 1" ETM R8 endmill holders that I occasionally use for my big corncob roughers.

Scishopguy
08-05-2008, 12:19 PM
As several have mentioned, gaining a little length of reach is sometimes a necessary thing. The BP at work had the 6" step block on the column and when I had to do plate work, as I often did, directly on the table on parallels, I needed that extra 3" to 4" that was gained by the holder sticking down from the spindle. I also did quite a bit of horizontal work on a rotary indexer and liked having holders to get in around the chuck jaws. I had a BP quick change holder set but it was pretty large in diameter and would not clear the clamps and spacer jaws in some cases. I used an ER 32 and the R-8 collets for most of my vice work, however. There are some jobs that you just need a holder for.

Just my $0.02 worth

PaulT
08-05-2008, 01:31 PM
I use ER32 collet holders in my BP sized manual mill and CNC machine, they definitely hold better than R8 collets and for me they work as well as endmill holders but give me more flexibility as I know I can hold any size endmill, drill or tap with them.

The only rub on ER32/ER40 is that most people (in the beginning including me) don't realize how hard you need to tighten them. If you look for specs on ER32 you'll see no less than 65 ft-lbs, with some companies recommending more than that. That's a pretty hard pull on the typical not so long ER32 wrench.

If you don't tighten them correctly you can have problems with endmills slipping, especially carbide ones since their shanks seem more slippery than HSS ones. I make sure the endmills and collet are free from oil with a quick wipe with lacquer thinner before installing, and since I've been torquing them correctly I haven't had anymore slippage.

I like the ER32/R8 holders and collets from www.maritool.com, he's a straight shooter that helps you both before and after the sale. I also use ER16/R8 holders for small endmills and drills.

Paul T.

BobWarfield
08-05-2008, 01:45 PM
I like my EM holders because they're fast to change with my powered drawbar. Setting up an we with a new cutter is pretty slow and it's expensive to buy multiples.

With that said, the eric's have less runout, so I use them with any cutter less or equal to 1/4". The cutter just lasts longer and works better.

tattoomike68
08-05-2008, 03:29 PM
If someone has never pulled an endmill from a collet they are obviously not pushing the cutter to its limits or trying to make money with it. Collets simply won't consistently hold a large endmill 5/8" or larger in diameter when worked hard. Light cuts they work great and will hold fine.

yep a collet wont do much work when you need to hog hard in hard metal. I have had to put a spot weld on a endmill shank to keep it from pulling out of an ER collet.

pcarpenter
08-05-2008, 05:16 PM
Paul, that's a classic corn-cob rougher:

I am quite familiar with them. :) I use them and like them. Saying "its a corncob rougher" still says nothing about what helix angle the flutes are presented to the work. I still maintain that end mills with higher helix angles are going to be far more prone to pull themselves out. Its simple force vectors....you have more force away from the center-line of the spindle. This in no way disputes your worthiness as a machinist, Mcruff, and there is no need to take a stab at those who are interested in this as a hobby. Machinists are generally fairly sharp people. So are some of the rest of us.

I believe you when you say you have had problems with end mills pulling out....especially since it sounds like you were taking huge cuts. I just also believe its going to be worse with an end mill that creates more force *trying* to pull the mill out of the collet as a higher helix mill will do. Thats not so complicated really.

However, if you take a look here, you will find that depending on application, the helix angle of end mill flutes is not all "pretty much the same".

These are kind of extremes, but here is one with a 45degree helix:

http://www.kennametal.com/en/e-catalog/ProductDisplay.jhtml?XMLArg=3745.xml&id=3745&level=&pid=8626753&navAction=push&item=category%3A3745

and here is one with a 25 degree helix:

http://www.kennametal.com/en/e-catalog/ProductDisplay.jhtml?XMLArg=3749.xml&id=3749&level=&pid=8626753&navAction=push&item=category%3A3749

and a lot fall in the 30-35 degree range.

Paul

John Stevenson
08-05-2008, 05:19 PM
I think we are missing the point.

The original post was given that he had a set of R8's and a ER40 system WOULD he need EM holders ?

As he's already set up with two systems to hold cutters then I ventured that I couldn't see a point.

Not extolling the virtues of one system better than others.

.

lazlo
08-05-2008, 05:23 PM
I am quite familiar with them. :) I use them and like them. Saying "its a corncob rougher" still says nothing about what helix angle the flutes are presented to the work.

I meant that McRuff's looked like a standard 30 degree corncob :) Back to the OP's question, I posted that the rare occasions that I've resorted to endmill holders (over R8 or ER40) were when I was plowing through stock with a big corncob.


I still maintain that end mills with higher helix angles are going to be far more prone to pull themselves out. Its simple force vectors.

Agreed, but the high helix (45 degree) endmills are almost always intended for aluminum, where the overall cutting forces are lower to begin with...

pcarpenter
08-05-2008, 05:33 PM
Agreed, but the high helix (45 degree) endmills are almost always intended for aluminum, where the overall cutting forces are lower to begin with...

That's what I always thought, but take a look at the link I posted. That high-helix mill is recommended for medium and harder steels. I think it has less to do with the material and more to do with the fact that the higher shear angle tends to produce more of a slicing action and less of a chipping action. With a sharp tool, slicing should take less cutting force than chipping. Helical slabbing cutters for use in horizontals tend to make for less jarring cuts from what I understand (as well as correspondingly smoother finishes). My guess is that this also may help with applications where you are trying to take heavier cuts.....its easier with a sharp cutter to slice than to chip at work.

In any case, with reference to the original posting...I too have a few EM holders. The small sizes I got because I found them cheap, used. The larger sizes are a necessity due to size constraints with the R-8 collet standard (they are for 1" and 1.25" roughers I have). It sounds like they merit a holder like this from a force standpoint...even if there was some sort of magic 1.25" R-8 collet :) Maybe the answer is that when you need them, you will know it:)

Paul

Mcruff
08-05-2008, 05:36 PM
I meant that McRuff's looked like a standard 30 degree corncob :) Back to the OP's question, I posted that the rare occasions that I've resorted to endmill holders (over R8 or ER40) were when I was plowing through stock with a big corncob.



Agreed, but the high helix (45 degree) endmills are almost always intended for aluminum, where the overall cutting forces are lower to begin with... Thats true most of the high helix angles like the 45* are intended for non ferrous materials. Not steel. In changing the helix angle to that high of an angle tends to thin and weaken the flute and the cutter becomes weak or useless for tough material. But my original statement is true, "most endmills have pretty much the same helix with a few exceptions". And actually my experience is that the higher the helix the less the pull, we use high helix drills all the time to drill in brass as they don't pull the drill into the stock as bad as standard jobber drills.
The picture I posted would be considered a shallow or low helix.
I also said that the endmill holder were only needed for certain situations and that I would not buy a set only a couple of key ones for roughing or heavy stock removal.
I also did not take a stab at anyone on here. I simply stated facts and gave an opinion based on years of use and experience. If you took it that way I'm sorry it was not intended that way. I have alot of respect for the guys on here that go blindly into some of the cool projects they make with little or no knowledge of how to do it other than the seat of the pants I can do it attitude and then come up with some really, really good results. I just try to offer my expertise and help them along the best I can.

pcarpenter
08-05-2008, 05:48 PM
No hard feelings and I am sorry if I was overly sensitive about what you wrote, Mcruff.

I agree with you on the issue of high-helix mills traditionally being for use with aluminum and that they don't leave much meat on the cutter. It looks like the one I linked at Kennametal which was for hard steels deals with this issue by making for rather shallow flutes, leaving more meat on the mill shank.

It seems a lot of the "rules of thumb" to some degree go out the window nowdays with regard to tool architecture. A lot of the modern, proprietary (read expensive) "carbide insert tooling design of the year" stuff, for example, seems to really bend some of the rules and allow for huge chip loads by old standards....something that most of us home shop types don't much need and can likely not afford.

In any case, I think we are all in agreement that tools that make lots of resistance either through heavy cuts or high shear angles or both make for good special cases for using an end mill holder if you otherwise might not.

Paul

lane
08-05-2008, 09:04 PM
Funny how every one can argue and say the same thing. It depends on what you are milling are the job its self. GET IT DONE.

LEOTECHCNC
08-05-2008, 09:12 PM
The high school kid came over the other day with a drill chuck in one hand, and a band aid on the other......asking me how to get the jacobs arbor back on the drill chuck. A 1/2 inch end mill was still in the chuck!
:p

Buckshot
08-06-2008, 02:59 AM
I recall a rather lengthly thread a year or so back about endmill holders on R8 shanks. As a home shop guy I get the impression that either the ER40's for the metric endmills I have, and if it's in the spindle whatever other cutter I need to use, or the regular R8's I have will suffice. I don't plan on pushing anything close to the limit :D

But from this thread too I can see the utility in having a couple endmill holders on R8 shanks, for the 'stickout' or their size.

One item from the older previous thread that has stuck in my mind is the fact that the cheaper endmill holders will bias the endmill to one side, due to the setscrew pressing it against the far side of the hole. It therefore describes an elliptic (to some small degree) instead of truly rotating about it's axis.

IIRC the better holders actually had the endmill hole finish honed slightly 'off' on the setscrew side to eliminate this? Would ETM be a company that does this offset deal?

Rick

toastydeath
08-06-2008, 03:42 AM
Tools don't pull out because of axial load sucking it down into the part.

They pull out because the torque on the tool causes rotational slip, and once it's overcome friction and is slipping, the axial load has a chance to pull it out or push it in. Helix has almost zilch to do with it, it's all about the torque on the collet. Look at an EM holder. The setscrew engages a wide flat area on the tool. It doesn't stop you from yanking the endmill down a bit, it only prevents the tool from rotating. If it was the axial load pulling the tool out you'd see some other mechanism to keep the thing in place, and no such provision exists.

Because of this dynamic, a low helix rougher is far, far more prone to pull out than a high helix finishing endmill of any sort, and the general experience around my shop echoes the same. Every single machinist at work setting up a rougher that's going to be involved in heavy cutting puts it in an EM holder. Sure, the runout is going to be worse, but who cares?

Personally, I never worry about runout for endmills (even finishers) in an EM holder because I think anything under 1/2" in one is a waste of time. If you're really worried about .0003"-.0005" of runout on an endmill over 1/2", you need more things to do with your time. If you want to finish a surface really purdy, use a collet. Or even better, flycut or facemill it.

I've only had a rougher pull out on me on a b'port once, under very heavy loading conditions. It isn't necessary 98% of the time, but it makes me feel happy to put a roughing endmill in a holder on a knee mill if I'm going to be wailing on it. It's that little bit extra to make sure something won't really go wrong. So I'd only buy one or two EM holders for home use, in the rougher sizes I like. Probably 7/8ths and 1/2".

Other than that, I don't see much of a need for EM holders on knee mills.

lazlo
08-06-2008, 10:02 AM
IIRC the better holders actually had the endmill hole finish honed slightly 'off' on the setscrew side to eliminate this? Would ETM be a company that does this offset deal?

Yes to both. I have several ETM endmill holders, and the hole is bored offset from the point of maximum TIR, so when the set screw is tightened, the tool is centered.

On the high-quality endmill holders you'll also get an airlock as you push tool into the holder: the hole is bored with a tight slip fit.

pcarpenter
08-06-2008, 12:27 PM
Tools don't pull out because of axial load sucking it down into the part.

They pull out because the torque on the tool causes rotational slip, and once it's overcome friction and is slipping, the axial load has a chance to pull it out or push it in. Helix has almost zilch to do with it, it's all about the torque on the collet.

Um...yeah...whatever.... The only thing that wants to pull the cutter out of its holder is force that comes from the helical nature of the cutter (other than a tiny amount from gravity acting on the mass of the cutter). When something slips in a holder, the frictional resistance to rotation does not go away. That frictional force is still there, its just overcome by rotational force. If you doubt that the frictional force is still there, let that cutter spin in its holder a while and watch it get hot.

Torque is, by definition, a rotational force. If the only force present on the cutter was torque, the mill would only spin in the holder. I have never had one come out of a collet so I can't speak firsthand, but mcruff (who is a professional as well) seems to imply that they do under heavy load. Without some force parallel to the axis of rotation of the spindle that can't happen. Given that the forces that are perpendicular to the spindle from a cutter that had no helix would only serve to push the tool *in* further (from the work pushing back on the cutter), what do you propose is the source of the magic "pull the cutter out of the collet" force? Gravity ain't going to do it because the work is going to prevent the cutter from merely dropping free under gravitational pull. Something has to actually pull the cutter deeper into the work to get it to come out...and that's a *lot* of force--all due to the helical nature of the cutter. Its so much force that it not only has to overcome the friction of the holder, but also has to drive the cutter deeper into the work. Increase the helix angle, increase the force. There are no little gremlins jumping up and down on the back end of that end mill trying to shove it out with that much force.

Really basic physics says that if you apply a force at an angle, there is some component force in each axis that makes up that composite angular force. With a helical cut mill, the contact between the cutter and the work is at an angle (on purpose) so that the cutter can slice rather than merely chop at the work. As you increase the angle, the portion of the total force that moves from being torque (perpendicular to the axis of rotation) to being axial (parallel to the axis of rotation) goes up. No need to argue with me, I am not making this up...talk to Isaac Newton.

Paul

ahidley
08-06-2008, 12:36 PM
Not to hijack the thread. But does anybody have a set that they want to sell cheap?

derekm
08-06-2008, 12:58 PM
...The only rub on ER32/ER40 is that most people (in the beginning including me) don't realize how hard you need to tighten them. If you look for specs on ER32 you'll see no less than 65 ft-lbs, with some companies recommending more than that. That's a pretty hard pull on the typical not so long ER32 wrench...



Paul T.

the typical hook wrench is short but then what are you tightening the hook wrench against?... There is no provision on my mill for a spindle lock and the flats on the collet chuck body are 46mm apart... and no spanner that large supplied (only the hook spanner came with the collet chuck) or in my toolbox. I had to make one.

I'm going to invest in a ball-race ER nut just to absolutely sure to go with the home made 46mm spanner.

BadDog
08-06-2008, 01:04 PM
pacarpenter: I realize you likely know much (or all) of this, but there are some other things to consider. What he's saying is that there are 2 basic categories of friction. There is static friction and "moving" friction. Static is generally much higher than moving, and this is what results in "stick-slip" behavior on ways. So, before that EM can move, the forces in some direction must be sufficient to overcome static friction. I think we can all agree that the rotational torque forces on an EM are much higher than axial forces due to the helix. Therefore, assuming that rotational friction and axial friction (or rather friction resisting forces in those orientations) is the same (or nearly so), and assuming that rotational forces are in fact much higher than axial forces, then it is safe to assume that it will rotate before axial movement is observed. But once that happens, the entire surface is moving relative to the collet, so we are now in the realm of sliding friction, which is considerably less than static. If that drop in friction suddenly drops below the axial force, then we get near simultaneous acceleration along the axis as well as rotation.

pcarpenter
08-06-2008, 01:15 PM
I think we can all agree that the rotational torque forces on an EM are much higher than axial forces due to the helix.

Yeah...until you look at a mill with a 45 degree helix like the one I posted. That was my point. A 45 degree angle means that half of the rotational force is converted into force attempting to pull the mill out of the collet-- that is not trivial. At say 30 degrees, less rotational force is applied in a direction trying to remove the cutter...but its still a substantial portion.

Its certainly true that a mill that pulls out may also spin. However, a hypothetical mill with no helix that spins is not likely to pull out, so its hard to make the argument that spinning causes them to pull out. The statement I was taking issue with is that helix angle had little to nothing to do with a cutter pulling out. Its a fair statement that slipping could happen with a no-helix cutter. However, I would argue that if there were no helix, the mill would just sit there and spin when the frictional force was overcome and its *only* because of the helix that it wants to pull out of a collet-- which was the original reason for suggesting that there are applications where only an end mill holder can prevent this. The greater the helix, the more the cutter wants to pull out under load.

A slipping end mill is bad news. An end mill that is trying to self-feed deeper into the work is something to really be concerned about.

Paul

BadDog
08-06-2008, 01:26 PM
Fair enough. When any force overcomes static friction, if other forces are above the moving friction (assuming no other interference), then there will be movement resulting from those forces as well. Exactly how much force/friction apply in each direction (particularly with the cutting edge of a helical EM) is a matter for much more complex discussion.

BobWarfield
08-06-2008, 01:35 PM
the forces are additive and will not act independently so it's a bit moot unless you just want to have a pointless argument.

The other problem with runout on small cutters is they're much more likely to break.

I do wish that instead of the assortments they'd sell a set with three half inch and two one inch em holders. That'd be handy!

Who has the best deal on decent holders these days?

BadDog
08-06-2008, 02:26 PM
Of course you are correct, the magnitude of the sum vector is certainly greater than either component. So, all things being equal, that is the force that will overcome friction. Of course, that assumes all things equal. :D But also as you say, the point is moot. Once it moves, at least port of that movement is likely to be downward, which generally means bad things...

toastydeath
08-06-2008, 02:44 PM
The reason I emphasized the "nothing to do with it" is because some people have a model where the tool pulls straight out, without any other events leading up to that. The point, and maybe I should have been more clear, is that by stopping the rotational slip of the tool, you remove a substantial component of the total force, and thus remove the ability for the tool to pull out axially under normal cutting circumstances. In the very first sentence of my second paragraph, which you quoted, I say "the axial load has a chance to push it out or pull it in." The only thing I could see that would generate that axial load was helix, and I thought that obvious. If it is not, that's my fault for not being more clear.

I used that phrasing to make a simple point, and did not want to get into component forces or the dynamics of the whole event. I did not want to get into the exceptions and caveats. Those do not occur under normal circumstances and are not useful to a machinist. I also did not state the obvious, such as a tool without helix would not pull out, or that a high helix tool will pull out faster. All of those things are absolutely true, but none of them are important to stopping pullout in the first place. And yes, there are all sorts of circumstances where the tool will move without slipping rotationally first. But none of those are what's being discussed, so I didn't discuss them.

Again, it wasn't my intention to be misleading, but what I'm saying is correct under the circumstances being discussed and is directly useful to someone who is concerned about a tool pulling out. That's why I phrased it the way I did, and I stand by that phrasing. Remove one component of the total force, and that remaining force has that much further to go before it overcomes static friction and pulls out. I can take your criticism, but I think negating what I'm saying is equally incorrect.

pcarpenter
08-06-2008, 03:59 PM
I know its minutia that most will not care about, but I hate to see physics butchered to explain something that is correctly explained with a different answer. No one has explained how exceeding a frictional force that resits rotation *removes or reduces* that frictional force such that you can blame the cutter spinning in the collet for it coming out.

Its certainly true that if something spins in a collet its not gripped well enough to prevent rotation and likely will not well resist axial movement either. That's not the same, however, as implying that its the spinning in the collet that allows the tool to pull out. Its the same lack of grip or frictional force that allows both. Until or unless you spin something enough to gall up or booger the surface, reducing surface area etc, the fricitonal force does not go up or down when the tool spins. Rather, you are just providing a rotational force that is exceeding the frictional force. The friction is still there. This of course ignores that if you have enough slippage, you may well weld the pieces together or at least increase their size until they sieze up....increasing (not decreasing) friction.

If you press a shaft in a hole with an interference fit and then turn the two until the shaft moves, have you removed the friction? The answer is NO. The resistance to rotation that friction creates has merely been exceeded by rotational force. The friction has not been reduced or removed by slippage. There is as much friction trying to prevent movement axially as ever. If slipping reduces friction, then lots of slipping should make almost all friction go away and you should be able to spin an interference fit like that faster and make nearly all the friction disappear. That would be magic and we would not need bearings or lubricants.

It is certainly true that if the friction of a collet was not enough to prevent spinning, it may well not be enough to prevent axial movement either--depending on what portion of the force is axial and what portion is rotational. Its this ratio of the two forces that is determined by the helix of the cutter, which is the reason I brought it up in the first place. It's this piece that may be the very reason that a high-helix cutter may be more likely to move axially--a really good reason to use an end mill holder. If your cutter was prone to spinning before it moves axially, then this is probably a moot point as it was never gripped adequately in the first place.

Please understand that I am not criticising *you*, but rather the argument that slippage reduces friction (in materials that don't easily disintegrate).

Paul

Evan
08-06-2008, 04:14 PM
Slippage DOES reduce friction. It's the stick-slip effect in action. The amount of force required to break the "stiction" effect can be a lot higher than the force required to keep something slipping that was formerly "stuck". It affects nearly any two surfaces in intimate contact and the better the surface smoothness the greater the effect as it depends on the action of Van der Waals forces which operate over very short distances.

John Stevenson
08-06-2008, 04:24 PM
it depends on the action of Van der Waals forces which operate over very short distances.

Wasn't he a Dutch detective on TV ?

.

toastydeath
08-06-2008, 04:52 PM
pcarpenter, you're replying to and rebutting things I am struggling to find in my posts, and so I guess I'm just going to drop it because I can't argue things I didn't say, or didn't mean to say. I'll give you the benifit of the doubt and assume there's a legitimate basis for what you're replying to. This makes me think I am not being clear enough, and others might be just as confused. I guess that's why I have to take a technical writing class as part of the ME curriculum.

I'm going to try to re-state my position one last time, and hope for some clarity:

The resultant force from an endmill with a helix yields two component forces/motions and I don't think anyone is disagreeing there - one is rotation, one is axial. As many have said, the resultant force is what determines breaking the static friction force. By using an endmill holder, the setscrew physically and positively blocks the rotation of the endmill, removing that force component from the friction equation in its entirety. The entire static friction force must now be overcome by the axial load generated by the helix of the endmill. As someone who has had endmills come out, I can say that the force required is very large and is highly unlikely to occur with just one component of the resultant force. At least without breaking the tool, that is.

This led me to simplify the situation by saying if you block the rotation of the endmill, the endmill will not slip out.

And I agree with Evan - the kinetic friction force is lower than the static force.

pcarpenter
08-06-2008, 05:16 PM
Edit-- to clarify, I started writing this in response to Evan's post and before Toastydeath's post so its largely in response to what Evan wrote.

So you are saying that in effect a collet and an end mill are "wrung" together and that that wringing is responsible for a substantive portion of the frictional force on the cutter? If initial friction is overcome in one direction allowing rotation in that direction, is the frictional force that resists movement in another direction also inherently diminshed (which is what is being implied)? I certainly don't question that there is an additional static resistance to be overcome initally through stiction, but I do question that movement in a different direction after that fact is because friction has been removed. Frictional forces are overcome and not removed in the case of a situation in which a fixed clamping force is applied. I have a hard time explaining that overcomming initial friction-induced stiction in one direction diminishes the initial frictional force in another direction.

Having pulled mills from collets, I would dispute the value of wringing as any substantial contributor to tool holding in that there is no where near the bond that you get with two better finished gauge blocks for example. Part of this is because while wringing will noticably prevent movement of two items laterally away from one another, those two items can be slid on one another much more readily (that's how you take "wrung" gage blocks apart) and with not even close to "tool holding force". If this tiny amount of lateral resitance to motion makes up a good portion of what is holding your cutter in place, then yes, indeed, you do have a problem and probably ought to tighten your drawbar more than finger tight. :D

Stick slip on way surfaces involves two highly finished surfaces *and* a cohesive fluid in between. I would like to think that as a group of machinists with good judgement, we are not lubricating our end mills before insertion into a collet.

Van der Walls forces are a molecular level atraction between objects...but has become one of those words that (however improperly) gets used to describe attraction between objects for one of several reasons...This reference seems to imply that three of these are correct.
In reverence to Tiffie :D http://en.wikipedia.org/wiki/Van_der_Waals_force

Paul

Evan
08-06-2008, 05:24 PM
Stick slip on way surfaces involves two highly finished surfaces *and* a cohesive fluid in between.

Stick-slip has absolutely nothing to do with a fluid film. Hard drive read/write heads have always had to be designed to deal with stiction, not always successfully. I assure you they are not oiled or otherwise bathed in any sort of fluid other than air. In fact, it is the air itself that helps to minimize the friction once the "seal" between the parts is broken. It acts as a form of lubricant, however poor, and reduces the friction forces in all directions once relative motion is established.

I shall also point out that one of the reasons that I chose bulk PTFE as linear way bearings for my mill is that PTFE is one of the very few materials that doesn't exhibit stick-slip. The reason for that is because it is a fluorinated polymer all "loose ends" in the molecules are tied up so that PTFE does not exhibit Van Der Waals forces on it's surface.

pcarpenter
08-06-2008, 05:26 PM
Toasty-- if you are not implying that friction is reduced by rotation, then I totally misunderstood what you wrote:



They pull out because the torque on the tool causes rotational slip, and once it's overcome friction and is slipping, the axial load has a chance to pull it out or push it in. Helix has almost zilch to do with it, it's all about the torque on the collet.


In re-reading this, it appears that perhaps "torque on the collet" may mean torque on the drawbar which determines frictional force. I thought you were implying that by applying enough force to turn the cutter in the collet, you were somehow negating the value of the frictional force between the collet and the cutter which would resist it moving the other direction.

The words "overcome friction" implied that if you spun an item it was no longer subject to friction that would otherwise prevent the cutter from pulling itself out.
paul

lazlo
08-06-2008, 05:27 PM
So you are saying that in effect a collet and an end mill are "wrung" together and that that wringing is responsible for a substantive portion of the frictional force on the cutter?

The Van der Waals force is a Red Herring -- as Paul implies, the endmill isn't wrung to the endmill holder. It's a tight slip fit, and on the better (non Chinese) endmill holders the endmill will make a sucking sound as it comes of of the endmill holder.


In reverence to Tiffie http://en.wikipedia.org/wiki/Van_der_Waals_force

Nah, if it was Tiffie, there's be a ton of unrelated links around it. ;)

toastydeath
08-06-2008, 05:38 PM
pcarpenter -

Nah, I wasn't trying to say that. What I was trying to say was that a setscrew deals with a major part of the resultant force that tries to overcome the friction holding the tool still, so that the friction only has to deal with the axial load to remain stationary. Sort of like the floor - I'm not going through the floor because the floor is physically blocking me; it has nothing to do with friction. If I stand on an incline and someone pushes me, I have to deal with both gravity and that person. If I'm standing on a flat, I only have to deal with that person pushing me (the axial force) and not the resultant of the two. Same with the rotary force on the tool and the setscrew.

And by overcome, I meant the resultant cutting forces becoming greater than the resisting friction force between the tool and the collet. Still subject to friction, but the friction is no longer sufficient maintain static equilibrium.

pcarpenter
08-06-2008, 05:48 PM
Evan-- Modern (last 20 years since I have been in the field) hard disk drive heads are not wrung to disk surfaces in any way. They are inherently "flown" over the surface of the disk in a controlled clean airspace so I don't understand where the frictional reference would in any way relate. Disk drives are assembled in clean rooms as even very small dust particles are large enough to span the gap between disk and head and at 15,000 RPM (on modern drives), the air speed of such particles inside must be really high. Any physical contact (caused by cohesive behavior or otherwise) is know as a crash and will damage the point of contact immediately. If you examine the platters from a modern drive, its very clear that there is no contact whatsoever. This is of course, not to be confused with floppy disk drives in which heads inerhently make contact with the magnetic media-- and subsequently wear it out.

http://www.storagereview.com/guide2000/ref/hdd/op/heads/opHeight.html

Paul

Evan
08-06-2008, 06:11 PM
The Van der Waals force is a Red Herring -- as Paul implies, the endmill isn't wrung to the endmill holder.

It's no red herring and wringing is not what is happening. The Van der Waals forces come into play whenever materials are in close contact. The smoother the materials the greater the area of close contact.

Friction and adhesion. Surface forces in friction and adhesion

B. J. Briscoe and D. Tabor
Atomic forces at the interface constitute the major factor responsible for friction and adhesion between unlubricated surfaces. For non-metals these are basically the van der Waals dispersion forces, though in special cases electrostatic forces may be involved. Some recent work on van der Waals forces at very small separations will be described. These forces provide a fairly direct measure of the adhesion between soft rubber-like materials and between polymeric solids. With polymers, such interfacial forces are sufficient to transfer portions of the polymer from one surface to the other when they are placed in contact or slid over one another. Frictional transfer occurs even for materials such as P.T.F.E.With metal surfaces, van der Waals forces are overtaken by metallic bonding when the regions of contact are separated by distances comparable with atomic dimensions. This leads to very strong adhesion between metals which are atomically clean.
(note that this describes the opposite case of what we are considering. In other words it is the Van der Waals forces that dominate since our end mills most certainly are NOT atomically clean.)
By contrast, very small quantities of active vapours adsorbed at the interface can produce a drastic reduction in adhesion. Another factor which greatly influences the adhesion of a metal is its ductility: metals which have a limited number of slip planes usually show smaller adhesion.The importance of ductility is also shown in the behaviour of very hard materials such as TiC or diamond in ultra high vacuum. Intimate contact is restricted to individual asperities, and the adhesion for very clean surfaces is far less than might be expected from calculations based on surface forces. This is partly because the area of real contact is very small; partly because of the brittleness of these materials. If one of the surfaces is soft or ductile adhesion may be quite strong. For example the adhesion of clean TiC to TiC is extremely small; of clean copper to TiC extremely large. Here again surface films can greatly reduce the adhesive strength.

http://www.rsc.org/publishing/journals/article.asp?doi=s19720200007

Here is a description of how relative motion changes the energy levels in such a manner that the Van der Waals forces may become repulsive.

https://www2.lsdiv.harvard.edu/labs/cohen/Research/NoneqVdW/NoneqVdW.htm

Evan
08-06-2008, 06:14 PM
Modern (last 20 years since I have been in the field) hard disk drive heads are not wrung to disk surfaces in any way. They are inherently "flown" over the surface of the disk in a controlled clean airspace so I don't understand where the frictional reference would in any way relate

The issue is when they are parked, not when they are flying. I just had a hard drive fail in one of my machines. When I took it apart one of the heads had been ripped from the arm. Since the hard drive failed at the moment of start up I assume that it was stuck to the landing zone.

lazlo
08-06-2008, 06:33 PM
It's no red herring and wringing is not what is happening. The Van der Waals forces come into play whenever materials are in close contact.

OK, so take an endmill, put it in an endmill holder. Hold it upside down. Endmill falls out. No Van der Waals forces here.

Not surprising, since an endmill shank usually has a tolerance of +/- 5 tenths, and the endmill holder hole has a tolerance of +/- 5 tenths, and hole is oversize by ~ 5 tenths.

Evan
08-06-2008, 07:07 PM
OK, so take an endmill, put it in an endmill holder. Hold it upside down. Endmill falls out. No Van der Waals forces here.

Yes there are, but not enough to matter since the points of near contact are extremely few. Clamp down a collet and that changes as it also does for a taper bore and many other situations. It isn't the only contributor to friction by any means but it is one that changes magnitude very considerably when relative motion occurs. That of course is part of what happens with stick-slip. Van der Waal forces only act over VERY short distances measured in atomic radii so casually inserting an end mill in a holder isn't going to reveal them. However, it is part of why you cannot insert a 1" rod in a 1" hole.

(related to gecko research and other applications)



In order for the dry adhesion to
function, a small preload force normal to the
surface is required to force the compliant hairs
to configure themselves properly. Once this
preload force has been applied, the material will
stick until peeled off. The adhesion force can be
as high as 10N per 1cm2 area

Since dry adhesion is caused by van der
Waals forces, surface chemistry is not of great
importance. This means that dry adhesion will
work on almost any surface.

.http://www.ensc.sfu.ca/~cmenon/Paper/2004_IAF_waalBots.pdf

oldtiffie
08-06-2008, 07:13 PM
No Van der Waals forces here.

Good idea.

That topic has been pretty well debated and flogged to death on several (many??) occassions in other (many??) other posts previously.

Can we please remain focused on the OP topic which is: "R8 endmill holders".

Evan
08-06-2008, 07:23 PM
The topic is focused on the issue of collets slipping or not as a reason to use holders. The issue of Van der Waals forces is directly relevant to the subject of such slipping and the possible reasons.

oldtiffie
08-06-2008, 07:40 PM
OK - point taken regarding the relevance of Van der Waal/s et al.

I appreciated the relevance of VdW in the case of "wringing (togther)" of "Slip" (Johannsen/"Jo") blocks and the like. That is a far cry from collets generally in the home shop.

Given the volume (wealth??) of knowledge regarding VdW and the ready access to it by way of links to previous posts and threads, any expanded reference to VdW may be able to be achieved by posting the relevant links - for those that are interested.

Given the title of the OP and the main interest being the practical application of and/or relationship/s to R8 collets in particular in the practical day-to-day use of them in the home shop, I'd prefer to stick with and to R8 specifically and collets generally.

Evan
08-06-2008, 07:51 PM
Well then, to complete the relevance chain of the VDW forces as pointed out by the quote I provided above, to engage the "real" frictional forces in a collet it is very important that the collet ID and the tool OD be as clean as possible. Not atomically clean as that is impossible in the shop situation but clean.

I use collets almost exclusively although I do have several holders. I have not yet had an end mill pull out of the collet, either in MT3 collets in the lathe or R8 collets on my mill. I have had an occasion where a 3/4 inch end mill was able to pull the work from a vise while being used in a collet. I do keep them clean. I always have a roll of paper towels handy.

derekm
08-06-2008, 08:06 PM
Wasn't he a Dutch detective on TV ?

.
No that was Van Der Valk :) unless the slippage is at "Eye Level"
if you can remember before 1992.

oldtiffie
08-06-2008, 08:22 PM
Right on Evan. Hygiene is a "must" for collets etc.

I'd have another and more urgent and immediate use for that roll of paper towels if a job was lifted from my vice - but it can and does happen!!.

Seriously though, you raised a couple of good points. I keep paper towels and clean/used rags in my shop as well - and they get used!!.

"Lifting from a vice" is a distinct possiblity that is rarely if ever addressed here. All of the emphasis seems to be on holding the vice to the table and just "clamping" the vice with all of the emphasis on holding the job down onto the fixed part of the vice or parallel strips etc. and not considering stopping it "walking up" the end mill cutter. I will concede that it might be assumed or inferred or that "everybody should or does know", but it is rarely mentioned.

The vice therefore is as important as the collets (R8 included) in terms to ensuring that the work or cutter does not move "up/down" relative to each other.

In that regard, your comments about the importance of adequate "grip" is "spot on".

mochinist
08-06-2008, 08:24 PM
gotta put a cheater bar on that vise handle :)

lazlo
08-06-2008, 09:01 PM
OK, so take an endmill, put it in an endmill holder. Hold it upside down. Endmill falls out. No Van der Waals forces here.
...

Van der Waal forces only act over VERY short distances measured in atomic radii so casually inserting an end mill in a holder isn't going to reveal them.

Exactly.