[EvolveES]

Hi Everyone, this weekend i saw something interesting and i thought i would share it. This may be common knowledge to many but it sure wasn't for me and i found it very helpful.

We were cutting out some 10" diameter discs (in two operations) in .25" thick 6061 and using the tool we usually do: a .25" diameter carbide coated stub end mill and we cut it in a single pass at .25" depth. The table clamps were a little close for comfort for me so i said to my friend i am going to switch the tool to a set screw holder (smaller diameter = more clearance around clamps). I had to grind a flat on the end mill for the set screw. I put it together and re-measured the length and on the next part the machine ran quieter and smoother than before, no screaming or chattering and the chips even looked better, a little thicker and more shiny. I couldn't believe it.

So we also switched out the .375 carbide end mill we usually use for roughing and did some cuts that we usually do for production and sure thing, it was much quieter as well. I am so used to hearing the carbide end mills scream unless you back way off on the speeds and feeds that i just assumed it was normal.

I guess the conclusion is that the set screw holders are much more rigid than the ER20 collet holders and from now on all heavy cuts we will use the set screw holders. I hope this was helpul to some people

[adamvs]

Evolve, it kind of *is* one of those things that is common knowledge. But thanks for the 'side by side' empirical data. And hey, set screw holders are cheaper too!

[wtopace]

Thanks for sharing!

I have normally preferred collet holders for their lower runout numbers, but I think I'll start using my set screw holders more now!

[EvolveES]

ya, i thought it may just be a newbie thing i just discovered that many already knew...and ya i was happy when i thought about the price difference too .

And ya my instinct was to use ER holders because of their precision too, but now i think i'll do all of the roughing with set screw holders and then do the finishing passes with the ER holders.

[SCzEngrgGroup]

And you really don't need to grind a flat on the tool - it'll hold just fine without it.

Regards,
Ray L.

[yulolaf]

Get tools with a Weldon flat if you can, the flat is important for holder rigidity, run-out and gripping force. "Hand ground flats don’t have a precision ground surface and can result in tool slippage and excessive run-out. When using traditional end-mill holders that use a set screw for gripping the tool. It’s important to have a Weldon flat ground on the shank of the tool." I'm only pointing out to the OP that his grinding his own flat is not recommended practice as I quoted from Niagara.Technical Information from Niagara Cutter, LLC There is a reason they make some endmills with Weldon flats (for setscrew holders) or without (ER holders) It's good practice to use proper tools and procedures.

[mak]

Good to know! I was always an ER20 user for the precision.

[SCzEngrgGroup]

Get tools with a Weldon flat if you can, the flat is important for holder rigidity, run-out and gripping force. "Hand ground flats don’t have a precision ground surface and can result in tool slippage and excessive run-out. When using traditional end-mill holders that use a set screw for gripping the tool. It’s important to have a Weldon flat ground on the shank of the tool."

I've used endmills without flats in set-screw holders for many years, and never once had one slip even the tiniest bit. The flats are completely unnecessary with the amount of power these machines have. At 5HP they may be necessary, but at 1.5HP, they are not. The flat has zero impact on runout. That is entirely determined by the relative diameters of the tool shank and the bore in the holder.

Regards,
Ray L.

[mountaindew]

I always want to learn the right or best practice if possible. not what I can get away with, also tricks and a bit of magic never hurts.
I find the Weldon flat holders and the cutters I put in them tend to have far less overhang then tools I tend to put in er20 holders.
I mostly figured I was seeing, a little better performance because of this reason.
md

[tmarks11]

I like the setscrew endmill holders better than ER20 holders because:
1. Cheaper
2. More rigid
3. Gives you a better view of what you are cutting
4. Easier to put an endmill in a set screw holder than in a ER20 collet holder (never really sure I get the thing tight enough).
5. Personal opinion: not convinced that cheap ER20 collets really give you enough of a difference in run-out to improve the cut quality. If I used really small end mills, I might care, but I don't.

I tend to use endmills with weldon flats because it is more convenient. Since I never buy any without, I can't really comment on how important this is.

[pickled]

I use them both and I will admit that I sidestep the best practice of grinding flats on occasion too. To be honest I'll even throw in R8 collets for simple parts without tool changes. One of the more difficult aspects of working with ER20 is getting coolant flow to tiny end mills when you are doing 3 D contours. I do tighten the sh!t out of my ER20's and have not had a problem with pull out nor chatter as was described by the OP. Set-screw holders sure are nice to set tools up in though.

[LeeWay]

My 2 cents. I was not aware that the ER collets made end mills complain. All my end mills with the exception of 1/8" carbide are in set screw holders. My ER holders hold drills and taps.
Some of my end mills have flats, some do not. If they have them, I use them. If not, I don't sweat it. I haven't ever had one slip in a set screw holder before.
Now all my holders are Tormach brand. Another brand might not do as well.
I have a couple of set screw holders from Tormach that do not have the ATC groove in them. They are pretty old. They did come with softer set screws, but once I replaced the screws, they have been fine. None of the newer style come with soft set screws that I have seen.

[EvolveES]

I did not know that you could run a set screw holder with an end mill that did not have a flat, that is interesting and good news to me. I have used mostly ER holders because i thought they were more precise, i put a .25" diameter precision rod in a 1/4" set screw holder and was VERY surprised at how little run-out it actually had, i don't remember the exact number it was a while ago, but it was on par with the ER holders. I will be using (and ordering) a lot more set screw holders now and can keep you posted on the experiences.

[keen]

Hi - The difference in cutter chatter between the two holders may be more to do with the different projected length from the spindle bearings cause different harmonics.

Cheers, Keen

[mountaindew]

Wow
I must have dreamed there was more posts on this thread!
I wanted to read and see answers to turbo steps questions. I find his experience and information or answers to questions very accurate and worthy of taking notes on
Maybe I was on another forum!
md

[yulolaf]

I did not know that you could run a set screw holder with an end mill that did not have a flat, that is interesting and good news to me. I have used mostly ER holders because i thought they were more precise, i put a .25" diameter precision rod in a 1/4" set screw holder and was VERY surprised at how little run-out it actually had, i don't remember the exact number it was a while ago, but it was on par with the ER holders. I will be using (and ordering) a lot more set screw holders now and can keep you posted on the experiences.

Here's some more information for your consideration, as per Tormach, "Set Screw holders are our most popular and affordable tool holders. They are commonly used for general milling applications. Set screw holders are intended to be used with end mills that have a Weldon flat on them." http://www.tormach.com/product_tts_holders.html It sounds like they understand the reason things are the way they are in the industry and try to get that info to their customers. take it or leave it.

[CNC-Dude]

Yeah man! This is common knowledge, especially among those who commonly already knew it ;-) As it turns out, I was completely oblivious to this fact, so thank you very much for bringing it up!

I do use the set screw more than the ER collets but due to cheapness on my behalf, not because I was scientifically aware that they are better. In my case, I have had little issue (as in none) with either, so I was under the impression that either was equally good. Have never gone through the experience of comparing them, so what you have detailed here is quite valuable.

What I can add to this thread, however, is that I had always been expecting the set screw mills to shift out of place, but as have been already explained, it doesn't happen. The way I saw this, if the mill is sharp enough, it will remove the material long before the upward forces can push it out of place. As a result, the end mill stays in place. I also imagine that if you are doing lots of plunges, then this might affect the mill position, especially if not done correctly. I guess this is a matter of which friction wins. The friction between the mill and the holder walls, and the friction between the mill blades and the metal.

The question I have, however, isn't the collet version supposed to give you better centricity? And if such, shouldn't the set screw offer more vibration (as it is somewhat eccentric)? Intriguing, isn't it?

[SCzEngrgGroup]

Yeah man! This is common knowledge, especially among those who commonly already knew it ;-) As it turns out, I was completely oblivious to this fact, so thank you very much for bringing it up!

I do use the set screw more than the ER collets but due to cheapness on my behalf, not because I was scientifically aware that they are better. In my case, I have had little issue (as in none) with either, so I was under the impression that either was equally good. Have never gone through the experience of comparing them, so what you have detailed here is quite valuable.

What I can add to this thread, however, is that I had always been expecting the set screw mills to shift out of place, but as have been already explained, it doesn't happen. The way I saw this, if the mill is sharp enough, it will remove the material long before the upward forces can push it out of place. As a result, the end mill stays in place. I also imagine that if you are doing lots of plunges, then this might affect the mill position, especially if not done correctly. I guess this is a matter of which friction wins. The friction between the mill and the holder walls, and the friction between the mill blades and the metal.

The question I have, however, isn't the collet version supposed to give you better centricity? And if such, shouldn't the set screw offer more vibration (as it is somewhat eccentric)? Intriguing, isn't it?

Never under-estimate friction. It can work miracles.

A collet chuck will give you better concentricity only if the collet chuck and the collet itself BOTH have near zero runout. Otherwise, it will be no better, and potentially worse, than a set-screw holder, which will at least have a very consistent run-out. Bottom line - unless you actually CHECK the runout on every holder, after mounting each tool, you have no idea which is better on runout.

Runout on a decent set-screw holder should be quite small - on the order of a few tenths, which is not enough to materially affect balance at the speeds these machines run.

BTW - For most tools, the forces created by the cutting edges are trying to pull the tool down rather than pushing it up.

Regards,
Ray L.

[Bryan Turner]

The bore in the set-screw holder defines the centricity of the tool. More precise bore with less room for wobble = more centricity. The set screw simply holds the end mill in place vertically. A really sloppy set screw holder with a large bore (say 0.379 for a 3/8" tool) would cause poor runout because the set screw will push the tool to the side of the bore, 0.002" out of center. Thus the need for good quality holders.

ER Collets have the problem of "stacked error": error in the collet, error in the bore of the collet holder, error in the 3/4" shank, and finally error in the spindle alignment. They work best when you 'clock' the tool in the spindle (mounting the tool at different angles of the spindle's rotation and measuring runout at each). They also have more opportunity for eliminating runout, since you can also 'clock' the collet in the chuck. But all of this is quite tedious.

So: Set-screw holders for roughing and semi-finish (more ridgid, less stickout, easier access to shoot coolant/air at the tool). ER collets for odd-size end mills/drills, and fine finishing/precision work when you 'clock' the tool holder properly to minimize runout.

[EDIT]: Ray is right about the "pulling down" forces on the endmill. I always pull the tool out as far as the weldon flat allows before tightening, so any slippage would be immediately terminated by the flank of the flat.

Hope that helps!
--Bryan

[EvolveES]

WOW that is a lot of great information everyone. I'm glad this is news to some other people too and they can benefit from things on this forum like i have. I like the idea of pulling out the end mill up against the set screw when tightening, that way IF it did move it would have moved up and you could always re-cut, where if it pulled out your part may be ruined. I have also had the thoughts about the repeat-ability of set screw holders vs collet holders. I feel more comfortable that the set screw ones will repeat whatever error they have, you just clean the bore and put the end mill in. the collet ones i find myself getting overly fussy about how they are going together, i usually blow off and wipe with a rag, the holder, the collet, the top nut, and the endmill EVERYTIME i adjust one or change a tool (even if it is the same size as the one that was just in there. This may not me necessary but if i don't do it i think it may not repeat...a bit neurotic i know.

I think i will be buying more collet holders and following the model of roughing and some low tolerance finishing with them, and then leave the custom sized and high precision finishing to the ER holders.