Collets: ER 11 vs ER 20

Thinking about a spindle and wondering if I should go with ER 11 or ER 20. I’m leaning ER 20 so I can use 1/2" bits. I don’t think I’d ever need a 1/16" bit which I’d be missing out on. Am I missing anything?

You can get 1/16" ER20 collets.

Okay, I was going by what was available on the PwnCNC site. So is there an advantage of one over the other; is bigger better?

I am fairly new to CNC machining, so I would wait to here from those more experienced. For my ATC build Ibought both ER20 and ER 16 ISO20 holders. Although the ER20 gives a wide range of options for end mill diameter, one consideration is the size of the holder. I can still put 1/4" end mills in my ER16 collet, but the smaller holder/nut diameter means I have more clearance when machining deeper in wood or aluminum, which for me was important.

The combination of spindle RPM and machine feed rates/accelerations available with the Onefinity machines, means you can use the full range of end mill diameters available for both collet sizes, while also achieving optimum chip loads and MRRs.

When purchasing a spindle, the most important thing I can think of to consider is the clearance of the motor body and the Z-axis stepper motor. If you have the first generation Z-slider (a.k.a. Z16) and are using the default 65mm mounting bracket, you will likely run into trouble with the top of the spindle motor hitting the stepper motor. There are posts here, and probably Youtube, about this.

If you purchased the optional 80mm mounting bracket for this Z16 slider, it should keep the spindle far enough away from the stepper motor.

With all that said, I believe any 65mm diameter spindle motor will use an ER11 collet, and you can get an ER20 size collet on the larger 80mm motors.

I’m not 100% sure, but if you have the new improved Onefinity HD slider, you should also have no problems with interferences or blockages.


Hey Ken,

I think you should buy the spindle that matches the work you intend to do, so first you have to decide this.

E.g. if you make only things like this,

you can see you can do everything with bits with a 8 mm shank (5/16", 0.3125"), so a spindle for ER-16 collets (bits with shank from 1 to 10 mm) would be enough, while a spindle for ER-11 collets (bits with shank from 1 to 7 mm) would be to small.

But if you are used to bits with a shank of 1/4" (6.35 mm) like you used on your hand trim router, then a spindle for ER-11 collets is fine.

Spindles with an outer diameter of 65 mm, like this one, are limited to ER-11 collets, as far as I know.

But this also means from the moment on you decide you want a 80 mm spindle, you have to choose between a spindle for ER-16 collets and one for ER-20 collets (bits with shank from 2 to 13 mm, including 12.7 mm (=1/2"). One question is, have you ever needed a bit with such a thick shank, or ever seen one? But this is not the only point to consider. As long it’s not a spindle with interchangeable tool holders (ATC, ATC spindles), the axle and the bearings are of different size on ER-16 and ER-20 spindles, which means the spindle differs in contruction.

Once the 80 mm spindle holder was out I ordered it and I came accross the question whether to buy a 2.2 kW spindle with ER-16 or with ER-20 collet. The first takes tool shanks from 1-10 mm and the latter from 1-13 mm, which would mean half-inch tools. But since at first I did not expect to use tools larger than 8 mm, I was unsure. I asked the manufacturer and he answered, the spindle with ER20 collet has larger bearings and a stiffier shaft. Larger bearings means longer life. Stiffier shaft means more precision. Also one should take into consideration that when using tools with a larger shank, the thicker the shank the stiffier the tool and so the longer the tools you can use – and thus the deeper the pockets you can mill into your workpiece. So I went for the ER20 spindle.

Further reading

1.5 kW or 2.2 kW spindle?

Regarding power, you can always choose the stronger spindle as well as the stronger VFD, as inside the VFD, you have to limit the max. power to be delivered as a mandatory setting anyway. You can use a weaker spindle on a stronger VFD by setting it accordingly, but you can even have a stronger spindle and use a VFD that only can deliver less power, and buy a stronger VFD later. What you have to consider as the most important thing regarding power, is what the supply circuit in your workshop can deliver. For this, you need to know the rated input current (in Ampères) of your VFD. For a 200–240 V VFD with single-phase input for a 2.2 kW spindle, this is usually 24 A:

(For the same power in 120 V this would be the double: 48 A).

Note that shown is the nameplate of a VFD for single-phase input (which is usual in the U.S. since you have split-phase electricity in U.S. domestic areas), which means that all the power comes over one input wire which explains why the input current is more than the double than the output current (where the current is spread over three wires, since any spindle is driven by three-phase electricity that the VFD, which in fact is an AC-to-DC-to-AC inverter, produces on the fly), and where the power is spread over three wires with 120° phase shift. On VFDs that have three-phase input, the input and the output current ratings differ less, only the VFD efficiency comes into play here.

In Europe you have 400 V three-phase electricity with at least 16 A per phase everywhere, which means you can buy a VFD with three-phase input and you can draw 11 kVA so use a 7.5 kW spindle on normal domestic supply (or the double if you have a 400 V three-phase circuit with 32 A), while in the US in domestic areas you have usually split-phase electricity with 120 V and 240 V which limits you to VFDs with single-phase input, and regarding available power on the supply circuits you can use a 1.5 kW spindle on a 120 V socket or a 2.2 kW spindle on a socket with 240 V.

Note 1: To sell you 2.2 kW spindles for U.S. 110 V, chinese VFD manufacturers simply omit the input current rating on their nameplate and in their manuals. The rating would be too high on this power (2.2 kW) for any available 120 V circuit in U.S. domestic areas.

Note 2: On chinese spindles (not only on cheap no-name, but also on Jianken spindles), the power rating is often wrong.

Hey Forrest, hey Ken @KenA

yes! One post about this phenomenon on the Z-16 assembly on Original Series here, with links to an interesting workaround:

Seel also here for more information about 65 vs. 80 mm mount on Z-16 assembly on Original Series.

I will most likely be taking advantage of the Elite upgrade. Along with that, I’ll need to get the heavy duty slider so must choose between the 65 and 80mm mounts. I’d like to upgrade to a spindle so figured now would be the time to do that as well and if I’m going to do that I’m going to go with pwnCNC. Among the choices there is ER 11 vs ER 20 so that’s what brought me to this question.

I appreciate all of the input.

If you’re possibly interested in automatic tool changing, wait a few weeks before buying a spindle. PWNCNC is about to release their ATC in November. It’ll use ISO20 carriers capable of holding ER20 collets and up to 1/2" shaft tools.

You’ll want the 80mm mount from Onefinity in any case.


Nick N. at Sola Fide Designs KC is also getting ready to launch his, but it will be an ISO30 with a unique mount as it is not an 80mm cylindrical bodied spindle.

Looking at his other stuff, and having read his posts on FB, I’d stay away from that like the plague.

Could you explain your concerns so that I, and perhaps others, better understand your comment?

1 Like

Hey Espressomatic,

I express myself the same way sometimes, but I don’t miss to justify it with references.

Unfortunately I blocked that person on Facebook a while back so I’m unable to copy any reference material. Anyone who hasn’t however can go ahead and read in both the official and unofficial 1F FB groups and come to their own conclusions.

For me, when it comes to supporting a vendor, I’m likely to go with someone giving back to the community and someone who comports themselves with honesty and integrity, which is why I’ve continued to give business to PWN.

This is not true. As it is a gated community, not everyone can do this. This is no reference.

And the question was not this. You say nothing with this. The readers here are left without without any idea what you mean and how you come up with it. And if Nick is a businessman, then your post would be an offense in my country and you could be legally sued for injunctive relief including payment of costs and damages.

My personal interest was not in views regarding the character of the vendor, rather the product. I provided the information so that others know there are a growing number of options when it comes to plug and play ATC spindle kits for the Onefinity.

From reading your comment, I thought there was a technical/mechanical reason for your opposition the Nick’s ATC offering, but given its tone and disparaging nature it would appear that there is a lot more involved here.

As you note, best let others decide for themselves which products and vendors suit them best and will meet there needs…

Hey Tom, hey @Espressomatic, hey all,


and that would be the matter of interest in this forum.

I’d love to see that attempted in any jurisdiction. I have legal representation waiting. * and I have some experience being on the offense side of such proceedings. Enough said about that.

But let’s not allow this to get any more off topic. I gave my position stating that I simply would not do business with that vendor under any circumstances. No disparaging content mentioned whatsoever specifically nor indirectly about same.

There is currently one and only one ATC product available and demonstrated for our CNC, and that’s the ATC offering from PWN, up for order as of next week. Waiting a week before ordering a regular spindle, not a big deal. Waiting on some unrealized vaporware for an indeterminate amount of time, well that’s not something someone in the market right now should consider.

you could better start to justify why you say the product mentioned above is not to recommend, or simply shut up, or risk to be plonked again.

PS: Just in case someone wants to know: Strafgesetzbuch (StGB) – Bundesrepublik Deutschland
§ 185 – Beleidigung
Die Beleidigung wird mit Freiheitsstrafe bis zu einem Jahr oder mit Geldstrafe und, wenn die Beleidigung öffentlich, in einer Versammlung, durch Verbreiten eines Inhalts (§ 11 Absatz 3) oder mittels einer Tätlichkeit begangen wird, mit Freiheitsstrafe bis zu zwei Jahren oder mit Geldstrafe bestraft.
§ 186 – Üble Nachrede
Wer in Beziehung auf einen anderen eine Tatsache behauptet oder verbreitet, welche denselben verächtlich zu machen oder in der öffentlichen Meinung herabzuwürdigen geeignet ist, wird, wenn nicht diese Tatsache erweislich wahr ist, mit Freiheitsstrafe bis zu einem Jahr oder mit Geldstrafe und, wenn die Tat öffentlich, in einer Versammlung oder durch Verbreiten eines Inhalts (§ 11 Absatz 3) begangen ist, mit Freiheitsstrafe bis zu zwei Jahren oder mit Geldstrafe bestraft.

Autotranslated with Criminal Code (StGB) – Federal Republic of Germany
§ 185 – Insult
Insult shall be punishable by imprisonment for a term not exceeding one year or by a fine and, if the insult is committed in public, at a meeting, by disseminating a content (Section 11(3)) or by means of an assault, by imprisonment for a term not exceeding two years or by a fine.
§ 186 – Defamation
Any person who, in relation to another, alleges or disseminates a fact which is likely to bring him into contempt or to disparage him in public opinion shall, unless such fact is demonstrably true, be liable to a custodial sentence not exceeding one year or to a monetary penalty and, if the offence is committed in public, at a meeting or by disseminating a content (Section 11(3)), to a custodial sentence not exceeding two years or to a monetary penalty.

OK, I see you’re back to your usual self of leveling insults to make up for the fact that you have nothing else in your life to do and lack the knowledge of any subject matter you can’t take the time to search on wikipedia. Please, like so many others have said in the past and will continue to do so in the future, stay away from me and my posts. You offer nothing that besides regurgitation of others work and knowledge.

You’re getting blocked again as I can’t stand to read your long-winded garbage.