But why can’t you use a 1/2 bit? on a VFD?
You can on the C3D 80mm spindle, the C3D 65mm max diameter is 1/4”.
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You can, you just need to get a VFD with a big enough collet.
Now if you want to know why you can’t use a 1/2" bit on the 65mm VFD, I’m guessing that’s just an engineering decision. A larger collet needs a larger shaft, it may need more cutting power than a 65mm can supply, and the bearings may not be up to the task for the larger loads.
The ER-11 can handle up to 8mm shaft. Not a common size in N.A., but I think more available in europe and asia.
The collet and bits mount on the spindle.
The Variable Frequency Drive drives the Spindle…
Since the original poster was talking about a ‘VFD with a 1/2" capacity"’, I just assumed that the entire system (VFD + spindle) was being referred to as ‘VFD’, and continued in the same vein.
I’m using half inch bits with my C3D spindle. Works fine, a 2" diameter surfacing bit with 1/2" shaft makes that operation a lot faster.
It’s a bit more common if one considers 5/16" tooling (7.9375mm) as an equivalent.
It’s also being popularized by various other products, and I’ve had good success with tooling in this size when I’ve tried it.
I got the 8mm ER-11, can’t remember where I found it. I was surprised by how little / thin it seems. There wouldn’t be room for anything bigger.
Each collet holder is machined specifically for the taper angle of the ER collets within that series. REGO-FIX developed the ER series and in 1972 it was released to the industries that required quick and accurate methods of tool holding.
You select your ER collet series based upon the tooling you wish to use. In my 2.2kW ER 20 spindle I can use collets in the range 1 ~ 13mm but if you were machining metals that were very hard, you may consider that a 13mm collet, while big enough to take a 1/2" tool, would not provide the machining accuracy.
Apart from the 1mm collet which has a clamping range of 0.5mm, the ER 20 collets in the range 2 ~ 13mm offer a 1mm clamping range. My ultra precision collets are from REGO-FIX and have a total indicated runout (TIR) of 5 μm (0.000196") It should be remembered that collets are regarded as a consumable item and they should be replaced at intervals where the performance has deteriorated from the specifications.
The following link provides the information and a technical drawing (click on the PDF link) for each collet size.
https://us.rego-fix.com/en/products/collets/ultra-precision?system=ER&country-detected=true#
The illustration below shows a full ER 20 collet range (1mm collet does not fit in this box) along with each collet’s clamping range.
The next illustration shows a 40 ~ 200 Nm torque wrench with removable head for castellated clamping nut.
Castellated clamping nut showing external and internal features.
Threaded portion of spindle which is the non-removable segment of the depicted spindle. It will only take ER 20 collets because of the machined taper that is specifically made for the ER 20 collet dimensions and angle
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