Fit Router Bits into collet on VFD

I am having a hard time getting the bit and collet to fit in enough to tighten the nut. I’m having the darndest time figuring it out.

I can fit the collet in and fix the nut if there is no bit. I’ve been able to successfully change the bits a few times, but now I cannot seem to get the nut on with the bit in the collet.

  1. I can insert the collet and thread the nut without the bit. I am not putting it in upside down
  2. If I thread it just 1/8th of a turn to get the minimal amount of purchase on the thread, the collet is too tight for the bit to fit, and it feels like the only way to get it to fit will result in cross-threading
  3. If i insert the bit into the collet and then try to attach it to my VFD, it will not fit. I am confident I haven’t cross threaded it as it works just fine without a bit in it.

The collet just doesn’t fit into the spindle with a bit in it - somehow, not always, but right now.

Does anyone here have tips for getting the bits in a VFD without trouble? It’s like the pirate with the steering wheel in his pants - drivin’ me nuts!

The collet has to snap into the inside of the nut before you thread it onto the spindle shaft. Be sure the taper on the inside of the nut is and collet are clean before before snapping it in.


That’s it! Thank you. Knew it was something basic. I will be able to sleep tonight, thanks to you! Looking forward to learning more of this so I can contribute back.

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One more issue with ER collets is the collets come in sizes with a limited range. So if using a 1/4" bit use a 1/4" collet. Same is true for metric bits. Use the correct size for the bit you are using. The range of an ER collet is very limited. If you buy collets get good ones. The trash Chinese ones on Ebay may not spin true and cause excessive run out of your bits.

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Before this thread gets locked, does anyone care to share their favorite collets to purchase?

I know the cheap game and none of us are here to go that route, unless it’s made clear by the community that extra cost isn’t worth it.

Good to know proper collets are clutch. The tolerances are very limited.

Hopefully this thread will prevent people from, well, cross-threading their spindle because I know if I got stubborn with those tool changes today I could have done exactly that.

The auto-timer is what locks most threads here — the forum is for folks to communicate.


I bought some collets, as well as a wrench from Maritool and am quite pleased w/ them.

Another source is Think & Tinker/Precise Bits, whose rep @TDA posts here from time to time.

I don’t think anyone has ever complained about buying good quality collets after the fact, but runout from a cheap collet absolutely will kill an endmill or cause chatter and a poor finish/cut.

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Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.

If that was the issue you were having be sure to check your collets for damage. If the taper got damaged they can damage the nut and then the other collets used in that nut. Here’s another thread with pictures and discussion of the same topic. Proper Collet Use - Whoops - #9 by rb_designs

While not the issue here this is definitely something to watch for. It’s always in the smaller direction too so you could (depending on the ER size) use a 1/4" collet for a 6mm shank, but never the reverse. Additionally, runout is only spec’ed to the actual collet bore and typically increases even when going down in diameter within spec.

I’m extra bias here so I’ll only address a few things. A lot of it depends on what you are cutting, tooling, and tool life. A big part of this is that collets are a source of runout (tool spinning off the center axis of the spindle). One of the issues with runout is that it can functionally add and subtract to your chipload (feed) in multi-flute tools (also always effects it in straight plunging). This can effect the tool life, limit your feeds, or just straight break tools.

Examples: In metal cutting even with bigger tools better collets pay for themselves eventually. The usual number thrown around is for every 0.0001" (0.0025mm) of runout reduction you pick up 10% extra tool life. For small diameter tools there is very little chipload available so runout can significantly reduce your feeds or break tools. If you are cutting soft media with decent size tooling you’re probably fine with anything decent but could pick up some tool life, feed, and a better finish with better collets.

One thing I usually recommend if you are looking for high end is getting collets that are actually spec’ed for runout. This is pretty hard though as most collets list a “typical” number which isn’t very useful. There’s 4 brands I know of that actual measure the collet YOU get:

  • Us (PreciseBits)
  • Techniks “UP” grade
  • Rego-Fix (creators of ER collets and what the R in ER stands for)
  • Pioneer

Although, we all have different standards for runout.

I’ll stop here as I’ve already gone long winded on this. If you want more info here’s some of the post I’m aware of (posted in) where this is discussed more.

The last one goes off the deep end…

Hope that’s useful. If there’s something I can expand on or help with let me know.


I am humbled by your well thought-out reply. It is such a core part of the physics of it, all this knowledge about seeking out optimal tolerances.

For now, I learn about collets and play in the shaft in Z. Makes a lot of sense. I ordered 2 more from Carbide, and as I experience more I’ll make those upgrades and in the meantime I will trust Carbide 3D’s hardware.

Thank you.

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