Undersized metric R8 collets

[Earl Hackett]

I need to make a small (~3 mm deep) dovetail slide and have not been abot to find affordable dovetail end mills other than metric sizes. The problem is that all the meric R8 collets I've tried are about .25mm smaller than the nominal diameter. I can force an end mill into them, but I don't know what the runout would be and for a dovetail slide it can't be very much. Is this normal for metric collets? All the internal diameters of my ANSI collets are spot on. Does anyone know if this is a problem other than being difficult to remove the end mill from the collet?

 

[extropic]

Welcome to H-M Earl.

Your question is outside my experience, but maybe I can help you converge on a solution.
First, a few questions.
What is the diameter of the cutter shank you want to hold?
Do you have a lathe?
When you push the cutter shank into the collet, are the slots splayed or parallel?
Are you buying super cheap metric collets? No-name or brand name?
Maybe a slightly better brand (Shars, Little Machine Shop, might solve the problem.
When you push the cutter shank into the collet, are the slots splayed or parallel?

 

[ChazzC]

Don't have a small metric Dovetail mill, but all of my small metric end mills have 6mm shanks and slip easily into the 6mm collet from my eBay no-name $40, Metric 12 pc. (3mm – 22mm), R8 collet set I bought in 2021.

 

[RaisedByWolves]

I need to make a small (~3 mm deep) dovetail slide and have not been abot to find affordable dovetail end mills other than metric sizes. The problem is that all the meric R8 collets I've tried are about .25mm smaller than the nominal diameter. I can force an end mill into them, but I don't know what the runout would be and for a dovetail slide it can't be very much. Is this normal for metric collets? All the internal diameters of my ANSI collets are spot on. Does anyone know if this is a problem other than being difficult to remove the end mill from the collet?

To a small degree the nature of an R8 and similar collets will work fine if the cutter shank is slightly smaller or larger than the collets nominal size.


The taper of the collet will form to the taper of the spindle under tension and consequently grip the shaft uniformly along its length.

Again, this is to be done within reason, a cutter shank 1/32" larger than the collets nominal size is probably a no go.

.

 

[rodm1]

What about a ER32 holder the collets have 1mm range depending on shank size.

Tool Holders, Collets and Machine Accessories ER32 Collets - MariTool

www.maritool.com