ER Collets, Set Screw, Milling Chucks – where to begin?
Selecting the right tool holder type for your CNC Mill can be confusing! Let’s review the major tool holder types and their pros and cons:
Collet Chucks
Pros:
- Very versatile. By switching collets and you can grab any size shank within the collet’s range
- Collet chucks are often used to hold drills, taps, end mills, center drills, counter sinks, reamers, and many other tool types. More than any other tool holder type.
- Tool breakage friendly. Break a tool and worst case it damages the collet. Replace the collet and you’re back in business.
- Strong grip good for medium roughing applications.
- Good runout, .0003″ or better is common.
- Inexpensive: Collet chucks are fairly inexpensive . Inventory of collets can become pricey, but in the beginning you can purchase only what you need.
- Many gauge lengths available. From short and rigid to very long.
Cons:
- Long tool change time. Collet nut and collet should be disassembled every time you put in a new tool for proper cleaning. The inside of the collet can build up with lots of small chips.
- Balance is decent but with so many moving parts balance can be thrown off.
- Nose diameter: Depending on the size collet system nose diameters can get fairly large and restrict coolant flow. May also restrict machining next to fixturing or clamps.
- Grip: Under heavy roughing the shank may slip in collet. This may result in a broken tool and sometimes damaged workpieces.
NYC CNC Comments:
- We have tooled up our HAAS VM3 and HAAS VF2SS based on ER32 collet chucks. We use the 1.85 gage length (the shortest offered) for maximum rigidity.
- ER32 collet chucks need to be tightened with a torque wrench! We TIG welded an ER32 wrench onto a 1/2″ adapter to fit on a standard torque wrench (we use this one) and tighten to ~85 ft lb
- Never use a torque wrench to loosen or remove collet nuts!
- Only buy high quality ER collets! We keep a few of the MariTool collet sets on hand and buy individual collets as needed
- Any MariTool ER collet chuck can be used for TSC (Thru Spindle Coolant) but you MUST use a TSC pull stud (a.k.a. retention knobs). Pull studs are machine specific; for our haas, we use this model.
- Clean often! The ID of the collet chuck, the nut and the collet all need to be free of chips, swarf, debris and should be degreased to maximize gripping! We use acetone and a lint-free rag.
- If you damage an ER collet (or collet chuck), you can repair it by immediately putting the damaged item in the trash and purchasing a new one. Joking aside, mistakes do happen, but do NOT keep damaged collets or tools around the shop. A damaged collet can ‘transfer’ its damage into an otherwise good tool or collet chuck.
- Of the ~75 CAT40 tool holders we own at the moment (writing this January 2018), I’d guess 60 are ER-32.
- We use ER-16 for situations where you have to reach into a smaller pocket; we prefer the “M” style from MariTool (click for example). These have a special collet nut that has a reduced outside profile to help get into tighter spots; they cost a few bucks more and require a custom spanner, but are WELL worth it.
End Mill Holders
Pros:
- Very simple and quick tool changeover.
- A quality end mill holder balance should be fair to good.
- Decent to good concentricity. Maritool especially makes end mill holders with tight on-size bores. Shank stays on center even when set screw is clamped.
- Great grip. Once set screw is clamped on the shank flat, slippage is rare.
- Cheap. Most tool holder companies will have plenty of stock and fair pricing.
- Small nose diameters. In most cases smaller than collet chucks.
- Rigid, good for heavy roughing.
- Many gauge lengths available, from very short and rigid to long.
Cons:
- Not tool breakage friendly. If a tool breaks and kicks back at the bore on the tool holder it may be damaged. Repair may not be economical.
- Not versatile. End mill holders can only hold one size shank. If shank is undersized even just a thousandths of an inch the tool will not be on center.
- The shank must have a flat for set screw to lock on to. If your tool does not have a flat on the shank you will need to grind one on it.
- Unless you grind your own flat you cannot choose how deep or shallow you grab the tool.
NYC CNC Comments:
- End Mill (a.k.a. set screw or side lock holders) are “solid” holders. We often hear people say they are outdated or inferior – that’s simply not true. Leading tooling manufactures continue to recommend them for certain tools. They would be great for holding a tool like a Shear Hog or another type of 1″ insert tool.
- If you think the side lock nature will “push” the tool too far off to one side, then set up a test! Compare the tool runout between a side lock and a collet holder!
- These have exceptional rigidity and dampening power. Period. Great for hogging material.
Milling Chuck Holders
Pros:
- Great grip. Tool slippage is rare.
- Within limitations you can determine how deep or shallow you grab the tool.
- Balance is good.
- Versatile. Bushings (sleeves) are often used to step down the bore so you can
- Hold smaller shank tools.
- Great concentricity. .0002″ or less is common.
Cons:
- Most milling chucks have a long gage length compared to collet chucks or end mill
holders. - Pricey: Milling chuck tool holders and sleeves are both pricey.
- Not very versatile. Even with sleeves the shank must be a common size and at most 6 or 8 sleeve sizes are available. Each sleeve only has one thousandth of an
inch range at most. - Damage to milling chuck is possible if you clamp on a shank too small. Bore can
be crushed and not expand back to normal.
NYC CNC Comments:
- We’ve started using milling chucks where we need to maximize tool life and/or ensure process reliability.
- Milling chucks can increase tool life by minimizing tool runout and their solid clamping force. We’ve heard of studies that indicate every 0.0001″ (aka “one tenth” or 0.0025mm) of tool runout can decrease tool life by 10%.
- Tightening a Milling Chuck for the first time was a peculiar experience! The chuck tightens with similar force until it suddenly bottoms out at a solid stop. This compares with something like an ER collet (two tapered surfaces) where the force increases gradually until reaching adequate torque.
Shrink Fit Holders
Pros:
- Great grip. Tool slippage is rare.
- Great concentricity .0001″ or less is very common.
- Small nose diameter. Smallest out of all other types. Excellent for 5 axis work and
milling next to clamps or tall part features. - No moving parts, best balance. Very well suited for high rpm applications.
- Medium pricing. Considering the advantages, shrink fit holders are a great value.
- Good variety of gauge lengths and nose profiles. Although shrink fit holders don’t
get as short as some collet chucks or end mill holders they are available in
shorter gauge lengths than milling chucks.
Cons:
- Shrink fit induction heating machine is needed to properly expand a shrink holder.
- Propane torch may be used, but not recommended.
- Although shrink holders are decent in price heat shrink induction machines tend
to be costly and run on 220 volt or higher. - Holders get very hot during the expansion cycle. Great care must be taken to
avoid burns. - Although changing tools can be quick it may be time consuming waiting for the
holder to cool to the touch. That is unless you have an air or water cooling unit. - Not tool breakage friendly. If a tool breaks and kicks back at the bore on the tool
holder it may be damaged. Repair may not be economical - Not versatile. Shrink fit holders can only hold one size shank.
NYC CNC Comments:
- Check out the NYC CNC Article on Heat Shrink Tooling here!
- You just cannot beat the concentricity, holding power and small holder size!
- There are other systems (we’ve heard great things about Rego-Fix system, but the holder cost and required machine exceed the cost of most heat shrink systems)
- MariTool’s Heat Shrink Tool Holders include a screw stop system that allows for tools to be replaced with similar tool stick out. This can help ensure process reliability when operators are replacing tools! It’s important to never stick a tool out more than required, yet too little stickup can lead to fixture or work holding collisions.
Hydraulic Chuck Holders
Pros:
- Great concentricity, .0001″ or better is common.
- Great grip.
- Decent variety of gauge lengths equal to shrink fit holders.
- Fairly slim nose profiles, slightly larger than shrink fit holders.
- Quickest tool change of all tool holders. Small Allen key releases and clamps new
tool.
Cons:
- Holders are expensive.
- Some holders are known to bleed pressure over time and lose grip.
- Not tool breakage friendly. If a tool breaks and kicks back at the bore on the tool
holder it may be damaged. Repair may not be economical. - Not versatile. Hydraulic holders can only hold one size shank (although adaptive sleeves may be available)
Drill Chuck Holders
Pros:
- Quick tool change.
- No collets needed. Can hold any size shank within its range.
- Good for holding drills and taps for light applications.
Cons:
- Grip is low.
- Concentricity less than .0008″ is rare and considered good.
- Nose diameter tends to be big.
- Gage length tends to run long.
- Costly.
- Cannot hold end mills. Not made to handle side loads.
- Not tool breakage or slippage friendly. In both cases the jaws will need replacing
which is costly and sometimes not economical.
NYC CNC Comments:
- We don’t like using Drill Chucks in our VMC’s. They are expensive, heavy, long gauge length and inferior tool holding compared to a collet.
- We keep ONE in the shop in case we need to use a drill but do not have an extra ER collet available.
Thanks to Frank Mari of MariTool for contributing to this article on CAT40 tooling! See more at http://www.maritool.com
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