Kurt screw down clamps with a new twist

Some of the best ideas are simple ones - with a twist. Holding parts in a fixture by clamping them down with a screw is as simple as it gets, the twist comes from applying the clamping force via the screw to a cleverly designed hex shaped clamp jaw called the Kurt MiniLock. A simple but effective fixturing solution that is now available in the UK from Birmingham-based workholding specialist Leader Chuck Systems.

The tiny MiniLock screw-down clamps exert internal clamping forces similar to the original Kurt Anglock vice, from which the design idea was developed. Just like a vice, MiniLocks are extremely rigid and hold parts in position for precision machining operations.

Jim Metcalf, president of D&D Tool & Cutter, has already seen the benefits of using MiniLock clamps to hold multiple parts in a pallet setup for high efficiency machining. He's an entrepreneurial workshop type, who after spending over a dozen years working for somebody else, decided he could do things better on his own. So he opened his rapidly growing precision machining company, which also does custom carbide tool and cutter grinding, just 18 months ago,

One of the jobs the company produced consisted of a series of heavy milling, drilling, boring and tapping operations on rectangular shaped aluminium parts, using the Kurt MiniLock hex shaped clamp jaws to hold the parts in multiples on a pallet setup in a Haas VF-6 machining centre.

Another application for the screw down clamps to hold raw material was designed by Jim Metcalf for Kurt Manufacturing, to fix multiple parts for three sided machining operations. This setup uses a pallet fixture mounted on flat plates with locator bushings. The MiniLocks perform the actual part clamping operation.

Through the use of machined pockets in the cast iron base, plus a series of nine MiniLocks, 18 part locations are configured to allow machining of six parts on three sides. For Kurt, Jim Metcalf has been running 750 parts at a time, produced with 0.5 micron Ra and a +/- 7.5 micron bore tolerance.

After completing two runs with a total of 1500 finished parts to complete the initial inventory requirement, the pallet fixture was moved to Kurt's plant where the parts will be produced on a just-in-time basis. The CNC program used by Jim Metcalf along with the MiniLock fixturing setup will be used in Kurt's machining centres without any major modifications.

Without the size, weight or cost, the MiniLock clamps operate in any machining centre exactly like full vices. For their size, the MiniLock clamps and holds with high precision and rigidity. For every 5 Newton clamping force applied by turning the flat head screw, there is a 2.5 Newton holding force extended down on the moveable jaw, assuring positive locking of the clamped parts during machining.

Made of nickel-free Ampco 18 aluminium bronze to prevent galling and wear, the MiniLock's clamp jaw is split on its centreline and the two halves are held together by an 'O' ring recessed in a perimeter groove. The tapered head of the screw, made of special alloy steel, is seated in a corresponding taper in the clamp jaw. When a quarter turn is applied to the screw, the split clamp jaw is forced both laterally and down, precisely clamping the part and preventing part lift at the same time.

"This isn't rocket science," says Jim Metcalf, "just a little workshop creativity using off-the-shelf components anyone can buy and use with their own ingenuity to solve their own machining problems. We're planning a number of different setups on new jobs using MiniLocks."

In addition to the type of setup used by Jim Metcalf, MiniLocks can be used in single holding, double holding or multiples of both single and double holding applications. They are ideal for hard fixturing using multiple pallets so while one pallet of parts is being machined, the operator can be unloading and loading a second similarly configured pallet away from the machine. MiniLocks add very little weight and their small size occupies minimal room on the pallet or machine worktable.

Another positive feature is when the MiniLock screw is released, the '0' ring automatically retracts the clamp jaw and holds it in. They will stay clamped under vibrating conditions and regardless of the cutting direction used in the application. And, the low profile allows the machining of complete top surfaces of parts without having to re-clamp.

The MiniLock uses standard thread sizes and standard Allen wrenches so no special tools are required for setup. They come in 17.5, 22.25, 24 and 28.5 mm hex sizes.