Workholding Guide

What is workholding and why is it important?

Workholding is how stock is held during operations on CNC mills and lathes. Unlike in CAD, parts don’t just float in 3D space. Something needs to grab onto the part to keep it from moving or flying off when the machine removes material. Workholding is one of the most important considerations when it comes to manufacturing. You can have perfect tools and toolpaths, but that doesn’t matter if there isn’t a surface to hold onto the part. Workholding also presents clearance challenges, can leave marks on your part, and therefore must be considered throughout the entire design and manufacturing process.

Types of part surfaces to clamp on

For workholding, there are 3 main types of surface finishes to consider before clamping down onto the stock.

  • Bandsaw cut: A surface that has been cut with a bandsaw. Bandsaws leave the worst finish and sometimes a large burr on the bottom edge. This burr must be removed, and the resulting surface can only be put inside snap jaws to ensure proper clamping.
  • Extruded: Raw stock from a factory is usually extruded. While the surfaces may look flat and parallel at a glance, in reality, they usually are not. So again, snap jaws are strongly preferred for clamping onto this type of surface.
  • Machined: A pair of surfaces that have been machined on a CNC mill and are known to be parallel. Since these surfaces are guaranteed to be parallel, they can be put inside flat jaws.

The reason we need properly-parallel surfaces to use the flat jaws is due to clamping area, as demonstrated in the exaggerated view below. If the two sides clamped are not parallel, then one side will have full contact, and the other side will have only a single point of contact. This reduces the effective clamping area and your part may fly out of the jaws during machining.

View comparing stock with non-parallel sides vs a stock with parallel sides

What workholding should I pick?

There are a variety of workholding options available at BIDC. The following flowcharts roughly show what you should be considering for workholding. They give you a general idea, but use the table below to know the full constraints of the workholding. The table contains pictures to give you a better visual understanding of how each option works. All workholding is also modeled in the BIDC Fusion 360 Team in the Workholdings and Stocks folder.

Workholding for CNC Mills

ViceJawDescriptionConstraintsHow it Clamps
Gepard 300
View of Gepard 300 Vice
This vice comes standard on the VF2 and the VF4, and can be placed on the UMC as well.Must be torqued down to 60 ft-lbs for proper clamping.Side profile of a detached jaw showcasing how it slides into the vice
How the jaws slide into the vice
Short Snap
Gepard 300 Short Snap Jaws
Has serrated teeth that dig into the part. Can grip onto rough surfaces.Maximum of 6″ between the shortest sides of the part. Leaves marks on the part.Top-down view of snap jaws clamping onto a piece of stock.
Side view of short snap jaws clamping onto a piece of stock
Short Flat
Gepard 300 Short Flat Jaws
Flat clamping sides allow clamping onto parallel surfaces without leaving marks.Maximum of 5″ between shortest sides of the part. Requires machined surfaces.Top-down view of the Gepard 300 short flat jaws clamping on material
Side view of the Gepard 300 short flats clamping material
Long Snap
Gepard 300 Long Snap Jaws
Has serrated teeth that dig into the part. Can grip onto rough surfaces.Maximum of 9.5″ between shortest sides of the part, or a minimum of 4″ between the longest sides. Leaves marks in partTop-down view of the Gepard 300 Long Snap jaws clamping material
Side view of the Gepard 300 Long Snap Jaws clamping material
Long Flat
Gepard 300 Long Flat Jaws
Flat clamping sides allow clamping onto parallel surfaces without leaving marks.Maximum of 9.5″ between the shortest sides of the part, or a minimum of 4″ between the longest sides. Requires machined surfaces.Top-down view of the Gepard 300 Long Flat Jaws clamping onto a part
Side view of the Gepard 300 Long Flat jaws clamping onto a part
Versagrips
Gepard 300 Versagrip Jaws
These jaws can clamp on round parts from the outside (OD Clamping). The 4 black studs can be rotated and shifted to correctly match the outer diameter of the part. Minimum diameter of 2” and maximum diameter of 8.5″. Can only OD Clamp, no ID clamping.Top-down view of a Gepard 300 Versagrip jaw clamping onto a part
Side view of a Gepard 300 Versagrip jaw clamping onto a part
Soft Jaws
Blank Gepard 300 Soft Jaws
Custom jaws cut out of a blank. Used only if all other workholding options cannot work for your part.Must machine the jaws before using them.Cut Gepard 300 Soft Jaws
Gepard 170
Gepard 170 Soft Jaws
This vice is nearly identical to the Gepard 300 except that it is smaller.Must be torqued down to 40 ft-lbs for proper clamping.Side view of Gepard 170 Jaws
How the jaws slide into the vice
Short Snap
Gepard 170 Short Snap Jaws
Has serrated teeth that dig into the part. Can grip onto rough surfaces.Maximum of 2.5″ between shortest sides of the part. Leaves marks on the part.Top-view of Gepard 170 short snap jaws clamping onto a part.
Short Flat
Gepard 170 Short Flat Jaws
Flat clamping sides allow clamping onto parallel surfaces without leaving marks.Maximum of 2.5″ between shortest sides of the part. Requires machined surfaces.Top-view of Gepard 170 Short Flats clamping onto a part.
Long Snap
Gepard 170 Long Snap Jaws
Has serrated teeth that dig into the part. Can grip onto rough surfaces.Maximum of 5″ between shortest sides of the part, or a minimum of 3.25 between the longest sides. Leaves marks in part.Top-view of Gepard 170 long snap jaws clamping onto a part.
Long Flat
Gepard 170 Long Flat Jaws
Maximum of 5″ between the shortest sides of the part, or a minimum of 3.25″ between the longest sides. Requires machined surfaces.Top-view of Gepard 170 long flat jaws clamping onto a part.
Soft Jaws
Blank Gepard 170 Soft Jaws
Custom jaws cut out of a blank. Used only if all other workholding options cannot work for your part.Must machine the jaws before using them.Cut Gepard 170 Soft Jaws
Kurt Vice
View of a plain Kurt Vice
A larger, more rigid vice compared to the Gepards that is also standard on the VF2 and VF4. Typically requires parallels to get the correct part height.
View of a set of parallels
View of parallels of different heights
Parallels vary in height as seen in the picture, and are magnetic, sticking to the vice.
View showing two parallels in a Kurt at differing heights
Talongrip
View of detached Kurt talongrips
Top-view of plain Kurt Talongrips
Snap jaws for the Kurt. Has serrated teeth that dig into the part. Can grip onto rough surfaces.Maximum of 8.75″ between shortest sides of the part. Leaves marks in part.Top-view of Kurt Talon Grips clamping onto a part.
Side-view of Kurt Talon grips clamping onto a part
Flats
View of detached Kurt Flats
Side-view of Flats installed in the Kurt
Flat for the Kurt Vice. Maximum of 8.75″ between shortest sides of the part. Requires machined surfaces and usually parallels.Top-view of Kurt flats clamping onto a part.
Side view of the Kurt flats clamping onto a part.
Versagrip
View of detached Kurt Versagrips
Top-view of Kurt Talon-grips installed.
Versagrip for the Kurt that can OD and ID Clamp. The 4 black studs can be rotated and shifted to correctly match the diameter of the part.Maximum of 9″ for OD clamping.Top-view of Kurt Versagrips clamping onto a part.
Side view of the Kurt versagrips clamping onto a part.
Dovetail
Side view of the 3 dovetails
Top view of all 3 dovetails
Clamps with an angled edge and a centering pin. Provides good hold and typically used on the UMC 5-axis.Can access 5 sides of the part for machining.Annotated view of the bottom of a dovetail on stock
Annotated side view of a dovetail on stock
0.5″ Dovetail
Side view of the 1/2" Dovetail
Top view of the 1/2" Dovetail
Smallest size dovetail.Requires stock prep before it can clamp.
0.75″ Dovetail
Side view of the 3/4" dovetail
Top-view of the 3/4" Dovetail
Medium size dovetail.Requires stock prep before it can clamp.
1.5″ Dovetail
Side view of the 1.5" Dovetail
Top view of the 1.5" Dovetail
Largest size dovetail.Requires stock prep before it can clamp.
Setrite 3-Jaw
View of the setrite 3-jaw
A 3-jaw clamp for the mill. Attaches to the zero point plate, or can be placed in the Kurt.
ODClamps the outside of the stock. Make sure to rotate the jaws if necessary to best match the diameter of the part.Maximum stock diameter of 8″.
Zoomed in picture showing the matching diameter steps on the 3-jaw
Matching to correct step diameter to maximize clamping area.
Setrite 3-jaw holding a long, thing piece of stock
View of the setrite 3-jaw clamping onto a large piece of stock
IDClamps the inside of the stock.Minimum inner stock diameter of 2″, maximum inner stock diameter of 8″.Setrite 3-jaw holding a cylinder from the inside
Top-down view of the setrite ID clamping
VF4 Fixture Plate
View of the blank fixture plate in the VF4 plate mill
An aluminum plate with a pattern of threaded holes in it on the VF4 plate mill.The entire table area is usable.
Toe Clamp
View of the size of toe clamps
Clamp downward onto the part via “toes” and threaded rods that go into the fixture plate.Model toe clamps in CAM and ensure the machine does not crash with the clamps.View of 2 toe clamps clamping on material
Snap Toe Clamp
View of jaw clamps
Once attached to the fixture plate, a set of teeth can extend outward to clamp onto the part from the sides.Model clamps in CAM and ensure the machine does not crash with the clamps.View of the snap jaw toe clamps clamping on a part
Mitee Bite
View of custom Mitee Bite workholding
A nut with an offset-headed bolt that moves side-to-side as the bolt is rotated.Usually used for small parts where clamping force can damage part, and high-production rate parts. Requires custom fixturing.
Square Collet Block
Top view of a square collet block


A square block to be put in the flat jaws that a 5C collet goes intoClamps onto round stock from the OD. Maximum OD clamp of ~1″.A square collet block with a 5C collet and stock inside a vice
A 5C collet holding stock

Workholding for CNC Lathes

ChuckDescriptionConstraintsHow it Clamps
LMC 3-Jaw
LMC chuck in a small OD or ID configuration
LMC chuck in a larger OD configuration
A 3-jaw clamp for the lathe.Maximum stock diamater of ~8″ for OD clamping. Minimum ID clamp diameter of 2″.View of a LMC 3-jaw chuck clamping on a piece of stock with googly eyes on it
Hex Collet Block
Top view of a hex 5c collet block
A hex block that a 5C collet goes into.Clamps onto round stock from the OD. Maximum OD clamp of ~1″.A hex 5c collet block in a LMC chuck holding stock