Woodruff & Keyseat Cutters: Easy Guide to Keyway, Key, & Keyseat CNC Work

6 months by cncdivi

Whenever we need to affix a part to a shaft, such as a gear or pulley, keyways, keys, and keyseat work or woodruff work comes into play.  So, let’s begin by getting our terminology straight.

A Keyway is a slot of some kind that is used to align the part on a shaft and prevent the part slipping as the shaft rotates.  A Key goes into the Keyway to lock things up.  Another name for a Keyway is a Keyseat, since the Key is seated in the Keyseat.  When a specialized cutter is used to cut the Keyseat, it’s a Keyseat Cutter.  A Woodruff Cutter is a Keyseat Cutter.

There are several kinds of Keys in common use.

Parallel Keyways & Keys

Parallel keys are the simplest, and involve a slot that goes all the way through at least the part with the shortest axial mating length (i.e. the gear or the pulley.  Cutting a parallel key is straightforward–just use an endmill and treat it as cutting any other slot.  Alternatively, you could use a Keyseat Cutter such as a Woodruff Cutter.

Key stock is available pre-cut in standard inch and metric sizes, and the ends may either be squared or rounded.

Parallel  Inch Key Sizes

Shaft Diameter		Width	Keyway (Shaft				Keyway (Hub)				Radius r
		Height	Width		Height		Width		height
Over	To/Inc	W & T	Min	Max	Max	Min	Min	Max	Min	Max
1/4	1/2	1/8	0.124	0.125	0.072	0.078	0.125	0.126	0.06	0.066	0.01
1/2	3/4	3/16	0.187	0.188	0.107	0.113	0.188	0.189	0.088	0.094	0.01
3/4	1	1/4	0.249	0.25	0.142	0.148	0.25	0.251	0.115	0.121	0.01
1	1 1/4	5/16	0.311	0.312	0.177	0.183	0.312	0.313	0.142	0.148	0.01
1 1/4	1 1/2	3/8	0.374	0.375	0.213	0.219	0.375	0.376	0.169	0.175	0.01
1 1/2	1 3/4	7/16	0.437	0.438	0.248	0.254	0.438	0.439	0.197	0.203	0.02
1 3/4	2	1/2	0.499	0.5	0.283	0.289	0.5	0.501	0.224	0.23	0.02
2	2 1/2	5/8	0.624	0.625	0.354	0.36	0.625	0.626	0.278	0.284	0.02
2 1/2	3	3/4	0.749	0.75	0.424	0.43	0.75	0.751	0.333	0.339	0.02
3	3 1/2	7/8	0.874	0.875	0.495	0.501	0.875	0.876	0.387	0.393	0.062
3 1/2	4	1	0.999	1	0.566	0.572	1	1.001	0.442	0.448	0.062
4	5	1 1/4	1.248	1.25	0.707	0.713	1.25	1.252	0.551	0.557	0.062
5	6	1 1/2	1.498	1.5	0.848	0.854	1.5	1.502	0.661	0.667	0.062

Per BS 46 Part 1 : 1958 Keys and keyways and taper pins. Specification. Keys and keyways.

Parallel Metric Key Sizes

Nominal Diameter		Key	KeyWay
d		b x h width x thck	Width b						Depth				Radius r
			Nom	Tolerance Class					Shaft t1		Hub t2
Over	Incl			Free		Normal		Close/Int	–	–	–	–
				Shaft	Hub	Shaft	Hub	Shaft/Hub	Nom	Tol	Nom	Tol	Max	min
				H9	D10	N9	Js9	P9
6	8	2×2	2	+0,025	+0,06	-0,004	+0,012	-0,006	1,2	+0,1	1,0	+0,1	0,16	0,08
8	10	3×3	3	0	+0,02	-0,029	-0,012	-0,031	1,8	0	1,4	0	0,16	0,08
10	12	4×4	4	+0,03	+0,078	0	+0,015	-0,012	2,5		1,8		0,16	0,08
12	17	5×5	5	0	+0,030	-0,030	-0,015	-0,042	3,0		2,3		0,25	0,16
17	22	6×6	6						3,5		2,8		0,25	0,16
22	30	8×7	8	+0,036	+0,098	0	+0,018	-0,015	4,0	+0,2	3,3	+0,2	0,25	0,16
30	38	10×8	10	0	+0,040	-0,036	-0,018	-0,051	5,0	0	3,3	0	0,40	0,25
38	44	12×8	12	+0,043	+0,12	0	+0,021	-0,018	5,0	+0,2	3,3	+0,2	0,40	0,25
44	50	14×9	14	0	+0,050	-0,043	-0,021	-0,061	5,5	0	3,8	0	0,40	0,25
50	58	16×10	16						6,0		4,3		0,40	0,25
58	65	18×11	18						7,0		4,4		0,40	0,25
65	75	20×12	20	+0,052	+0,149	0	+0,026	-0,022	7,5		4,9		0,60	0,40
75	85	22×14	22	0	+0,065	-0,052	-0,026	-0,074	9,0		5,4		0,60	0,40
85	95	25×14	25						9,0		5,4		0,60	0,40
95	110	28×16	28						10,0		6,4		0,60	0,40
110	130	32×18	32	+0,062	+0,18	0	+0,031	-0,026	11,0		7,4		0,6	0,4
130	150	36×20	36	0	+0,080	-0,062	-0,031	-0,088	12,0	+0,3	8,4	+0,3	1,0	0,7
150	170	40×22	40						13,0	0	9,4	0	1,0	0,7
170	200	45×25	45						15,0		10,4		1,0	0,7
200	230	50×28	50						17,0		11,4		1,0	0,7
230	260	56×32	56	+0,074	+0,220	0	+0,037	-0,032	20,0		12,4		1,6	1,2
260	290	63×32	63	0	0,100	-0,074	-0,037	-0,106	20,0		12,4		1,6	1,2
290	330	70×36	70						22,0		14,4		1,6	1,2
330	380	80×40	80						25,0		15,4		2,5	2,0
380	440	90×45	90	+0,087	+0,260	0	+0,043	-0,037	28,0		17,4		2,5	2,0
440	500	100×50	100	0	0,120	-0,087	-0,043	-0,124	31,0		20		2,5	2,0

Per BS 4235-1:1972: Specification for metric keys and keyways – Parallel and taper keys.

Woodruff Keyways & Keys

Woodruff Keys are an alternative to Parallel Keys.  They are semi-circular, and fit into a Keyway shaped as a circular-segment in the shaft and a rectangular slot in the mating part.  The semi-circular slot is cut by plunging a Woodruff Cutter (the correct Keyseat Cutter  for this style Keyway) into the workpiece.

The advantages of Woodruff Keys over Parallel Keys are:

• They eliminate the milling near shaft shoulders which reduces stress concentrations and makes it easier to maintain circularity constraints.  
• They are therefore better suited to higher speed operation of the rotating shaft.
• The key typically has a more exact fit which reduces play and improves the reliability of the key.
• A Woodruff key may be easier to remove with a hammer blow since the circular profile will push the key out of the slot.  A Parallel key requires the key to be pushed axially a longer distance.

Woodruff Keys were developed in 1888 by W.N. Woodruff of Connecticut, USA.

Woodruff keys may be full radius or flat bottom, but the keyseat will always be radiused by the Keyseat Cutter / Woodruff Cutter.  A flat bottom Woodruff Key has part of the radius shaved right at the bottom:

Woodruff Key Dimensions (Inch)

Like Parallel Keys, Woodruff Keys come in standard sizes:

KEY NUMBER	KEY DIMENSIONS		SHAFT DIAMETER		HEIGHT OF KEY ABOVE SHAFT	DEPTH OF KEYWAY
	DIAMETER	WIDTH	MINIMUM	MAXIMUM
204	1/2	1/16	5/16	3/8	0.0312	0.1718
304	1/2	3/32	5/16	1/2	0.0469	0.1 561
404	1/2	1/8	9/16	3/4	0.0625	0.1405
405	5/8	1/8	9/16	3/4	0.0625	0.1875
505	5/8	5/32	13/16	15/16	0.0781	0.1719
406	3/4	1/8	11/16	3/4	0.0625	0.2505
606	3/4	3/16	1	1 1/8	0.0937	0.2193
507	7/8	5/32	1 1/8	15/16	0.0781	0.2969
807	7/8	1/4	1  5/16	1 1/8	0.125	0.25
608	1	5/16	1	1  7/16	0.0937	0.3443
1008	1	5/16	1  1/16	1 5/8	0.1562	0.2818
609	1 1/8	5/16	1  1/16	1  7/16	0.0937	0.3903
810	1 1/4	1/4	1 1/4	1 3/4	0.125	0.422
1210	1 1/4	3/8	1 1/2	1 7/8	0.1875	0.3595
1011	1 3/8	1/2	1 13/16	2	0.1562	0.4378

Woodruff Key Dimensions (Metric)

w x  h1  x  D……	Width b					Depth				Radius R
	Nom	Tolerance Class				Shaft t1		Hub t2
		Normal		Close
		Shaft	Hub	Shaft & Hub P6		Nom	Tol	Nom	Tol	Max	min
		N9	Js9
1,0 x 1,4 x 4	1	-0,004	+0,012	-0,006		1,0	+0,1	0,6	+0,1	0,16	0,08
1,5 x 2,6 x 7	1,5	-0,029	-0,012	-0,0031		2,0	0	0,8	0	0,16	0,08
2,0 x 2,6 x 7	2,0					1,8		1,0		0,16	0,08
2,0 x 3,7 x 10	2,0					2,9		1,0		0,16	0,08
2,5 x 3,7 x 10	2,5					2,7		1,2		0,16	0,08
3,0 x 5,0 x 13	3,0					3,8	+0,2	1,4		0,16	0,08
3,0 x 6,5 x 16	3,0					5,3	0	1,4		0,16	0,08
4,0 x 6,5 x 16	4,0	0	+0,015	-0,012		5,0		1,8		0,25	0,16
4,0 x 7,5 x 19	4,0	-0,030	-0,015	-0,042		6,0		1,8		0,25	0,16
5,0 x 6,5 x 16	5,0					4,5		2,3		0,25	0,16
5,0 x 7,5 x 19	5,0					5,5		2,3		0,25	0,16
5,0 x 9.0 x 22	5,0					7,0	+0,3	2,3		0,25	0,16
6,0 x 9,0 x 22	6,0					6,5	0	2,8		0,25	0,16
6,0 x 11,0 x 28	6,0					7,5		2,8	+0,2	0,25	0,16
8,0 x 11,0 x 28	8,0	0	+0,018	+0,015		8,0		3,3	0	0,40	0,25
10,0 x 13,0 x 32	10,0	-0.036	-0.018	-0.051		10,0		3,3		0,4	0,25

Keyseat Cutters (aka Woodruff Cutters or Woodruff Key Cutters)

Woodruff Keys take a special Keyseat Cutter called a Woodruff Cutter.  It’s basically a small saw.  They look like this:

Woodruff Cutters are a subset of the broader category of Slotting Cutters.

A Woodruff Cutter may be constructed from HSS or Solid Carbide.  The solid carbide versions are capable of both higher material removal rates (e.g. shorter cycle times) and longer tool life, so they are often preferred for production work.

Woodruff Cutter & Keyseat Cutter Feeds and Speeds Calculator

Woodruff and Keyseat Cutters behave like Saws.  Learn a lot more tips and deeper feeds and speeds info from our article on Slitting Saw Feeds and Speeds, Tips, and Techniques.

Our G-Wizard Feeds and Speeds Calculator has special support for Woodruff Cutters & Keyseat Cutters. To set up the Woodruff Cutter cut in the Calculator, we go left to right, top to bottom:

1. Select the Machine

2. Select the Material

3. Select the Woodruff Cutter from the tool menu (Note:  Keyseat cutters are referred to as Woodruff cutters for feeds and speeds):

4. Select what material the tool is made from, either HSS or Solid Carbide, and what coating it has (if any).  A good coating can provide some added lubricity to make the material cut more easily.

5. Enter your cutter’s diameter and number of teeth.

6. Enter your cutter’s thickness

7. You can optionally add information such as shank length, neck diameter, and overall length.  This information won’t affect feeds and speeds but will make your tool tables more complete.

8. Enter the Depth of Cut. This is the total depth of the keyseat.  G-Wizard should remind you to keep cut depth less than 4x saw thickness:

Note that in the case of a Woodruff key, you want to choose a saw diameter (cut diameter) that is equal to your woodruff key’s diameter.

Here is the finished result:

Typical setup to find Feeds and Speeds for a Slitting Saw…

If you’re not a registered G-Wizard user and you’d like to try our free 30-day trial, check it out on this page.

Sneaky Stuff:  What Else Can a Woodruff Cutter Do?

They can be quit useful for making undercuts in a workpiece.