View Full Version : D shaped hole

02-22-2004, 11:42 PM
Picture a 1 inch shaft which has a 0.25 inch flat along it's length. How can I make a 0.5 inch deep hole which the shaft will fit into?

02-23-2004, 12:29 AM
Ralphe, the flat is for a set screw. just make the hole round, and the set screw will keep it from turning. Doug.

02-23-2004, 02:31 AM
This probably isn't the right way but if it was steel and a if it was a blind hole and IF I absolutely had to have a hole like that... I'd drill or bore the 1" hole 1/2" deep then slice a piece the right size off a piece of 1" shaft then tig weld the piece in with a .040" tungsten and .023 filler. That's a pretty small piece but it can be done.

02-23-2004, 02:58 AM
torker - The material is series 7000 aluminum

Paul Alciatore
02-23-2004, 03:53 AM

I frequently need to make holes for D and other odd shaped shafts. In my application I do not need tight contact between the shaft and the hole at all points around the circumference. I have developed a technique that produces a hole that has at least four point contact and along the full length of the flat. For the D shaped shafts I use a rectangular hole with rounded corners. The corner radius is the radius of an end milling cutter that is selected for the "best fit" to the desired hole.

I use a CAD program and draw the D shapped shaft outline on one layer. I then lock/freeze that layer and on another layer I draw a rectangle that is as long (d) as the diameter of the shaft and as wide (w) as the width measured at the flat. So that rectangle is d x w. I then select an end mill diameter as large as possible while still allowing the full length of the flat (l) to be milled without cutting outside of the long dimension (d). Formulae for this are as follows:

Cutter Diameter <= d-l


Cutter Diameter <= w

Both conditions must be met. Select the largest diameter mill you have that meets both conditions. The larger the diameter of the cutter, the less the misfit will be and the fewer passes required to do the interior of the hole if it's blind.

Now add filets to the rectangle with a radius of 1/2 the diameter of the selected end mill and trim. The rounded corner rectangle should be outside of or on the D shape at all points. The flat of the D should coincide with one of the long sides of the rectangle.

Finially, add a smaller rectangle inside of the rounded corner rectangle. It's sides should be offset from the outer rectangle by 1/2 the diameter (the radius) of the selected mill. Dimension this rectangle. These dimensions are the X and Y values that the milling table has to be moved to cut the rectangular hole. When cutting the hole I usually start at one corner (upper left) and do two sides to the opposite corner. I then return to the first corner and do the other two sides. This avoids any backlash problems.

This rectangular hole will not be in contact with the shaft at all points of the circumference but the shaft will fit tight and will not rotate in it.

This technique can be adapted to cut holes for a variety of odd shapped shafts or other components that are not round.

Paul A.

02-23-2004, 03:55 AM
I suppose you could run a bead of aluminun weld inside the 1 in. hole, then mill it to a flat. Using a suitable, probably home made chisel tip, in the mill, you could broach it to shape. Not much metal would fit in that small space so it should be possible to build it up with weld.

02-23-2004, 09:01 AM
It is recommended that you do NOT weld 7075 alu. If you have to, resistance welding is the only acceptable method.

02-23-2004, 11:58 AM
Being a novice, I thought rotary tables handled things like this. Humm ... what am I missing here?


02-23-2004, 12:08 PM
Torker is right, don't try welding 7075. It is considered to be unweldable. The proper way to make a through hole like that is with a broach. If it's not a through hole then it can be approximated as per Paul.

02-23-2004, 12:25 PM
Do you have room around the hole in the 7000 aluminum part? If so you could cross drill a hole and press in a pin that would form the "flat" for your D shaft. A 1/4" pin would be easy to place in the right spot.

[This message has been edited by glenj (edited 02-23-2004).]

02-23-2004, 01:38 PM
7075 considered not weldable, hmm. I learn something everyday.

Paul Alciatore
02-23-2004, 02:08 PM
<font face="Verdana, Arial" size="2">Originally posted by Smokedaddy:
Being a novice, I thought rotary tables handled things like this. Humm ... what am I missing here?


I agree it could be done with a rotary table. Use a small diameter end mill and cut the round part first then the flat with the main table feed. It sounds like a bear to set up and get accurate and you would have to overshoot the flat on both ends to obtain clearance to the corners. This would make a better fit than my rounded rectangle but would still have some gaps by the flat.

Another thought is that the voids in either this way or my rounded corner rectangle could be filled with something like epoxy or body filler after cutting the hole. Use the shaft or a slightly oversized, temporary plug in it's "D" shape when pouring the filler. That would make a far better appearance and be easier than welding.

Frankly, I would consider redesigning this part if possible.

Paul A.

02-23-2004, 02:18 PM
Here is a good page about welding aluminum alloys.


03-27-2004, 01:48 PM
I would like to thank everyone who answered my original request for assistance. I have incorporated your suggestions in the final piece (see photo below), using a piece of keystock which I inset to form the straight portion of the "D".
Incidentally, the part is a foot peg bracket for a motorcycle.

G.A. Ewen
03-27-2004, 03:42 PM
A beautiful piece of work!!! I,d give you a trophy if there was one in the smilies.

03-27-2004, 04:50 PM
Looks like a very practical solution to me....

John Stevenson
03-27-2004, 04:53 PM
What is appealing about the design is that if it wears or frets in use only the key steel insert needs to be changed.
At a pinch you could also move up a size if it got really bad.
Very practical.

John S.

Paul Alciatore
03-27-2004, 07:04 PM
Good show! I'll remember this one.

Paul A.

charlie coghill
03-27-2004, 11:21 PM
Wished I had thought of that.