A Shop-Made Compact Rotary Broach

Bookmarked and thanks very much for posting the drawing. I need to get some drill rod and now have an excellent reason to get it soon.
 
Brooches are things that ladies wear on their clothes, broaches, on the other hand, are used to make multi faceted features in holes.
 
Very nice design, I think I’m going to try this. Thanks for posting
 
I know this is a relatively old thread, but then again, I’m a relatively new home shop machinist! I have a couple of quick questions regarding the unlisted dimensions in your drawing if I may ask:

First, what is the clearance dimension between the broach holder and tool body? Next, what is the centerline dimension for the 4-40 set screws in the tool body and broach holder? These may not be critical, but in order to maintain that 1 to 2 degree taper in cutting angle, it seems to me that they would have some stated tolerance for the pivot around the ball bearing. Additionally, I am considering Kasenit as a surface hardener on the bearing surfaces of the holder and body. Is this overkill?

Thanks in advance for the info, and an even bigger thanks for providing the drawing. I’ve found that I have many applications for a tool like this (including odd shapes, etc.), and as a hobbyist building small IC engines in my garage workshop, I can’t possibly justify buying such an expensive tool.

John W
 
A41capt said:
I know this is a relatively old thread, but then again, I’m a relatively new home shop machinist! I have a couple of quick questions regarding the unlisted dimensions in your drawing if I may ask:

First, what is the clearance dimension between the broach holder and tool body? Next, what is the centerline dimension for the 4-40 set screws in the tool body and broach holder? These may not be critical, but in order to maintain that 1 to 2 degree taper in cutting angle, it seems to me that they would have some stated tolerance for the pivot around the ball bearing. Additionally, I am considering Kasenit as a surface hardener on the bearing surfaces of the holder and body. Is this overkill?

Thanks in advance for the info, and an even bigger thanks for providing the drawing. I’ve found that I have many applications for a tool like this (including odd shapes, etc.), and as a hobbyist building small IC engines in my garage workshop, I can’t possibly justify buying such an expensive tool.

John W
Click to expand...
The OP has made one post (4 years ago) in the last seven years so I doubt he'll answer your questions.

I'll try: Regarding the missing dimensions = wing it. Their function should be pretty clear.

Regarding hardening, I would, but before hardening I would add center drill points at the bottom of both halves of the spherical sockets
(as lubricant reservoirs). Also, I would mount a 1/2" ball on a handle and use it to lap the spherical sockets to insure circular elements. In reality, the contact between the pivot ball and the socket halves will be narrow circular bands. Worst case would be the ball contacting at the bottom (single point) of a socket or at three points. More contact area and smooth, lubricated, hard surfaces = less wear/damage.
 
A couple years ago in a burst of enthusiasm I made a similar rotary broach. I broached a couple hex holes to test, worked actually quite impressively. Since then, I've used it by actual count zero times.

But a fun project in any event. And if I ever need a hex or other shape, I'm covered.
 
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