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Rotary broach
- Thread starter Malave16
- Start date
With a moderate speed on the drill press vibration is not an issue at all. The only thing you get is a constant up and down of the quill. When i get a hold of my neighbor ill try it on his mill and post a vid.
Is that what the little "divots" on the corners of the bit are for? To give the relief for the gyrating movement? If so they limit the cutting speed and ability? :thinking: Also, Do you have to drill a "starter" hole and if so does it need to be the size of the finished square hole?
example" a 1/4" hole for a 1/4" square hole?
Mark Frazier
example" a 1/4" hole for a 1/4" square hole?
Mark Frazier
- Joined
- Feb 2, 2013
- Messages
- 3,957
:rubbinghands:
thanks for the great idea!!!!!
and I subscribed!!!
thanks for the great idea!!!!!
and I subscribed!!!
Last edited:
- Joined
- Dec 25, 2011
- Messages
- 599
Hi Mark,
The ones that I made (just 3/8 and 1/4 square) You have to drill a pilot hole and taper it to get the cutter centered in the hole.
I drilled a 17/64 hole for the quarter inch and that worked much than a 1/4 hole. Not a lot of precision needed on the holes I was doing. I ran the mill at a really slow speed and it just works it way down the hole.
I like the OP's idea of using hex wrench to make a cutter---never crossed my mind.
The divots on the side are for relief. They allow for the oscilating movement that produces the cutting. The pilot hole needs to be at least the size of the hole you want to make. You also want a chamfer at least as the widest point of the cutter.
- Joined
- Jun 24, 2012
- Messages
- 14
Great work Malave16! I make rotary broach holders commercially and am always impressed when I see people making their own or coming up with modifications on the design. Our three basic principles for setting up a rotary broach include chamfering the hole a little larger than the sharp corners, using a slightly oversize pilot hole diameter (10% for squares) and leave room for chips to accumulate. Hope that helps.
- Joined
- Nov 12, 2013
- Messages
- 32
Help chaps,
As an electrician I'm an absolute beginner machinist, and I'm having trouble understanding the operation of the Broach described here.
I've achieved a square hole before by bashing a HSS tool thro with a big hammer, the requirement was for carbon brush mountings in DC motors. The results were erratic to say the least.
Mention is made of the tool gyrating, and looking at the designs it is pretty obvious that the tool is meant to be powered.
Could someone please explain ...!
Thank you,
Norm.
As an electrician I'm an absolute beginner machinist, and I'm having trouble understanding the operation of the Broach described here.
I've achieved a square hole before by bashing a HSS tool thro with a big hammer, the requirement was for carbon brush mountings in DC motors. The results were erratic to say the least.
Mention is made of the tool gyrating, and looking at the designs it is pretty obvious that the tool is meant to be powered.
Could someone please explain ...!
Thank you,
Norm.
Most can probably explain this better than me but here goes.
The piece that has the eccentric turned on it has a socket drilled in it to receive a single ball from a ball bearing. This socket is drilled to run off center, hence the eccentric, and there's also a socket on the part that holds the toolbit that the same ball sits in, the two are held together only by the downward pressure on the quill. When the machine spindle rotates, the upper end of the toolbit rotates off center because the ball that drives it rotates with the eccentric hole. This causes a rocking action if you will on the bottom of the toolbit, and the end of the bit is ground concave, leaving, in effect, four cutting edges, each alternating as the bit rocks. Relief is ground on the sides of the bit to allow for the rocking motion as it gets deeper in the hole. Hope that makes sense. He also posted a link to a video. Great job, by the way, been going to make one myself but haven't got around to it.
The piece that has the eccentric turned on it has a socket drilled in it to receive a single ball from a ball bearing. This socket is drilled to run off center, hence the eccentric, and there's also a socket on the part that holds the toolbit that the same ball sits in, the two are held together only by the downward pressure on the quill. When the machine spindle rotates, the upper end of the toolbit rotates off center because the ball that drives it rotates with the eccentric hole. This causes a rocking action if you will on the bottom of the toolbit, and the end of the bit is ground concave, leaving, in effect, four cutting edges, each alternating as the bit rocks. Relief is ground on the sides of the bit to allow for the rocking motion as it gets deeper in the hole. Hope that makes sense. He also posted a link to a video. Great job, by the way, been going to make one myself but haven't got around to it.