Any tips on how and tooling needed? There is a new CNC Machine shop in my area that subs out all of his oddball stuff along with turning & welding. He has a need for some broaching some through and some blind.
-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
Blind Broaching
- Thread starter Charley Davidson
- Start date
Slater rotary broach. You will need a relief groove in the bottom of the blind hole for the chips to break into.
Well I guess I'm equipped then as I just got one recently. Now for making the needed broach
Round shank, tapered back 1-2° more than the "wobble" and hollow ground on the front. Or you can buy common styles. If it isn't too deep, you can make them out of end mill shanks. Or HSS drill blanks. Takes some time and tooling to make them accurately, so for standard shapes, I'd probably just buy them.
an you broach key ways the normal way with them or do you need to broach the key way first then drill the shaft hole? What is max depth with a rotary broach?
Care to show me an example?
OK, you threw me with the reference to the shaft hole. You'll have to explain that one a bit.
I don't know of a picture of the relief groove right off hand, but I think I can describe it. Let's say you are going to broach a hexagonal hole for a 1/2" hex key. Standard tolerance for that is 0.5100/0.5050 If I remember right. So, you drill a hole the depth of the finished hex (think wrench engagement) and then with a groove tool, go to the bottom and cut a groove just large enough to clear the corners of the hex. It needn't be very wide, 0.050-0.075 is plenty. What this does is give the chips a place to "break off" at the end of the cut. If the customer doesn't mind a wad of chips mashed into the drill point at the end of the hole, you can skip this, but most people don't want that. Although, if you look at the lower tier hex socket cap and set screws, it's sometimes there. Other times, those are done on a heading machine that forms the hex without cutting. It's just brute force, and the OD swells and is taken down afterward as needed. No chips made there. Sometimes it's done cold, sometimes hot. Doesn't qualify as broaching though/
I don't know of a picture of the relief groove right off hand, but I think I can describe it. Let's say you are going to broach a hexagonal hole for a 1/2" hex key. Standard tolerance for that is 0.5100/0.5050 If I remember right. So, you drill a hole the depth of the finished hex (think wrench engagement) and then with a groove tool, go to the bottom and cut a groove just large enough to clear the corners of the hex. It needn't be very wide, 0.050-0.075 is plenty. What this does is give the chips a place to "break off" at the end of the cut. If the customer doesn't mind a wad of chips mashed into the drill point at the end of the hole, you can skip this, but most people don't want that. Although, if you look at the lower tier hex socket cap and set screws, it's sometimes there. Other times, those are done on a heading machine that forms the hex without cutting. It's just brute force, and the OD swells and is taken down afterward as needed. No chips made there. Sometimes it's done cold, sometimes hot. Doesn't qualify as broaching though/
Like in this picture would you be able to put the key way in after the bore is drilled or would you need to broach a square then drill the hole in the precise location making a key way in it?
That's not a good candidate for the rotary broach unless you do the square/rectangle first. Then it would be very difficult to drill accurately. A shaft fit would be impossible with a simple drilling operation. That would need to be bored. On the other hand, if that weren't blind, a standard broach with a properly sized bushing and shims would make quick work of that.
Is that an example of a blind one?
Is that an example of a blind one?