Wobble broach that doesn't Wobble.

[Kram]

Ok, this means I may need an MT2 capable AX toolholder. More toys/expense. :-)

You have a lathe and your on a welding site... I'm sure you could adapt something.
The holder you linked is a 1/2" shank... But perhaps the one you have is MT2. Get a cheap mt2 adaptor and weld 12mm bar to go in the post.

 

[DanClarke]

To clarify what we're talking about, the "wobble" will show as the shaft centre moving around in a defined circle when viewed from the end (using the vice method) as you spin it.

I started making a broach with the idea that I could have the bearing concentric to the tool axis and then offset in a tool post. It was only once I bored, and ruined, the blank arbour that it dawned on me that I hadn't appreciated exactly how it functioned.

Thanks @ Seadog .... Yes, with the shaft of the broach holder firmly in a vice and a run-out gauge on the shaft of a tool in the actual business end of the holder there is no "orbiting" of the tool's shaft which there would be if there was an inbuilt 1° offset.
I guess the suggestion is to put the 1° into the process by using the offset capability of the toolpost.

As the workpiece is probably junk now I am going to just put the Broaching bit in a toolpost mounted drill chuck and set the toolpost off by 1°

Thanks for all the help folks.

 

[DanClarke]

You have a lathe and your on a welding site... I'm sure you could adapt something.
The holder you linked is a 1/2" shank... But perhaps the one you have is MT2. Get a cheap mt2 adaptor and weld 12mm bar to go in the post.

See the post immediately above. Great minds think alike.

 

[Kram]

Thanks @ Seadog .... Yes, with the shaft of the broach holder firmly in a vice and a run-out gauge on the shaft of a tool in the actual business end of the holder there is no "orbiting" of the tool's shaft which there would be if there was an inbuilt 1° offset.
I guess the suggestion is to put the 1° into the process by using the offset capability of the toolpost.

As the workpiece is probably junk now I am going to just put the Broaching bit in a toolpost mounted drill chuck and set the toolpost off by 1°

Thanks for all the help folks.

View attachment 478456

Could it be thats a self aligning type spherical outer race bearing? It may need a radial load to align?

Can you return it? If not, I would see if it comes apart for closer inspection.

 

[iNf]

Ok, this means I may need an MT2 capable AX toolholder. More toys/expense.

Your broach holder looks to be straight shank? So you don't need a mt2 holder. There's no point putting a drill chuck in the toolpost and then the holder in the chuck it's just creating lots of overhangs. Just put the holder directly in the toolpost. You can make a simple holder to fit in your current toolpost. Something like these,

 

[Seadog]

If it doesn't work in a pillar drill then it's not a wobble broach. It's a live centre with a tool-holding attachment

 

[DanClarke]

If it doesn't work in a pillar drill then it's not a wobble broach. It's a live centre with a tool-holding attachment

Yup, this is what it is effectively.

 

[DanClarke]

Your broach holder looks to be straight shank? So you don't need a mt2 holder. There's no point putting a drill chuck in the toolpost and then the holder in the chuck it's just creating lots of overhangs. Just put the holder directly in the toolpost. You can make a simple holder to fit in your current toolpost. Something like these,

View attachment 478457 View attachment 478458

I meant using something like this ... which provides a free-spinning chuck. Sadly this one only goes to 6mm bit size.

So I will mount a 12mm bar directly on the shaft of that Rotary Broach (aka live-centre tool-holder). and put it in a standard tool holder on my toolpost and use the toolpost angle to give the offset.

 

[DanClarke]

Update:
Thank you all so much, it "works"!
As suggested I welded the "dodgy" tool to a bit of 12mm plate, popped the whole thing in a tool holder and set it up as best I could (by eye).
And a lovely 1" deep hex hole appeared. Hurrah!
Weirdest "feedback" feeling on the carriage wheel as it nibbled its way through.

But the job was jobbed.

 

[Kram]

Im not sure that works? Doesn't the broach need to wobble to get the cutting action?

Another option is to mill the hex and 12mm is large enough to be done this way. To mount in tool post
I used a bit of 12mm hex bar, which if you turn a section round you can superglue to your parts, gentle heat to remove after..

The hex means you can rotate it for each face, the tool post lets you set the correct height. You can set the height by chucking a pin same diameter as your cutter, perhaps 2mm is a good choice.
From the centre high point, move 5mm each side. Perhaps 2mm deep per pass.
I'll try it some day.


Edit: clearly not, well done!
I may have to make one of these to try it myself. Thanks!