Boring bar bushing slitting recommendations

[WobblyHand]

I need to make a bushing for my 3/8" carbide shank boring bar to fit in an AXA holder. The AXA toolholder bore diameter is 3/4". I know how to make one, (drilling through a blank bar through your toolholder with a drill held in the spindle,) but want to know what is typically done for the slitting when the bushing thickness increases. I'd also like to make a bushing for a 6mm boring bar. For thicker walled bushings does one partially slit the other side of the ID? I made a bushing for my 1/2" boring bar and didn't bother with adding the cut opposite the slot.

This is a bushing sketch for a 3/8" bar in a 3/4" holder. Slit is 1/16" wide. Slit is 0.050" deep on left side.

So for a 6mm carbide shank boring bar in a 3/4" holder, I can use something like this?

Kept the same saw depth of cut, 0.6125" from right side, is this approach good enough?

Realize this doesn't amount to a hill of beans, but thought I'd ask what preferred practice is. Might as well make them right the first time.

 

[mmcmdl]

Why not just use the bar in an AXA-2 holder ? But to answer the question , that'll work fine .

 

[WobblyHand]

Why not just use the bar in an AXA-2 holder ? But to answer the question , that'll work fine .

For a steel bar, I don't mind an AXA-2. For carbide shank bars, I don't like the idea of point contact with the potential for breakage. Paid too much $$$ for the Circle Machine carbide shank boring bars, so rather sleeve them.*

*Well except for the 6mm bar. eBay let me keep the 6mm carbide shank bar for free, since it was a bait and switch. Got a much different and worse bar than depicted. Might as well try it out, as there's nothing to lose on that bar.

 

[JRaut]

I made an adapter bushing for my Wohlhaupter boring head not long ago.

To do so, I basically emulated the design features of the genuine Wohlhaupter bushings, which use an extra offset hole to accomplish the same task as your over-depth slit.

The effect is essentially the same, but the extra-hole method is perhaps a little better as (1) it reduces stress concentrations, and (2) looks a bit more intentional.

 

[WobblyHand]

I made an adapter bushing for my Wohlhaupter boring head not long ago.

To do so, I basically emulated the design features of the genuine Wohlhaupter bushings, which use an extra offset hole to accomplish the same task as your over-depth slit.

The effect is essentially the same, but the extra-hole method is perhaps a little better as (1) it reduces stress concentrations, and (2) looks a bit more intentional.


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Nice. How did you make the two overlapping holes? Were they non-overlapping at first and then the main bore widened (bored out)?

For my application, think the simple slit is fine. If the bushing cracks, it isn't that hard to make another one. Maybe on the new one, I'll attempt your slick solution.

 

[JRaut]

If memory serves:

1) Turn OD to size on the lathe
2) Drill / ream out the 'functional' adapter hole
3) Part off to length
4) Move over to the mill and center up the spindle
5) Use a slot drill / 2-flute endmill to hog out the overlapped hole (as you are obviously aware, a standard drill wouldn't work)
6) Grab edge-wise in the milling vise and slit the slit

 

[frankly2]

Been buying and using “Marcellus” split bushings for 50 + years. Have always found them accurate and dependable for many applications. Marcellus makes them in many od’s and id’s to suit virtually any tooling. Pic’s of 1/2” od bushing.

 

[Janderso]

for my Wohlhaupter boring head

Nice!