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Larger SGIH cutoff blade was needed

For cutting bars off in the Clausing 5914 lathe, I have been using a up-side-down SGIH19-2 blade in a up-side-down Dorian D30BXA-7-71C holder, which fits a Aloris BXA toolpost. The lathe is run in reverse, so the cutoff blade will not self feed into the groove.

This works quite well, up to maybe 1.5" diameter steel, but at the larger workpiece diameters the surface finish deteriorates markedly. What I think is happening is that the blade is on the verge of elastic (sideways) buckling, and is vibrating laterally. I have been using it anyway, manually and with care. I had read that using a heavy feed helps, and it does, at least to control chatter (where the vibration is vertically). But one must be too careful.

The Dorian catalog states (on page P-23) that the maximum workpiece diameter for a SGIH19-2 blade is 1.57", which is consistent with my experience.

Clearly I needed a beefier cutoff blade if I was to cut larger steel workpieces off.

So, I got a Dorian D30BXA-71-26 holder with SGIH26-3 blade. The blade is rated for up to 3.00" diameter workpieces, which will cover most of what I do.

This made a big difference. Cutting a 2.5" diameter 12L14 bar off left a mirror finish under power feed when flooded with soluble-oil coolant. Coolant is essential, and one can hear the difference if there is too little coolant.

The only problem was that it turned out that the Dorian D30BXA-71-26 holder with SGIH26-3 blade is slightly oversize for the BXA toolpost, requiring the D30BXA-71-26 holder to be about 0.2" above the top of the BXA toolpost. My current solution is a 0.25" thick heavy steel spacer washer 2.5" in diameter with a 5/8" hole that goes between lathe compound and BXA toolpost. We'll see how well this works.

As for toolpost rotation under cutting force, there is a 0.25" diameter blind hole in the bottom of the BXA toolpost that looks perfect for an anti-rotation pin, so I may make an adapter plate with a ridge to fit into the compound's T-slot on the bottom and has the anti-rotation pin on the top.

Joe Gwinn

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Joseph Gwinn
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That sounds like a decent setup. My 6903 is sporting an Aloris AXA on a spacer block which is too small for the lathe. I've been holding off on more holders as not to get locked into something I'd rather change to BXA.

Parting is where my set up is weak. Making it to 3" would satisfy most of my needs.

Now if only some extra money would stay in the budget, I'd be upgrading.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Reply to
Wes

It turns out that it chatters with the D30BXA-71-26 SGIH blade holder, but not with the smaller SGOH blade and holder I had been using. I had theorized that the thick washer wasn't quite flat enough, allowing slight rocking, so I undercut both faces so the toolpost and compound would rest firmly on rings at the outer diameter. Made no difference.

Research continues. This with an upsidedown blade and reverse rotation, so static stiffness is not the issue. That leaves dynamic stiffness. So, ways to increase both stiffness and damping are needed. Maybe a piece of sheet lead in a critical spot.

Actually, this toolholder will accept a HSS T-section cutoff blade, if I recall, so there is an experiment to try.

For a 6900-series lathe, an AXA is far too small. Which you already know. Aloris recommended the BXA without spacer for my 5900-series lathe, and it does fit well, except for this larger Dorian toolholder.

If the 6900-series lathe works with a CXA toolpost, as seems plausible, the big Dorian D30BXA-71-26 toolholder and blades would just fit.

Joe Gwinn

Reply to
Joseph Gwinn

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