T-style parting blade shimming necessary?

[Christianstark]

Hi all,

Still waiting on my lathe delivery, but I have been accumulating tooling to be prepared.

One of my latest purchases are HSS parting blades. The top of the parting blade is around .0925", and the bottom is about .06" thick by my old used micrometer measurement.

I know some practices have been to use s shim between the skinnier part of the blade, and the BXA Holder, but I have 2 questions.

1 - Is the shim necessary? What can go wrong if it isn't perfect?

2 - Has anyone instead milled a relief slot into their holder, front to back say .01625ish deep and wide enough for the blade to simply rest vertically? Seems that even with a non T-style blade, the bulk of what the tool rests against would be enough to hold perfectly vertically until it is tightened down...

Thoughts?

 

[benmychree]

I use 1/8" wide T style blades in my CA holder without shimming or a relief slot, and it has never been a problem since the 1980s.

 

[Christianstark]

I use 1/8" wide T style blades in my CA holder without shimming or a relief slot, and it has never been a problem since the 1980s.

Do you just slide in the blade and tighten, or do you try to space the thinner bottom of the blade out slightly to achieve a more vertical mount?

 

[benmychree]

Yes, pretty much just insert and tighten.

 

[pontiac428]

I machined a slot in my toolholder, but it's only perfect with one size of blade. Larger blades don't touch at the base, and smaller blades don't touch at the milled slot. The blade is held by downward pressure on the top of the blade. Too tight and it will flex.

Basically, I realized I'm not going to get any magic improvement with the milled slot, and that I can do good parting in tough materials so long as my blade is sharp, the point is on center, and the cross slide is perpendicular. I still break blades if they dig in, and my lathe is worn, so I need to keep everything tight/locked going in. I don't think the shim or milled slot do very much compared to a sharp tool. Just my experience with it.

 

[rabler]

I've never used a shim, but I do find it is necessary to be somewhat careful to align the parting blade close to vertical, as I've found I can accidentally push the bottom in if I don't pay attention.

 

[MrWhoopee]

I'm with John, put the blade in, push the top of the blade against the back of the pocket and tighten. The clamp against the top of the blade squares the blade as long as you haven't pushed the bottom all the way in.