Tool Height On A Lathe

Regarding preference for wedge or piston type QCTP.

I had a piston type on my Grizzly that I sold with it. When replacing it, I did some research and the general advise seemed to be that wedge types made more solid contact with the dovetails in the tool holder.

Generally, I have to say that I don't like the wedge type. It takes fidgeting and wiggling to remove and insert the tool holders. There doesn't seem to be a positive place to rotate the handle to loosen the thing. To loosen it, the handle has to be in some arbitrary middle position.

With the piston type, there were two positive positions of the tightening handle. The only fidget was sometimes I had to push the piston in to slide a tool holder on.
 
I prefer a wedge type by far. Perhaps some of the China ones don't perform well & need messaging. My Dorian SQCTP is very smooth, I never have to fight with it to remove & place tool holders on it even with China tool holders. Lockup is solid & very repeatable. Handle locks in the position I prefer but even though is adjustable.

I've used a few different piston types. Weren't on my own lathe but I found they tend to have poor lockup at times although they all could have just be worn. Tool holders coming loose on heavy cuts unless I really crank down on the handle. I just don't like how the lock up feels on piston tool posts.

I had a China QCTP on my old lathe. It wasn't too bad but the quality of the China ones compared to Aloris, Dorian, DTM, etc is beyond night & day.
 
Franko said:
Rigidity is definitely good. The time it happened to me, my ways had gotten a little loose. It wasn't something that I checked very often. When it happened, I actually saw the tool moving and was thinking, "that can't be good."

The next moment before I could shut it down, Bam! Gouged part pulled crooked in the chuck and broken insert, in an instant.

I'm sure I'm the only idiot in the world who has done such a stupid thing.
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I forgot to lock down a 4-way tool post once. That was exciting.
 
I fabricated a four tool post, found that I had miscalculated the height and finally put a .015 shim under it. The cut off tool and the facing/turning tool now do not leave a tit at the center, but are (it appears) exactly on center. Wish I'd been more careful with my calculations. However, now it works really great.
 
Franko said:
What I am trying to determine is how much more material would I ever want to remove from my turntable seat for the maximum lowering of the tool I might require. The answer seems to be enough so the lowest the tool can go is about 1/8" below center.
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Franko, in looking at tool holders on the Shars website, I noticed that they have a 250-101-XL tool holder with 5/8" capacity. The additional 1/8" is removed from the bottom seat for the tool bit so the 5/8" tool bit comes out at the same 15/16" height. If used with a 1/2" tool bit, it will drop the top of the bit by 1/8".
 
Thanks, RJ. That could be very useful to know.
 
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