What's the Differance? Tool Post Styles, Piston or Wedge

[Splat]

I forgot to mention that yes, I too had jamming problems with the wedge type. Yes, the rigidity was there but so was the aggravation I got when changing tooling.

 

[ryanH]

I think when they are both new your not going to see a difference, as they start to wear I'm guessing but would the wear of the piston style become exponentially more rapid? As the further out the piston pushes gives the tool more leverage against the dovetail, and the dovetail will become weaker to further out the tool is seating? Where the wedge style just the opposite? "This is just my theory, and have no data to support it" maybe some guys with much more experience can offer an opinion

 

[bill stupak]

I have a Swiss made TriPan tool post that is a piston type that acts like a wedge type.

 

[Jimsehr]

After 70 years of machining all I care about is if the cutter tip gets on center any tool post is fine wit me. In a home shop I would buy the cheapest.

 

[DevinSS]

I have done testing on both types (BXA size), using various brands of holders, using a TDI and actual cutting.

The piston type is more prone to repeatability errors depending on the fit of the holder to the tool post. A loose fitting holder can be locked up slightly tilted fore or aft several thousands of an inch where a tighter fitting holder is more likely to true up when tightened. This can be dealt with by applying pressure to the front or back of the tool holder when locking to fully seat the dovetail.

Some holders from other manufactures may not fit the piston type holders due to that large variation in dovetail dimensions between manufacturers. I have not run across this problem with the wedge type.

As stated above the contact area between the holder and tool post is greater with the wedge type but in the testing I have done, taking maximum turning and parting cuts, the real world performance was negligible between the two.

That being said my personal preference is the wedge type because any brand of holder will fit and there is less chance for repeatability errors.

 

[RaisedByWolves]

I have the wedge type on a lathe I purchased from a friend. No issues with my toolholder. The friend got a new lathe and a piston type. He has commented he prefers the wedge type. I did not try to get details on the difference.

The benefit of the wedge type is that the wedge pads downward pressure ion the tool holder as its tightening.

This helps the tool bit land at the same height more repeatedly avoiding errors.

We have the piston type at work and tea until recently all I ever used.

I got a cheap wedge style for my 5” Prazi and was blown away. It just flat out work’s better than the piston style I’m used to.