Never used one myself and I expect they are professionally priced but a quick search reveals that most of them appear to have a mass / spring / damper assembly within the (hollow) body. The damper element being a viscous oil or mechanical friction mechanism.

Anyone here tried to make one of these?

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I have heard wrapping the bar in lead sheet can sometimes assist in removing harmonic vibrations.

Nick

That 2CV damper was of course filled with oil, and worked very well, and never leaked, so never failed the MOT. I had a fail once 'cos the man had never seen one before and assumed some bits were missing. I am in the process of making a long boring bar, from pipe, and plan to fill it with lead. I will report back when done, about next xmas at the speed things are going just now.

Sand in a tube might also be an option. I wonder if lead shot would work better than solid lead.

If you remember mixing custard from powder you were instructed to add a very little water to start with and mix. The paste at that point is a tixotropic substance.- sudden movement causes the particles to lock together, but slow movement is possible. Quicksand is another example. Blutack is just a paste (too much liquid phase) and swarfega is a gel so no better than a thick oil.

Gordon – apart from changing the mass of the bar which may have a marginal effect on the onset of squeal and chatter, filling the bar with lead doesn't seem likely to affect the outcome much. It's going to be a fine balance, as the very act of hollowing out the boring bar enough to affect anything will reduce its rigidity.

To make a real impact I suspect you will need to allow the internal mass to have some degree of movement against a spring plus a damping medium such as a viscous fluid to absorb enough energy to damp out any resonance.

Murray

Solid carbide boring bars work very well as regards dampened vibration. Bit more expensive but worth it I have found.

I would imagine a hole down the centre, needs to be below the size were the strength reduces rapidly.
Then bond a hard rod in with a small gap using a rubber type solution.

The hardened rod will resist bending and the rubber solution will allow a small amount of flex for the boring bar and should help dampen the vibration.

Steve

Obviously if you have room to fit a big f*** off boring bar, then you have a simple solution. The difficulty arises where the combination of small bore and big length results in enough spring to make it impossible to machine without encountering instability, even with fairly exotic materials for the bar.

Even if you eliminate the nonlinearities in the system (backlash etc), you still have a mass and spring resonant system that will be prone to resonance under certain conditions. The best solution is often to damp out the resonance rather than simply trying to move it out of the way. Given the wide range of operating conditions (load, speed, materials etc), it's going to be pretty difficult to move the resonances where they won't be encountered – and there isn't much of a choice of materials that would allow a significantly stiffer boring bar body. Carbide and expensive steels are possibly the best that are realistically available and we use those already.

I don't know if the systems used in high speed industrial tooling (mass, spring, damping fluid etc) would actually work in the conditions we encounter in our workshops. And to be honest, I doubt I would be able to do the calculations to start designing them myself. I suspect there will be quite a few PhDs in this area. Might be an area for experimentation!

Murray

I forgot to mention that with a VFD you can change the rotational speed to potentially move away from the bar resonance that is causing the problem.

Has anyone ever experimented with using an offset drill (of decent size) as a boring bar?

It strikes me that a drill of, say 3/8" or larger, would be sufficiently rigid enough for may purposes and have excellent cutting angles, clearance and chip clearance.

Neil

Neil,

A drill is far too flexible to use as a boring bar and the outside land would rub. A slot drill, used for milling would work but not for a deep bore. The best thing for boring is a boring bar.

Another way of stopping chatter is to mould a piece of Plasticene around the bar, it's an excellent dampener.

Bob Strawson