https://www.youtube.com/watch?v=rbfm4nyu8Ro
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Dammit. More stuff I didn't know I needed.
Like it? Same effect by hollowing out a boring bar [even shopmade] somewhat [a tapered hole is even better] then drill and tap end for big set screw or pipe plug. Fill with small lead shot [not molten] and thin grease. Tighten plug and top off repeatedly, until you don't get any more compression. Some guys put in a little vent hole, plugged by grub screw. Another expedient is to lube the ways heavily.Quote:
Originally Posted by nova_robotics
Voila. No, it might not get feed rate demonstrated, but isn't many hundreds of dollars apiece either. Also C1045 is among highest machinability rating, they don't mention spindle bearings or other conditions.
Videos with excess show-boating like the intro, always peak my suspicion meter.
Awesome tip. Thanks.Quote:
Originally Posted by Toolmaker51
I have several large boring bars that I made from thick wall steel tube which are filled with lead. That is, poured in when molten. This gives more mass than lead balls.Quote:
Originally Posted by Toolmaker51
It would be interesting to compare results with your lead shot and grease. Lead does not resonate.
Way back in time, working in 70's era mold shop, the lead and grease thing came in this way. One mentor [a cast bullet shooter] advised us lead shrinks slightly as it chills. The plug tightens it, dampening vibration well, in a tapered bore. Our non-scientific hypothesis said that a cylindrical shape wouldn't attain as much contact between lead and the bar interior. Cerro/ bismuth metal would have worked but the volume meant high cost, I suppose.
Regarding tapered bore, a true taper is possible but depth was an issue. They relied on mere step drilling. The difference of which end, tool bit or tool holder, worked better wasn't solved. IMO, variables of machine condition, feed & speed rates, tool form, cavity size of mold etc too extensive to formulate. These were large trashcan like profiles, radii at top lip, stacking band, and bottom, requiring male radius form tools. That allowed good feed rate but a real pucker-fest disengaging at exact depths while backing off cross slide. Carriage stop not good for that. No DRO's or CNC's back then either, just creeping up on long travel indicators or Trav-A-Dial.
Come to think of it, still prefer watching an indicator count-down instead of DRO doing that slot machine act.
I thought about shrinkage and as a (probably unnecessary) precaution I heated the steel tube to red before pouring in the lead. This gave scope for the tube to contract onto the lead. I never attempted to measure if it did but there has never been any sign of a loose core and I must have made three 55+ years ago. I did think of trying to "tin" the inside but it worked without it and it did not seem an easy thing to do. In any case I am not so sure that a loose core would be detrimental.Quote:
Originally Posted by Toolmaker51
I once tried something just for fun without intention of using it for real. I fixed a relatively small diameter rod to the back end of a boring bar with a mass that could be moved back and forth. This was an harmonic damper and it could be tuned to stop chatter. It was great but I considered it too much hassle to use as a workshop device. I wonder if the bar in the video works on a similar principle but inverted and put up inside instead of dangling out the back like mine.
Interesting concept and design and will check it out. Several years ago I started using only solid carbide boring bars for holding my carbide inserts. A world of difference when doing internal lathe boring with no chatter but an expensive initial cost. Also, changing out the carbide inserts sooner than latter makes a big difference. There are some great solid carbide boring bar bargains currently found using eBay.
The adjustable damper/ balancer is worthy but cumbersome yes. But those are used on rifle barrels for tuning out harmonics. They are threaded because there is no concrete setting, once again due to variables.
There is a tendency in boring to run inefficient RPMs and feed rates, sometimes bumping one up or down is all that's needed.
On boring bars, tightly wrapped strip of inner tube is one remedy, and secure wraps of lead wire work too. Noise or not, two simple tests; very laborious. As bar enters hole watch the chips. They should pour off, not hop around and fall off. Lay something like a pencil on the bar, chatter does not always result in sound.
Either way, chatter is not effective cutting. Looses size control, surface finish, and both interfere with mating parts.
Just occurred in the foggy mist; try a split shaft collar, or split tubing and hose clamps........
The principle shown in the video seems to be different than filling the boring bar with lead. The latter increases the mass, the former induce a dumpening due to the internal mass but mediated through the elastic rings. (Intuitively) the transfer function seems to be different because just increasing the mass simply shifts the frequencies at which the oscillations take place, while adding those elastic elements insert somewhere a constant factor (dumping) into the formula.
The grease and lead balls seems to be similar to the solution shown in the video, but cheaper and simpler :) , because the grease can't introduce any delay* but only a dumping factor (due to [the small] compressibility).
I wonder what happens to rigidity.
Remarks:
*The delay comes from the Newton's second law: F = m a = m (dv/dt). The "dt" argument introduces the "delay", or better a time shifting factor in the transfer function of the motion from workpiece on the spindle (in the case of the lathe) to the boring bar holder. We can use this transfer function to assess the stability of the system composed by the workpiece in rotation (as action) and the boring bar (as reaction) and a noise generator determined by the point of contact of the tool with the workpiece. This noise will induce oscillations that could increase in aplitude if the system resonates (i.e., it's not stable).
N.B. This is to explain my intuition, I do not know if this is the common way to model a system like this.
That's a very good deduction, I'm no physics major, but it visualizes well enough. There always seems a vibration feels more pronounced at one spot, usually not midpoint. Certainly mechanical conditions alter what vibrations would do on their own.
And why some boring bars have a taper that work well, while others might have taper yet can't generate a decent cut. It's worse in unprogrammed milling machines; having limited feed rates compared to any lathe.
Remarks:
*The delay comes from the Newton's second law: F = m a = m (dv/dt). The "dt" argument introduces the "delay", or better a time shifting factor in the transfer function of the motion from workpiece on the spindle (in the case of the lathe) to the boring bar holder. We can use this transfer function to assess the stability of the system composed by the workpiece in rotation (as action) and the boring bar (as reaction) and a noise generator determined by the point of contact of the tool with the workpiece. This noise will induce oscillations that could increase in aplitude if the system resonates (i.e., it's not stable).
N.B. This is to explain my intuition, I do not know if this is the common way to model a system like this.
M4A says: The correct solution for this mass-spring system is...
Attachment 38304
The lead does more than add mass, it is exceptionally good at adding damping.Quote:
Originally Posted by Claudio HG
This keeps rolling around the old bean;
Even if a molten lead plug shouldn't adhere, plugging the end to restrict movement, still dampens naturally in what little space it does have. Lead probably has no significant harmonics. Back-filling a viscous fluid would be very effective.
Yeah but that only applies to undamped systems that are allowed to naturally oscillate. There is damping when the tool touches the workpiece, or when you use fancy boring bars with lead and grease in them. As soon as you start using the tool you have to take damping into account.Quote:
Originally Posted by machining 4 all
Thank you for the solution for mass-spring, here however we have an active motion (either propelled by a motor or by human labour). Anyway even with the mass-spring the time enters into account: ω = 2 π f; where f = 1 / t.Quote:
Originally Posted by machining 4 all
Well, I agree that lead has some kind of dumping properties, that's because lead has a very low modulus of elasticity (14GPa, lower than concrete which is 30GPa), and with one of the most larger mass. But grease and (probably) those rings have even lower modulus of elasticity, for instance rubber has ~ .1 GPa.Quote:
Originally Posted by tonyfoale
