For years, I've been reading posts where many people here and on several other forums state categorically that TTS is only suitable for very light-duty milling, due to "the pull-out problem". I've always disagreed with that position as I've been using TTS for a number of years now, on several machines having 1-3HP spindles, and I have never once experienced pull-out. I have always argued that TTS works very well on machines at least up to 2-3 HP, provided sufficient drawbar tension is provided. Here is some visual back-up for my position:



There are three operations there, all being performed at 6000RPM, using a cheap, low-quality (Interstate brand) 2-flute HSS endmill:

1) Roughing a 1.006" diameter by 1" deep circular pocket - Cut in two steps, each of 1/2" depth. Helical entry at 77IPM, with w/10 degree ramp angle, followed by 110 IPM constant-engagement cutting at 0.050" stepover.

2) Finishing the same pocket - Cut at full 1" depth, at 65 IPM, in two passes of 0.010" each.

3) Roughing a large, odd-shaped pocket - cutting parameters are the same as operation #1, except depth is only 0.325", though I can just as easily cut the same pocket at 0.5" depth - that's just not what this part called for.

Unfortunately, on the fourth operation a programming error caused the spindle to stall, so I had to hit E-Stop. But, despite the fact that much of this was near the spindle power limit of the machine, and the spindle actually stalled at the end due to tool load, there was absolutely NO pull-out of the TTS holder.

Again, the "secret" is simply providing adequate drawbar tension. My power drawbars actually torque the drawbar to 30 ft-lbs, providing a drawbar tension in excess of 3500# - more than can be reasonably achieved using Belleville springs - which is enough to keep the TTS holder in-place under any load a 2-3 HP machine can muster. Many/most TTS users who have experienced pull-out seem to have power drawbars that provide no more than 2000-2500 pounds drawbar tension (many have much less), which is simply not enough to properly retain the toolholder with much more than a 1/4" tool.

Regards,
Ray L.