How to hold solid carbide small (4,5,6mm) diameter boring bars in the lathe QCTP

[SteveIParticipant @stevei]

Hi,

What is recommended practice on how long the clamping part of a split sleeve should be relative to the stick out and diameter of a boring bar? Furthermore what are the optimal methods for clamping small diameter bars?

I've acquired some new to me nicely priced solid carbide shank (with coolant hole) boring bars with diameters of 4,5 and 6mm. They are long, 150mm and I need to use them in my QCTP. I've been recommended to not use a regular boring tool holder with hold down screws. I plan to use these for deep hole boring up to 10-12 times the diameter of the bar and experiment with mist coolant down the coolant hole. so i want to keep the end accessible.

For my other boring bars from 8mm diameter and up I make a split sleeve to go from the diameter of the boring bar to the 30mm inside diameter of the multifix bush J type tool holder I have. Up to now these are easy to make and I make them all with approximately 80mm clamping length as that is the size of the tool holder I have. This will not be trivial or i think necessary at e.g. 4mm diameter so a shorter length will be optimal.

My other idea to avoid deep boring was to make a ER collet chuck with a Ø30mm shaft to clamp in the tool holder. This will be much easier to make than do a super deep bore. I have some ER16 and ER20 collets in the 4,5 and 6mm sizes. The clamping length of these is not long at all. Perhaps 10-15mm. My initial thinking is that this would be a nice flexible solution for different sized small diameter bars but is the clamping length sufficient?

Thanks,

Steve

[SteveIParticipant @stevei]

[EmgeeParticipant @emgee]

Hi Steve

Split clamp works for me but I never have such lengths of small diameter boring bars, even solid carbide will vibrate at those lengths/diameters, suggest you use successively bigger tools as the diameter increases, for boring I always use the largest diameter that will enter the drilled hole.

Emgee

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