[QuinnSjoblom]

On my current machine, tooling for turning will be held in a quick change tool post mounted next to the main milling head, but im thinking about possible future machine configurations. In serious mill turn machining centers, it seems common for the turning tools to be held right in the main spindle. This makes things really convenient in a lot of ways. No clearance issues to deal with when trying to mount turning tools next to head, tool offsets become much more simple, auto tool changer handles turning tools same as milling tools. This machine would have a servo driven bt30 spindle. Since it will be servo driven, it will have the ability to hold a specific orientation. Im not sure how much rotational play there is between the dogs of a bt30 spindle and it's holders, but maybe good enough to line up the turning tool at proper angle? I'm sure this would also require a brake on the spindle since as I have already found with the mill turn spindle, servos don't really hold a completely rigid position, so it needs to be locked. I'm not really sure how exactly I would hold the turning tools in a bt30 holder, but I'm sure there's a few options. One would be a heavy duty boring type tool holder held in an er collet bt30 holder since it has a round shank. B axis head would be required if I want to do boring with turning tools in the spindle, but it would open up a lot of other possibilities as well.
Basically this machine would look alot like the swissmak, but with a few differences. No turret since turning tools would be in spindle. Would have dual servo driven horizontal spindles, both on the same set of x linear bearings but each having their own ballscrew for independent control. This would be capable of doing part transfers so full automation of multiple parts. The dual spindles also allow another interesting feature, large 4 axis fixtures that are supported and driven at both ends. Once the fixture is installed, the secondary horizontal spindle is slaved to the primary horizontal spindle in both x axis and rotation. This would allow the option of a more traditional milling setup unlike the swissmak. Probably wouldn't be putting a 6inch kurt on one of these fixtures, but maybe something smaller. Could also do 4 sided fixtures, basically a long horizontal tombstone supported at both ends by the horizontal spindles with parts on all 4 sides held with mighty bites or something similar.

Anyway, kind of getting off track. For now I'm mostly thinking about how well it would work to hold turning tools in the bt30. Any obvious issues with this? Rigidity, Rotational repeatability in the dogs, etc?

[Jim Dawson]

I just checked the dog engagement on my BT30 spindle, looks like about 2-3 degrees of play. For most turning that should be close enough. I would expect the repeatability to be better than that.

Rigidity should be fine as long as you stay within the limitations of the overall machine, and keep the tool stick out as short as possible

[QuinnSjoblom]

I just checked the dog engagement on my BT30 spindle, looks like about 2-3 degrees of play. For most turning that should be close enough. I would expect the repeatability to be better than that.

Rigidity should be fine as long as you stay within the limitations of the overall machine, and keep the tool stick out as short as possible

Ok sounds good. I could probably design the tool changer in a way that the dogs get bottomed out in one direction. While the holder is still being gripped in the changer, the spindle could rotate a few degrees before releasing the draw bar. Something like that.