[Bill_B]

2 Questions.

We have the Tormach 440 and I have a deep part that is 2.25 tall with a center bore. We have the long-reach arbor TTS tool holders with the 25mm mill head.

The question is can I use this tool for my finishing passes? Surface quality is not a huge factor for this application but we still want a nice-looking part. The cylinder that makes up the bore ID and OD is not a dimensional aspect of the part function.

Deep drilling, same depth I need to make 4 .25 holes in this part all the way through. Holes will be drilled after facing, then will cur the bore.
Should I go with a carbide drill bit for this? or will standard tin coated jobber bit be fine?
Should I do a pilot hole all the way threw

[Advil]

Yes your arbor tool seems like one of the better options to get it done. Low axial depth of cut and fairly high feed. Should keep your part accurate with no taper even if surface finish isn't ultra good.

I'm just thinking out loud here but rather than trying to drill all the way through 2.25" of material with a 1/4" drill on a 440 (that's pretty deep at 9x drill diameter)... maybe go ahead and machine the bore with your extended arbor and then plunge mill the remaining portion of the feature with a long reach 1/4" end mill. No chance of the drill getting overloaded that way and it looks like well less than 50% stepover from the pic there so maybe a good option to do in just one plunge. Lots of axial rigidity and plenty of chip clearance. You have 10" of travel on the Z axis so should be enough room?

[Bill_B]

Thanks, Good thought on the plunge milling opp VS drilling. I guess in Fusion that would just be a modified drilling opp, correct? I spoke to Tormach tech support and he told me the 440 would do fine drilling this hole but I still question it as well.