I'm not sure why you can't drill it in the X3 as I have drilled similar sort of lengths with my X3. You may need to use MT collets and put along series drill into a part drilled hole before moving it under the spindle and fitting the drill rather than having 7" part plus 7" drill exposed but it can be done.

On the lathe you could use the method of drill in a collet and feed pressure applied by the tailstock ctr in the opposite end of te work, flipping it around so you drill half way from each end, I've done 9" that way..

J

PS how to you get the diff gear in there?

Edited By JasonB on 03/04/2020 18:22:09

Should be enough height, 15 1/2" under the collet, as said if you need more then drop the drill into a part drilled hole and then lift up into the collet. I'd start with a stub drill to get the hole going with minimum risk of wandering then upto a jobber length, long series and then extra long series though you could save on the last if you came at it from each end but risk them not meeting.

If the worse comes to the worse the bearings could be set in something like JBWeld with a rod through them to correct any wander.

Edited By JasonB on 03/04/2020 18:39:56

Edited By JasonB on 03/04/2020 18:42:06

With a collet, or 4 jaw independent chuck in the lathe, you have the best chance of getting the hole straight. I would drill from both ends using a new split point drill, followed by a long series of the same diameter. Keep lubricated with AC90 or paraffin, and clear the swarf often.

I'm going to suggest the lathe for this job. If you made a jig with a base plate and two upright V blocks you could hold the part stable and at correct vertical centres by the end bosses on the axle. The plate or V blocks would be shimmed to needed height while sitting bolted down to the carriage's flat top. Couple of U bolts or even a couple of hose clamps (jubilee style screw / gear ones) would secure the part to the V blocks. Long series extension drill in the tailstock for the drilling, frequent retract / clean the drill.

This sort of plate and V block jig would work in the mill of course also, but I think it might be more stable in the lathe on the good foundation of the carriage or cross slide.

Just my $0.02 worth. Good luck!

Similar to Jeff Dayman but in a mill, mount on a sub plate & set up on angle plate, pick up boss centre from a known datum on the sub plate & drill through with say a 5/16” drill, finish bore first end to take bearing.

Rotate sub plate 180 degrees & pick up 2^nd bore position again using the known datum, finish bore 2^nd end for bearing.

Or you maybe could use a skinny between centres boring bar & do it in one set up on the lathe?

Tony

Long drills tend to wander, given the chance, so shortest possible drill is best. Use the lathe. Centre-pop each end of axle and set work between centres. Fix to cross slide with packing, whatever (improvise!) and clamps.

You now have intended entry and exit points coaxial with lathe's axis (having remembered to adjust tailstock's alignment…). Fix drill in headstock chuck/collet and drill half way.

Reverse the job, repeat.

If the hole isn't good enough, you could then consider making a small-diameter between-centres boring bar and taking very light cuts.

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+1 for undersize drill from each end, mounted in a four Jaw chuck, follewed by boring right through in one operation.

Probably a D bit to finished size.

Howard

Good luck with boring through a 71/2" long hole with a 5/16" diameter boring bar.

Tony