Don Busby's High Speed Drilling

Project 'Musical Box Comb Making' includes drilling holes 0.5/0.6/0.7mm diameter in ground flat stock steel, as described at shots 15/16/18 of that write up (click here)

Ideally such drill sizes need to run at about 10,000rpm.  Maximum spindle speed on the Model B-Super being 1360rpm called for extremely slow and careful Leadscrew feed.  Attempts to drill with a 0.4mm diameter bit, which needs 14,000rpm, were totally unsuccessful:  All bits sheared with little or No Penetration.

Enquiries for a speeded up chuck elicited a suggestion by Bill Jewitt (Sales Manager of Chester UK), to use a 'Flexi-Drive' as described below.  Working speed of this device is 0-14,000rpm, control being by a footswitch.

Holes of 0.4mm diameter were successfully drilled although some bits sheared, possibly due to variation in speed as discussed.

Shot	Description	Notes	Photo
1	Model B-Super from Belt Cabinet End	a. Please make sure the machine is ISOLATED from mains supply b. Flex-Drive is passed through lathe spindle
2	Flexi-Drive Motor and Footswitch	a. Footswitch is placed on Lathe tray for operation by hand.  Initially it was operated on the floor by foot, but inadvertent operation occurred by accidental treading on the switch.  Cutting fluid was not in USE! b. It was difficult to hold the Flexi-Drive speed constant by hand operation.  Even by foot operation was variable.  This could have accounted for some shearing of bits.  A variable clamping mechanism could be contrived.
3	Flexi-Drive Handpiece held in lathe 3-Jaw Chuck	a. Handpiece is clamped firmly, but not over-tight, in 3-Jaw Chuck b. Although 3-Jaw Chuck is Self-Centering it was found necessary to centre the handpiece chuck because its outer casing is not regular enough for it to self centre.
4	Drilling with a 0.4mm Diameter bit	a. The arrangement shown is steady enough for this Light-weight type of operation. b. Heavier work might call for a fixed steady to hold the outer end of the handpiece