Greg Krummel
11-29-2015, 12:38 AM
I found that the #2 Phillips bit for my spiral screwdriver was rounded in the drive direction, so the bit would cam out prematurely. After finding that adapters may not be the best option (reports of slop, and some only support short bits) and that old bits are expensive to buy used online, I decided to find a cheap alternative.
For middle size drivers (9/32 in or 7mm shank, North Bros or Stanley 30 and 130, Miller Falls 61 series), modern hex bits are the perfect diameter. The bit needs two notches to be cut to seat properly (both aligned with a peak of the hex):
- Square notch at the far end from the tip
- A little more than halfway through
- 1/8 in (3.175 mm) from the back end
- Triangular notch near the middle
- 95.5 degree triangle
- 0.65 in (16.5 mm) from the far end
- 0.05 in (1.27 mm) deep (to get a 0.11 in, 2.8mm wide notch)
I just used a triangular file (cut the depth, then angled the file to get the width) and a mill file. After chamfering the edges, it fits well into the chuck and drives well.
This could be used to fit a driver type, hex bit size, or hex shank accessory that weren't originally available and/or wouldn't fit the hex adapters. To speed up the cuts with a mill, an end mill and a chamfer bit could be used to make the cuts.
If anyone tries this, a few tips on fine tuning:
- Start with a square notch halfway through the width of the bit at the end, and if the back end doesn't seat cut the notch a little past halfway. It'll add some rotational slop, but the old bits also had slop to allow an easy insertion.
- If the middle notch isn't seating, the collar at the front will be loose in the axial direction and may turn less easily.
- The triangular notch isn't deep or wide enough for the lock to seat fully. Increase the depth, angle, or width.
- The notch isn't aligned (refiling the notch, or removing some material from the back notch, will help).
- If the bit is catching internally, make sure the edges are chamfered. The back square notch originally had a large chamfer, as shown in the pictures, to allow the chuck internals that mate the middle notch to slip past.
Hope this helps as a cheap solution or a solution in a pinch. A few pictures are included to make the solution a little clearer.
326002326001326000
For middle size drivers (9/32 in or 7mm shank, North Bros or Stanley 30 and 130, Miller Falls 61 series), modern hex bits are the perfect diameter. The bit needs two notches to be cut to seat properly (both aligned with a peak of the hex):
- Square notch at the far end from the tip
- A little more than halfway through
- 1/8 in (3.175 mm) from the back end
- Triangular notch near the middle
- 95.5 degree triangle
- 0.65 in (16.5 mm) from the far end
- 0.05 in (1.27 mm) deep (to get a 0.11 in, 2.8mm wide notch)
I just used a triangular file (cut the depth, then angled the file to get the width) and a mill file. After chamfering the edges, it fits well into the chuck and drives well.
This could be used to fit a driver type, hex bit size, or hex shank accessory that weren't originally available and/or wouldn't fit the hex adapters. To speed up the cuts with a mill, an end mill and a chamfer bit could be used to make the cuts.
If anyone tries this, a few tips on fine tuning:
- Start with a square notch halfway through the width of the bit at the end, and if the back end doesn't seat cut the notch a little past halfway. It'll add some rotational slop, but the old bits also had slop to allow an easy insertion.
- If the middle notch isn't seating, the collar at the front will be loose in the axial direction and may turn less easily.
- The triangular notch isn't deep or wide enough for the lock to seat fully. Increase the depth, angle, or width.
- The notch isn't aligned (refiling the notch, or removing some material from the back notch, will help).
- If the bit is catching internally, make sure the edges are chamfered. The back square notch originally had a large chamfer, as shown in the pictures, to allow the chuck internals that mate the middle notch to slip past.
Hope this helps as a cheap solution or a solution in a pinch. A few pictures are included to make the solution a little clearer.
326002326001326000