Benesesso
Hot Rolled
- Joined
- Jan 20, 2006
- Location
- Phoenix, Arizona
I have noticed my DD 750X does a fairly decent job on larger drills but is terrible on small bits under ~1/4". Got to checking things over, and it's apparent that the "indexing" sheet metal tabs are to blame. Their purpose is to align the bit in the chuck by rotating the loose bit in the chuck until the smallest diameter [at a point slightly behind the tip] is along the horizontal plane. The plastic chuck is then tightened.
Problem is that different diameter bits are grabbed at different distances from the tip--fat bits are grabbed further back. Assuming the same helix angle [?], the bits will be ground differently.
I've been grinding everything to 135 deg., and noticed that if I use the 118 deg. indexing mark for smaller bits they come out much better--when ground at 135 deg. Bits down around 3/16" actually need to be set to ~110 deg. or less, but there is no way to do it except to slightly rotate the bit by hand before tightening the chuck.
Problem is that different diameter bits are grabbed at different distances from the tip--fat bits are grabbed further back. Assuming the same helix angle [?], the bits will be ground differently.
I've been grinding everything to 135 deg., and noticed that if I use the 118 deg. indexing mark for smaller bits they come out much better--when ground at 135 deg. Bits down around 3/16" actually need to be set to ~110 deg. or less, but there is no way to do it except to slightly rotate the bit by hand before tightening the chuck.