Drill size for 5.5mm self tappers

[Cal Ando]

12 minutes ago, Man 'o Kent said:

If you are into a bit of DIY like this first go buy a little  "ZEUS" book, everything you are  likely to need is in there and only 6" x 3" x 1/4" so it don't take up much space.

 

If drilling by hand, (including an electric drill), always drill a pilot hole first followed by a drill a tenth or two of a millimeter smaller than the required size and then finish with the final size drill. You will that way finish up with a hole that is more round and straight. Always use a lubricant, (down Mabel), even a smear of cooking oil is better than nothing but small tubes of specialist lubricant are available.

 

Always make sure the drill tip has a good sharp even point. Here I am lucky being a 'sinister', (left handed), I've lost count of the number of right handers that I've instructed on how to do it the "wrong way", if you don't tell 'em they don't notice!

 

The action is all in the wrist, a right hander will tend to use their right hand to move the drill against the grinding wheel and will get in a right old mucking fuddle. The trick is to use the right hand to support the drill bit and the left to do the down/rotate movement, easy to demonstrate, hard to describe!

 

Equally important is that each flute has an equal cutting edge if the drill is to cut to size. Here the Mk.1 eyeball comes into its own, held up to a strong light and shaded very small errors are easily seen and corrected.

 

Brilliant advice all round.  Especially the Zeus book and the pilot hole of whatever sized finished hole.   Do Midland Chandlers do Mk1 Eyeballs as I only have Mk4s

 

[Tacet]

5 minutes ago, Machpoint005 said:

 

 

Unifed Fine, as opposed to Unified Coarse (UNC).

Both the work of the devil. Metric threads every time for me - at least then you can always tell whether A is bigger or smaller than B!

Most thread systems, including metric, have clumsy changes in sizes.  For example 3mm to 3,5mm is proportionately a larger change than 5.5mm to 6mm; same applies to pitch.

 

The BA system (much loved of Bizzard and his Meccano sets) has the advantage in in its constant 0.9 factor and is metric inasmuch as it starts with  BA 0 at 6mm diameter with a 1mm pitch. 

 

And with Whitworth, at least a spanner with 1/4" marked on it fits a 1/4" nut or bolt.  Unless you try to interchange before and after the AF size was reduced, which wasn't so clever.

 

 

[Man 'o Kent]

"Do Midland Chandlers do Mk1 Eyeballs as I only have Mk4s "

 

Dunno, I'm a suvvener . . .