Thursday, February 21, 2013

Leading by a nose

Partially prompted by the comments, something of a follow up to the last post. Some 19/20thC advertising blurb to ruin your confidence in what you think you know about lead screws:


  "The bits in this set are our Fig. 100 and have our standard double thread point, and are unsurpassed for accurate work in seasoned woods not extremely gummy or hard. It is the thread used by cabinet makers.

  "We also have a similar bit, our Fig. 101 with single thread point for quick boring which is especially adapted for hard or gummy woods, end grain boring, mortising doors, etc."

And from Josh Clark via the Old Tools List:

  "The 1911 Sargent catalog says that the RJ bits with the double lip, double twist, and double thread screws (the bits everyone wants these days) are "not adapted for rapid boring or in hard wood where fine lead screws tend to clog. .. fine double thread screws are intended for pattern-makers and are for use in soft wood"


  "Sargent is also quite definitive as far as the distinction between the double and single thread bits: 'It should be clearly understood that the double thread bit is intended for soft wood, the single thread for hard wood, as the latter will not clog up as readily as the former.'"

So if, like me, your initial introduction to auger bits was an all encompassing "coarse for soft woods, fine for hard woods", like me, you're probably either a) Grumbling a little about this, or b) Going "Ahhh, so it's not just me then" as personal experience is finally explained.

Going through my Irwins yesterday, they threw me another loop. Bit after bit, pretty much, was single thread - and then the numbers 6 and below all went double thread. Didn't see that coming at all.


  1. Hi Alf, I'm one of the (few?) who agree with Josh on this. My RJ bits are terrible in hard woods, even sharpened and with cleaned-up lead screws. The Irwins are much better for hard woods (and all-around usage). So I've fit into both a) and b) above!

  2. Oh yeah, I'm absolutely with Josh's findings on this one. I think it's telling that expansive bits (at least all the ones I've seen and own) have finer threads, and I really don't think they were aimed at boring hard wood. Trouble is, all this has not helped me narrow down which bits to keep and which not - which was the original purpose! Heigh ho.

  3. Well, the double lead is in effect a coarser thread. There are just two of them. Of course if you take Sargent's word, you go against the gospel of Jennings. Oh dear. Maybe this will be the next pins or tails first or saw nib debate.

    I just took the simple approach and only have one set of Irwins that I have never even looked to see which thread they have. Of course I use my brace much more often for driving screws than I do drilling anyway. The eggbeater is my main drill although I have been considering a push drill in my future.

  4. Oh, definitely get a push drill, David. One handed operation and will get into the tightest corners - endlessly useful.

    And now I shall go away and fervently hope that the Lead Screw Question does not become another saw nib. The horror. ;)


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