Effect of knot length, ie long one set deep vs shorter set more shallowly

Discussion in 'Workshop and Restorations' started by halvor, Mar 17, 2019 at 5:57 PM.

  1. halvor

    halvor Esquire

    Location:
    Norway
    As the title, I wonder if anyone has any insights to glean on what sort of difference one gets from a tall knot versus a shorter one? Ie all other things — loft, notably — equal. (Thoughts on how this possibly interacts with socket to knot width also interesting.

    I’m finding myself in a position where I need to choose between knots of 55 or 67mm height for a spare handle — yet to be bought, so can’t test.
     
    2hot 2trot likes this.
  2. R181

    R181 Grumpy old man

    Are both knots the same size as measured at the glue plug base?

    Bob
     
  3. Nishy

    Nishy Forum GOD! Staff Member

    Slightly confused by the question, but generally speaking the higher loft (with all other factors constant) the less backbone, more splay and better flow through. The taller lofts also hold more product in the knot. Larger lofts are usually better painters than scrubbers.
     
    bambrit, Matsilainen and 2hot 2trot like this.
  4. halvor

    halvor Esquire

    Location:
    Norway
    Yup. On offer are fans and bulbs, both 67mm, and the so-called chubby at 55mm, also a bulb shape. The splay will probably be different regardless, and there’s also the glue bump x-factor.
     
  5. MntnMan62

    MntnMan62 Über Member

    Location:
    New Jersey
    I'm guessing that a shorter loft set higher in the handle will splay much more and have less backbone than a taller loft set deeper in the handle.
     
    Dr Watson and halvor like this.
  6. halvor

    halvor Esquire

    Location:
    Norway
    Sorry! I’m not talking lofts, as those could be the same. I’m talking one knot which measures 55mm from centre tip to glue plug, and one which measures 67mm. Set to the same loft and with the same diameter, what characteristics would each have? Clearer?
     
    Nishy likes this.
  7. Nishy

    Nishy Forum GOD! Staff Member

    Yep sorry I was thinking, as I was typing my answer, surely Halvor knows this already :)
    Unfortunately I cannot help, or would be guessing.
     
    halvor likes this.
  8. R181

    R181 Grumpy old man

    Thank you for the clarification. It is probably best if you PM Oscar11 with the question as he has experience building brushes or hopefully sees this thread and answers.

    Bob
     
    halvor likes this.
  9. halvor

    halvor Esquire

    Location:
    Norway
    In one sense this is plausible, but why? Wouldn’t the hairs of the longer knot once they exit the handle be just as prone to folding out as it were? Or even more, as the glue would be much closer to the exit point in the case of the shorter knot?

    I suppose that, as long as I have sufficient depth in the handle, had better go for the longer knot to allow for greater variety to play around with when testing loft.

    I have handles ready for 26 and 28 knots, respectively, drilled to ~17 and 20mm. In the case of the 28 the longer seems a good call. In the case of the 26, I have experienced knots of the same size which would have benefitted from going below 50mm loft, however, so maybe a shorter one here...

    Oh the first world dilemmas!
     
    MntnMan62 likes this.
  10. SeanC

    SeanC Forum GOD!

    Location:
    SE London
    I strongly suspect that the taller knot would allow more splay due to the potential movement in the fibres between the glue plug and the top of the handle

    Sent from my CLT-L29 using Tapatalk
     
  11. Batch300

    Batch300 Extraordinarily Uncomplicated

  12. Dr Watson

    Dr Watson The Other James

    Location:
    West Sussex
    FWIW this is exactly how Simpsons manufacture their Chubby brushes, tall loft set very deep in the handle:

    1chubby_zps8ea6bc2c.jpg
     
    Nishy, halvor and MntnMan62 like this.
  13. Geofnay

    Geofnay Forum GOD!

    It's been a few decades but this reminds me of the sort of question you might get on a Physics paper. I didn't do so well in Physics (still passed) so my question is, what do you mean by 'all other things equal'? Density is almost certainly key here, so you probably need to consider whether the knots are the same density by volume.
     
    Last edited: Mar 18, 2019 at 9:49 PM
    halvor likes this.
  14. halvor

    halvor Esquire

    Location:
    Norway
    They are. ‘All other things equal’ really means just that. On offer are several types of knots (two band xtra density, two band finest, three band xtra density, three band, pure, etc), each of which come in fan, bulb (both 67mm) and chubby (55mm). I’m looking at extra high density.

    That said, it could very well be that either the shorter or the taller knot would benefit from more or less density to fulfil its potential towards being an optimal knot for me. In other words, maybe the 55mm would be better at normal density and set at loft xx, while the 67mm is best in extra density and a loft of yy.
     
  15. halvor

    halvor Esquire

    Location:
    Norway
    Batch300 likes this.
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