Purpose of tapered slider?

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Purpose of tapered slider?

Postby MickBauer » Thu Mar 20, 2014 1:19 pm

Hi, all:

I realize this is a total-newbie question, but why do some makers (e.g. Mr. Preshaw) use tapered tubing on drone sliders? The wooden socket which the tube encases has a straight bore (but tapered outer profile), right? This puzzles me; it seems like putting a taper on the outer profile of parts that are straight on the inside (at least in the socket itself) is a lot of extra work.

Just re-read Martin Preshaw's old Pipers' Review article on hand-rolling ferrules and tubes, and this has been nagging at me. ;-)

Thanks in advance,
Mick
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Re: Purpose of tapered slider?

Postby djm » Fri Mar 21, 2014 2:56 pm

I'm not a pipemaker but my understanding is that the ferrule on the outside is intended to protect the wood from splitting at the point where a piece of pipe is shoved up inside. It is tapered to provide what is called a "friction fit", i.e. it is supposed to slip on tightly so that it won't come off easily.

And you are incorrect about the bore of the drone: it is actually a very long, shallow taper, as well. This is what makes the rolling of the pipe parts in the drones such an awkward process for the pipemaker.

HTH

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Re: Purpose of tapered slider?

Postby MickBauer » Fri Mar 21, 2014 3:51 pm

djm wrote:And you are incorrect about the bore of the drone: it is actually a very long, shallow taper, as well. This is what makes the rolling of the pipe parts in the drones such an awkward process for the pipemaker.


Hi, DJM:

Thanks for the reply. But I chose my words carefully: the socket of the assembled slider has to be straight, because the tenon that the slider moves over is straight on the outside. ;-) Obviously the bore inside the tenon is conical.

Anyhow: I guess I get it, it's a friction-fitting thing. This is counterintuitive to me -- if the wood contracts (e.g. with seasonal changes), a conical sleeve should slip off as easily as a cylindrical one would, no?

Maybe I'm just being dense...

Regards,
Mick
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Re: Purpose of tapered slider?

Postby wooff » Fri Mar 21, 2014 4:48 pm

There are several reasons for using tapered ferrules and yes Mick you are correct that if the wood shrinks then the ferrule will come loose just as a parallel one would. Good reason then to use very well seasoned wood.

Firstly, although it may be a little more work to turn the wood to an accurate taper it is actually easier to roll a tapered ferrule than a parallel one. The reason for this is that after Rolling and Soldering the ferrule it has to be mounted on a mandrel to bring it to a good 'round' form. It is much easier to draw a new ferrule up the taper of a tapered mandrel by rubbing and burnishing... draw it up untill it is perfectly round and has reached the desired size.

Making the taper of the turned wood the same angle as one's mandrel is the start of making a good tight fit between the wood and the ferrule. By fitting the ferrule into place by lightly 'sanding the wood untill a fit is achieved between the two. Glue can be applied and rubbed into place with the tapered ferrule so as to cover the whole surface of the tapered joint in an easier fashion than with a parallel joint. In other words the tapered ferrule covering a drone slide , and its glue joint, can be better made to support the wood along the entire length.

Tapers that are of a shallow angle (or Rate) will 'lock' or ' self hold' when assembled. The Classic Self Holding taper is the 'Morse' taper that is used on Drill bits and reamers for machine work. The Morse Taper has a 'rate' of approximately 5/8" per Foot and the taper that I use is approximately 1/8" per Foot... so it 'LOCKS' very well.

There are also asthetic reasons for using tapered ferrules to perform diametric transitions between parts.
I use tapered metal ferrules in several places on the pipes.... the Bass Regulator top section cover tube and its wind cap, for instance ,( this mostly for asthetic reasons) and the ferrule on the mainstock.
Geoff.
Last edited by wooff on Sat Mar 22, 2014 3:30 am, edited 1 time in total.
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Re: Purpose of tapered slider?

Postby djm » Sat Mar 22, 2014 3:07 am

All my tapered ferrules are held on by thread - never glue. I learned the hard way when I ordered a half-set from an Irish pipemaker (who shall remain nameless and should have known better) where all the African blackwood in the set was so green that it shrunk out of shape and all the ferrules on the stock and drones fell off, revealing a good 2-3 mm of failed glue inside. Also, a threaded ferrule can more easily be removed if repair/refurbishing of the set is ever required in the future.

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Re: Purpose of tapered slider?

Postby wooff » Sat Mar 22, 2014 3:50 am

A good many of my ferrules are also originally held by thread bindings for the very reasons of wood movement, however, on these drone sliders I feel that a glue joint is a better option ( only with properly seasoned wood, of course), if well coated it will help prevent longways cracks, which most 'old' drone sockets have, from spreading.
Since adopting this tapered ferrule system( these last 30 years) on the drone sliders I have had very very few failures.

Of course, sending out a set made of unseasoned wood from humid Ireland to some super dry climate (or anywhere for that matter) is just asking for trouble.
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Re: Purpose of tapered slider?

Postby djm » Sun Mar 23, 2014 6:28 am

I sold that set on. The chanter was very good, just the stock and drones were a disaster. I replaced the glue on the ferrules with marine silicone. The silicone would have the flexibility you mention to move with the wood. The average RH here is 35-45%. I sold them to someone in inland California where the RH is 20-25%. I didn't hear back so I assume there were no further problems.

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Re: Purpose of tapered slider?

Postby MickBauer » Tue May 27, 2014 12:07 pm

wooff wrote:...It is much easier to draw a new ferrule up the taper of a tapered mandrel by rubbing and burnishing... draw it up untill it is perfectly round and has reached the desired size.


Thanks as always, Geoff, for your thorough and clear answer! One follow-up question: with the rubbing and burnishing, is diameter-expansion (caused by thinning the ferrule's wall) ever a problem?

Seems to me that if it was, tapered ferrules are "self-correcting" in that one could start out with a slightly oversized (length-wise) blank, and then simply sand/file the finished ferrule down to the correct length. But maybe I'm just imagining an opportunity for sloppiness that would in fact be more trouble than it'd be worth. ;-)

---Mick
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Re: Purpose of tapered slider?

Postby wooff » Wed May 28, 2014 1:00 am

Mick,
if the trapezoid shape of the flat metal blank is cut and filed to size carefully then when it is drawn up the mandrel it should arrive at the correct diameters ( at each end) when it has become exactly circular. Thus no stretching or thinning of the metal should occur unless the burninshing is of such a violent nature as to move into the realm of 'metal spinning'.
As an idea of the accuracy that can be achieved here is the very simple formula that I use for arriving at the flat metal sizes:

Desired diameter of the finished ferrule +one thickness of the metal sheet x Pi . This gives the circumferencial length to be marked out plus a bending allowance equal to the metal sheet thickness . I don't know, or care, if this is text book correct... it has worked for me for 36 years.

Making this calculation for each end of the tapered ferrule, marking out the shape and leaving a little bit of spare material at each end ( so as to be able to cut the ferrule to length with straight ends) I then file the mating edges to size, keeping these edges STRAIGHT (so that the resulting ferrule will maintain an even taper throughout its length)... to size that is within a couple of thou.

Now, we know that the circumference of a circle is (roughly) three times that of the diameter SO any error in making the circumferencial width of the ferrule will be divided by 3 for the diameter... making the the flat piece within 3 thousandsth of an inch with have the ferrule diameter within a Thou! Not that we need that sort of accuracy when fitting metal to wood.

One other point whilst I am at it;
when wood loses moisture, due to 'seasoning' or other changes of humidity, that moisture exits more readily through the end grain and thus the end of a piece can become slighly maturated, more fully dried out and shrink more than the rest of the piece. In this situation the end of the female drone slide can shrink away from its supporting ferrule and crack due to the pressure of the male section. My thinking is that a Tapered female drone slide has less wood at the open end, less end grain face to lose moisture through, is more likely to be better seasoned due to the smaller crossection.

Sorry for late reply Mick, we went down the country yesterday chasing an ancient Cabrette (my wife's prefered bagpipe) that was for sale... a bit like seeing a advert for a Coyne or Egan set......

Geoff.
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Re: Purpose of tapered slider?

Postby MickBauer » Thu May 29, 2014 2:16 pm

Geoff, if I get to wait two months before asking a follow-up question, then you get to wait at least one day to reply to it without apology. ;-)

In case anyone is wondering: yes, I'm tinkering with pipemaking, strictly for my own amusement (the journey is the destination, etc., etc.). (Reedmaking, on the other hand, I'm practicing out of urgent necessity because of the Upper Midwest U.S.'s volatile climate.) All of these things are giving me vital glimmers of insight into how this instrument works and how to keep it working, and I'm having loads of fun with the learning and, of course, playing.

Regards,
Mick
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