![Image](https://i.ibb.co/t80n8wJ/20220602-002027.jpg)
Forstner/3d bit style. Self explanatory construction, will detail a drawing once refined. Modified spade bit riveted in steel bar with spurs.
The 12mm diameter bits on a 10mm shaft so far have been slightly variable in accuracy, and possibly using The Flintstone rig that would improve. That is a trial for another day, but the difference as stands is very roughly 0.5 to 1.5 cm for the various bits on 10mm shafts , and 1 to 4 mm for the 12mm shaft, over around 65 cm.
The length is from bearing, because that governs the flex possible more than length of wood.
The first bit I made for the 12mm shaft shown above is nominally 16mm. It looks like a forstner, but the rim is open and the horizontal cutting blades (chippers) stretch to the perimeter. The idea with that is that the bit corrects itself after walking around a knot or similar. A forstner would tend to assume any new direction taken because the rim would act as guide.
This worked quite well both in terms of reaching target, as well as giving a smooth bore. On the first slightly knotty piece of Carob (that I went on to make The Tuareg with) the bore was not ribbed, was slightly wavy (around knots), and slightly rough but only around knots (for grain direction there). On the seasoned dry pear it gave a very slightly waved bore for where it wandered around knots.
On pear I drilled 1cm at a time then allowed bit to cool. Maybe for being dry, but the bit heated up faster in it. A HSS bit could be used hotter I suppose, but this bit is plain steel wings and carbon/tool steel spade bit which might be ruined if overheated. For the Carob it was 3cm at a time. Adjusting the bit further for contact points might allow cooler running, but either way the bit did not become too hot to touch.
The first two bores were drilled before refining the bit, and it was drilling at @ 0.5 cm per minute (total time IN PRACTICE - including clearing swarf etc.) with quite a heavy pressure, giving scrapings more than shavings.
Then a bore was drilled after shortening spurs, adjusting cutting angle, and "in practice" times for part dry Carob were
Hard hardwood medium pressure 3cm in 4 minutes.
Soft hardwood light pressure 3cm in 2 minutes
For Pear seasoned endgrain SPEED TEST it was 2cm in under 15 seconds.
![Image](https://i.ibb.co/sPy70Sp/20220602-001818.jpg)
Boring dry hardwood endgrain is difficult, when green a little faster but not easy. A spade bit would drill across the grain at 1cm in 10 seconds maybe, for example. A new ok but plain quality spadebit on the Carob, trying to ream out an already drilled 10mm hole to 16mm was much slower, and slower than the 16mm made bit without that pilot hole. These figures are only relative, i.e. the drill used and the amount of pressure I normally place etc.
It is said cutting spurs are not needed when drilling endgrain, but I think they act as guides to create a smoother bore.
Thinking I deserved some modern bits to compare performance with, a standard 12mm screwed ship auger and a 12mm brad tricut twist drill bit were bought.
The Auger
The standard auger was no good in hardwood endgrain, the screw would pull loose and drilling would slow or stop, smaller pieces of wood split. It might work as hand auger on thicker diameter wood (see video in a link below), on green wood end grain, but dry hardwood end grain on a drill was too much for it . Apparently vintage ship augers were tapered along their whole length (examples in a link somewhere), but more recent ones 1850 onwards maybe, seem parallel. Some drawings seem to show slightly wider tip, but not sure on that. Anyway, this modern basic design creates a lot of friction and heat. On all bits so far the hottest was still cool enough to hold after a few minutes of drilling, but this auger was burning hot after under half a minute of drilling, too hot to hold. So the search was on to turn that auger into a barefoot auger, because they are recommended for end grain and directional stability . I could find no detailed drawing, but a few pictures and descriptions online, for example...
![Image](https://i.ibb.co/Rv5fM8w/20220602-001946.jpg)
The lead screw is cut off, the cutting edge is extended to (past) centre, and preferably a downward wing is ground to shape to smooth edge of bore (not absolutely nescessary per my trial, very difficult to shape... but worked slightly better once added). My one now looks like this...
![Image](https://i.ibb.co/pZBFVFh/20220602-002729.jpg)
I had my doubts if it would cut well , because it looks so basic, but it was fast through the seasoned pear, giving shavings and clean bore. It did not need much pressure either. So good, except for the heating. Supposedly it drills very straight but I must test it on a few bores first. I might taper off the shank to reduce friction, must fit it to a shank (or make similar on end of a shaft etc.) for that, so that is for another day.
Something just amazed me also. To speed test bits I sawed a 20cm diameter log of olive, as basis for hard hardwood. I tried the Tri-cut shown just below on an offcut because it was fast on pear and Carob, but it was quite slow needing a lot of pressure. Oh well, olive is tough. I took the barefoot auger to try that on olive and that bored through fast with little pressure but a fair amount of torque. That was just a couple of cm, so the flutes were not much acting as a screw either.
Tri-cut
This bit is good on soft hardwood end grain . Fast, eventually hot but not as much as the auger, smooth hole, nice shavings etc. At start it didn't mind wandering, so probably not as accurate as the auger in that sense. This needs to be fitted or made on a shaft also to test accuracy. First test on hard olive wood though and it was quite a lot slower, still giving nice shavings.
![Image](https://i.ibb.co/YQ7JjS8/20220602-001745.jpg)
Here are some old catalogues that include barefoot augers, and show other details...
https://archive.org/details/IrwinHowToS ... 3/mode/2up
https://archive.org/details/SnellMfgCo1 ... 9/mode/2up
https://archive.org/details/SnellMfgCo1 ... 1/mode/2up
https://archive.org/details/GreenleeCat ... 5/mode/2up
https://archive.org/details/GreenleeThe ... 9/mode/2up
......
That third test piece of Carob wood for a flute was a length I had actually set aside for a trial bore and an approximate design for a cylindrical flute. With the now refined 16mm bit , that drilled at around 1cm per minute "in practice" averaged out, with light pressure. The exit was a measured 4mm out, acceptable but a little much.
![Image](https://i.ibb.co/28kB83B/20220602-001859.jpg)
The reasons for this off centre is that the Carob has very hard heartwood and noticeably softer new wood (see below for density) , and it is grained out in unusual patterns and towards knots, here an example from online
![Image](https://i.ibb.co/gdXYcs8/20220602-003424.jpg)
and as can be seen on the blank also. Also I used a fair amount of pressure when meeting hard hardwood instead of letting the bit do its job accurately.
The previous two were under 2mm out, e.g
![Image](https://i.ibb.co/dJmBQD0/20220602-002152.jpg)
The solutions for improved accuracy are therefore either going slow on knots, using a barefoot auger possibly, or I might redesign the above bit with a half rim. That piece of difficult Carob I take as an exception for now though, I knew it would drill awkwardly. I suppose a 15 mm shaft could be used, with 5cm length reduced to 12mm behind bit to collect swarf, that would be very accurate I think, but cumbersome.
......
So there is one idea for a bit. I don't think any other bit would have done the seasoned pear much faster, unless on a lathe, or with high revs and pressure, chip clearance and cooling by compressed air... that is not what this way of making flutes is about though. Gun drills on lathes are self centering due to spinning work not bit. I hope to try the very best available bits on hard hardwood end grain using hand drill at some point, I am starting to think there is a reason there are no videos online of those :/ [and having just tried those, well the answer for hardest wood seems to be to use a bit design two centuries or so old and which is only available by special order nowadays via https://www.wlfuller.com/html/barefoot_ ... ation.html ] . Here is one of the older methods at work ...
https://davidffisher.com/2016/10/12/the-t-handle-auger/
.... a very fine screw tipped auger with a screw reaming channel (to allow self centering ?) attached to a plain shaft is a possible idea, as well as looking at centerpoint bits again for a modified kind.
In practice, hand drill and rig is a quite acceptable way to make a few flutes. As I test and refine the method I will note down improvement. Historically, I expect wood was bored when green if possible.
Engine powered lathes were from mid 19th century possibly, and before that it was manpower or just possibly water powered. Even with a worker dedicated to powering a lathe, to drill a bore in hardwood (and they did) would have been a major endeavour...here is an example of speed in hardwood using the above style auger :
"Diderot writes that one man could bore a 5 cm diameter hole through 11.6 metres of pipe per day in alder or elm, but only 1.95 metres per day in oak. "
https://www.lowtechmagazine.com/2010/12 ... hines.html
Very very roughly, Alder and Elm are around 500kg/m3 and Oak is around 700kg/m3 , depending. The above would have been in green wood also, I guess.
So it is possible to imagine that the flutes made before engine power were very much an artistic labour, where much time was then spent trying to make the best of them for want of appreciating the effort already given .
I should (at some point) run a proper series of trials on different woods at different dryness to see if boring green wood is much easier, and to compare drill bit designs. Clearly that will be limited to battery drill at available torque and revs, but should give an idea. Am just collecting various log ends to do this with now.
My previous (but later melted during case hardening) bit left a slightly ribbed bore, and would have been no faster I think than the 16mm bit.
One added problem is that fitting a 16mm bore onto the pole lathe for turning is difficult. I did so with The Tuareg, using a 16mm steel tube, but had to first sand the bore near perfectly straight to do that. I suppose a set of pipes of slightly varying diameter might work, but that is a lot to organise.
Another difficulty is that using The Flintstone, clearance at the point bearings is minimal. For it to drill smoothly, the bit would have to be made on ground shafting (which can be bought). Here I used store bought rod, and spent several hours grinding it near perfectly round. Even so, a tenth of a mm or so makes the revolution uneven, it doesn't catch nor is loose, but there is a fast/slow in each rev due to that uneven friction. It is actually being polished fully round by the bearings, so eventually should run smoothly.
Also, shafting should be very straight. The shop bought rod had to be straightened (the drill tip should spin on one point the whole length of drilling +/- less than a mm). For this I used calipers and not a straight edge this time, mapping out where there was variation along the shaft. To do this support the shaft at ground round ends and measure difference in height at any point along length as turned.
http://www.repairengineering.com/shaft- ... ening.html
For filing the bit to diameter (and the shaft round) I used this jig.
![Image](https://i.ibb.co/RcJnZgc/20220524-222250.jpg)
Well, it is a bit that works and costs little to make, except for time. I have to test it on varieties of woods at different levels of dryness to get a better idea, but for now and for the occasional flute it is one solution. I will try making a 12mm / 12mm bit now, probably barefoot auger style, for the bore to fit the lathe, will try refining the above bit, as well as other ideas and will post drawings when I think I have any at best.
The bore drilled the above way with 16mm bit came out at around 16.5 mm on the Carob (for being wetter/softer probably) , and on the pear the start of the bore which sees the drill go past repeatedly was somewhere under 16.5 mm, and at the end was just a tad over 16 mm.
Finally a good description of D-bit lathe drilling, and gun drilling, for those going that way
https://www.labellenote.fr/en/lutherie/ ... ageslongs/
In short, my setup seems more accurate...the D-bit was not timed, but the gun drill is much faster, although first speed test in seasoned pear of the above bit refined would match the speed but for clearing swarf and heating, if I remember the gun drill was on ebony which would take the estimated @ 200 seconds for given length on pear (at 16mm, not the gun drill 3mm) to several minutes or much more. The auger bit might be an answer for hard hardwood though. Either way, accurate fast enough drilling on hardwood without lathe looks possible now.