Welcome and good morning on Sunday 26th May 2013 at 04:03:36 am
Here are some questions raised at earlier quarterly meetings on :
Hints & Tips, Techniques, Design Ideas, Software, Data and Plans
We would hope to hear from members on:-
any problems they are having with their current
any tips which they might like to pass on to other members.
any other Ornamental Turning topic they would like to air.
The discussion will be moderated for suitability and content by the
Council of the SOT who will control what appears on these pages.
Questions should be submitted using the Response Form and will either be answered immediately or
referred to experts
within the SOT. In the latter case it will take a little while for the answer to be
published here but the question will be posted on this page with the expectation that other SOT members
will supply an answer.
FREQUENTLY ASKED QUESTIONS (F.A.Q's)
Q. What kind of lathe do I need to do ornamental turning?
A. In the absence of a purpose-built OT lathe, a metal turning lathe is easiest adapted;
the standard small lathe with 3½" centre height is adequate but a larger machine with 5"
or more centre height is preferable. A wood lathe can be converted but you will need a
lot more extra parts. As a minimum you need a compound slide (or slide rest), a means of
indexing (to divide the circle by regular intervals and arrest the spindle at each chosen
interval), an overhead drive or back-drive to power a flying cutter mounted on the cross
slide (like a drill spindle) or a self-powered cutter (like a power router).
Q. How can I obtain ornamental turning equipment?
A. Sellers of Antique Tools or, there are a few makers of modern OT equipment.
Alternatively, if you have a metal turning lathe, you can design and make your own
equipment or, find a hobby machinist who will help you for a small fee!
(see also the Contacts page).
Q. Where can I get books on OT?
A. Specialist booksellers such as Astragal Press, Dover Publications, TEE Publishing,
Cambden Miniature Steam Services, Argus etc Some of the more important works have been
reprinted and most others become available second-hand from time to time.
(look in the Library for a list of relevant titles)
For the future this section will include questions raised at the "Any Questions Forum" which has
proved a successful part of the quarterly meetings. The full transcript of this forum will appear in
the Bulletin and a selection will be published here. The newest question and answer will always be at
the beginning and eventually old ones will be deleted from the bottom of the list.
HEALTH WARNING - the answers and opinions expressed here are those of individual practitioners of
Ornamental Turning. If you adopt any of the suggestions you must consider the safety implications
for your own circumstances and modify or adapt accordingly. If you are in any way doubtful then
play safe and don't do it.
The Society of Ornamental Turners accepts no responsibility for injury or damage caused as a result
of your adopting these procedures.
Elliptical Division Plate
SOT Member Richard Lynche-Blosse asks:-
If one wishes to cut an elliptical division plate how are the divisions calculated?
In a general discussion of this question it was pointed out that the great disadvantage of elliptical division plates is that a
separate one is needed for every different ratio of the axes of the ellipse.
Any member wishing to make elliptical division plates should contact Bill Newton (see Elliptical
Turning Association on the Contacts page of this site). Bill's son, Andrew, some years ago derived the formulae for plotting
equal divisions of ellipses of all ratios and he made his calculations available to SOT members on a computer disc. However, a far
simpler and quite accurate method is to turn an ellipse of the required size, wrap it with a strip of paper and cut the paper to the exact length of the periphery of the ellipse. Then place the paper diagonally over a sheet of paper on which as many equidistant lines have been ruled as the number by which the ellipse is to be equally divided. It is then a simple matter to mark off the strip
where it intersects each line and then glue it around the turned ellipse. The cutter may be aligned with each mark in turn and the
headstock locked in each postion for making the cuts. When gluing the paper to the periphery of the ellipse it is important to
make sure that the cuts on both sides and ends of the ellipse will be mirror images of each other.
Safe Running Speed
SOT Member Roy Turnage asks :-
What is the maximum safe running speed for the Mandrel of a traditional OT lathe?
Michael Wood - The top sustainable speed for a treadle lathe is about 60 presses per minute and
using the largest pulley groove this gives about 1000 r.p.m.
Nick Edwards - 1000 rpm is a good guideline figure. However, many instrument lathes are made with plain hardened
steel bearings and are run considerably faster; the critical factor is the pressure of cutting which,
if excessive, breaks down the oil film causing friction of the bearing surfaces.
Paul Coker - It should be remebered that if tools are sharp it is not necessary to turn at high speed.
John Edwards - Roger Davies used to recommend 1000-1100 rpm as a safe maximum. OT lathes are
quite delicate and should only be used for light cutting at moderate speeds; my lathe runs
comfortably at between 200-500 rpm and I rarely find it necessary to take it faster.
Michael Wood - Roger Davies used to recommend light machine oil such as is used for sewing machines
John Edwards - Some people think that another way to ensure a lathe is not run too fast is to
lubricxate it with Tallow. Tallow will smoke if it becomes hbeated by friction and should give
ample warning of over-heating. I do't know if Tallow is a sufficiently good lubricant and I don'y know
if it is possible that it could cause a fire when there is a lot of fine wood dust about. So
if you want to try it - BE CAREFUL
Earliest Ornamental Turning
Question from David Manuel - What is the earliest known example of Ornamental Turning?
Paul Coker - The frist mechanically decorated turning was Rose Engine Work. Roger Davies and John Ferguson
in Bulletin 83 showed evidence of ornamental turning in the form of a rose turned box made in 1539. This
piece was suffuciently advanced to indicate that the techniques had been developing over two or three
generations, ie since the late 1400s.
John Edwards - A German book (Mittelalterlichen Hausbich) printed about 1480 shows a screw cutting lathe with
a cross slide and in 1500 Leonardo da Vinci sketched a centre lathe with a continuous drive by treadle
and flywheel. Innovations such as these would have been necessary for ornamental turning to be possible.
Derek Pearce - The screw cutting lathes of this period worked on the Abbe principle, with the screw guides
in line with the mandrel.
SOT Member Andrew Curl asks :-
" I have a Pittler B2 Lathe and with the help of fellow SOT members Anning, Smith and Spicer,
am aiming to reproduce the special fitments that could be obtained for these machines
Would any other members (or anyone, come to that) be prepared to make drawings of the fitments
and accessories on their Pittlers for the benefit of all? "
(The Pittler B2 and C3 series of lathes produced in the decade before the turn of the century.
These were engineers lathes incorporating complex (ornamental) turning features, and are an
important machine within the S.O.T)
Andrew Curl may be contacted by E-mail: firstname.lastname@example.org or via the SOT
Turning a Box
Member John Hopewell asks (via the Bulletin ):-
"What us recommended as the best order of procedure for turning a cylindrical box and lid, prior to ornamental decoration?"
John Edwards replies:-
" In response to John Hopewell's query, a short answer might be:-
Rough out the lid and base with under-sized recesses and let them dry out for a few weeks before finishing them. (If the material is grained the pieces should be fitted together in their original orientation so that the grain patterns can be matched as near as possible.) Next, finish the bottom and fix to it with a glued paper join a piece of scrap wood; turn the scrap and re-chuck onto it. Next thread the lid, cut a matching thread in the base and fit so the grain matches when screwed tight, then finish turn the inside so the wall is thin but strong. Finally turn and ornament the outer surfaces taking care not to penetrate them.
If a more detailed explanation is needed, my preferred method is:-
Turn a good cylinder slightly longer than the planned box plus an allowance for the overlap of the lid. I then cut off the piece for the lid and put it aside, marking the parted off end of the lid piece if it is required to match the grain of the material. Then I bore and rough turn the inside of the base piece so that the wall is about 1/8" thicker than the finished piece will be. Then I chuck the lid piece so that the newly cut face is outward and I excavate the lid, again leaving a generous finishing allowance. Ideally I leave the two pieces in a dry atmosphere for 3 weeks or more so that any shrinkage may take place. Then I re-chuck the lid (relying on the original chucking could cause problems if the material has shrunk), skim the inner surfaces and, if the lid is to be screwed, I under-cut the bottom and then cut an internal thread. I use a screw-cutting guide or leadscrew and change-wheels as I have not yet developed the skill of cutting threads by hand as demonstrated by Bill Jones. Also, to get a really fine finish on the threads I mill them with a Drilling Spindle and, if the material is at all unstable, I pour superglue over the cut thread and when it has hardened, I re-cut the thread to improve both its strength and finish. I cut the internal thread first as it is the more difficult one to re-cut when fitting.
The next step is to finish turn the bottom of the base and re-chuck it so that the whole of the cylinder may be turned and/or ornamented. A good way is to stick a scrap piece on the finished bottom using a glued paper joint and turn the scrap down so that the base may be chucked by it accurately. I then cut a step around the open end slightly less deep than the recess in the lid and with the outer diameter equal to the root diameter of the lid thread. If it is required to match the grain with the lid, the base thread should be started at, say, one tenth of a turn behind the lid thread, so that when fitted the lid will be tight just before the grain patterns match. I cut only about one turn at the end until I am certain the threads will fit snugly then cut them to full length; about three turns should be enough. Then using a right side cutter it is possible to shave the seat of the base thread until the grain patterns match when the lid is screwed on tight. I use a Vertical Cutting Frame to mill the external thread (again improving them with superglue if necessary). Of course, it is far easier to match the grain by making a push-on lid, perhaps with a key and keyway to locate the match.
Boxes with thick walls look clumsy so it is a good idea to skim out the bore of the base until the wall is only sufficiently thick to avoid breakage of the threaded portion.
Now the box is ready for exterior finish. By screwing the lid on tightly all the outer surfaces may be re-cut. By this method it is usually possible to make the join appear almost invisible. However, it is important to have measured the internal dimensions and to check carefully that no cut penetrates too far, particularly in the thinnest area where the lid joins the base. Finally the glued paper joint is broken apart and the glue carefully cleaned off the bottom.
I look forward to seeing John Hopewell's next box!"
KEEP THOSE QUESTIONS (AND ANSWERS) COMING
NOTE THAT WE CAN INCLUDE SKETCHES AND PICTURES TO ASSIST THE EXPLANATIONS
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members without Internet access can contribute.
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