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The Threaded Box
1. Thread Steps:
(A) (B) (C)
A) First, cut threads for the top
B) second, cut threads for the base
C) third, check your fit, sand and wax them with paste wax
Then you're done and that's all there is to it
A slip fit box is nice; a "pop" fit box can be technically challenging. But a carefully crafted threaded box with a perfect grain match adds a touch of elegance to even the most ordinary work. Last year I sold four little slip fit lidded boxes on a stand. The purchaser went to retrieve her prize and inadvertently knocked a lid off and it fell to the floor and chipped. If it had been threaded instead of a slip fit, it wouldn't have been broken. Sometimes you want a lid that doesn't easily come off when your 2yr old tips it over or picks it up and it has a favorite ring or bracelet or watch in it.
It took me three months to get my first decent set of threads, 2 wks for the second set and now I can turn them just about any old time. I first tried hand chasers and after wks of pain and suffering I got one set of threads that actually worked and they were ragged. When I lapsed off practicing for a couple weeks, my hands had to start learning from scratch again. I vowed never to try again. Enough’s enough. Then I met Bonnie Klein in Vancouver, BC, and she showed me her little jig that works well on small boxes of pretty much any kind of wood, bone, horn, and plastics. And that's what we'll use today.
2. Prepare the Wood
A)
B)
Start with a wet log: end grain works best (less movement)
Band saw to length (~6-8")
B) Pith out
A) Pith in (less movement but you get more cracks)
3. Mount to Lathe: drive point to live center on tailstock
A) B) C) D)
A) Make the cylinder
B) Spigot the tail end
C) Mount the spigot in the 4jaw chuck and spigot the other end
D) Part top from bottom and label for future reference
(Instead of mounting top in a 4jaw chuck at this time you could mount the top and the Bottom glued to face plate blocks which are double-sided-taped to a Face plate—Bonnie Klein uses this method)
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4. Rough Turn Top:
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A) Starting with the top's cylindar
B) Rough turn the outside of the top
C) Rough turn the inside of the top, leaving a lip 3/8" wide allowing for the threads
5. Rough Turn the Bottom:
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A) Chuck the bottom cylinder
B) Rough the outside bottom
C) Rough the inside bottom, leaving a lip 3/8" wide to allow for the threads
(Remember : Ym and Yn (the inside and outide diameters of the Bottom) must straddle Yf (the inside final thread diameter of the Top) If not, you won't have enough wood margin to make the male threads
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6. Microwave Magic:
To Dry Stabilize the bottom and the top:
Remove from lathe and mark the chuck-hold position for future reference
Weigh the bottom/top and pencil-record on bottom
Put in Paper bag and close the bag's top after CA gluing any cracks or punky spots
Microwave ~3minutes at #5power setting (i.e., until very warm but not hot)
Open bag and let cool 12 h
Weigh and record
Inspect and CA glue any cracks
Repeat microwave process until 3 successive recordings without a total of 5g loss
(for ex: a top/bottom pair is ready to complete when the following
Wts sequence is recorded: 700, 640, 610, 580, 560, 550, 545, 540, 540, 540. Go pot.
The foregoing process has been uniformly successful without a single lost piece
Over 140 successive tops and bottoms. And there hasn't been a single
Instance of unstable threads after the pieces met the 3-successive stable
Weight criteria. And it's never taken more than
7 days to get a wet pot ready for final turning.
7. Ready the top for Threading:
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A) Retrue the Face, removing as little as possible to assure future top/bottom Grain match
B) 3/8" Rabbet at the lip. Crucial: sides must be straight and parallel to the bed
C) 1/16X1/16" 1st clearance recess on the rabbet at the lip
D) Bevel the clearance recess to avoid a first weak thread ring
E) Sand the inside of the top to final smoothness (400)
8. Poose and Thread the Top (female, inside threads, overfitting lid)
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A) Mount the Threading jig on the lathe
B) Mount the Chucked Top on the jig and hand tighten
C) Mount the Mandrel and Cutter on the lathe spindle and hand tighten
D) Flow Thin CAglue onto the Rabbet to be threaded and wipe xs off with a Cotton Cloth to keep the glue from spattering into your eyes or glasses
E) Accelerator to Speed dry the glue (this process firms the wood to be threaded)Poose it (blow on it) 'til the smell is gone (~30 seconds)
F) Wing Nut the jig tight to the lathe bed at the point where the cutter teeth barely touches rabbet
9. The 40thousandths solution:
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Turn at ~3000rpm (some woods will burn at lower temps and they require slower Speeds but most yield better threads at 3000.
.040: BestOverall thread depth is usually about .040"
3-6 passes for completion of threads: dense woods like ebony, blackwood, can be completed In 1 pass, but most local woods require 3-6 passes to avoid tear out, 5-15thousandths/pass.
One hand on the jig handle and one hand on the chuck at all times so the chuck can’t be caught and twirled by the spinning cutter.
Slowly wind the jigged top into the cutter’s teeth until you hear the sound of The cutter touching the shoulder of the top at the deepest part of the rabbet
5-6 Thread Rings is about the right number for the inside threads (better to have too many than too few because you may need an extra when you're trying to match bottom/top grain.)
Back out the cutter by unwinding it while the lathe is running advance the Cross Slide dial by 5-15 thousandths (it's calibrated in thousandths')
Before each new pass reapply thin CA glue/accelerator/poose as before if any tear-out occurs in the emerging threads.
Sharp Threads: repeat wind/unwind until the new threads are sharp and that will occur at about .040" depth of thread.
Oversharp: the correct concept is sharp but not oversharp. If you continue cutting after sharp threads appear, you start getting tear out and crummy threads and the only way to fix that is to re-cut the rabbet and then re-cut threads.
10. Brush your teeth (er, threads) after eating (er, cutting) lightly sand threads, then wax threads or apply sanding sealer (this will raise grain and necessitate buffing/polish/wax)
Apply it and wipe it off in 5 seconds (no more). One cloth to apply and one to wipe off immediately (if you take more than 5 seconds for this wipe on/wipe off, you get ridges you have to sand off.
11. Safety
Always wear glasses/safety glasses
Dust Mask when sanding lightly
Continuous Air flow mask when sanding heavy
Face Shield when making cylinders from logs or when working with cracky wood
Inspect for cracks and punky wood that can take flight
12. Ready the Bottom for Threading
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A) The 44Thousandths solution: Dial Caliper the thread diameter, X, of the inside threads and add 44thousandths--That number is the outside diameter of the outer (male) threads.
B) Chuck the bottom at the chuck mark and bring up the tailstock
C) Re-true the face (removing as little wood as possible)
D) 5/16" outside rabbet: create a 5/16" outside rabbet at X+.040 d.
E) 1/16" second clearance recess: turn a 1/16" recess at the base of the outside rabbet and a 1/16” Bevel: turn a 1/16" bevel on the lip
13. Poose 'n Thread the Bottom (outside, male) Threads
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A) Mount the bottom on the chuck
B) Mount and hand tighten the chuck on the threading jig
C) Flow thin CA glue and Accelerator on the rabbet to be threaded and poose 'til dry or drunk
D) Mount the Mandrel and Cutter as for the top and hand tighten
E) Tighten Wing Nuts on the jig block so the cutter barely touches the surface of the rabbet (as shown)
F) Turn lathe to 3000rpm
G) Keeping one hand on the jig winder handle and one hand on the chuck at all times, slowly wind the bottom past the cutter
The Dreaded Threader Disaster of the Outside Threads
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H) The Dreaded Outside Thread Disaster: Stop winding when you hear/see the cutter touch The shoulder of the bottom—there should be 2-3 thread Rings (not 5 or 6 rings as on the top). If you continue winding after the cutter has just barely brushed the shoulder, the cutter will suddenly grab the bottom's shoulder and will spin it and the chuck right off the jig and onto the floor (oops). Hold on tight!
I) Plan for 3-4 passes, advancing about 5-10thousandths” each pass, inspect threads and re-flow thin CA glue if tear out is occurring (depth of thread is usually ~20-30thousandths.) There is a little movable wire in a little groove on the threading dial and this can be used for reference.)
J) ‘Flats’: perfect outside, male, threads have small flats on them (hmm), unlike the sharp female threads (ouchy), for the best fit.
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14. Test the Fit:
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Before removing bottom from the threading jig, test the thread fit by unwinding the jig with the jig winder and clearing the bottom by using the jig dial. Do not unscrew the wing nuts since this will make it hard (but not impossible) to reposition the cutter exactly in the thread trough so you can cut deeper threads if the thread fit is too tight. You may have to remove the cutter/mandrel to get clearance enough to screw the top on the bottom to see if it screws good. Cut deeper threads as necessary to improve the fit. The Shoulder of the bottom should be what stops the screw, shutting the lid onto the bottom. You don’t want the Top to stop because it ran out of threads or runs into the unthreaded area of the bottom.
15. Finish the bottom
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A) Mount the Bottom/Chuck on the lathe and finish hollowing the bottom sand to 400 and apply Universal Sanding Sealer (use the 5second method ) to the inside.
B) Mount the Top/Chuck on the lathe
C) Screw the Top onto the Bottom and bring up the tailstock after making a tiny tail stock center depression so it seats well
D) Finish completely the shaping of the Bottom, completely removing the spigot. Sand to 600 and apply sanding sealer to the outside (5 second method) and remove it from the top (by unscrewing it).
E) Finish Shaping the top except for the spigot
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16. Undershot Grain Matching aka, the ½" Shy” Solution: A)
Sometimes it’s important visually to match the grain lines from bottom to top. If you remove wood from the Top’s lip or the Bottom’s shoulder, the Top will move toward the LEFT as it is screwed shut.
A) Undershooting the Match of bottom/top grain: the top grain should be ~½” to the Right of the bottom grain match at this point. (Sand the Top's lip bottom on a flat surface in order to get an almost Perfect grain match shy by ~1/2" undershooting of a perfect match.)
For example, 1:
If you would have to rotate the top 180degrees in order to gGet a perfect grain match, you have to remove ~180/360 X 1/16"=~1/32" (since the threader is a 16threads/inch device). Generally, it is by far preferable to remove the wood from the Top's lip bottom. So, you put the Top on a sheet of sandpaper on a flat surface and remove sand a little, then test the fit, then sand, then test the fit, etc until the bottom/lid screws shut when the grain is just about ½" shy of a perfect match.
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For example, 2: Overshooting:
If the grain lines match perfectly now, then any further shaping, detailing, vibration, cooling, or stabilizing of the wood will move the top LEFTWARD with respect to the bottom and will wreck your perfect grain match by Overshooting the match (Damn). If you overshoot (even if you overshoot ¼" or ½") you have to remove almost another whole ring (1/16") from the top in order to get your perfect match again. Therefore, at this point you should try for a ½" Shy match, not a perfect one.
17. Finish the Top
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Remove the Top from the chuck
Make a Jam Chuck to fit the screw end of the top
Mount the Top to the jam chuck (use a little painter's tape if necessary or bring up the tail stock to assist stability)
Shape the top, Sand to 600, apply sanding sealer (5 second method)
18. Perfect Grain Matching: the Final Solution
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A) let it sit a few days to let the threads stabilize, cool, settle. Then,
B) Lightly sand the threads, apply sanding sealer, sand lightly, wax, buff, polish
C) Sand the Top’s lip bottom carefully, lightly, on a flat surface checking match frequently. Each time you’ve sanded a little, re-check the grain match. You will note the Top moves Leftward a little bit with each sanding. Move the Top to the left by this successive, progressive sanding technique until you’ve achieved that perfect grain match. Then Stop quick.
19. Finishing Touches
Sanding Sealer: after all surfaces and threads have sanding sealer on them
1st Coat Finish:
Wipe on Poly (minwax) can be applied with 400-600 wet or dry sandpaper or with 0000steel wool. Just wipe it on with abrasive sanding, and wipe it off in about 2-4 minutes as soon as it gets a little stiff not tacky) but still real easy to wipe off. Thread fit must be checked to see if you should avoid further finish on them.
2nd-6th coat minwax wipe on poly with a cotton cloth. Just wipe it on, and then wipe it off (in 3-4 minutes) as soon as it gets a little stiff but is still real easy to wipe off without any ridges or swirls. Beal Buff with red rouge, then white rouge, then carnauba wax. This really improves the feel of the screwing threads.
What Next?
Turning threads is a handy little skill to have. It’s occasionally of great value…like, when you really need it.
If it's good, send it to the gallery
If it's bad, send it to the wood stove
If it's truly great, give it to the queen.
Appendix
Box Design Solution Notes:
Leave enough vertical space in the Tops to accommodate 3/8" of threads: Top at least 1" tall
1 ½ rotations is about the right number of turns for any box top
Minimum inside thread diameter limited by cutter diameter (3/4")
Inserts can be easily made for the inside/outside of bottom or top
Finials, Chatterwork, Embossing, Piercing, carving, painting all enhance visual appeal
Form Follows Function: salt shakers, promise boxes, needle cases, spin tops, eggs, apples pPears, balls, ring boxes, necklaces, ear rings: many uses for the threaded box
Four Major Forces, each of which can wreck perfect threads:
1. Water-logged wood. I.e., wood-swelling. Cure: follow the microwave magic sequence of bag, weigh, inspect, record, wave, rest, be patient
2. Heat: put a little threaded box in a hot window and it will most likely be ok. Put a larger threaded box in hot sun and in 2 hours, the threads will seize. Cure: don’t put bigger boxes in sunlight or heat.
3. Tension Release caused by Removing wood from a cylinder. It’s the same thing that occurs when a straight, flat 2X6X6" board is tablesawn into #2 boards 1X6X6". The 2 boards are no longer straight or flat because of tension released by the sawing. Cure: turn all lidded boxes half way and dry/weigh and let sit a few days before final turning and threading.
4. Humidity Changes: Moving a piece from the Dry side to the Wet side of the mountains results in wood taking on water that will swell it and distort the shape as well as the threads. Cure: don’t travel your boxes.
Remember: all these 4 effects are size dependent and thus, larger pieces will be affected more than small ones. Cure: keep your dimensions small.
Sanding Sealer Ridges: occur when you don’t wipe off your sanding sealer within 5seconds of aplication. Cure: wipe sealer on with one cloth, and follow that immediately with wipe off wh another cloth.
Runout in the Cutter/Mandrel does occur and makes cutting threads slower and the threads aren’t as nice.
Solution: let a little debris/ resin/sanding sealer/oil sit on the inside surface of the mandrel and that tightens the space between the mandrel and cutter shaft, diminishing runout. Or, wind the threading jig slower.
Books
Turning Boxes (book by Richard Raffan)
Turned Boxes (book by Chris Stott)
The Threaded Box (DVD by Bonnie Klein)
Turning Boxes from Unusual Materials (DVD by Bonnie Klein)
Tools and Supplies
Klein Design 16/1" threading jig
Jet Minilathe Variable Speed
Penn Craft Barracuda 4 jaw chuck with dove tail 2” jaws
Live center
Eliminator (Mini-sized) for hollowing
88degree square end scraper for making the two rabbets
½" Packard detail gouge with finger nail grind (David Nittman’s nemesis)
½" Lacer bowl gouge with David Nittman's 45degree grind
Diamond Parter 1/8”
1/16" parter
Dial Caliper .001" (harbor freight:$20)
Roughing Gouge 1" Packard
Chatter Tool
Embossing Tool
Electronic Scale
Delvies Plastics
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