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Home Articles Page David@DavidReedSmith.com This article was published in the February 2013 (#41) edition of Woodturning Design. Foam Cone Sander as a 5 page pdf Optional spreadsheet for calculating foam shape
Foam Cone Sander
Introduction
A while back I wrote an article on a Foam Ball Sander (Woodturning
Design Spring 2008). I thought it
was terrific to use--very stable in use, consistent scratch pattern, and capable
of being used very aggressively without shedding its abrasive and leaving a
smear of velcro stickum across the wood.
But alas, it was quite sub-optimal when it came to preparing or changing
the abrasive. Life involves
compromise. The Foam Cone Sander is
a different compromise. It's stable
in use, but you won't be tempted to hold the drill with one hand as you can with
the foam ball, and it wouldn't work well for the interior of a hollow vessel.
It gives pretty much the same consistent scratch pattern, without swirls,
and can be used aggressively without shedding abrasive due to overheating.
It's reversible to make it easier to get into some areas.
You have to pay a bit more attention to presentation, but it's WAY easier
to prepare and change the abrasive.
I think a consistent, swirl free sanding pattern is more efficient.
Also I tend to use a power sander for the first grit or two and then
switch to hand held abrasive when all you're doing is removing the scratches
left by the prior abrasive. Except
for perhaps the very center of a bowl the scratch pattern is straight and
similar to hand held abrasive, as shown in
Fig01.
Fig01:
The scratch pattern on the outside of a bowl.
I tend to drop my hand to see what I'm doing so it's not perfectly
vertical.
First the article will discuss preparing and turning
the cone blank. Then the cone will
be covered in foam, tape, and velcro.
The abrasive will be prepared and applied, and then the using the foam
cone sander in various bowl situations will be discussed.
Making the Cone
Begin the blank by bandsawing a disc, 2-3/4" in diameter, out of wood
about 1-1/8" thick as in Fig02. The
next step is to drill and tap the center of the disc for 3/8x16 threads.
Fig03 shows a mini-tap guide, on top, which enables you to easily tap
threads perpendicular to the blank because of its spring loaded point that
follows the tap, and two slightly different styles of taps.
The tap in the middle has a shank that is the diameter of the outer
threads. This style limits the depth
you can tap. In this case, it will
tap deeply enough. If you made the
cone of thicker wood it would have trouble sanding more concave surfaces (or you
would have to use a lot more foam
layers). The bottom tap, a cheaper
one with a reduced shank, could tap more deeply.
Fig02: The cone blank, a
2-3/4" disc of wood about 1-1/8" thick.
Fig03: The mini-tap guide
and a couple of styles of taps.
Mount the blank on your lathe using a 4-jawed chuck (or faceplate,
etc). Mount a combined drill and
countersink or spotting drill in your tailstock mounted drill chuck as in Fig04
and drill a small dimple to aid in getting the tap drill started straight.
Then mount a 5/16” drill bit in the chuck as in Fig05 and drill through
the blank.
Fig04: Using a combined
drill and countersink to drill a starter hole.
Fig05: Drilling through
the cone blank with the tap drill.
Now mount the mini-tap guide in your drill chuck.
Place the nose of the tap in the drilled hole and bring up the tailstock
so that the point of the mini-tap guide engages the dimple in the back of the
tap (or the tap handle if you're using one).
Advance the tailstock ram to compress the spring of the mini-tap guide.
Lock the lathe spindle and turn the tap so that it cuts the threads.
The spring loaded mini-tap guide will follow the tap in (at least for the
critical first half inch), keeping it aligned with the axis of the lathe and
preventing skewed threads.
Fig06: Tapping threads
with the aid of a mini-tap guide.
Now prepare a drive stud for the cone.
Use either 2-1/4” of 3/8 x 16 all-thread or cut the head off of a 3/8 x
2-1/2” bolt. Thread on two nuts and
lock them against one another about 1/2" from one end as in Fig07.
Then remove the blank from the chuck and thread the short end of the stud
into the cone blank.
Fig07: The completed
drive stud.
Mount your drill chuck in the
headstock, and then mount the cone blank, via the drive stud, in the drill
chuck. Bring up your tailstock so
that you won't have worry about the drill chuck vibrating loose as in Fig08.
Using a small bowl gouge, reduce the diameter of the blank to 2-1/2" as
in Fig09.
Fig08: The cone blank
mounted on the lathe.
Fig09: After reducing the
blank diameter to 2-1/2".
Then use the bowl gouge to taper the nose of the blank so that the
shape becomes a truncated cone. A
good general purpose slope to aim for is 45°, or measured as in Fig10, 135
degrees. This angle works fairly
well both inside and outside of bowls unless they have very concave surfaces.
Another tactic would be to use a pair of cone sanders, one flatter, maybe
155 degrees for bowl insides and one steeper, perhaps 125 degrees, for the
outside.
Fig10: Checking that the Cone is 135°.
Covering the Cone
The wooden cone needs to be covered with 3 layers of 2mm craft foam
to allow it to conform to the bowl surface and sand efficiently.
It is possible to calculate the exact size and shape of foam needed (it
will be on my website if you're into the math) but it's easier to start bigger
than necessary and trim, as craft foam isn't very expensive (unless you splurge
on the new sparkly foam). Start by
making a template out of poster board or cereal box cardboard.
Begin by making a 5" circle, then a smaller 1-1/2” circle with the same
center. Draw two radial lines
starting at the center at right angles to another.
The result is three quarters of a ring as sown in Fig 11.
Use the template to trace out 3 of the foam shapes on the craft foam
using a fine lined sharpie or pencil.
Now cut out the foam pieces.
Fig11: After tracing out
three foam pieces.
Lay the foam pieces out on newspaper or another disposable surface
and spray one side of the foam pieces with 3M 77 spray adhesive as in Fig12.
Wait for the glue to set up following the directions on the can.
Then apply the first piece of foam to the cone blank as in Fig13.
The foam will overhang top and bottom and overlap.
First trim away the overlap with a knife or scissors.
Then trim the overhang at top and bottom as in Fig14.
Repeat the foam application for the two additional layers, being sure to
put the overlap in a different place for each layer.
The result is shown in Fig15.
Fig12: After applying
spray adhesive to the foam pieces.
Fig13: After applying the
first foam layer and removing the overlap.
Fig14: After trimming
excess foam from the first layer.
Fig15: After applying and
trimming all three layers of foam.
The foam is somewhat fragile—if you had to change the Velcro it would
likely take some foam with it so protect the foam with a layer of duct tape.
I've not discovered a terribly efficient way to cover a cone with duct
tape...so just get it done, a couple of layers worth, and trim away any overlap
as in Fig16. Now apply the hook
layer of “Industrial Strength sticky back” Velcro.
Again, there is no magic way, just apply and trim.
The result is shown in Fig17.
Fig16: After applying
duct tape to protect the foam.
Fig17: After applying
velcro.
Using the Foam Cone Sander
The first step in using the Foam Cone Sander is to size and attach
abrasive. Use 5" discs.
Unperforated discs would be best, but perforated discs from Home
Improvement big box stores will work fine.
Lay a disc abrasive side down on a work surface and find the center.
Draw two radial lines at right angles from one another.
Then measure the side of your cone.
Add 1/4" to that (this lets a little abrasive fold over the nose if you
need use just the nose for bowl bottoms).
Subtract the total from 2-1/2" and draw a circle with that radius as in
Fig. 18. Cut the abrasive on the
lines as in Fig19.
Fig18: The layout for
cutting out the abrasive.
Fig19: After cutting out
the abrasive.
Now apply the abrasive to the foam cone, trying to match at the
widest diameter, and overlap it on the side as in Fig20.
Trim the overlap as in Fig21, leaving about 1/4" of overlap.
You can now use the trimmed abrasive as a template for any future ones.
Fig20: After applying the abrasive.
Fig21: After trimming the
abrasive to a 1/4" overlap.
Mount the foam cone with abrasive in a power drill.
You can use any drill you like, but if you have an air compressor, I
recommend using air powered drills.
An environment of sawdust and abrasive is not good for electric drills that suck
in outside air to cool themselves (I ruined a really nice close quarter drill
this way). Air drills, however, use
the clean air from your compressor for cooling and will be none the worse for
sanding duty provided you remember to oil them occasionally.
You can mount the cone with the large end close to the drill for most
uses as in Fig22, or unscrew the mounting stud and screw it in the other end to
mount the cone with the large end out as in Fig 23 for hard to reach areas.
Reverse the overlap when you do this.
Fig22: The foam cone
mounted on an air powered drill.
Fig23: The foam cone
mounted reversed (with overlap reversed as well) on a drill.
To maximize sanding efficiency when using the Foam Cone Sander ensure
that the bowl surface and the abrasive surface are moving in opposite directions
at the point of contact. Depending
on your lathe and drill you can reverse either if necessary.
Also make sure the overlap is trailing.
Try to do most of the work with the side of the cone, not the rim or
nose. The following figures show
several applications in sanding a bowl.
Fig24 shows sanding the foot of a bowl in close to the chuck.
The cone is in the reversed position, and a right-angled drill is being
used.
Fig24: Sanding the foot
of a bowl with the cone reversed.
Fig 25 and Fig26 show sanding the inside of a bowl.
The cone is in the regular position and the side of the cone is in
contact with the work. The foam
gives enough to allow the abrasive to adapt to the curve and make contact over
most of its side.
Fig25: Sanding near the rim of the inside of a bowl.
Fig26: Sanding in towards
the bottom inside of a bowl.
Fig27 shows sanding the foot of a bowl.
In this case, little but the rim is making contact and some swirling is
present in the pattern. In Fig 28,
which shows sanding on the outside of the bowl, the whole side of the bowl is
again making contact and the abrasive pattern is straight.
Fig27: Sanding the foot
of a bowl.
Fig28: Sanding the
outside of a bowl.
Tools and Materials
3/8" x 16 tap
Mini-tap guide
5/16" drill
drill chuck
2-3/4"D x 1-1/8" wood disc
2-1/4” of 3/8 x 16 all-thread or 2-1/2” 3/8” bolt
2 each 3/8" x 16 nuts
Adjustable bevel
2mm craft foam
3M Super 77 or other spray adhesive
Duct tape
Industrial Strength Sticky Back Velco
5" hook and loop abrasive discs
Power drill
Author
David Reed Smith lives to turn and tinker in Hampstead, Maryland.
Regular readers may be surprised (or relieved) there was no blue tape
visible in this article, but be assured there was some behind the scenes when
the bowl was reversed. This article,
along with perhaps a supplementary video will be available at
www.DavidReedSmith.com along with 60 or so other articles.
He welcomes comments and questions at David@DavidReedSmith.com.
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