5 If board width is sufficient, it would be preferable to use three rows of slotted retaining blocks
per board. This provides the best pattern of restraint against warp of each individual board.
With narrow boards where space is sufficient for only one row of blocks, it is better to place
them near the center line to avoid creating tension close to the board joins. It is not consid-
ered advisable to use the blocks to reinforce or span board joins, a practice that can frequently
be seen with fixed-cradle members.
6 Teflon/PTFE skived tape, with a pressure-sensitive adhesive coating on one side, has been
found to be the best of the range of PTFE products for reducing friction. A cheaper alterna-
tive recently found available is polyolefin tape. This is an ultrahigh molecular weight (UHMW)
polyethylene material with a coefficient of friction comparable to PTFE. The pressure-sensitive
rubber adhesive coating is more suitable for timber, and it also has improved mechanical char-
acteristics, such as lower elongation and higher wear resistance to abrasion. As yet, it has not
been in use in the author’s studio long enough for full evaluation.
7 In the United Kingdom, this means that the panel has been stabilized at 55% RH.
8 Plastazote is a closed-cell, cross-linked polyethylene foam available in a number of densities.
The one used as a core in the timber mounting pads is the low-density LD24.
9 Tables of values of modulus of elasticity of timber relate to data obtained from testing in a
direction parallel to the timber grain. Figures do not exist for E values perpendicular to the
grain. However, a useful reference can be found in a British Standards Institute (BSI) publica-
tion (1991:pt. 2, clause 11 [“Additional Properties”]): “In the absence of specific test data, it is
recommended that, for tension perpendicular to the grain, torsional shear and rolling shear,
values which are one-third of those parallel to the grain should be used. For modulus ofelastic-
ityperpendicular to the grain, a value of one-twentieth (i.e., 0.05) of the permissible modulus of elas-
ticity should be used”(emphasis added).
Properties ofSitka spruce are giv en in table 11 of the BSI publication. Information for
obtaining complete copies of the publication can be found in the “Materials and Suppliers”
section below.
10 Alexander Keirincx (1600–1652) and Roelant Savery (1576?–1639). The painting depicts
Orpheus, who could enchant the beasts, being attacked by the Thracian women.
11 Aspan of not less than one-quarter or more than one-third of the batten length has been
found in practice to be a good dimension for which to aim.
12 Restoration of the painting was carried out at Lank Sanden Studio in London.Ball units,Alwayse Engineering Ltd., Warner Street, Birmingham B12 0JG, England. (Large
range ofBall transfer units available; the type in use are from the Solid Body Unit range.)
BSI Publications,BSI Customer Services, 389 Chiswick High Road, London W4 4AL, England.
Evo-Stik, wood adhesive, waterproof, or extra fast resin “W,”Evode Ltd., Common Road,
Stafford, England.
Linear-motion slide bearings,SKF Engineering Products Ltd., 2 Tanners Drive, Blakelands,
Milton Keynes, MK14 5BN. (Small units are available in the standard slide range, RM series.)
Plastazote(a closed-cell, cross-linked polyethylene foam, REF LD 24), BXL Plastics Ltd., Mitcham
Road, Croydon, Surrey CR9 3AL, England. (Distributed by Hemisphere Rubber Co., 65 Fairview
Road, Norbury, London SW16 5PX, England.)
Polyolefin ultrahigh molecular weight (UHMW) polyethylene tape with a pressure-sensitive
rubber adhesive (marketed as Polycohr), CHR Industries, Inc., 407 East Street, New Haven,
CT06509. (The European supplier is Furon CHR Products, P.O. Box 124, 7640 AC Wierden,
Netherlands. Distributed in the United Kingdom by Polypenco Ltd., now part of DSM
Engineering Plastic Products UK Ltd., 83 Bridge Road East, Welwyn Garden City, Hertfordshire
AL7 1LA, England.)
Teflon/PTFE (polytetrafluoroethylene) tape with a pressure-sensitive silicon adhesive
(marketed as Temp-r-tape HM series), CHR Industries (see information for polyolefin tape).Materials and Suppliers
T D F A A S 401