Conventional Surfacing
- Pat Gauvin
There are several parameters to control surface block selection and calculations. These are found on the “Blocking” tab in “System Settings”, as follows:
Blocking Method
The “Blocking Method” parameter allows different rules to be used for selection of LOH blocks, as follows, the valid values are “Y”, ”0”, “1”, “2”, “3”, “4”, “5”, “6”, “7”, “+”, “-“, “P”, “M”, “N”, “U” or “A”. A setting of “N”, “0”, “+” OR “-“ indicates that LOH blocking is not used, and LOH “set” and “actual” values will NOT be calculated nor printed on the work ticket. The other settings all indicate that LOH blocking is used, with rules described below.
The “+” and “-“ parameters are not specific to LOH equipment; but are linear adjustment values to calibrate the generator thickness whenever an older style manual generator is used with a blocking system that was not specifically designed for it. This is used in conjunction with the 2nd, 3rd, and 4th parameters of the LOH system variable in order to compute the adjusted thickness values for setting the manual generator.
“Y” -
If the diameter of the lens blank is > 72mm, a 63x10 block will be chosen
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 63x10, then 63x13, then 48x10, then 48x13
For resin multifocals, where the segment protrudes from the front surface of the lens, if the block rests on the segment (more than the allowable overlap specified in LOI), if current block diameter is 58, block will be changed to 63x10 (if true front curve is <= 8.75) or 48x10 (if the true front curve is > 8.75). Note that an additional check is done to ensure that the lens doesn’t “bottom out” on the block if it does, the height will be increased by 3mm to 13mm.
“0” - forces the block size to always be what is specified in the block height and diameter fields, and does not change block size based on cutter crash, segment placement, blank diameter, etc.
“1” -
If the diameter of the lens blank is > 81mm, a 63x10 block will be chosen
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 48x10, then 48x13
For resin multifocals, where the segment protrudes from the front surface of the lens, if the block rests on the segment (more than the allowable overlap specified in LOI), if current block diameter is 58, block will be changed to 63x10 (if true front curve is <= 8.75) or 48x10 (if the true front curve is > 8.75). Note that an additional check is done to ensure that the lens doesn’t “bottom out” on the block, if it does, the height will be increased by 3mm to 13mm.
“2” -
If the diameter of the lens blank is > 72mm, a 63x10 block will be chosen
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 63x10, then 63x13, then 48x10, then 48x13
For resin multifocals, where the segment protrudes from the front surface of the lens, if the block rests on the segment (more than the allowable overlap specified in LOI), if current block diameter is 58, block will be changed to 63x10 (if true front curve is <= 8.75) or 48x10 (if the true front curve is > 8.75). Note that an additional check is done to ensure that the lens doesn’t “bottom out” on the block, if it does, the height will be increased by 3mm to 13mm.
“3”-
If the diameter of the lens blank is > 86mm, a 63x10 block will be chosen
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 48x10, then 48x13
No adjustment is made for resin multifocals with this option.
“4” -
if the diameter of the lens blank is > 86mm, a 63x10 block will be chosen
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 48x10, then 48x13
For resin multifocals, where the segment protrudes from the front surface of the lens, if the block rests on the segment (more than the allowable overlap specified in LOI), if current block diameter is 58, block will be changed to 63x10
“5” -
No change in block size is made for large diameter blanks
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 60x11.8
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 60x11.8
No adjustment is made for resin multifocals with this option.
“6” - This option differs from Option “1”, primarily with respect to the selection of a 63 x 7 block, instead of 63 x 10 block.
If the diameter of the lens blank is > 81mm, a 63 x 7 block will be chosen
If the specified block size results in cutter crash, then the block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), the block size will be changed to first 63 x 10, then 48 x 10, then 48 x 13.
For resin multi-focals, where the segment protrudes from the front surface of the lens, if the block rests on the segment (more than the allowable overlap specified in LOI), if current block diameter is 58, the block will be changed to 63 x 7 unless the front curve is so steep that it will bottom out (in the 8.00 + range depending on the requested edge thickness), in which case it will switch to either a 63 x 10 or a 48 x 10. In extreme cases an additional 3mm may be added to make it 48 x 13.
“M” or “P” (for use with LOH MT1 generator ONLY)
If the diameter of the lens blank is > 72mm, a 63x10 block will be chosen
If the diameter is < 60mm, a 48x10mm block will be used
If the specified block size results in cutter crash, then block will be changed to 48x10
If the blank will “bottom out” in the block (due to height or curve), block size will be changed to 63x10, then 63x13, then 48x10, then 48x13
For resin multifocals, where the segment protrudes from the front surface of the lens, if the block rests on the segment (more than the allowable overlap specified in LOI), if current block diameter is 58, block will be changed to 63x10 (if true front curve is <= 8.75) or 48x10 (if the true front curve is > 8.75). Note that an additional check is done to ensure that the lens doesn’t “bottom out” on the block, if it does, the height will be increased by 3mm to 13mm.
Additional calculations are done to calculate the “MT1 Setting Radius” and “MT1 Setting Angle”
“7” (user defined selection rules) - This option allows the lab to set their own rules and priority for selecting blocks. See the “Surface Block settings” section for details on setting these up. If you select option “7”, but neglect to set up a sequence of blocks, Rx-Universe will revert to the block specified as the system-wide default. If a sequence is set up, the system-wide default block is IGNORED.
“N” or “A” - These settings allow for the choice of either a SatisLoh Nucleo blocker or a SatisLoh ART blocker. See ART / Nucleo Blocking.
NOTE - For cutter crash calculations, the lens is checked along the axis of the thinnest point, and also along the spherical and cylindrical axes. Cutter crash often occurs on small frame sizes with a 58mm or 63mm block, but is not limited to these cases.
Default block height and block diameter
The fields “Default block height” and “Default block diameter” specify the default system block size to be used for surfacing. This can be any valid block size. Note that this is a system default setting, which can be over-ridden by other parameters both on this screen, and block sizes specified for materials or lens styles.
Generator Block Diameter
The “Generator Block Diameter” parameter is used in conjunction with the “+” and “-“ options and was not designed specifically to LOH generators.
Allowable overlap on blocks
This factor is used only when LOH blocking is used and the blank is a plastic or poly multifocal where the segment protrudes from the front of the lens. When this is the case, the block is checked to ensure that it will not “sit” on a portion of the segment. Certain labs will tolerate a small amount of overlap. To allow some overlap, specify an amount in this field. If you do not want to allow overlap, set this field to zero. If you use special rings with cut outs for the segments, set this field to 9.9. This will indicate that overlap is not an issue and hence will never reject a block because of the segment location.
Force same block both eyes
If checked, this causes blocks of the same diameter and height to be selected for both eyes. If not checked, different blocks could be selected for each eye, based on the Rx and requirements of each eye separately.
LOH prism settings
The following settings are found in the “Devices” tab fo the “System Settings”.
This parameter has two parts. The first part is to specify which prism conversion formula to use when converting the prism in diopters to angular prism. You can select the formula that OMICS developed when LOH blocks were first implement; the formula LOH originally released with their blocks (dis-satisfaction with this by some labs is what led to the OMICS formula); or you can select the revised formula that LOH released in 1999. The revised formula is the best choice for V-series generators.
A check box allows the lab to choose whether or not to round the LOH angular prism value. As a rule, if you use prism blocking rings, then round the prism; if you grind or block prism directly (without prism rings), then do not round prism.