By Allyn J. Thompson
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One hundred twenty. the employee is therefore supplied with comparability surfaces of those grades, however the similar texture shouldn't be hunted for, appropriately remembered that there's a distinction within the hardness of pyrex and plate glass. Prevention here's the easiest medication. If the employee completely grinds down 8 fees of every grade of abrasive, with strain continuou"ly utilized, he desire waste no time searching for pits. bankruptcy eleven/ THE PITCH LAP Making the Lap. we're now prepared for the sprucing lap. First, minimize a strip of newspaper at the least 20" lengthy, and percent" wider than the thickness of the device; run it via a few melted paraffin and set it apart. this can be to function a collar, to be wrapped round the device to maintain the new pitch whereas it units. Now soften the pitch slowly at the range, in a pot or can. it really is hugely inflammable, so continue the flame low, and feature available a board or different conceal that may be instantly positioned over the pot to smother any flames. Use a large, skinny stick for stirring. If a can is getting used, it can be gripped with a couple of pliers whereas pouring. whilst the pitch is totally melted, pour a wide drop onto a bit of scrap glass and allow it cool. test denting it together with your thumbnail. If after approximately 15 seconds of strain, there's hardly ever any indentation, the pitch is just too tough; too tender if it has yielded simply. a few reflect makers use the chew try out, even though this can be much less determinate than the thumbnail try out. Chip the chilly drop of pitch unfastened from the glass and position it among teeth. If it instantly shatters into fragments stressed, it can be too difficult. There could be simply the slightest yielding prior to breaking. The top-rated strategy to know about the mood is to move forward and make the lap, and notice the way it works in sharpening. to melt pitch, upload quite a few drops of turpentine. don't do that over the range. It takes little or no turpentine for this, so use it carefully. Stir completely and back try out the mood. To harden pitch, cook dinner it for a protracted interval. including a volume of rosin will harden it. No pitches are alike, so distinctive proportions can't be given, however the quantity of rosin additional ought to not exceed the quantity of pitch. a few laps are made entirel y of rosin; those are best suited for decent climates. whereas the pitch has been melting, partly fill the pail (which has heen completely wiped clean Ollt) with water as sizzling because the hand" fifty one S2 MAKING your personal TELESCOPE can tolerate, and fully immerse reflect and gear, standiug them on their edges and resting them opposed to the perimeters of the pail, on the way to be fast reached whilst sought after. Have a section of cleaning soap available in a fresh dish. The instrument and replicate might be al- Fig. 27. The channeled lap. lowed to warmth via prior to you pour the lap. After the pitch has been totally melted and tempered, get rid of it from the range and make allowance it to chill a bit of, because it is better to not pour boiling scorching pitch at once onto the software. Now get rid of the device from the new water, dry it, and wrap the paraffined paper collar round it. There could be sufficient warmth within the glass to reason the overlapping ends of the collar to advert· the following.