Fig. 2569.
In cases in which it would not be permissible to drill so many holes through the beam on account of weakening it, we may use patch bolts with countersunk heads, as in [Fig. 2569]. Two only of the bolts pass entirely through, and it is best to let them be taper, as at a in the figure, the head not meeting the patch. The hole in the beam, after being reamed taper, should be filed out on the side b, and that in the patch plates on the other side, as at c and d, so that the bolts will serve as keys. After these two bolts are in place and their nuts firmly screwed home, the holes for the patch bolts may be drilled through the plates and into the beam. When the countersunk head bolts are fitted they should be turned down behind the head, so as to leave a part weaker than the bolt, and then screwed in until the required end breaks off. The taper bolts should be of steel, but those with countersunk heads may be of iron.
Erecting an Iron Planer.—If an iron planer be properly fitted and erected, the table will be quite solid in the V-ways in the bed, and will not rock or move even though a heavy vertical cut be taken at the extreme sides of the table, but any error of truth of alignment or fit either in the bed-ways or the table V’s will cause the table to lie improperly in the V’s and to be apt to rock as it traverses. The author has had planed upon a planer thirty years old, at the Freeland Tool Works, in New York City, a cast-iron surface 12 × 20 inches, the metal weighing about 60 lbs., and the surfaces were so truly planed that one would lift the other by reason of a partial vacuum between the two. These planed surfaces were exhibited by the author at the American Institute Exhibition in 1877, and were awarded a medal of superiority.
The manner in which this planer was fitted and erected, and the principles involved in such fitting and erecting, are as follows:
While it is essential that the foot or resting surface of a planer bed (whether it stands on legs or rests direct upon its foundation) be as true as it is practicable to plane it, still it is more essential that the V’s or ways be true, and as the casting will be apt to alter its form from having the surface metal removed, it is best to plane the side on which the ways are the last.
When the bed is placed upon the machine to have its resting surface planed, the casting being uneven, it will be necessary to place packing pieces of suitable thickness beneath the places where the clamping plates hold it, so that the pressure of those plates may not spring or bend the casting.
These packing pieces require to fill up solidly (without lifting the bed) the hollow places, and it is a good plan to place among them a piece of strong writing paper for reasons which will appear presently.
In planing the bed all the surfaces should be roughed out before any are finished. Before any finishing cuts are taken all the clamping bolts should be loosened and the pieces of paper tried by pulling them, so that if the casting has altered its form it will be made apparent by some one of the pieces of paper becoming loose.
In this case the packing must be readjusted, clamping both as lightly as will hold the work, and all as equally as possible, when the finishing cuts may be taken.