road and workshop
Page 45
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by Handyman
Benchwise: lathe sense (5)
MENTION a reamer to a young mechanic or garage fitter and he will think at once of the variable diameter reamer with detachable blades and fine cone adjustment, a tool obviously for hand use; he will, of course, be familiar with certain fixed-size reamers used for finishing off swivel pin bushes, etc. These fixed-size reamers have long, plain pilot sections and often two cutting areas, but normally also a large square-section end drive for manual use with a tap wrench. On the other hand, the turner has another range of reamers for use in the lathe, and where accuracy and a good finish is essential, a far better job can be turned out in the lathe whenever it is possible to mount the newly bushed item.
Spiral-fluted tool Unless beaten by sheer size, the skilled turner can always manage to mount a workpiece, however odd in shape, and the result is always worth while. The reamer for lathe work is mainly spiral-fluted, with, a taper shank for tailstock use, and most turners prefer the spiral-fluted tool as there is far less risk of cutting edges gripping the work, jumping, chattering, or expanding to the detriment of the finished hole as indicated earlier with over-loaded twist drills. As a rule the machine reamer is provided with a shorter cutting area than the hand reamer, with a reduced diameter between the flutes and the main shank—for the obvious reasons of releasing swarf.
One common fault in adjustable hand reamer use is that the young mechanic may ream out a newly fitted road spring-eye bush, and put a considerable amount of "beef" into it due to the depth of cut he is tackling. This attempt to rush the job through results all too often in the finished bush being scarred internally with long chatter marks; while it may be a near-fit on completion, a lot of metal will have been raggedly removed that will be needed later, and the pin to bush fit will soon be sloppy, to say the least.
It should always be remembered that the reamer is intended solely as a finishing tool, whether it is for hand or machine operation; its purpose is to take out the final four or five "thous' and leave a perfect finish. It was never intended for hacking out large amounts of metal, which is what is all too often attempted; this particularly applies to the adjustable reamer which has its blade life shortened unnecessarily by this treatment.
In the same way, the machine reamer in the lathe must never be made to enter holes that are obviously well below finishing sizes, as this is an unfair and often impossible task that can only result in a bad finish or damage, together with an element of risk for the operator.
With the machine reamer for use in the lathe, the operator has a choice of three methods of operation which can extend the range of work or items that he can tackle, and in the vehicle repair trade this can prove invaluable in time-saving and the accuracy of the finished job. Machine reamers are as a rule taper shanked for tailstock use, but there are parallel shanked reamers for use in the three-jaw chuck in the same way as a drill, and this, of course, means that the workpiece has to be mounted and secured to the cross slide or a vertical slide if available. To ensure accuracy with this method there must be an absolutely true, straight line through the work piece between tailstock and lathe mandrel—the slightest variation and the hole will not finish true.
The second choice is, of course, with the tailstock-fitted, taper shank reamer and a revolving workpiece in the three or four-jaw chuck, or as occasion demands fixed on the face plate; this is a much used method, the criteria being that the tapered shank of the reamer and its tailstock seating are always clear of scars or grit, which could throw the finished hole out several "thous".
A method favoured by the, professional, strongly recommended for the trainee as it guarantees accuracy, is known as the "floating" reamer. This may look a little tricky to the trainee or spare-time turner, but in fact it is really simple and very reliable, and by its use a first-class job can be made of all classes of bushed brackets, hangers, housings, etc; the main point to remember is to centre the workpiece carefully.
If you take up a machine reamer you will note that the shank end has a machined centre, and to use this method you need one additional item, a strong tap wrench long enough to reach the cross slide for anchorage. Assuming that you have the workpiece already mounted and bored or turned out to the four or five "thous" under finishing size, set the finishing reamer into the workpiece aperture and slip the wrench over the reamer shank, then follow up with the tailstock bodily on the lathe ways; do not wind out the tail centre any undue amount, it pays to keep the tailstock as short up to the work as possible from the start.
Constant load Close the tailstock centre into the reamer centre, holding the reamer firmly up to the tail centre with the tap wrench, but do not apply tail-wheel load other than to close the gap lightly; select the lowest backgear speed and start up, applying light, steady tail-wheel pressure to travel the reamer. Remember that once you start the operation you must maintain a constant load or feed on the centre, never pause or slack off, keep the reamer feeding through the work at the same pace, then, as you pass the reamer clear through keep the lathe running, and as you will have one hand still on the tap wrench, you must maintain the pressure on the reamer against the centre as you wind back the tailstock wheel, bringing the reamer all the way back and clear of the work.
Do this carefully, and you will have every satisfaction with the finished job; this method is one of the most dependable ways of machine reaming and is specially recommended for the trainee or spare time turner, with particular reference to motor vehicle repair work.