by Harold Hall
Needing to make a batch of turned parts that require to be drilled on the lathe, the reader will have found the need to repeatedly interchange drill and centre drill quite a chore. If needing to be tapped also then it will be even more time consuming. This though can be avoided by the use of a simple tailstock turret such as the one in this project.
Whilst turrets with up to six stations are available the three way version described will satisfy the need of most home workshops owners. If though it is considered that a fourth station would be beneficial then the size of the head is sufficiently large to accommodate this, more about that later.
Photo 1 shows the completed turret with Photo 2 showing it in use on the lathe for what is likely to be its most frequent use, that is, a centre drill, drill, tap sequence. The tap holder may appear to be on the big side but this will be explained when I comment on the method of holding items in the turret.
Links to the drawings are at the end of the project.
Photo 1. The complete tailstock turret
Photo 2. The tailstock turret in use for a centre drill, drill and tap sequence.
Making the tailstock turret is not overly complex but there is a need for accuracy in the alignment of holes between the body and the turret, also some turned parts need to be a close fit in their mating bore. The order of making the components is therefore important and is detailed below.
I should add here that this project is being written up after the item was made some time back so I do not have photographs of the machining operations. In a few cases I will though show the basic operation using an already completed component. The full set of parts is seen in Photo 3 prior to assembly.
Photo 3. The complete set of part prior to assembly
Start by making the body (5) using 40mm square steel, this necessitating both 30 and 60 degree angles to be cut. If available, use a horizontal band saw to remove the bulk of the material otherwise it will be a case of using a vertical band saw, some hard graft with a hack saw, or, equally slow, removing the metal on the milling machine.
To illustrate the method using a horizontal band saw I am using a scrap of thinner metal. First cut the 30° as shown in Photo 4, doing this first will ensure there is a longer length to be held in the vice.
Photo 4. Using a horizontal band saw to rough cut the 30° angle on the body. In this case the photograph illustrates the process using a scrap of metal.
Next, with the vice returned to the 90° position cut to a length of 68mm, the extra length being required because the length will ultimately be reduced when the sharp corner of the angle just cut is removed, see drawing. Next place the body in the band saw vice with the angled face against the rear jaw and clamp in place. Do ensure that the jaws are parallel using some packing at the other end, Photo 5 showing that I used a screw threaded into a tee nut making it possible to set the distance accurately. With that done cut off the scrap to produce the 60° angle. However, set the part in the vice such that the surface being cut and the first surface do not quite meet leaving just a little (say 4mm) of the 40mm width still present, as a result leaving some material to be removed when machining to size on the milling machine.
Photo 5. The method of cutting the 60° angle on the body.
Having produced the rough cut blank, place it in the milling machine and surface the cut face indicated as view Z on the drawing. The angle is not critical as any error will be canceled out by the method of boring the holes in the turret. Remove the part from the vice and reposition such that the face just machined is set at right angles to the table surface using an engineers square. With this done, face Y can be machined in a similar manner but this time to a level where it just meets surface Z. Whilst still in position on the milling machine, drill hole D, this will ensure that it is at right angles to the face and, as a result, the shoulder on the Morse taper will seat properly.
For those wishing to make this item but not possessing a milling machine, these operations could easily be carried out on the lathe with the part mounted on the cross slide and using a fly cutter. Whilst, in theory, the part could be held in a four jaw chuck and the surfaces machined, obtaining a secure hold would likely be difficult. The reader may like to look at the following page on my web site that shows an alternative form of four jaw that would certainly make the operation possible. Web site address. http://www.homews.co.uk/page40.html
Mark out for all the required holes, drill and tap as required except for hole B that will be made later, do however, drill hole A right through and only 5.8mm diameter at this stage. Hole C should be at right angles to the face as this will help to ensure the pivot spindle (3) is at right angles, thus allowing the turret (4) to rotate freely. Note the counterbores on holes C and E. That on C permits the spindle to be screwed fully into the hole, whilst that on holes E avoids the necessity to tap a deep hole with a delicate M4 tap.
Regarding hole C this must be placed a distance of 33.5mm from the edge of the 30° angled face, as shown on the drawing, as the 31mm dimension is from an edge, non existent at this stage.
Place a short length of say 16mm diameter steel in the chuck and turn down to 8mm over a length of 12mm and thread M8. Screw the body tightly onto this and then loosen the chuck and slide the assembly in such that the body is supported by the chuck jaws. With the body now in position it can be machined to the 62mm dimension, Photo 6. The part being driven by an M8 stud and the cut being intermittent, the operation should be undertaken with due care.
Photo 6 Machining the body to 62mm diameter
Return the body to the milling machine and create the 12mm wide step on which the spring box (6) will sit. Follow this by finalizing hole B as M8. This is the only area where the design for this project outwardly differs from that seen in the photographs, Originally, hole B was a finer thread but not one commonly available so I changed it to the courser M8, Because of this I felt spanner flats should be included on the spring box and to make this accessible I changed the provision from the recess, seen in photograph 3, to a 12mm wide step.
If you are concerned regarding the appearance of the finished unit then the sides of the body can also be lightly machined, held in the four jaw or in a vice on the milling machine.
Turret Three Way (4)
Cut a blank from a length of 65 mm diameter steel. If you have a cut off saw which can cut squarely, or are skilled with the hand held hack saw, then 27 long will minimize the material wasted, otherwise, a little longer. Place in the chuck, using the reverse jaws, and machine the face, followed by drilling and boring the 12mm diameter hole. This will ensure the hole is at right angles to the face, as it is the face that will bear against the body. Machine also the outer diameter, as far as the chuck jaws will permit, to a little over 62mm, say 62.3mm.
Using the chuck jaws as a reference, assuming a three jaw chuck is being used, scribe a line on the outer face with three lines using a lathe tool, these to assist in positioning the locating holes, accuracy of the 120° spacing though is not important.
Reverse in the chuck and machine the remaining faces with the exception of the angled one, again leaving them a little oversize for final machining at a latter stage. Also machine the 22mm recess at this stage. If your chuck is reasonable accurate then this can be machined to finished size, diameter and depth, otherwise it can be made a little on the small side and finished when finalizing the outer surfaces whilst mounted on a taper stub mandrel.
Pivot Spindle (3)/Washer (2)
At this stage make the pivot spindle (3) and the washer (2). These are quite straight forward, the only critical area being that the 12mm diameter of the pivot must be a very close running fit in the turret, hence the reason it is made from 15mm diameter to allow it to be turned down to size.
Screw the pivot spindle tightly into the body and place the turret over the spindle. Position one of the marks on the turret against some suitable reference point on the body, piece of masking tape with a line maybe, and clamp tightly using the washer and a suitable screw. Place the assembly in a vice, screw head down, and supported with two parallels. At this stage the reason for not machining the angle on the turret can be seen, as had the taper have been machined, then there would have been no surface suitable for resting on the parallels. Again using only a 5.8mm dia. drill, drill through to create the plunger hole in the turret. Rotate the turret to the next marked position and drill the second hole in the turret, then similarly the third. Exact positioning of these holes is not crucial, as any departure from the theoretical 120 degrees will be accommodated in the final boring of the turret. After drilling the third hole do not loosen the screw but ream through both body and turret 6mm diameter. Then loosen the screw and ream the other two holes in the turret, each time though the hole in the body.
Return the turret to the chuck and machine the angled portion as seen in Photo 7, again a little over size. It is intended that the turret should be finished whilst mounted on a taper stub mandrel, and this point may appear the correct time to do this. If however you wish to ensure a reasonable appearance when new, then this will be best left till after other machining operations have been completed.
Photo 7. Machining the angle on the Turret.
This is not fully dimensioned as it will depend on so many factors individual to the situation in which it is being used. Mine is number two Morse taper, but in addition to this consideration, the length must also be sufficient to permit easy operation of the plunger (7/8) without fouling the tailstock or tailstock barrel.
There are many ways of setting the top slide for turning a precision taper and the one making this turret will no doubt has his or her own method. However, for another method to consider the reader may like to study my method of setting the top slide for turning an accurate taper. This, basically uses a simple turned part that enables two diameters to be accurately measured using a micrometer and at a set distance apart making it easy to check if the top slide has been accurately set to the required angle. Using the method I achieve an acceptable fit without any need for checking the result. The method is available on my website at www.homews.co.uk/page47.html
Place a length of steel in the three jaw with sufficient length available to produce the taper plus the parallel portion, centre drill the end and support with the tailstock centre. With the top slide set to produce the smallest end at the tailstock and a boring bar set up as in Photo 8, produce the required taper. Follow this by turning the parallel portion using a left hand knife tool and part off.
Photo 8. Using a boring bar as illustrated avoids the tailstock interfering with the operation of the top slide, depth of cut will though have to be set relatively shallow.
Machine the flat on the parallel portion, being very shallow it can be done with a file or if you prefer, use the milling machine. If your taper has a larger diameter than a 2MT you may need a flat on the top of the taper at the larger diameter end to enable the plunger to be fully operated, this will be evident when you first assemble the turret and can be done then.
Place a short piece of steel in the three jaw face then end and drill and tap M8, countersink to about 10mm to allow the screw to enter fully. Screw in the M8 x 20mm long screw and drill 5mm diameter 13mm deep and then 3.4mm completely through. With that done partially tap the hole using an M4 taper tap, testing the result with an M4 screw that should enter to a depth of about 18mm. Whilst still in the chuck face the head of the screw to improve apperance, also remake the chamfer.
The slot in the screw can be made with a slitting saw in the milling machine or just using a hand saw.
When eventually assembled the screw can be adjusted to eliminate end play and then locked in position by using the grub screw which will expand the screw into the pivot spindle.
This is a straight forward part with just the 6mm diameter being vital as this needs to be a close sliding fit in the body and the turret. Because of this it is turned from 8mm steel allowing it to be reduced to precisely the size required. The length of the M3 thread is also important as it sets the distance that the plunger enters the turret. To achieve this, make the thread on the short side, say 8mm, and measure how much the plunger projects out of the back of the body when assembled, the parallel portion should project by 3mm. From the result it will be possible to determine how much longer the thread needs to be made.
The Washer (2) and the knob(7) need no explanation.
Boring the turret:
With all the parts now made, albeit some still require work on them, the items can be assembled. The next operation is to bore the three holes for the various items that will be fitted to the turret. It would be possible to mount the turret assembly into the tailstock and then drilled with a drill mounted into a chuck in the headstock. However, a better approach would be to bore this whilst mounted in the headstock, as a more precise hole can be produced by this method. Unfortunately though, some lathes have a larger Morse taper in the headstock than the tailstock and the method will only be usable if an adaptor is available.
If you do not have a 12mm hole gauge, place a piece of steel in the three jaw chuck and turn a length of this accurately to 12mm, then reduce the first 4mm to 11.9mm for an early warning that the hole is close to size.
Fit the faceplate to the lathe and fix the complete assembly into the headstock using the Morse taper. The main purpose for fitting the face plate, is to add weights to minimise the out of balance created by the irregular shape of the turret assembly. Having fitted the faceplate however, use it also to add some extra support to the body of the assembly as seen in Photo 9. Just visible at the bottom of the faceplate is one large tee nut added to counteract the out of balance of the turret assembly.
Photo 9 Boring the turret with holes to eventually take the required tooling.
For this operation the plunger should be fully engaged in the body and the central screw tightened fully, then, centre drill and drill hole A in the turret, but a little under size. Next, bore the hole to 12mm precisely, using the hole gauge to check progress.
Having completed the first hole loosen the centre screw disengage the plunger and rotate to the second position. Make the second and third holes by the same approach.
Finalizing the turret:
Remove the assembly from the lathe and dismantle., mark out, drill and tap the remaining three M3 holes. With the main machining of the turret complete make a 12mm taper stub mandrel and mount the turret on this. With the turret in this position, the outside diameter, front face, 22mm bore and the tapered face can all be lightly machined to improve appearance and make the outer diameter match that of the body.
If you are not conversant with taper stub mandrels then the following details how to make and use them.
Set the top slide to an angle of about 0.5° and in a direction that increases the diameter towards the chuck. With a short length of steel in the chuck turn this to 12.3mm over a length of 25mm. Then, reduce the first 15mm to be a very close fit in the central bore of the turret using the saddle to do this. On the final pass, complete the machining over the 25mm using the top slide resulting in the diameter slowly increasing from that point.
Now push the turret firmly onto the mandrel using a turning action resulting in a grip sufficient to permit light machining as mentioned above. Whilst not important in this case the method enables outer diameters to be turned perfectly concentric with the bore. However, once the mandrel is removed from the chuck that level of concentricity will be lost if it is used again but would be usable where concentricity was not a requirement.
Finally clean all parts and reassemble, use a little oil on the plunger assembly and the central spindle. Adjust the central M8 screw for zero end float and lock using the grub screw.
Tools for the Turret:
To make full use of the turret a range of tooling will eventually by required, it is probable though that the most likely use will be that of carrying a centre drill and a twist drill, with in some cases a tap also. I use two chucks that were salvaged from electric drills which had long since been relegated to the scrap yard and made adapters (10) to suit the turret these being seen in photograph 1. If you have to purchase suitable chucks the centre drill could be held in a longer adapter drilled to take the centre drill and tapped with a grub screw to secure the centre drill, in which case, only one chuck would have to be purchased.
To achieve concentricity both threads and the shank outer diameter must be
made without removing the part from the chuck. First turn a short length to gauge the size of the locating recess in the rear of the chuck and when a close fit is obtained measure the diameter and make a note of the value. Now turn down to the required diameter for the thread in the chuck, if you are fortunate enough to possess a suitable die, then produce the thread by this method. More probably you will require to screw cut the thread on the lathe.
Follow this by making the short portion for locating in the rear of the chuck, to the dimension already established, and finally whilst still in the lathe, turn the shank to fit very closely the holes in the turret. It now remains to make the vee shaped recess to take the clamp screw, this can either be made with a file or alternatively on the milling machine.
To hold a tap an additional chuck could be considered, needing the lathe chuck with workpiece to be turned by hand. This though has two largely insurmountable problems. 1. With very small taps there would be insufficient feel of the torque being applied to the tap and breakages would be very likely. 2. In the case of larger taps were breakages would be less of a problem it is unlikely that the chuck would have a sufficient grip and the tap would rotate in it. A simple device will have to be made that allows the tap to be rotated whilst the mounting device is held in the turret.
This brings me to an explanation that was promised at the beginning of the project regarding the size of the tap holder seen in photograph 2. This is a part taken from my tapping stand that features automatic feed equal to the pitch of the thread being cut. Being part of the stand it is larger than necessary when used on the lathe, however its benefits are considerable as it permits threads to be made using just a plug tap that start without any need to provide pressure of the tap on the workpiece. Used in the stand it has the same benefits and is particularly useful when taping thin sheet metal as there are no partial threads at the commencement of the hole as so often happens when using a taper tap.
For details of this stand see my website at www.homews.co.uk/page41.html
A slightly more ambitious use for the turret would be to use it for producing external threads, screws maybe. For this a box tool would be used for reducing the bar to the thread diameter and a die held in an adapter for making the thread. If you are not conversant with box tools then put “box took” or “turret lathe” into your search engine and some examples will come up in the list though they would likely need scaling down for use in this turret.
Four Way Turret:
Having completed the unit, it would now seem probable that the turret’s dimensions are large enough to accept four tools and would be an easy change to the design if chosen to make it this way from the commencement.
If you’d like to leave a comment or ask a question, please visit the forum post linked to this project (via the link below).
Click below to view and download the drawings in PDF format.[download id=”50″] [ad]