THE standard arrangement for changing tooling on the EMCO FB2 milling machine is a pressed steel spanner locating on two small flats on the end of the spindle. while at the same time using an 8mm Allen key to undo the drawbar, with your third hand you must try and catch whatever it is that you are removing. Not an easy task, the other alternative is to select the lowest gear and use this to stop the spindle rotating. While this is effective what many people do not realize is that it is a Tufnol woven helical gear taking quite a bit of the strain.

Initially, in this design I did try to use the existing spanner on an arm pivoted from the side of the milling head, but it was soon realized that due to the small operating radius some means of parallel linkage would have to be used which was going to add a lot of bulk to the design. I therefore came up with this simple attachment that fits into two existing tapped holes, which once held the guard on the machine. In operation this is easy to use, increasingly I now find I am using this to lock the spindle while removing and inserting drills etc in my keyless drill chuck.

This handy little attachment can in all probability be fitted to the Oriental copies that were marketed. However, those with the Myford spindle nose may need the design to be adapted to fit, having had no experience of these machines I cannot give any precise details. During the design stage a great deal of attention was paid to the swarf that accumulates on the under face of the milling head, to this end the slide ways were intentionally kept protected at all times when not in use and there is plenty of clearance for the slide to miss the accumulated debris. I can only remember having one piece of swarf finding it’s way into the slot in the slider; it is obvious when this happens, as the ball handle does not reach its full range.

The movement of the ball handle is restricted via the die-block abutting the end of the slot in the slider, giving a total movement range of 180°. It was not felt necessary to provide any means of lubricating the slide; as it was thought that oil seepage from the quill and coolant spray would no doubt find their way into the slide. In use now for 15 years this has proved to be the case. It was felt however that a greasing point for the spindle that operates the eccentric would be beneficial and this receives a shot of EP grease about once a year.

The main body is a piece of mild steel there is no reason why aluminium cannot be substituted for this if it is to hand provided it is drawn section it should prove to be more than strong enough, but I would not recommend an aluminium casting. All the forces tending to resist the spindle rotating are taken along the axis of the slide with a small component force acting at an angle to this. There is a good deal of material to be removed from the body and some thought should be given to a sequence of operations otherwise it may prove impossible to recover from, a bit like painting yourself into a corner.

A clearance slot is machined in where the slider goes and this slot is deeper by 0.5mm to make cutting the slideway easier, thereby keeping the cutter off the bottom of the slot. This slot also allows for any damage or distortion that might occur to the end of the slider in use over time not to cause the slider to stop functioning, so it’s purpose is, therefore, twofold. However, in making one operation easier there is a trade off, the die block would have tended to catch on the edges of this relief so it became necessary to face the area around the 20mm bore in order to stop this.

The operation was carried out using a stout HSS internal recessing tool, (width not important), at 26mm diameter for the facing this means it runs into the one slideway. This operation is best carried out before machining the slideways, then that way the burrs from the slideway milling are in the recess formed by the undercutting tool and not the other way about, which would make for a difficult de-burring operation. The facing cut was taken a further 0.5mm deep so as to ensure the accumulated tolerances did not cause binding, the dimension from the upper face of the main body to the 26mm diameter face would then become 27mm the same as the bearing length of the eccentric shaft. A photograph has been included showing the facing cut and the undercut in the slideway produced when carrying out this operation. This facing operation and the 20mm bore are best carried out in the 4-jaw chuck.

To accurately establish the 20mm bore I usually put in a 6mm reamed tooling hole that can be clocked true, it would also be a good idea to put the 4mm cross hole for the dowel and the reamed hole for the greaser in before boring to 20mm. In the case of the cross hole it will ensure that the hole is true and does not wander. The fit of the gauge plate or ground flat stock slider needs to be fairly good not more than 0.05mm, (0.002”), clearance both on the width and on the thickness. This should be the last operation as regards milling if using mild steel due to stresses being released. If the majority of the material has not already been removed prior to this, then these stresses could quite easily distort the slide way sufficiently to cause binding to occur. However, if it is decided to use aluminium then this distortion due to stress release will not be so much of a problem.

The cutter used to machine the slot was a T- slot cutter about 5mm wide, this then allowed some latitude as regards getting the fit right for the thickness of the gauge plate. Again if using the aluminium then I would not advise the omission of the greasing point, it is more important with aluminium than with the mild steel body to avoid ‘picking-up’ of the spindle that works the eccentric. There is a 15mm pocket required in the back or mounting face to clear the hexagon headed bolt that is the key that stops the quill from rotating, it is visible in the photograph that shows the parts for the attachment. The depth of this needs to be monitored as if this is drilled too deep then it will break into the 20mm bore and allow the grease out. It is first drilled with a 12mm drill after centre drilling with an extended centre drill, such that the drill point goes about 4.3mm deep this was then opened out to 15mm using a slot drill to a depth of 4,2mm.

The one M6 cap screw location needs the surrounding material relieved above the counterbore, as the location is half in the block that carries the eccentric and half in fresh air, this is seen in the two photographs showing the locked and unlocked positions of the attachment. This was machined with a 12mm slot drill as the 11mm slot drill for the counterbore does not have sufficient length of cut to machine this all in one go, it might be possible with a long series cutter but obtaining one of these is an additional expense for no real gain.

The slider width can be made a nice sliding fit in the body with no binding, try to achieve the best finish you can on these edge faces. I find a light cut with an offset carbide face mill gives a finish, which is close to a ground finish on gauge plate, a photograph of the technique I use can be found on page 379, of the May 2008 issue of Engineering in Miniature. These edges do need to have a chamfer along each edge to clear any radius left by the tee slot cutter that was used to form the slot in the body, they can be filed on but I consider it looks so much more professional when these are machined on. The slider needs to be left oversize on length to allow for some adjustment to the length when the attachment is finally fitted. This is necessary due to the variation in the dimension from the edge of the mill head to centre line of the spindle, plus any deviations in the across the flats dimension on the end of the spindle.

The rectangular pocket that the die block works in can be produced using co-ordinate milling from the outer end, leaving the excess length on the inner end. It will be found easier if the four corner holes are drilled 2.8mm and the bulk of the material in the pocket removed by drilling two 7mm diameter holes at 8mm centres, i.e. 4mm either side of the longitudinal centre line of the slider. If the sizes of the slot are kept as near to nominal as possible then any fitting required can be done to the die block.

If, for instance, the ball handle does not lie parallel to the milling head when in the locked or unlocked positions then material can either be removed from the end of the slot or better still from one face of the die block. The beauty of removing material from the die block is, that if a mistake is made and too much is removed form the die block face, then another bite at the cherry can be had by turning the die block through 180° and trying again. Furthermore, the die block is the more likely candidate to wear out first thereby allowing the slider to remain as drawn and the new die block fitted as before. If the die block is altered then a light centre dot adjacent the modified face will save much frustration later, on final assembly.

The shaft carrying the eccentric was made from silver steel, which wears well with the mild steel body. If, however, the body has been made out of aluminium then this shaft could well benefit to be made out of mild steel, if only from the point of view of easier machining, but generally I have found these two materials work well together.

The spigot on the end that carries the ball handle was turned and the undercut 4.2mm wide machined using a 2mm wide parting tool, this does not need to be a tight fit on the cross dowel, a small chamfer on each corner will remove any burrs thrown up by the parting tool, but be sure to achieve full depth on the undercut, thus avoiding the cross dowel fouling the bottom of the undercut. The shaft was then parted off minus the eccentric portion; I find it far easier to fit a separate shaft than to spend ages turning this out of the solid.

After facing the end to length the shaft is held in the machine vice vertically with the aid of a V-block against the moving jaw and the 20mm diameter against the fixed jaw, the 6mm reamed hole is put in using coordinate location to not more than 10mm deep to the point of the drill, a small chamfer around the hole will help stop Loctite from migrating to the die block on assembly.

It will be noticed from the drawing that there is a relationship between the eccentric and the 5mm diameter cross hole for the ball handle. If the part is again gripped in the machine vice such that a 7mm slip gauge or packing piece to this dimension is introduced between the 6mm shaft and the parallel that the part is resting on this then will automatically align the shaft to the correct orientation to drill and ream the 5mm hole for the ball handle. The shaft is then returned to the lathe so that the M4 tapped hole that grips the ball handle can be machined. The 6mm eccentric portion is best made out of silver steel in all instances and can be assembled with Loctite 603, and it is easier to position the shaft if the die block and circlip are on the shaft, but be sure to introduce some grease into the 6mm hole in the die block as a second line of defence to stop the Loctite migrating into this part.

The die block was made from mild steel it has shown no signs of wear in the past 15 years but this could quite easily be changed to phosphor bronze if preferred. It is a straightforward piece to machine and reference has already been made to easing one of the faces on assembly to get the correct movement if it is required.

The ball handle is a piece of 5mm silver steel, the ball that I used came from Emco, it is used on the Unimat 3 drilling attachment, part number ZGF 19 2005 and it is threaded internally, so an M5 thread was formed on the end of the silver steel to suit. Some small balls available commercially come with a plain hole these generally are just a push fit, and some of these commercial balls come with a smaller thread M4, but there is no reason why a ball cannot be machined out of a piece of black Delrin. One can usually get away with a tool machined from mild steel, or gauge plate left soft, when making plastic parts provided the speed is kept down and there are only one or two parts to make. A small flat 4.5mm wide can be machined 0,5mm deep 9.5mm from slot centre line to the end of the bar if desired to allow for the M4 grub screw to impinge on, at this dimension it does mean a small portion of the shaft protrudes through the boss, which I preferred to the end being flush with the boss.

Assembly of the parts is pretty straightforward; the slide does need to go in the main body first before fitting the eccentric shaft. Initial lubrication with something like Castrol BD68 or similar would be an advantage. Once assembled it is then possible to assess how much needs to be removed from the end of the slider. If the block is loosely attached to the machine and the quill flats orientated to align with the end of the slider, using the ball handle move the slide to the locked position, if the ball handle does not reach it’s full travel slacken off the M6 cap screws a little further. If the ball handle has reached its full travel but is loose then tighten these screws evenly but not excessively. Using feeler gauges assess the gap; between the mounting face and the milling head, try to aim for a parallel gap in order to get a true indication of what needs to come off.

Dismantle the attachment and machine off the end of the slider by the amount measured. It would pay to rig up some form of stop for the work in the vice just in case there is a need to take further light cuts, as I found that the two flats on the end of my quill were not symmetrical about the centre line, and it is Sod’s Law that you will pick the flat nearest the centre line. Re-assemble the attachment and see if the attachment works as intended or needs further adjustments. A salvage scheme or enhancement can be brought into play if the slide has had too much machined off, I have attached a drawing should it be needed, it may be thought however that this enhancement should be fitted as standard, and can be included by the constructor if preferred. The introduction of a hardened pad on the end of the slide held on by an M2 cap screw and two 1.5mm dowels will overcome the undersize slider problem.


MILLING SPINDLE LOCK
by
Graham Meek

Something of the order of 6mm square would seem about right, but the length and thickness would benefit from being 0.4mm undersize, as this will ensure the hardened pad does not baulk on the slideways during use. It would be best if the M2 cap screw is counterbored, a countersunk screw I feel is not appropriate in this instance and finally it would be best assembled with a thread locking compound, the two dowels could do to be fixed into the pad with Loctite, but left free to go into the slide, this will permit dismantling should it ever be required. Of course this salvage scheme can always be applied at a later date should the slider show excessive wear, judging by the condition of my own I think it I have reached this stage. I would not advise attaching the pad with two cap screws, as the counterbores will probably come exactly where the quill spindle flat wants to impinge on the pad. However, if all went well and there was no need to apply the salvage scheme it would be wise to put a drop of Loctite on the 4mm cross dowel and at the same time just work a shot of grease into the greaser just to make sure the Loctite does not migrate onto the eccentric shaft.

Position of ball handle when unlocked

Ball handle shown in locked position

Slide engaging flat - spindle is locked

Spotface showing undercut in slideway

The main parts - note relief slot for slide