by Harold Hall
Material: Cast Iron
The more usual form of rotary table comprises a round table rotated manually via a worm and wormwheel. For many though, making this type would be too involved, a situation that the table described here seeks to overcome (Photo 1)
In simple terms, the worm/wormwheel drive is omitted and the table rotated directly using an extended handle. The main disadvantage of this is that control of the table position is much less precise. To overcome this, I have included two features that are not to be found on a conventional table, at least in the smaller sizes.
- The inclusion of a stop mechanism will enable, when set, for the table to be repeatedly stopped at the same position. This avoiding the need to closely follow the movement visually and attempting to stop at the same position on each pass. Typically, this will be beneficial if attempting to machine a 180° curve on the end of an arm. Similarly, machining a closed end curved slot (Photo 2).
- Twenty Four holes are drilled around the edge of the table to achieve divisions of 2, 3, 4, 6, 8, 12 and 24 (Photo 3).
A feature that needs consideration at this stage is the size of the tee slots. I have chosen the sizes shown on the drawing as these can be made with a 16mm x 4mm (5/8” x 5/32”) woodruff cutter. The one making the table may though like to standardise on some other size which is being used in the workshop, in this case, the 30mm height may need changing. Also, if you’re rotary table requires larger tee slots, having only four rather than six slots might be appropriate.
Another consideration is whether the table should be divided into 360° divisions, or more likely, 180 x 2° divisions, but as I suspect those interested in making this will not have the provision for making 360/180 divisions I have not included it. However, should this be possible for some who would like the provision, there is space below the vee slot for this to be done.
It is likely that you may need to make some thinner table clamps so that the stop assembly seen in photograph 2 can pass over them, the alternative would be to make a larger base, say 150mm x 125mm.
These choices must of course be made before manufacture commences. Also, perhaps the 24 holes for dividing purposes could be omitted to simplify the construction. In any case, this is a feature that can easily be added at a later date. However, I have used the 24 holes to position the tee slots and the holes for the handles, but if omitted, the method used for positioning the 24 holes could be adopted for placing the tee slots and handle holes.
Step 1: Turning the Table (item 2 from plans)
Take your piece of cast iron bar, which should be a little greater than the 30mm quoted, and drill and tap the two M8 holes as shown. These are for securing the material to the faceplate so first check that the dimensions will suit the faceplate you will be using.
Secure the material to the faceplate and set to run approximately central, but precision is not required as the process is only to face the outer surface. However, placing something as heavy as this, even approximately, can be a problem and using faceplate dogs as seen in Photo 4 would make the requirement very much easier to achieve. The photograph is though of an aborted operation due to a slight change to the design and has no connection with the methods I am describing here.
With the surface faced, return the tool to the centre of the table and advance it a further 0.05mm and face the surface once more but this time stopping about 20mm from the outer diameter. This ensures that in the final assembly that the table will only contact the base around the outer edge helping it to sit more accurately. Remove, turn over, and refit.
From this point, to achieve concentricity between bores, the table must not be removed from the faceplate until all the main turning operations have been completed. This time, pack the table from the faceplate using a piece of hard card, also setting the material to run sufficiently true to permit it to be machined to the 120mm diameter.
First, machine the outer face to the 30mm dimension. Next, make the 10, 16 and 30mm bores, but whilst these need to be a close fit on the mating parts, these parts will be turned to a close fit when made, diameter of the bores is not therefore critical (Photo 5).
Then, set your saddle stop so the tool being used just contacts the card, but not the faceplate, and machine the outer diameter to 120mm (Photo 6). Also, produce a very small chamfer on the outer corner, say 0.5mm wide.
I have not included centralising circles on the drawings, but if you feel these would be advantageous to you then now is the time to produce them. I would suggest spaced at 8mm increments. These could be seen in photograph 1.
Using a parting tool, or similar, make a 6mm wide by 6mm deep groove round the periphery ready for finalising as a vee slot (Photo 7).
To make the vee form the most obvious method would be to used left and right hand knife tools. However, they would have to be narrow to get into the 6mm wide slot so for most an alternative method must be found. As cast iron machines very easily, once the surface skin has been removed, the shape of the tool is not that critical. I therefore used a parting/grooving tool (Photo 8).
This was first set at 20° one way, and then 20° the other (Photo 9), then using it just as one would if a knife tool were being used (Photo 10), the angle is of course not critical. This did make recesses in the base of the vee slot but is of no importance.
Step 2: Machining the Component Carrier (item 8 from plans)
My preferred method for machining this is to mount the available length of steel in the three jaw and support the outer end using a fixed steady with just sufficient projecting for machining and parting off the component. The alternative would be to mount a shorter length in the chuck, but with this method you will be left with a short stub which may not find a use. Otherwise, the process is the same.
Turn the outer diameter to a close but free fit in the table bore, and then make the 12mm bore, again this diameter is not critical as the mating parts will be made to fit. However, having machined the outer diameter and bore at the same time concentricity is assured, this being essential. Finally, for the turning process, set the top slide to 10° and make the tapered bore (Photo 11). Part off at 11.5mm in length.
If you are uncertain regarding making and using such a small boring tool look here and here. Whilst the 7mm diameter is not critical do try not to make it oversize. Leave the top slide at the 10° setting for a later task.
If you are using a fixed steady to support the material as suggested above, then this would be a good time to make the rotary table positioning bush 7 whilst still set up and using the same size material. This is though detailed later.
Next secure the part in the three jaw using the reverse jaws so that one step can support the part and face the parted off face, but still leaving the part over size, say 11.2mm. It is though possible, depending on the size of the chuck, that the chuck will not secure a part that is just 30mm diameter. In this case, one possibility is to do as I did and used some soft jaws in the chuck (Photo 12). The alternative is to use the standard jaws in the chuck and use a piece of packing between one jaw and a pair of jaws to support the part. DO remove packing prior to switching on. The aim is to get both faces of the part parallel though precision is not necessary.
Next, fit a guided centre punch(see Sk4 here) to the top slide and set it to mark out the three holes on the 21mm PCD. To set the 120° divisions, place a suitable length screw into a tee nut and these between one of the chucks jaws and the lathe bed. Adjust the screw in the tee nut such that the jaw is level, visually will be adequate. Then, using the centre punch mark out the position of the first hole. Repeat, using jaws two and three (Photo 13). Remove from the chuck, centre punch the marks made, and at this stage drill tapping size holes for M3.
Step 3: Workpiece securing nuts (item 13 from plans)
More than one will require making to suit a range of workpiece sizes, as obviously, larger parts are likely to benefit from a larger clamping screw. Therefore, with the topslide still set at 10° now is the time to make these with a range of thread sizes, I am suggesting M3, M4, M5 and M6. Manufacture is straight forward and needs no explanation.
Step 4: Rotary Table Positioning Bush (item 7 from plans)
See my comments above regarding using a fixed steady for the component carrier. Turn the outer diameter to achieve a close sliding fit in the bore in the table, then, using a largish centre drill produce a centre of about 8mm diameter. This sequence will ensure the centre is concentric with the outer diameter, which is essential.
Drill and tap M4 as shown. Its purpose being to enable a screw to be fitted which can then be used to lift the bush out after the table has been positioned. Part off at a little over 11mm. Leave at this length at this stage.
Step 5: Workpiece Locator (item 14 from plans)
These will have to be made to suit the workpiece bores so can only be made as a need surfaces, the following is though the method to adopt.
Turn the outer diameter to a close sliding fit in the bore in the component carrier and diameter Z a close fit in the workpiece bore. Concentricity is normally important so these must be turned whilst still in the chuck. Part off, reverse in the chuck and face the parted off end. Length is not critical as at 3.5mm it is shorter than the depth of the bore in which it goes. Occasionally, though, diameter Z may have to be the larger, method of manufacture will be essentially the same.
Step 6: Handle (item 6 from plans)
I would suggest that you initially make this 400mm long but you may, with experience gained, and the type of work being undertaken, decide that a shorter handle would be satisfactory. Of course you may chose to have two lengths using them as the type of work differs.
Step 7: Stop screw (item 3 from plans)
Fix a scrap of steel in the three jaw, face the end, drill 5mm diameter by 2mm deep then drill and tap M4. Fit the M4 hex head screw and produce a dome as shown on the drawing. I have not quoted a value for the radius as it is not important but it does need to be sufficient so that it locates on the dome rather than the edge of the screw. See assembly drawing.
Step 8: Table Spindle (item 9 from plans)
Again you can use the fixed steady if you do not have a short length of 25mm diameter available. This is a simple turning task with only the 10mm diameter being important. First drill and tap M4 hole, followed by turning the 10mm diameter, which should be a close running fit in the table, even slightly stiff would not be a problem. Also at this stage, make it a little longer, say 16mm. Skim the outer diameter so that it is concentric with the 10mm diameter, part off, but again with the 25mm diameter also longer to allow for facing at the next stage.
Place the part in the three jaw holding it on the 10mm diameter and face the available end. Do protect the 10mm diameter with a piece of thin copper, or similar, wrapped around it. Mark out the positions for the three holes using the method suggested above for the component carrier, DO though only drill tapping size holes for an M3 thread.
Step 9: Detent (item 11 from plans)
I have placed this here so that all the main turning operations are listed together. However, it cannot be made until the stop post is made as the 4mm diameter has to be made a close sliding fit in the 4mm hole in the post. Otherwise, turning the part is straight forward and needs no explanation.
Step 10: Plug (item 9 from plans)
Again, this is a simple part and needs no further comment.
With the turning operations now largely completed the milling and other operations can commence.
Step 11: Base (item 1 from plans)
It is essential that the material being used is adequately flat, testing with a straight edge should though be sufficient. If distorted, then the only option for most will be to acquire another piece of steel. The reason for this is that machining the complete surface will relieve internal stresses and maybe causing the part to distort even more. If you have access to a surface grinder then lightly surfacing the piece would be possible and worth doing even if the material looks sufficiently flat.
Other than machining to 125mm square, drilling the two 9mm holes and making the two M4 tapped holes, at this stage only drill an 8mm hole in the centre. Do note that the two 9mm holes have to line up with the M8 holes in the table. If therefore you chose to reposition these to suit your faceplate this must also be done for the 9mm holes.
Stop Post (item 11 from plans)
This is an interesting little component to make but needs no comment other than to say it has to be made before the next operations, as it is needed to complete them. Also make the Detent (12) making it a close fit in the 4mm hole in the Stop Post
Step 12: Table 2 / Component Carrier (item 8), continued …
There remains three main operations to carry out on the table and a few minor ones. The three main ones being, drilling the 24 holes for indexing, drilling the 3 holes for the alternative handle positions and machining the 6 tee slots. All these require the table to be divided into angles of rotation, being, 3, 6 and 24 divisions. With both 3 and 6 being divisible into 24, the 24 divisions will meet all three requirements.
The next stage is therefore to establish the 24 positions for the indexing holes, with the proposed method assuming that a dividing head is not available. Even if one is available the method is probably still the best.
A strip of ordinary white paper will suffice, but using self adhesive paper as used to make large labels, etc. when using a computer printer will be better. Even here, an A4 sheet will not be long enough and two pieces will have to be joined. To do this, first cut 2 pieces, 15mm wide, across the width (210mm) and join as follows. Peel the release paper back about 30 mm on one piece and using the exposed adhesive area join the two together. As it is unlikely that the two pieces will be perfectly in line, trim one edge using a straight edge and sharp knife and then the second edge to provide a 10mm wide strip.
With the release paper still on the strip wrap the strip tightly around the table and cut through both where they overlap. You will now have a strip equal in length to the circumference of the table which will require dividing into 24 equal divisions. As the spacing will require to be 15.708mm (Pi x 120/24) it is not something that can be done with a ruler.
The method to use is one that you were probably taught at school in your geometry lessons. Fix the strip onto a large sheet of hard board, or similar, or even the bench top, and from the left hand end of the strip place a rule at an angle to it
With that done, and using a draughtsman’s square placed against it, set the angle of the rule to the strip of paper so that the square when at 360mm also lines up with the other end of the strip of paper. Secure the rule using adhesive tape. Now, step the square along the rule in 15mm steps marking the strip at the corresponding point. Your strip of paper will now have 24 equal divisions (Photo 14).
Of course there will be some minor errors along the length but with the spacing being 15 +mm any errors will be proportionally small and the result more than adequate for its purpose here.
Remove all the release paper and fix the strip around the bottom half of the table. A short piece of transparent adhesive tape across the joint would also be worth adding for additional security. DO CHECK that you have got 24 divisions.
Making the 24 holes At this stage we need to make a temporary spindle for the table. Using a length of 12mm diameter steel, place this in the three jaw and turn the outer diameter to a close fit in the table bore and over a length of 18mm. Do face the end to ensure that it is true to the outer diameter and drill and tap M8 to a depth of 20mm, part off to a length of 18mm. As the thread does not require a lot of holding strength I would suggest a largish tapping size hole of 7.2mm to ease the tapping process.
Fit this spindle to the Base, faced end against the base, using a 16mm long screw. This ensuring that there is at least 10mm of free thread to be accessed from the other end.
Put the table onto the spindle and place a length of M8 studding fully into the tapped hole in the temporary spindle. At this stage the table can still be rotated but to prevent this place a plate over the M8 stud and with a nut tightened onto this making the table captive. Also now add the stop post.
With that done, using a vice on the drilling machine as seen in Photo 15, set an edge of the base at 45° to the worktable. Next, align a 4mm drill with the hole in the stop post and secure the assembly to the worktable.
The photograph shows that I have the luxury of an XY table on my drilling machine, but as the assembly has only to be positioned once adding it to a normal drilling machine table should be no problem
However, before drilling can commence it is essential that one of the holes about to be drilled is in line with one of the M8 holes that have been used previously to secure the table to the faceplate. The easy way of achieving this is to loosen the table and rotate it until one of the holes is at the top, as is also the stop post. This ensures that the first hole will be in line with the M8 hole, and eventually therefore in line with a tee slot being made. Drill the first hole 7mm deep.
Whilst still at the first hole it is essential to add some form of fiducial line so that it lines up with one of the division marks on the table. The photograph shows that I used a piece of adhesive paper, suitably marked, on the base and against the table. It will now be possible to index the table round for the remaining 23 holes. The photograph does show though that I added the fiducial line before setting the M8 hole to the top, no doubt I had to remove and reposition it once I had.
With all 24 holes now drilled the paper strip can be removed as the tables own inbuilt divisions can be used for positioning the handle holes and the tee slots.
Making the handle holes now, with the assembly still in the vice, rotate the table such that the axis between the two M8 holes is horizontal and engage the detent, also re-clamping the table. Move the assembly so that you are now in a position to drill the hole for the handle and once more secure the assembly to the drilling machine table. Centre drill, drill 8mm to a total depth of 20mm, move through 8 holes and repeat and repeat again for the third hole.
Making the tee slots. Next, transfer the assembly to the milling machine table setting one of the edges of the base at right angles to the tables movement, secure the base but still leaving the table free to rotate. With the rotary table positioning bush in the table, centralise the table below the machine spindle using a centre in the machine spindle as shown in Photo 16 and lock both the X and Y axis table movements.
Set the rotary table with the 2 M8 holes in line with milling machine axis and engage the detent. Do not though rely on the detent to secure the table but add an overhead clamp as was shown in photograph 16. Now, free the X axis (left-right) and using a 10mm slot drill, machine the centre section of the first tee slot. Do this to a depth of just under 10mm so that the tee slot cutter will, when eventually used, fully machine the width. Of course, you will need to step the cutter down producing the groove in stages. Set the table stop to fix its length, thereby ensuring that all six grooves can easily be made without the need for further measuring.
With the first groove complete release the table, remove the detent, move the table through four holes, refit the detent and secure the table once more and machine the second groove. Repeat for the remaining tee slots.
However, it would be a good idea first to move the table through four holes, mark the table, move through a further four holes, mark the table and repeating for all six slots. By doing this you will be sure that you are not doing anything wrong when counting the holes.
There is now an additional task required by the two slots having the M8 tapped holes in them. Take the plugs and distort the first two threads at the slotted end using a centre punch into the thread’s groove, doing it at a couple of places around the circumference. The purpose of this is to make them become tight as they are screwed into place. With the plug screwed firmly home the 10mm cutter can be passed through again at the same setting to level off the screw with the remainder of the slot. Do ensure that the plug is very firm in its thread and that only a small amount has to be removed, say 0.2mm. Take it steady machining it as the rotation of the cutter will be attempting to unscrew the plug. The purpose of the plug is to stop swarf entering the hole which would be difficult to remove and could effect the rotation of the table when in use.
Replace the end mill with a tee slot cutter and finally machine each slot, still using the same table stop position to set their lengths. Photo 17. If you do not have a suitable tee slot cutter then making one is not difficult for machining cast iron, which machines easily. For details see here.
Whilst in milling mood set the table upright on an angle plate and machine the 12mm entry into the vee slot for fitting the vee nuts. Whilst it is shown on the opposite face to one of the handle holes its position is of no importance.
Step 13: Component Carrier (item 8), continued …
With the table removed from the milling machine, place the component carrier in the table bore and secure with an M6 screw, washers and nut through both carrier and table, then transfer the tapping size holes to the table. Remove, tap the table M3 and drill and counterbore the carrier, return the carrier to the table securing it with cap head screws.
Using the M8 fixings again, fit the assembly onto the lathe’s faceplate and centralise it with the tailstock centre located in the 7mm bore. Then, lightly resurface both the table and carrier so that the carrier surface is level with the table, remove and dismantle.
Step 14: Rotary Table Positioning Bush (item 7), continued …
Having machined the component carrier you can now measure its thickness and replicate this on the positioning bush. Using the three jaw fitted with its reverse jaws would give a step onto which in can be placed, alternatively using soft jaws suitable machined.
Step 15: Base (item 1), continued …
Place the base onto the lathe’s faceplate and centralise it using the tailstock centre in the 8mm hole and secure in place with screws through the two 9mm holes. Now, make the 10mm bore and the 25mm counterbore (Photo 18). Do make the 10mm bore a close fit on the table spindle else the table locking screw will be able to move the table sideways. A light push fit would be even better.
Remove from the faceplate and place the table spindle in the base and secure in place. Typically, do this with a short length of tube over the 10mm diameter and with a large washer secure using an M4 screw in the tapped hole in the end of the spindle. Transfer the M3 tapping size holes in the spindle into the base and tap the base M3.
Step 16: Table Spindle (item 13), continued …
Open up the three holes, counterbore and fit to the base using three M3 cap screw. Take a piece of paper, about 125mm square, and roughly cut 3 holes to take the spindle and allow screws to pass through the two 9mm holes. Place this, then the table, over the spindle and the tables positioning bush in the tables bore.
Place the assembly onto the lathe’s faceplate, centralising it using the tailstock centre and secure using fixings into the two tapped holes in the table. As the depth of the tapped hole is now restricted by the plug that has been added, use a stud with nut and washer rather than a screw which may contact the plug before the table is fully secure.
Having removed the positioning bush, and with an end cutting boring tool in the lathe, machine the end of the spindle and the end face of the 16mm bore so that they are both at the same level (Photo 19). This will ensure that when the paper is removed the table will be able to run freely. A thickness of 0.1mm would be ideal for the paper used.
Step 17: Stop Screw Carrier (item 4 from plans)
We now have a chance to put the table to use and almost certainly with one of the most demanding tasks you are likely to use it for, but first of course, it has be be assembled. This is straight forward but if you think the table can lift too much then the table spindle can be reduced in height a very little. Otherwise, there is little that may need attention other than to add a little lubrication in the obvious places.
First, a locating plate for the carriers has to be made. Take a piece of scrap, size relatively unimportant, but would say 120mm by 35mm, and 8mm thick. The three dimensions being minimum.
Mark out a position for a centre drilled hole, 8mm from the right hand long side and 8mm from the end and drill using a centre drill. Fit the table positioning bush and with a centre in the machine’s spindle, align the table with it and secure the table to the machine’s table. Lock both the X and Y traverses. Now similarly position the locating plate just made and secure to the table (Photo 20).
The piece of 20 x 12mm material to make the stop screw carriers, seen bottom left of the photograph, needs to be at least 80mm long.
Fix a toolmakers clamp to the left hand side of the locating plate such that when the material for the part being made is placed against it the right hand side is level with the right hand side of the locating plate. The toolmakers clamp will take much of the force eventually developed by the cutting action and must therefore be correctly tightened. That is, that it cannot be pivoted about either clamp’s tip or adjacent to the central screw. This is absolutely essential when used on the milling machine and if the viewer has any doubts regarding the requirement see my web site here were it is fully explained.
Now place the material for the workpiece against the toolmaker’s clamp and position it such that the end just overlaps the edge of the table by about 3mm and secure using two toolmakers clamps, again do ensure that they are correctly closed. Photo 21, I think, adequately illustrates the set up.
If you do not have sufficient clamps the first could be replaced with a fence, secured using tapped holes in the locating plate and screws through clearance holes in the fence.
At last the table can now be put through its paces. Not having used a rotary table in this way before I have to confess I started the machining with a degree of apprehension. Despite this, I still started by attempting to remove too much at one pass, though a longer handle would probably have improved the situation.
Eventually, I worked on the basis of lowering the cutter by 0.5mm at a time and this worked fine. However, on the first cut the width must be gradually widened until the curve is complete across the 20mm width. At this stage the curve should be just inside the tables periphery such that it has a very marginally smaller radius than the table itself. This ensures than when placed against the table it contacts it at the edges of the part rather than centrally when it may rock.
With the radius fully across the width, and a little less than tables radius, the curve can be completed by stepping the cutter down by 0.5mm at each pass (Photo 22). DO take note that it is vitally important that the direction of rotation of the table is opposing that of the cutter.
Eventually though, when almost fully down, I increased the width by about 0.03mm and moved the cutter backwards and forwards a few times. Apart from removing the bur on the top edge (Photo 23) shows the part just as it came off the machine and that is was a very acceptable result.
Cut off at just over 13mm and repeat the operations for the second part. Machine the sawn face and drill and tap as per the drawing and the parts are complete. For me this was a stern test for the table which it completed with flying colours proving therefore that it will quite easily cope with the simpler tasks that it will most often be called upon to undertake.
Step 18: Vee Nuts (item 5 from plans)
If you have a tilting vice, or angle plate, then this is obviously the method to use, machining sufficient for two and splitting them afterwards. If these are not available then they could be filed to shape as dimensions, angles, etc. are not critical. The tapped holes should be made, both before making the angles and splitting.
Add the various parts that make up the stop mechanism and test to see that all’s well, making any adjustments that are seen to be necessary.
With that done, dismantle and tidy up all the parts, debur, lightly chamfer edges, etc. and the the table can be finally assembled. Photo 24 shows the complete set of parts.
However, just one further thing worth considering. About 10mm in from the tables edge on the underside, drill four holes 6mm diameter and 6mm deep, approximately equally spaced on a PCD. On assembly, these can be filled with oil to act as a reservoir.For the copper pad, H1, take two or three strands, about 40mm long, from a piece of flexible electrical cable and roll into a ball. Its purpose is to make the stop screw slightly stiff to turn but not too loose so that its position can change due to the vibration of the machine.
With the table now finished it seemed appropriate to make a link with radiused ends, being typical of the tasks it is likely to be called upon to perform. This can be seen in Photo 25.
A workpiece locator was made to suit the 6mm hole in the link and the link secured using an M5 screw. For a single end this would have been, I think, sufficiently secure but the photograph shows that I added a post to resist the link turning as a result of the machining being done. However, this was not its main purpose, this was, so that the link could be set in exactly the same position for the second end, as a result, ensuring that the stops that had been set for the first end needed no alteration.
In conclusion, I was very pleased with the end result with it performing better than I could have hoped and can see me using it in preference to my more usual tables for many applications. The inbuilt workpiece locator is a very definite plus.
Harold Hall (about the author)
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