How is one supposed to use a rotary table or dividing head?

[Ian PParticipant @ianp]

[Ian PParticipant @ianp]

I need to make several parts like the one shown in the picture and whilst I have used dividing heads many times I'm not sure whet the best or correct technique is to make something other than a conventional ring of holes.

Given a choice (without CNC) would it better to have the X-Y movement on top of a rotating table, or as more conventionally with the RT on the mill table?

I have a Vertex BS-0 which is great for indexing and its what I used to make the item shown, but its not really designed to revolve the job continuously whilst cutting.

I centered the RT to the cutter axis and zeroed the DRO so I could easily cut the outer diameter and stop at the correct point (angles worked out in CAD programme) but whats the best way of then doing the straight cuts?

For the above I initially bored the central hole and then mounted the part using a mandrel in the RT chuck.

Is it best to make a straight cut direct to the start of one section of the OD and once the correct radius is reached, lock the slide and rotate the job cutting to the end of that curved section where the procedure is reversed.

Ian P

[Michael ToppingParticipant @michaeltopping17870]

Ian,

Usually a dividing head is used to position a part for machining. It is not usually used to rotate the job against the cutter. Mounting the part on the rotary table will give a more rigid set up.

I would machine the central hole and then turn a location disc to centralise the part on the rotary table on the mill. Then I would machine the X & Y faces which if you have it drawn in 2d you can get the coordinates for finally machining the radius.

Michael

[JonParticipant @jon]

I do stuff like that all the time in fact two jobs tomorrow a bit more intricate.
Had to do one today 1" thick in 6082 at 30 degree angle meaning flute length in excess of 30mm, easy on.
I do use a Vertex 8" RT with small 5 1/4" Bison drilled and tapped to RT, been in use since 1999 that much use the dividing plate holes are oval.

The only thing I can see with making that is slippage on the mandrel. I would thread something up that would clamp against mandrel downwards. Most of what I do are clamp styles so can clamp cylindrically around the mandrel and at same time mill through excess screw length.

Fine what you have done swing it up so horizontal, the cutter radius will leave those radiuses.
Easiest plunge in leaving material for clean up and rough out in one. Have profiled out 1/2" thick in 6082 with only a 4.5mm long cutter, just feel for whats happening.
Against the cutter take a finishing cut, leaves very little to clean up after for puka finish. Or in the case of that delrin no need to clean up.
Angles best done in straight cuts down to desired depth leaving the profile to cut after. Also confirms your on the right track and can visualise.

[JonParticipant @jon]

Here you go Ian one i did earlier for a chap in Estonia, didn't know I had uploaded this.

Aluminium 6082 thickest and offset around 1", bands probably 3/8" thick leaving 0.72mm to act as a spring. **LINK**/

[Ian PParticipant @ianp]

Jon

The mandrel I made is shouldered and I have a thick washer and central bolt (bore is 50mm)

On your part are you saying you drill and tap the clamp bolt before you machine the external profile?

The single projection from my Delrin part is there so I have a starting face where I am going to drill and tap for an M3 screw which will initially sit in a deep counterbore, I will then return the job to the mill/RT and do the finishing cuts on the outer profile without the cutter contacting the screw.

The reason I have the part on the Vertex is because of its tilting capability, as I can machine the angled faces that are needed on the 'ears'.

I find that its impossible to eliminate all backlash in the Vertex worm and pinion. This part is not too critical and for the only operations that require any precision I can use the indexing pin and holes on the table spindle,

Ian P

[David Clark 13Participant @davidclark13]

Use a mandrel in the centre and a location pin. The pin could be in the waste material (cut that away last) or one of the lugs could be left longer and cut off after. This way you could do a batch of components one operation at a time.

[Ian PParticipant @ianp]

David

I understand your idea, in this case I only have to make three and as my mandrel is held in a 3 jaw on the RT it would not be easy to mount a locating pin. The ends of the lugs will be machined and drilled at an angle so extending them is not ideal.

I'm fortunate, but using a RT on a mill would be a real pain without a DRO on the X and Y axis. At least on can get back to known locations without having to count handwheel turns and account for backlash.

Ian P

[JonParticipant @jon]

Have done a fair few non clamping Ian such as yours.
Mandrel decent fit up to a shoulder and threaded internally. Screw down tight even a boa adequate no lug needed.

Clamp yes drill through, drill, counterbore, thread then saw down.

For the doubters heres the easy one only 6.5mm deep using 5.5mm cutter patterning out. Didn't even use collets just drill chuck now 12 yrs old and Chinese at that.

[Ian PParticipant @ianp]

Posted by Jon on 12/10/2015 22:16:47:

Have done a fair few non clamping Ian such as yours.
Mandrel decent fit up to a shoulder and threaded internally. Screw down tight even a boa adequate no lug needed.

Clamp yes drill through, drill, counterbore, thread then saw down.

For the doubters heres the easy one only 6.5mm deep using 5.5mm cutter patterning out. Didn't even use collets just drill chuck now 12 yrs old and Chinese at that.

Jon

The ones I am making will be slit and have a clamp screw but the screw will be within the outer band radial thickness so no external lugs.

When you do your clamping arrangement prior to machining the external profile do you use long series drills, counterbores and taps, or do you machine material away to make access?

Ian P

[David Clark 13Participant @davidclark13]

Hi Ian You could still use the hole as a location but use a pin in the spindle to line it all up then cut the lug off.

[JonParticipant @jon]

Done them that way as well Ian, grub screw on to mandrel but a bit more likely to move.

All are pinned to mandrel but advise screwing something down on to them over a mandrel.

[Ian PParticipant @ianp]

Posted by Jon on 13/10/2015 20:40:19:

Done them that way as well Ian, grub screw on to mandrel but a bit more likely to move.

All are pinned to mandrel but advise screwing something down on to them over a mandrel.

Jon, what I meant was, what method (very long drill?) to you use to drill and tap for the clamp bolt when the material is still just a rectangular plate. The lugs are still uncut so the point where the bolt will be, is still buried in solid material.

I would not rely on a grub screw to grip the mandrel for machining. The clamp screw on the ones I am making is a normal pinch bolt (on a chord contained within the ring thickness).

Ian P

[JonParticipant @jon]

Just a standard jobber drill but of course depends on diameter and clearance of chuck.
Last one above 30mm bore, from 2 1/4" round parted off. Or flat suitably cut then bored in prior to any fixing locations.

What tend to do is mill one side or both sides of centre, work out the centre point, add some on for strength pulling through plus depth of cap head for counter boring. Split after.
The material surrounding is then around 12mm above bore size, I am aiming to leave .72mm wall running in to the lugs etc using 4.5mm end mill. 6mm just leaves the radiuses to large. Cant emphasise and not publicised much at all, get a feel for whats happening rather than specified speeds and feed rates.

[Ian PParticipant @ianp]

I'm still in the dark as to which of the outer profile surfaces are cut (finish cut say) and in what sequence.

Assuming I'm making a split clamp ring with just one projecting (split) lug fitted with pinch bolt. After setting up, centering etc I use the X axis to finish one face of the lug by moving the part until the cutter reaches the correct radial depth and I then lock that slide and then rotate the part cutting the external diameter (moving the correct number of degrees) until I reach the second side of the lug, so far so good.

Although the cutter is now in the right place to start machining the second face of the lug, the surface of the cut is not coincident with the X or Y axis of the mill, so I'm cornered!

Does on rely on the repeatability of the slides DRO etc to reposition the part so the cut is now lined up with the X axis? My concern is not to leave a small but visible step in the profile that detracts from the parts cosmetic appearance.

Ian P

[JonParticipant @jon]

Right I know what your on about I have the same trouble. Meeting up to another lug.

Cut the lugs in first down to depth offsetting the cutter with Y axis moving Z inwards.
Easier to visualise rotating around up to next lug otherwise calculator needs to come out working out the rotation needed in degrees for that exact operation.
Unless you move X or Y you wont be able to pattern it out in one ie cut right of first lug offsetting Y, down to thickness using X the rotating job will have to deduct cutter dia transferred in to degrees. Assuming worked that out the rotary tables are no where near that accurate so would either end short or over cut.

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