SIP coax indicator

[BillTodd]

One of my house-arrest projects has been the fixing up of my newly acquired SIP tilting rotary table and part of this is adding a setting pin/ball to allow the easy alignment of the table and workpiece.

SIP supply the table with a neat coax indicator (regular viewers will know how much I like coax indicators ;-)) . Unfortunately mine has been lost , so I've been looking to design and build one.

The SIP is a clever design : it uses a pin, off-set from the spindle, on an arm, to describe a perpendicular plane. The pin both keeps the rest of the indicator aligned and , with a curve face , pushes on a lever to activate the dial indicator. The lever mechanism has considerable 'gain'  so even the slightest variation from the described plane can be detected.

ATM I'm unsure whether the top centre pivot should be spring loaded (upwards) .

[JHovel]

Hi Bill. That looks interesting. I can't figure out quite how it works though: which bit rotates and which bit stays still? Will any out-of-round condition just wobble the cast body with the lever acting on the gauge?

[BillTodd]

In use the whole thing and the spindle is rotated by hand.just like conventional sweeping with a dti.

 Any offset of the setting ball at the bottom, will move the whole lever assembly out of the reference plane (established by the arm & pin perpendicular to the spindle) and the error is shown on the dial.

[JHovel]

Thanks Bill.

[PekkaNF]

I want to see how this works out. This is very interesting. I am wondering if it needs spring loading anywhere to take up lost movement or is there somewhere some safe flex to keep this solid without crush?

[BillTodd]

I want to see how this works out. This is very interesting. I am wondering if it needs spring loading anywhere to take up lost movement or is there somewhere some safe flex to keep this solid without crush?

This was designed to work with a SIP jig-borer. I suspect its spindle can be lowered to any height without it springing back .

I've designed another, slightly simplified, version with a spring offset in the bottom pivot (the inverted cone) . Thinking about it, I decided the top could not move since it would effect the reading (wouldn't make it inaccurate , just a PITA to use)

I've offset the spring to make sure there is a bias on the bottom pivot so is does not wobble and cause erroneous readings.

This afternoon I roughed out a body in 7071 and, visitors allowing (crisis , what crisis?) , should make more progress this weekend.

[BillTodd]

Body nearly finish (both the indicator's and mine!)

[Sea.dog]

That's coming along nicely. However, I've looked at this post several times and can't understand how the whole lot stays together. There seems to be no positive location of the main body to the spindle in the chuck. From the drawing it seems to float against a centre, defying gravity 

[BillTodd]

It is in three parts:

a centre with arm and pin that  is fixed into the spindle. It is turned manually (spindle  in neutral)
 
A centring ball (in this case fitted to a rotary table, but could be fitted to any feature to be located)

An indicator that ia sandwiched between the two. On the original SIP jig borer the quill would lightly press the parts together, for my knee mill I have had to add a spring between the bottom cone and the body , to keep the indicator pushed up against the locked quill.

[Sea.dog]

Hence your comment about whether or not the centre should be spring loaded 

I did wonder about the ball, but thought that it was a rather elaborate piece for swinging around, gauging the centre from its surface. I had the traditional coaxial indicator firmly lodged in my brain.

[BillTodd]

Getting there...

managed to trip over by band saw and punched something to stop me falling base over apex , took a chuck out of my little finger :-(

[awemawson]

Ouch 

Next thing you know Ade will be asking for pictures 

[PekkaNF]

This looks really interesting. Hardly can wait out how this turns out.

How do you put the pivots on the same axis? Just extreme manufacuring accuracy ot there was a cunning plan? I can get drilling, boring (and maybe reaming) the central hole and then plugging them with very carefully machined "divots"....but is it ever that simple?

[BillTodd]

This looks really interesting. Hardly can wait out how this turns out.

How do you put the pivots on the same axis? Just extreme manufacuring accuracy ot there was a cunning plan? I can get drilling, boring (and maybe reaming) the central hole and then plugging them with very carefully machined "divots"....but is it ever that simple?

The pivot alignment is not actually that important. The only position that puts the lever 's top-flat perpendicular to the spindle axis ( and hence the same reading on the indicator 180 degrees apart ) is when the two pivots are directly inline with each other along the spindle axis. 

So , even if the two pivots are wonky , as long as the lever/indicator can accommodate the necessary offset, there is a position where the lever and indicator will give a consistent reading.

[BillTodd]

After my completely legal and necessary trip over the band-saw - Yes I know i used the lathe while bleeding but I had to check I would be able to make it back to the kitchen for the first aid, before I set out... (does filling in the comments on the tax return form, make me a government advisor??) - I have finished sort of..

Upper centre , Arm and pin made  (I will remake the arm as i ballsed it up while trying to give it some shape)

Setting up was not too difficult , I clamped a parallel in the vice and dropped a spare ball in its countersunk hole. Lowering the centre towards the ball , I found I could centre fairly well using only the reflection on the centre.

To set the position(up/down) of the arm  (to set the position of the lever) I used my 5mm mitutoyu DTI   and centred the travel of the lever while adjusting the arm clamp. Then I centred the XY of the table to get minimum deflection on the dti .

Once roughly centred I could swap to the +/-200um compac DTI and tweak it to zero the XY and then tweak the DTI position to zero it  at 12:00.

Observations:

Once set up it is easy to use and repeatable

It is very sensitive  - seems to have a gain of about 2:1 100um in the dial is less than 50um in the DRO

Jury's out on the sprung bottom cone: it certainly helps setting up but makes the thing sensitive to knocks. I found the whole thing was more stable if I just lightly preloaded the indicator with the quill feed until the spring was squashed.