Rotary Table - another dumb question...

[AdeV]

....how _do_ I set one up on the mill, so I know exactly where the centre of the rotab is in relation to the spindle centre?

I have at my disposal: A regular DTI, a finger type DTI, and a small quantity of patience...

basically, I'd like to know when I'm plumb above the middle of the rotab with the cutter, so when I offset by X, I know i'm now cutting a circle with radius X (assuming the work is also centred on the rotary table).

However, this leads to my next question, along similar lines; I need to cut a curved section out of a piece of work (see the attached "metallic 3D" Crap-o-Cad). I don't (yet) know the radius but I'm hoping it'll fit on the rotary table, let's assume it's 8" & my rotab is 12". What's the easiest way of setting the block up so that it'll cut the desired 8" radius? I'm thinking, once I've got the rotab centered, dial 8" of X-axis offset, and with a centre point tool, locate the block square on the table with the pointer pointing at the line, then simply fettling until it follows the right course. However, whilst that should certainly work for my purposes, it doesn't seem like a terribly accurate way of doing things; Surely there must be a better (more accurate) way?

[Darren]

To centre up the RT put your finger dial in the mills spindle and rotate it around the RT centre hole or fitting if you have one.

Then move the x or y axis by the arc you wish to make radius.

Hope that makes sense?

[AdeV]

Hi Darren,

Yep - I think so - I presume the dial should read the same wherever it's rotated to; I did try that a while back, but got all screwed up trying to work out offsets & other things, 'cos the finger isn't the dead centre.... I have got a central spindle in my rotab which I can use for this purpose. Annoyingly, a 3MT dead centre just drops through the hole, so I can't use it to centre by eye to another point...

Shame, because it strikes me that if you could stick a dead centre in, then have an "inverted point" edge finder (i.e instead of a sticky-outy-point, it had a sticky-inny-point), you could centre a rotary table in a matter of seconds....

Reckon I just found me another project... 

[krv3000]

HI right sos for spelling but dus the mill have digitel reed out ? as described put your finger dti in the mill and clock in the center of the rotary tabel
set the dro to 0 on bothe the X and Y then from the center move the mill tabell out to the desierd radius then reset the dro back to 0 clamp up the work up sqer  ones you have dun that move the mill tabel past your radius  then start cuting moving the mill tabel in till you get the dro reeding 0 hope you can folow that    

[No1_sonuk]

You probably need a spinning-type edge finder. 

[raynerd]

Shame, because it strikes me that if you could stick a dead centre in, then have an "inverted point" edge finder (i.e instead of a sticky-outy-point, it had a sticky-inny-point), you could centre a rotary table in a matter of seconds....

Reckon I just found me another project... 

That is exactly what I have. I use a 2MT soft plank blank - my intention was to use a centre drill but as it happened it already came with a centre hole of correct angle for my centre to match into - I`m guessing from where it has been machined and held in the centre!! I simply pop it in my rotab and put the centre in my spindle. That gets me very near and then I can use a DTI to check

Chris

[AdeV]

hope you can folow that    

Yep, pretty much, ta I do indeed have a DRO - I guess once I've moved the X-axis to my radius, I can use the pointy edge-finder to set the work in the right position, and the finger clock to get it dead nuts straight.

no1-son: Do you mean a co-axial (centring) indicator? If so - yep, I'd love one... they're properly cheap in the US (some less than 40 bucks), but for some reason they're nearly unobtanium over here, and expensive (70 quid, about 100 dollars), and none of the usual suspects (RDG, Chronos, Axminster or Arc Euro) stock them. £70 is a lot to pay considering the minor use it'd get...


Chris - After some thought, it did occur that I was trying to do it "upside down" as it were; it would be better to have a dimple in the exact centre, that a wiggler or standard pointy edge finder could utilise. For whatever reason, my rotab has a straight 1" bore, so I just need a precision 1" bar with a perfectly centred dimple, and it's job done.



Here's another thing.... I've seen various references to using a pin & some blue-tac to find the exact centre of something; but I've never quite worked out how it's supposed to work, exactly. Anyone got a video of the process?

[Bluechip]

Adev

By Mr. Stilldrillin ...

http://madmodder.net/index.php?topic=1116.0

Dave BC

[Lew_Merrick_PE]

Ade (and all),

A test dial indicator (as opposed to a travel dial indicator) is the primary tool.  An indicator extension/holder, most often referred to by the brandname of the original product (Indicol) is more than a little-bit helpful in finding the true center of your rotary table (R/T).  There are several variations on indicator holder/extensions, they merely give you the radius necessary to read the table OD (picking up on the taper of the ID can lead to errors).

Quick Approximate Center:  I purchase the least expensive appropriately size MT center that fits my R/T and anneal it.  I centerdrill it to fit my non-Wiggler-type center-finder.  I drill-and-tap the largest thread size that will not interfere with my center-finder and mill a "vacuum breaker" flat (or slot) down one place along the center and clean-up the edges so it fits nicely in my R/T.  Now I can put the modified center in my R/T and a center-finder in my spindle and rapidly get within a couple of thou just like I can pick up a hole in a part.  The threaded hole & vacuum breaker allows me to remove it from the center taper.  The test indicator and extension/holder are only used to get from "close" to "dead nuts."

Additionally, I make up tooling plates for my R/T's.  These are nicely dressed steel or aluminum plates with (3) index keys in them to fit the slots on my R/T.  Counterbored for SHCS, they allow me to have a surface to add indexes, hold-down bolts, etc. to to locate and clamp the parts to be mounted on my R/T.  They have a reamed hole for a tooling ball at their center (drilled & reamed when zero'ed on the R/T) so I can make set-up's on them when not risking drilling into my R/T surface.  With care (and denoting one slot as the "base of the T index), I an remove and replace them with less than .0005 inch repeatability.

Finally, I keep a set of RH-cut, LH-spiral cutters so that (when possible) cutting forces are "down" into the R/T.  This can save what's left of your sanity.

[Jasonb]

I use an edge finder in the hole. Touch the right hand side of the hole and zero X axis, touch the left side of teh hole and use the 1/2 function on teh x axis. Then repeat for the Y axis. No need to take the dia of teh edge finder into account.

Other option is to turn a bit of bar to a good fit in the 1" hole and at the same lathe setting turn a spigot to say 1/2". Grip the 1/2" spigot in your mill collet, bring the quill down so the 1" end fits into the RT and then bolt the RT down tight and set your DRO to Zero at the same time. You could also tyrn a large conical end if you are not happy about getting a good fit for the 1"

Jason

[No1_sonuk]

no1-son: Do you mean a co-axial (centring) indicator? If so - yep, I'd love one... they're properly cheap in the US (some less than 40 bucks), but for some reason they're nearly unobtanium over here, and expensive (70 quid, about 100 dollars), and none of the usual suspects (RDG, Chronos, Axminster or Arc Euro) stock them. £70 is a lot to pay considering the minor use it'd get...

I mean something like this:
http://www.arceurotrade.co.uk/Catalogue/Measurement/Edge-Finders
http://en.wikipedia.org/wiki/Wiggler_%28tool%29
http://www.metalwebnews.com/howto/edge/edgefind.html

[Ned Ludd]

I think he means one of these;
http://www.machine-dro.co.uk/index.php?target=products&product_id=295
I bought one recently and am somewhat disgusted that they have since dropped their price. It works fine but it does take up a lot of quill to work room.
Ned

[AdeV]

That's exactly what I mean Ned - and even at that discounted price, it's _still_ twice as expensive as an American unit... Mutter grumble don't know they're born humble grumble etc.

No1-son: I have a set of edge finders from Chronos; I did try using them last time I mounted the rotab - but got all confused & gave up in the end...

Anyhow, as it transpired, I didn't put the rotab on the table, because it wouldn't fit! Unless I move the vice.... and since the vice is dialed in at the moment, I didn't want the faff.

[Bogstandard]

Ade,

You really need to find a friend that goes to the US regularly.

Mine just orders the things I want, gets them sent to his destination, and brings them home in his hand baggage for me.

If you come across again, just ask and I will go thru all the setup routines required on the RT. Seeing it done is much easier than trying to read about it.


John

[Lew_Merrick_PE]

That's exactly what I mean Ned - and even at that discounted price, it's _still_ twice as expensive as an American unit...

It's listed at 57L.  At $1.60/L (ballpark right), that's $91.  American stores (as opposed to E-Bay sellers without the investment) sell that brand for $70.  We here in the U.S. have this set-up that allows people to buy and sell products without registering as a business and avoid paying the local (State or City/County) that an actual business pays.  When I, as a business, hire someone to do work for me, I have to pay (on average) 38% of their gross pay in various "employer paid" taxes and fees that someone not registered as a business does not pay.  This is one of the many pressures driving small businesses here in the U.S. into the ground.

[techno ludite]

Hi All

Just adding my 2p worth, when I was machining the pump, what I used to do was put a large diameter rod in the rotary table chuck, line it up with the drill chuck make sure both are nice and tight, and then bolt the table to the cross slide, once done tighten the clamps so not to lose the zero/zero setting. Then remove the rod.

I don't know if this is going to work in your case or with your equipment.

And one other thing make sure the machine is isolated otherwise your gonna get some expensive scrap lying around or a trip to A + E.

TL