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| Rotary Table - another dumb question... |
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| raynerd:
--- Quote from: AdeV on September 23, 2010, 09:12:40 AM ---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... :proj: --- End quote --- 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:
--- Quote from: krv3000 on September 23, 2010, 09:14:16 AM ---hope you can folow that :D --- End quote --- 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 |
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