Convert 4-jaw to front-mount?

[hopefuldave]

I'd like to put a 4-jaw independent chuck (an Ebay cheapo, threaded holes in the back) on my Vertex rotary table (about the same size as the chuck...) - but to keep it low-ish profile, I don't want to put it on a Morse taper adaptor and threaded backplate - is there any reason I shouldn't clamp it upside-down to the rotary table (using its jaws...), drill holes at 90-degree intervals and then flip it over and counterbore the front face, then just bolt through into T-nuts? I appreciate that I'd have to indicate it in when attaching it to the rotary (or make up a Morse taper stub to fit the chuck bore), but I'd be indicating the work in anyway!

It would be use-on-the-rotary only, so worries about balance and centrifugal force Vs strength disappear...

Dave H. (the other one)

[DICKEYBIRD]

Hey Dave, I had a similar issue a few years ago and copied Sir John's method which worked well.  It has 4 holes drilled around the perimeter of the existing chuck adapter and some clever T-bolts/screws he came up with.  Here's a link with some pics.

http://bbs.homeshopmachinist.net/threads/24344-Mounting-a-160mm-chuck-on-a-150-mm-rotary-table?highlight=ROTARY+TABLE

[hopefuldave]

Thanks, Dickey,

Sir John's does need a backplate though, which is something I was hoping to avoid - ideally I'd add a D1-5 camlock nose to the rotary so I could pop the chucks / faceplates straight on from the lathe, but I'd lose a bit too much headroom with that and a D1-5 backplate! D1-5 backplates seem as rare as rocking horse droppings, too, and I only have a couple left which I want to save for the lathe...

If I were to turn the chuck "upside down" and centre it on the table and then crank and rotate through 90* a few times, I should be able to spot and drill the four through-holes pretty accurately, at least on the back... hopefully they wouldn't wander too much before they emerged on the front (visible) face!

So... any *structural* reasons not to drill the chuck?

Dave H. (the other one)

[andyf]

I suppose you could use John S's method, but drill/tap the chuck itself, rather than a backplate, for the clamping screws.

But in principle, there's no reason why you shouldn't drill though the chuck so you can pass bolts through into T-nuts. After all, the body of an independent 4-jaw is essentially a big lump of iron, and as long as you space the holes evenly between jaw slots, there are no internal mechanisms to damage.

You might need to consider how in practice you are going to line up the T-nuts so their threaded holes are in the right places for the bolts to drop into them ready for screwing home. Not too difficult, if things are arranged so that when the outer edges of the T-nuts are flush with the outside of the rotab, and the chuck is more or less centred on the rotab, the holes in the T-nuts are in the right places to receive the bolts. Chamfers in the T-nuts would help the bolts find their way in.

Andy

[sshire]

Here's what I have on my rotary table. Easy on and off. Nicely made.

http://www.grizzly.com/products/3-1-4-4-Jaw-Chuck-for-4-Rotary-Table/T10053

Best
Stan

[DaveH]

Hi Dave,

I drilled thru and counter bored (the front face) to take 4 cap head screws of my 4 jaw chuck to fit on my RT.
To help to align it (centre it) on the RT, I also counter bored the back part of the 4 jaw chuck to act as a register.
 
DaveH

[Jonny]

Dave if you take the chuck apart and see where the workings are, you could then drill through at 90 or 120 degrees to line u with T slots.
Easy done it 13 yr ago and still in use daily. My trouble was small 3 jaw 5 1/4" scroll chuck on to an 8" RT with 4 slots. Less is more substantial, i drilled through and tapped the RT. Heres a piccy took whilst doing one of the dros, patterned out 3/4" thick aluminum one pass- good enough not moved yet?
][/img]

[hopefuldave]

It sounds like drilling the chuck body's feasible, then...

Right, time to steel my nerves and drill it! To get the holes to line up with each other quickly, I think I might put  "keep plates" on the end of the tee nuts so it stops 'em disappearing towards the centre, then (knowing the diameter of the holes' PCD in the chuck) mark and drill - this would at least leave the chuck roughly centred, and with a 4-jaw I'll be centring the work anyway

Thanks for the suggestions, chaps!

Dave H. (the other one)

[Jonny]

Try clamping the actual chuck and centre up and zero all dials.
Then just offset either way 90 degrees X amount and drill that hole. Back on centre move X axis either way same x amount and drill, no need for marking, cr drilling etc.
Just make sure theres no mechanical bits where going to drill through as in 3 jaw scrollers.
I wouldnt go any larger than the screw size you are using.

Could stamp a mark to line chuck and RT up when refitting.

[75Plus]

If the chuck is about the same diameter as the RT it would seem that you could just drill the existing holes through to the front. Then counter bore the holes to recess the heads of socket head cap screws. Depending on the size of the existing holes you may be able to use a smaller diameter cap screw or, if necessary, the same size screw can be reduced just above the threads that enter the tee nuts. The latter would keep the screws captive.

Joe

[hopefuldave]

More advice - thanks!

Jonny, I was going to bolt the rotary firmly to the drill press table (no mill, as such), flip the chuck jaws down and grip the rotary's table in it, indicate it in and then line up between the jaws, drill first hole, then crank the rotary through 90*, drill, rinse and repeat!

I think the existing (rear) holes are a bit small (I'll  use M8 capscrews for fixing as that's what the T-nuts take) , and perhaps too close to the edge of the chuck and wouldn't leave enough room for the counterbores - if the drill wandered they could even emerge from the side of the chuck, not the front face...

Thanks again,
Dave H. (the other one)

[Jonny]

Not too sure on that method but should be ok if just drilling through the chuck only. Use final size 6.8mm or 8mm for now.
Flip back over line chuck up and with drill hole.  Just keep pecking away whilst moving the job to position. If drilled through 8mm use same drill but change over to 6.8 for drilling without moving anything. Its amasing how accurate you can do it by mark 1 eye ball just look for drill veering off or deflecting whilst plunging down.
I would use that hole tapped with your M8 bolt tightened up to hold whilst doing the next, no need to clamp the job.

Alternatively can pick up off holes in the table.

I was limited to 5 M5 cap hds on mine due to the inner workings and no room for error. Broke the jaws today.