The Center of a RoTab...how to make it work for me?

[Bolster]

I'm a new owner of a 6" rotary table, it has 4 T-slots in it. While I haven't used it much, I have been wishing I had a way of quickly centering my work by way of an indexing pin (sticking up) or a bolt (going down) into the center of the rotab. But the center of the rotab is just a 2MT hole.

I'll bet you experienced guys have nifty ways of making the center of your rotab useful. Do you have any ways of making that center hole into an indexing device?

Guessing at possibilities: Buying an inexpensive MT2, cutting it off below the surface of the rotab, and center drilling it with a 1/4" or 3/8" hole? Possibly threaded? But how do you hold a taper in a chuck to center drill it?

You probably get my drift here...I'm looking for some enlightenment on clever ways of centering over that hole.

 

[hammers-n-nails]

mine is a 10 or 12" so it may be different but on mne there is a short shoulder between the surface and the mt3 i made a "washer" that fits tightly in the shoulder area with a hole in the center for whatever size im using.

i also sometimes locate the center with an edge finder, zero the scales, put a piece of shaft or whatever i need to locate my part in the collet then let the spindal hold the part centered while i clamp it down. these two ways work reasonably well.

drilling out a mt2 adapter as you suggested is probably the best option, if you or your local machine shop has an adapter to go from whatever the taper is in the tailstock of the lathe to mt2 you could hold it that way chucking a reamer in the head and there you go. if you decide you want to thread it you should make sure that the threads arent the only thing to keep your center pin in alignment.

hope that all makes sense

 

[Lew Hartswick]

I don't understand why so many rotary tables have taper holes in them. Ours a 12 inch
one has a straight 1.000 hole in it. I've made a lot of very simple adapters for in it.
including a stub witha 1 1/2 " -8 thread for a small chuck (from an old SB or something).
Can someone explain the reason for the tapers? I'd be tempted to have it bored
straight.
...lew...

 

[pete]

Guessing here, But maybe for machineing parts between centers? That is the most accurate way to do it for shafts anyway. Maybe due to tradition? They started out with MTs in them so they just keep doing it? Mine has a MT 2 in it but I'd much prefer that straight hole. Or even better being able to use a machined washer as mentioned.

Pete

 

[JimM]

What is the headstock taper of your lathe ? Can you not just pop an arbor in the headstock and drill

Apologies if this is stating the obvious or if your lathe doesn't have a taper but sometimes these things get overlooked

 

[Maryak]

What is the headstock taper of your lathe ? Can you not just pop an arbor in the headstock and drill

Apologies if this is stating the obvious or if your lathe doesn't have a taper but sometimes these things get overlooked

Beat me to it. ;D

Best Regards
Bob

 

[Bolster]

Thanks for the replies. To answer some questions: First, I don't own a lathe. Maybe I can find someone at SCHSM who has a lathe with an MT2 headstock, though, and pay 'em. Or someone with a lathe and the correct adapter. Thanks.

Bogstandard, thanks for the inspiration. Yes, currently using a DTI to center now. So slow.

 

[mklotz]

Bogs is right about centering by sweeping the existing hole with a DTI. That's more accurate than sweeping a plug. Nevertheless, the plug is handy for locating parts on the table.

I turned an MT2 slug to fit my table hole. It has a reamed 1/4" center hole so I can make various adapters to fit it. Make the center hole blind, not through, and at the bottom of the hole drill and thread for a jack bolt to get it out of the hole when the RT is bolted down and you can't access its back surface.

Morse taper devices can be held in the lathe for machining by use of the cylindrical sockets sold for use on tailstock turrets...

http://www1.mscdirect.com/cgi/NNSRI...re=ItemDetail-_-ResultListing-_-SearchResults

 

[Bolster]

See, your MT2 slug sounds like the perfect solution. I wish such an item were available commercially (and maybe it is!) to people like me, who are trying to pull together tooling, with an incomplete shop. Sometimes it gets frustrating because it seems like everything you need, requires some other set of tools you don't have, to make it!

If anyone does make a mklotz-style MT2 plug commercially, please let me know.

 

[pete]

Since you don't yet have a lathe,
If? your mill is R-8 or even a MT taper you can buy fairly cheap adapters to go to MT 2 You then use this along with a boring bar mounted vertical on the mills table to do the machining. You then have a accurate method to get what you want as far as a plain bore goes. I'd also have to agree about the MT being more accurate than just a straight bore.

Pete

 

[bentprop]

I'm in more-or-less the same boat.My table is 5",but the same principle applies.
I had thought of getting a blank 2MT arbor,and just putting a small centre mark in the soft end.Unfortunately,soft blanks appear to be as rare as rocking horse poop around these parts.
So I'm thinking of a standard MT2 drill chuck arbor,and annealing the chuck end,then centre drilling.Only thing is,I don't have oxy/acetylene gear,so the annealing would have to be done in my neighbour's log burner.Trouble is,that would soften the whole arbor.Don't know if that would be such a problem though,since there's no real stress on it when used simply to center the ro-tab.

 

[MachineTom]

There is no need for a special tool, stick a mt 2 dead center in the RT, and indicate the OD with a DTI.

 

[picclock]

Hi Bentprop

Quick and dirty method I've used is to put a dead centre in the mill then lower the head until the centre pushes the RT to the right position.

You can get very close like this (<3 thou). My mill and RT have MT2 centres but they don't have to be the same. As long as the dead centre maximum diameter is larger than the opening in the RT.

I'm sure I will get hammered for using such an unproffessional approach, but it works and its fast.

Dead centres are only a pound or two, and may come in handy if you get a lathe ;D.

Other thing I found very useful for edge finding is a piece of 6mm steel rod (mine's ex printer), fitted with a 10mm OD - 6 mm ID bearing. Top of bearing coated with tippex and black segments coloured in with marker. 6 mm is the holding size of most small mills so no collet change needed. To get the edge just mount it as you would an endmill and move it to the edge of the work until the bearing starts to touch and segment speed changes - then subtract 5mm. Very kind to aluminium leaving no visible marks (unlike my Starrett 827B).

Best Regards

picclock

 

[bentprop]

I like the shaft and bearing idea,picclock.I have some nice bits of printer shafting.I'll look into that.
Up till now,my quick and dirty method was to mount a piece of 10mm shaft in the mill chuck,then close the 3 jaw chuck on the rotab onto the 10mm rod.
Invariably the table shifted a little while tightening,so I've gone completely off that idea.Really the dead centre idea is pretty much the same,so presumably I'd get the same shifting problem.
I'll have another think about it all while I'm laid up recovering from a bout of pneumonia.

 

[picclock]

I didn't realise you had a chuck attached to the RT.

I normally mount my stuff directly onto the RT after its aligned. The weight of the head pressing on the RT stops it moving. I then align the work before/during clamping (small mill, no chuck, more height). I've got an old 3 jaw chuck I considered using with the RT but most of the stuff I do on the mill is not round - anyway that's what lathes are for :

I got the shaft/bearing idea from a posting on the internet a while back. It's one of my most used tools - accurate, cheap and simple.

Sorry to hear about the pneumonia. Good excuse for avoiding the inlaws over xmas though ;D

Get well soon

picclock

 

[Bolster]

Speaking of alignment...according to Harvey (Machine Shop Trade Secrets), he says you first center the work in the rotab (which can be done with the rotab pretty much anywhere your DTI can reach on the table), and THEN center the work under the quill. I don't remember the reasoning but he said it was faster and more accurate this way...