Orac spindle nose taper

[RNR107]

Hi Emgee,
For concentricity... no problem, I use the same fitting on my manual lathe (Boxford) and concentricity is perfect, DTI does not move at all.

For reversing the spindle, why would you do that? I never use the spindle in reverse ?
(In fact since the Mach3 conversion, I removed this facility)

Laurent

[lsteele]

I've been wondering about fitting (or making) a collet chuck for my Orac. It looks like no-one knows definitively what the taper is on the spindle nose. I'm wondering about simply using the morse 3 taper on the inside of the spindle to provide concentric registration, and using the m8 bolt holes to hold the thing in place. Seems like a simple solution but no-one seems to discuss doing this - is there an obvious reason why not that I haven't though of?

Thanks,

Luke

[EVguru]

As far as I've been able to find out it is a variation of the DIN 55021 spindle nose standard. The standard starts at 3" (size 3), so the Compact 8/Orac is smaller than the definition of the standard. However, the taper is the same on all sizes; 7 degrees, 7 minutes and 30 seconds, or 7.125 degrees.

Setting the compund angle to match a taper is a pretty standard machining operation.

[RNR107]

I've been wondering about fitting (or making) a collet chuck for my Orac. It looks like no-one knows definitively what the taper is on the spindle nose. I'm wondering about simply using the morse 3 taper on the inside of the spindle to provide concentric registration, and using the m8 bolt holes to hold the thing in place. Seems like a simple solution but no-one seems to discuss doing this - is there an obvious reason why not that I haven't though of?

Hi Luke,
I thought about that, The problem with that is you loose in spindle bore... 20mm is already not very big.

Laurent

[lsteele]

Yes I've just realised that myself!

But you could still make the morse taper hollow. Like this (attached)

Obviously it's a compromise between wall thickness and smaller clearance diameter.

The ideal would be to know what the outer taper is - seems crazy that no one knows!

-Luke

[lsteele]

As far as I've been able to find out it is a variation of the DIN 55021 spindle nose standard. The standard starts at 3" (size 3), so the Compact 8/Orac is smaller than the definition of the standard. However, the taper is the same on all sizes; 7 degrees, 7 minutes and 30 seconds, or 7.125 degrees.

Setting the compund angle to match a taper is a pretty standard machining operation.

The problem is even if you know the taper angle, you still need to know the diameter of the taper coincident with the plane where the flat of the spindle nose meets the backplate surface (if you see what I mean). The taper and flat surfaces need to be in contact at the same time. It's hard to get an accurate measurement of that diameter. Perhaps it'd be possible to do it by some amount of trial and error, but that doesn't sound like fun.

[RNR107]

Yes I've just realised that myself!
But you could still make the morse taper hollow. Like this (attached)
Obviously it's a compromise between wall thickness and smaller clearance diameter.

Exactly...

The ideal would be to know what the outer taper is - seems crazy that no one knows!

Well, what's even more crazy is that you can not even machine your own back plate on the ORAC itself!
The traveler will hit the motor before the tool gets close enough to touch the face of the backplate!
(I am use to machine my own backplate on my manual lathe so it is perfectly concentric to the spindle...

Laurent

[lsteele]

One complication for me is that for about a month I have access to a really well equipped workshop with a couple of large lathes and a bridgeport clone. Unfortunately geographically no-where near the Orac.

What I'm thinking about is this: Take the Orac 3-jaw chuck with me, and on a second lathe face piece of steel, then turn down a 7mm long, 42mm diameter spigot. With the cross slide set to 7.125 deg, start turning down the spigot - once the diameter at the base is getting near the desired diameter, apply some engineers blue to the 3-jaw, then offer it up to the taper. Once I'm getting really close make really small cuts until I get a perfect fit. Then I'd use this as a stand-in for the Orac spindle nose, and machine the taper on the collect chuck adaptor using basically the same process. I could also make a backplate for a 4-jaw in the same way.

I'm something of a novice so I'm looking for some guidance - does this sound feasible?

-Luke

[RNR107]

Well, in theory it is possible... But how do you plan on setting the angle of 7.125 deg ???
I don't know what kind of lathe you have but, I don't have such precision on mine.

Also,
You could bring the headstock of the ORAC with you. It is small enough and fairly easy to remove.
Just 4x M8 nuts / bolt to remove and the belt...

L.

[EVguru]

Well, in theory it is possible... But how do you plan on setting the angle of 7.125 deg ???

You could learn what a sine bar is.

[lsteele]

Well, in theory it is possible... But how do you plan on setting the angle of 7.125 deg ???
I don't know what kind of lathe you have but, I don't have such precision on mine.

Also,
You could bring the headstock of the ORAC with you. It is small enough and fairly easy to remove.
Just 4x M8 nuts / bolt to remove and the belt...

L.

Well, I was going to put a piece of ground steel concentric in a four jaw, then stick a dial indicator on the toolpost with the angle set approximately, then move the cross slide a given distance (e.g. 50mm), then from the displacement of the dial indicator and some trig calculate the angle. Ok, it doesn't make _setting_ the angle easy, but I think it should be possible to get a fairly accurate reading of the angle, hopefully quite a bit better than a 10th of a degree. Never done it before I admit, but I think it should work!

I can't find any drawings of the headstock. Is it pretty obvious how to remove it?

Cheers,
-Luke

[RNR107]

I can't find any drawings of the headstock. Is it pretty obvious how to remove it?

Yes... There are 4 M8 nuts tightening the casting against captive screws in the bed.
2x of them are at the back of the head (You can see them just by looking behind it in a recess at the bottom of the casting.
and 2x of them on the front (hidden behind the black ali plate with the Denford logo on) Just remode the 4x M4 screws holding the plate and you will see them.

I thought of something else... If the lathe you want to use is big enough, you could mount the headstock of the ORAC!
I mean, you grab the back of the spindle of the ORAC with a 4 jaw chuck and support the head side of the spindle with the tailstock.
Place a piece of wood between the bed and the casting of the ORAC headstock (Just to make sure it does not start spinning)
This way, you could machine the recess for the chuck on the back plate (Once fitted the the spindle) on the spindle of the ORAC and get it perfectly concentric!
Or could even re-machine very slightly the taper of the nose spindle with the same setup and get the exact same angle on the nose and back plate....
See what I mean ? Maybe a bit too crazy...

Laurent