Tramming the Rusnok vertical head on my Sheldon is complicated

[Bob Engelhardt]

When a vertical mill head has a pivot axis that intersects the spindle axis, tramming is simple. When an actual vertical mill head pivots, the spindle axis rotates about the pivot axis. Not so with a Rusnok: it pivots around its attachment to the horizontal overarm:



Which is offset 3" from the spindle. When a DTI is held by the spindle & extends 7", the distances from the head's pivot point to the DTI is 4" (right) & 10" (left).


When the DTI is zeroed on the left & swung to the right and reads 0.010, say, then rotating the head so that the reading is halved to 0.005 does NOT tram the head. It does on a real mill because a counter clockwise rotation raises the right and lowers the left by the same amount. With the Rusnok, raising by 0.005 on the right lowers the left by 0.0125 (10/4 * 0.005) - it's still 0.0075 off!

Once this is understood, it's easy to accommodate: zero on the left, read on the right & adjust the right by 30% of the error ( 4/(10 + 4) = 30%, more or less). In the 0.010 example, 0.003 up on the right & 0.007 down on the left.

[Doozer]

When a vertical mill head has a pivot axis that intersects the spindle axis, tramming is simple. When an actual vertical mill head pivots, the spindle axis rotates about the pivot axis. .

Nope. Not on a Bridgeport. A BP has the nod axis behind the spindle CL. Just like your setup. Not sure what mill you are thinking of. Your setup is just like tramming a BP.

--Doozer

[Doozer]

The only mill I am aware of that had the spindle CL and the tilt axis CL intersecting is a Tree mill.

[Bob Engelhardt]

OK ... there is a qualification: my mill head only swivels about 1 axis & I wasn't even thinking about 2 axes. The BP's nod/tilt axis does have the same problem. But the BP's side-to-side rotational axis does intersect the spindle axis.

[The Metal Butcher]

Reading your post, initially I agreed. Then I read Doozer's and decided he was right. I was surprised it has never been an issue for me. But I guess with the old school machined markings, not the crappy stamped plates, my starting point is so close it hasn't mattered.

Therefore my takeaway is: ... I need a tree mill!

[Randy]

I used to struggle with zeroing the nod on a BP until a co-worker showed me his method. Adjust the swing of the indicator so that it touches the table directly under the pivot. (That would be at the back on a BP.) Zero the indicator there, then swing the indicator 180°, and adjust the head to zero the indicator there. The reading at the back will have barely moved. You can home in on tram more easily. In your case you would be swinging only a 6" circle rather than 14", but that's still pretty good. Or do as I do, use a two-dial unit, aka spindle square. When you can watch both readings simultaneously it's easy to match them as you adjust the tilt. But if you've found a method you like, that's great.

[Doozer]

(On a Bridgeport), first tram the side tilt,
Then use that "zero" value to tram the front/back tilt.
Tram the side tilt a second time, then the front/back a second time
then there you have it. Getting the side tilt done first
because it is "on axis" with the Z to get a zero value
to shoot for is the key to making it easy.


-Doozer

[old mart]

With that offset head on the Sheldon, I would put a long ground bar in the spindle and then use a matching trysquare against it. That should get it quite close.

[MyrtleLake]

Opposite the side the OP's picture is taken is a ground section next to the quill micrometer stop. It is ground on two 90-degree sides accurate to the quill in two planes.

For all but extremely fine work, a try square can be placed on the table, aligned against that ground section of the head. No indicator necessary.

Obviously, some work will require a more demanding tram. Still, it's good enough for the vast majority--especially since the quill has such limited travel.

[nickel-city-fab]

Reading your post, initially I agreed. Then I read Doozer's and decided he was right. I was surprised it has never been an issue for me. But I guess with the old school machined markings, not the crappy stamped plates, my starting point is so close it hasn't mattered.

Therefore my takeaway is: ... I need a tree mill!

Hey TMB... take a look at this. My dream machine (German-made)
BOTH Z-axes go thru the same pivot (look closely at the vertical/adjustable head)
(lookit all the pics...) drool
Nope, can't afford it even if I had the room (it costs about a new silverado or a used corvette)
https://www.knuth-usa.com/us/servomi...machine-301254
This is a manual mill with servo motors and rapids, like a HLV-H lathe.
Electronic handwheels/leadscrews are ball screws.

[john b]

I like Doozers way of tramming. Did it that way 40yrs