centering square stock in 4-jaw

[Rayanth]

Doc, I was referring to the fancy tools people have been posting.

- Ryan

 

[rklopp]

I center rectangular stock in the 4-jaw similar to the way shown in the video. However, I mount the DTI on the cross slide, come at the stock horizontally, and use the DTI only as a null device. I use the digital readout (DRO - I could use the screw dials if I didn't have a DRO) as a measuring tool to find out how far off center are the opposite sides of the stock, cranking in the cross-slide and rocking the chuck until the DTI reads 0.000 at the low spot. I back out the cross-slide, turn the chuck 180 degrees, and wind the cross-slide back in until, while rocking the chuck, the DTI reads 0.000 again. The difference between the two DRO readings (or screw collar readings) is the eccentricity. I then know I need to park the cross-slide at the average of the two readings and then drive the stock laterally with the chuck jaws until the DTI again reads 0.000. That usually gets me darn close. Then I switch to the other pair of sides and bring those into truth. I then go back and check the pair of sides i did first to make sure it's position didn't change. It usually does a little.

I also use this technique to produce known amounts of eccentricity, as for a steam engine eccentric. However, once eccentricity becomes too large, the chuck jaws don't grip the part correctly, and I have to switch to alternate ways of holding the part.

 

[Philipintexas]

There's a method I use often, turn a sleeve with the ID a tight fit equal to the corner-to-corner dimension of the square stock and a couple inches long. The OD can be anything larger but concentric with the ID. Part it off and split it down one side so it can compress and grip the square stock when chucked in a 3-jaw chuck. I use this often to make square connectors on turned rods. Of course this works only if you want to drill or machine the center of the square material but it is very accurate.

 

[Rayanth]

Big thanks to all, as always, for the inputs. I should be able to figure out what I am doing wrong, and if not...well that's why I bought three times as much stock as I need for the project.

Unfortunately it will be a while before I get to give it another try. I will be signing a new lease on a new home on Friday, and it will take me a bit to finish moving. The workshop is a low priority on the move list.

Fortunately the new place is literally right across the cul de sac from where I currently live, so the move well be cheap and easy, but sometimes the lack of structure in a local move almost makes it harder.

I am still checking in daily, but between graveyard shift at work, school right after that, and a SWMBO to keep happy, and now the move... I won't be cutting chips for a little while.

- Ryan