Centering on a vacuum chuck

[Jim Colombo]

I'm in the process of refurbishing a number of bowls. I have a HoldFast vacuum chuck and am having a tough time centering the bowls. Does anyone have some tricks that could help me?

[Roger Chandler]

I'm in the process of refurbishing a number of bowls. I have a HoldFast vacuum chuck and am having a tough time centering the bowls. Does anyone have some tricks that could help me?


Jim,

Hold Fast makes a tailstock adapter with morse taper 2, I think that will allow you to mount your chuck onto, which will automatically align it to center with the vacuum chuck head.

otherwise it is pretty much a trial and error process, except when you can see where you had the original center mark, unless you turned it off or sanded it off.

HoldFast makes the adapters to fit 1-1/4" or 1x8" spindle threads and has a lot of other adapters to make a fit for most lathes.

[Darryl Hansen]

Yep If you leave a dimple in the spigot to begin with you can use that to center your bowl using the center. If you do not have a sigot or for some reason it is gone then put the bowl on the chuck and turn on the vacuum. I assume you can control the amount of vacuum with a relif valve. Turn it down so it just holds the bowl. Put your tool rest level with the point of your center and run the center up to the bottom of the bowl. If you have a center that includes a small point then use that. Put your tool rest close to the bowl and turn it by hand. When you see a wider gap than the rest of the bowl using the tool rest as the guide gently tap the outboard side of the bowl till it is half the distance it was before tapping then the bowl turn again. A couple of turns and taps will put the bowl on center. Bring the center up to the bowl turn the vacuum up high and go for it. Remember you only move the bowl 1/2 way each tap. works very well. If you remember to leave a dimple in the spigot it makes it much easier.

[Harvey Schneider]

On the outside, use a center finder to mark the center of the foot. Then use a cone live center to point to the center mark before you pull vacuum. It should stay pretty well on center.
On the inside, you can't mark the center, so what I do is pull only a partial vacuum. I make the vacuum just strong enough that I can make small adjustments as needed. I position the tool rest as a reference point so that I can see what the run-out is. Move to the point of maximum gap and correct half that distance. It takes some trial and error, but you will quickly get a feel for the process. This process can also be used to fine tune the outside positioning if the center mark isn't close enough.

[Robert McGowen]

I do this in a similar way as above, but I put the rest on the outside of the bowl. (Like where it would be if you were turning a spindle.) I turn the bowl by hand and whatever part of the bowl moves closest to the rest, just slide the bowl over a bit away from the rest at that point. You know it is centered when you can move the rest almost right up against the bowl rim, give it a spin, and there is no movement between the rest and the bowl rim.

[John Keeton]

Jim, I do what Roger described and get dead center alignment everytime.

CSUSA has this (http://www.woodturnerscatalog.com/store/Lathe_Accessories___Spindle_Accessories___Reverse_ Chucking_Alignment_Adapter___reverse_chuck?Args=) for $29, and PSI has a live adapter here (http://www.pennstateind.com/store/LTCA18.html) for $35. Amazon has the Holdfast version for $33 here (http://www.amazon.com/Hold-Fast-Chuck-Reversing-Adapter/dp/B0036AYYFS).

Mine is not the live version, and works fine. I also use it for centering on my donut chuck.

[Bernie Weishapl]

I use the adapter from CSUSA. It aligns it perfectly.

[Ken Glass]

X3 on the CUSA adapter.

[Jim Colombo]

These are bowls which have been finished at one time or another so there is no centering point and no tenon. I have the centering attachment but I don't see how that will help me because it assumes the bowl is mounted on a faceplate.
It looks like trial and error is the most popular method.

[John Keeton]

...there is no centering point and no tenon.Bummer!!! Jim, I now understand what you are doing, and you are right - I know of no other way than just 'fiddle' with them.

[Larry Marley]

adding a bleeder valve to the vacuum side of the Holdfast will allow you to reposition easily while you fine tune your mounted piece.

[Joshua Dinerstein]

Bummer!!! Jim, I now understand what you are doing, and you are right - I know of no other way than just 'fiddle' with them.

Here is what I did. Your mileage may very. I made a big flat facelpate out of 3/4" MDF and a threaded wooden block. I got it trued up as well as I could. I bought a roll of closed cell hobby foam from Michael's and glued that to the mdf. The face plate was darn close to 24" in diameter so that anything I turned could be used on it.

I then using different colored pens drew in circles on the 1/2" marks from the center out. This was on the foam. My foam was a nice dark red. So blue and black alternating worked really well for me. (Use felt tip pens to do this.)

Then when I go to center up an older turned bowl for refinishing etc... I it aligned within or one of those circle lines and it has really really helped!

If what you are re-working is warped enough then you are to some extent going to be out of luck as the turning won't be circular but for the most part it has worked amazingly well for me.

But now that I have seen that CSUSA adapter I am just going to have to drive down there this next week and pick one up.

Joshua