Your register on the backplate can be turned a fraction undersize then with the fixings just nipped up the chuck can be tapped about to get it to run true at which point you can fully tighten the fixings

Its something that always puzzled me that one would take care to machine a register accurately and then not use it as a precise and repeatable locating device.

The only function of a loose fitting spigot and recess is to roughly align the two before getting out the Manchester screwdriver!

I suppose its an acceptable method for something that is not intended to be taken apart.

Ian P

Apologies if this is a Granny & eggs situation, but have you tried rotating it around the three different hole positions on the backplate?

..there's usually a 'right' one..

The horrible automatic smileys are a feature. When computers only had text screens, no graphics, it was the height of sophistication for folk to make emoticons by concatenating characters. Loads of possibilities such as:

• smile : – )
• sad : – (
• confused :-J

When everybody got graphics screens it became fashionable for software to show off by automatically converting text emoticons into their graphical equivalents. This forum does it, which is very unfortunate because engineers often use symbols like " that have been stolen by the emoticon crew. The text combination " ) is a wink. I stopped " ) being converted into a winky in this post by inserting an extra space. Type (0.003" )

Back to run-out, my guess is that the new collet chuck is a close fit to the register and either the register is worn, or the matching part of the chuck isn't quite true. So when the nuts are tightened the register pushes the chuck out of alignment. If a tight fit, I suggest opening up the chuck slightly to create room for it to move relative to the register. Then centring by tapping as per Jason's advice will work.

Registers wear a little every time they're used. How good or bad they are depends on the history of the lathe and the years are often unkind. A lathe that's spent its life constantly switching chucks is unlikely to have as good a register as one owned by a gentle hobbyist who did everything with the same 4-jaw.

Dave

The runout is not described properly, is it radial or something else? Assuming that the register is running perfectly radially and the face of the backplate has been skimmed, and the collet plate fits it snugly, where is the runout measured from? The OD of the plate or the bore? With a test bar held in a collet? Has more than one collet been tried? Is the collet bore concentric with the register in the back of the plate? With a test bar in a collet, if the only error is radial, then the error will be the same right up against the collet as it is 3" further out.

There is nothing wrong with having an undersize register, the bolts holding the collet plate and friction will never allow unwanted movement. In the real world, you have to make these things work, not just say it is not allowed.

Dave, we are talking the freshly cut register on a back plate not the spindle that may wear or get damaged over time

Chucks are usually hardened to some degree so easier to just take a bit more off the backplate register

Edited By JasonB on 05/06/2023 19:29:16

Glad you got things running well. I have an R8 er25 collet holder that has problems with similar runout which would probably need internal grinding to rectify. The other two that we have are fine. You also have to be cautious with cheap collets, they can be poor if you are unlucky. I usually buy the sizes to match milling cutters from APT, they have three grades that you can choose from, and good prices.