Creating a concentric reference surface on ER collet adapter

[Nubbles]

I have a Sherline lathe and a Taig ER16 spindle adapter that threads onto the spindle of my lathe. However, because the differences of the Sherline and Taig spindle noses, the threads in the adapter don't start at the base, causing it to only engage one or two on the Sherline spindle:


The base of the adapter sits on the shoulder of the spindle, which is the reference surface for the Sherline.

My goal is to shorten this end so more threads engage. I was able to find one other person that has talked about doing this, but I don't have the same tooling as they do.
My issue is that I want to ensure this surface is concentric to the collet's bore, otherwise I assume the collet and therefore the stock it's holding could be pointing at an angle to the bore of the lathe.

This is my current plan, and what I'd like input on: I want to turn a piece of steel to 3/8" (the largest collet I have), mount the adapter onto that rod backwards using a 3/8" collet, then face down the end.


Questions:

1. Would this maintain concentricity, at least to a reasonable degree?
2. Should I use a center in the end of the stock? (Would it even it matter that much?)
   1. I was planning on using a center to remove most of the material, but create the final shape without a center so that only the chuck is influencing the stock. Then shorten the adapter without a center as well.
   2. For my particular lathe, I do know that when I turn using a tailstock center I get less taper.
      1. Now that I'm thinking about it, it seems like using a center the whole way may be best?

A few things:

• I have Techniks collets, so not the cheapest ones out there. I feel like I can count on their accuracy in this instance.
• I feel like the "true" way to do this would be to hold the adapter backwards in the 4-jaw and dial it in with an indicator on its internal ER taper, but I don't think that's viable with what I have

 

[piper184]

Is the adapter supposed to register against the face of the spindle or is there a step that is supposed to contact the inner bore of the adapter just before the threads start?

If it registers against the face of the spindle, what you are proposing certainly seems reasonable to me. I would definitely use Tail support on the rod, both while turning down to size and when facing off the adapter. Also don't touch the jaws in the chuck once you start to make sure you don't loose concentricity part way through process.

Once you have the collet on the turned rod and locked down tightly, I would want to see if the rod runs true. It should even without tail support. Then check the body of the adapter to see if it is running true. I know that the body is not a valid reference point in comparison to the bore but it is about the only surface you have available. If it does have runout, put a witness mark on it and turn it 180 degrees on the turned rod. Test again to see if the runout stays with the rod or if it travels with the body.

To my mind, if the runout stays with the body then the body is not true on the outer surface. If it stays with the rod, then the collet and/or taper are not true. Hopefully my words accurately describe what I am thinking. If I am way off base I hope someone will correct me.

 

[homebrewed]

Is the adapter hardened?

 

[Nubbles]

Is the adapter hardened?

It is not, fortunately

Is the adapter supposed to register against the face of the spindle or is there a step that is supposed to contact the inner bore of the adapter just before the threads start?

I don't see where else it could, so I'm fairly sure it's supposed to register against the face of the spindle. I appreciate your input!

 

[Nutfarmer]

On a regular thread on chuck mount the threads don’t position the chuck to the spindle.The face and the counter bore does. The threads just hold the chuck on the spindle. This is what you are proposing to cut off. I haven’t worked with ether a Sherline or Taig so I can’t say if they are the same as a standard thread on chuck or not. Just be careful that the chuck will still has a reference to center on the spindle after it is machined.

 

[mikey]

In my opinion, the set up in your drawing is going to result in significant runout in the end. There are so many stacking tolerances that it's unavoidable. Can't grab a hex securely in a 4 jaw either, and nobody makes set-tru 6 jaw chucks for Sherline lathes.

Do you have a milling machine? Could you lock the chuck in the vise and indicate it dead vertical off the inside machined bore, then gently fly cut the excess material off?

 

[markba633csi]

I disagree with Mikey- I think the setup shown could work well, especially if you use a tailstock center, and take light cuts.
3/8" rod is pretty substantial. Use an accurately ground piece of drill rod.

 

[francist]

I think I would like the proposed setup better if the collet chuck could be gripped on the inside of the chuck as one normally would rather than chucking on a piece of 3/8” rod. One could still use a rod in a collet to indicate off of but it wouldn’t be relied on for the stability of the part. I just see a whole lot of potential for a chatter as soon as you start cutting on the end. Maybe the present chuck size won’t allow for that though.

 

[piper184]

Runout stacking is the main problem. That is why turning the rod on the lathe and not disturbing the chuck is important. It is the closest you will get to having the rod on the spindle center line. Using a precision ground rod would only translate the chuck runout to the rod. Tail stock support is a must for either.

The big problem is the taper in the adapter concentric with the bore? Is the taper in the collet concentric with it's bore? Any runout in either can be additive or one can be used to counteract the other. As best as you can determine by testing, marking and re-clocking each item to each other item. It is a lot of possible combinations but is doable with patience and time.

By using the OP's setup it should be possible with the right indicator to check the inside of the counter bore and the outside of the adapter for concentricity with the rod. IF, and this is a big IF, you find that the outside of the adapter is magically concentric with the rod you could then mount it in the chuck if you can counteract any run out in the chuck you can turn off the excess. Barring that, I think his idea is probably the most accurate solution.

This is all just from my thought process as I have never done this kind of operation except to try and make a straight arbor for a drill chuck. That only turned out so-so.

 

[Nubbles]

I very much appreciate everyone's input and the discussion! It sounds like I should probably set it up and see what kind of measurements I can take to gauge the situation. Unfortunately I haven't gotten around to getting a test indicator (one of the reasons dialing in on the taper isn't an option for me at the moment).