Moving chuck back on spindle

[GunsOfNavarone]

I was thinking of Winky’s workshop & him moving his chuck on the spindle back to reduce flex. As this was just a prototype/proof of concept, I used some steel I had on hand, it wasn’t ideal as it was almost .250” shy on diameter, but worked out fine but just not to my preference.
As I have a screw on chuck, I had to consider the lock downs, which are really the problem in the first case. This is what pushes the chuck forward about .650” more than I’d like just so you can access the locks.
This is what did to squeeze their size down.

Here is where the stock cast iron backplate sat (1.5” from headstock) which has about .002” of flex.
Stock back plate
Here is the steel back plate moved .650” closer to head stock
New back plate
And for what it’s worth, the chuck plate made on this lathe has about .0005” runout.
Runout
New position
Original position
Now , I’m sure there is something I overlooked or did I correctly, let me have it before I make version II, not to mention I plan on remaking all my back plates. I have chased after small gains of rigidity on the compound, no reason to to chase that dragon on the chuck! No?

 

[benmychree]

Not a good idea to use steel for a threaded on backplate, it can gall the threads on the spindle and chuck backplate, that is why backplates are made of cast iron.

 

[GunsOfNavarone]

Would anti-seize avoid this at all? Am I to assume my spindle is cast iron as well? This is something that happens with dissimilar materials?

 

[stupoty]

Would anti-seize avoid this at all? Am I to assume my spindle is cast iron as well? This is something that happens with dissimilar materials?

I would think most spindles are steel of some kind. (this is me presuming and there is a saying about that).

Is the chuck still hitting the back surface (registration flat on spindle) ? you say it's "forward" am I just missunderstanding what your saying ?



Stu

 

[GunsOfNavarone]

I did a search for cast iron spindles with steel back plates, other than the dampening properties, I really couldn’t find any negative. (Doesn’t mean there aren’t, hence my posting here before I jump in) Yes, it has a register that I made sure was snug, tight tolerances. I moved the chuck/back plate closer to the headstock as the videos show. I definitely see positive outcomes from the less flex of the setup. I can get cast iron blanks if it comes down to that, but like many people, I hate machining cast iron.

 

[benmychree]

Very unlikely a spindle would be cast iron, use of an anti seize would be helpful to avoid galling; I have seen spindles with galled threads and for that matter, galling of the register fit, in my experience, the register fit need not to be tight, the angle of the threads centers chucks and other spindle accessories up nicely.

 

[benmychree]

I did more or less the same thing when I mounted a large new 4 jaw chuck on a 24" swing Nebel Lathe that I had years ago, more or less just turned the backplate backwards so that the hub was inside the ID of the chuck, this was done to increase rigidity of having a big heavy chuck overhung past the end of the spindle, the only downside was that it decreased depth inside the chuck.

 

[GunsOfNavarone]

So what would be the galling issue if the spindle is steel and the back plate is steel? I guess I’m trying to figure where the issue for galling is coming from? The threads are very nice fitting, no wiggle at all, it is the shoulder of the register that I made sure it was just over an interference fit. I did find a few high end manufacturers out there that offer steel threaded back plates ($300+) I will apply a light layer of anti seize, don’t want to risk and issues getting chuck off for sure.
I’d go a step better & question if there are chucks out there that are not so deep. I’m not looking at mine right now but I’d guess it’s 3” thick. This isn’t an obsession, but again when you have a small lathe, you’re always looking for ways to increase rigidity. This is something I had no idea about a few years ago when I got this machining bug. Thanks for the insight.

 

[markba633csi]

Using lube increases the hassle factor, that's the downside. Lube can pick up swarf
that's why most chucks are mounted dry hence the use of cast iron to minimize galling

 

[Provincial]

Dry graphite or other dry lube product will avoid attracting foreign material. It only takes a little to do the job.

The spindle is likely a very smooth finish, even hardened and ground on better machines. Put the dry lube on the internal threads of the back plate, which is likely a rougher finish that will hold the lube particles better. You can "impregnate" the internal threads with dry lube by repeated applications, mounting and dismounting the back plate (and chuck, if still attached), which will push the lube particles into the low spots.