Threaded Chuck Retention?

M

Mikeskid07

H-M Supporter - Silver Member
H-M Supporter - Silver Member
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Nov 19, 2023
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Hi all,

I recently set up my Atlas 3996 to machine(read grind) a rubber contact wheel for a mobile belt sander at work. It didnt go particularly well, but the wheel is in use and so far doing what we wanted.

Something that came up whilst I was working- I absentmindedly flipped my fwd-off-rev switch the wrong direction, spinning the spindle reverse for about 20 mins of work. During a break from the grinding smog, I ran an indicator check and noticed that my chuck had backed off 1.5-2 turns without me noticing. Ive never had this happen with "normal" turning ops, but it has been 5-6 years since I've run the lathe.

This got me thinking something again that I had debated when I originally brought the lathe home- machining a flat on the spindle nose thread and a set screw into my chucks. Ive dreamt up several other ideas, but don't see the clearance to be able to do them...

I have a new to me spindle sitting in my eBay cart, basically in case I muck up the milling job.

Has anyone done anything along these lines, if so, is it worth the effort and what surprises would I be up against?

Order of Operations:
1) determine size of setscrew & flat
1a) measure spindle thread depth
1b) measure rear stubs on most used chucks (8" 4 jaw, 5" 3jaw, future ER40)
2) spindle in v-blocks and mill vise trued to mill x axis
3) cut keyway/flat on spindle nose
4) mark spindle nose and rear exposed portion of spindle to give visual for step 5.
5) install chuck on spindle at recommended torque.
6) mark chuck stub
7) drill/ tap for setscrew
8) reinstall chuck, tighten setscrew- turn in reverse to dumb heart's content!

This is still in the 'once I have time, if it makes sense' stage, therefore I'm running it by y'all first.

Thanks,
Ian

PS. After I hit 'post' I got thinking of things that could go wrong, maybe brass/plastic setscrews would be pertinent in case of a crash (never had one, but...).
 
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Elaborate plan, it may work.


It may be simpler to transverse drill the chuck flange and tap to something like 1/4- 20 tpi. Install a grub screw made from brass, bronze, aluminum and add a locknut to retain the grub screw.
 
Personally, I would not do it at all, I have had many lathes with threaded spindles, and although I have had them occasionally start threading off, I have never had a chuck hit the ways, so far as I can remember, when mounting chucks, etc., I simply give it a good sharp snap against the spindle shoulder, and am able to reverse to slow down the machine without "losing it". I presently have two lathes with threaded spindles.
 
On the Sheldon group, one of the members had made a clamp to lock the chuck’s register boss to the spindle for his Linux run lathe. Looks like a good idea.
 
Ulma Doctor said:
Elaborate plan, it may work.


It may be simpler to transverse drill the chuck flange and tap to something like 1/4- 20 tpi. Install a grub screw made from brass, bronze, aluminum and add a locknut to retain the grub screw.
Click to expand...
Seems like your idea only lacks one step from my elaborations? I guess it could be a first step, basically a slightly less invasive try at the same thing- maybe a slug of copper or brass, then a steel setscrew and locknut, or three sets 120° apart...

benmychree said:
Personally, I would not do it at all, I have had many lathes with threaded spindles, and although I have had them occasionally start threading off, I have never had a chuck hit the ways, so far as I can remember, when mounting chucks, etc., I simply give it a good sharp snap against the spindle shoulder, and am able to reverse to slow down the machine without "losing it". I presently have two lathes with threaded spindles.
Click to expand...
I'd like to be able to turn both forwards and back without fear. Your comment seems to imply that the fear is in ruining the lathe/ways... I'm far more concerned with ruining parts. That being said, I'm far from old hat at machining, but I feel like there is room in all of your statements for the word "yet".
OTmachine said:
On the Sheldon group, one of the members had made a clamp to lock the chuck’s register boss to the spindle for his Linux run lathe. Looks like a good idea.
Click to expand...
I'm not finding it, but am certainly interested! I see several other posts regarding clamps and groves on spindles- some careful measuring would have to take place, but I think my differing chuck bosses would lean more toward my original thought, or it would wind up being multiple clamps...

G-ManBart said:
You might consider making a chuck keeper rather than modify the spindle. Take a look at this post:

https://www.hobby-machinist.com/thr...y-chuck-on-a-south-bend-10k.90750/post-825501
Click to expand...
This idea has a TON of merit short term, as it allows me to work with all chucks nearly immediately with the work I currently have lined up... However, I lose the thru- bore advantages I currently have for long stock, which is important to me long term. I'll probably make this before I do @Ulma Doctor ('s) plan.


I don't mean to sound as if I'm not open to other ideas... I'd love to know of mote solutions. Thanks so far!
 
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I would definitely not modify your spindle. Drill and tap a 1/4-20 hole in the spigot of your chuck backplate. Spin your chuck on, drop in a piece of nylon rod to protect the spindle threads and thread in grub screw. Crank it down and you're set.
 

Securing a threaded on chuck for reverse rotation

Good evening, I do little gun smithing but I note this forum is more accommodating of Asian machine discussions than the general forum so I thought I would ask the following: I have a Grizzly 12X37 lathe (along with an SB Model A and Wells Index 747 mill, and access to a Lodge and Shipley...
www.practicalmachinist.com
See post #6
 
The import 9x20 lathes have a retaining clasp. Basically just a sheet metal "L" clip screwed to the back of the chuck. The clip interacts with a groove in the spindle.

I can assure you this works, as it has prevented me from intentionally removing the chuck when I've forgotten about the clip.

I have spun a chuck off of a threaded spindle, but complete operator error and not running in reverse. This occurred when I got distracted and soft threaded the chuck on, and started the lathe without properly securing the chuck.

John (Benmychree) has in the neighborhood of 60 years machining. His comment of it not biting him, and the fact I'm only aware of one model of lathe (9x20) with a threaded spindle including any sort of spindle retaining method (and a very inexpensive solution) had lead me to believe it is more of a hypothetical concern, than a serious issue. Yes it can happen, but paying attention seems to be the real key to prevention.
 
The Grizzly G0602 has two retention dogs which engage a groove on the spindle. It positively prevents a chuck unscrewing. However, it requires an extension of the spindle flange from the bearing and seal and a boss on the backing plate.

My Atlas/Craftsman 6x18 has a threaded chuck with no retention method and although I have used it many times in reverse over more than fifty years, I have never had the chuck loosen.
 
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