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Reverse threading with a screw on chuck.
- Thread starter Jim F
- Start date
- Joined
- Oct 11, 2016
- Messages
- 3,869
It still presents a risk. Perhaps you have moderated the risk and that's a great step. Some of the UK metalworkers in Model Engineering found creative ways to grab the spindle to further reduce the risk of unscrewing the chuck. Once the force of static friction is overcome, the chuck comes off very fast...
The best method I saw was an an additional grip on a Clausing lathe: the backing plates all had a boss that seats to the face of the spindle. A hole in the boss was tapped for 2 set screws, and then 2 dog-point set screws with copper inserts were tightened onto the spindle flats - only for reverse threading, mind you - and it worked for the guy very well.
-- just my 2 cents worth. better safe than injured.
The best method I saw was an an additional grip on a Clausing lathe: the backing plates all had a boss that seats to the face of the spindle. A hole in the boss was tapped for 2 set screws, and then 2 dog-point set screws with copper inserts were tightened onto the spindle flats - only for reverse threading, mind you - and it worked for the guy very well.
-- just my 2 cents worth. better safe than injured.
- Joined
- Sep 24, 2020
- Messages
- 1,921
Using back gear, at the low speed and only taking .002 cuts, it worked.
spindle was going about 50 rpm.
- Joined
- Jul 8, 2018
- Messages
- 880
I have not had a mishap while threading.
I did, however, have a mishap where I had just put the chuck on the spindle, stock in the chuck, and fired up the lathe in reverse instead of forward (on the logan it's a three-position switch, so my mind sent the STOP signal instead of the START signal). The chuck unscrewed immediately even though the motor was powered on for less than a second. About a foot of the stock was in the spindle so the chuck was suspended between spindle and carriage long enough for me to grab it, avoiding all but psychological damage.
So a couple pieces of advice come to mind:
* always turn something in the standard direction before running a screw-on chuck in reverse
* use the smallest chuck you can get away with - I downgraded from an 8" to a 6"
* try to use collets (or between-centers) as much as possible
I did, however, have a mishap where I had just put the chuck on the spindle, stock in the chuck, and fired up the lathe in reverse instead of forward (on the logan it's a three-position switch, so my mind sent the STOP signal instead of the START signal). The chuck unscrewed immediately even though the motor was powered on for less than a second. About a foot of the stock was in the spindle so the chuck was suspended between spindle and carriage long enough for me to grab it, avoiding all but psychological damage.
So a couple pieces of advice come to mind:
* always turn something in the standard direction before running a screw-on chuck in reverse
* use the smallest chuck you can get away with - I downgraded from an 8" to a 6"
* try to use collets (or between-centers) as much as possible
- Joined
- Mar 21, 2018
- Messages
- 1,600
The whole idea of reverse threading (ie, threading a right hand thread with the tool upside down on the back side and running the machine in reverse) is to be able to thread FAST and thus not using the back gears.
And, the "it works fine..." comment will hold true until the chuck finally breaks loose and goes barreling onto your ways then across the room. With a screw on chuck, the risk is way higher than the reward.
- Joined
- Oct 31, 2016
- Messages
- 2,649
I have not tried this yet. There was a post on one of my threads about how to keep the chuck from coming off while in reverse. Use a drawbar through the spindle with different TPI than the spindle to hold a keeper (wrong terminology??) on the inside of the chuck. The theory being that the different TPI's will counteract each other keeping the chuck from unscrewing. I might do an experiment with this using my lightest chuck and everything protected to prevent damage to me and my lathe.
- Joined
- Mar 26, 2018
- Messages
- 8,412
Hugh?
I just can't picture it. What is the draw bar threading into?
- Joined
- Jan 2, 2014
- Messages
- 8,854
The one I saw had basically a (~1/4") thick washer with threaded ID.
It was just big enough to nest in behind the chuck jaws, but too big to go thru the chuck backing plate.
This may require a special arrangement and be built in when the chuck is first mounted.... and also could interfere with the maximum diameter stock that could be passed thru the chuck.
That same idea could be done with a left-handed draw bar and keeper.
-brino