Small Lathe Extended Point Live Center

[rossbotics]

While turning a part in my small lathe the other day I found myself having to grind a tool bit in all kinds of configurations just to clear the live center, which I have had to do many times before, so I decided to make a small extended point live center and end that aggravation.

I had on hand a #2 Morse taper shank with a #3 Jacobs taper that went to an old drill chuck that had been discarded, I started out by installing the #2 shank in the spindle of the small lathe and machined a 5/8”-18 thread and a 1/8”wide by .660” diameter land on the Jacobs taper end for locating the bearing housing, I took a piece of 1.250” round 4140 pre-hard steel for making the bearing housing and machined the same threads and land in the housing as I did on the #2 shank, I used a couple drops of red loctite on the threads and screwed them together tightly and let cure, I installed the shank and housing back into the spindle of the machine and bored it for a light press fit to accept two 5200 double row angular contact bearings, I then machined an extended point center in one setting without turning it around from a piece of 5/8” round 4140 pre-hard steel, the very end of the 60° center point was then further hardened.

Below you will find a few photos of the machining process along with the assembled live center.

As always thanks for looking and happy machining
Doug

[LMMasterMariner]

Nice job as always. It's very, very useful live center. Since I started with carbide inserts cutting tools I had problems with regular live center when turning small diameter shafts, barrels, etc. I found it very cheap (USD 18) in China, accuracy 0.003 mm, so I bought it 2 years ago. No more problems.

Best regards
LMMasterMariner

[rossbotics]

Thanks LMMasterMariner
Can't complain about that price !

Doug

Nice job as always. It's very, very useful live center. Since I started with carbide inserts cutting tools I had problems with regular live center when turning small diameter shafts, barrels, etc. I found it very cheap (USD 18) in China, accuracy 0.003 mm, so I bought it 2 years ago. No more problems.

Best regards
LMMasterMariner

[old_toolmaker]

rossbotics,

That is a very well executed and nicely done extended ball bearing center, Doug. I have also experienced that same issue more times than I can remember on my 7 x 16 mini lathe. This is especially true when using carbide insert tooling. I am going to put this on my to do list. Thanks for posting this!!

[rossbotics]

Thanks old_toolmaker
It really made a difference

Doug

rossbotics,

That is a very well executed and nicely done extended ball bearing center, Doug. I have also experienced that same issue more times than I can remember on my 7 x 16 mini lathe. This is especially true when using carbide insert tooling. I am going to put this on my to do list. Thanks for posting this!!

[PJs]

Great build and write up Doug. It solves a source of needs & creative frustration in many ways, especially with that shallow taper prior to the point. Thanks also for all the details on materials and ops!!

On bigger lathes the OA length of a center like this is not a problem but on "peanuts (7x10-14) and micro's" every inch of travel counts. I've often thought of different ways of shortening the whole assembly, perhaps using thrust bearings or combo of thrust and angular contact. Holding the point solidly by its shank is the issue. In your case you have 2 5200's rated at ~7k N (~1600 lbf) each and More than adequate, but at 14mm width gives a probable 1.5" OA on the housing plus the point. Also a big part of the issue for peanuts is the difference between the MT2 shank and socket when seated has about a 1/4-3/8" gap. If one could turn a taper that fit further in to minimize that then shorten the live center part it would give valuable travel back.

Sorry for all this blah, ba, blah, just to ask your thoughts on reducing OA length and using needle thrust bearings with much higher dynamic rating, but I think its a good topic for others and your wisdom is Always appreciated.

PJ

[rossbotics]

Thanks PJs for your compliment.
Your right about every inch counting on small lathes, like you say you could make the live center with just one double row angular contact bearing and a thrust bearing at the bottom of the bore on the live center housing, that would shorten it up a bit, you could get real critical and probably shorten the entire center up by 3/4" or so, but I really wasn't over concerned about the O.A. length beings I have another lathe with a much larger capacity (14" X 48")

Have a Good One
Doug

Great build and write up Doug. It solves a source of needs & creative frustration in many ways, especially with that shallow taper prior to the point. Thanks also for all the details on materials and ops!!

On bigger lathes the OA length of a center like this is not a problem but on "peanuts (7x10-14) and micro's" every inch of travel counts. I've often thought of different ways of shortening the whole assembly, perhaps using thrust bearings or combo of thrust and angular contact. Holding the point solidly by its shank is the issue. In your case you have 2 5200's rated at ~7k N (~1600 lbf) each and More than adequate, but at 14mm width gives a probable 1.5" OA on the housing plus the point. Also a big part of the issue for peanuts is the difference between the MT2 shank and socket when seated has about a 1/4-3/8" gap. If one could turn a taper that fit further in to minimize that then shorten the live center part it would give valuable travel back.

Sorry for all this blah, ba, blah, just to ask your thoughts on reducing OA length and using needle thrust bearings with much higher dynamic rating, but I think its a good topic for others and your wisdom is Always appreciated.

PJ

[old_toolmaker]

rossbotics,

I was back looking at your pictures once again and noticed you have milled one corner off the leading edge of your compound. What a great way of providing more clearance!

[rossbotics]

old_toolmaker,

yes I machined that off to give some more clearance working close to the chuck, seams to work fine, it didn't interfere with the working mechanics of the compound.

[MountainMan]

Great build Doug!!!! I definitely need to put this on my to-do list. I have ran into this problem a lot and this will absolutely solve my problem. Thanks for sharing.