Extended Point Live Center

[rossbotics]

I have found from time to time that the need for a extended point live center would sure be nice, the longer nose gives you a little extra tool bit clearance, especially for those smaller diameter shafts that require machining on their ends, but to overcome that I would just grind some of the tool bits corner off to clear the point of the live center, some people use carbide inserts with the correct angle to overcome that problem,
I prefer Cobalt H.S.S. bits and I don’t liked to grind the corners off !

The body has a # 3 Morse Taper Shank; the center rotates in two 5203ZZ double row angular contact bearings,
The body and center point were constructed from 4140 Pre Heat Treated Steel which has a RC hardness of 27-32 which will be quiet sufficient,
Start by machining the Morse Tapered end on the work piece, set the compound slide to approximately 1 ½ °, then chuck up something with a #3 Morse Taper Shank then indicate in the O.D. where it is running true, check both ends for trueness, mount a dial indicator onto the compound slide and indicate the compound in with the taper shank, chuck up your stock and turn down a straight section 3.313” long and .960” in diameter, using the compound cut the taper onto your work piece, or you may have a taper attachment, the small end of the taper should measure .778” and large end .938”, great care should be taken when machining tapers, machining this taper to the measurements I have described and expect it to fit perfectly will not happen, this is just a starting point, when you get the small end turned down to about .790” you need to start checking the fit with something that has a # 3 internal Morse Taper, (this will be your gage), the two tapers should fit perfectly together with no wiggle in the front or back, take several small cuts and adjust the compound as needed to achieve this fit, you should apply high spot bluing to your tapered piece and slip the gage over it and rotate it, this will show the high spots that need some attention, I just use a fat magic marker, your gage should slide all the way up within an 1/8” from the big end of the taper, make sure it doesn’t bottom out in the gage, if the gage bottoms out you can always machine some off the small end the work piece, if you machine some off the small end of work piece chances are great you will have to machine the taper further back on the big end as well, leave a couple thousands on the O.D. to polish for a nice smooth finish and that final fit, the key factor here is taking your time.

Once the taper was completed I removed the chuck from the lathe and inserted the Morse Taper reducing sleeve that came with my machine into the spindle bore, I inserted the Morse Taper I just machined into the reducing sleeve and gave it a tap with a plastic hammer to seat it firmly, I then proceeded to machine the bearing measurements into the body of the center, See Photos

The machining of the center point was done in a one step process, meaning it was machined all at one time without turning the part around insuring 100% concentricity, I started by chucking up a piece of 1” 4140 round 7” long leaving 3 ½” protruding past the end of the chuck jaws, after setting the compound to 30° I machined the center point and confirmed the angle with a 60° thread grinding gage, then the 16° secondary angle was machined, I ground up a turning tool similar to a parting tool only it had about a 30°angle on front, this allowed me to plunge into the work piece and feed to the right up to a shoulder to complete the machining of the bearing journal, .003” was left on this diameter for polishing and a press fit for the bearings.

I have supplied multiple photos, drawings, two sheets containing Morse Taper dimensions and this documentation for anyone wishing to make this tool; although this is how I made the tool, it doesn’t necessarily mean it’s the only way.

As always
Thanks for looking
And happy machining
Doug




Roughing in the shank




Finished shank




Shank reversed and ready for boring




Bored for the bearings




Center made and being parted off




All parts finished




Partially assembled




Assembled live center




Front view




Drawing of the body




Drawing of the center




Morse Taper dimensions

[bobs409]

I agree, could be useful some times.

[olderdan]

These extended centers are great and you made a typically nice job of yours.
We used to use these at work and I bought a new Gepy No 3 in anticipation of also buying a Bantam lathe but the receivers got it first.
I cant use it so its going on Ebay if anyone wants to look out for it.

Regards
Olderdan

[DanLins]

These extended centers are great and you made a typically nice job of yours.
We used to use these at work and I bought a new Gepy No 3 in anticipation of also buying a Bantam lathe but the receivers got it first.
I cant use it so its going on Ebay if anyone wants to look out for it.

Regards
Olderdan

Looking !

[Paul Jones]

Doug,

Thank you for posting your excellent photos and instructions. The 4140 pre heat treated steel is great material and as always your precise machining shows in your live center.

Regards,

Paul

[rossbotics]

Thank You Paul

[petertha]

Some more questions if you don't mind.

Can you comment on fits & ultimately how things are secured? For example, do you fix the center point to the 2 bearing ID's with a retaining compound & maybe insert the whole rotating assembly into the body cup pre-warmed up or something so it resides in place with a bit of interference?

Would you consider this a use-it-till its worn type tool or could it be disassembled? (Its the reverse of above ^^ that got me wondering about this to begin with).

Sorry I am kind of naive about these 5203ZZ double row angular contact bearings. Does that mean each bearing unit has 2 internal rows & stacking two units together just gives you that much more thrust rating or stability on the center shaft? Is there a left/right orientation to these bearings or they are equal so you can just install them as a stack like you show?

[rossbotics]

Hi Petertha
the fits on the bearings are very minute, I bored the housing .0003" smaller than the O.D. of the bearings, I turned the shank on the live center .0003" larger than the I.D. of the bearings, I also put a drop of red Loctite on the shank of the live center before I pressed them together, there is a 25/64" hole all the way thru the shank of the live center, this so you can install a 3/8" rod thru the body of the center a drive the bearings out if need be.

Any of the 5200 series bearings are known as angular contact, they have two rows of balls, meaning they will take radial and end thrust from either direction, there is no orientation of the bearings, they can be installed in either direction, stacking two bearings together just gives the center point much more stability and will take more end thrust than just one bearing, I use this Live Center on a regular basis and I have yet to see any wobble in the center point

Thanks Doug

[ddickey]

Can I purchase these plans?
Oops. Guess I should start from the beginning.

[ddickey]

Always check your bearing OD & ID before boring or turning your final dimensions. The bearings I have are exactly 40mm on the OD. That's 1.5748 - .0003". So I want to shoot for 1.5745". The bearings Doug used are .02mm larger than mine.