Anyone with Experience using a Spring-type Live Center?

[mksj]

I have a hydraulic SFJ Fischer Swiss Live Center with a pressure Gauge I picked up years ago, but they rarely come up at a reasonable price. Interestingly the Phase II has a pressure compensating spring for thermal expansion, at $70 it is inexpensive and Phase II can make decent machine accessories. I would think that if someone like Royal made a spring live center, it would work as advertised, the one I looked up had an accuracy of +/-0.0001" for $339.

CONCENTRIC 17103 3MT Standard 60 Degree Angle Live Center

BenefitsLow profile design gives less overhang, greater load capacity and increased rigidity.Smaller turning radius allows higher RPM's lower bearing speeds.Needle bearings distribute stress for up to 6,800 lbs. radial load capacity, extend life 2 to 3 times that of conventional live centers and...

www.travers.com

PHASE II Precision Heavy Duty Live Centers

Allow For Higher Turning Speeds With Less HeatAchieve Precision Results Without The Need For Separate LubricationReduce Thermal Friction when Turning with Phase II Precision Heavy Duty Live Centers. These heavy-duty live centers are well-adapted to hold a workpiece in a lathe or other machine...

www.travers.com

Phase II Live Center Description:
The rotating spindle is extended right through the tapered shank.
Two specially designed adjustable needle-roller bearings carry all radial loads.
A heavy duty ball thrust bearing takes all axial thrust.
Thermal expansion and shock loads are absorbed by a special compensator spring.
Complete protection of bearings from the ingress of coolant dirt or swarf is provided by the built-in oil seal which also prevents loss of lubricant.

 

[Titanium Knurler]

In school, we were taught to bring the center (a dead center) snugly up to the part, lightly clamp the binding lever on the tailstock, and let slack into the tailstock screw, and heat expansion could push the center back.

What about when the work piece cools?

 

[Titanium Knurler]

Here is a photo of what I was working on that prompted this discussion:



I was making a collared test bar. I started with 1-1/2” OD O1 bar, used a cutoff tool to turn the bar down to 1” OD where I wanted the collars and then whent back and forth using the longitudinal feed and stops at both ends. The depth of cut was about .020” so it took about 12 passes, each taking about, five minutes. So each relief cut took about an hour of lathe time, stopping only to reverse the longitudinal direction at the end of each pass. Since I am a newbie and the relief cut was not critical, I looked at this as an opportunity to try different speeds, feeds and depths of cut with this insert. I did eventually find settings that gave me a really nice, almost mirror-like finish with the insert I was using. This went into my log book so I can repeat it in the future when I actually cut the collars.

I sort of got off track here. My point of this is to say that because the lathe was running a long time I eventually noticed that the dead center end began to discolor from the heat and I had to stop the process to move the tails stock. Maybe because I had a lot of time to think(always a dangerous thing) during these multiple passes I started to wonder about a constant pressure live center. Since this is a test bar and I would eventually be going for the best accuracy I could achieve I did not want to move the tail stock or create so much pressure I could possibly flex the workpiece. Even if the piece does not flex what kind of strain does the expansion of the workpiece put on the spindle bearings? I know this is unlikely during the cutting of the collars but why not get rid of as many variables as possible?

To me, a newbie, the spring-loaded or constant pressure live center could be a useful tool. It has the potential of saving time that would be spent adjusting the tail stock, may improve accuracy, again because you are not moving the tail stock, and if one is doing a lot of turning between centers it may be cost effective if it prolongs the life of your spindle bearings. I think it has the potential of becoming my go-to tail stock center. At least this was my rationale(exscuse) for purchasing what looks like a good used one on eBay. As always, I appreciate everyone’s input...I will let you know how it works!

 

[Titanium Knurler]

I tried one on a cylindrical grinder; it was not accurate enough, the part was always slightly moving around, sparking intermittently.

benmychree, was it a Royal? Was it new? Just curious because Royal lists TIR at “0.0005” or better”. Thanks, TK

 

[richl]

I have never tried to do anything like what you show. I can see why you are asking , I do wonder if having a higher percision live center would also work better for this. I purchased a royal live center a couple years back used, it weighs a bit, is very massive in size. Mt3 with an mt3 sleave. When locked in, it tends to stay there as long as the tailstock does not wander.
A live center new from royal like I have is well over 1000.00 though. I do not think I ever had an issue with the center traveling though.

 

[Titanium Knurler]

richl, thanks for your input, I appreciate it. I do have a Royal live center also, the one with interchangeable tips, that I like very much but unfortunately it does not help with the thermal expansion of the workpiece. I like the simple and zero cost solution of benmychree of just not tightening down the tail stock tightly so it can move as the workpiece expands but what do you do when your work is interrupted and the workpiece cools and contracts? Obviously you re-adjust, but this is what I would like to avoid.

I don’t plan on doing this type of work often, so I am sure I would be fine without a spring-type live center but if it works as advertised it will probably become my primary live center. Remember I am a newbie, and as such I will do silly things. It is likely that I am wrong about this whole thing, if so, I hope I have at least provided some food for thought and maybe even a few laughs compliments of a newbie. Anyway, thanks again for your thoughts, I will let you know when I have had a chance to use it. TK

 

[Titanium Knurler]

I have never tried to do anything like what you show. I can see why you are asking , I do wonder if having a higher percision live center would also work better for this. I purchased a royal live center a couple years back used, it weighs a bit, is very massive in size. Mt3 with an mt3 sleave. When locked in, it tends to stay there as long as the tailstock does not wander.
A live center new from royal like I have is well over 1000.00 though. I do not think I ever had an issue with the center traveling though.

richl, I did switch to a Royal live center and would periodically back off the tail stock until it just stopped turning, then retightened it a bit until it just started to rotate. I think that worked OK but is a bit of a pain and not sure it is the most accurate way to do it. TK

 

[Tozguy]

but if it works as advertised it will probably become my primary live center.

Looking forward to reading about your results TK. The concept of a spring/hydraulic self adjusting live centre on a budget is very appealing to me too.

 

[mikey]

TK, for this specific application, where you are making a bar to do a 2-collar test, maximum accuracy by turning between centers is not necessary because you are only going to hold the bar on the chuck end. The cuts that matter will be on the surface of the two collars. I think the use of your Royal live center will be more accurate than a spring-loaded center, which has to have clearance for the plunger tip to work. A Royal live center will have a lot less movement, I think.

However, to address the question, any dead center will heat up in use. Using a good high temp lubricant inside the hole on the tailstock end will help reduce the heat. You will periodically need to loosen the tailstock and readjust it; this can't be helped. When adjusting tension, apply only enough pressure so that you can feel some resistance to rotation of the work piece by hand. Doing this during your work flow should not affect the accuracy of your part much at all.

 

[darkzero]

Using a good high temp lubricant inside the hole on the tailstock end will help reduce the heat.

I use this with dead centers. Well, actually I use it anytime I use a center even if there's no rotation between the center hole & center. It helps prevent scoring.

I buy it from Mcmaster but MSC also sells it. Can also buy it from some automotive places under the Dart name. It's made by Chicago Manufacturing & Distribution Co. though.