Chuck Weight?

[Flyinfool]

Most lathes have a spec listed in the manual of the maximum weight between centers. The spindle can support half of that weight.

There are so many factors that affect cutting force like how sharp is the tool at the moment, the tool is constantly getting duller as the cut progresses causing the cutting force to climb, the hardness of the material the geometry of the cutting tool the speed and feed are all major factors some of which are nearly impossible to measure. I don't know of a formula that can calculate it.

With all that said here is one calculator that may get you in the ballpark with a bunch of assumptions built in.

Cutting Force Calculator | Turning – Kennametal

Cutting Forces, Torque, and Horsepower for Turning Applications

www.kennametal.com

 

[Tozguy]

I do understand what you are saying; however, I referred to "unsupported" only to be better able to allow me to understand better the weight bearing capacity of the just the spindle on this lathe.

I have not found the weight capacity spec for my 12x36 lathe but I am curious about it. Not that I think I will ever come close to turning that big a piece.
However it is interesting to note the work piece weight capacity spec of live centers. This one for example
https://www.kbctools.ca/itemdetail/1-435-44103
fits my lathe and is rated for 500 lbs. I expect that the headstock spindle can handle much more than a live center.

 

[ShagDog]

Interesting links, Tozguy and Flyinfool. Good analogies. I spent some time on the links. As to the kennametal one, not sure if I plugged in the right info for calculations. As to the KBC one, I also looked up MT3 dead center that fit in my lathe spindle; however, I could not find any weight capacities on the dead centers.

 

[Flyinfool]

I have a 13x40 lathe. so not much bigger than yours. According to the manual it weighs 1100 lbs. it lists the max weight between centers as 1340 lbs. I will need to eat a lot of Wheaties before I can lift that into place. Not to mention I would be terrified to spin something that weighs more than the machine. because of that number I figure anything I am strong enough to lift into position is good.

As for the weight rating on the live center, my tail has a MT2, the live center would need to be able to hold 700 lbs, it would take this one.

ROYAL PRODUCTS,2MT SPINDLE-ROYAL LIVE CENTER,1-533-10102,KBC Tools & Machinery

ROYAL PRODUCTS,2MT SPINDLE-ROYAL LIVE CENTER,1-533-10102,KBC Tools & Machinery

www.kbctools.ca

I have the light weight that can only handle 300 lbs. as I will never even get close to that.

Go to the website for your lathe and/or contact the manufacturer to see if you can find a max weight spec.

 

[Toolmaker51]

Ability of spindle to take weight load unsupported, and full load is not just setting a machine on a concrete floor. It is when each footpad bears its proportion and the machine is correctly level. Weight is beneficial unless off balance. Also why iron chucks are lower RPM rating than semi-steel or forged.
The 3:1 ratio of chucking or running a center is reasonable, if on center and with properly ground cutters.

 

[ShagDog]

...

Go to the website for your lathe and/or contact the manufacturer to see if you can find a max weight spec.

I wish I could. I don't have a manual, and the company that put it's name on it is no longer in business. The lathe was made in Taiwan in 1979 or 1980, approx.

Also, my lathe only has an 8" swing, and weighs over 275 lbs with a 1 1/2-8 spindle thread.

 

[mikey]

Much depends on the quality of the spindle bearings, the size of the spindle and the overall rigidity of the lathe. You're working with an 8" lathe so I'm going to guess your max work piece weight to be somewhere near 50#. I own an Emco Super 11 CD lathe with precision spindle bearings and a 2" spindle and it can handle just over 90# unsupported at the chuck, more with a live center.

I would go much lower on max weight given that the chuck is extended out beyond stock distances. Cutting forces are minuscule compared to the weight of the work piece and chuck on the spindle.

Even Logan recommended using the smallest chuck that would get the job done, primarily to spare the spindle bearings.

 

[ShagDog]

Thank's, mikey. I'll never approach 50 lbs, even with the weight of the chuck, so your response pleases me.

 

[mikey]

To reassure you further, cutting forces are measured with a force dynomometer. Typical cutting forces (there are three) for a single point tool in common materials found in a hobby shop are usually in the single digits (kgs), and this is with brazed carbide. If you use a well ground HSS tool, cutting forces are even lower.

With that said, it is good to keep in mind that spindle bearings do not have an easy life. They must bear the weight of the chuck and the work piece, while also keeping the work concentric while resisting the cutting forces from the tool. This is one of the key reasons to keep your chuck size and its overhang within reason - to preserve your spindle bearings. If you had a 13-14" lathe with a huge spindle, this is not that big a deal but on a little 8" lathe with a spindle close an inch in diameter, yeah, it is a big deal.

 

[ShagDog]

Bottom line me, mikey . Is the 14lb chuck that extends about 3" from the end of the spindle fine on an 8" swing with a 1 1/2"-8 spindle (MT3) with tapered roller bearings a little over 2.75 od? Here's some photos of the spindle and the headstock from when I had it apart. Thank's.