USING THE LATHE SPIDER ON MY PATRIOT

[smallblock]

I was turning the ends of a steering shaft this weekend and got a chance to use the lathe spider on my machine. In the past, I used to wrap duct tape around the shaft where it went into the spindle to keep it from whipping around when I turned the ends to fit into the steering knuckles. The patriot has a lathe spider as standard, so you just adjust the 3 bolts to support whatever shaft you are turning and keep the long end from bending. The spider is just a long hex nut that also serves as the nut for the drive pulley and the bearing pre-load. It has a lock screw to keep it in place once its adjusted. Its a simple idea, but a big improvement over those double spanner nuts on the old machines.

[Geof]

That is a handy feature but your picture is a bit scary looking.

I do hope you worked at very low rpm. Really for a long life with all body parts intact it is better to work at zero rpm with that much material sticking out the back of the spindle. You might get away with it many times but the time things do go haywire can be very exciting as the machines hops around the floor swinging a three feet long metal flail. Having more than about six diameters of un-supported tube or bar sticking out the back end of the spindle is not wise. If you do this regularly you really should build a sturdy frame with a tube that the protruding material is inside. It does not need to touch the tube although a plastic lining is a good idea; the purpose of the tube is just to contain it if it tries to start whipping.

[smallblock]

Geof,
I know what you are talking about- I learned my lesson the hard way on my old machine trying to turn the end of a piece of 3' foot long 3/8 threaded rod. That's when i started using the duct tape wrap. The picture is a bit deceiving because of the end shot- this steering shaft is heavy wall so it can take the torque of car steering without twisting. Between the lathe chuck jaws and spider you get about 15" of material that is supported with another 24" sticking out the end. Turning at 1500 rpm, I had no noticable whipping of the end.

[Geof]

...... Between the lathe chuck jaws and spider you get about 15" of material that is supported with another 24" sticking out the end. Turning at 1500 rpm, I had no noticable whipping of the end.

My comments are aimed not only at your setup but also at other readers maybe with less experience.

You are below the borderline, I think. The following is my crude rule-of-thumb:

6 or 8 diameters sticking out? I admit I do it but the rpm should be kept down and the centering bolts should be used.

12 diameters sticking out? I am not that daring although you might get away with it depending on material size and rpm.

More than 12 diameters? Better put on full body armour but leave the helmet off...there may not be much common sense up there to protect

The really big risk in my opinion is when you are using a CNC in constant surface speed mode. You might aim on keeping the spindle rpm low but if you forget the spindle speed clamp and have a machine that can spin up several thousand rpm things can get bad really quick. The centrifugal force that takes over as soon as the end starts to whip a little bit varies with the square of the rpm so at 2000 rpm it is 4 times greater than at 1000 rpm.

And I know that centrifugal force is called a fictitious force by physics purists; but it sure seems real when a piece of 1-1/2" dia. steel bar bends at 90 degrees and starts flailing away.

[grandscale]

smallblock,

Did Shopmaster set any length limitations for using the lathe spider? I would think you might shorten bearing life if the shaft hangs out too far or if it is not completely centered to the spider. Which raises the next question of how difficult was it to set center with those three set screws? Also, you're one of the first to trial run this new Patriot machine. Can you share with the members your general opinions so far? It seems like you're having loads of fun.

[toastydeath]

I think Geof has said basically everything that needs to be said.

We had one guy rip the entire back end (all the covers, wires, et cetera) off a machine by having a little too much material sticking out the rear end. The problem is that you often don't get much warning when it decides to go - once you sail on past that yeild point of the material, it's gonna go. If it's rattling around, then it's rattling. If it is going to go, it's not going to rattle for a minute then decide to give out, it's going to give out right away.

And while centrifugal force may be nonexistent, centripetal force is certainly real. And it's waiting right around the corner to bite an unaware machinist in the ass.

[sharpshooter90]

That spider is a nice feature- it will be real useful in Gunsmith work, as you could put the barrell through the spindle and work the chamber without worrying about it flexing around. JT says its a direct replacement for the older machines, and he will have some available in his next shipment.