Slant bed lathe cutting forces

[BrianGar]

Its soon crunch time when I'll need to get a cnc lathe.

I dont do a huge pile of lathe work but I need something that can turn out 50 pieces with a few hrs notice as sending time critical stuff off site is now driving me mad with delays.

Been keeping my eyes open of late when visiting factories and eyeing up slant beds.

Pros of slant bed,

Fatter bed in most cases, mass, rigidity etc.
Slideways not under chuck so hot chips dont drop down and effect slides thermally + wedge up with chips.
Setup room/reach space for loading.

Now..here is the part I cannot get my head around and something that worries me, and I feel makes no sense.

Sticking my neck out and going to say I think every slant bed Ive ever seen is spinning the wrong way?

They all spin the chuck towards you at the top - meaning tool/topslide/carriage behind is being lifted off the bed under cutting force?

I know it might have the advantage of throwing the chips down to bed but in aluminium + other semi long chip metals but they all seem to come around and over the top anyway.

Is it the fact that 'new style' recirc ball linear slides dont care which way they feel the forces?

It still seems wrong not to put the whole assembly under compression thus pressing the rails down onto castings rather that trying to lift them off.

Have I it all wrong and am I missing something?

Is there anything stopping me running my possible future slant bed with the chuck turning topside away from you and mounting the tool cutting face up?

Thanks,

Brian,

 

[MikeHalloran]

If you're getting long stringy chips in aluminum, consider pushing the cutting tool speed up, a lot. If your spindle won't go that fast, consider live tooling, e.g. a milling cutter spinning at scary speed against a workpiece rotating at whatever speed you can manage.

... but you knew all that.

WRT slant beds and which way they turn, I think for long runs/ unattended operation, getting the chips out of the way, onto a conveyor, and into a barrel, trumps everything else.





Mike Halloran
Pembroke Pines, FL, USA

 

[BrianE22]

You can turn the spindle either way. But the manual for my Hardinge Cobra recommends spinning so the top of the chuck is going away. I don't quite remember the reason given but I believe it is as you say, to direct the loads into the bed in a certain way.

 

[BrianGar]

@ Mike, ya, those dam chips...fine when you have room and can speed in on the manual lathe, but when in tight quarters with teeth clenched I have to slow down and the chips come out long - you know the score!

@ Brian, yes - that makes sense(your way). The next time I'm in one of the factories I'm going to ask why they spin them the other way - lifting tool. The ironic thing is going against reason, all the chips, short and long seem to come up and around the chuck in a spray anyway!

A perfect example of the upside down cutting but chips getting thrown up and around can be seen below, seems to go against logic..

https://www.youtube.com/watch?v=kh6_rl2FgzA

That one in my mind is turning wrong way.

Now, to go hunting for something,

Thanks

Brian,

 

[JNieman]

I've ran Haas ST20SS doing prototyping and limited production runs including unattended bar-puller production. And yes, small parts right up against the chuck jaws at times, too. It ran like the slant bed you linked. It ran just fine, chips cleared (sometimes with a little help of coolant blasting in the right spot) and tools didn't budge (minus the inevitable face-palming errors). I think you're making a mountain out of a mole hill.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[BrianE22]

Quite a few shops run parts in their CNC lathes with the tools upside down. I think for most it's so they can keep using their right-hand tooling. When running upside down you'd then run the spindle in the other direction.