Left or Right han tooling

CNC for dummies · Mar 4, 2021

hi Guys,
i have just purchased my first CNC live tooling c axis lathe for my workshop, i am agonising whether to use right or left hand tooling, i understand that 80% of machines are using right hand tools. I have been a manual machinist for over 20 years and my thoughts are that i would use left hand tooling. can someone give me some pros and cons for each hand.

cheers

yardbird · Mar 4, 2021

Using right han tooling you don't have to reverse the spindle to drill, tap or thread. Depends on who you're talking to as to whether the transfer of the cut load down on the bed matters. Long standing debate. I'd rather use left

Brent

gregormarwick · Mar 5, 2021

It's not usually a case of one or the other. You use what suits best for a given situation and machine.

Typically in a slant bed lathe, right hand tools let you keep the spindle running without reversing if you are drilling and screwcutting like yardbird says above. Another benefit is the chips fall away easier sometimes. For a typical user not concerned with squeezing every last second out of a cycle, these are not significant advantages IMO.

If you're doing heavy boring in a steady, a right hand bar generates cutting forces down into the steady, whereas a left hand bar is trying to lift the part.

Otherwise, left hand tools generally provide better stability for heavy cuts and generate cutting forces in a direction that are more favourable to the machine. Accordingly, like yardbird, I usually prefer left hand.

There are fringe cases where it depends on the machine. I have a Y axis lathe with a physical Y axis instead of a wedge, on that machine the Y servo is under constant load to hold the turret up against gravity, and using left hand tools makes it work harder. Never been an issue, but it's just something that I'm aware of.

lumley32 · Mar 5, 2021

I go with right hand for standard tooling, I'm not a fan of stopping and reversing for drilling.

just to add, with some tooling setups will decide for you, I would have to get new tooling holders for my VDI turrets to run "upside-down".

FrankieB · Mar 5, 2021

Od tools i run right hand up side down so the chips fall down. Boring bars, doesn’t matter.

Jashley73 · Mar 5, 2021

Left hand. Left hand always for me.

-Easier to change inserts.
-Easier to SEE the inserts for wear.
-Heavier cuts will compress the machine together, instead of try to pull everything apart.
-MUCH more rigid & better performance on interrupted cuts.
-The above (2) points apply equally to linear guide machines too. Remember that linear rails are held on with bolts, and bolts can stretch.

-The "chips falling into the conveyor" thing is only a half-truth really. This is all dictated by chip formation, and you can change the direction that chips will fly by messing with your feed override knob.

-Spindle reversing direction - Unless you're trying to shave fractions of seconds on tiny machines, then this "issue" actually, isn't. You're going to give the proper speed & M code for each new tool anyway...

DouglasJRizzo · Mar 5, 2021

Much of this depends on the machine, the type of turning, and personal preference.

On my Okuma LB-15 I use LH turning tooling, and run the spindle in M04, so that the machine is turning "down" into the ways. I find it better that way. When I need to drill or thread, I reverse spindle direction on the tool change and machine accordingly.

Scruffy887 · Mar 5, 2021

I cannot think of any part I make that does not have a hole in it at the very least, and many have boring and threads. Your Manual Machine Mind thinks very heavy cuts to cut down of hand cranking time. But you have a CNC now so multiple passes with less depth of cut are no big deal.
You do need to give some thought into tool hand if you have a sub spindle. Sub will pick off sync rpm with main spindle, but that is a reverse direction and after pick off the sub reverses rotation for "normal" turning, drilling, tapping/threads. You could keep a tool in the turret only for those parts that get just turning/back face on 2nd OP. Your processes may vary.
Both of my lathes have threading OPs on main and sub spindles, and the 3rd machine arriving soon will be set up the same.
Congrats on new machine. Full CNC Bar operations give me a very satisfying feeling when they are making parts, and I am fookin off doing something else.

SIM · Mar 5, 2021

I had same idea of using LH tooling as the better choice.

Aside from heavy interrupted cuts I did not notice a difference. Buying tools became tricky as the LH stuff was not always available. Many times when I was looking I needed sooner then possible so took what was available...which meant one op was LH, then RH...oh it didn't fit so swap tools...now swap spindle direction.

Steel a tool from the conventional machines...RH. After awhile I found it was just easier to keep it all going the same direction using the more standard RH tooling.

Rob L · Mar 5, 2021

Jashley73 said:
Left hand. Left hand always for me.

-Easier to change inserts.
-Easier to SEE the inserts for wear.

Those two points are so easy to forget about but so obvious when it actually comes to running a lathe.

What I use depends on what machine I'm running and what I'm doing, for heavier roughing I generally use left hand on my slant bed lathe, but on my gang tool lathes it'll be right hand to avoid changing spindle direction, unless...

... the part has a left hand thread, in which case I'll try and have all left hand tooling where possible, and if I can't I'll try and order the operations so all the LH tooling ops are done in a row then all the RH ops in a row, or vice versa.

I would count on buying a RH and LH version of most tools though eventually, it's just going to happen.

CORONA VIRUS · Mar 5, 2021

With right hand chips fall down instead of riding on top of the insert. And, you keep same rotation as drills. Less machine wear. Less cycle time.

cosmos_275 · Mar 5, 2021

I have zero experience, so grain of salt. I'm getting my first lathe also. I'm going all RH. I visited a shop where a real experienced guy was running all the lathes. He had all RH except one.

The push pull thing: Most cutting positions put the cutting off the rails of the turret. So, it's like a see-saw, when the near rail is getting pushed, the far rail is getting pulled. Yes, in LH, the near rail gets compressed, but the far one is pulled up (tension). With RH, the near one is in tension and the far one is compressed. In the RH case, the tension on the near rail is going to be larger (maybe 2x) than the tension on the far one in the LH case. Maybe it matters on some machines, but I'm not going to worry about it. The machine is built to go either way. If you've overcome the preload on all the bolts holding that rail on and it's sliding around, I think you're outside what the machine is rated for.

I do like the visual of LH better, but I'm going all RH to keep it simple. My 2 cents.

Jashley73 · Mar 8, 2021

CosmosK said:
The push pull thing: Most cutting positions put the cutting off the rails of the turret. So, it's like a see-saw, when the near rail is getting pushed, the far rail is getting pulled. Yes, in LH, the near rail gets compressed, but the far one is pulled up (tension).

Don't forget about what's going on with the Z-axis slide as well. Do you want it in tension, or compression?

CosmosK said:
If you've overcome the preload on all the bolts holding that rail on and it's sliding around, I think you're outside what the machine is rated for.

Don't forget about crashes**. When the lathe get's "bumped" - Do you want those forces putting the bolts holding the linear rails in MORE tension, or compressing the rails into the bed castings?

** Former employer has a big Mazak Variaxis machine. CAT50, 30"ish table, overhead gantry-style 5-axis machine. They're cutting some aerospace parts that require some pretty tight straightness & flatness tolerances. Over a phone call, the owner is telling me how they kept seeing a bow in the top of the part, along the X axis, around the center of the machine's travel. One of the techs explains how it was most likely crashed in the past, and stretched the bolts near that location, and let the rail lift slightly. Then, oils & contaminants seep under the rails & harden over time, and now the rail is "set" in place. The only permanant fix, is to disassemble the machine, pull (and repalce?) the rails, clean & reinstall. That's an extreme example, but certainly possible elsewhere. By comparison, lathe crashes usually involve A LOT of energy, and can get really ugly.

So I'm all in favor of directing forces into the bed of the machine. In these case of a bad crash on a linear-guide machine, you may stretch the bolts in the case of a RH tool getting crashed. That same crash but with LH tooling, might instead knock the turret out of radial alignment, which is a much easier, and quicker fix. (Which might also happen to the RH equipped machine, still...)

cosmos_275 · Mar 8, 2021

The shop I visited had an older lathe that had been crashed and the current operator who ran all the lathes said it couldn't make good parts anymore. The owner was too cheap to bring in support techs to realign so there it sits.

CAMasochism · Mar 8, 2021

Another thing that may not be considered as much is that in the event that a part comes out of the jaws, the spinning of the part when it impacts the inside of the machine will cause it to want to bounce towards the back of the machine rather than towards the door and operator.

SIM · Mar 8, 2021

If there were true hard reasons for either direction the choice would not be there, it would become the Rule and not the Exception.

Climb milling is the standard with CNC Milling. Sure you can conventional mill in CNC's and at times there is good reason for it, it is however the exception.

I think a strong case could be made for turning with LH or RH tooling in a lathe...but the final vote comes down to personal preference, jobs being run and tooling on hand in my humble opinion.

toolsteel · Mar 8, 2021

Had some personal experience hard turning on a lathe (60 Rc +) not specifically designed for it. Results were noticeably better LH vs RH. We chalked it up to pushing against the ways. Sure we could be wrong.....but whatever the reasoning....results were better. Ran it.

706jim · Mar 8, 2021

Scruffy887 said:
I cannot think of any part I make that does not have a hole in it at the very least, and many have boring and threads. Your Manual Machine Mind thinks very heavy cuts to cut down of hand cranking time. But you have a CNC now so multiple passes with less depth of cut are no big deal.
You do need to give some thought into tool hand if you have a sub spindle. Sub will pick off sync rpm with main spindle, but that is a reverse direction and after pick off the sub reverses rotation for "normal" turning, drilling, tapping/threads. You could keep a tool in the turret only for those parts that get just turning/back face on 2nd OP. Your processes may vary.
Both of my lathes have threading OPs on main and sub spindles, and the 3rd machine arriving soon will be set up the same.
Congrats on new machine. Full CNC Bar operations give me a very satisfying feeling when they are making parts, and I am fookin off doing something else.

I was going to choose a section of your post to quote, but just wanted to congratulate you on your new "status" at 2000 posts!

cgrim3 · Mar 8, 2021

Generally, our go-to is right hand tools. That way you don't have to reverse the spindle when drilling, threading, etc. Reversing the spindle on an 8 inch autoblok chuck (think chuck & part inertia), in my opinion, puts more wear and tear on your machine than using right hand tools. Right hand tools want to "lift" the turret off the ways while left hand tools want to "push" the turret against the ways.

Nevertheless, we still use both left and right hand. If the part is small/medium and doesn't have a ton of roughing but has drilling, threading, boring ops we will use the right hand tool. If the part is larger and has a ton of OD and face roughing, we use the left hand tools. That way it is easier to change inserts, easier to inspect the insert for wear, and the force is applied against the ways.

It really depends on your situation, but regardless, we find ourselves using right hand tools more often than left. There is something I don't like about reversing the spindle of an 8" chuck, especially with the inertia behind it.

My .02 cents

Chris

gregormarwick · Mar 9, 2021

cgrim3 said:
Generally, our go-to is right hand tools. That way you don't have to reverse the spindle when drilling, threading, etc. Reversing the spindle on an 8 inch autoblok chuck (think chuck & part inertia), in my opinion, puts more wear and tear on your machine than using right hand tools. Right hand tools want to "lift" the turret off the ways while left hand tools want to "push" the turret against the ways.

Nevertheless, we still use both left and right hand. If the part is small/medium and doesn't have a ton of roughing but has drilling, threading, boring ops we will use the right hand tool. If the part is larger and has a ton of OD and face roughing, we use the left hand tools. That way it is easier to change inserts, easier to inspect the insert for wear, and the force is applied against the ways.

It really depends on your situation, but regardless, we find ourselves using right hand tools more often than left. There is something I don't like about reversing the spindle of an 8" chuck, especially with the inertia behind it.

My .02 cents

Chris

I have lathes with 6" chucks all the way up to 18" chucks and I have no concerns about wear and tear from reversing. I've been doing it for years without consequence.

This is not to denigrate anyone who fits this description, but I do think that a lot of the pro-right hand arguments come from people with small lathes taking ~1/8" roughing cuts on small bars. Usually the same people who claim that WNMG's are the best roughing insert because you get six edges instead of four.

When you're taking 3/8"+ DOC on an 18" piece of forged 34CrNiMo6, the difference between cutting against the bed rather than away from it becomes pretty clear (and why WNMGs are terrible roughing inserts...)

Again, I know this reads as pretty condescending, it's not intended that way.

Left or Right han tooling

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