We have been unhappy with the repeatability of our new 8l lathe. After powercycles or estop, when we reference the machine the home position varies by .006” - .010”. Tormach is aware of this and are dependant on a workpiece touch off to maintain accuracy. We purchased a CNC lathe so we didn’t have to manually touch off everytime you power the machine up. As unhappy as we are with this situation, a solution must be found.
Has anyone tried upgrading to a much higher end, more accurate prox switch??? I can live with a couple thou of variation but when the home position varies by .010” that’s giving me a diameter variation of .020”
Seems odd but my 15L is like that too while my 1100 mill does much better. On the 15L I cut a little piece of scrap with tool #1 and measure it, then plug that correction in after a power cycle.
For those of us reading this who are not familiar with turning operations (and are contemplating a Tormach Lathe) this older thread seems to explain this issue/limitations and workarounds.
I have an1100 mill, 24r router and a 8l lathe. They all require setting x,y,z after startup or shut down. In very simple terms there is no stepper driven machine that I know of on planet earth that does not require this for accuracy. If you want to avoid that one very simple step then you need servo driven machines that retain position.
I must say that every time I purchased one of these machines I had people line up and tell me how bad they are, how they are not accurate and how you have to do this or that like set x,y,z and how they would never buy one.
Well I’m glad to report back after extensive experience with over 10k plus hours using these machines that this is no big deal and takes a couple minutes to do and then you can run for hours making parts.
There are hundreds of steps to follow to create accurate cnc parts and setting x,y,z is just one of those steps. I spend far more time prepping materials, fixture design and CAD/CAM then the couple minutes at the machine setting x,y,z. In short you are stepping over a ten dollar bill to pick up a dime.
My 440 is the same class of machine. I home the machine upon startup and I have to use something establish the WCS with an edge finder, 3D tester, probe or another method.
It would be an interesting experiment to see if inductive switches or alternate devices and minor software tweaks were lower variability/more accurate for all of the platforms but I would think that this would have been already explored during R&D and were not implemented because they did not significantly improve the homing.
The 8L appears to have accessory inputs. I guess you could try to implement tool and work probes but on a $50-60k MSRP new “big iron” lathe, the tool pre-setter option is $6k, which is half the base price of an 8L…so, yeah, I can see the justification for the answer given in the other thread…
For a lathe tool, you have to touch off in both X and Z dimensions. That requires the equivalent of a high end mill ETS that can measure both tool height and the diameter. The one I saw was mounted on an arm that swings out to touch off and swings out of the way for turning operations. Not sure that you can mount an ETS somewhere that won’t get in the way while turning or not be reachable by the tool post.
They seem to use a mill probe in one of the tool locations of a 15L style lathe with an offset probe tip to probe the work.
Otherwise, you take a conservative cut on the OD and mic it (or the bore) and set your offset for facing…which is what I would understand is the normal process for a manual lathe that doesn’t have a probe or tool touch off…
Cliff Hall of ITTP touch probe fame sells lathe toolsetters that can help make this process more palatable:
My 2006 1100 will hold a G54 reference to +/-0.001” or so when power is cycled whereas my much newer 15L is as much as 0.015” off or more. I’ve always assumed, perhaps incorrectly, that the limit switches on the 1100 were of better quality or somehow repeated better than the switches on the 15L. One day I may actually check out that theory by installing better quality limit switches.
I got really tired of the proximity sw getting gummed up. So in made some brackets to hold 10ths dial indicators. Once I set all the tool offsets, with #1 as the master, I can ref and turn usually .0005 to .0008". I cover them with rubber gloves (even plastic 3d printed covers get splash underneath) cheap and easy. Only if you drive an axis to its limits, before ref, you can slip the drive and will have to reset that axis. Works for me.
