ST20 lathe with BMT-65 turret

Guys

Can anyone with first-hand experience on an ST20 with the BMT-65 turret tell me a little bit about accuracy and rigidity?
If you use an ST20Y or SY, I am still interested in your responses regarding rigidity.

Will likely be pulling a trigger on an 8" lathe within the next month or so, and so far the ST20 with the BT65 turret is the only contender.

I am looking for a plane-jane 2 axis lathe with tailstock.
No bells, no whistles, no milling, no chip conveyor, just a lathe with tailstock and toolsetter.
The #1 issue I am not willing to compromise on under any circumstance: chuck-turret clearance!
I will NOT! consider any machine that cannot clear adjacent tools with the 8" chuck.
I will NOT! remove an unused ID tool tool from the turret just because it would be busted off by the chuck.

Unfortunately, that one criteria knocks out 99% of all possible candidates that I know of.

Thankfully, Haas offers the BMT65 without the motor as an option.
There is no live tool or anything, it is just a substantially larger turret that provides the tool clearance I require.

Problem?:: It is a Haas!
With that larger turret, I am absolutely concerned about loss of rigidity and accuracy!

And before anyone starts banging on Haas, please, just don't!!!
I have 2 of their lathes, one is 21 years old, the other is 18, and both will absolutely hold a .001 total on anything, one will hold .0005 total on Inco.

All I need to know is if there is anyone that can shed some light on what I can expect?

Thank You

My ST20Y has the VDI40 turret. Only time I have clearance issues is live tooling. You don’t want that so not an issue. Plenty rigid. Holds 2 tenths easily if you have the machine warm and keep it running. Otherwise see about 1 thou change as it warms up. The ST series lathes were a big step up from the SL series for HAAS.

The BMT is a completely different turret than the standard bolt on or VDI.
It is considerably larger, which is what makes me concerned about rigidity and tolerance holding.

Yes, it is quite a bit heavier than either of the standard turrets so that should help, but the larger size also means more torque on the indexing mech.

Hmm… never noticed that it was bigger than my VDI turret. Actually thought it was more compact when I saw it in person. Either way if it is larger I would think the drive would be sized for it.

The turret itself is a bit larger, but what makes it bigger yet is that all of the tools - let it be ID or OD - require a bolt-on adapter, which is what eventually give me the clearance I need.
Basically, all tools will be approx 3" or more further from the turret center, and when compared to the VDI, it is likely 5" or more.

Trying to figure out how to post a picture of my turret. It is the 24 station VDI which they no longer offer. Looking at how the static holders mount to a BMT, I would rather have my VDI especially if I were just doing 2 axis work. I think you would find more rigidity losses in the ways than the turret, but I have run mine at 160% spindle load roughing 4140 prehard before and the spindle was the weak link. Not the turret or ways.

I have BMT60 on both of my 30 size lathes (albeit with live tools on both), and its a great Turret, and the machines have been quite impressive. That being said I also have 2 Okuma Genos Lathes, a 250 and 400, and both of those are quite nice machines also.

MaxPrairie said:

Looking at how the static holders mount to a BMT, I would rather have my VDI especially if I were just doing 2 axis work. I think you would find more rigidity losses in the ways than the turret,.

Click to expand...

Why would you prefer the VDI?
The benefit of the BMT is that it puts the tools out on a larger diameter, which eliminates the clearance issue around the chuck.

As far as the rigidity, it is exactly the ways that I am concerned about.
The turret itself will likely be more rigid just due to the larger mass, but it also puts higher lifting force onto the linear guides.