The ST-10 and ST-20 are the two Haas turning centers you are most likely to run into used. Capacity separates them cleanly. Price does not. Across a wide run of model years the two overlap enough that price stops being a useful tiebreaker, which leaves one question that actually decides the purchase: what has to fit through the spindle bore?
Capacity: 1.75 inch bar or 2.5 inch bar
The ST-10 is rated at 11 x 16 inches maximum capacity, 1.75 inch bar capacity, and spindle speeds up to 6,000 rpm. The ST-20 is rated at 11.75 x 22.5 inches, 2.5 inch bar capacity, and up to 4,000 rpm.
Two of those differences are three quarters of an inch, and they are not remotely equal. The swing difference of three quarters of an inch will not change a single job you can bid. The bar-capacity difference of three quarters of an inch changes everything, because bar capacity is a hard wall. Run 2 inch bar and the ST-10 is out. No price puts it back in.
Confirm the number on the specific machine, though. One aggregator lists ST-10 bar capacity at roughly 32 mm, which is closer to 1.25 inches than to 1.75. That is the difference between a machine that runs your stock and one that does not.
The rpm gap reads worse than it is. Surface speed depends on diameter as well as rpm. An ST-10 turning 1 inch stock at 6,000 rpm is running about 1,570 surface feet per minute. An ST-20 turning 2.5 inch stock at 4,000 rpm is running about 2,600. The faster spindle earns its keep when the parts are small, which is exactly the work the smaller machine exists for.
Submodels change the machine
Neither model number tells you what you are buying. The ST-10 is tracked with ST-10Y and ST-10T variants. The ST-20 is tracked as ST-20SS, described as the standard configuration with live tooling and bar feed, ST-20Y, which adds Y-axis travel and high-torque C-axis spindle rotation, and ST-20SSY, which combines both.
Which means the capacity figures above come from a single spec table and need cross-checking against the actual submodel, since the Y-axis and live-tooling variants are meaningfully different machines. And while we are here, one misstatement worth killing on sight: a Y-axis on a turning center is not a 5-axis machine. It is a lathe with one more linear axis on the turret. If a seller frames it as 5-axis, you have learned something about the seller.
What each one sells for
ST-10 by model year: 2011-2013, $32,950-$33,523. 2014-2017, $35,500-$42,500. 2018-2020, $39,900-$49,900. 2021, $52,900. Among current listings, a 2023 unit at $46,500, which sits below the 2021 figure. The curve is not monotonic, so do not assume newer means dearer on a specific machine.
ST-20 by model year: 2011-2012, $36,500-$39,000. 2013-2016, $42,500-$68,100. 2020, $73,900. Current listings include a 2023 ST-20Y with bar feed at $109,000 and a 2011 base machine at the other end.
You will also see a dealer-published "used market average" of roughly $39,000-$50,000 for the ST-10 and roughly $59,000-$70,000 for the ST-20 circulating. Check it against the year data before you let anyone quote it at you. The ST-10 average lines up with the 2018-2020 band and sits above every machine older than that. The ST-20 average sits well above the observed 2011-2016 listings and below the 2020-and-newer ones. It is a blend across model years, not a current price. A seller quoting that average on a 2012 machine is quoting you the wrong number, whether or not he knows it.
The overlap that decides most purchases
The ST-10 tops out at $42,500 for 2014-2017. The ST-20 starts at $42,500 for 2013-2016. Those two bands meet at exactly the same number.
So at roughly $42,500 the choice is a newer, smaller, faster machine against an older, larger, slower one for identical money. Capacity should settle it before price gets a vote. Under 1.75 inch bar, the ST-10 buys you three or four fewer years of wear at the same price. At 2 inch bar or above, the ST-20 is the only machine on the list and the extra age is a cost you absorb.
Rebuild costs: nobody has published them for these machines
Here is the part nobody gets to fake. There is no ST-series-specific spindle rebuild or replacement pricing in the public record. The widely cited Haas spindle figures, $4,800-$7,200 for a rebuild and $16,000-$24,000 for a replacement, are for VF-series milling spindles. Different spindle, different machine. Do not carry them across, and be skeptical of anyone who does, because those are the numbers that get copied around the internet without the sentence explaining what they apply to.
What does exist is a documented full rebuild of an ST-30, one size class above the ST-20 in the same family. Read it as a list of what wears on a Haas turret lathe, not as ST-10 or ST-20 evidence and not as a cost estimate. That teardown found:
- Backing plates on both chucks broken and unusable by the time it came apart
- Rail covers and rails needing replacement, with chip, cable, motor and linear-guide wear found under the wedge
- Sub-spindle drive belt and pulley damage attributed to a chip jam or a flung part
- Bed twist severe enough to require a laser level and machinist jacks to correct
- X-axis ball-screw bearing wear, addressed with a bearing upgrade kit
That is what neglect looks like on a turning center. And none of it has a public price attached, which is the real budgeting problem here. Get written quotes on backing plates, rail covers and a ball-screw bearing kit before buying a machine showing any of these symptoms. There is no catalog to estimate from.
Two failure modes with cheap answers
Tailstock sticking is a named, on-model problem for the ST-10 and ST-15, and Haas publishes its own service video on the fix and frames it as straightforward. So a sticking tailstock is an inspection note, not a walk-away signal. What it does tell you is that a seller who never bothered with a documented, easy fix has a maintenance habit worth thinking about.
Hydraulic power unit noise is the one to know before you look at any lathe. Per Haas service guidance, a noisy pump with a fluctuating pressure gauge is commonly misdiagnosed as a failed pump, when the actual cause can be foamy or aerated hydraulic oil under hard running, which produces inconsistent loading and noise. Check the oil condition before anyone condemns the pump. That cuts both ways at purchase: HPU noise on a machine you are inspecting is a reason to pull an oil sample, not automatically a reason to discount hard or walk.
Separately, if the machine cuts a taper when it should not, Haas publishes an alignment and wear diagnostic for exactly that symptom across the ST line. Run it before you accept anyone's explanation about tooling.
Inspection order
- Confirm the submodel on the serial plate and verify actual bar capacity against your largest stock.
- Turn a test part and check it for taper. If it tapers, work the published alignment diagnostic before accepting any other explanation.
- Pull both chucks and inspect the backing plates. This is the item the ST-30 teardown found destroyed, and it is easy to hide behind jaws.
- Get under the way covers. Look for chip packing, damaged rail covers and wear on the linear guides.
- Listen to the HPU at idle. If it is noisy or the gauge fluctuates, pull an oil sample and look for aeration before drawing any conclusion about the pump.
- Cycle the tailstock through its full travel repeatedly and note any sticking.
- Price the machine against its model-year band above, not against a blended dealer average, and get written quotes for anything the inspection turned up.