Kevin Mark Klughart
PhD, PE, JD, MIP, LLM
Patent Attorney / Engineer
The JET GH-1840-ZX
I must admit that the best shop tool I own is a JET GH-1840-ZX big bore lathe. This machine is AWESOME! While the bed is a bit shorter than I would like at times, it just fits in a corner of the garage and for 99% of what I do it is just what I need. The three great features of this lathe are (1) the 18-inch swing (27.5 inches in the gap), (2) the 3.125-inch spindle bore, and (3) the GEARBOX. It also has a DRO, taper attachment, and collet closer. Unlike some other big bore lathes sold by Grizzly and others, this unit is hefty and weights about 3 tons and is supplied with a 7.5 horse motor.
While there are many lathes out there that boast of an 18-inch swing (in fact the JET ZX line also has a 22-80 model), few of these have 3.125-inch spindle bores. This permits you to thread a full 20-ft joint of standard 2-7/8 OD drill pipe, or anything smaller. I can't tell you the number of times turning/threading/parting a long joint of material has been made so much easier with the big bore feature of this lathe.
Another feature present on the 18-inch and up versions of the ZX series is gearing of the spindle down to 25 RPM. This is EXCELLENT for automatic tapping and a variety of other tasks where you really want the spindle to rotate slowly. To my knowledge this low-end gearing is absent on many other large lathes.
Of the large swing big bore lathes out there, I haven't found ANY others that have the GEARBOX of this machine! It is simply AWESOME. The specs on the machine indicate 61 inch threads (1-5/8 to 72 TPI), and 24 metric threads (0.05-20 mm), as well as Diametric and Module threads (for inch/metric gear cutting). However, if you look at the gearbox faceplate of the lathe you will notice that it has four dials:
Thus, there should be a total of (4)(9)(5)(3) = 540 combinations of thread cutting arrangements, not accounting for duplicates. However, if you look at the threading chart on the machine you will see that there are far fewer combinations documented:
I had intended to investigate the combinations not detailed on the thread cutting faceplate of the machine when I installed the lathe, but as luck would have it I had a bad thrust bearing on the leadscrew when the machine was delivered and it required some disassembly of the machine to determine what in fact was broken. In doing so, I was able to decipher the exact gear ratios of the lathe and produce the following pictorial description of all thread cutting arrangements:
This chart has been compiled into a gearbox chart (PDF) listing all the possible combinations of gearbox settings and their equivalent threading or feeding results for the apron. From this chart it is possible to thread many standard threads that are not listed on the threading chart provided with the machine. This breadth of threading makes this machine far more versatile than advertised, especially in situations where both inch and metric threading must be performed on a routine basis.
While other machines may provide for a wide variety of inch/metric threading, the ZX line of machines is the best I've seen in one machine that doesn't require ANY change gears. Compare the ZX gearbox to that of the JET 1440-W below, and you can see that while there may be some finer threads on this machine, the full range provided by the ZX gearbox chart is not available.
Additionally, note that in some circumstances the traverse feed can be engaged for threading of single-pass single-point threading with thread pitches as high as 654 TPI. Furthermore, with proper gearbox selections, the lowest TPI available is actually around 0.73 TPI, not the 1.625 as advertised.
The JET ZX lathe requires 3-phase power. There are generally four ways to supply this requirement:
I chose the VFD route and opted for a model PC1-100 from Drives Warehouse (www.driveswarehouse.com). This unit is rated at 10HP and takes 220VAC single phase input and generates 240V 3-phase output.
The unit is quite small (19x10x10) compared to a rotary phase converter and the price is roughly equivalent. It is light enough (30lbs) to be mounted to the wall, and this was easily accomplished using the horizontal rails used to support the shelving system.
As a side note, I delayed purchasing this lathe because I had heard from reliable sources that JET was at one point going to sell an Electronic Variable Speed (EVS) lathe much akin to their EVS drill press. I have the Jet JDP-20EVS drill press and it is a remarkable piece of equipment. No belt changes! Two gears - 60-500 RPM and 100-2000 RPM. Speed determined by a potentiometer with digital tach readout. I waited and waited for them to come out with the lathe equivalent of this but I guess they scrapped the idea because of the failing economy.
An Alternate Source
I purchased my lathe from www.southern-tool.com, and found their pricing (especially during certain time of the year in which JET is having sales) better than anywhere else. For those of you who might balk at the pricing of JET tooling, ENCO (www.use-enco.com) sells a series of big bore lathes that appear to come from the same overseas manufacturing line. A front view of this lathe is below:
The specs seem to be identical, and from looking at the gearbox on the machine, the dials, positions, and markings seem to be identical to that of the JET product. With the exception of the machine paint color, ENCO nameplate, painting of machine nameplates, this machine appears to be identical to the JET unit.
Domestic vs. Import
Before I purchased my lathe, I spent a long time trying to find a domestic lathe that had the features of the JET product. I couldn't find anything in the price range or functionality that was even close. The key feature of the lathe - the gearbox - is something I figured I would be using a lot to thread a wide variety of fasteners, both for new equipment and for repairs. The JET was simply the best available. SUMMIT (www.summitmt.com) had several lathes with their NORTON gearbox that had in some cases more options than the JET gearbox, but their implementation required change gears for 11.5 TPI threading and this was a non-starter for me because I do a lot of NPT pipe threading. Additionally, this machine with all the standard options available on the JET was almost twice the price of the JET product.
No product is perfect. The JET lathe is no different. Here are a list of things that I wish were different:
All things considered, however, I must say I'm very impressed with this machine!
Kevin Mark Klughart
Registered Patent Attorney, USPTO
3825 Leisure Lane, Denton, TX 76210-5589
tel: 800-353-1211 / 940-320-0580 - fax 940-320-0581