A few months back, I posted an inquiry about levelling an engine lathe as well as asking about industry standards for accuracy on new lathes. We wer ein the process of buying a LeBlond 25" x 96" NK 2516 Heavy Duty Engine Lathe. The NK 2516 is a very heavy duty lathe for its size. It had been ordered special by the US Government in the late 1960's or early 1970's and really had not seen much use. The pre-selector mechanism in the ServoShift headstock had been chronically acting up, so the lathe had been put in storage for some years. We had been shopping for a replacement engine lathe (having gotten rid of a southbend/Nordic 25" x 96" lathe). We wanted a heavier duty, US Made engine lathe. After a few fool's errands to inspect used/worn lathes, Yancey Machine Tool advised they had this 25" x 96" LeBlond engine lathe in their warehouse. We inspected it and went to contract with Yancey. At the time of my inquiry to this Bulletin Board, the lathe was being rebuilt and modified by Yancey Machine Tool Company of Portland, Oregon to our specs. Jim K. responded and kindly sent me the "Machinery's Data Sheets" for "American Standard for Accuracy of Engine & Tool-Room Lathes. Armed with those standards, I asked that the lathe be levelled and tested to them.
We went out to Portland, Oregon to inspect the lathe and test it in place at Yancey Machine Tools a few months back. The lathe had been setup and levelled on Yancey's shop floor. It was levelled using precision levels such as Starrett 199 levels and a boring mill level. Levelling was "dead nuts accurate", and I turned the levels end-for-end to be sure of it. This was more accurate than what is allowed in the standrads for new toolroom lathes. I then asked for a dial indicator and checked the tailstock quill, carriage alignment and a few other things listed in the standards. The lathe was tighter than what the minimum requirements were, even for toolroom lathes. We then took some test cuts in the shop and found the lathe was cutting within a few tenths in a run of several feet. The lathe was then shipped to our powerplant in NY State. It travelled cross country on a flatbed truck, and was offloaded using our plant gantry crane. It was on skids, and was let down into our powerplant. It was landed on Hillman rollers (another subject that this forum has discussed), and moved through the plant into our machine shop. No problem with the Hillmans as we have clean, level concrete floors.
We mounted the lathe using drilled-in anchor sleeves, setting them in resin grout. This gives a clean job with no anchor bolts sticking above the floor line. Sole plates were then set on "Adhaesium Felt"- a resin-impregnated felt which takes up any irregularities between the floor and the sole plates and bonds the soles solidly to the floor. It avoided the need to chip off the floor for bedding the soles on regular machinery grout. The lathe was then landed ont he soles( jacking it up to get it off the skids, then jacking it down). On the soles, in place, we then screwed in lengths of B-7 (chrome-moly) all thread rod for anchor studs. LeBlond uses hollow fine-thread bushings to jack the lathe level. There were (4) anchor/jack bushings on the headstock, (4) ont he middle support leg and four (4) more on the leg at the far end of the bed. We levelled the lathe using Starrett 199 levels along the bed. For cross-levelling, we made a bridge, using a Busch Precision Straight edge to span the width of the bed. Differences in bedway height were made up using a parallel and shim stock. We got the lathe DNA level in a matter of an hour or so from the time we landed it. Let the resin in the Adhaesium Felt squeeze out and set, then re-levelled a few days later. We let the lathe sit for a few weeks as we had some emergencies int he plant to deal with. Yesterday, (9/29), Portlantd Machine Tool Services/ New England CNC was in to install a DRO on the lathe and final level it as well as to witness acceptance testing for Yancey Machine Tool. The lathe was found to be very slightly out of level on one headstock corner using starrett 199 levels. The headstock jacking bushing was adjusted in, and the lathe was again DNA. Portland Machine Tool then mounted what they call a "Top Hat" fixture on the spindle nose. This is a precision ground test bar which is indicated in and squared to the spindle nose. With the tophat in place, it was established that Yancey Machine Tool had rescraped things correctly; the headstock spindle pointed slightly outwards & upwards by a 3 tenths over a run of 14". This is within toolroom accuracy per the standards.
With the lathe levelled and checked, PMTS then installed a Newall "spherosyn" DRO system. Newall uses tubular stainless steel packed with steel ball bearings for the scales and really neat readers. The scales are infinitelty more rugged than glass scales. Setup went a lot quicker than I thought. The DRO keypad/display was mounted on an arm off the back of the carraige wing. It made a nice clean job.
With the DRO in place, we moved to turn a test bar. I had decided to turn a bar seven feet long between centers. To minimize deflection, I ran some numbers and came up with a piece of mechanical tubing, 8" OD x 3/4" wall as being a good test bar. This would have minimal static deflection and minimal spring from the toolbit if it were turned on centers without any steady or follower rests. We had prepared this piece of tubing by machining two end plates from 1" hot rolled structural plate burnouts. These had been faced, a step turne don them so they were a light drive fit int he tubing, and centers bored in. These plates were then welded into the ends of the tubing. I had the mechanics weld on a drive lug to engage the slot in the drive (or dog) plate. We put the test bar up on centers and for a first cut, ran a ball bearing live center in the tailstock. Not a real accurate thing, but we wanted to see how this heavy hunk of pipe was going to run. We ran at 140 rpm, with a carbide insert tool. We cut three (3) separate lands; one at the tailstock end, then backed out the tool and rapid-traversed down to midpoint, cut another land at the same depth as the previous one, and repeated the cut at the headstock end. This was a first cut, had not touched the tailstock base since Yancey had set it in their shop in Portland, Oregon. We had not indicated the tailstock quill bore to the spindle. Just figured to take a cold cut and see what we got. Three of us took our own sets of mike readings. The land diameters at the tailstock & headstock ends were within 5 tenths of each other. Midspan land was bigger by 1 thousandth. We attributed the 1 thousandth larger diameter to spring of the workpiece. Having a lathe which turned within 5 tenths in 7 feet, I accepted the lathe on the spot and did not have any further adjustments made or test cuts taken. The fact we took the three test cuts by backing the tool out and re-establishing it's depth of cut meant that the lathe is nice and tight and the DRO and micrometer collars all have good repeatability.
Jim K. had advised me not to expect too much out of a big heavy duty engine lathe in the way of close accuracy.
We are all quite happy with how the "new" LeBlond lathe came out. Yancey machine Tool had really gone far beyond what we were expecting. Aside from the overall accuracy of the lathe, they had reground the bedways and rescraped the carriage wings, putting about 0.0015" of relief int he center of the wings to allow the wings to settle down onto the ways. They had re-worked the oil gallery drillings in the carriage wings to provide quicker delivery of way lube and suggested we add a Bijur hand pump on the carriage to prelube the carriage wings before we moved the carraige. They provided a tapping for the purpose. We did that as well. They had also fitted a heavy duty taper attachment, using cam follower bearings. The lathe was sold new as a "Servo Shift" machine, but the pre-selector mechanism had been almost impossible to keep in order for any length of time. I had asked Yancey to convert the machine to a manual shift machine, which they did. They used levers from another LeBlond headstock and made a better-than-factory shifting system. The put laser-cut selector quadrants on the headstock and made a really sharp looking job of it. They also got rid of all the fluidic devices and Rube Golberg servo shift stuff. Instead, they retrofitted a programmable AC drive. This drive was programmed for a dither function, which rocks the input shaft and headstock gearing slowly up and back to make shifting the gears quite a lot easier. They made a really sharp control panel on the headstock, integrating the new progammable controls with the existing lathe. The result is this really incredible, user-friendly lathe. It looks like it came from the factory that way- no real signs that it was a heavy modification job. We have plenty of heavy turbine work for it, and need the ruggedness plus the accuracy. I could not stomach the idea of buying a new lathe made overseas, let alone some lathe with not enough iron or simply the not having the right "feel" to it. There simply is no substitute for a well made heavy duty US machine tool. We are looking forward to many years of good work on that lathe. Thanks again to Jim K. for the information and for the advice he gave me via a phone call. BTW: I did not have to use my Paragon optical level- the Starrett 199 levels were plenty adequate for levelling the bed of the lathe.
Joe Michaels
