Extra Large Face Driver Turns Up Production and Cuts Machining Expenses and Downtime
Cutting 10'-long steel bar stock weighing six-tons with diameters approaching 28" is tough on any lathe. . .making a roughing cut in only one pass while taking up to a one-inch cut depth is even harder on the equipment. But Dayton Forging & Heat Treating Company (Dayton, OH) discovered how to do this while keeping productivity up and meeting customer demands.
Dayton Forging & Heat Treating Vice President Eric Wilson says the company had a problem cutting an entire bar in just one pass, which can't be done using a conventional, manual three-or-four-jaw chuck. Dayton Forging & Heat Treating didn't want the machinist to pull the bar stock out of the lathe and flip it around to machine the other side, because this caused about 30 minutes of lost production time.
Dayton Forging & Heat Treating is a job shop that also does commercial heat treating, forging and stocks forged/rough turned bars in popular carbon and alloy grades. It produces about 12 million pounds of forgings per year. The company provides saw cutting, machining, drilling and heat treating for cut slices of bar stock. Turnaround times on slices range from same day to five days depending on part specifications and requirements. Dayton Forging & Heat Treating has extensive machining capacity which includes over two dozen lathes and is capable of processing large forgings up to 25' in length.
Cutting large diameter bar stock in one pass
According to Wilson, the company needed to increase its productivity on its lathes by being
able to make one roughing pass to cut a bar rather than two when using a conventional,
manual-jawed chuck.
He says, "In our machine shop, we have one operator running two lathes. On one lathe,
the operator needs to spend most of his time tending the equipment to get a part machined.
The second lathe has a straight bar to run. So he can just put a bar in, set it and let it cut.
In the second lathe the cut is very long, so the machinist can concentrate on the first lathe's operation. Before we had the face driver we could only cut up to the chuck's jaw area, and then we had to flip the bar around and cut the remainder of it. By switching to a Neidlein FSB 75 face driver from LMC Workholding (Logansport, IN), it allowed us to cut the part in one pass and not flip it. So we could just load the bar, set the cut and let it run while the operator spends his time on the other machine where he's needed."
With the new face driver, the company is able to save the time it takes to get a crane to the lathe, hook up the bar, pull it out, flip it around and reposition it in the lathe, check the bar's straightness and then make the cut.
Wilson mentions, "On the initial cut the jawed-chuck is not so bad, but after the part is flipped, we have to indicate it in. A machinist has to set up an indicator, adjust the bar to get it within a couple thousands of straightness on the lathe and then run it. This means he has to manually adjust and tighten down each jaw of a four-jawed chuck. All this takes about 30 minutes. We probably turn 500 bars a year with the face driver lathe seeing half of them. So we're talking 250 bars times a half an hour a bar, roughly 125 hours. The new face driver picked up the machinist's productivity 125 hours, all because he didn't have to flip the part. Therefore, being able to run the spindle 125 more hours is an excellent increase, probably saving us about $12,000 in hourly costs.
"However a three-jaw chuck is nice, as they scroll down all at once. But when we're turning a rough forging, a three-jaw chuck won't work, because there are small flats and peaks on the part that won't let the chuck properly grip the bar. Also we can only turn as much as we're gripping. So the more surface area we can cut, the better it is for production."
The Neidlein face driver is mounted on a 75-hp American Lathe. It can cut up to a 28" diameter part depending on where the feed and speed rates are set.
Wilson adds, "We try to avoid interrupted cuts if possible. If we can take the roughing pass all in one cut, we try to, because it's just so hard on tooling coming in and out of the cut. Plus you have the scale which is extremely hard and abrasive and tough on the tooling. If we have to, we'll run an interrupted cut and the tooling does okay with it, but we'd prefer to hog the metal all off using one pass. We use a 1.5" tool cutter that allows us to take up to two inches off in a pass. Of course when we're talking about that big of a chip, we have to slow down to handle it."
Jaw chucks versus face drivers
The difference in setting up the part using a chuck versus a face driver is minimal says Wilson. For them, it's just a matter of making sure they have the right torque on the tail stock to load up the face driver and not overload it. It's quicker because the operator doesn't have individual jaws to worry about. Wilson says, "But the tail-stock pressure is the critical thing. However that's only one wheel versus four jaws."
He adds, "Some of our cuts are not perfectly square. With these large bars, I don't know of one that is square. So we get a couple of degrees out from our face, and the face driver has the compensation medium in it to adjust for some of these irregularities. So squareness has not been a problem. The benefit of this self-correcting compensation feature means that the machinist doesn't need a perfectly flat or faced part. It can be bandsaw cut, because it's close enough."
Dayton Forging & Heat Treating is looking to add another large face driver to its inventory.
Wilson says, "We're committed to a second face driver, but we're having Neidlein and LMC
Workholding look at building us a larger one."
Brandon Morris from LMC Workholding mentions, "This new larger face driver is even
more special than their current one, because it will have a dual-drive diameter on it. It will
have a bigger drive diameter for a greater range, and will be able to handle bars from 34" down to 8". There will be 12 drive pins in it, but the machinist will only use one set of drive pins at a time for the bar diameter being turned."
As to the drive pins themselves, Dayton Forging & Heat Treating is tough on them. They use a double-chiseled pin instead of a single-chiseled pin for better gripping strength and for heavier cuts. The double-chisel pins give more surface area to bite into.
Mechanical face drivers in general allow turning applications to achieve increased flexibility to lower cycle times, turn both the small and large parts, and even allow interrupted and heavy cuts.
The major benefit of a face driver is its ability to allow a part to be turned completely, from one end to the other, in one non-stop operation. Some parts that are routinely cut using face drivers include automotive transmission parts, crankshafts, cam shafts, pinion gears, electric motor shafts, and axles up to 36" in diameter.
Dayton Forging & Heat Treating basically does rough turning while finishing is done by their customers who make the cut bar-stock slices into many different types of products, including gears. They're basically turning semi-finished rolls, working with 1/16" tolerances for length and diameter. Steel bars they stock and machine include grades: 1022, 1045, 1055, 4140, 4150, 4320, 8620 and 4340. They stock bars from 12" to about 34" in diameter and usually 10' to 15' long random lengths.
As to whether Dayton Forging & Heat Treating will continue to use LMC Neidlein Face Drivers, Wilson says, "Sure, as long as the payback is there, we'll do it." And the face driver's payback has proven to be there.
