Shop Doc

Today’s Machining World Archive: October 2005 Vol.1, Issue 08

Dear Shop Doc:

We are an aerospace company in California running Aluminum 6061-T6, generating 100,000 pounds of chip waste per month. We work in eight to twelve hour shifts, seven days a week. We use 10-weight hydraulic oil with sulfur added, paying $4.50 per gallon. Right now we are disposing of our chips in bins, and selling them wet to a scrap metal dealer for .40 per pound. The chip waste is machined in “6’s and 9’s,” curls for the most part. We have 500-square feet of floor space available for handling the scrap (not heated).

How can we consolidate our chips to get the highest resale value for them? Would we maximize the value of our scrap by using a briquetting system? Or is simply spinning the chips a better option? We also want to know the best method for recovering coolant for both economic and environmental reasons.

CHIPS

Dear CHIPS:

I contacted three manufacturers: Meaden Precision Machined Products of Burr
Ridge, IL, Manth Brownell of Kirkville, NY, and Curtis Screw of Buffalo, NY, to see
how they disposed of their aluminum chips. All three use centrifuges to spin the oil
out of the chips, rather than using briquetting systems, which compact chips into
solid pucks, which are easier to store, leave little residual oil, and can sometimes
bring considerably more money than loose chips. I tried to find out why these
three manufacturers dispose of their chip waste the way they do, and if there is a
better way.

Wes Skinner of Manth Brownell said he receives, from a scrap dealer, about fifty cents per pound for a mixture of aluminum 6061 and 6262. According to American Metal Market, aluminum scrap sells for 55-56 cents per pound; Skinner says he receives a bit less than the market price because there is still about 2% of the oil remaining in the chips after he spins them. He also recovers oil after the chips are spun, which can save significant money.

I also contacted an aluminum broker/ingot producer in California, who wanted to remain anonymous (all aluminum brokers I talked to wanted to remain anonymous), to find out if they prefer pucks to chips. He refused to quote me a price on aluminum scrap, like every aluminum broker refused, but he told me that his company does not pay a premium for pucks because it is difficult to know if the metal is pure.

Then I called PuckMaster, a company that manufactures briquetting equipment, and Prab Inc., a company that makes both centrifuging machines for drying chips and briquetting equipment. Tim Sernett, National Sales Manager at PuckMaster, said that in puck form (produced from the PuckMaster system) aluminum 6061-T6 is presently worth about $0.72 to $0.75 per pound delivered to a primary mill, which will not accept aluminum in chip form, wet or dry. According to Tim, primary aluminum mills typically buy scrap only from a select group of brokers, so usually a manufacturer’s only option is to sell its scrap to a scrap dealer, but PuckMaster says that it offers a brokerage service, via contract to market, and sells this material in puck form to primary mills or to direct export to eliminate the middleman scrap dealer network. Tim calculated that CHIPS could be making $0.25-$0.32 per pound more than he is collecting presently, by selling directly to the primary mill (Tim subtracted between $0.03 to $0.07 for the cost of shipping to the mill, and a brokerage fee). This would mean that the revenue for CHIPS, producing 100,000 pounds of aluminum per month, receiving $0.40 per pound presently, could be $320,000,00 more if the maximum $0.72 per pound was redeemed. However, it is important to realize that if CHIPS produces 100,000 pounds of aluminum chips per month not spun, a significant fraction of that weight comes from residual oil.

Another advantage of PuckMaster briquetting systems is their PLC display, which shows how many pucks have been produced. This helps insure that manufacturers get paid for the true amount of metal that they have recycled.

Also, PuckMaster and other briquetting systems reclaim a significant amount of coolant, which would otherwise have been lost. According to Tim, PuckMaster will remove approximately 18 gallons of cutting fluid per 1000 pounds of aluminum chips processed. Therefore, processing 1,200,000 pounds of aluminum per year will recover 21,600 gallons of coolant, which will be claimed for reuse every year. At a cost of $4.50 per gallon for coolant, CHIPS would recover $97,200 per year in coolant, which could be recycled and reused. This will be a significant increase from CHIPS’ current methods of oil conservation.

Bob Meyers, vice president of sales and marketing from Prab Inc., a company that produces both centrifuges and briquetting systems, has a different perspective. He said that the market for disposing aluminum chips and briquettes can be very regional, and that the most likely destinations for manufacturers to capitalize on their aluminum scrap in California are scrap dealers, who themselves briquette wet, clean chips for bulk shipment to Asia. He said that the value of chip to dealer is pretty much the same if it is brought in wrung or briquetted. Bob calculated that if CHIPS is getting $0.40 per pound for wet chips (10%-15% moisture by weight), he should get approximately $0.50 per pound if the chips are wrung (resulting in 2% or less residual moisture) since he will not be penalized for the moisture. Bob concurred with PuckMaster that any real premium price would be at the large volume broker level who is handling a specific, clean, mag- separated, alloy briquette ready for bulk export shipment. He said that in the case of CHIPS, a Prab Inc. chip processing system (shredder, wringer etc.) could be provided for about $110,000.00 vs. a Prab Inc. briquetter system (including pre-conditioning of the turnings and solids) for around $160,000.00.

So CHIPS, You’re cheating yourself out of money, and you don’t have to. Now that you have some knowledge, call Prab Inc. and PuckMaster and get the chips rolling (or maybe the puck). And tell ‘em Shop Doc sent ya.

Today’s Machining World Archive: August 2006 Vol.2, Issue 08

Dear Shop Doc,

I have a medium sized turret type 2-axis CNC lathe. I followed the tips regarding the laydown threading systems from last month, and my tool life increased a great deal by using the proper adjustable anvil. However, when using this style of threading system, I still seem to struggle with the smaller diameter threads.

The No-Go Gage we use goes on 2-3 turns when cutting threads under .500 in diameter. These parts are made of low carbon steel (like 1018), and I try to follow the recommended SFM provided by the tool manufacturer. With the coatings typically seen on these tools, it seems the SFM range can be very high, thus resulting in high RPMs. It seems that if we do slow down the RPM, the No-Go Gage doesn’t go on as far, but the tool life isn’t as good.

We have tried several thread cycle options such as “infeed” variations, depth of cut, etc., but it doesn’t seem to change the results.

I’ll take thread quality over tool life for now, but is there something I can do to get great results for both?

Loose Ends

Dear Loose Ends,

When you said your lathe was a medium sized turret type CNC, that was a great clue to your problem. When you mentioned smaller diameters, it was another great clue. I think you are starting too close to the thread starting point in your Z axis. When you do that, the turret can’t synchronize quickly enough with the spindle.

It’s not uncommon for turrets to travel at 300 IPM while threading. To synchronize that much weight with the spindle is difficult at those feed rates. Until the turret and spindle synchronize, the form of the thread may not be correct.

Here’s what you should do. Keep the RPM range the tool’s manufacturer recommends. Then, do the following equation: ((1/TPI) * RPM) / 400 = Start Point in Z.

The result of the equation equals the distance in front of the thread starting point where I suggest you start the Z axis in your threading cycle. By positioning the tool far enough in front of the thread for the spindle and turret to synchronize (calculated from the RPM to achieve the proper SFM for cutting the specific material with the specific grade of carbide), I’m confident you will achieve great thread quality as well as improved tool life.

Good luck!

Jim Rowe
Application Specialist/Medical Accounts
Mahar Tool Supply, Warsaw, IN.

Today’s Machining World Archive: June/July 2005 Vol.1, Issue 06

This month’s question about Wickman threading attachments comes from Bob Schneeberger of LD McCauley in Orchard Park, NY.

Shop Doc. this month is AL Seniw of New Lenox Machine Co., Inc. in Dwight IL. Al has been working on Wickmans for forty years and he has taught machining courses at community colleges.

BOB’S QUESTION:

Our client needs a thin walled brass part. My screw machine is a 1” 6-spindle Wickman. We were concerned about flaking in the threads with brass parts so I knew I had to come up with a cut thread. Our two options were thread milling and thread chasing. We couldn’t get the brass to gauge on our Johnson Gauges because of the flaking. I tried running a drill inside the part while I was thread rolling to avoid crushing of the part but it still didn’t gauge. I tried putting a thread chasing die on the machine and saw that the lead on the threads (or the pitch) was off. We had tracking problems. The thread die is 400 thousandths wide. It wasn’t tracking properly as it ran across the part.

We went through the machine and the chasing attachment looking for the cause of the problem. The attachment had just been rebuilt by a very reputable source. We did see a little play as the cams rode inside the thread chasing attachment. We eliminated the problems in the attachment but our pitch was still off. We are now going to try a thread milling attachment and a thread milling die. How can we eliminate the play in the thread? What caused it? Do you think this will solve the problem on the thin walled part?

Worn parts subject to “slopposis.”

AL’S ANSWER:

On a 1” Wickman, on the center drive shaft where the spindle speed gears are mounted, there is a coupling between the back half of the drive shaft and the front of the drive shaft. As the machines get old, and typically because people run hex material on these machines, they start to pound out the spline on the shaft and the coupling gets loose. This creates looseness or play in the machine, which I call “slopposis.” Toward the spindle end of the machine there is a drive key that engages the main spindle drive gear. That key can get pounded out and you get slopposis at that point. On each spindle there is a drive gear that engages the center drive gear. If the keyway on the spindle is pounded out that is another source of slopposis.

Thread chasing.

When you chase a thread with a single point thread chasing attachment you use a multiple tooth chaser. If for some reason there is play in the machine and the lead does not repeat itself, in other words it doesn’t track in the same place every time, you will get a very sharp crest on the major diameter of the thread. If you look at the thread on a comparator it will show a very sharp crest on the major diameter of the thread and you will notice a wide area at the minor diameter of the thread. What is happening is that the chaser is not following the lead of the thread, and the chaser is shaving the sides of the thread.

You should check the lead on the thread chasing attachment. Usually what I do is mount a dial indicator on the thread chasing head manually (without the machine running). I turn the spindle one complete revolution to advance the thread chasing attachment to the lead of thread. Now lets say it’s supposed to travel .062 per revolution – if you do this three or four times, the lead should be within a tenth or two at the end of it.

The attachments do wear out, but that is probably not the case with yours because your attachment was rebuilt by a reputable source. However often people will put the thread chasing cam on the attachment and forget to put the spacer washers on. This would result in the cam flopping back and forth, which will throw the lead off.

Thread milling for a 1” Wickman.

BOB’S QUESTION:

Do you think using a thread milling attachment and a thread milling die will solve the problem?

AL’S ANSWER:

Thread milling is a completely different system than thread chasing because the lead is built into the tool itself. There is probably less chance for slopposis to affect a thread mill than to affect a thread chaser because the load is constant all the way through the cut. On a single point thread chasing attachment every time that attachment makes a pass the machine is loaded and then unloaded. So thread milling could be the way to go, especially because it’s a thin walled part. The chip load per tooth is much lower with thread milling than with thread chasing.

Today’s Machining World Archive: May 2007, Vol.3, Issue 05

Dear Shop Doc,

We can’t accurately control the depth of the tap on our CNC Swiss lathe. The type of component we are making has a blind hole that goes .200” deep. The threads are 6-32 and need to have a fully formed thread of a minimum depth of .185”. The tool is a thread forming tap with a blunt point. We are using a Floating Tap Collet, and we program about 10 percent slower than the tap pitch, stop the spindle, slight dwell, then feed off at 100 percent of the tap pitch. We’ve tried many variations of this method with different spindle speeds, different floating collets and different tool positions, however, we still cannot accurately control the depth. One of the issues of not being able to control the depth is that we “bottom out” frequently and break the tap. Down time, tool cost and scrap material is eating into our profit margin for this job.

Tapped Out

Dear Out,

I can relate to your pain. I know how it feels to quote a job and not be able to manufacture at the production rate you thought you would be able to achieve. Tapping on CNC Swiss Lathes used to be fairly adventurous. It appears you have done your homework in selecting the correct tap style. The problem you are having is caused by the floating collet. It’s assumed that because you are machining on a CNC machine that you have absolute control of all of the dimensions, but when it comes to tapping with floating collets, you don’t have as much control as you think. What is happening is that when the part engages the tap, it is not starting at the same position along the polar axis (C-axis) every time. This is critical to how many threads are produced based on the Z-axis movement. For example, if your part begins to tap at 12 o’clock, which starts to pull the collet because of the 10 percent slower feed, you’ll get one depth, but if it starts 180 degrees later at 6 o’clock, you’ll get a different depth. With floating collets, this is the variable you live with and in most applications it’s ok.

For this particular application I would go to Rigid Tapping. Rigid tapping is something relatively new to CNC Swiss-type machines. Some of older CNC Swiss machines are not capable of this process, but with more manufacturers offering C-axis as a standard option, rigid tapping is a great solution. Rigid tapping has been around for many years on most CNC Lathes & Milling Centers. The programming of it is fairly simple, and you don’t have to worry about using any special collets. Check your machine manual to see if your machine is capable.

David Cogswell
Director, Precision Machining Operations
Bal Seal Engineering, Medical Products Group