Heavy duty lathe steady rest

Recently I started a large (secret) project for my wife that will take the better part of a year to complete. Right away I realized there were some missing infrastructure items that would be required that would be hard to built right in the middle of the larger project. The first tooling deficiency I ran into was my lathe steady rest.

The large Yam lathe I bought last year came with a significant amount of tooling. A three point steady rest was one of the tooling pieces. Initially everything looked pretty sweet. My large secret project has need of several long large diameter shafts which is one reason I chose this particular lathe. I figured get the big Conan lathe first and hold out for the sweetheart deal on a really nice smaller lathe when it appears in my machinery shopping sights.

During the secret project design phase I made a decision that was connected to the lathe acquisition. Since it is so long I decided to increase the basic size of the project considerably. Hey, if you're going to go to the trouble and expense to build your own secret project then go for the gold medal. Who the heck wants a bronze anyway?

So it turns out the steady rest that came with my lathe is way too small. It can pass 7.85 through the frame and I need to pass at least eight inches through. So this is how a tooling project is born. A steady rest is a pretty straightforward project in a machine shop. There is nothing too fancy or critical to the proper functioning of a steady rest so if your lathe is missing one I encourage you to go ahead and make one.

First order of business was to take some measurements of the stock Yam steady rest. The only semi important number is the center height off the ways. From these measurements its easy to develop the larger size I need.

For the new steady rest I wanted anti friction roller tips instead of the bronze tips that the stock Yam unit has. I figured if I was going to build one I'd make it slightly different and better just for good measure. Roller tips mark the work less but have a nasty habit of sucking chips between the roller and the work. Non rotating tips generally don't allow chip between the work and the rip but at the the expense of marking the work more and with higher friction. Its a common and simple enough matter to make a thin plastic shield to keeps chips from finding the roller tips.

Measuring the vee way depth on the stock steady rest. I got lucky that it was a ninety degree angle instead of some oddball thing.

The large steady profile was cut from the electronic layout you see above. Material used is one and a half inch thick steel plate. I added some extra material in the center and at the bottom so I could cut the profile in half and still clean up the machined surfaces and end up with a proper circular opening.

Check out the awesome oxy fuel cutting provided by Nowell Steel in Antioch. These guys do all my heavy steel cutting. Talk to Ted or Chris if you need some steel cut.

I scribed the base block directly off the stock steady rest. This was just for the roughing of the vee groove. Once I was close I started taking measurements for precision depth.

When the groove was shallow I had to use my multi-anvil micrometer because the pin was above the surface. These handy versatile micrometers have the ability to measure from a flat surface up as well as a multitude of other measurements. Once the gage pin was below the surface of the block the normal depth micrometer could be used with more stability.

I used the trusty Doall vertical band saw to split the profile. It took about ten minutes to make the split I left material between for machining the ears to thickness after the saw cut. I still have to make the latch and hinge for the two halves. All the time I was sawing the profile I was wondering which way it would spring. This is one good reason to cut a profile as a closed shape. In particular if you use a heat producing process. If I would have waterjet cut this I most likely would have cut them as halves with a small amount of material for machining. On this thickness of material the oxy fuel process is faster and cheaper. My time is free in my shop.

This is the clamp plate that secures the steady rest to the underside of the lathe. The bolt will pass through the bottom of the steady rest and be tightened from topside.

This last weekend I worked on the roller guides. There was quite a bit of work in these puppies. Early on I thought I wanted a single side support with a stud type cam follower. I was looking at one of the lathes in the main shop the other day and it had a very nice roller setup on its steady rest. The lathe was a Cazeneuve. Once I decided to make the support double sided it doubled the amount of work in these parts. My milling machine looks like a steel sliver bomb went off near it.

 The axels for the cam followers are made from the hardened shanks of shoulder bolts. The shaft is clamped in the roller support tightly for minimum vibration.

I have been documenting the build with video. Check out the Oxtoolco YouTube channel if you want to see some live machine shop action on this project.

Thanks for looking.

Simulated Dovetail Knurling Tool

One of my blog readers suggested a subject regarding knurling in the lathe. He had watched one of my YouTube video's where I ask viewers to submit their metalworking problems. If I think the problem is of general interest to the community and will make a good presentation I'm all for it.

The first problem I ran into on this request was I don't actually have a knurling tool holder. I have never bothered to buy one because their expensive and don't get used that much. Typically I will put a gripping surface on a knob or handle with a different method, partly because I don't have a knurling tool. Your classic catch 22 self fulfilling prophecy.

What I was able to do to move forward on this project was to borrow a smaller knurling tool holder and make a new quick draw simulated dovetail tool block that fits my large Aloris tool post.

Here is the knurling holder I  was able to borrow. It fits an baby AXA sized tool post and my lathe uses the Conan  arm breaking CXA size. Aloris in their wisdom at least made the knurling head separable from the tool block probably so they can do the same thing I was planning on doing. 

After dissecting the holder you can see how it was attached to the AXA tool block with two cap screws and a pair of locating dowels. Now all I need to do is make a CXA sized block that has the same bolt pattern in it. 

Scrounging around the steel bin I found some likely accomplices for the tool block. The larger round bar is for the height adjustment knob that rides on the stud in your typical Aloris tool holder.

A few months ago I wrote an article about this Skeleton tool holder concept. I made this one to hold my button indicator in the lathe so I didn't take up a valuable tool block to keep an indicator set up all the time. This is when I had the four jaw mounted on the lathe for a long period of time. The rods that interface to the Aloris toolpost are .500 diameter. When spaced correctly with my handy dandy rod spacer they form a facsimile of the dove tail cut in a normal tool block. My reasoning for doing it this way is one, I have some smaller material I can use right now to make a block, and two cutting large dovetails like on a CXA tool block takes a long time. I figure for a tool that I won't use that often it will be just fine.

I had to add some to the front face of the new block so the dowel pins would have some meat around them. Welding was a quick way to widen the face instead of the alternative which was start with a much larger piece and hog off most of it. I didn't have larger piece so this is it.

Here is the block all welded up with the simulated dovetail rods. Time for some knob action.

So here is the catch 22 part. I don't have a knurling tool so I added some circular cutouts to provide a gripping surface to the knob. I suppose I could have waited and knurled the adjustment knob as the first test part. The stock Aloris tool posts use a 7/16 stud of all things. I only had 3/8-16 studs in stock. I like to use long set screws for fixed studs like this. They are easy to bottom out in a tapped hole and get tight with the internal hex drive. The ID of the knob is tapped to fit the stud to provide the height adjustment. Incidentally the knob is 1.38 in diameter. I held it down with a single 10-32 screw in the center to do the fluting. I mention it because most machinists would probably prefer a larger screw. When torqued down a little 10-32 can give over a thousand pounds of clamping force. The fluting cuts were done with a 1/4 inch end mill. 

So here is the finished product. Now I can set up to do the knurling video demonstration. Sometimes its easy to find the long way around. I like to think of it as a nice walk in the woods before you get to your destination.

Thanks for looking.

What are friends for?

The planets finally aligned for a friend of mine recently. While scanning Craigslist for interesting items I found something that caught my interest. The price was a little steep but it looked like a nice specimen. The listing didn't have a phone number so I sent the seller an email inquiring about the item. I always include my phone number in the hope that the seller will respond likewise and include theirs. To my surprise the seller called me. We spoke for a while on the phone about the machine I had written about. After talking for a while he mentioned some other equipment he wanted to sell. I quizzed him on the other machines and struck pay dirt. Well almost pay dirt. A friend of mine has been looking for a 2 axis CNC Prototrak milling machine. This guys wanted to sell one. As soon as I got off the phone I called Marty and gave him Kent's contact information. This was the best situation you could ask for. It was not actually on the market yet so there was not a line of competitors going around the corner. I threw the whole thing over the fence to Marty and let him run the touchdown for the score.

 A couple of days later I get a call,  "So what are you doing this weekend? Want to help me move a milling machine?" Heck yes I do was my instant reply. Tell me where and when. Marty made the deal and now we are on the hook to get this large milling machine out of a little rats nest of a shop No offense to Kent but his busy shop is loaded with tools, equipment and materials and not much air space. In fact it took a week of prep work on his end just so we could access the machine that Marty bought. Sounds like an adventure to me. Mentally I started my list of tools and equipment that I would bring to the party.

The day started with an excited friend pulling a trailer arriving. I had my pile of gear ready to go but Marty convinced me a lot of it wasn't needed. A little voice in my head was telling me to just go ahead and load it anyway. But the lazy guy won out. At least the adjustable head prybar made it on the truck.

As we pulled up to Kents shop my riggers eye was surveying the slanted driveway and low garage door opening. Kent's shop is located in his one and a half car garage and extends into the basement and crawlspace of the three story house. I hopped out of the truck to guide Marty into the garage and noted a drainage swale and asphalt rim right at the entrance to the garage.

Ok I don't know about you but what kind of architect designs a driveway sloping into the garage without proper provision for runoff? This seems like house design 101 to me. Water has to go somewhere and its usually down hill. The pipsqueak swale the architect specified apparently is easily overwhelmed during a good rain. Kent did what he had to do to defend his shop from flooding by adding the asphalt rim to the undersize swale to protect his garage from flooding. All this is just complaining on my part because we had to deal with the drainage swale and rim while trying to move a 3200 lb machine.

You know the job is starting out on the wrong foot when the owner tells you, "Oh by the way we need to move this lathe out of the way first" On top of that we cant disconnect the power from it either. Ok, lets move the lathe first.

I didn't get as many pictures as I normally would like. I gave the camera to one of Kent's buddies to shoot progress pictures while we worked. I guess he is from the film camera era where you only get 24 shots per roll. He came up a little light on quantity but I'm glad he did what he did.

Moving the Tuda lathe wasn't too bad. They already had it most of the way up when we got there. All we had to do is lift it a little higher and get the Hilman rollers Kent had under the machine. We barred it as far out of the way as the electrical would let us to give us room to work on the mill.

 The general idea was to raise the machine enough to get a pallet jack under the mill. We used a bar and my wood wedges to slowly elevate the machine. I'm doing the bar work and Marty is slipping the wedges under the machine. The wood wedges are great because they are infinitely adjustable unlike a pile of wood scraps. The angle of the wedges is low enough that there is no slippage under load. These are just doug fir four by fours cut at an angle. Hardwood might be better but I like to see the machine bite into the wood a little.

Once we had the machine raised enough for the pallet jack we sucked about ten years worth of chips and cat litter out from under the machine. Once the mill is on the pallet jack you can move it around quite easily and safely. This particular mill is quite heavy. Its a 10 x 50 with box ways and a 40 taper spindle. Bridgeports are like drill presses compared to this machine. It really is a two person show to move one of these.

It took a couple of tries with the pallet jack to get the right center of gravity. This oversize mill is heavier on the front side because of the massive knee casting. Once we found the spot where the machine was stable one person could push it around easily. We danced around the garage for a while trying to get the machine lined up with the trailer. There was a lot of backing and filling to orient it for the tug into the drop bed trailer.

My empire for a come along right about now. I really wanted to just gently winch the machine into the trailer with a controlled simple setup. When Marty picked me up in the morning I had everything we would need all laid out. When we started talking he had some of the rigging equipment already and had spoken to the seller, Kent who had a bunch of stuff also. Red warning beacons should have been going off in my head.

OK, here is my wisdom for all eternity. Take everything you will possibly need to do the job with you when you leave. Pretend your going to the moon and there will be nothing available to use except moon dust. Marty convinced me to break my rule and we suffered because of it. Kent didn't have a come along of any kind. What he did have was a Harbor Fright 12VDC cheapco winch. The winch was attached to a section of thin wall pipe with U bolts. To operate the winch we had to attach a battery charger to the leads for the 12V supply. Definitely a jury rig.

Well what are you supposed to do? You cant stand around and whine about it. Just start and get cracking. We strapped the winch to the front of the trailer with some motorcycle straps to reinforce the weeny winch assembly. There was a up slope going into the trailer because of the driveway. We managed to span the swale after a dozen tries backing the trailer into the garage. Marty's truck is a diesel so that operation probably took a few years off my lifespan.

To my surprise the cheapco winch actually pulled the machine up into the trailer. It was a bit herky jerky with the battery charger as the power supply but not bad compared to my expectations.

So I know Marty is feeling better about now. The machine is safely in the trailer and fully under control. We took it off Kent's pallet jack. Here is where it would have been great to leave it on the pallet jack and block and strap it down. It would have saved us two machine lifts if we would have brought my pallet jack. This is where the adjustable head pry bar earned its price tag. With all the trailer structure around you couldn't use any kind of a long bar. It really saved the day.

Thanks to the machinery gods the road trip was very un-eventful. Just the way you want it when your hauling iron like this at sixty miles per hour. Now for the exhausting part.

Marty's garage is west facing so it gets the full brunt of the afternoon sun. The weather was nice and warm in the eighties for this next part.We must have lost a few pounds of water weight unloading the mill.

Everything was a tight fit at this end of the job. I think Marty had an inch or two to back and fill between the telephone pole and the garage. He looked tired when I asked him to move the trailer over a few inches to the left in this picture.

Finally back on the ground. All we need to do now is get my wedges out from under the machine. Once we got it down you should have seen the look on Marty's face when I said, uh-ohh. The head was looking mighty close to the garage door.

I call that close but no cigar for Murphy. It clears by a whole inch and a half. Good thing this is not a drawbar machine.

You cant tell from this picture but this is one happy guy. All the hard work is worth it when you get to this point. It was almost as good as getting a new machine myself. Well not quite that good. That's what friends are for, to share some fun and enjoy a job well done.

I learned my lesson,

I hereby promise to take every bar, chain, strap, jack, wedge and scrap of lumber necessary to complete the job from this day forward.

Thanks for looking.

What makes a Journeyman?

Every now and then somebody asks me what I think the definition of a journeyman is. For such a simple question I find it can be a difficult concept to explain to people outside the trades. There are many aspects of the relationship between the apprentice and the journeyman, and the journeyman and the master craftsman that people cannot easily relate to. There are some close professional parallels, but the differences are enough that full appreciation is not an easy concept for me to explain.

 If you could wrap up the definition of a journeyman in a tidy bow, it might read that its a certain number of years of experience at a given occupation or that the person has a particular set of skills in a their chosen trade.This is the simplified explanation that I give when asked to explain what a journeyman is to curious people.

What is typically accepted as minimum requirements for journeyman status is 10,000 hours of direct work experience in a particular trade. That time is spent working with established journeymen and master craftsmen with roughly ten percent of that total time in an actual classroom setting such as college courses or accredited vocational training.

 Here in the United States for many trades there are no established standards as to what makes a journeyman. Peer review and demonstrated knowledge of the trade is generally accepted for many occupations. Another rough rule of thumb to attain journeyman status is a minimum of four years combined with four different jobs. In the building trades written testing and state licensing are used to establish accepted journeyman status.

One of the key distinctions of a journeyman is that their broad work experience and practical skills allow them to teach and train others in their chosen trade. This giving back of knowledge is one of the most important contributions we as journeymen give our trade. We all stand on the shoulders of the people that have gone before us, so part of the requirement of the title is to help the less experienced.

A true journeymen will have enough trade knowledge and experience to work unsupervised. They have the earned the trust and autonomy to decide how the work will be handled and processed. This trade knowledge has been gained through more than a single work assignment. A single organization with average turnover does not provide the necessary critical mass of new ideas and the deep cross section of problems to create true journey level experience. The true journeyman has absorbed the experience through hours of training and work that now enable him or her to function maturely and independently on a wide variety of problems and situations.

Through years of work and observing others in our trades journeymen will continue to learn and can adapt their skills to the changing methods, materials and economic trends of the world around them. In the "olden days" the journeyman actually traveled around the country honing their craft and expanding their trade knowledge working for, and being vetted by several master craftsmen.

For me it has a much deeper, and emotional meaning. It is much more than a checklist of accomplishments completed. It is an attitude and ethic as well as a deep commitment to the craft, not just a simple toolkit of skills and a pile of time cards related to a given trade.

In the martial arts the relative ranking of the students is highly visible from the color of their belts. Talk to any black belt and you will be surprised to hear that the black belt is really just the beginning instead of the more popular belief that it is the highest achievement. The black belt in the martial arts and the journeyman trades person share that same starting point.

Just like the martial arts, the trades demand a similar level of humility and respect for the craft. You start at the bottom for a reason. This right of passage teaches the key ingredients in a way that bonds the person to the trade and the more experienced crafts people by common shared experience. Without the humble beginnings of every journeyman's career one cannot fully share and appreciate the journey. True journeymen are bonded together through the work and mutual respect of their achievements. The ability to cope with crappy work assignments, obnoxious co-workers and dismal working conditions is part of the tempering process that the apprentice goes through on the road to being a journeyman.

The title of journeyman must not be handed out casually. It reflects badly on all the people who's shoulders we are standing on to allow an apprentice to be awarded journeyman status, or a journeyman to be deemed a master craftsman without the proper depth and breadth of experience required for the title.

Early promotion and relaxed skill requirements handed out by the uninitiated diminishes every craftsman's gift of knowledge to the trade. The promotion without jury or real peer review does a tremendous disservice to the trade when its allowed to happen. Just as we would not want an unlicensed and untrained doctor performing surgery, or an airplane pilot with limited flight experience in the captains seat we don't want to promote inexperienced trades people just to placate a lack of patience and appreciation for the path our fellow craftspeople have left for us to follow.

Chop wood, carry water, clean the shop for a few years. And if you don't complain, we might let you pick up a tool and lend a hand. So if you really want to be a journeyman and a master craftsman follow these simple rules.

Suck it up.Work really hard. Learn to love your work. Be proud to let it define you .You wont be sorry.

Thanks for looking

Tom Lipton

Pot Metal Prosthetic

One of my neighbors dropped off a small part with my wife to see if it could be welded. Scott is a metalworker artist that lives down the street. He really doesn't have much of a shop and ends up building most of his sculptures out in the alley with his MIG welding machine. He builds metal animals and furniture with found objects, typically metal and aged wood. For this reason he is always on the lookout for metal objects for his work. I think the word is out to all his friends too because his pile seems to grow when any of them stops by or has some metal bit they don't want any more.

One of his recent acquisitions was a wood cutting vertical band saw. I didn't hear the story about where it came from but somehow it was damaged. If you have been following the blog then you know I have a soft spot for machinery repair. Add this onto the fact that Scott is a cool cat and fellow metalworker and you have the makings of a good project.

Looking at the part it appears the saw was tipped over and fell on the band wheel side of the machine. The part that he brought over is the bracket that does the upper wheel tensioning and blade tracking. Obviously this is a pretty important part. Scott was thinking it would be an easy welding job for TIG so he gave it to my wife to see if it could be welded. My wife is an extremely talented welder and immediately noticed it wasn't aluminum but non other than the dreaded pot metal.

Most welders have a couple of stories in their inventory about trying to weld pot metal. Nobody can really tell you what it is other than pot metal 101. The alloy contains all the most difficult to join materials all rolled into one alloy. Zincalumagleadalloy would be as accurate a description as pot metal as any. It is the scourge of the welding community. To a person it is hated everywhere.

The density is always the give away for me. Many of these materials that are collectively called pot metal contain high levels of zinc in them which is fairly dense. This is a common permanent mold casting material and was never intended to be repaired by any welding process or mere mortal. You can see in the picture the large chewy coarse texture of the break.  My wife smartly tossed the job over the fence to me to see if I had any special tricks up my sleeve.

I took a look at the part and came to the same conclusion as my wife. Welding was not the way to repair this part. My second instinct was to see if you could easily buy one. Zinc is used for a reason, its very inexpensive to produce. If spare parts are available for this saw then I would guess this is a sub $10 piece. But where's the fun in that? I do this stuff because I like to. Its pretty cool when you hand back a job and the customer is totally blown away by something you had fun doing. For this reason I decided to make a completely new part from scratch. I shot a bunch of video so check out the oxtoolco YouTube channel in a couple of days to see live action.

The first step was to take some measurements of the original part and make a shop sketch. I find this light marinating helps me form the plan of attack for the work sequence as I measure and examine a piece like this.

 The first step was to rough out a rectangle the same size as the exterior of the sample part. I started with 1-1/4 thick 6061 plate. Band sawed then milled on all six sides. In general with a part like this with some curves and steps you try to keep it square and blocky as long as you can so its easy to pick features up and hold on to the part. I poked all the holes in it when I had it in the mill. The original part had a shaft pinned in place in the .590 hole. I bored this hole so the pin is a press fit. The reason for this is the roll pin was put in willy nilly and would be a pain to locate and re-use. With a press fit and maybe a setscrew as a chicken bolt the shaft is not going anywhere.

I decided to do the .940 bosses first. I made a quick holding spud to fit the large hole in the part accurately. This spud will be used to turn the bosses on either side of the part.

 The spud is tapped to take a 1/2-13 bolt. The length is a whisker shorter than the length through the part so when the bolt and washer come up against the part it is clamped securely. The boss will be an interrupted cut so I used a large fastener to hold it to the fixture.

In this picture you can see the washer and bolt holding the part to the spud. I just tapped the washer into alignment so it didn't run out so much and get cut by the tool as I turned the boss to the correct diameter.

The next operation was to cut the small round bosses on the end of the part. I decided to do this in the four jaw chuck. I suppose I could have done it in the mill but I was in the mood for lathe work.

I had already put the small holes in so I had something to indicate on. With two chuck keys and a good indicator its easy to align something in the four jaw. I used to hesitate to use the four jaw chuck, but since getting my chuck changing setup down pat and having a second jaw key its really not a serious roadblock anymore.

 This is after the four jaw work. The part is starting to look like something. Next step is cutting the radius on the outside of the part. For this I'm going to use an old time toolmaker technique to step the radius with a ball nose end mill. I have heard several names for this technique but the one I like the best is "Kellering".Keller machines generally followed templates or models but they made their cuts as a series of stepovers that look very much like this method.

Here is a screen shot of the layout for 5 degree steps with a 1/8 ball end mill. I plotted the coordinates in AutoCAD for the Y and Z positions on the left and the X positions on the right. Because of the boss I need to stop the tool short as I come into contact with the curve of the boss. All the coordinates are off the centerline so I can use the same numbers for the opposite mirrored half. Its a lot a numbers to keep track of but you can do some cool stuff with manual machines using this technique.

Here we are partway through the process. Its the same technique that modern day CAM software calculates the toolpaths for three dimensional milling.

Here is my cheat sheet. You see I marked off each set of coordinates as I used them. If I didn't do that then I would be lost after a few passes.

Here is the part right off the machine.

The X positions bumped into the boss by a small amount. At first I was puzzled why that happened. It turns out it was the small difference in the radius in the sample part. My Z touch off was on the smaller diameter when it should have been on the slightly larger size. For this part its not a big deal but it easily could have mattered. I like to go back and understand what went wrong so hopefully I don't do it next time.

Here is the completed part. I re-used the shaft out of the original part and pressed it into the new bracket with a couple of grand of interference. I heated the part with a propane torch to expand the diameter and make the assembly easier.

The curve was cut on the band saw and hand draw filed until it matched the original. I added the chicken set screw just in case.  Here is one of the video's I shot that shows the fitting of the shaft into the new part.

Be sure to check out all the video's in this series. I had a some fun making the part and Scott is jazzed to get his saw going again. Its a win win dealeo.

Thanks for looking.

Manual Helical Mill Turn

We had an interesting job come through the shop the other day. We have been working with a physicist who is taking magnetic measurements of the magnetic field quality of one of our large superconducting dipole magnets. He measures and maps the field generated by the magnet when the magnet is operational.

This entails that his magnetic measuring probe must move up and down through the bore of the magnet that is cooled to 4.2 Kelvin. He uses an interesting anti cryostat device inserted down the bore of the large magnet. And inside this his probe rotates, and is moved up and down axially through the bore of the magnet to map the magnetic field. The purpose of the anti cryostat is to keep the measuring probe at room temperature when it is inserted in the super cold bore of the magnet.

The problem we were asked to solve was a failure of a plastic part at the end of the magnetic measuring probe that couples to the rotational motor. During the test run this part somehow got warm, and the small set screws holding the coupling to the probe collapsed the probe end. There are very small instrumentation wires that pass through the center of the coupling and the probe end that really don 't like to get twisted around.

The part that had failed had some semi-complex geometry so the way they were manufactured was by the 3D printer or FDM process. This was fine for previous tests and the parts performed well. On this particular test there was a heating problem that caused the FDM parts to soften and fail. The first step was to make the probe end out of something a little more durable. We had a good sample and a drawing so I gave the job to one of the new technicians to fabricate. We chose PEEK for the probe end material. This is a tough strong high performance plastic that has a wide operational temperature and excellent machinability.

While the probe end was being fabricated I had another discussion with the scientist and we decided that the failure was most likely from eddy current heating of the metal bearing spacer that happens to ride on the probe end. With this realization we decided to try to eliminate as much metal from this particular area as possible.

One of the parts that needed to be made of some non metallic material was a small helical shaft coupling. This type of coupling is used because of its zero backlash ability. The magnetic measurements are correlated to the probes position inside the magnet with rotary and linear encoders so a map of the field can be determined for that particular magnet configuration.

Our task was to duplicate this coupling in PEEK as quickly as we could, with stuff we had around the shop. There is limited measuring time and the cost per hour of the large magnet test is quite high so speed was important. I scrounged some tooling together and formed a plan of attack.

This is just the kind of job many machinists love to do. A tricky job with a minimum of detailed constraints, and the freedom to do the job anyway you can. The only thing that machinists generally don't like is the time constraint. When I was learning this stuff I would have liked to sink my teeth into a job like this every day of the week. In fact, I have never done this type of operation before. Sure, I've cut lots of helices and all manner of threads, but I never had to make a coupling like this. Honestly I really wanted to do this one myself but now its more important for me to allow other folks to have the experience and successes in the trade.

Part of the tooling we needed was a special holder to fit in the toolpost of the lathe. I made a quick hand sketch and gave the job to the other new technician I'm looking after. If this was going to work we would do it as a team. The tool block was needed to hold the hand piece of a Foredom tool. 

The general plan of attack was to use a thin saw blade mounted on the tool post to cut the helical groove in the coupling. I had a couple of small saws with arbors that would fit in the Foredom tool.

The blade width with was pretty close to the cuts on the sample. Definitely close enough for this operation. So both technicians, Matt and Nick were busy prepping the tooling and coupling blanks at this point.

 

There was a little more to the setup than mounting the slitting saw in the lathe. We wanted to match the pitch and number of flexures on the sample coupling as closely as we could with the tooling we put together. A quick calculation gave the helix angle of the "thread" we were going to cut. The pitch on the coupling was 12.5 TPI which is a bit of an oddball. We went with 12 TPI because this would thicken the flexure membrane a little and the Monarch could do this pitch.

 From this calculation we get the helix angle of the thread which we use to set the compound rest and the tool holder.

We also had to pitch the toolholder at the same angle since the tool we were using extended below the machine center line. If you look at the picture above showing the hand piece clamp you will see a set screw in the tongue of the holder. This was used to tip the tool in the Aloris holder to the helix angle. 

The idea was to use the lathe as a synchronization and holding tool as opposed to a machine tool. This little Monarch 10EE has a nice DRO so we could control the Z axis position well. We set the threading levers to our pitch (12 TPI) and engaged the half nut. We then ran the saw up to the face of the part by hand with the threading lever engaged and picked off the Z position.

The saw was set on centerline because I couldn't think of a reason why is should be anywhere else.

The first pass was to see how things went. PEEK is easy to get hot so we had the koolmist setup going. The saw blade would be passing through quite a bit of material so I was worried about overheating the material.

Here Nick has done a few passes along the helix. We used the DRO to reference the start and stop positions of the groove. When the end was reached he backed out the compound that was set at the helix angle and then just hand reversed the spindle by hand to get into position for the next pass. There was a fair amount of backlash in the system but with the DRO it was easy to get back to the start.  Nick and Matt cut the helix on their own. I had to go to a meeting right around the time they were cutting the helix. There was enough time for me to try my hand at one pass. So I did get to actually try it. Thanks Nick and Matt for giving me a go at it.

The results speak for themselves. Not bad for throwing some stuff together in a few hours. So with some Yankee ingenuity and some curious and willing teammates you can get a tricky job done and have some fun too. I know I still feel satisfied and proud even when I didn't turn the cranks myself. It would have taken me three times as long if I had to do all of the work myself. This is an excellent example of how team work can pay off.

We shot some video of the operation which I will put up on my YouTube channel in the next couple of days.

Thanks for looking.