You were taught wrong. I say that, based on 4 years of machine shop in high school, 2 years of College, a 4 year apprenticeship, and 30 years working in the trade. I got my Tool and Die cert in spring of 1988. I've had some good teachers, and some bad teachers, worked with some good craftsmen and some real idiots, nobody runs their cutting tools below center.
Hi Saltflats - yes they do.. but iirc one needs to machine the shaft down first.. either that or machine it down and run a tighter seal..
ONE MORE THOUGHT- To greatly reduce any chance of tool shudder, or inaccuracy, or tool deflection, or unwanted toolstock movement, ALWAYS try to adjust the cutting tool where the cutting edge is as close to the tool post as the workpiece will allow. That provides the strongest support and least deflection as you cut. The only time you want to stick the tool out farther than absolutely needed is when it is needed to reach out to the workpiece to avoid bumping into something or limiting your cut. The farther the tool has to reach out away from the toolpost, the smaller the cuts it can tolerate. The shorter the reach, the less the tendency to chatter, and the more precise the cut. Thats why internal boring and internal thread cutting is done with many many passes. I also like to sneak up on the final dimensions. Say, when I mic it and see that I have 8 thousandths left to cut, I never set it to cut 8 or even 7 or 6. Thats an easy way to go past in one cut. I have an old old lathe, so I would set it to cut a 4 or 5. mic it - hmm 3 to go... set to cut 1 or 2 mic it - 1 thousandths to go... make a fine fine cut.. When you take a measurement that tells you "2more to go" On an old old lathe the temptation to go ahead and take that 2, can sometimes lead you past it. If your lathe is super good, you may not have to do it the way I do, but if you havent yet put on many hours to get intimately familiar with yours, you should ease your way up to the final stages until you know exactly what to expect from yours. You will have much fewer wasted parts that way. My stuff was bought well used WWII surplus, so not everyone might have to sneak up on the final dims like I do, but its prolly the best way to get to know your machine. WHY BE ORDINARY ?
I feel your pain. I bought a used Chinese lathe to make round stuff. I am frustrated that I never was trained to use a lathe so all I can do is make round stuff but I self taught to the point that I make pretty good round stuff most of the time. I agree that taking on that yoke is Machining Graduate Course. You need to start with Machining 101, learning on ruining some mild steel bar that you buy at Home Depot. That Yoke is a grinding project not even a turning project with carbide tools let alone HSS. I was able to bore out a ring gear from a '40 Ford banjo rear end to accept late model 9" side gears for a removable axle conversion on my Mysterion clone project using carbide bits and light cuts so some hardened steels can be machined but don't try it as your first project.
Last night, after-hours at work, I machined a yoke and an output shaft. Or rather, the machine did. I am not fool enough to hand-run this job. I set both up as CNC jobs the night before, and used Sandvik Coromant cubic Boron nitride inserts. These are about $200/each. At 0.004" per pass (I cannot damage tooling or machines, or I could get fired), with flood cooling, it took 4-hours of run-time for the machine to do the work. Use a Speedy Sleeve to fix the seal issue.
oh, ONE MORE THING, as Columbo used to say.. Please note that some mfgrs calibrated their tool feed dials to directly indicate the change in workpiece diam, while others will indicate direct tool movement. On one machine, turning the feed dial 2-thousandths will reduce the workpiece diam by .002 with OTHER machines if you turn the feed handle 2 thousandths, it will move the TOOL .002 and result in a FOUR thousandths reduction in diam. Keep this in mind and allow for it until you get to know your machine very well. WHY BE ORDINARY ?
That Home Depot Chicom steel is dirty as hell - full of hard inclusions of who-knows-what, that dull your HSS bit. Find some good old American old rusty scrap at a salvage yard to use.
A place that I worked at for several years as a maintenance machinist back in the 70's was bad about buying angle iron made outta that remelted scrap and then expect us to build frameworks that had to be pretty accurately built and with critical hole locations drilled in it. Hit "hard spots" in that crap right where you had to drill an accurately located hole, and you had to blow it out with a cutting torch, grind the hole edges smooth, weld or braze up the hole and after again grinding flush on both sides, drill the hole. The purchasing agent thought he was saving money buying that shit, but the increased labor cost more than was saved on the remelt steel.
Uk, I wish I could talk to the men that taught me, some forty years ago, and find out if I heard wrong or that was the way they did in that shop. But they are both dead now. Seems some others were taught that too. I thought I was standing on granite when I gave that info on positioning the tool slightly below center. Been using it successfully for forty years. Like I mentioned in previous post, never had any formal training, my small high school didn’t offer machining and vo techs were not available in my time, in my area. I’ve always tended to trust the guys with the most experience and coupled with a formal education on the subject,that just puts icing on the cake. Bones
^^^^ Yep, import steel can be real crap. Took a couple of fab welder job calls in the '80s to work on north slope pipeline modules for Arco then BP, and we'd find unmelted ball bearings and other miscellaneous bits in the steel when cutting/drilling. Those hard spots don't machine worth a damn...
Again, the bad part about general terms like "slightly" is everybody has a different interpretation of what slightly is, could be .010, could be 1/16". There was a big old Monarch lathe in the assembly department where I worked that was used for polishing shafts and minor modifications, I would use it once in a while if I had a setup in my machine and something needed to have a "quick and dirty" job done. Always hated it because NONE of the tooling was on center and there was always a box of used carbide with the points broke off, you can tell someone was lazy and was using a turning tool for a facing tool, nothing wrong with that when center is maintained and only skim cuts are taken.
Steve, you can find that also in Chevy truck frames. I outfitted new trucks with new beds as part of my business. This process sometimes required cutting 2inches off the rear of the frame to get the bed placed right on the trucks. Ford and Dodge were never any problem, using the portaband saw, but every time we did a Chevy, we would use up several blades, hitting “ hard spots” in the steel. Not sure why, had some guesses..... Bones
When I hear HAS to be on centerline that tells me “ on the nuts” slightly means just that .. error to the low side of centerline going the other direction is worse
Fstar, going to maybe get the last word in here. Get you some black pipe, old USA made stuff, about 1 to two inch, cut it in 4 to 6 in lengths and practice on that. Put your tool on center, to make everyone happy, and make some cuts, turn it down some, make groves, taper the ends, make the ends square, practice, practice, practice. Nobody learns a trade in a couple of days. Bones
tx boneyard - i have some aluminium stock - when i have some time ill get to it - appreciate the advice.. i was just under the impression that the cast steel wouldnt be totally difficult to cut and assumed it was not hardened..
That would no doubt require a different seal size, since marine stuff is pretty standard id prefer to keep the shaft on the same OD (or close enough) for the stock seal to sit well on. Or id have to clearly mark the seal number with an oil pen.. problem is seal kits are standard for these things..
It probably won't. Speedy Sleeves are very thin, an usually can be used with a stock seal. I honesty cannot remember ever using a different seal, and I have been patching up heavy farm and construction equipment, and big trucks, since the mid-80's.
I'm another greybeard with decades of hands-on experience. More on tool height: What style toolpost do you have? If it's a square block that holds the cutting tool horizontal with set screws, as in post #42, use shims to set tool height. If you have one of the old lantern style toolposts with a rocker, it's a lot more difficult to get tool angle and height right. High speed steel or brazed carbide tools can be ground with relief below the cutting edge, they will work slightly above centre. Carbide insert tooling with no relief will not work well above centre, especially on smaller diameters. Above or below is measured in thousandths, not sixteenths. If in doubt, I put a piece of bar machined to a sharp point in the chuck, roll the tool cutting edge up to the point with the machine off, shim accordingly. The only time I might machine slightly above centre is when using a boring bar- internal turning. Re cutting speed: Different materials cut best at different speeds, speed meaning surface feet per minute at the cutting edge. Softer materials like aluminum can be cut at faster speeds. Tough steel alloys require slower speeds. At any constant rpm, surface speed is greater at larger diameters- surface speed decreases as the diameter is turned smaller. As a starting point, try this: use 90 sfm for mild steel, 200 sfm for aluminum. Machine speed is determined by this formula: four times the cutting speed divided by the workpiece diameter. This works for high speed steel tools, multiply by up to four for carbide, either brazed or insert. This is for single point tools, turning or facing. Parting or form tools generally require slower speeds. Use the same speed formula for drilling, diameter is then the diameter of the drill- larger drill, slower speed. Always choke up on the tool in the toolpost, support it as close to the cutting edge as possible. The tool should never chatter, that'll break carbide quickly. Most importantly, BE CAREFUL. Stay away from the spinning chuck, don't get any hair/ clothing/ jewellry/ body parts tangled in moving parts of the machine. Good luck, enjoy. Shiny finished parts will give you a sense of accomplishment.
tx halfdozen- yes i turn the chuck by hand everytime i turn it on and observe where the tool post might contact anything during the cut. I have the lantern style holder - but will get the newer design once I have enough permission from the wife
IMHO, lantern tool holders are fussy to work with and not very rigid. I'd suggest making yourself a selection of tool shims - I assume you're using 1/2" square tools? Make 1/2" wide strips about 3" long from different thicknesses of metal, put them between the rocker and the bottom of the tool as required to get the tool horizontal and a few thou below centre. One thick shim is better than three thin ones, take light cuts. Turn the carriage feed by hand at first to get an idea of how much pressure it takes to make a cut. It should take very little, when you get nice little curls that aren't turning blue, you're in the ballpark. Check out tubalcain on YouTube: This guy knows his stuff, lots to learn there. Over the years I have used everything from large CNC turning centres with live turret tooling, to my own 1950's Atlas bench top lathe. There's no substitute for actual time spent using the machine. Experience is the best teacher. If you know or can find an old time machinist, ask questions and ask to watch. South Bend made quality machines, they have a cult following, you can still find parts for them online. If yours is in good shape, $450 is a bandit price. This is a good source for tooling and related things for small machines: https://littlemachineshop.com/ Again, good luck, enjoy.
halfdozen thanks yes ive seen some of his vids but sheesh didnt know there were THAT many - looks like i bit off a little too much then. When im done welding up a 12ft gantry ill play with thee ol southbend some more.. after some reading too from the handbook..
There are two books available online in PDF form that I would suggest will help you. One to set up and look after your lathe and the other to help you use it. If you Google "South Bend Army Lathe" you should find a few sources. This is great for machine setup, operation, maintenance and care. The other is called the "Hercus Book of Turning" and is long out of print. Hercus was a prolific maker of South Bend copies in Australia, so much so that South Bend imported some into North America. If you can not find one or the other, shoot me a message and I will email them to you. They are both a great resource. Cheers, Rob
No, you haven't bitten off more than you can chew, you're still on the steep side of the learning curve, that's all. It'll level off once you learn the basics and get comfortable with the machine.
Well since hardened steel is a pain thought id compensate for my lack of skill/equipment then! Had to machine down the seal area for my 40's black and decker motor pump - it came out beautifully smooth and polished! No more leaks. Started with a pink (alu oxide?) dremel stone then final polish with the roll of sandpaper -
Looks nice, just be damn sure to clean ALL the abrasive particles off your lathe before you run the carriage up onto that area.
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