More mini lathe issues



I bet that this is a good idea in any case, but I would use Hi-Spot Blue (http://www1.mscdirect.com/CGI/NNSRIT?PMAKA264101) instead of the marker, and a set of small machinist scrapers (such as http://www1.mscdirect.com/CGI/NNSRIT?PMAKA844113) and small hand stones in place of the files (which can cut too quickly).
The process is simple and safe albeit slow:
Disassemble sliding part and remove extraneous hardware. (Take lots of pictures while doing this.)
Clean off the mating surfaces. Smear a very thin layer of hi-spot blue onto the bed (not the sliding part). Set the sliding part down on the bed and slide back and forth. Pick sliding part up carefully in a vertical motion. Flip sliding part over and look. If everywhere that is supposed to contact the bed is a more-or-less even mottled shade of blue, you are done. If the pattern is uneven, which is likely especially at first, carefully scrape a tiny bit of metal (like 0.0001") off the highest (usually the bluest spot, unless down pressure is too high yielding a donut pattern) spot. Repeat.
Reassemble. All rocking should be gone.
This scraping-in process always works, and cannot get away from one, but does require patience. And wear old clothes. Hi-spot blue will stain everything. And your hands will look like you got the dye pack at the local bank.
Joe Gwinn
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Sounds like you are a tad above center. It cuts OK on large stock, binds then grabs as the work gets smaller. Take a piece of thin stock or feeler gage, run the tool up to the work with the gage in between. If you are high it will tilt toward the lathe, below it will tilt toward you.
Your choice of SS for your first parts is unfortunate. If the bit ever stops cutting, you will work harden the surface, you will never get the cut restarted on your small machine.
You are regrinding CARBIDE? I'd be using some good cobalt high speed steel bits. Much sharper.
Bob La Londe wrote:

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My screw / pin is complete. Took some doing since I don't have any of the right tooling for this.
I do not have an center drills either so I center marked it with a 1/64 ball mill in the drill chuck, and used that hole for my live center.
Cranking the speed up to max helped a lot. I used a very narrow cutter to rough to size, and then a wider cutter at .001 per pass for the last .003. The gave me my pin shaft diameter. Then I had to cut a little smaller to make an extended shaft for a nut. The original was just pressed and peaned over. I cut mine to press in and then have a nut threaded on. I cut a shoulder and then extended shaft was threaded to 10x32. Didn't do that with the lathe though. I just don't have a tool bit I felt comfortable doing that with. Instead I used a die, and then reversed the die for the last 2 thread up to the shoulder. Sadly I got some marks on the head in the vice even clamping the pin between two blocks of wood.
NOT GONNA POST A PICTURE. As a shoulder screw sitting on the desk it looks pretty good, but when I snapped a picture I could see all the imperfections. LOL.
Definitely want to get some other bits before I tackle something this small again.
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Bob La Londe wrote:

Excellent!
I took a machining course at a local community college and learned some good stuff, very inexpensively. 'Enjoyed the heck out of it because I had a pal along to share the experience.
Highly recommended.
--Winston
--

Congratulations Robert Piccinini and Steven A. Burd, WalMart Publicists of the
Year!

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Bob....what is the maximum size tool bit your lathe can use? The "normal" size?
Ive got a fair amount of HSS kicking around and Id not mind grinding you up a couple sets of tools and sending em off to you to play with. Right,left, groove, cutoff and threading types ok?
send your shipping address to snipped-for-privacy@lightspeed.net and Ill get something out to you by next weekend
Gunner

"I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. In my youth I travelled much, and I observed in different countries, that the more public provisions were made for the poor the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer." -- Benjamin Franklin, /The Encouragement of Idleness/, 1766
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The first suggestion I would make is to use hand-ground HSS cutting tools for use with any of the light duty imported lathes, for typical turning and facing operations, on large or small workpieces. Carbide cutting tools aren't a solution or subsitute/shortcut for small lathe users. Most carbide cutting tools don't even have particularly sharp cutting edges.
I'm not a machinist, I'm just familiar with the small lathes from China and the issues involved with the low quality of finishing that these machines exhibit. I had a little previous experience from a 1 year high school machine shop class, and later set up and operated machine shop for manufacturing light duy machinery. More recently, I became interested in metalworking again, and started buying small lathes and associated tooling.
There are some tool dealers that sell pre-ground HSS cutting tools in sets. http://www.lathemaster.com/HSS%20LATHE%20TOOLS.htm This 3/8" set isn't appropriate for a mini-lathe, but I've seen 5/16" sets on eBay.. maybe some dealers have 1/4" sets, too.
All beginning small lathe users should familiarize themselves with tool grinding geometry as a starting point. Get a handful of HSS blanks to begin the learning process, and duplicate the grinds of the pre-ground tools, and also other configurations that might be needed.
Read the excellent Tool_Grinding tutorial by Harold Vordos concerning grinding wheels and procedures for hand grinding HSS cutting tools. http://twoloonscoffee.com/download /
For general lathe usage, read some instructional info such as South Bend's How To Run A Lathe booklet, or some basic machining practices type books.
Another useful source of info is Shop Reference for Students and Apprentices available from Enco, published by the same company that produces Machinery's Handbook. http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKAP5-3550&PMPXNO7354
As Anorton pointed out, there are often quality issues with new small lathes from China. One can't assume that everything is snug and properly fitted.
One method that will show the user where problems are, involving fit and or adjustments, is to place a short bar (about 8") in the toolpost (simulating a long cutting tool) and apply finger or thumb pressure to see where loose-fitting dovetailed components are causing problems.
Any beginner should buy some easily machined materials to work with, starting out. Cold and hot rolled steel are cheap, but they aren't easy to produce good finishes with, as introductory materials. Choosing some leaded steel alloys will generally produce much better results. Choosing machinable grades of stainless steels will eliminate the frustration of trying to make parts from unknown grades of stainless/mystery metal. Some grades of stainless are very difficult to machine on small lathes.
Setting the cutting tool edge on the centerline of the workpiece (also the center of the spindle and tailstock bore) can be accomplished with a center gage that the user fabricates, or aligning the cutting edge with a dead center point in either the spindle or tailstock, or by using the steel rule method.
The steel rule method involves placing a pocket-sized rule beween the cutting tool tip and the outer surface of a piece of mounted round stock. As the tool tip approaches the rule against the round workpiece (or test bar), the rule becomes confined between two points, pointing in a direction that indicates if the cutting tool edge/tip is on the centerline. When the cutting tool is adjusted up or down, the rule changes position. When the rule is "perfectly" vertical, the cutting tool edge is located on the centerline. The steel rule doesn't need to actually be a steel rule, it can be any flat, straight, smooth piece of thin flat stock, such as a section of stiff feeler gage stock. A section of stiff feeler gage stock is actually better than a steel rule, since it's surfaces are completely flat, where a rule is partly covered with engraving.
Some users of small lathes from China will make a tall toolpost with a wide base that mounts directly onto the cross slide, eliminating the compound slide when they are just turning stock, and don't need the compound feed. This is a work-around to eliminate the extra flexing introduced by the compound slide.
It may be necessary to investigate many other potential quality issues with the mini-lathe, although it can get quite involved. The spindle bearing on my 9x20 model wasn't seated properly, and caused a lot of chatter, for example. There were various other problems that had a detrimental effect on performance with that model.
I doubt that the flex shaft-endmill will work, as the setup won't be rigid enough. The combination machines that I'm familiar with aren't capable of operating the mill and lathe simulaneously, as most of them only have one motor, and it's only engaged for one operation or the other.
--
WB
.........
metalworking projects
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You REALLY need this book: (Amazon.com product link shortened)
Has how to actually set the thing up to do various tasks as well as improvements. It's the manual that should have come with.
I've not used carbide in those small lathes, it really needs something more rigid. HSS is easy to grind to whatever profile is needed and if you pick up a thread gauge, you can make your own threading tools.
There are also mini-lathe web sites devoted to the 7xs, you might want to google up a few.
Stan
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Hi, Bob. I see that you have already gotten a ton of great input on this topic. I read all the first level posts, but not all of the deeper ones, so I hope I'm not wasting your time, but here's my 2 cents:
The work should never stick out of the chuck more than 3 times the diameter. This means that you really need to get some center drills and get used to turning between centers. In case it didn't come clear already, the reason that carbide cutting tools aren't good for you is that carbide chips easily and therefore they have to make the cutting edge very strong, which means, essentially, dull. The posts that say to switch to HSS are "right on". But, here's a thought about the carbide tools, just don't tell anyone I told you this: Suppose you have a chipped carbide cutter. You may be able to actually use the chipped part as a sharper-than-normal cutting edge.
Last point: To get the final finish, you may be able to mount a Dremel tool on the tool post and use that as a tool post grinder to get that last tenth or two off. Just make sure to cover EVERYTHING around the lathe to keep abrasive dust off important surfaces.
Pete Stanaitis -----------------------
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LOL! I thought I was the only one who did that!
A lot of the advice in this thread was right on, and I see Bob has already machined his pivot, so there's no use adding to the confusion except to say I make knife pivot pins like this on my mini-lathe all the time and have finally learned what works, after wasting yards and yards of good A2 pin stock.
-Frank
--
Here's some of my work:
http://www.franksknives.com /
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Verrry nice!
For work that isn't worth $100 an ounce, does A2 hold up well enough without hardening?
jsw
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