More mini lathe issues

A manual should have come with the lathe showing the correct turning speed for the diameter you are working with. At this point you should be using the highest speed possible for your lathe. Second possibility is your tool is not exactly centered on the shaft you are turning, and finally, the tool may not be sharp enough. Any and all could contribute to what you are experiencing, and there are probably some other possibilities, but check these first.

Paul

You prolly have forgotten more about this than I will never know so please pardon the question.

Is your tool bit set a tad low in the tool post? As on page 21:

--Winston

HSS, honed sharp after grinding, at center height, removing ~0.005 per pass. Support the work with the tailstock. I've made stainless #0-80 screws 1.25" long that way.

jsw

Not really. It showed gear change and safety stuff, but not much else.

I did not know that. I will try max speed and see what happens.

Second possibility

Well, if I look closely it actually looks like it is a tiny bit above center, but that could be an illusion. Maybe a few thousandths.

A good possibility. I suppose I could swap out to a brand new tool for last few hundredths.

Thanks Paul.

Bob

LOL. I know next to nothing about running a metal lathe so I don't think so.

I do not think so. Not sure how to measure it, but if anything when I bring the free center upto the tool the tool looks like it might be a couple thousandths above center.

I will read.

Bob

Wow, that's pretty aggressive. I have been only removing .002 .003 per pass. I will try a much faster turn rate as one poster suggested.

I need to get some center drills I guess.

I've made stainless #0-80

With my beginning level of skill that task looks all but impossible. I am impressed.

Follow rest to prevent the part from climbing up over the tool bit?

When I got my mini lathe, one of the many issues I found was that the slide could rock slightly even with the gib plates tight. I took off the slide, put sharpie marker on the ways, and set it back down and slid it back and forth. The areas where the marker rubbed off showed where it was making contact. As expected there were high spots in the middle of both the flat and V-shaped ways on the slide. After adjusting this with some careful manual filing and grinding, the slide was much more stable.

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 regr> I am trying to make my first real part. A replacement pivot pin for a

If you do not have a bench grinder or belt sander, you ought to think hard about getting one. Grinding a HSS tool bit seems to be a problem for a lot of people. But it is really quite simple. If you already have a HSS tool bit, you can use touch it up using a bench stone or some sandpaper backed by something flat.

Why don't you post where you are located. There might be someone close who could show you a lot in not too many minutes. Or maybe you could use a digital camera or webcam to show close ups of what you are doing. Just do not post pictures in RCM.

=20 Dan

A common trick is to pinch a 6" scale vertically between the tip of the tool bit and the workpiece. If the top of the scale leans away from you, then you're tip is above the workpiece centerline. If the top of the scale is leaning towards you, then your tool bit is below the centerline. Basically you're using the scale to indicate the tangent of the circle (if viewed from the end).

That is a good trick. I will remember that one.

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.

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.

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.

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.

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.

I bet that this is a good idea in any case, but I would use Hi-Spot Blue

instead of the marker, and a set of small machinist scrapers (such as 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

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

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

Hmm ... I have never seen a modern lathe manual which has this information -- just how the controls work -- if you are lucky.

Accessory books, like the _How to Use a Lathe_ books by South Bend and Atlas (each focused on their particular line of machines) may have general information about how to calculate the speed for a given SFM (Surface Feet per Minute), but you need another book (like _Machinery's Handbook_), or to look it up on the web to determine the proper cutting speeds for a specific combination of workpiece alloy and tool material. You get faster speeds with carbide tools than with HSS, and faster with HSS than with the old carbon steel tools. So -- you look up the SFM from the workpiece alloy and the tool material, then calculate the RPM from the starting diameter of the workpiece and the SFM which you just looked up.

Given the maximum speed likely available in a "mini lathe", and the size of your workpiece, yes, I think that this is probably right. If you start getting chips which turn blue and you are using HSS tooling, you may be turning too fast, but I doubt that you can turn that fast with that diameter of workpiece.

Indeed so.

Good Luck, DoN.

Looking at this part again -- I have to ask -- how far is the workpiece sticking out of the lathe chuck? Generally, for something held only in the chuck, the maximum extension should be about four times the diameter -- and as you turn the diameter down, you have to shorten the workpiece a bit. The workpiece tends to flex upward, and climb over the tool bit.

Now -- do you have a live center for the lathe's tailstock? If so, can you center drill the end of the workpiece and support it with the live center? You may have to leave a piece of larger diameter near the live center, and cut it off when you are done. Oh yes -- also beware of parting off while the workpiece is supported with a live center. It will jam interestingly as you get to the final cutoff point.

Good Luck, DoN.