Edison 1340 finish quality issues?

[justin1]

Hello me and my buddy were playing around with the small lathe the other day and been trying to figure out were this problem is coming from. The machine is fairly worn so thinking some of the issue resides with that but curious of any ways to maybe correct the issue or mitigate it atleast.

Anyways the issue is as the carriage is traveling side to side in long cuts it seems to hit tiny bumps causing ever tiny low spots or high spots as the carriage travel threw the cuts.


Thought it maybe chips getting under carriage causing it but still happens if ways are covered. Also tightened the ways up as well. Except for the main carriage to the bed ways not sure how to adjust that one or if there is an adjust for it.

Using a cemented carbide cutter that we sharpened also tried it with new kennametal cemented carbide cutter more or less same results.

The rpm we tried was 320 and 240 for most runs and step over of .0025 up to .0080 something the lathe doesn't have a large step over rate range. And cut was less then .001 most of the runs more or less got similar results in different spots. Only a few .0001s if I a had to guess didn't measure didnt have test gauge with me.

The material is 2.375 shaft stock 4140? Maybe

Any insight on stuff we can try or maybe somewhere that isn't clean would be helpful. I would like to get better finishes then this if possible and get rid of the high low problem.

also the gear that feeds the carriage back and forth is very worn the gear teeth look like sharp vees more then gear teeth. Also think maybe part of problem.

 

[Tecnico]

I think the guys really in the know on these things must have stepped away to the water cooler so I’ll toss in what I’ve found helps until they’re back. I posted a thread a while back when I had a really good day: Reference Thread

What I think you’re seeing is the result of your cutting tool smearing the surface rather than making a perfect clean cut. That’s not necessarily your fault or your machine, steel, especially mild steel tends to smear & tear vs cut cleanly like aluminum. You see that in what look like scored line and deposited blobs of material on the surface. Does aluminum work better for you?

I’ve ground HSS and carefully polished the cutting edge for decent results, you need to have a sharp edge & enough rake to improve the finish.

In the thread above, what I did was an experiment with dressing a carbide insert to sharpen the cutting edge. Carbide insert tools for steel usually are not as sharp as I expected. I got lucky dressing the edge on that one and hit a sweet spot. I have also been told that inserts made for aluminum do a nice job of finishing steel because of their greater rake and greater sharpness. In my case that would be a DCGT shape but they are also more fragile.

Another tool that is good for finish & sizing is a so called shear tool, they are good to size the last few thousandths or tenths but not deep cuts like carbides. Instead of cutting with the top face of the tool, the front face with about a 15 degree back rake, does the cutting/shearing. Not a good explanation but there are good descriptions and photos on the web.

I experimented with grinding a shear tool and eventually got something that worked pretty well.

Well, there’s that for now until the experts are back in the room. Good luck!

D

 

[Susquatch]

@justin1 - I'm no expert either. But I agree with @Tecnico .

Welcome to the world of learning to make nice smooth cuts. This is something that takes practice.

That said, looks to me like you are not taking a big enough cut considering that you are using Carbide. Carbide doesn't generally like light cuts. As a result, your swarf is getting into the cutting edge and smearing.

You also said you sharpened the bit. Well, that's not always a good idea with Carbide. HSS likes to be sharp. Carbide not so much. That's not to say never sharpen carbide, but it's definitely happier less sharp than HSS. REGARDLESS, you will need a radius on the tip to cut nice smooth surfaces.

Keep in mind that all the above is subject to the weather factor. Which basically means, there are no real hard rules. Sometimes things just work, and sometimes you fight them all the way to Australia and back.

But each fight will make you a better fighter. Stick with it and don't give up.

Start by getting a proper cutting tool for the job you are doing and then check your speed, feed, and depth of cut against the material you are turning.

As @Tecnico says, if you need to do shallow smooth cuts, try a shear tool. I luv them.

I'd also suggest that you make another cut as is and watch your cutting tip closely. Be careful to keep your hair and clothing away as you do that. A close examination might tell you all kinds of things. Watch especially closely for swarf curling back into the cutting action. A deeper cut helps to prevent that.

 

[justin1]

Mk I'll dig around and try less sharp carbide see If that changes a bit I have had some good finishes in the past with hss. I'll try some hss out and see if the little ridges still appear I don't remember it being a issue in past but maybe not. I don't usually do long cuts like this but would be nice to figure out the secrets of a machine shop finish.

Don't have a shear tool may look into making one as I read threw a thread about them here bit ago seemed like good addition to tool colletion

 

[Susquatch]

Don't have a shear tool may look into making one as I read threw a thread about them here bit ago seemed like good addition to tool colletion

The thing about a shear tool that is nice is that you can clean up a nice surface without having to take a deep cut and blowing your dimension.

But the best method is to learn what depth of cut, feedrate, and speed you lathe likes for a given material and cutting tool. There are lots of charts and references on the web.

I think most people just starting out are afraid to take a decent cut figuring that they can "sneak up" on a dimension. With the right tools, you can do that. But not as a rule.

As a rule, you should know what your situation requires (maybe doing a bunch of test cuts) and then calculate the best final cuts to get it done by measuring what it takes to do so. Do a pre-cut measurement, cut, then measure again and see what happens. When you know what works, setup a series of cuts to get you there in a predictable way with no surprises.