Smooth Cuts and Cutting Tools

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

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ctwo
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Smooth Cuts and Cutting Tools

Post by ctwo » Sun May 06, 2012 5:34 pm

I'm not having any luck getting a smooth surface.

This is a steel stake I think used with rebar, so hot rolled? IDK...

Spindle speed is 576 and feed is very slow, about 2-5 thou cuts, using the various tools shown at various angles - the result is always the same...I get a finish about as good as a vinyl record, without the uniformity...


BTW, I'd like to get some new inserts, but do not know how they are identified - and the one with the spur, I need another spur for another holder.
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hammermill
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Re: Smooth Cuts and Cutting Tools

Post by hammermill » Sun May 06, 2012 6:31 pm

form stakes like rebar are made from recycled low grade steels( maybe not the new coated stuff??) but they are a blend of what ever the scrap pile holds. so one will be hard another soft etc. so even if you get one turning right you will need to start over with the next.

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ctwo
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Re: Smooth Cuts and Cutting Tools

Post by ctwo » Sun May 06, 2012 10:57 pm

Well, I figured it's junk metal, but still hoped I could make use of it. To go along with a poor finish, I'm having a hard time parting off...it seems like it hits or catches during the cut and I thought I had broken the tool a couple times. I'm trying to run it with a steady feed and a bit slower - down to 228 RPM. It goes good for about 1/2 the cut then starts chattering and jumping.

Here is what I was able to turn out this afternoon...a companion for my little 4-jaw chuck...
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Standards are so important that everyone must have their own...
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hammermill
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Re: Smooth Cuts and Cutting Tools

Post by hammermill » Sun May 06, 2012 11:28 pm

on smaller machines parting can be troublesome. make sure everything is snug,aligned to center and not binding

Harold_V
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Re: Smooth Cuts and Cutting Tools

Post by Harold_V » Mon May 07, 2012 12:02 am

ctwo wrote: To go along with a poor finish, I'm having a hard time parting off...it seems like it hits or catches during the cut and I thought I had broken the tool a couple times. I'm trying to run it with a steady feed and a bit slower - down to 228 RPM. It goes good for about 1/2 the cut then starts chattering and jumping.
It's not conclusive, but indications are that the parting tool has issues. It should have a gentle relief towards the shank, so the groove that is generated is slightly wider than the back portion of the blade. That lowers friction and can compensate for minor misalignment, preventing one side from contacting the generated groove.

The other issue that may be responsible is that the tool appears to have worn edges. Looking down on the tool (from the photo), note that the corners appear to be rounded off towards the rear of the tool, as well as towards the bottom of the tool. The very top edge of the tool should be the only place it contacts the work. If you allow contact any other place, cutting resistance rises astronomically, resulting in poor cutting and the potential for the tool to wedge in the cut, or for the material to climb the tool.

You may benefit by grinding a gentle positive rake on top of the tool. I use the periphery of the wheel, relieving the material slightly behind the cutting edge (which you should not disturb). It's easy to do if you don't have a (work) rest in the way.

If you're parting small diameters, you likely could justify higher speed. Should be able to tolerate 500 rpm (or more) without issue, assuming the part is not overly extended from the chuck (chatter). That often creates better chip flow. Be certain to lubricate well (sulfur based cutting oil).

Hope this helps.

Harold
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ctwo
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Re: Smooth Cuts and Cutting Tools

Post by ctwo » Mon May 07, 2012 8:46 am

I'll try to freshen the edges and grind some more relief. I already broke that one off once.

Also, I tried a straight blade mounted on an angled Ajax? tool holder when cutting a 1/4 inch steel rod and the work jumped up on top of the tool. :shock:
Standards are so important that everyone must have their own...
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Harold_V
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Re: Smooth Cuts and Cutting Tools

Post by Harold_V » Mon May 07, 2012 2:46 pm

I should have commented on the surface finish.

Rarely will you encounter a tool that has the ability to take a light pass and yield a good finish when machining carbon steel. It has the potential to tear, and does so with reckless abandon when being turned. You can avoid the problem by taking deep cuts at high speeds, using carbide. That introduces other problems, however, like losing the ability to control diameters closely. That being said, assuming the material choice isn't critical, use leaded (free machining) materials when finish is important, or learn to turn close, then polish for finish and size control. I never recommend the use of a file ----which has the potential to pin (ruins the finish), or to yield out-of-round turns.

Harold
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swatson144
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Re: Smooth Cuts and Cutting Tools

Post by swatson144 » Tue May 08, 2012 7:26 am

That carbide tool looks hammered! the cutting edge seems to be rundown and not straight. The edge looks rounded over, and it looks like a radius is worn into it. I'd either replace it or touch it up on a silicon carbide or diamond wheel. You'd get a poor finish in 12L14 with that tool.

I have no idea of the origin of the tool but most Chinese imports I've seen lately need work right out of the package and quickly get worse unless dressed up before use. Last batch I got are actually over square instead of slightly under square. I may get blasted for this but I keep cheap imports around for interrupted cuts and things that don't really matter. They really don't seem to cut as well as tools from more expensive countries. I don't know if it is the material, the shank, or my ability to dress them.

Using good magnification shows a lot of what is wrong with tooling, especially if your arms aren't as long as they used to be.

Steve

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Re: Smooth Cuts and Cutting Tools

Post by stevec » Tue May 08, 2012 7:43 am

swatson144 wrote:That carbide tool looks hammered! the cutting edge seems to be rundown and not straight. The edge looks rounded over, and it looks like a radius is worn into it. I'd either replace it or touch it up on a silicon carbide or diamond wheel. You'd get a poor finish in 12L14 with that tool.

I have no idea of the origin of the tool but most Chinese imports I've seen lately need work right out of the package and quickly get worse unless dressed up before use. Last batch I got are actually over square instead of slightly under square. I may get blasted for this but I keep cheap imports around for interrupted cuts and things that don't really matter. They really don't seem to cut as well as tools from more expensive countries. I don't know if it is the material, the shank, or my ability to dress them.

Using good magnification shows a lot of what is wrong with tooling, especially if your arms aren't as long as they used to be.

Steve
More fuel for the fire of learning to grind your own high speed steel tooling :wink:

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swatson144
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Re: Smooth Cuts and Cutting Tools

Post by swatson144 » Tue May 08, 2012 8:34 am

I try not to grind anything but specialty tools, it's just me, I don't like grinding. Here's a HSS tool I use fairly often for finishing. It allows me to take a thou or so off a piece and get a near polished finish. Seen as it would be from the work, or should I say looking through the work from the backside of the lathe. I can see it needs touch up and I've pretty much used the whole length of the cutting edge.

finishing tool.JPG
I have no idea where the original design came from but it was certainly not my idea. Works a treat as you simply run it in until it touches and let it feed. It'll make very fine steel wool for swarf. You can cut at any height and use the whole edge. The geometry may not be perfect on this tool as I ground the 1st one for my home shop from memory, and since it works well later ones will be copies.

Steve

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Re: Smooth Cuts and Cutting Tools

Post by JackF » Tue May 08, 2012 10:39 am

Steve,

Forgive my ignorance but is that tool upside down in the tool holder or is it used for turning the work with the lathe in reverse? Once again, forgive my ignorance but I can't figure out how this cutter is used. Once it is explained I am sure it will hit me square in the face. :)

Jack.

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Re: Smooth Cuts and Cutting Tools

Post by swatson144 » Tue May 08, 2012 11:46 am

Nope that is the way it is used. Picture it as like a knife slicing a tiny bit off. another view.
finish1.JPG
Imagine the metal is wood and you were to hold a knife edge to shave just a smidgen off as the work was turning. That edge orientation is how this tool cuts. it is the smoothest finishing tool type I have ever used. slanted vertical towards the direction of the cut and angled in. The only draw back is that it won't turn to a shoulder.

OK all that made little sense so I add this as an edit. Picture is worth a thousand words.
finishing2.JPG

I cut a skim on some 3/4" 1018 CRS with an AR-5 tool much like the OP's picture. Then followed it up with the finishing tool and caught a little swarf in my hand to toss on top for reference. You can't feel the step between the cuts with a finger nail but you can sure feel the difference between the rough and finished.

I hope it makes more sense now.

Steve

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