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cut-off tool frustration


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  #1  
Old 08-28-2014, 03:28:40 PM
10thumbs 10thumbs is offline
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Default cut-off tool frustration

What is the proper way to use a cut-off tool?
Seems I'm forever resorting to a hacksaw due to the blade sliding or breaking off.
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  #2  
Old 08-28-2014, 03:39:46 PM
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Default Re: cut-off tool frustration

I would also like to know. These have always been a frustration to me.
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  #3  
Old 08-28-2014, 04:43:48 PM
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Default Re: cut-off tool frustration

I think the biggest reason people snap off part off tools is one, they are using high speed steel, 2 are not using lubricant, and 3 they dont allow the chips to evacuate which causes it to bind up and break tools. If you are using high speed steel you have to take it easy and use lots of oil or coolant and let it do its thing. Plus make sure it has all the proper relief angles ground into it so it doesn't bind. My advise, if you are using high speed, would be to spend the money and get a part off tool with a carbide insert. It will make your life from miserable to wonderful in a minute, and you can get really aggressive with them unlike HSS. Plus they already have the right geometry in the insert to evacuate the chip a lot better.

I dont ever use high speed steel anymore except when having to grind a special shape, or some plastics dont like carbides because they aren't sharp enough. Carbide insert tools are the way to go
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  #4  
Old 08-28-2014, 04:52:07 PM
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Default Re: cut-off tool frustration

there are a few important factors. 1: the tool should have relief behind the cutting edge( the sides). 2: the height should be set to center or just below, Never higher then center. 3) Speed. Thats hard to answer because each material is different. If it is taking gudges your feeding in to fast. I all ways try to feed in as slow as i can. 4) And remember a Cool Tool is a Happy Tool. Sometimes tapping fluids seem to work a little better. Hope this helps, i crashed many a times before learning all the dos and don'ts
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Old 08-28-2014, 06:19:11 PM
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Default Re: cut-off tool frustration

To add to what Tanner posted make sure the tool is 90° to the workpiece. A few degrees either way will cause binding and excessive heat.
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  #6  
Old 08-28-2014, 08:17:24 PM
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Default Re: cut-off tool frustration

Quote:
Originally Posted by 10thumbs View Post
What is the proper way to use a cut-off tool?
Seems I'm forever resorting to a hacksaw due to the blade sliding or breaking off.
Show us a picture of your setup and you'll get better answers. I've had no issues with HSS cutoff tools on my 10EE. None.

Get the geometry right, make sure your work is well supported (ie not sticking out 8 diameters past the chuck) run around 50 SFM in steel or 300 in aluminum, and dribble in a little lube. Easy...
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Old 08-28-2014, 09:18:02 PM
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Default Re: cut-off tool frustration

Yeah, I'm so good of a machinist I never have problems with a cutoff tool.

Ok if you believe that I have a bridge to sell you.

One of the problems we induce is when sharpening it on a wheel we put too much angle on them therefore they dig in with expected results. I run it slow in back gear with the belt very loose so when the *%&# thing sticks it will stall and not break anything.

Grind the angle not much more than 90 degrees so the edge is not so aggressive. The side angle that let's the part drop off can't be too much or the side thrust while cutting will also help it stick. Another problem with small lathes is that the machines have a lot of flex to them which allows the tool to climb.


Check the pics and these angles work pretty well.
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  #8  
Old 08-28-2014, 09:43:06 PM
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Default Re: cut-off tool frustration

Ha - I never claimed to be a machinist.

I just tinker at this stuff...

But HSS works fine. I suggest the Empire-style cutter, and I've never needed the 'dished out' spot on the top. But my tool holder has about 3 degrees of relief built in.
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  #9  
Old 08-28-2014, 09:53:05 PM
Bill Hazzard Bill Hazzard is offline
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Default Re: cut-off tool frustration

I've never ground the top of my cut off tools, I use them as they come and rarely have a problem. I do use cutting oil and run in back gear.
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  #10  
Old 08-28-2014, 10:51:38 PM
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Default Re: cut-off tool frustration

I've had better results since I got a wedge style quick change tool post to replace the piston style. I also use carbide insert cut off tooling.

Consistent feedrate is important too. Here's a video I took of my Monarch CK 12 with an Aloris BXA QCTP. ( the things I did "wrong" were having the part out too far from the chuck and an inconsistent feedrate due to holding the camera in one hand while feeding with the other hand )

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Old 08-29-2014, 07:12:10 AM
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Default Re: cut-off tool frustration

I come from a machining background, and I believe everyone's advice is pretty spot on, there is one thing I'd like to add, I have found that thinner materials tend to flex and climb the cutter which will break the end off the cutter, I have found, providing the part you are making allows, is to use a live centre, this will minimize flex and climbing. Always use coolant, especially if you are cutting stainless and tool steel.
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  #12  
Old 08-29-2014, 09:14:06 AM
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Default Re: cut-off tool frustration

Quote:
Originally Posted by slugga View Post
...I have found, providing the part you are making allows, is to use a live centre, this will minimize flex and climbing....
Interesting. I haven't experimented with this, thinking the center would be a bad thing - tending to squeeze the end being parted off back into the work, and causing binding just as the end should be falling away...

---------- Post added at 09:14 AM ---------- Previous post was at 09:10 AM ----------

Quote:
Originally Posted by Jeff in PA View Post
... inconsistent feedrate due to holding the camera in one hand while feeding with the other hand
I just use power feed. It frees up my hands to apply lubricoolant throughout the whole cut...
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  #13  
Old 08-29-2014, 10:31:03 AM
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Default Re: cut-off tool frustration

I was trying to part off a piece of aluminum the other day; the tool kept pushing to the left, trying to cut concave on the left, & hardly cutting at all on the right...finally figured out the blade had slipped in the holder, & the right side was rubbing, not cutting...so, make sure your blade is perpendicular.
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  #14  
Old 08-29-2014, 10:44:18 AM
Pete Spaco Pete Spaco is offline
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Default Re: cut-off tool frustration

"A cool tool is a happy tool" has already been said.
I was told that the chip you make when parting off is actually wider than the slot when the chip gets hot (it expands, rright?). So you need to be cooling the chips all the time. I learned to use the sulphurized cutting oil that is like what plumbers use for pipe threading--- on steel, anyway.
When parting off, I prop my left arm over the headstock holding quart can's spout right over the part and try to constantly dribble a tiny bit of oil as I go.
I think it has already been said a couple of times, but I think it is important to keep a steady feed rate and to keep the tool cutting so it doesn't heat up from rubbing.

From the sound of some of the other posts, it looks like I should look into a carbide cutoff tool myself.

Speed: my Atlas "how to run a lathe" book says to use back gear and I do that if I have a large diameter to part off, but for stuff an inch or less in diameter, I use the slowest non back gear setting.

Regarding concerns about using a tailstock center: You don't need or want much inward pressure on the part; all you need to do is to keep it from chattering or bending. If you are worried about that, part the thing almost all the way off, back the tool out, retract the center and finish with the hacksaw.

Pete Stanaitis
----------------
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Old 08-29-2014, 08:55:44 PM
beezerbill beezerbill is offline
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Default Re: cut-off tool frustration

I've broken a few but none recently.

Two things are most important - rigidity and cutting fluid.

A lack of rigidity can allow the part to ride up on the tool, which will likely break the tool. This could include the cut being too far form the chuck (or collet), a flexing tool holder, loose gibs, the tool sticking out too far, the tool too high, the tool holder cantilevered out too far, or even loose headstock bearings. Or some subtle combination of these.

Parting off on a rigid lathe can get to be routine but on a lathe with a lot of flex requires a lot of care and slow feeds and speeds. I can run speed and feed as fast as I dare when parting off on the Monarch EE but I have to be real careful when parting off on the 6 inch Atlas. The 10 inch South Bend is somewhere in between. I suspect some of the smaller "value priced" import hobby lathes are absolutely horrible to try parting off on.

As far as the parting tool, I have had no trouble with high speed steel. One important thing is to have enough, but not too much, back rake. A couple degrees seems to be enough. What is most important is to keep the tool sharp - I touch up the edge frequently.

Cutting fluid is the other thing - the more the better. I have had the best luck with a heavy cutting oil - the kind of oil used in pipe threading machines is good and is available at some hardware stores. And remember, as the slot gets deeper, it gets harder to get the fluid in there. I often hold a fluid-soaked acid brush in the groove while it is cutting, and re-soaking the brush about every three seconds. During the time it takes to re-soak the brush I can hear the cut drying out, approaching that hideous galling noise that indicates something bad is going to happen real soon unless I get that brush right back in there. As soon as the lube hits all sounds fine again. One of these days I hope to get the fluid pump running on the Monarch so I can dispense with the silly acid brush. I may have to try the spray mister also - something I can do that I didn't think of. (But with the proper water soluble fluid - not pipe cutting oil - Yuck!)

This is all for steel, stainless, and aluminum (and copper - have done lots of that). Brass is a bit different - not so needy for the lube but a few degrees of NEGATIVE top rake keeps the tool from trying to dig in.

Having the tool slightly out of square seems to cause a dished cut but doesn't break the tool for me.

Hope some of this helps, and good luck!
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  #16  
Old 08-30-2014, 12:54:31 AM
Richard W. Richard W. is offline
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Default Re: cut-off tool frustration

Quote:
Originally Posted by Tanner Remillard View Post

I dont ever use high speed steel anymore except when having to grind a special shape, or some plastics dont like carbides because they aren't sharp enough. Carbide insert tools are the way to go
I don't have a problem with either carbide or HSS. Its about how you set up the part to be cut and even more important how you setup the parting tool. At home I use HSS and at work I use what ever is handy, usually carbide. You are right about plastic, HSS is the only way to go in most plastics.

Richard W.

---------- Post added at 09:44 PM ---------- Previous post was at 09:39 PM ----------

Quote:
Originally Posted by Jim McIntyre View Post
Ha - I never claimed to be a machinist.

But HSS works fine. I suggest the Empire-style cutter, and I've never needed the 'dished out' spot on the top. But my tool holder has about 3 degrees of relief built in.
You have a different style of parting tool so grinding the top isn't necessary or a good idea with the parting blade you show. I call these a "T" type parting tool.

Richard W.

---------- Post added at 09:54 PM ---------- Previous post was at 09:44 PM ----------

Quote:
Originally Posted by I like oldstuff View Post
One of the problems we induce is when sharpening it on a wheel we put too much angle on them therefore they dig in with expected results. I run it slow in back gear with the belt very loose so when the *%&# thing sticks it will stall and not break anything.
I run everything so the machine will not stall.

Quote:
Originally Posted by I like oldstuff View Post
Grind the angle not much more than 90 degrees so the edge is not so aggressive. The side angle that let's the part drop off can't be too much or the side thrust while cutting will also help it stick. Another problem with small lathes is that the machines have a lot of flex to them which allows the tool to climb.


Check the pics and these angles work pretty well.
I think you did a good job showing how to grind this type of parting tool. They work really good even if they are a bit old fashioned. I have pretty much switched over to the Aloris wedge type tool post and got away from the lantern style tool post. The first parting job I did with this type of holder was 2" diameter 316 stainless steel. Worked really well when used with a lot of cutting oil.

Richard W.

Last edited by Richard W.; 08-30-2014 at 01:34:43 PM.
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  #17  
Old 08-30-2014, 01:07:00 AM
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Jim McIntyre Jim McIntyre is offline
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Default Re: cut-off tool frustration

There's a series of 3 excellent videos on you tube.




Part1:
https://www.youtube.com/watch?v=82LtUTBmxwQ

Part2:
https://www.youtube.com/watch?v=w0N6K9y2i2M

Part3:
https://www.youtube.com/watch?v=PgS5GFQXSQo

Part 3.5:
https://www.youtube.com/watch?v=tLNYDEqs6fI

Last edited by Jim McIntyre; 08-30-2014 at 01:22:36 AM.
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Old 08-30-2014, 01:41:10 AM
Richard W. Richard W. is offline
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Default Re: cut-off tool frustration

Quote:
Originally Posted by Pete Spaco View Post
From the sound of some of the other posts, it looks like I should look into a carbide cutoff tool myself.
Depends on how often you need to part things off. You can lay down a lot of money very quickly for a good Iscar parting tool.

Quote:
Originally Posted by Pete Spaco View Post
Speed: my Atlas "how to run a lathe" book says to use back gear and I do that if I have a large diameter to part off, but for stuff an inch or less in diameter, I use the slowest non back gear setting.

Regarding concerns about using a tailstock center: You don't need or want much inward pressure on the part; all you need to do is to keep it from chattering or bending. If you are worried about that, part the thing almost all the way off, back the tool out, retract the center and finish with the hacksaw.

Pete Stanaitis
----------------
I always look in the handbook for the proper surface feet and use the formula as a starting point. Running to slow can create a different set of problems and running to fast can burn up the tool really fast.

One thing that really helps is to have a larger lathe for the extra rigidity. Unless you are using thin parting blades and doing a lot of small parts. I think a 12" swing lathe or larger is a better option for when you have to part something. I am sure a lot of people have moved up from a 9" lathe to something bigger and found parting gets a whole lot easier to do. My lathe is a 16" that will actually turn a part a little over 18". I haven't broke a parting tool with it yet. Even when I showed a college student how to part 1 1/2" steel with HSS. He could really see the difference a good solid lathe made over the little lathes they have at the college.

I have only used a center when parting 3 or 4 times in the last 40+ years and that was on some really worn out lathes. What you say about using a center for parting is about right on in most situations. I am sure there are times when it is a good idea.

Richard W.

---------- Post added at 10:41 PM ---------- Previous post was at 10:16 PM ----------

Quote:
Originally Posted by Jim McIntyre View Post
One thing to notice is he keeps the parting tool over the cross slide! That is very important especially on smaller or really worn out lathes.

Richard W.
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Old 08-30-2014, 12:40:22 PM
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Default Re: cut-off tool frustration

make sure tip is dead center with work once i figured it out no more problems Jon
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Old 08-31-2014, 03:21:27 AM
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Default Re: cut-off tool frustration

I have a well worn big old lathe which years ago came with a heavy HSS cutoff tool (abt 3/16" wide) and set in a spring type holder. This allowed the tool to deflect downward instead of digging in or chattering, and as long as I fed it enough to deflect slightly, it would cut most things without complaint.
Another smaller well used machine with a rigid holder was always a pain unless all gibs were screwed up stiff and the tool was set well over the saddle.
My modern rigid machine uses an Iscar carbide tool and is usually no problem as long as some lube is used. For big jobs I still resort to the old brute and the spring tool. Combustor.
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