# Broke a parting tool



## ARC-170 (May 15, 2020)

I broke my brand new parting tool blade. I bought two; a thin kerf one (0.040") and the normal kerf one (0.062"), both 1/2" high by about 3" long, US made. I was using the thin one to part off a small piece of steel rod, type unknown (probably CRS), but it wasn't anything fancy, since I got it from the school shop where I work.

Here's a picture of the broken blade:



I think I was feeding it too fast, but how would I know? I switched over to the thicker kerf and that worked, but I fed it VERY slowly. The machine (Atlas Craftsman 101) chattered/groaned/vibrated a bit whenever I engaged the blade, only stopping when I got to a smaller diameter. It made noise whenever I engaged it and at any feed speed. I was on the 2nd lowest spindle speed. I used cutting oil. I also used the tail stock and that seemed to help a bit.I also cut the slot a little wider than the blade, backing out the bade, moving over 0.005", then making another cut, etc.

Here's a picture of the setup that worked. When I broke the blade, there was no tail stock and the blade was only extended out as much as I needed.



Anyone have any insights as to what I did wrong? Is there a technique to parting?

Thanks!


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## T Bredehoft (May 15, 2020)

You were using a cut off tool for its intended purpose, breaking. Happens to everyone. Yes there is a technique. It must be learned, cannot be taught. 
Sharpen your tool and try again. Maybe practice with the 1/16 tool until you're comfortable, then try the thin one.


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## benmychree (May 15, 2020)

Feeding very slow tends to increase chatter, and very slow speeds may not be helpful either.  I would not use a parting tool less than 3/32 wide, personally.  An Atlas lathe  ( I am guessing is a 6"?) is certainly not the best platform for parting.  I use TapMagic for parting, and most other machine work as well, it tends to make the tools cut more freely which lessens the tendency for the chips to pile up on the top of the tool and cause galling and subsequent tool breakage.  I see that you have a QCTP, On my 9" Monarch, which is in excellent shape, I have the same situation; if you have the TP pretty much centered in the compound's T slot, the parting tool is hung over the left side of the cross slide , and the tool tends to lean to the left when parting and twists the blade and binds on the partially parted slot, either stalling the machine or breaking the tool; if the TP is moved to the right in the slot so that the tool is not overhung, the tendency goes away and parting can be done without problems.


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## mickri (May 15, 2020)

I have had lots of issues with parting with my craftsman 12x36.  Rigidity is the key.  When I need to part something I tighten everything down except for what I am using to advance the parting tool.  And it still doesn't go that well.  On my last attempt at parting I inadvertently ground the parting tool at a very slight angle.  This actually seemed to help a little bit.

Parting on the backside is just not doable with our lathes.  Running in reverse with the parting tool upside down is fraught with the danger of the chuck coming off.  In another thread that I had on parting issues it was suggested to use a draw bar through the spindle to tighten a keeper (probably wrong term) against the chuck.  Theory was that as long as there were different TPI on the drawbar verses the chuck the two different threads would work against each and the chuck could not unscrew when running in reverse.  Haven't made the keeper yet so no experience with this idea.


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## BGHansen (May 15, 2020)

Parting is probably the toughest operation on a lathe (or bump knurling), so expect some troubles and a learning curve.  I've parted well over 1000 times (closer to 10,000) on the lathe while turning stainless steel, aluminum, brass, CRS, Delrin (plastic), O-1 tool steel, 4140, etc. and still snap a carbide insert (I used GTN-3 or GTN-4) on occasion.  Just snapped an insert a week ago parting aluminum of all things.

Tom Griffin (Google Tom's Techniques) has a nice video tutorial on parting with a HSS blade.  He has a great tip of sharpening the blade before every use.  I tend to use the HSS T-shaped or double-tapered blades which give some side clearance.  I'm comfortable with open spindle speeds like 500 RPM+ with the HSS.  I tend to go to back gear when using carbide (though you'll likely see posts that carbide likes to run fast).

Biggest thing is to stay safe and don't get discouraged.  EVERY one on this forum has likely had a problem parting on the lathe at one point or another.  

Bruce


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## Aukai (May 15, 2020)

Exactly perpendicular, and exactly on height, I'm going at 250-300 rpm, and using the cross feed at the slowest advance, with lots of lube. It will scream, and make noise if it's not right, just my experience. I'm totally new at this, and I used to set tool height by the point of the dead center in the tail stock. The blade on the chuck, or a 1 2 3 block on the tool holder, and chuck for perpendicular. The closer it is to perfect, the less noise there is, also just my experience. I have a T type blade for now, you can't just slap it in, and go, setup is number one. If you look, there are some different ways guys do it.


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## ddickey (May 15, 2020)

Upside down blade on the back side I bet would work much better.


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## Aukai (May 15, 2020)

I ran one upside down yesterday from the front, but hand fed, my height was off, it climbed the nub at the end. Not sure where the play came from on that.


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## mattthemuppet2 (May 15, 2020)

slow speed, high feed. If it screams it's because it's rubbing - either due to too high rpm or too gentle feed. Slow it down and RAM it into the work (well, almost). If you're getting shavings, feed harder until you get little curls rolling off the top of the tool.


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## mickri (May 15, 2020)

Jeff has a craftsman lathe.  Virtually impossible to have a holder on the backside.  He is pretty much limited to the front side.  Mikey has educated me on the forces involved and how everything flexes that makes parting on a craftsman lathe difficult.  To have any chance of success you need your setup as rigid as possible with a properly sharpened blade exactly on center.

When parting on the front side the carriage, cross slide and compound all want to lift on the outside and press down at the work.  This flexing is what causes the blade to go below center line and into the work resulting in the work riding over the top of the blade.  There are gooseneck tool holders designed to compensate for this flexing




I bought some but they were too big to use on my lathe.  So I have not used them and can not attest to how well they work.  I have seen pictures online of gooseneck tool  holders for a QCTP.  I have thought about making one.

Jeff you just have to keep experimenting until you get a setup that works for you.


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## ddickey (May 16, 2020)

You could try this.


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## mickri (May 16, 2020)

This is my current parting blade tool holder and my set up.










I have the compound at an angle for a better picture.  In use the compound is inline with the cross slide.  I lock the carriage in place and I tighten the gibs on the compound so that there is no movement on the compound.  The only thing that moves is the cross slide.  And I tighten the gibs on the cross slide as tight as possible while still allowing the cross slide to move.  I never extend the compound slide past the edge of the compound base (wrong terms??) as shown in the middle picture and depending on the clearances the compound is set as far outboard as possible as in the bottom picture.  The height adjustment screw which is locked in place acts as a support to keep the post on my QCTP from flexing.


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## aliva (May 16, 2020)

One thing I noticed in you pic is that you have a live  center on your part. Do not use a center, its too rigid not allowing the part to flex a bit. Remove the center just before you break thru. When parting my rpm is no more than 200, I feed by hand and lots of coolant, flood if you can.


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## ericc (May 16, 2020)

I've found that when parting longer pieces, it helps to use a center. Just remember to take it out before the piece cuts completely off. With short pieces or disks, no center, of course.


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## ARC-170 (May 16, 2020)

Thanks to all!
I think my problem was caused by (for anyone following along):
1. Didn't sharpen tool. I assumed it was sharp out of the box.
2. Improper alignment. I used a "fishtail" and aligned it perpendicular by eye. I aligned it parallel by eye, but it may have gotten slightly out of alignment when I tightened it. I thought it was good, but I'll need to check it better. The video was very helpful. Thanks, BGHansen!
3. Too slow RPM.
4. Use more cutting oil. I would put some on, then cut, then put more on. It needs a steady supply.
5. Use tail stock until the part is ready to come off, or try not at all.
6. Tighten the compounds and make sure the tool post is not hanging out. Mine are loose due to age, but I think I can get them tighter. 

I will sharpen the tool and see what happens. I'll try that before making a tool holder.


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## ARC-170 (May 16, 2020)

mickri said:


> Jeff has a craftsman lathe.  Virtually impossible to have a holder on the backside.  He is pretty much limited to the front side.  Mikey has educated me on the forces involved and how everything flexes that makes parting on a craftsman lathe difficult.  To have any chance of success you need your setup as rigid as possible with a properly sharpened blade exactly on center.
> 
> When parting on the front side the carriage, cross slide and compound all want to lift on the outside and press down at the work.  This flexing is what causes the blade to go below center line and into the work resulting in the work riding over the top of the blade.  There are gooseneck tool holders designed to compensate for this flexing
> 
> ...



I found this when I searched for "gooseneck toolholders for lathes". Though you might like it:








						Gooseneck or spring-tool holder
					

Since I bought my mini lathe, a decade ago, I had never managed to make a decent parting-off procedure.  I always put the blame on the tool so I moved from a simple blade tool (like the one in the next picture) that I have bought with my lathe...    ..to a more sophisticated one with inserts...




					www.hobby-machinist.com
				




I think I have something similar in the parts that came with the lathe. It had a short, broke parting blade in it.


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## mickri (May 16, 2020)

When I align my parting blade I like to put the side of the blade against the end of the work at a slight angle.




  A piece of white paper on the ways sometimes makes it easier to see when the blade is flush against the work.  I do it mostly by feel.  With the tool holder loose I slowly advance the carriage towards the head stock until I feel the blade go flush against the end of the work.  The blade is now square to the work and I tighten the tool holder to the post.




 If you go too far the tip of the blade will point towards the tail stock.  It only takes a couple of tries to get this down pat.

The above pictures are not something that I am actually working on.  I just put a round bar in a chuck to show the concept.

I have looked at that thread about making a goose neck tool holder and have done a drawing to fit on my tool post.  Another project on the list.


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## sdelivery (Feb 2, 2021)

One thing to look at is tool height.
I tend to run my parting tool a little higher then center line. There tends to be alot of leverage with a parting tool and when it engages the material can be pushed below center line of rotation which make the material try to climb on top of the tool tip......


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## epanzella (Feb 3, 2021)

From the picture you have more stickout than necessary. I'm guessing (hard to see in the pic) that you have 2 dovetails on your toolpost and one of them is facing the live center. If you turn the TP so that the flat side is facing the center you can reduce stickout by a half inch or so. Rigidity is the grail with parting. Once the tool flexes everything tightens up and "bang".


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## Janderso (Feb 3, 2021)

I've never broken a HSS cutoff tool. I can brake carbide inserts all day long. It's a dance between RPM and feed speed IMHO.


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## mickri (Feb 3, 2021)

I made a tool holder just for parting.  I followed a video from Winky's Workshop adapted for my Norman style QCTP.  The tool holder rests on the base.  This is as solid as it can get it.  Since making this I have not had any problems with parting.  Parting has become just another task instead of a challenge.


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## macardoso (Feb 3, 2021)

I have an Enco 12x36, 1000lb. Parting usually goes OK for me, but I am always adjusting to avoid chatter. Peak rigidity is key. Minimize chuck stickout, use a tailstock live center whenever possible, keep the tool short. Wide blades chatter more due to the higher cutting forces, but thin can snap if going too deep. Tool alignment is important too!

I've found lately that a medium speed, 300-600 rpm, and feeding the tool faster than you think gets the cut done with no chatter. Once chatter starts it is hard to stop since the tool rubs over the ridges from the previous pass and has vibrations induced. Again, a hefty enough feed can help. Also a heavy tapping oil is my go-to for parting.


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## Dgrose (Feb 15, 2021)

Rigidity and alignment are key.  Cut as close to the chuck as possible.  Lock everything down except for the cross feed.  Minimize stickout as much as possible.  One trick is to make sure the blade is held properly.  the blades can be T shaped or slanted.  Put a shim on the lower side to get the blade held vertically in the holder.  I cut on a slow speed but once you get it, feed agressively to get the chip going.  I used to cut timid and slow and didn't produce a good chip.  I have had several blades shatter.  Parting is the one operation where I wear safety glasses and a face shield.  you must have both!  I also have a coolant feed on my lathe that I feed cutting fluid rather than coolant.  That lubricant helps tremendously.  If you get lazy and forget any one of these things that affect rigidity, the tool will bite you.  (I am not a production shop so I don't need coolant.  I only use the lube feed when I part.  I used to dip a brush but for parting but I found that was best.  I use the brush for normal turning etc...)  Sharp tooling is essential.  You must grind and hone in my opinion.  Center height is critical although I cheat on the high side slightly at times.  Low is no good.  Hope that helps.


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## savarin (Feb 15, 2021)

Rigidity is the key, swap the compound for a solid plinth, if you have one set up a dial indicator to the top of the parting blade and watch it deflect as you start cutting.
I also diamond hone my parting blades before every use.


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## Logan Novice (Mar 30, 2021)

The most important factor I've learned in parting is that the cutting edge must be sharp and everything should be nailed down as solidly as possible before aligning the cutting edge on the center line.  I actually part with the blade perhaps .001 below the center line (it seems to work better. and make absolutely certain the parting tool is at a perfect right angle to the material I'm parting.  Then, with everything solidly in place, my lubrication is continuous and my feed as constant and steady as possible.  Any noise, I stop to identify the source.  Cutting tool too long; cutting angle too steep or too shallow (bind on the long axis of the parting tool) speed too fast or too slow.  I still break a tool once in a while.  But it happens with less frequency that it did when I first attempted the task.


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## benmychree (Mar 30, 2021)

mickri said:


> I made a tool holder just for parting.  I followed a video from Winky's Workshop adapted for my Norman style QCTP.  The tool holder rests on the base.  This is as solid as it can get it.  Since making this I have not had any problems with parting.  Parting has become just another task instead of a challenge.
> 
> View attachment 353696


Parting tools function better if they have back rake, your holder does not provide that.


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## benmychree (Mar 30, 2021)

If you do parting off, you will break blades, a fact of life in any machine shop, but it does get better with time and experience; being timid with speed and feed will cause more problems than the opposite approach.


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## mickri (Mar 30, 2021)

While my holder doesn't provide for back rake there is about 3* of back rake ground on the blade.  The blade came with the back rake ground on the blade.  Might need more than than.  Seems to work so far.  Thanks for the suggestion.


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## Winegrower (Mar 31, 2021)

I had plenty of problems parting on my old 10” Logan, and too often would finish the last part of the cut with a hacksaw.

Parting got a LOT easier with the 2500 pound Takisawa, and pretty much resolved when I was given an Aloris #71 blade, and
I made an adapter to mount it in a CXA holder.   The blade is about 1.5” tall and uses GTN-3 inserts.   Mikey gave me some tutorial support and now I can power feed through 2.5” steel rounds, pointing a koolmist mister at it and standing out of the way of the blue chips that come off.   I align the blade with a dial indicator, a la Joe Pie.  Occasionally an insert chips, so possibly buying the cheapest eBay stuff I can find is not a perfect strategy.   But I have lots of them.


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## Optic Eyes (Apr 9, 2021)

,I learned about parting watching automatic screw machines, 
Rule 1. make a curling chip, not shavings
Rule 2. It's just metal and has no friends in the shop
Rule 3. lots and lots of cutting oil put on the tool tip
Rule 4. Push the tool in, no sissy crap, get the speed up


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