# Parting For Idiots



## kyler (Feb 23, 2015)

This topic has got to be one of the most discussed yet I'm still having problems.  I apologize for bringing it up again.

The symptom is a concave surface on the cut-off piece.  I mainly turn aluminum and haven't parted steel yet.

I shorten the tool to the minimum necessary.

I put the tool against the chuck and check for perpendicularity.  I've even tried using a dial indicator to set the tool holder perpendicular.

ANy ideas?


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## David S (Feb 23, 2015)

How is the front of the parting tool ground?  Is it ground parallel to the axis of the part, or is it tapered so that the part cut off will not have a "nub"

David


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## Wreck™Wreck (Feb 23, 2015)

kyler said:


> I put the tool against the chuck and check for perpendicularity.  I've even tried using a dial indicator to set the tool holder perpendicular.
> 
> ANy ideas?



Indicate the tool itself not the holder.


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## Ski (Feb 23, 2015)

I am curious how this happens. Insure it is ground right as mentioned. It seems like if you had the cutoff blade turned a bit at an angle the contact with the side maybe causes this as it gets pinched and driven over gradually?  I learned parting by asking questions so you will get it figured out here. there are also some videos out there on you tube on parting.  I simply adjust the tool as short as needed as you did. I adjust it flat to the the faced off end of the piece and centered on the side of the work. I have also used the face of the chuck to adjust the cutoff tool flat as well and that worked too. There are several ways to get the cutoff tool adjusted to the center of the piece. Ski


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## higgite (Feb 23, 2015)

Hi kyler,

After the parting is done, continue to run the tool all the way across the face of the work piece with the cross slide. If it continues to take off metal, the blade isn't perpendicular to the work. If it doesn't continue to take off material, but the face is concave, something is flexing under the load of parting, the blade, tool post, work piece, or whatever. Do you lock your carriage down when you part?

Tom


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## Tony Wells (Feb 23, 2015)

Once you reach center, if you try to cut the "far side", don't forget to reverse the spindle.


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## higgite (Feb 23, 2015)

Tony Wells said:


> Once you reach center, if you try to cut the "far side", don't forget to reverse the spindle.


 Good point, Tony!


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## darkzero (Feb 24, 2015)

If you have a concave face after parting, could be your carriage is moving under pressure or your parting blade is flexing during the cut. Are you able to lock the carriage? Although I don't have the issue, it would,t matter to me cause I compensate & generally reface the part after parting anyway.


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## MozamPete (Feb 24, 2015)

Do you get a perfectly flat surface when facing the end of a bar?  If not could be the cross slide is not travelling 100% perpendicular to the lathe axis.


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## Bishop (Feb 24, 2015)

My vote is the carriage isn't locked down, been there done that


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## kyler (Feb 24, 2015)

nope, have not locked down the carriage.  The tool is as it came from Little Machine Shop.  Haven't done a thing to it.  I can face just fine and that is what I have been doing to date.  I have been putting the cut off part back in the lathe and facing it.

I'll try a test with the carriage locked.

thanks for the feedback and more to come!


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## juiceclone (Feb 24, 2015)

every normal parting blade/tool I've used can be seen to flex left or right during cutting. That could account for a concave or convex  face, on either the stock or the part cut off.


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## dulltool17 (Feb 24, 2015)

Ahh.... parting is such sweet sorrow.

Sorry, guys...need to go to the humor section of another forum...maybe later.  

Seriously, all good advice- tool relief, position and rigidity are key.

Doug


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## RVJimD (Feb 24, 2015)

On one of my many practice parting sessions I did see a concave.  I would point out it was a curve and NOT simply an angle from start of cut to the center.  If I remember correctly, it was due to a dull or chipped cutting edge and a thin 1/16" blade which allowed the cutter to work better on the un damaged side of the cutter and flex the blade under pressure during the cut.  I'm pretty sure this was on a piece of 1 1/2" aluminum 6061.  Please note I am most certainly no expert...

Jim


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## hermetic (Feb 27, 2015)

You have GOT to lock off the carriage! I hate parting off, and my confidence took a great boost after someone said to me "you are locking the carriage off aren't you?"
Phil


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## Frank Ford (Feb 28, 2015)

My parents always tried to teach me "right" way to do things.  Grandpa, on the other hand, taught me, "there are two ways to do it - hard or easy."

So, taking Grandpa as a model for my work, I cheat as often as possible.   

After setting the tool square to the Z axis, here's how I align the cutting edge of a parting blade, and sharpen it simultaneously:




You may notice I have a rubber sheet lying on the cross slide and lathe ways - it stays there pretty much all the time because I hardly know from day to day what the hell I'm likely to be turning.  It keeps wood dust off things, and catches the small grinding particles for a quick touchup like this one.


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## kwoodhands (Feb 28, 2015)

kyler said:


> This topic has got to be one of the most discussed yet I'm still having problems.  I apologize for bringing it up again.
> 
> The symptom is a concave surface on the cut-off piece.  I mainly turn aluminum and haven't parted steel yet.
> 
> ...


Use a parallel between the chuck and the tool to set it square.Loosen the tool holder just enough so it can move when you crank the saddle towards the chuck.When the parallel shows no light ,tighten the tool holder.Make sure the parallel is against the cutter ,not the holder.Also ,the cutter is ground square. Set the height by placing a 6" steel rule between the cutter and the work.If the top of the rule lays out of plumb towards you,raise the tool holder til the rule is plumb.
Just the opposite if the rule lays away from you.Now lock the saddle.There are a number of shop made saddle locks on the web if your lathe does not have one. Use a lubricant,mineral spirits or kerosene works well with aluminum.WD-40 also works well.Widen your cut every so often so the cutter does not bind.A few thousands is enough. 
This should help a lot. If their is any crown to the work piece,remove it by facing off.Often a nib is left at the center and a facing cut is needed anyhow.Use the saddle lock when facing off too.

mike


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## randyc (Feb 28, 2015)

I think that Mike covered it about as well as it can be covered -
_
Using a lubricant can't possibly be over-emphasized !   _ Anything is better than nothing; I've used charcoal starter for aluminum, LOL, and have heard of people using bacon grease or milk for copper !

My favorite "universal" is black pipe cutting oil (sulphur based).  It's available at local hardware store in pint containers but way more economical to buy from a distributor in one gallon containers.


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## smallfly (Mar 2, 2015)

Frank Ford said:


> My parents always tried to teach me "right" way to do things.  Grandpa, on the other hand, taught me, "there are two ways to do it - hard or easy."
> 
> So, taking Grandpa as a model for my work, I cheat as often as possible.
> 
> ...


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## smallfly (Mar 2, 2015)

kyler said:


> This topic has got to be one of the most discussed yet I'm still having problems.  I apologize for bringing it up again.
> 
> The symptom is a concave surface on the cut-off piece.  I mainly turn aluminum and haven't parted steel yet.
> 
> ...





kyler said:


> This topic has got to be one of the most discussed yet I'm still having problems.  I apologize for bringing it up again.
> 
> The symptom is a concave surface on the cut-off piece.  I mainly turn aluminum and haven't parted steel yet.
> 
> ...


i had this very  same problem just  last week.  examine the parting  tool  very  closely. the  cutting tip  must be the  widest part of the parting blade. look  closely at the part of the blade that enters the cut after the  cutting tip.  i bet there is a  portion that  is  wider than  the cutting  tip  and  is  ''rubbing'' on  material u are  cutting. if  so  i  guarantee  u this  will cause a cut   that  is  exactly  like the  one  u  are  getting. at  least  that  is  what  i  found  to  be  true  in  my  case. good  luck--re  steve  in  montana.


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## nightowl499 (Mar 2, 2015)

might want to check and see the gibs on your compound slide are snug, I had this same problem and found if i held the compound wheel 
it stopped my compund was set at 30 degress and had enuff slop for it to be pulled out to the left a bit which gave me the same concave you are 
discribing,,


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## Raydel (Mar 7, 2015)

So here's what I discovered last night while parting a piece of 2" Delrin rod. As everyone here has experienced, my parting tool was taking a trip towards the chuck creating a concave on the chuck side of the work piece and a convex on the tail stock side. After taking all the precautionary measures as outlined in this thread, I decided to focus my attention on how the parting tool was being held in the QC tool post. I came to realize that because the parting tool is tapered, when clamped in the tool holder, the center line of the blade is no longer perpendicular to the ways,
as one face is clamped tight against the vertical flat of the tool holder (imagine the hands of a clock reading twenty five mins past eleven). So here's what I tried.
Loosen the parting tool and clamp it so that the center line of the tool is at 90* to the ways, then made another cut. Voila! A perfectly straight cut through the material.
I just made another trial cut this morning to make sure it wasn't an isolated event. This time I was able to part off a 1mm thick slice of the same Delrin perfectly straight.
Try it out and make sure I'm not blowing hot air.
Cheers,
Ray


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## gheumann (Mar 7, 2015)

I cut a lot of aluminum. My two cents:

1) "Tap Magic Aluminum" is the best cutting fluid I've ever used for aluminum. Better than WD40. I have some plastic applicator bottles with a fine steel needle - get them at Tap Platics, they're made for dispensing acrylic cement (thin as acetone.) I can easily dispense a drop at a time into the slot when parting. 

2) The most accurate, easiest centering method (and I've tried several) - Chuck a piece of 1/8" rod in the chuck or tailstock. Bring the parting tool up against it with a thin rigid sheet of something in between (I like using an x-acto blade for this). When the blade is vertical, the cutting edge is perfectly centered.


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## benmychree (Mar 9, 2015)

Parting is always a struggle, and speaking for myself, one should seldom use a as parted surface as a finished surface, the finish and accuracy are seldom there, so cut off and reface should be the normal practice.  My best luck with parting with HSS is the Tee type HSS blades, I generally use one 1/8" wide.  My early experiments with insert carbide parting was not so good, but after years of sacrifice and self denial, I am now able to accomplish it, even on large diameters without lubricant; it does not want to be babied, enough feed to make constant curled chips is necessary; too little feed makes the chips jam up in the cut and disaster is not far behind;  the thing is that the chips are deformed narrower than the cut when sufficient feed is applied, and they can freely exit the cut; when insufficient feed is applied, they do not narrow up, and are likely to pile up and bind.  In parting steel, I like to use TapFree as the lubricant with HSS tools, with carbide I use Cimcool soluble coolant in water.  As I said previously, with the carbide parting inserts, cutting can often be done dry.  If the parting tools are not sharp, especially the corners must not be dull, do not expect anything but poor results. 
I appreciated the comments regarding the tapered blade type parting tool needing to be adjusted to fit the holder so that there is clearance on both sides of the tool; if one uses this type of tool, perhaps the tool holder should be altered so that the parting tool can lie against the face of the holder and be centered as he suggests.  I think using the Tee type tool makes this of little importance, as there is more clearance, especially at the extreme bottom of the tool bit.  I have seen parting tools in HSS that have a concave ground in the length of the top of the blade, I assume this acts to narrow the chip so that it can more freely exit the cut, much like the carbide insert tool does.


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## Bill C. (Mar 9, 2015)

randyc said:


> I think that Mike covered it about as well as it can be covered -
> _
> Using a lubricant can't possibly be over-emphasized !   _ Anything is better than nothing; I've used charcoal starter for aluminum, LOL, and have heard of people using bacon grease or milk for copper !
> 
> My favorite "universal" is black pipe cutting oil (sulphur based).  It's available at local hardware store in pint containers but way more economical to buy from a distributor in one gallon containers.




I like to flood the cut when parting.  I used to run a turret lathe.  I hate to say it but use a thick blade.  The thin ones may tend to flex it they are extended to far.  I like to keep lathe tooling as short as possible.


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## Bill C. (Mar 9, 2015)

Another tip I've used in the past.  If the part is hallow or drilled, I use a small brazing rod chucked in a drill chuck in the tailstock to catch the part so I can focus on finishing the parting cut.  Good luck


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## itsme_Bernie (Mar 9, 2015)

dulltool17 said:


> Ahh.... parting is such sweet sorrow.
> 
> Sorry, guys...need to go to the humor section of another forum...maybe later.
> 
> ...



Doug, you made me actually laugh aloud!  That's perfect!! And true!!  Hah hah!  You made me wonder why I never thought of that!! Hah hah!

Bernie 


Sent from my iPad using Tapatalk


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## brino (Apr 21, 2015)

Tony Wells said:


> Once you reach center, if you try to cut the "far side", don't forget to reverse the spindle.



......unless doing so would unscrew your chuck!
In this case stop at centre and use another technique to judge "square".


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## planeflyer21 (Apr 21, 2015)

Tony Wells said:


> Once you reach center, if you try to cut the "far side", don't forget to reverse the spindle.





brino said:


> ......unless doing so would unscrew your chuck!
> In this case stop at centre and use another technique to judge "square".



Is there any reason he could not cut from the backside with the parting tool inverted to upside down, allowing the normal spindle rotation?


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## brino (Apr 21, 2015)

Hey planeflyer21,

The original recommendation (in this thread) for cutting thru centre and into the back side was to help judge if the parting tool was 90 degrees to the lathe centre line. If the tool is off angle and cuts on the diagonal towards the head stock for the first half, then it should continue on that same path, and keep removing material from what would essential be a facing cut on the rear half (with spindle set to reverse). So for this discussion the idea of the upside down and backside parting tool doesn't help.

In general however that'll work fine. Search for "back tool-post" it's a real thing.

Some say it's better for parting because the tool then springs out of the work if it "snags" relieving some of the pressure, instead of being wedged between the work and the carriage/bed ways making matters worse.

-brino


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## RJSakowski (Apr 21, 2015)

smallfly said:


> i had this very  same problem just  last week.  examine the parting  tool  very  closely. the  cutting tip  must be the  widest part of the parting blade. look  closely at the part of the blade that enters the cut after the  cutting tip.  i bet there is a  portion that  is  wider than  the cutting  tip  and  is  ''rubbing'' on  material u are  cutting. if  so  i  guarantee  u this  will cause a cut   that  is  exactly  like the  one  u  are  getting. at  least  that  is  what  i  found  to  be  true  in  my  case. good  luck--re  steve  in  montana.



It sounds like everything has been covered. But to recap, a parting tool has by necessity, flex and will yield to unbalanced forces.  If the tool is ground at a slight angle, either in error or intentionally to cut the last remaining nub from the part, as David S has suggested, there will a force causing the tool to flex.  Similarly, a dull tool, as mentioned can cause these unbalanced forces.  You mentioned that you had carefully aligned the tool to be perpendicular to the axis and that your facing cuts a true so you should be able to rule out those as the cause. It is really amazing how little force is required to deflect a parting tool.  On occasion, I have used one for facing the right hand side of a narrow groove and even with a few thousandths cut on aluminum, there is deflection.

It is also important to make sure the tool is vertically aligned.  Too low and the the tool is scraping rather than cutting; too high and it will catch and be deflected downward and spring back up causing chatter.  Mike, above, gives a very good method for vertical alignment.

I have watched You Tube videos of parting  with envy as it seems that they part with ease with no chatter, perfectly true cuts, and a mirror finish on the parted piece.  It is easy to forget that these are on much larger lathes than I have.  Their parting tool is larger and the whole mechanism is more massive and rigid.

One possibility, if nothing else works, would be to offset the tool slightly in the direction opposing the bias you are seeing so when the tool cuts, it will deflect into a perpendicular parting cut.  I would not lock down the carriage in that case  but allow the tool to follow the cut.


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## BillWood (Apr 22, 2015)

I have an SB 9" clone.

What would be the maximum diameter you could part on such a small lathe ?

Biggest diameter I have ever tried was 2"

I tend to finish off with a hacksaw in a bench vice as I dont want the parted bit jumping off onto the ways


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## brino (Apr 22, 2015)

BillWood said:


> What would be the maximum diameter you could part on such a small lathe ?



Hi BillWood,

Certainly managing the off-cut is one aspect, but for me the bigger issue is how much of that thin parting blade I want extending from the holder. Yes the parting blades are "tall" and therefore have fairly good rigidity in the up/down direction, however, the more it sticks out the longer the lever is and it takes less force at the cutting edge to flex the entire parting blade, holder, tool-post, etc. Any "compressibility" or just plain slop is really magnified and can easily lead to chatter.

Besides tool rigidity, it also depends on material, speed, feed, and sharpness of your parting tool.

All that is my long-winded way to say that your 2 inch diameter (1" parting blade extension)  sounds like a good rule of thumb limit to me.

-brino


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## Bill C. (Apr 22, 2015)

planeflyer21 said:


> Is there any reason he could not cut from the backside with the parting tool inverted to upside down, allowing the normal spindle rotation?



Did it all the time on a turret lathe. They usually have a rear tool post.


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## tomw (Apr 22, 2015)

Frank Ford said:


> My parents always tried to teach me "right" way to do things.  Grandpa, on the other hand, taught me, "there are two ways to do it - hard or easy."
> 
> So, taking Grandpa as a model for my work, I cheat as often as possible.
> 
> ...



Where did you get that grinding wheel? That is very slick.


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## kingmt01 (Apr 30, 2015)

I started with a 7x10 & never did learn how to part on it so I quit trying. It wasn't till I got my 14x40 that I even tried it again. I don't know if I got more skill(probably) or it was the better bigger lathe(I know this helped) but I do know I figured out a few things I didn't know before. The part isn't what needs to be cooled. It is the tool that you have to keep lubed & cool at the cutting edge. A constant stream at least as fast as you can get it there. I sharpen this cutter often. I sharpen it with a 10° edge so it takes the nub off the part dropping first. I cut slow & steady.


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## Frank Ford (May 4, 2015)

tomw said:


> Where did you get that grinding wheel? That is very slick.



I bought it as a tool post grinder wheel, but didn't notice the size was incompatible with my grinder, so it sat in the drawer until I had time to make a little arbor for it.


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## Bill C. (May 10, 2015)

Ski said:


> I am curious how this happens. Insure it is ground right as mentioned. It seems like if you had the cutoff blade turned a bit at an angle the contact with the side maybe causes this as it gets pinched and driven over gradually?  I learned parting by asking questions so you will get it figured out here. there are also some videos out there on you tube on parting.  I simply adjust the tool as short as needed as you did. I adjust it flat to the the faced off end of the piece and centered on the side of the work. I have also used the face of the chuck to adjust the cutoff tool flat as well and that worked too. There are several ways to get the cutoff tool adjusted to the center of the piece. Ski



A good point but parting tools are design to cut straight in and not on the sides.  I have done it with thicker blades since they don't tend to flex.  To check the front face use a six inch scale or straight edge. Place the edge of the scale against the front face of the blade.  There shouldn't no light showing through.


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## pn6 (Jun 9, 2015)

Frank Ford said:


> My parents always tried to teach me "right" way to do things.  Grandpa, on the other hand, taught me, "there are two ways to do it - hard or easy."
> 
> So, taking Grandpa as a model for my work, I cheat as often as possible.
> 
> ...







Great Idea!!!!


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