Parting For Idiots

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!
 
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.
 
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
 
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
 
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
 
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:

grindcutofftool02.jpg

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.
 
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?
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
 
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.
 
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:

grindcutofftool02.jpg

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.
 
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?
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?
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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