Parting tool chatter

[SmithDoor]

FYI
On some metals I have use 20° rake angel. I use this with both carbine and high speed steel.
Form cutter 1" wide too.

If read books be for high speed steel they take about high rake angles

Dave

 

[goldstar31]

I'm now being that bit careful as he probably have had a lathe for more than 20 years.

 

[tornitore45]

In the round be lathe, the 'virtual' hinge axis is

.......
Good analysis, however round bed lathes are fairly rare except for watchmaker duty where parting is not much of a problem.

 

[Steamchick]

Thanks all I am just a contributor. But agree that machine stiffness is the limiting factor. Reduce all slide clearances by setting of gib-strips, etc.... Slow rpm - Agree 1/ 2 - 1/3 of normal cutting speed. I prefer a back tool post as then only 2 slides affect the Physics, not 3. But the saddle must not lift at the back at all. I have learned a lot of snippets from your various comments. Thanks!

 

[firebird]

Hi
I know I have joined this a little late but I can offer a few ideas that might help. I have had a lot of the problems mentioned above so decided to solve a lot of the issues I was having. I completely re designed and built a rear parting tool

I wrote an article describing the build which has just been published in the July issue of Engineering in miniature

Cheers

Rich

 

[OrangeAlpine]

I am the OP and am still here, reading and learning. I still have the problem as I have changed nothing. Life is keeping me out of the shop, I'm hoping that changes soon. What really mystifies me is that immediately after making the new holder, parting became a dream with zero problems and nicely coiled chips. After 20-30 cuts, the chatter suddenly appeared. Suddenly appeared using the same setup, cutting the same bar of steel at the same speed and feed, using the same cutting oil. There are some things that challenge the minds ability to cope. This fits in that category.

Looks like checking the rigidity of everything will be the first task, then I'll start exploring changes to the actual cutting operation.

Bill

 

[Dusty3v0]

The big problem : is with lots of helpers but the questioner has solved the problem yet ?
I saw some people ask questions and then disappear.

True but give us something to talk about.

 

[goldstar31]

Engineer's Blue or black permeant ink the cutting edge. Then sharpen it until ALL the marker disappears.
Let ME know what happens, please.

I was using my rear parting tool to the GHThomas design just now. I dropped the speed a pulley and hand fed.

Unless someone has failed to tell you, this is screwcutting as well

 

[justintime]

Primary importance is properly adjusted spindle bearings including preload. Solid tool & holder with “textbook” grind ( On Center - “no pip” ) will help you get the best results. Good luck.

 

[BaronJ]

Hi
I know I have joined this a little late but I can offer a few ideas that might help. I have had a lot of the problems mentioned above so decided to solve a lot of the issues I was having. I completely re designed and built a rear parting tool

I wrote an article describing the build which has just been published in the July issue of Engineering in miniature

Cheers

Rich

Hi Rich,

Certainly looks solid enough !
Just a couple of criticisms if I may. Overhang ! The loading on the tool is outside the top slide width and will cause twist into the direction of the headstock.

Angle ! The tool angle will change as the cutting tip is set for the center line of the work. More so if the height of the tool blade is changed. While I can see that the holder is designed to handle only a specific height. Many will object to the cost of the inserts and holder.

Not having seen your article I can't say more.

 

[BaronJ]

I am the OP and am still here, reading and learning. I still have the problem as I have changed nothing. Life is keeping me out of the shop, I'm hoping that changes soon. What really mystifies me is that immediately after making the new holder, parting became a dream with zero problems and nicely coiled chips. After 20-30 cuts, the chatter suddenly appeared. Suddenly appeared using the same setup, cutting the same bar of steel at the same speed and feed, using the same cutting oil. There are some things that challenge the minds ability to cope. This fits in that category.

Looks like checking the rigidity of everything will be the first task, then I'll start exploring changes to the actual cutting operation.

Bill

Hi Bill,
Make sure that your parting blade is still sharp !

 

[SmithDoor]

Thanks all I am just a contributor. But agree that machine stiffness is the limiting factor. Reduce all slide clearances by setting of gib-strips, etc.... Slow rpm - Agree 1/ 2 - 1/3 of normal cutting speed. I prefer a back tool post as then only 2 slides affect the Physics, not 3. But the saddle must not lift at the back at all. I have learned a lot of snippets from your various comments. Thanks!

When running screw machines I cut off 3/4" hex 12L14 steel at 1,500 RPM. All cutters was HS steel.

Just look at the rake angel on drill bit.
Have you had chatter on drill bit???

Dave

 

[BaronJ]

Hi Guys,

I know that I've posted pictures of my Norman patent rear tool post and parting blade holder before. But since its relevant to this thread...

Since this picture was taken I've modified the holder and rounded the back edge to match the front one.

The mounting position is such that the body of the post is inside the width of the top slide and the blade can be set against the face of the chuck in order to ensure that it is dead square to the work.

That blade is 2 mm thick by 12 mm wide and is 200 mm long. It cost less than £2 from Banggood. In this picture the blade has not been sharpened yet.

 

[SmithDoor]

It looks great

A lot what have I read on this thread is what try back 1960's when first started.

Here list what try back 1960's
1) feed down 0.000,5"
2) use back gears
3) very fast feed in backs do not do this the blade breaks into thousand pisces.
4) lot of oil
5) wide blades
6) thin blades
7) carbide.

One many tries the blade broke with rake and it cut great.

The books I just did not cover the cut off tool angle.

I can remember my pain and see everyone pain here.

Grinding the rake so hard to do the first few times.
But upside is the blades lasted longer since they not breaking off.

Dave

Hi Guys,

I know that I've posted pictures of my Norman patent rear tool post and parting blade holder before. But since its relevant to this thread...

View attachment 117248
Since this picture was taken I've modified the holder and rounded the back edge to match the front one.

View attachment 117249

View attachment 117250
The mounting position is such that the body of the post is inside the width of the top slide and the blade can be set against the face of the chuck in order to ensure that it is dead square to the work.

That blade is 2 mm thick by 12 mm wide and is 200 mm long. It cost less than £2 from Banggood. In this picture the blade has not been sharpened yet.

 

[tornitore45]

12L14 steel

One can cut 12L14 with a butter knife and no lubrication.
One has to try hard to get chatter with free cutting steel.

 

[SmithDoor]

I can remember the setting for that stock.
I have run DOM tub and A36 steel just good but do not remember the settings I used.

Dave

One can cut 12L14 with a butter knife and no lubrication.
One has to try hard to get chatter with free cutting steel.

 

[goldstar31]

I was re-reading 'Thomas' again and noted that in addition to making a parting tool capable of cutting 2" diameter but GHT also had a small parting tool using a piec e of 3/16th round HSS. After grinding the tool was positioned pointing up 6 Degree( avoiding unnecessary loss of blade but each blade in his collection was do wn to 15 thous or 0,015". Then each of his ser=t of homemade tools was 'waisted'

I think that he had a professional tool and cutter grinder but from photos, he also had his own prototype 'Kennet' tool and grinder which was the prototype to the 'Worden one.
My Kennet was damaged and bits lost when howling gales removed- for the second time

It is keeping me occupied as I am not only locked down but 'shielded' in the pandemic- and my new shed

Something to think about, perhaps?

Norman

 

[OrangeAlpine]

Managed to find some time for the shop and I'm back. Tightened up everything, especially around the headstock.

Initially, I saw almost .002" of spindle movement at the front edge of the chuck. After tightening the inner bearing (tapered roller) it is now almost .001". Spindle rotation is stiffer. Stange thing, I tightened the bearing to the point I could not rotate the spindle by hand and still had almost .001" of movement. Don't know where the slop is, but its going to stay.

Discovered and rectified a problem with the chuck mount. I had gotten a little sloppy when mounting the chuck and it might have been the main problem. Checked the crossfeed gibs, tightened ever so little. Cross compound was already plenty tight. Besides, I lock it down unless its in use.

Performed one cutoff operation, went beautifully at about 75 rpm and power feed. This is better steel than I was using when the problem appeared. No changes at all to the cutting tool or holder.

So all the talking about machine rigidity paid off for me.

Thank you, one and all.

Bill

 

[Tim Wescott]

I must be freaking lucky, because I don't have much problem with my Smithy 1220 -- which probably isn't any better than any other cheap lathe.

Something not mentioned here, but which I heard somewhere, is to keep the feed rate up. If you're tentative, at least on my lathe, it will chatter. I take a deep breath, act like I'm jumping into ice-cold water and feed it in. Sometimes it'll start to chatter and I can make it stop by feeding it harder.

I suspect this works the same as reducing the spindle speed, because either way you're increasing the amount the tool is cutting.

I use a cutoff tool with a 1/16" top. I have it ground nice and sharp, then I take a Dremil cutoff wheel and grind a dish into it, so the part that touches the work is a bit "U" shaped (maybe only 5-10 mil deep -- it's just barely perceptible). This seems to help make the cut smoother, by keeping the chip a bit narrower than the walls of the groove.

Disclaimer: I'm not an expert. I'm an electronics circuit/embedded software/high-tech systems designer by day, the last time I earned money doing metalwork I was 18, and I was bending thin-wall square tubing and making crappy welds, in the pursuit of reinforcing fiberglass molds.

 

[jack620]

Something not mentioned here, but which I heard somewhere, is to keep the feed rate up. If you're tentative, at least on my lathe, it will chatter. I take a deep breath, act like I'm jumping into ice-cold water and feed it in. Sometimes it'll start to chatter and I can make it stop by feeding it harder.

Absolutely.

And sharpen your parting blade regularly. I have a USA made high cobalt HSS blade in an Aloris style holder that presents the blade at 7 degrees (I think) from horizontal. So the back-rake is built in. All I have to do is give the front face of the blade a light touch on the grinder and it good to go. It's amazing how a light sharpen can turn a parting-off horror show into an easy job.