parting with a fixed steady disaster

[prepman]

As apprentices we were banned from parting off. Too much shrapnel flying around. Alway used to be a hit and miss + sixpence/halfcrown situation.
But now using the fixed rear toolpost I don't even consider failure any more. Power feed every time. Just changed out the pricey Iscar tip for no real reason, rather than necessity.

 

[fizzy]

As apprentices we were banned from parting off. Too much shrapnel flying around. Alway used to be a hit and miss + sixpence/halfcrown situation.
But now using the fixed rear toolpost I don't even consider failure any more. Power feed every time. Just changed out the pricey Iscar tip for no real reason, rather than necessity.

I have always heard a rear toolpost is the best option. Do you have a picture of your setup?

 

[prepman]

I have always heard a rear toolpost is the best option. Do you have a picture of your setup?

It isn't just that it's a rear toolpost, but the fact that there is no overhang (tool supported directly underneath) and the only play is in the saddle gib strip, which is locked.
By contrast using QCTP with overhanging tool, has play in top-slide, cross-slide and saddle gibs to contend with. Then if the tool leans over under pressure it'll dig into the side wall and boom. IMHO it will always be a possibilty using a tool mounted on the topslide. With normal surface tools it isn't an issue as they're not trapped in a gulley with no where to go.
One other advantage is that swarf falls away. Took me a long and expensive time to realise the dynamics of what was going on.
Don't even think that the super duper Iscar tool has much to do with it. Even 4" bar isn't an issue either as the tool is aligned perfectly just once.

Even better... my YouTube vid...apologies for music

 

[fizzy]

It isn't just that it's a rear toolpost, but the fact that there is no overhang (tool supported directly underneath) and the only play is in the saddle gib strip, which is locked.
By contrast using QCTP with overhanging tool, has play in top-slide, cross-slide and saddle gibs to contend with. Then if the tool leans over under pressure it'll dig into the side wall and boom. IMHO it will always be a possibilty using a tool mounted on the topslide. With normal surface tools it isn't an issue as they're not trapped in a gulley with no where to go.
One other advantage is that swarf falls away. Took me a long and expensive time to realise the dynamics of what was going on.
Don't even think that the super duper Iscar tool has much to do with it. Even 4" bar isn't an issue either as the tool is aligned perfectly just once.

Even better... my YouTube vid...apologies for music

The music I can live with - at least it wasn't vertical video
What lathe is that and is the tool set bang on centre height?

 

[Kram]

How did you mill the slot to be on centre hieght? Did you do it in lathe or carefull measuring and mill?

but the fact that there is no overhang (tool supported directly underneath) and the only play is in the saddle gib strip, which is locked.
By contrast using QCTP with overhanging tool, has play in top-slide, cross-slide and saddle gibs to contend with.

I dont use a top slide unless Im doing a taper. Saddle locked and cross play is going to be the same for either

Overhang on a qctp is easily solved with a jack underneath tool holder. My parting holder sits lower than the others so it doesnt interfere with anything else

 

[prepman]

Overhang on a qctp is easily solved with a jack underneath tool holder. My parting holder sits lower than the others so it doesnt interfere with anything e

Yes a good workround and you remove your topslide?

 

[prepman]

The music I can live with - at least it wasn't vertical video
What lathe is that and is the tool set bang on centre height?

Colchester Student and post shimmed to centre.
The lathe topslide base had been modified, not having the original fitting. A foot plate had been made to clamp a different (replacement?) topslide, which raised the original turret. I had to remove this to get a QCTP installed as it was too high. Ground out the nut wells in the sides of topslide and then tee nuts to original clamp. Bit rough but all works,



.

 

[E T]

Some serious parting here with a 12mm? button insert, steady rest and tailstock.
We're just a bunch of sissies.

 

[Erie Fred]

Some serious parting here with a 12mm? button insert, steady rest and tailstock.
We're just a bunch of sissies.

Pretty rigid set-up, and you can see he is moving the tool side-to-side as the groove is wider than the insert.
You can hear it's right on the verge of chattering.

 

[Seadog]

Some serious parting here with a 12mm? button insert, steady rest and tailstock.
We're just a bunch of sissies.

Have you seen the size of his lathe?

 

[E T]

Have you seen the size of his lathe?

I was always told "Size doesn't matter".
You're telling me that's not true?

 

[Seadog]

I was always told "Size doesn't matter".
You're telling me that's not true?

I've always had that in mind

 

[Erie Fred]

I was always told "Size doesn't matter".
You're telling me that's not true?

I learned on an American Pacemaker 18" chuck 5' centers and probably 20 hp.
All negative rake carbide (after we learned to grind & use HSS).
I graduated to a Bullard VTL 56" dynatrol with center turret & side head, 50 hp behind it.

 

[mcostello]

Ask Her if size matters.

 

[slim_boy_fat]

Have you seen the size of his lathe?

What kind of question's that to ask?

 

[Erie Fred]

I learned on an American Pacemaker 18" chuck 5' centers and probably 20 hp.
All negative rake carbide (after we learned to grind & use HSS).
I graduated to a Bullard VTL 56" dynatrol with center turret & side head, 50 hp behind it.

Let me add to this....At home for many years I had a Logan 9" bench lathe, and parting off was more challenging with that lathe.

 

[prepman]

Pretty rigid set-up, and you can see he is moving the tool side-to-side as the groove is wider than the insert.
You can hear it's right on the verge of chattering.

It's certainly an impressive slab of steel he's working on, but he's not technically parting off and the only plunge cut is 30mm? Did think I was going to see a >300mm part-off. Still impressive, but not dramatically so.

 

[prepman]

Made a holder for the button insert and tried to work out it's best use and plunge cutting isn't one of them. Internal radiusing for stress relief is one.
So hopefully my next space launch shouldn't suffer from metal fatigue fractures......again?

 

[minimutly]

How did you mill the slot to be on centre hieght? Did you do it in lathe or carefull measuring and mill?



I dont use a top slide unless Im doing a taper. Saddle locked and cross play is going to be the same for either

Overhang on a qctp is easily solved with a jack underneath tool holder. My parting holder sits lower than the others so it doesnt interfere with anything else
View attachment 439847

View attachment 439848

Difficult to see what you have there @Kram - have you removed the topslide and made a solid qctp holder?
Of course you're right, how often does one use the topslide???
More details pics please? A qctp is on my wanted list, but one for the Triumph will cost me more than I paid for the lathe, and I would struggle to justify it.

 

[prepman]

I learned on an American Pacemaker 18" chuck 5' centers and probably 20 hp.
All negative rake carbide (after we learned to grind & use HSS).
I graduated to a Bullard VTL 56" dynatrol with center turret & side head, 50 hp behind it.

Pacemakers ....I didn't know they also made lathes?