New to me - Colchester Triumph

[Kram]

Interesting, what DoC would you use?

You being serious, 0.005mm/rev?

Its a rough guess based on a 0.2mm division of the wheel per second (or, a kram-second, may have a vastly different length to a real second ) and 500-2200 rpm. Depends on material some prefer a fast feed. By hand, so far from being consistent but I can say it is painfully slow on any longer parts.

 

[Lewis_RX8]

So you do know relationship between tool radius and DOC and maintaining cutting forces axial to workpiece?

Umm , Maybe not quite these are just what I find works for me takes trial and error. I think very generally the bigger the radius the higher DOC cut you want trying to not do a DOC under the radius dia but completely lost on maintaining cutting forces axial to workpiece lol. Please feel free to inform me

It will if you swing the compound the wrong way, advancing the tool away from the feed direction, as I did it the other week cutting an internal thread. First couple of passes went fine, but then instead of cutting properly, the tool would luch forward in the backlash, wait for the leadscrew to catch up with the nut and then chew a really nasty thread into the rest of the part, eventually getting to the point that it cut the crest off the partially formed thread and I gave up. Took me a couple of days to realise what I'd done wrong.

I got a nice internal bar threading and a few inserts for it but thought I would get the external technique down first then give that a shot seems a little more complicated but good to learn.

Just looked at the POS, oops I mean Triumph.
Well seems my feeds are similar to what I use on the CNC. 0.12mm/rev for finish and 0.3mm/rev for max roughing.

Looks about the same as what I was feeding converted to thou 0.12 is 4.7 TPR so almost bang on.

Not having as nice results on facing cuts but I think that would be the insert as the shape doesn't seem like it would facing cut well and not really designed for it.

 

[Hood]

You will never get the perfect facing cut on a manual lathe as there is no real way to keep the surface speed constant. Having said that you can get nice enough cuts, just takes a bit of practice I suppose.
CNMG is a good choice for a facing tool but personally I tend to stick to DNMG inserts as they are so versatile and can take a decent facing cut as long as you are not too greedy and stick to nose rad or less per pass. For external turning CNMG are ok but you can get swarf trapped between the insert and the work due to the small clearance, again DNMG is better in that respect, well in my opinion anyway.

 

[Maker]

I got a nice internal bar threading and a few inserts for it but thought I would get the external technique down first then give that a shot seems a little more complicated but good to learn.

The hardest part is grinding the tool, if you've got insert tools its not really any harder, just a pain to see what you're doing. Luckily 9 times out of 10 you'll have the tap for an internal thread so it's usually external ones that need single pointing.

 

[Kram]

It will do facing just turn it for the same approach angle as you have external.

One hand on the vfd speed nob, faster as you get smaller, or in my case just leave it on max, as you can never really be too fast just not fast enough on the small dia. Slow to start may be more consistent over the whole face if thats what your after.

I often have better results facing inside to outside, you get a wider contact on the insert with a thinner chip. Depends on material can cause chatter.

 

[Lewis_RX8]

You will never get the perfect facing cut on a manual lathe as there is no real way to keep the surface speed constant. Having said that you can get nice enough cuts, just takes a bit of practice I suppose.
CNMG is a good choice for a facing tool but personally I tend to stick to DNMG inserts as they are so versatile and can take a decent facing cut as long as you are not too greedy and stick to nose rad or less per pass. For external turning CNMG are ok but you can get swarf trapped between the insert and the work due to the small clearance, again DNMG is better in that respect, well in my opinion anyway.

Yea I heard CNC speeds up as they get to center to keep the feed rate right don't know if it's so easy to do with your wrist lol, I have the nice quality DNMG holder so will have to try some 04 radius inserts in them see if finish is similar.

It will do facing just turn it for the same approach angle as you have external.

One hand on the vfd speed nob, faster as you get smaller, or in my case just leave it on max, as you can never really be too fast just not fast enough on the small dia. Slow to start may be more consistent over the whole face if thats what your after.

I often have better results facing inside to outside, you get a wider contact on the insert with a thinner chip. Depends on material can cause chatter.

Good idea , the triangle shape would normally have a straight flat agasint the face so normally not work but turn the toolpost would get the point to take the cut again.

The hardest part is grinding the tool, if you've got insert tools its not really any harder, just a pain to see what you're doing. Luckily 9 times out of 10 you'll have the tap for an internal thread so it's usually external ones that need single pointing.

Yea would only ever plan on internal thread cutting on bigger stuff where I don't have the taps smaller.common things would just tap.

 

[daedalusminos]

Please feel free to inform me

From Sandvik...​

Depth of cut and cutting forces​

The relationship between nose radius and depth of cut affects vibration tendencies. The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.

It is preferable to have more axial forces than radial. High radial forces can have a negative effect on the cutting action which can lead to vibration and bad surface finish.

As a general rule of thumb, choose a nose radius that is equal or smaller than the depth of cut.

 

[Hood]

Yea I heard CNC speeds up as they get to center to keep the feed rate right don't know if it's so easy to do with your wrist lol, I have the nice quality DNMG holder so will have to try some 04 radius inserts in them see if finish is similar.
...

The spindle turns faster as the diameter decreases to keep the surface speed of the tool on the material constant.
The feedrate will stay constant per rev to keep the chipload constant but the axis movement will actually speed up because the spindle speed is increasing.
You also have to be aware of the max diameter and weight and how securely it is held. Obviously you do not want to spin a 500mm dia part at high speeds so with CNC you can limit the max speed when using CSS, there have been lots of accidents where an operator has not set a max rpm for CSS or has programmed it too fast.

 

[Hood]

With my POS I can sort of do a manual CSS as I have a servo fitted to the spindle so can vary the spindle speed via a pot, just like you would do with a VFD except I can go from fractions of a rpm right up to max rpm via the pot. It doesn't usually help much however as you are just guessing how fast you increase the rpms. Most times I just leave it be but on occasions when it is a fairly large diameter I am facing I will increase a bit as it approaches the centre.

 

[Maker]

From Sandvik...​

Depth of cut and cutting forces​

The relationship between nose radius and depth of cut affects vibration tendencies. The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.

It is preferable to have more axial forces than radial. High radial forces can have a negative effect on the cutting action which can lead to vibration and bad surface finish.

As a general rule of thumb, choose a nose radius that is equal or smaller than the depth of cut.

You can prove that works by machining a really slender or thin walled part in plastic. If you creep up on the dimension, it'll deflect and you'll get somewhere between a taper and a mess, but a deep cut is no problem.

Skip to 9:55 to see what I mean.

I will admit, even knowing it works I'm always apprehensive to do it when I've already put a load of work into a part.

 

[Sean64]

Umm , Maybe not quite these are just what I find works for me takes trial and error. I think very generally the bigger the radius the higher DOC cut you want trying to not do a DOC under the radius dia but completely lost on maintaining cutting forces axial to workpiece lol. Please feel free to inform me



I got a nice internal bar threading and a few inserts for it but thought I would get the external technique down first then give that a shot seems a little more complicated but good to learn.



Looks about the same as what I was feeding converted to thou 0.12 is 4.7 TPR so almost bang on.

Not having as nice results on facing cuts but I think that would be the insert as the shape doesn't seem like it would facing cut well and not really designed for it.

Strange how nobody has mentioned HSS tooling ,less cutting pressure nicer finish grind it to your own style . I use it all the time ,anytime finesse is needed I reach for HSS ,for roughing heavy cuts I used carbide tooling .

Sean

 

[Lewis_RX8]

From Sandvik...​

Depth of cut and cutting forces​

The relationship between nose radius and depth of cut affects vibration tendencies. The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.

It is preferable to have more axial forces than radial. High radial forces can have a negative effect on the cutting action which can lead to vibration and bad surface finish.

As a general rule of thumb, choose a nose radius that is equal or smaller than the depth of cut.

That diagram makes alot more sense thanks , Good rule of thumb and easy to remember about the radius and DOC .

The spindle turns faster as the diameter decreases to keep the surface speed of the tool on the material constant.
The feedrate will stay constant per rev to keep the chipload constant but the axis movement will actually speed up because the spindle speed is increasing.
You also have to be aware of the max diameter and weight and how securely it is held. Obviously you do not want to spin a 500mm dia part at high speeds so with CNC you can limit the max speed when using CSS, there have been lots of accidents where an operator has not set a max rpm for CSS or has programmed it too fast.

Ah I see I thought they increased the feed per min to change cutting speed but as you say its specced in mm/min so increasing RPM would increase mm/min ,

You can prove that works by machining a really slender or thin walled part in plastic. If you creep up on the dimension, it'll deflect and you'll get somewhere between a taper and a mess, but a deep cut is no problem.

Skip to 9:55 to see what I mean.

I will admit, even knowing it works I'm always apprehensive to do it when I've already put a load of work into a part.

Wow that is certainly proof in the pudding easy to flex by hand but stiff in the lathe with that DOC.

Strange how nobody has mentioned HSS tooling ,less cutting pressure nicer finish grind it to your own style . I use it all the time ,anytime finesse is needed I reach for HSS ,for roughing heavy cuts I used carbide tooling .

Sean

I do have some HHS that came with the lathe but little idea on grinding although plenty time to learn a a nice selecta grinder , I like the easy of use of carbide aswell as the mirror finish can almost impossible to get from HHS i understand however it can create really smooth finishes just not mirror which I want because erm it looks nice lol

 

[Hood]

Ah I see I thought they increased the feed per min to change cutting speed but as you say its specced in mm/min so increasing RPM would increase mm/min ,
...

Feedrate on a lathe is mm/rev (or IPR if you are old or American ) That way no matter the spindle speed the chipload remains constant. As you say with CSS the mm/min will vary with rpm but mm/rev is constant.

 

[Lewis_RX8]

Feedrate on a lathe is mm/rev (or IPR if you are old or American ) That way no matter the spindle speed the chipload remains constant. As you say with CSS the mm/min will vary with rpm but mm/rev is constant.

I'm not old or American but work with that now its all my lathe plate says

 

[Hood]

Strange how nobody has mentioned HSS tooling ,less cutting pressure nicer finish grind it to your own style . I use it all the time ,anytime finesse is needed I reach for HSS ,for roughing heavy cuts I used carbide tooling .

Sean

HSS has its place, usually in the drawer

It is useful for making form tools or specials but that is about the only time I use it and that is not very often.
For someone messing about in the workshop where time is not important then it can be useful but you will spend a lot of time at the grinder.

 

[Hood]

I'm not old or American but work with that now its all my lathe plate says

25.4, that is all I will say

 

[Sean64]

HSS has its place, usually in the drawer

It is useful for making form tools or specials but that is about the only time I use it and that is not very often.
For someone messing about in the workshop where time is not important then it can be useful but you will spend a lot of time at the grinder.

Not if you use the correct HSS and grind it properly, especially useful if turning small delicate parts . Anyways I'm never in a hurry

Sean

 

[Hood]

Learning how to use carbide is the biggest problem for people, once you get a feel for it it works like magic.

 

[Sean64]

That diagram makes alot more sense thanks , Good rule of thumb and easy to remember about the radius and DOC .



Ah I see I thought they increased the feed per min to change cutting speed but as you say its specced in mm/min so increasing RPM would increase mm/min ,



Wow that is certainly proof in the pudding easy to flex by hand but stiff in the lathe with that DOC.



I do have some HHS that came with the lathe but little idea on grinding although plenty time to learn a a nice selecta grinder , I like the easy of use of carbide aswell as the mirror finish can almost impossible to get from HHS i understand however it can create really smooth finishes just not mirror which I want because erm it looks nice lol

Learning how to use carbide is the biggest problem for people, once you get a feel for it it works like magic.

I know how to use carbide , hhs is a forgotten skill , Joe pieczynski on YouTube, who is a fantastic machinist is a great believer of HSS . Of course he uses carbide also . Me being a hobbyist, I do it for my chill time and love using HSS tools .

 

[Hood]

I used HSS for too many years, I have no wish to go back to it unless I need a form tool or a special.
Granted most of my work is stainless and F51 and my time is better spent turning than grinding and my customers agree