Selecting cut off tool width

[wmpy]

For those of you that are running parts in your lathes off of a bar, how do you select the width of the cut off tool that you are using? Do you just go with the thinnest tool that has the reach to cut off the part completely without interference? Is there any downside to having a really thin tool doing your cutting off? The upside, obviously, is that there is less material wasted. I've seen cut off tools ranging in widths from 1 mm up to about 8 mm and am just wondering how you choose.

Thanks.

[Cmailco]

Use as narrow an insert as possible, within reason.

Sometimes I will look at part lengths, possible cut-off tool candidates, calculate # of parts per bar and make my choice that way. If going with the 2 mm wide insert means one more part per bar than the 3 mm, I'll typically choose the former. But then, you can't push the smaller insert as fast, so for all out production, you have to look at cost per part-off vs. getting another part from your bar. Usually, getting another part wins, but it's worth a little calculation –at least in an all out production setting.

The thinner insert is going to produce a great deal less cutting force as well. Good for thin-walled parts and small diameters. I try to avoid 'blade' type holders unless I really need to part a large diameter, relying on the reinforced holders for the majority of the work. They're a lot more versatile.

Regards,
Chuck

[RotarySMP]

Great question WMPY. Especially ponient for those of use with little machines lacking rigidity.

Does the 5x overhang limit for tooling also apply for cut off tools?

I have 1.5mm T section cut off blades, but that are not well supported in the Phase II AXA cut off tool holder, so I'll have to make something better.

[wmpy]

Thanks for the reply. I guess I never considered that you couldn't feed a thinner insert as fast as a thicker one. Do you ever have problems with the thinner inserts walking and not producing a flat cut off? We use mostly 3 mm wide tools, and I'm beginning to think that might be a waste to loose all that material. I'll probably try some thinner ones to see how it works out. Do you have a preferred brand that works well? Also, on the integral blade tool holders, do you worry about destroying the whole tool when an insert breaks as opposed to just needing to replace a blade with the others?

[RCaffin]

Originally Posted by wmpy Do you ever have problems with the thinner inserts walking and not producing a flat cut off?

Oh yes! Withthe thinner and more flexible blades you really MUST get the end square, or it will curve - and snap.

on the integral blade tool holders, do you worry about destroying the whole tool when an insert breaks as opposed to just needing to replace a blade with the others?

Yes.

I have used a ground Stanley knife blade as a parting-off tool - on plastic, with great care. Possible, but easily broken.

Cheers

[Shane123]

we have a 3mm sandvik blade parting tool and a 4mm sandvik insertable. with the blade, i can reach farther but is suspect to chatter/walk so feed is slow. with the 4mm insertable, i can feed hard, light turn, radius, but i can only part off 2" round or smaller, unless i have a bored/drilled hole. I use the 4mm whenever possible because time is money.

as for plastic, we have a couple special blades we made with high curl to chip out better, but if you must use insert i suggest the sharpest edge prep (uncoated) insert possible with high feed

[corndog67]

Well, at home, I use whatevers laying there by the lathe. .093, .125, .187. I really like those inserted jobbies, Iscar, Kennametal (I think they were Kennametal), you can run them pretty fast, and they leave a good finish. If I have to, I'll use a high speed one, but only as a last resort, slow and wet.