Back once again with the idiot questions…

[Nick WelburnParticipant @nickwelburn]

Well I’ve had a play. The Chuck is made of something really hard. I’ve made some impact but not much. Are my HSS bits the right stuff for this job? I’ve been making some impact but not much !

[SillyOldDufferModerator @sillyoldduffer]

Posted by Nick Welburn on 06/02/2021 17:47:09:

Well I’ve had a play. The Chuck is made of something really hard…

Probably cast-iron. It develops a hard skin when the hot casting is quickly chilled. Done on purpose and by accident. The skin is hard enough to give HSS a beating, though it will work. Better to grind it or use carbide to get through the skin. Once penetrated, cast-iron machines well with HSS, though a second problem emerges. It's filthy – black smudges absolutely everywhere, and worth containing the mess with paper shields or whatever.

A cast-iron chuck should machine OK once past the skin, but other cast-iron can be very nasty – full of slag, inclusions, blow-holes and chilled hard throughout. Foundries making cheap items like sash-weights didn't care if they were full of rubbish and might hose them with cold water to get them out of the way quickly too. Such are a nightmare to turn on a lathe. Even expensive castings go wrong sometimes, and a hard outer skin isn't unusual.

Dave

[old martParticipant @oldmart]

Its a shame that it is proving difficult to drill, I have not had much trouble with top quality new drills. You will also have to be thinking of whether the cast iron can be tapped, if there is a hard spot.

I once turned a solid piece of cast iron to make a chuck backplate. Part of the od turned like an interrupted cut, and I was glad to have a choice of carbide insert grades to deal with it, HSS would have had no chance.

[Nick WelburnParticipant @nickwelburn]

Hi there. No need to drill it, it has suitable front mount holes. It’s just getting the Chuck to register nicely. It sits on but doesn’t go home yet. I am quite astonished at how hard It is to machine. It’s just doesn’t seem to respond to the cutter. It’s taken maybe two hours turning to increase the diameter by about a 1.5mm

[DiogenesIIParticipant @diogenesii]

What speed and shape of tool are you using?

[Nick WelburnParticipant @nickwelburn]

I’m using and HSS cutter. At about 800rpm.
this shape

**LINK**

and we have these to choose from:

**LINK**

any advice would be muchly appreciated!

[peak4Participant @peak4]

Posted by Nick Welburn on 07/02/2021 16:38:53:

I’m using and HSS cutter. At about 800rpm.
…….

I'm thinking your speed is way high here for a HSS tool
There's lots of speed and feed calculators on line, to save you having to do the maths for the time being.
Try This One

I think you're taking the edge off the tool by spinning the workpiece too fast.
I'd enter 100Feet/Minute.
Measure the chuck yourself, but if it's a 4", then lets say the register is about 3"; that equates to about 125rpm

Bill

Edited By peak4 on 07/02/2021 17:14:02

[DiogenesIIParticipant @diogenesii]

I think that's a carbide insert you are using in the link..

Could it be that something is rubbing?.. ..Just check that the 'heel' of the tool holder isn't rubbing on the uncut-portion of the work.. if it is, you may be able to raise the tool slightly to get lift the part that's rubbing clear, or it try taking 'wider' (wider towards you) cuts in towards the chuck so that the bottom of the holder is always just clearing the freshly cut face.

Or you could even relieve the offending portion of the t-h with a gentle and carefully-targeted grinding..

..and check that the insert isn't chipped…

I'd be slowing down a bit, too, perhaps 400 to maybe 500 or so if I was uncertain of the material.. If it is just plain hardness that is the trouble, then you might find even lower is better and some kind of oil will help.

Apologies to Bill – if you are using HSS, then use his suggested speeds..

 

Edited By DiogenesII on 07/02/2021 17:51:01

[peak4Participant @peak4]

Posted by DiogenesII on 07/02/2021 17:47:07:

I think that's a carbide insert you are using in the link..

……………..

Apologies to Bill – if you are using HSS, then use his suggested speeds..

Edited By DiogenesII on 07/02/2021 17:51:01

You're quite correct, it is. I couldn't get the first link to open fully earlier for some reason, so I only saw the recess, and not the tool and toolpost in the bottom half of the photo.
There's a good chance that the bottom edge of the toolholder will be rubbing there as you say; at first glance, it's a straight turning/facing tool, rather than a boring one .

Bill

[Nick WelburnParticipant @nickwelburn]

Ok 200rpm it was. Feels weird the lathe almost stops on contact then winds back up and surely enough two clean cuts and we are almost there. One last pass and we are golden!

thanks again for all the advice. I’ve learned so much on this forum. The satisfaction of sorting this when it first registered was great.

[Howard LewisParticipant @howardlewis46836]

It sounds as if you might be feeding too hard.

basic principles.

The tool needs to be sharp

The tool needs to set on centre height (Too high and it will rub not cut )

Cutting speed for a HSS tool should be about 100 feet per minute.

Feed rate should be no more than 0.005" / rev. You need to learn how to turn handwheels steadily. About the first thing that my Turning instructor insisted we do.

So cutting a register about 3/8" deep recess, running at 125 rpm should take 40 seconds, MINIMUM.

You should not be trying to take it all out in one pass. Your aim is to produce a register to a fine limit.

Boring tools are notorious for Springing, so that taking a second cut, without altering anything will result in more metal being removed. For what you are aiming to do, I would suggest a depth of cut of 0.005", stopping the machine, winding back the saddle and measuring., and taking at least one spring cut until required size is reached. I have known as many as six spring cuts being taken before the tool stops removing metal!

HTH

Howard

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