Lathe bit choice help

[jgarrett]

Hello,
I am needing to cut a recess on the inside of a piece of 3" steel for a flywheel.
I will be going about 1/4" deep. I have tried a couple of boring bits and all it does is chatter. There will be a uncut hub in the center.
What type of bit is best to accomplish this???
Julian

 

[blighty]

do you have a drawing?

 

[Wizard69]

Any short bit properly sharpened should work. It is a bit hard to understand what you are describing but if this is a flywheel with recessed sides I'm not sure this is a task for a "boring bar".

Rather id suggest that you might want to consider left and right handed tools. These should be ground in the normal way for lathe tools. A sharp Vee pointed cutter that is ground to cut bidirectionally would also do the trick.

In either case you are facing to shoulders in my mind not really boring. There are a number of cutter geometries that would work here but you will need switch or reset tool positions to do both shoulders.

 

[jgarrett]

Yes, it is a typical flywheel with recessed sides having square shoulders on each side.
I tried a 60º threading bit and it did not want to cut either. I guess I need to try different geometry settings for the tools....
It is for an Elmers #17 pumper.

 

[Cogsy]

Look up (google) trepanning tool geometry. Far too difficult for me to try and explain with words (I'll just confuse myself).

 

[RM-MN]

Chatter happens when the bit cannot make a clean cut, bends enough to relieve the stress, then springs back into the cut. You need one or more of the following.
1. Less depth of cut
2. Stouter tool
3. Less distance from the toolpost
4. Slower feed
5. Sharper tool
6. Different tool geometry
I'd start with sharper tool and look hard at the shape of the tool. If using a boring bar, the bigger the bar that will still fit will be stiffer.

 

[goldstar31]

Simply Google a trepanning tool. Only in the past couple of weeks, I was discussing with JCSteam the same principle.

Really, it's only a boring bar that is curved to suit the cut without binding on the kerf being cut.

Hmmm. The Egyptians trepanned skulls and were followed by the Brits who trepanned their way into the German magnetic mines.

My daughter has sort of inherited her mother's trepanned skull from the time that she was an active Fellow of the Royal College of Surgeons. She used to keep it in a Jacobs Cream Cracker Box.

N

 

[jgarrett]

Thanks for the replies!!
I will give the trepanning tool a try..
Julian

 

[rlukens]

Trepanning requires specific tool geometry (relief on all sides)) of the tool. I assume you're wanting to leave a hub in the wheel. If not, start with a bored hole and work your way out with a stout boring bar. If your leaving a hub in the center, start with a shallow cut on a facing tool and and slowly increase depth of cut as you face in (or out). Do this repeatedly until you get to the desired depth of cut. Then, use a right and left hand tool to square up the corners.

 

[goldstar31]

The savants have always used a tool which was round. With care in grinding, one such tool will cope with quite a range of diameters. If one is really 'with it', it can do a spare task like parting off.

If one has a shaper, the same tool can perform another set of tasks. Again, if one hasn't, such a tool works quite well , sweep facing using a faceplate or a catch plate, provided one hasn't been bothered to to drill two holes in a bit of square bar to take-- TWO trepanning tools.

Of course, one can 'doing Variations on a Theme' and do Vee slots in the absence of a proper drill.

It's why the lathe is called the King of Tools-- always assuming that one can grind appropriate tools for it.

Where I came in?

Norm

 

[jgarrett]

OK..finally got it turned. Had to use a combination of LH, RH and pointed bits..
My major problem was chatter because my chuck is 6" and will not hold a piece of 3" stock, so having to use my larger 4 jaw with jaws turned around. That makes them stick out so far they would hit the X slide if I got close, so I had to have my bits sticking out way more than I usually do. But anyway, its turned and headed for the rotary table..
Thanks for all of the advice and help,,
Julian

PS: I did try the trepanning tool but could not make it work sticking out so far,,will try it on a smaller one next time...

 

[michael-au]

Found this video

https://youtu.be/6PcEBaset1I

Shows how to make the tool

 

[jgarrett]

That is the one I used to make the bit!!!
Thanks,,

 

[Charles Lamont]

My major problem was chatter because my chuck is 6" and will not hold a piece of 3" stock

If we are talking about a 3-jaw self-centring chuck, you should have a set of internal jaws which would easily hold a 3"workpiece.

 

[tornitore45]

A tool that is above center may chatter especially when parting.
As was mentioned before a "Finisher" tool like a treading tool but a 30* V with a rounded nose is very versatile. it works RH and LH. The shoulders on a recesses flywheel do not need to be square and a small fillet at the bottom is better than a sharp corner.

 

[Journeyman]

Have a look *** HERE *** for trepanning a flywheel, also shows use of three jaw for holding same.
John

 

[jgarrett]

I seem to have the tool working on a piece of scrap....
That is an interesting site...
Cheers,
Julian