Using A Rotabroach Cutter In A Lathe

Assuming your lathe can go real slow, no reason it won't work.

I'd be sure and use LOTS of coolant or cutting oil, go real slow 50 or 100 RPM and keep the pressure up. If you work harden that 316, you'll be sorry. One advantage of using a standard drill bit would be that's its not as big a deal to resharpen and try again.

Karl

I have never used a rotabroach in a lathe, but I think you need to understand some things about Morse tapers.

The Morse taper in your tailstock is held in place by friction.

As your cutting tool approaches the tapers diameter, the tools friction eventually overcomes the friction of the taper and spins it. This will screw up your tailstock socket, the taper on the arbor and probably your cutting tool.

Drill presses solve this problem by using the tang on the end of the taper to prevent rotation. Lathes (because of the screw that feeds the tailstock barrel) don't have this feature.

Were you cutting something else, I would say you might get by using light cutting pressure. Stainless, however, requires a "Low speed, High feed" approach to cutting. The object being to make each tooth cut deep enough to get under the work hardened surface left by the preceding tooth. This strategy requires you to push the cutting tool into the stainless as hard as you can and not let up on the pressure until you are through.

Bottom line, if you have enough horse power, it will work but you need to devise an additional strategy to keep the arbor from rotating. Milling a couple of flats on the arbor, clamping a wrench on the flats and letting the wrench handle ride on the compound is one approach.

Paul K. Dickman

I have done this a lot- works great, and its lots quicker than using a twist drill. Like he said- slow speed, lots of coolant.

Thanks everyone.

The lowest speed of the lathe is 100rpms and it is rated at .47hp. I'd just have to decide on what coolant to use.

As far as the wrench handle riding on the compound. I assume that you are referring to the compound slide. The Rotabroach cutter has a two inch max. hole depth, so if I want to use it for thicker material that may pose a problem.

What about making a special tool holder? Though a Morse Taper #2 tool holder is on my shopping list, perhaps a tool holder can be made

*specifically* for the cutter itself. That way I can use the power feed to get the consistency I'd need for drilling Stainless steel.

And I wouldn't have to buy one of those expensive and hard to find MT2 Rotabroach Arbors. It appears that the only place to get them is abroad:

But if anyone know of another place I'd appreciate a pointer.

Thanks a lot.

Darren Harris Staten Island, New York.

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Why can't you just put them in a boring bar toolholder? You don't have to bear on the flats. Or get an Aloris toolholder that takes 5C collets and hold them with a collet. I don't like the tailstock idea, I like the toolholder idea.

GWE

I can't see you saving time by using your lathe, the motor is a toy by comparison with the drill. You'd be better off setting the drill up on a steel plate & clamping your ss plates to it. If your plates are of uniform length & width, simple stops would speed it up even further.

Tom

I would use the mag drill as well- the lathe I use the rotobraoch in is

7hp. .47 hp changes things a bit.

We drill holes with the mag drill in non magnetic stuff all the time- we have a piece of 1/2" x 4"mild steel flat bar, about 3 feet long, and bolt or clamp it to a workbench, with spacers under it so it is above the material we are drilling. The mag drill sticks to the flat bar, but drills what ever we put under the flat bar- stainless, aluminum, you name it.

...

I agree with Tom's comments.

I think you'll need to do finish boring, anyway, after drilling through with the lathe. If you're making very many parts, it will be faster having a rough drilling setup on one machine (the Rotabroach) and boring on the other (the 7x14).

Re the 7x14's 100 rpm min speed, for 30 rpm mods see

don't know if that will apply to your lathe - the page says newer machines don't need the mod - but I'd look inside the speed control anyway and try some adjustments.

The headstock probably is MT3, vs the MT2 tailstock taper. For heavy drilling on the 7x14, consider using a rotating, MT3-taper drill bit, with the work fastened to the compound.

-jiw

The maximum diameter hole I can drill using my Rotabroach is 1-3/8", but I'll need to make holes that are about 2-3/4" in diameter. and accurately centered holes at that.

Even after I build a set-up for the Rotabroach(which would include a positioning jig for the 4-1/2" square plates I'll be drilling), I can't see how it would be faster than on the lathe. And if I have to do finish boring anyway, then that makes the lathe even more convenient, becausse the work would be already in place.

So I guess the big issue is if a 1/2hp motor strong enough to deal with

1/16" thick stainless steel.

Thanks.

Darren Harris Staten Island, New York.

> I don't know if that will apply to your lathe - the page says

Hang on a minute, that doesn't relate to your original post above, you've gone and changed all parameters of what you want to achieve.

Tom

> > I don't know if that will apply to your lathe - the page says

How do you figure?

I mentioned 1/16" thick stainless steel which is actually part of the same project. I still need to drill the 1/4" thick S.S. But the 1/16" thick pieces are 4-1/2" square, whereas the 1/4" thick pieces are 4" square.

I think a 5" chuck should hold both sizes.

Thanks.

Darren Harris Staten Island, New York.

> > > I don't know if that will apply to your lathe - the page says

Where?