aluminum boring question

[metlcutr55]

im working with 6061 alum tube 3 od 1.5 id 3 lg. the blanks get rough turned then returned later for a skin finish cut. i can easily rough the od's but having a tough time rough boring, not breaking a chip and loading up inside. the lathe is an 8 hp cnc nardini, top rpms available for this operation are 750. any ideas? i have taken to moving the parts over to the cnc mill and interpolating the rough ids, but its twice as slow as the od rough operation.

[MBG]

How much are you taking? What I.P.M. are you running? What type of tool are you using? This guy I used to work for had a pretty sweet boring tool. It looked like a drill but had an insert in it. I think it was made my ISCAR.

[HuFlungDung]

It can be tough to not scuff up the bore. About all I've figured out is to rough within about .005" of final ID, then take the finish cut. An air blast can be useful to blow the chips out before they go around the bar.

It might be worth a shot to bore coming out of the hole. This will help because the chip nest will just be starting as the bar pulls away from the bottom of the hole.

[Tinmuk]

Your boring cycle should have a chip break step in it. If not just program a slight pause. You couls also use a chip break insert or modify yours. How much total material are you removing?

If your starting bore is 1.500, I would use a 3/4 shank tool and go .100 DOC up until you are .020 to .040 away from finish diameter.

With an 8 hp machine you can take a big bite which helps break up the chip. Don't forget to shoot some coolant in there too!

I'm curious tho, why can't you run over 750 rpm?

[metlcutr55]

thanks guys. ive played with all kinds of doc, feeds, speeds. darn stuff just wants to string and jam chips between the bar and bore. this is a roughing only op they are put back on for finish, if i could get big chips id be happy. i have no thru tool coolant so im sure that hurts. bore starts out 1.5" ends up 2.35" dia almost all the way thru. only trace of sucess ive had is at 500 rpm and .1 doc about .015 feed, stuff breaks up a lil but still jams in there. i asked the iscar man about that tool, he said i dont go near fast enuf for it. im stuck on 750 rpms cause im rural single phase and run of a 20hp rotary phase converter, i actually need more power into the shop but the elec co is not being helpful there. the 750 rpms comes from a start at 375 then an electric shift into hi range, i might be able to get up to 1200 in the next gear but you can just hear the machine reaching for juice. 10" heavy chuck prolly hurts too but im a garage 1 man show, thats what i have. i may get a flat face spade type drill and grind it to -.04 or so under the small dia, try that, if it works also use it to R the other bores. job runs 10 or 15 pc lot 2x a year hard to justify special tooling.