Need Help!- Boring

[opshop]

I am boring 6061 and I can't seem to get a nice finish its gumming up almost going 5" deep with a 3/4" bb as of now I am doing 2 .005 finish passes and it still isn't turning out any pointers? My finish speed is s1500 with a .003 feed

[RICHARD ZASTROW]

What's the bore ID? You seem to have exceeded the 5:1 length/diameter ratio normally used as the limit. Is your tool tip on center? above center? below center? excessive tool nose radius?

As you can see, lots of things not mentioned could cause your problem.

Dick Z

[opshop]

Thanks for awnsering I see their is alot more to it! I am using a carbide bb I was told the ratio was 9:1 I think I am finally getting there it just gets irrtating ! Excuse me if I sound silly but how would I know if the tip is above or below center I assume it was always at center still learning alot and anytime saving advice is so helpful . I learn something new everyday! As faar as the rest of questions tip radius is .016 and the bore is 3.600 and I'm predrilling with a 2.5" drill its taking forever!!! One time I can set it up with no problems next time it wants to give me hell. Thanks again for your help

[CaseyCAM]

1500 rpm is very fast for that size ID and such a small boring bar.

make sure the radius on the cutter is very sharp (minimal radius as possible) and sag the cutter slightly below center, and use about .004" ipm.

Use about 500rpm MAX.

[RICHARD ZASTROW]

opshop, with a 2.5" drilled hole you could use a much larger bar than you're using now. That alone would probably solve your problem.

Is this on a lathe or ?

Dick Z

[PixMan]

Originally Posted by CaseyCAM 1500 rpm is very fast for that size ID and such a small boring bar. make sure the radius on the cutter is very sharp (minimal radius as possible) and sag the cutter slightly below center, and use about .004" ipm. Use about 500rpm MAX.

The problem isn't the speed as related to the size of the boring bar, but the length-to-diameter ratio of the boring bar as compared to the bore. If I had to use a boring bar that size for the bore, I'd be running at least TWICE that speed, run with the tool on-center and double the depth of cut to load the boring bar and keep it from vibrating.

Finish problems in a bore is common. And IMO, it's easier to solve by selecting the right insert (radius, edge prep, chipbreaker, grade and coating) than it is by running a tool above or below center. Aluminum cuts best with a dead sharp edge, polished or smooth-coated top surface and high-positive chipbreaker. The depth of cut and feed-per-rev rate is something determined by the top form geometry (chipbreaker) of the insert. The cutting speed is determined by the matching of the insert grade and coating to the material being cut.

[packrat]

I know this is BLASPHEMY on this site, but why are you using carbide inserts on a HSS job?

For most aluminum work( and even CRS) you get a much better finish when using HSS cutters. Especially on a hobby grade machine, or even an older industrial machine.

cary

[dertsap]

Originally Posted by opshop its gumming up almost going

if its gumming the its either probably a wrong choice of insert or its not getting enough cutting oil or coolant

[ctate2000]

could be you are not getting the chips out of the hole. Swarf can cause this problem. Cutting speed and feed rate sound fine to me. A .015 rdius and .003 feed rate should yeild a 32 micro inch finish give or take. That is a calculated number and there are many variables which come into play as stated earlier.

[sambo67]

to answer your question there are several ways to determine if your are on center.If you have a live center for your tailstock you can use this for a reference.If you make a light face cut with BB before you drill hole you can adjust until you don't leave a tit in the center.You can also place a 6" scale on side of your material holding it there with insert .If insert is on center scale will be vertical , if not scale will tilt one way or the other depending on if you are above or below center.CaseyCam was right on with feeds and speeds.With a carbide insert 500 sfm is a good starting point.Also you need a smaller nose radius , especially for your light cuts.if the land of your insert is bigger than your depth of cut you are doing more rubbing than cutting