Boring Bar question.

[l u k e]

I'm going to be doing a job that requires a 2" diameter hole, 5 1/2" in length (Through hole). The material is 6061 aluminum.

I have a Boring Head but the longest bar is 3". If possible I would like to avoid boring from both ends.

I was wondering if this bar can be used with a boring head? >>bar<<

If so what would you recommend as a tip for 6061, with or without chip breaker grooves?

Also what lead angle would be best for aluminum, -1* or -5*?

[Mcgyver]

i can't see why you couldn't do it with a boring head, except that a 1/2 bar with 5" of over hang seems like a lot - it'll work but with light cuts and very fine/no feeds cuts before measuring to work the spring out. You'd be better off with a carbide boring bar (less flex) but its still not an ideal length to dia ratio (iirc 5 or 6x). All this assumes the 1/2" comes from the size of bar your boring head will hold.

If the part allowed it, i'd do it in the lathe with a larger dia boring bar.

[l u k e]

Originally Posted by Mcgyver i can't see why you couldn't do it with a boring head, except that a 1/2 bar with 5" of over hang seems like a lot - it'll work but with light cuts and very fine/no feeds cuts before measuring to work the spring out. You'd be better off with a carbide boring bar (less flex) but its still not an ideal length to dia ratio (iirc 5 or 6x). All this assumes the 1/2" comes from the size of bar your boring head will hold. If the part allowed it, i'd do it in the lathe with a larger dia boring bar.

Yea, my head is 1/2" and I don't have a lathe.

Would you suggest just boring it from both ends.

[mxtras]

I recently used a boring head with carbide tipped tooling to bore a 5.25" hole, 1" deep in 6061. I broke some of the rules by raking the bar back by about 3 degrees (a guess) and I honed a small radius (maybe a 1MM radius) on the tip for the finishing cuts.

I started with a 1" drill, then plunged with the largest end mill I had which was a 1.5" rougher. I then hogged material from there manually plunging the cutter in a pretty hap-hazard fashion to get the majority of the material out of the way using a scribed line as a visual reference. Once I got most of the material out of the way I switched to use the adjustable boring head and positioned an old boring bar on the OD of the boring head. When I got close to size, I switched the cutter to a more rigid bar and took fine cuts from there. It took a bit of time, but I had no issues with finish cutting.

This was prior to completing my CNC - now I would interpolate then true it up with the boring head.

Scott

[l u k e]

Yea, thats the same head I have. The problem is the 5.5" deep hole.

[mxtras]

I read right over that without really thinking about the length/diameter relationship - sorry!

Carbide bar or light cuts is all that comes to mind at the moment. I guess a reamer is out of the question (cost).

Another option would be to get your hands on a smaller diameter boring head that would allow the head itself to go into the hole - then you would be set. Something like a DeVlieg boring head as shown below.

What machine are you doing this on? Do you have enough quill stroke?

Scott

[l u k e]

Originally Posted by mxtras I read right over that without really thinking about the length/diameter relationship - sorry! Carbide bar or light cuts is all that comes to mind at the moment. I guess a reamer is out of the question (cost). Another option would be to get your hands on a smaller diameter boring head that would allow the head itself to go into the hole - then you would be set. Something like a DeVlieg boring head as shown below. What machine are you doing this on? Do you have enough quill stroke? Scott

I have a manual import, I have plenty quill stroke.

The hole actually has a capped end. (sort of like a U-joint cap on a drive line)
So I do have some room for deflection on the bar. What kind of tolerance might I expect with the bar I linked here?

I'm going to take 2 separate pieces of stock and drill and tap the 2 sides, then bolt them together. Then I'll bore the hole between the two pieces. There will be another part that will be "sandwiched" between them. I can always mill a few thousands off one of the halves if the hole is a little off.

I guess I didn't really give enough information with the original question.

I guess really what I was asking was if the bar was suitable for a boring head and what lead angle and tip should I buy for aluminum? Being new to machining (and self taught) I always assume I'll end up buying the wrong tool for the job....

[mxtras]

I think the bar you have will be fine. For aluminum (right or wrong) I use a positive rake tool with a small corner radius and I use Tapmagic for finishing cuts to improve the finish quality. The bars I use the most are cheapies that have a neutral face so I cheat by grinding a bit more radial clearance and rotate the tip forward to falsely create a positive rake.

For finish cuts, I use .001" per rev downfeed at a relatively slow RPM to eliminate vibration from the cutter being off-center. I am thinking around 500RPM or so.

Scott

[l u k e]

ok, it's sounds right to me, thanks for the info..

[tim-tbl]

Have you tried using an SR bar and cutter mounting that in the quill, however having bored plenty of holes in plenty of metal you could really do with boring the part in a lathe.

[mxtras]

Tim -

Do you have a pic of what you are refering to?

Just curious.

Scott

[miljnor]

well I going to be "that guy" and say the obvious an since you are new.....


Use the force luke use the force!