Boring techniques need better solutions

[themuffinman]

Hi, I am still a student in the MTT program and I was given the opportunity to work on a research project contracted to the school from an engineering school. I cant go into detail about what it is as its still R&D, but Ill do my best to explain my situation.

I have to bore an internal taper that starts out as +4" and goes down to a .314" that is 4.7" deep. The only bar i could get in that far and that small only had about an inch of length to it. So I cleared extra material away with staggered drill sizes until I could get my BB and its CR steel extention I made to clear the rear hole.

This worked very well, BUT it took me over 3 hours to complete this one operation as I was getting insane chatter. The Finished bore has to have an extremely nice finish and be completely free of any abrasions because this taper will be used to control the flow of fine iron powder.

I guess my question would be: How do I get rid of the chatter while speeding up the process? (original DOC was .002 F.006 SFP600.) Im using a Haas TL2.

Also, the material will be Be-Cu. (did a technique run on 6061-T6)

[Geof]

If it took you only three hours on your first attempt, insane chatter or not, you did pretty good given the final diameter and the depth.

Your approach with multiple drills is a good one but you may be able to speed things up and get a better finish by making/modifying some larger boring bars.

Do the taper in stages: The angle is around 45 degrees which means at a depth of 3 inches the diameter is about 1" so you can use a nice beefy boring bar to hog it out to this depth. To give your self a bit more clearance near the end of the bar machine the back side on a steep taper matching the taper of the hole.

Once you have roughed out with this beefy tool switch to a second tool which is a small boring bar held at an angle matching the taper in a nice beefy extension. Again machine the back side of the small bar to match the taper of the hole so you can use the largest diameter possible for the small bar. Also clamp the small bar in the extension with four setscrews in pairs at 90 degrees to each other so it is held rigid.

[themuffinman]

Here are a couple pics explaining how i went about it.

First I bored the closest part of the profile 2.75" deep.
(Picture depicts the profile with a #3 prepared for a clearance hole.)


This picture is my set up for the rest of the profile. Note the custom made BB extention.


Again.


You can see the chatter marks.



P.S. Thank you for the support on my times... Gives me more confidence in what Im doing.

[Geof]

You are on the right track. The Beryllium-Copper is going to be very different to the 6061 and you may tend to get a very different type of chatter. On the other hand though because you will have to run slower you may get less chatter. One thing to aim for is to have the boring bar as stiff as possible by making it tapered as I mentioned and then you can keep a good feed to keep the bar loaded and with a bit of luck reduce the chatter.

Your final cut may need a very slow speed, very small depth of cut and a slow feed to get a nice finish all the way down. Using G96 for constant surface speed may tend to induce chatter as the rpms climb with the smaller diameter. I suggest finish boring the first one maybe .05" undersize to get all the bugs worked out to get a good finish then open the hole up cautiously.

[themuffinman]

Thanks again for your support and tips, this is all new to me as like I said, Im still a student.

The bar im using is carbide but not inserted (as per its size limitations).
Do you have any suggestions for the design of the bar extension to help with rigidity? Besides the 4 hex bolts and taper.

What if I made a smaller one and slid it into an outer one? Kinda like a reinforcement jacket? Or would it be better to just have a solid sleeve?

Sorry for all the newbie questions. :/

From what I read the BE CU will cut similar to Al-Bronze. Is this correct? Being that it is 6" stock what would be a good spindle speed? Or should I just experiment with it til it doesnt chatter?

[Geof]

Solid extension holder for the small boring bar is best. As soon as you introduce extra connections as with multiple sleeves you introduce more opportunity for chatter.

Yes Be-Cu alloys are similar to aluminum bronze alloys, in other words a real !@#$%^ to machine. Slowish speed and healthy cut are needed to avoid the work hardened surface from the previous pass. 'Healthy cut' would be minimum 0.01" for depth and 0.002" per rev for feed, or something close to that. You will have to experiment a bit which is why I suggest finish boring one undersize slightly to get all your conditions sorted out.

Or get the guy with the checkbook to by you an extra piece?

[themuffinman]

He will buy what ever I tell him to buy. haha.

Right now Im looking at 2' of 6"D. Roughly $4500!

[Geof]

Originally Posted by themuffinman He will buy what ever I tell him to buy. haha. Right now Im looking at 2' of 6"D. Roughly $4500!

Oooooh, not cheap. I would say it will be worth cleaning your machine and collecting the chips for recycling.

[Delw]

why dont you get a set of pie jaws and finish the small bore from the other side" this way you will have a shorter b bar.
not to mention you should be using pie jaws on the operation above as well

[themuffinman]

Originally Posted by Delw why dont you get a set of pie jaws and finish the small bore from the other side" this way you will have a shorter b bar. not to mention you should be using pie jaws on the operation above as well

The smallest (and farthest) hole is done while still in the od profile set up....
but that hole is only .3xxx deep, and there is a step directly after it so it doesnt solve the length issue.

[Delw]

how small is the step? you might be able to get a micro100 groove bar and finish the back bore form the otherside.

[themuffinman]

Originally Posted by Delw how small is the step? you might be able to get a micro100 groove bar and finish the back bore form the otherside.

well the smallest hole is .314 and the step is .4xxx but that doesnt solve the issue with the taper...