Rotational Wobble

Gentlemen, I have stumbled into a problem while boring on my micro mill. It has to do with oscillation of the whole mill and appears to get worse the deeper I go.

Long story short : Dropped a clanger when boring the cylinders of the sealion block eg forgot the layer of aluminium below the head level which forms the water jacket. Turned a centre finder plug. After aligning the bore fixed a longer boring bar to the boring head.

Now as I bore down into the second layer an osculation sets in (nominal SFM 1200ish) and no amount of speed alteration will cure it.

I'm guessing it's a combination of boring bar flexing as it is too long and the off set of the boring tool throwing it out of balance too.

Any work arounds people?

Jesse

What length of boring bar are you using?

"Now as I bore down into the second layer an osculation sets in"

Well you'll have to stop snogging it!

Is the back of the cutting edge rubbing or even the bar itself.

You do need to set the speed of a boring head so it runs without getting out of balance which may well be below the normal cutting speed or add some counter balance weight in the empty bar holes.

KWIL:Boring bar 70mm long. Will try shorter if possible.

Jason:Not rubbing but will try counter weight thanks.

Norman: Is it valentines day again?

Jesse.

No, no, no! I can't bear it, Stop picking on me!

Stop worrying, Valentines day was 8 days ago, according to the Wife anyway!

Edited By V8Eng on 22/02/2015 17:10:27

Thankfully I don't have a wife, so I don't need to worry about it!

Hi Jesse,
Are you feeding down into the bore using the quill or moving the head down the column ? I Was wonering if it is a function of how far the quill is extended rather than how deep you are into the bore.

Les.

Edited By Les Jones 1 on 22/02/2015 17:18:48

Smallest boring bar I can use with counter weight makes very little difference.

I might try locking the table and tightening the gib down feed but I fear the head will stick and hold off as it's tight enough already. Norman no more sexual innuendo please.

PS: using column as drill handle isn't fine enough being one to one so to speak.

V8eng : I remember those problems, don't get them any more.

Edited By Jesse Hancock 1 on 22/02/2015 17:20:19

Edited By Jesse Hancock 1 on 22/02/2015 17:45:36

"Norman no more sexual innuendo please. "

????????

I was pleased to see your thread back on course but fail to see where the sexual innuendo came into it.

I was just trying to have a bit of fun.

So was I Norman, near split my sides. It's the weigh I tell um.

Jesse.

Hi Jesse,
Can I check that I fully understand the problem. My understanding is the you bored the top of the cylinder to finished size (Presumably with a short boring tool.) then realised that you had to bore the bottom of the cylinder. (Which required using a longer boring bar.) If my understandingis correct then it mean that you do not know if you would get chatter boring the top of the cylinder with the longer boring bar. (And you cannot try as the top is at finished size.) Another possiblity is there is a hard spot in the casting at the bottom of the cylinder.

Les.

Hi Les, that's right more or less. I still have two untouched bores to do. It was after the second cylinder top half I noticed my error. Stare at the plans and see nothing it seems.

Stage two on half finished bore = the problem I'm having and yes it is a longer boring bar being used now.

Tried Jasons suggestion with no real improvement and that was with the shortest bar I can get away with.

As I have said I don't really fancy tightening the gib any more as I have had the head drop on more than one occasion already. It grabs now and then?!! Cheap mill.

I wish to resolve the problem before I venture on to the untouched bores if possible. In fact up until now I was having a whale of a time with it everything going great.

Les I think I will lock the table down some how, add weight to the column and tighten the gib as far as I dare.

Jesse

Edited By Jesse Hancock 1 on 22/02/2015 18:17:32

Edited By Jesse Hancock 1 on 22/02/2015 18:20:35

Jesse, what type of boring bar are you using? HSS, Brazed carbide or insert.

A picture might help us spot soething

Edited By JasonB on 22/02/2015 18:23:41

Hi Jesse,
I am assuming it is an aluminium casting (Which is easier to machine and less likely to have hard spots.) I am also assuming that you are using the carbide tipped boring bars supplied with the boring head. If the casting is aluminium then it might be worth making a boring bar with an HSS tip. this would be much sharper than a carbide tipped bar and thus would require lower cutting forces. I have made some for my boring head using 3/16" round tool steel mounted in the end of a turned down high tensile steel bolt.

Les.

Jason they are HSS with a concave shape and spur cutting edge. I'll try and down load a picture.

Jesse, can you confirm your speed as 1200SFM equates to about 4800rpm assuming the liner OD is 1" dia

Edited By JasonB on 22/02/2015 18:44:50

Les Right again, ally it is and see answer to Jason above. These boring bars are a shade under 6mm (5.94mm) (.234 inches).

Guys I will give you an update tomorrow. I want to try some or all of these ideas for now. I thank you all for your input.

Jesse.

Sounds a lot too thin, assuming your head holds 1/2" tools then either a 1/2" bar with a HSS toolbit at teh end or one that is sold for boring heads with a 1/2" shank and slightly reduced neck dia.

Sketch here to show the job in hand