Boring head confusion!

Here's the scenario:
- Milled out a hole. Want to make it larger, so I thought I'd use the boring head for practice (but also because I don't have a jobber drill bit in the size I need).
- Removed the end mill & collet.
- Inserted the boring head arbor, then screwed on the head.
- Did NOT move the table at any time.
- Tried to adjust the head so that the bar just starts touching the inside top of the hole, but can't get it to touch all the way around!?!

It's like the hole or the head is out of round? Or the table moved (but it hasn't because I reinstalled the collet & end mill and they still line up).

Shouldn't the boring head line up with the hole? Why does it appear that I need to move the table to center the boring head with the hole? What am I missing?

tom

Did you have cutter comp on? "Zero" when a tool touches an edge, isn't zero of the column.

It is very easy and common (depending on your drilling practice) for drilled holes to be off center and/or out of round.
Are you talking .005 or .080 off?

@MrWild: Forgot to mention that this is manual milling. I'm actually milling the parts to convert it to CNC (X2).

@DareBee: Closer to .005.

So do I assume it's my (newbie) technique or end mill and further assume that the boring head is positioned correctly?

What can cause off-center or out-of-round holes?

thanks.

tom

how you started your hole. If you just drilled without locating the hole with a center drill, the drilling drill can walk the drill point that far before digging in. Once started, the drill follows the hole path. As I wrote that, two things popped into my head. If the deviance is front to back, the column may have flexed from the stress of the drilling forces. If it's out side to side or a combo of both, it could be you need to tram the head.

Newbees don't realize they need to tune up the mill before they start cutting. Not a problem though, just a bit of experience will fix that. If I were doing a X2, the first thing I'd add is a back support. Are you doing an X2 Freak? Lots of good info in Hoss's threads, and he has a sale at the moment on all the mods in one CD for Zoners.

Are you doing this in a vertical mill like a Bridgebort? If yes - did you move your knee down to get more room for your boring head? If yes- you may want two check the alignment of your head and tram it again.

Quote:

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Originally Posted by MrWild

how you started your hole. If you just drilled without locating the hole with a center drill, the drilling drill can walk the drill point that far before digging in. Once started, the drill follows the hole path. As I wrote that, two things popped into my head. If the deviance is front to back, the column may have flexed from the stress of the drilling forces. If it's out side to side or a combo of both, it could be you need to tram the head.

Newbees don't realize they need to tune up the mill before they start cutting. Not a problem though, just a bit of experience will fix that. If I were doing a X2, the first thing I'd add is a back support. Are you doing an X2 Freak? Lots of good info in Hoss's threads, and he has a sale at the moment on all the mods in one CD for Zoners.

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I did use a center drill. Checked it again just now and it looks like it's off < .015 in the X axis. Y looks okay.

I definitely need to tune it up. I thought I'd do that while I was installing Hoss's CNC conversion (which is what I'm milling right now). All his parts are pretty non-critical, so I think I'm okay.

And back support is on the list. I just gotta figure out which solution I like best.

Quote:

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Originally Posted by juergenwt

Are you doing this in a vertical mill like a Bridgebort? If yes - did you move your knee down to get more room for your boring head? If yes- you may want two check the alignment of your head and tram it again.

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It's a table-top mill from Harbor Freight. Got ahead of myself and haven't trammed, shimmed, etc, anything.

Thanks for the help. Looks like a tune-up is in order.

tom

Back to the drilling thing.
Correct sharpening of a drill bit is critical to its proper function (oversize, wondering, etc).
You did use a center drill which typically will get a drill started in the correct location.

If I can get away with drilling a hole rather than boring a hole I will drill it every time. This is off topic of your question, and practice is always good, but I would go and get a jobber, and forget about the boring head, and drill it if gets you in print.

Quote:

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Originally Posted by tooManyHobbies

I did use a center drill. Checked it again just now and it looks like it's off < .015 in the X axis. Y looks okay...tom

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Being off in X but not in Y is diagnostic for the head out of tram; correct this before boring the hole ecause if you do not your hole will not be perpendicular to the top of the work.

Quote:

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Originally Posted by Geof

Being off in X but not in Y is diagnostic for the head out of tram; correct this before boring the hole ecause if you do not your hole will not be perpendicular to the top of the work.

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What Geof said.

You mentioned you never trammed the mill. So here's the deal:

When you're out of tram, the column is not perpendicular to the table travel. As you move the head up and down the column, it's moving on a diagonal, which changes the X.

So, very likely your boring head is at a different head height than the twist drill. There's your issue. Tram right away!

The hole, BTW, is not straight down. I'd be tempted to tram, center up on the hole again, redrill, and then get on with boring.

Cheers,

BW

Okay guys I'm having the exact same problem. Now I am trying to make a pinion gear adapter. 10mm od cylinder 15mm tall with a .1245 center hole.

Now my machine (x2, manual, solid column) its trammed to no greater than .0003 an ill shoot for .0001 on very percise things. I am very meticulous about checking before every operation and a stickler in getting things dead nuts.

So this piece started as 1/2 bar stock mild steel. I trammed the upright of this bar to the column. Used a center drill bit 5mm down then a jobber to depth of 20mm. Reamed to .1245.( I did not drill dead center of bar due to using my boring head for od) Machine is locked during all of this. Threw boring head on to cut outside diam. Once I got to about 14mm I noticed my boring head is cutting about 1mm diag. +xy. I'm so lost center of boring head should be center to column right? If nothing ever moved I even checked with center finder once noticed this how is this od off from I'd???

OK I found my problem . I guess that's not a one time thing but the head isnt parallel to the column anymore. I usually tram the x2 doin column to table .( I did do head to column first week) Must have moved :( ... if the lowest position is 0.0000 in 8in at highest point im out 0.0043 to the right and 0.0068 to the rear. Ha so that's exactly why I'm cutting heavy diagonally (+x+y). As I raise, my center changes. Sweet! Self fix on that on haha. P.S. Shars boring head best 80$ ever spent this feels like a Kaiser

you have to tram the head to the column in both directions. scraping the back of the spindle block/slide block is far better than shimming...if you have the equipment! shim/scrape for the Y deviations, gently tap with rubber mallet for the X with the clamp bolts slightly loosened. if you could handle it... insert locating pins when satisfied its perfecto.... then its easy to reassemble after the occasional maintenance or modification, and "shouldnt" lose location if it happens to crash... unless youre going to try replacing that solid join with a rotating section... sort of pointless on an X2 unless you have a feather spindle.

really, the whole machine needs a good scrape. gibs particularly need attention, they flop, they lift in the slot and bear on the wrong part, yarda yarda. the adjustor screws really need to be pointed.
then you have to tram the column/spindle to be square with the bed. once again...scrapings best in the Y axis. finding a shim THIN enough to get the column squared up in the Y is a nightmare... very narrow face in that axis means the slightest change makes a huge difference! and you dont have much width on the bed in that direction to get a good reading. 0.01 across 100mm is shocking compared to the 0.01 you can very easily get across the 600mm of the bed...

yesh, i use metric. :p

i know i personally preferred scraping each part to be square with a surface plate rather than the fiddly tediousness of inserting shims, checking, rechecking, triple checking... each to their own. there was some fiddly tediousness in making the plate itself! but now its there, when i need one ;)


as far as i can tell, it doesnt matter a hoot if the face of the column isnt parallel to the bed. when looking down the Z. why should it? as long as everything else is square it works.