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View Full Version : Armstrong boring bar holder ??s



J Tiers
03-07-2008, 12:17 AM
OK, as part of a pretty good deal, I got an armstrong boring bar holder that seems to fit the Logan. It is a tad high, but I can face off the bottom slightly to bring it on-center.

Or I could just make an offset sleeve for the largest (3/4") position, to adapt it to smaller bars. I'll have to do that anyway, since I also got at least one Armstrong boring bar, which is 9/16"diameter, but the holder has 3/8, 1/2, and 3/4 positions.

Anyhow, the question is: The t-nut for it has a threaded rod brazed-in. Now with a fixed thread, it won't tighten down the center spindle at just any position, it will be loose in most, because the t-nut won't turn, and the center spindle of the holder has to allow the bar through aligned with the lathe spindle axis.

I assume that the idea is that the nut on top tightens the two parts of the barrel down on the bar and draws the whole works tight, more-or-less regardless of the degree to which the center spindle is tight. All that would seem to be required is that the center should clear the bar so the bar is held by the outer barrel halves. The center spindle apparently need not be in any way tight.

Correct?

I have some boring bar holders that I made, but decided this one would be appropriate since it allows the use of long bars over-hung both ways, which seems to work better as far as chatter etc.

But, never used one of this barrel type before. Hence the questions.

wierdscience
03-07-2008, 12:29 AM
Correct,but the bottom is supposed to have a T-bolt,basically a round head with two flats milled on to fit the T-slot in the topslide.It adjusts out to fit just loose enough to slide in and the top nut as you already know clamps everything together and holds position.

I have three,a small one like the one you have the medium sized one that goes up to 1-1/8" and the big fellow that runs up to 2-1/2" bars.

I made my own solid blocks a few years ago and don't use them much anymore.My blocks are just square,but have a hole for a different sized bar in each corner.They work out to be much more ridgid than the Armstrong im my experience.

Beware of the T-bolt in those holders.Some are cut smaller than the OD of the holder.Ever see a lathe topslide who's t-slot has the lips busted out in the shape of two opposing cresents?That's how that happens,a little too much feed or a crash and pop!

BadDog
03-07-2008, 01:04 AM
I've been wanting one of those for a while, just haven't yet found one that was priced what it was worth to me. Some day...

But I think you are right about how it works. The key is the outer shell. And apparently HSM Mag ran an article a while back that covered how to make your own. Haven't seen it though.

Someday I'll probably just make what Wierd describes. Main reason I wanted an Arstrong is that I've got a couple of big bars that either won't fit anything else I've got, or like the 3/4" x 8", would be a bit much for the little AX post. And we won't even talk about the big ol' 1.25 bar! :eek: Main reason I've got those big bars is just to have a super rigid bar for diameters that will allow it, and mounting it on the AX kinda defeats the purpose...

J Tiers
03-07-2008, 08:09 AM
Thanks

In this case, the t-bolt is a large rectangular item that fits the compound, with a raised area for the opening of the compound. It used to be square with no slot filler, but I had to mill it down to fit mine.

So if it wants to tear any "bites" out of the compound, it is just as likely to break something else instead. The entire t-slot would have to be broken off, and I am not looking for any crashes THAT big.......

I made the block style long ago, and they are OK for the "sheep's-foot" bars. But the long bars overhung seem to have some good points, not the least of which is the fact that they use inserted bits, either standard triangles screwed down, or sections of HSS ground to suit and poked through square holes. I have some of both.

Your Old Dog
03-07-2008, 08:25 AM
The rookie here might not be understanding you completely but if what I think you saying is you are going to make a bushing then I'd offer this. I made a mount for my Dremel and made a plexiglas bushing but made it eccentric, this allowed me to tweak where it meets the work. If you're going to make a bushing, I'd suggest making two and make one eccentric.

J Tiers
03-07-2008, 11:01 PM
Yah, offset = eccentric, that was what I meant.

Don't need two, the crossfeed will take care of mis-position in vs out, while the offset takes care of vertical. I think Hardinge made a toolholder that was an offset bore in a larger cylinder, could be set anywhere and put on-center, or off-center. Same idea.