School Me On Boring Bars And Holders

I would have to change the adapter from the R8 that is used in the mill.
I just use either the 3/8 or 3/4 carbide tipped bars in the boring bar attachment that came with the quick change set.
3/4 is easy, the 3/8 I had to make up a split sleeve to adapt to the 3/4 hole.
 
I have made some split bushings as well. For the most part though, I use my other QCTP toolholders that have a vee grove along the bottom of the holder. The set screws lock the boring bar into the grove.
 
great white said:
I would be doing bores probably no bigger than a few inches at best. Usually under an inch I would think (motorcycle parts: axle spacers, bushes, etc).

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For anything 500" and under, I use Micro boring bars. They a carbide and a little expensive, but work well. The ID on them is easy to identify.
For example, a "BB 1601000"
The "BB" a boring bar
160 id the minimum diameter
1000 is the depth of bore.

I have also ground some out of HHS for diameter as small as .060.

For larger holes I have a 1/2" and 3/4" boring bars that uses HHS bits.

Rodney
 
In my opinion, the simplest, cheapest way to a good holder is to buy or make an Aloris AXA 4D boring bar holder and use reducing sleeves with split bushings in it to accommodate any bar up to 3/4" dia. The 4D is 3" long, which is exactly the length required to hold a 3/4" bar securely. This type of holder, and any sleeve you put in it, will completely surround your bar and hold it solidly, thereby reducing the potential for chatter. Any other boring bar holder that locks down directly on the bar itself with screws will have more potential for chatter and may mar your bar.

When making sleeves for smaller bars it is wise to ream the central hole with a sharp reamer and cut it in a single pass to get the finest finish you can get; this also reduces potential for chatter in the bore.
 
This as been mentioned before, but the cheap( read inexpensive) eBay boring bar sets, (available without the adjustable head) need to be touched up before use. The ones I've used were not relieved enough behind the cutting edge, nor were they relieved away from the cutting edge (they were square when viewed from above) A diamond wheel is ideal, but I've found a diamond coated disc from Dremel mounted in a drill press will do an excellent, if slow job. Clamp the tool in a small vice and slide it around under the spinning disc.
 
If you are starting and you grind your high speed cutters you can get a set of bars that use high speed. .If you have a AXA Qctp one of the holders has a grove that will hold a round bar. Play with that till you get the hang of it.
 
Deeper you bore the hole the larger diameter bar is needed. Chatter due to deflection because the length needed to bore the hole is always a challenge. A smaller diameter with a sharp bit could be used but the feed and depth of cut would have to be very light. If after a cut there is a scratch on the inside wall of the bore then there is still a lot of tool pressure.

You could take a practice piece of stock and test the amount of tool pressure by re-cutting the bore without making any adjustment to the settings. Sorry but I can't remember what the ratio is, if it one or two more passes before the signs of deflection is removed. I was using a heavy boring bar on a turret lathe and asked a senior toolmaker why I was getting a scratch on my finish bore. One would think a two inch diameter boring bar there would be much deflection.
 
Those bars (the carbide tipped ones) can do a good job, within limits. Keep in mind "normal" length ratio for a steel bar is 4 to 1. That being said, the larger the bar the better for stability sake. Sounds like the 3/4 bar would do most of what you have. You will have deflection on just about any bar you use. When taking final pass, either touch off the bore and dial from there, or take a shallow 'spring' pass at the last setting and measure for the last cut.
 
A good trick on finishing a bore without a scratch, feed out after you feed in. You've gotta be comfortable with doing this, though, maybe do it on the last two passes, so you take into account the metal you remove on the feed-out pass.
 
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I use the boring head bars often, but as was mentioned they do need some work to cut well. I also picked up a carbide bar with inserts at a flea market a while back for very cheep and it works great. It is my little workhorse because it will go through about anything with very little chatter. In general I prefer HSS over carbide so I have a few home made bars that use HSS blanks. The only trick to making them the way I did is I broached the holes for the HSS cutters. If you want I can post some pictures of the ones I have. They are nothing special but they cut good and are cheap to make if you have access to the right size broach or you make a broach.

Jeff
 
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