5c Collet holder for boring bars.

[737mechanic]

I was thinking of making a 5C collet holder for my BXA tool post to mainly use to hold any size boring bar but would like to get feedback on if this would work ok. Has anyone used one of these to hold a boring bar and if so does it work good or is it best to have a dedicated size boring bar holder for the tool post. Below is a picture of what I am talking about.

[GlennW]

5C has a fairly short contact area on what it is holding, so i would imagine that it would induce chatter fairly easily.

[737mechanic]

Thanks Glen that is what I was wanting to know. I will scrap the idea of making one.

[Comstock-Friend]

I use the 5C holder on my KDK set all the time to hold boring bars. Works a treat. Go ahead and build one, you'll like it. Think I have some photos, I'll look when I get home...

John

[SteveM]

I have one of those, but only because I picked it up dirt cheap.

Haven't used it yet, because all my boring bars fit the AXA boring bar holder, but I figured it's nice to have for when I have something an odd size, maybe even to hold a work piece; who knows.

For what I paid, it can sit on the shelf until I need it.

Steve

[Comstock-Friend]

Here's the KDK setup.

7/8" engagement on a 1/2" diameter bar. Rock solid, chatter free.

John

[737mechanic]

I can clamp a 1/2in boring bar in my regular holder. What I was hoping to do is have a 5c collet system that I could use for any size boring bar up to 1-1/8.

[Carm]

If you have 5C collets, I understand your reasoning.
I use ER series, you can get a 3/4" straight shank that fits Aloris, DTM, et al.
Good grip throughout the range, though you won't get that big, and nice for drills.

Big bars get their own mounts and I like 'em close to tool post center.

[Comstock-Friend]

The KDK boring bar holders I have fit 3/4" (shown), 1" and 1-1/4" bars.

My best boring bar set is 1/2" shank, so I have the most experience with it in the 5C collets (title of this thread) and they fit the BP's Criterion boring head I have also. If I had bars other than the 3/4", 1" and 1-1/4", I would certainly throw the appropriate size 5C in the holder and go for it. And you can hold square shank bars in square collets and adjust the top rake by rolling the collet...

John

[SteveM]

And you can hold square shank bars in square collets and adjust the top rake by rolling the collet...

On mine, there is an anti-rotation key. Square collets locate with the sides parallel and perpendicular to the bed (i.e. not on a 45).

Steve

[pete]

Thought I'd mention one other holding method for a range of boring bar shank sizes. Haven't seen them advertised for awhile so not sure if there even still made. But a Google image search should pull them up. At one time Armstrong and maybe a few others made what were basically two short sections of round caps with a central hole for the threaded and bored top slide's tee bolt that had an enlarged center section for the bore that allowed clearance for the boring bars to fit through. That bore for obvious reasons faced the lathes head stock in use. And the top cap had a short machined ring that fit inside the bottom cap to keep it centered. The joining line for both caps was at the lathes C/L. If my memory isn't too faulty I seem to remember that simple design was quite expensive and Armstrong being who they were my guess is everything was forged, heat treated and ground where required. I also seem to remember that the boring bar holes were meant to be machined in by the end user in whatever sizes they needed. In use the correct size holes to fit each bars shank size were bored through both sides of the caps, fit the bar through the holes and through the hole in the tee bolt. Tightening the nut on the top of the tee bolt both locked the holder down to the top slide and the bored holes in the caps tightened up and locked the bars in position. Generally the user put at least 3 different bar holes around the perimeter of those caps.

My guess is that the QC tool post has pretty much killed the idea, but it wouldn't cost much to build your own unhardened version. I've also thought it could be maybe a bit better method for reducing harmonics in the bar while doing over length extended bores since the boring bars are supported at two separated points. (maybe my thinking about the bar harmonics is right, or maybe not since I haven't used one yet). But I'd be real surprised if someone here doesn't have at least one in there own shop and can correct anything I'm wrong about.

Edit, I just checked and Google images using Armstrong boring bar holder as the search term shows lot's of them. Looks like Armstrong used pins instead of that inner ring like I'd thought to keep both caps aligned. But it would be real easy to use those images to build your own version. Obviously a boring bar already pre set in a QC tool holder would be far faster to set up and use, but it's an idea that may work for someone for very large boring bars that won't fit the common tool holder sizes. Thought it was worth a mention in case someone hadn't come across that design yet.

[SteveM]

At one time Armstrong and maybe a few others made what were basically two short sections of round caps with a central hole for the threaded and bored top slide's tee bolt that had an enlarged center section for the bore that allowed clearance for the boring bars to fit through.

Here's one, showing an exploded view.

Steve