What to make a small/long HBM boring bar with?

[Garwood]

I had a walk in job today to bore a 2.5" A513 tube to 2.635 for 30" length. I tried to turn it away, but the guy can't find anyone else to do it.

I got permission to bore each end 8" deep in my big lathe and I have a 30" long boring bar I can relieve the center a few thousandths so the pin will slip through if there's a couple thou misalignment.

However, I have a pretty good HBM with a tailstock, but my smallest bar is 2.5" diameter. After the guy left I was thinking it would be easier to do this job in one shot in the HBM instead of all the flipping crap and running a steady in the lathe.

I could buy some TGP and machine pockets for cutter bodies, but I have no idea what is out there for cutters to do this (I'd really like to learn, I have the HBM sitting here).

Can anyone suggest tooling for this? I would guess a 2" bar would be the right size, but would smaller/larger be better for some reason?

Thanks for any help!

 

[Herding Cats]

Matt Maguire would likely have an answer. I seem to remember him talking about special brazed carbide geometry for lineboring.

Maybe someone can get him over here or even knows him......

 

[Mud]

I have a couple micro adjustable micro set inserts for Devlieg type bars, they are right angle so you just bore a stepped hole in the side of the bar and bolt it in place. IIRC they take triangle inserts, like TNMG, nothing fancy. I didn't do what i bought them for, so I can spare one or 2 if you are interested. The required hole is fairly large, like 1". With 2 you might be able to do dual opposing tool boring(what is that called).

 

[DeVlieg driver]

DeVlieg cartridges are old school. They were also available in HSS to grind high rake geometry.

I think for a boring tool I'd put a 3/8 hole in the bar and make a cutter from a drill blank. I wouldn't worry about fancy adjustment for one piece.

Personally, I'd use a shell reamer.

 

[Vancbiker]

For a one off I’d do like DeVlieg driver said and use hss in a bar made of 1144. 1144 seems to have a damping effect IME that helps prevent chatter. With hss you can easily play with rake angles and nose radius to get best cut.
The microset inserts Mud mentioned are excellent and would be nice if this was a repeat job.

 

[Garwood]

I have a handful of Devlieg bars I use for finishing in the cnc mills. They mount in a 45 degree pocket and they look too fragile to rough an 1/16th off.

Mud, what you have sounds about right, but maybe too big for a 2" bar 5 or so feet long?

Are there 5/8 or 3/4 shank versions of those?

Tnmg or even tpg would be fine id think?

 

[Garwood]

DeVlieg cartridges are old school. They were also available in HSS to grind high rake geometry.

I think for a boring tool I'd put a 3/8 hole in the bar and make a cutter from a drill blank. I wouldn't worry about fancy adjustment for one piece.

Personally, I'd use a shell reamer.

This is probably a dumb question, but how does a shell reamer work? I'm guessing you have a bunch of them so you're not buying one for one job. Do you actually have a 2-5/8" +.01" shell reamer or an adjustable one? Or is there a trick to cut oversize with a 2-5/8 reamer? Something like using thin brass shim stock on a couple flutes to get a small reamer to cut oversize? I wouldn't think going 30" in HSLA steel would be a worker with shim stock.

 

[Garwood]

For a one off I’d do like DeVlieg driver said and use hss in a bar made of 1144. 1144 seems to have a damping effect IME that helps prevent chatter. With hss you can easily play with rake angles and nose radius to get best cut.
The microset inserts Mud mentioned are excellent and would be nice if this was a repeat job.

My concern, maybe unfounded, is if I use hss I'm going to have an edge melt and create a hard spot when I'm 15" deep in a $400 chunk of tubing.

 

[Mud]

It's been a while since I've looked at them, I forget exactly what size they are. I'll take and post a photo tomorrow. Or PM me your email if you'd rather get them that way.

 

[Vancbiker]

My concern, maybe unfounded, is if I use hss I'm going to have an edge melt and create a hard spot when I'm 15" deep in a $400 chunk of tubing.

Hard for me to imagine that happening in A513 That's pretty soft and gummy low carbon steel. If worried, run at like 80SFM.

 

[Garwood]

Hard for me to imagine that happening in A513 That's pretty soft and gummy low carbon steel. If worried, run at like 80SFM.

Hmmm...

Maybe I have something wrong. The customer is supplying the material. He said it was a special HSLA tubing like T1 plate. This is part of a crane boom and the OEM approved this alloy and engineered this repair.

I swear he said A513, but I just looked it up and you're right- A513 is nothing great.

 

[Delw]

I'm trying to figure out how your going to machine it with a 30" 2" dia boring bar. wouldnt it flex to much? or would you make a reverse box tool so to speak with bearings?

 

[Garwood]

I'm trying to figure out how your going to machine it with a 30" 2" dia boring bar. wouldnt it flex to much? or would you make a reverse box tool so to speak with bearings?

If I do it in a lathe I can reach in atleast 8in with a 2in bar with a positive insert. I can bore from each end. That leaves 14in to take out of the center. I have a homemade 2in bar 30in long that I can chew the center out with- just clearance. I'd take the center out from each end so only reaching 15" max

If I used the boring mill I'd need to put the tailstock on (never used it before) and make a 2" or so boring bar long enough to clear the table.

The other thing I don't know is if its better to bore using the quill, letting the bar slide through the tailstock bushing, or if it'd be better to use the table feed. Quill seems like it would be more rigid?

 

[lobust]

You can get 10mm/3/8"/12mm/1/2" shank tools with neutral rake for TCMT inserts that work great in line boring bars.

Just drill and ream a hole in your bar and tap a cross hole, adjust with an indicator mounted on the bar.

Sandvik example:

Sandvik Coromant

www.sandvik.coromant.com

 

[Mud]

Found the cartridges. They use small square inserts and are way too big to put 2 across in a 2.3" bore. I have carts that take normal triangles, but they are huge.

 

[Mud]

Is there any way to rotate images after uploading? The top pic was take horizontally, shows horizontally on my PC, but is sideways here.

 

[Herding Cats]

Hmmm...

Maybe I have something wrong. The customer is supplying the material. He said it was a special HSLA tubing like T1 plate. This is part of a crane boom and the OEM approved this alloy and engineered this repair.

I swear he said A513, but I just looked it up and you're right- A513 is nothing great.

I didn't look anything up but when I worked in boilers the suffix made a huge difference. IE SA335 P11, SA335 P22 and SA335 P91 are very different materials. IIRC it's chrome content. 1.25% for P11 VS 9% for P91

 

[Garwood]

I'm learning a lot here and I appreciate all the advise.

Mud- Those boring units look nice. I don't think they'll work great in a long 2" bar though.

Lobust- The shank tools seem like they'd be the easiest to install. I was thinking the graduated Devlieg style units would be advantageous- I know with the old ones I use in my mills it's not hard to adjust a few tenths on diameter reliably using the collar. I think the problem in this boring bar application is I have to mill away a lot more of the bar to install the indexable cartridge style units VS just using an indicator and stick tools with the right geometry like you linked to.

The cartridge style units seem to be easy to get in smaller sizes that would be right for this application, but they are brazed carbide. I don't feel like that's a step forward. The ones I use in my mills are brazed carbide, and they last forever taking .005" DOC in aluminum. They look way too fragile to take out pounds of steel.

The shank tool seems like the way to go for this. A straight shank set screw tool would likely leave the most of the 2" bar intact for rigidity.

The two boring bars I have are 2.5" and 4" diameter. They have drilled and reamed holes with square inserts pressed in. The 2.5" bar is made for 1/2" square tools and the 4" bar for 5/8" shanks.

I'm still curious about the shell reamers. It seems like the least versatile way to do the job, but it might nail the size quickly if I used it correctly? There are new import 2-5/8" solid shell reamers on Ebay for about $40 and new adjustable McClosky 2-5/8" shell reamers for around $160. I doubt I would ever use that size again and I'd have to make/buy an arbor.

 

[DeVlieg driver]

Get 2 3/4 or 2 11/16 reamer and grind to suit. Make your arbor long enough to go clear through the part. It's just a taper on a long shaft with a cross pin to drive the shell. Here is a 2 1/2 I set up for a pull reamer.

 

[Garwood]

Customer dropped the material by yesterday. Not what he said it was going to be, as is typical.

Tube is just regular DOM crap. Bore is 2.495". Bore needs to be 2.512-2.515"

I thought about how that's just 10 thou off a side and how that could be done in one shot.

I called and got a price on 1144 stressproof. $400 for 6 ft of 2-3/16" the only size in stock on the west coast. Must be some real great stuff.

Went to my rem pile and pulled out a 4' long bar of 2" 1045 and some bronze bushing stock.

Turned a step in the end of the shaft and pressed on a short piece of bronze. Turned the bronze about .0015" under bore diameter. I ran a rigid hone through the tube to verify size. I don't want my bar to get stuck.

I put a scotch key in the bushing in hopes it stays on there.


I reamed a .376 hole about an inch back from the bushing for a broken carbide grooving tool I found. Drilled and tapped 3 holes to clamp the bar with set screws.

Only took a few minutes to indicate the tube in within a couple thou. Surprised how straight this tubing is. The tubing is 48" long and I only need to bore 29" so I clamped the outboard clamp tight and used a piece of hard rubber under the close clamp and just barely snugged the clamp. I put an indicator on the tube next to the clamp and tightened until it deflected about a thou.

In the morning I'm going to break out the old carbide grinder and fine tune my cutting edge, take a test cut, adjust size and see what happens.

You guys think it might work?

Any suggestions for corner radius and feed? I'm thinking around .01" and .007"/rev feed to start.

Never done anything like this before.

This boring mill sure is neat though. I've been moving this thing around for years and finally had the ability to set it in place, level it up, clean and use it. This thing came out of one of Esco's big foundries. They beat the shit out of it and I guess it's a testament to Kuraki that it's still pretty damn tight.