Cutting a 3in Cope on rectangular tubing - bridgeport production

jellywerker · Apr 17, 2018

Hi,

At work, we have a job that requires coping a piece of large rectangular tubing (2x4, 1/8th wall) to mate onto a 3in tube. Originally the job was done with a hole saw, but this left an awful surface finish (it's a cope, so no support in the middle/other side) and it required flipping the material. We moved to a boring bar, which is better (can do the cope in one setup, improved surface finish) but it's still incredibly abusive to the tool, slow, and I think there has to be a better way.

I've seen annular cutters, but we'd need 4in+ depth and 3in OD, which makes the tool cost incredibly steep.

We use the mill too much to set it up for horizontal milling every time we make these parts (made to order shop - we don't run parts for inventory) plus I don't think we have the skills to set that up and reset the mill correctly each time.

Long story short - is there a better tool we can be using to cut this cope, that I can stick in an R8 spindle somehow? Plunge cutting preferred so we can make the cut in 1-2 passes. If the answer is "get a 3in end mill" do you have suggestions on an insert tool that can do the job? We're cutting soft alloys, but I can't take the resharpening downtime when somebody chips the cutter.

Thanks all!

jellywerker · Apr 20, 2018

Bump.

Any thoughts anyone?

dsergison · Apr 20, 2018

buy a beefy ass hole saw. DITCH the shit arbor they use. the poor stiffness and wobble is the reason for the poor finish attach it directly to a solid 3/4" or 7/8" bar, Hell, you can WELD it together, I have. It will cut nicely.

Better still attach it to an R8 slitting saw arbor or boring head arbor

just buy the annular cutter and the r8 annular cutter arbor and get on with life.

litlerob1 · Apr 20, 2018

Bridgeport isn;t the right tool for the job.

UniPunch is more along the lines of what you NEED, your trying to carve the Turkey with a Spoon man.

LINK; https://www.google.com/url?sa=t&rct...tube-coping/&usg=AOvVaw1lnvF7swaFzITua4k25Xyl

jellywerker · Apr 20, 2018

Thanks guys, those ideas are all helpful - definitely hear you on the poor quality arbors - it's why we moved off the hole saw in the first place. I'll look into trying a stiffer arbor there before I pitch for an annular cutter.

For the cope punch - I had no idea that existed. It looks great, but we don't have the other tools needed to take advantage of it.

litlerob1 · Apr 20, 2018

jellywerker said:
For the cope punch - I had no idea that existed. It looks great, but we don't have the other tools needed to take advantage of it.

Yeah, you gotta get all the parts for the whole set-up???

You asked; "if there is a better way", so yeah there is, if you are constrained by something like Shipping location, or Floor space, or Money it helps to put that in your post.

Clive603 · Apr 20, 2018

#2 on a much stiffer arbor. Also consider using a sacrificial piece alongside the cope to give support to the other side of the hole saw. Last time I did such I tack welded a bit of spare tube on the end of the one to be coped ensuring that the welds were inside the waste piece. Much better. Presumably because the cutting loads are pretty much balanced.

Another trick I was told to try after welding the extra bit on was to drill right through first for a suitable pilot size and arrange an extension piece on my upsized arbor to run in the hole in the other side of the rectangular tube. Idea is to provide support on both ends of the hole saw. Ought to work if the pilot is decently beefy. Half inch diameter maybe.

If you had such an extended through the middle arbor I guess you could make your fixture whit a hole to receive the extended pilot and just roughly carve away clearance in the end of the rectangular box with an angle grinder or similar. Probably no need to weld a bit on to balance cutting loads then.

If you aren't in a position to get the designed for purpose tooling I think you are lumbered with bit more prep work to get a decent hole. I've frequently been impressed by how good a result you can get from a decent hole saw if you give them half a chance by presenting them rigidly to the work.

Clive

Job Shopper TN · Apr 20, 2018

Perhaps a 3" diameter side milling cutter on an arbor. I do not know what thickness you could get away with on a Bridgeport, perhaps 1/2"? Figure out where you need to stop, set up a table stop or X0 on the DRO, and cut it out that way.

For plunging applications, yep, I would recommend finding a way to support the "air" part of the cut... I wonder if you could make a sort of trepanning/face grooving tool for a boring head. No starter hole that way, just set it to the right diameter and plunge through...

jellywerker · Apr 20, 2018

litlerob1 said:
Yeah, you gotta get all the parts for the whole set-up???

You asked; "if there is a better way", so yeah there is, if you are constrained by something like Shipping location, or Floor space, or Money it helps to put that in your post.

You know, you are right.

Anything over about $1000 isn't going to be an option right now. The annular cutters I've seen with the specs I need are up around/past that. Additionally, I worry about having such a valuable tool around - I have a hard time keeping sharp end mills around with all the damage that happens.

Floor space is an issue, but it depends on the option - we could squeeze 4 square feet for a small new tool (the punch could probably be fit into that with an air/oil cylinder) but running the air, getting people up to speed on how to use it safely, etc... is more than I can invest for the current volume.

I'll see what I can do revisiting it with a good hole saw - I'm not concerned about the guys have to make 3 nicks with the bandsaw to prep the piece and allow for the cutting depth needed.

dsergison · Apr 20, 2018

Job Shopper TN said:
Perhaps a 3" diameter side milling cutter on an arbor. I do not know what thickness you could get away with on a Bridgeport, perhaps 1/2"? Figure out where you need to stop, set up a table stop or X0 on the DRO, and cut it out that way.

For plunging applications, yep, I would recommend finding a way to support the "air" part of the cut... I wonder if you could make a sort of trepanning/face grooving tool for a boring head. No starter hole that way, just set it to the right diameter and plunge through...

bang bang bang bang......every revolution? hell no. a hole saw or a annular cutter is a trepanning tool. one with lots of tiny teeth. no intermittent impact. and the ability to feed at a rate multiplied by the number of teeth.

an r8 shell mill or slitting saw arbor can be bought for <$40 you can make up a pilot for any hole saw. or..... just weld it.

Mud · Apr 20, 2018

Long story short - is there a better tool we can be using to cut this cope, that I can stick in an R8 spindle somehow?

A 3 inch roughing shell mill on an R8 shell mill arbor. Will dramatically reduce the tooth pressure and stop all the chatter and grab of a regular mill cutter or hole saw. In mild steel tubing you can get away with a cheap chinese shell mill, and it will last for a long time. I'd suggest using a mist coolant nozzle to cut down on the heat so you can feed aggressively and fly through the parts. I wouldn't go to an insert tool, they will need a more rigid setup than you can get with tubing.

Illinoyance · Apr 20, 2018

I know this is above what you have budgeted but it is the ideal machine for the job and you should see rapid payback.

Abrasive Tube Notcher | Grizzly Industrial

There are other, better machines than Grizzly but I can't remember the brands.

wheels17 · Apr 20, 2018

I have had good luck with large hole saws on a #$@&$ mill by drilling through both sides of the tube with a 1/4" drill (or center cutting end mill on big angles) and using a long pin in the saw arbor through both holes right from the start. The pin is much stiffer than the pilot drill and really controls the saw.

Limy Sami · Apr 20, 2018

Qs, because it can make a big difference;-

Does the coping cut include feathering the edge that runs along the round tube axis?

How are the two parts to be joined? detailed please.

Degree of accuracy and fit up required?

Rob F. · Apr 20, 2018

You did not say how long the part is being coped. You could do two at a time so you are just boring a 3" hole through the end of both tubes at on time. Or maybe easier to bore the hole in the tube that is long enough for two parts and then cut in half through the hole.

kineticmx · Apr 20, 2018

Sounds like you might not be super comfortable machining stuff so for not much cash paragon machine works sells a variety of hole saw arbors, way more stout. I'd give them a go and if you still aren't satisfied with finish go from there. Try the easiest low cost solution first.
FT211 hole saw arbor Threaded 1/2"-2, 3/4" OD x 2-1/2" Long

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DDoug · Apr 20, 2018

You have not indicated how many different configurations you need.

It could as simple as a wrap around template guiding a hand held plasma torch.

Or a single axis slide and rotary axis couple to a plasma cutter on a machine torch. (with torch height control)

upthebikes · Apr 20, 2018

The paragon stuff just works, and Mark and the crew there are great people as well. I have about 10 of their arbors and 8 of my own shop made. If you decide to stick with a hole saw, ditch the pilot drill and for sure use a nice stout arbor. Also if you have a lathe at the company you can turn a “regular” hole saw into a deep cut cavity hole saw. silver braze a tube extension to the saw body, turn down the extension OD a hair under the saw body OD so the body clears the cut, and then drill/bore the old “bottom” of the saw out of the cavity. Cap the end of the tube, tap for arbor threading of your choice or even weld a straight shank directly on. Once you make 1 it doesn’t take much longer to make 10 to have on hand.

adama · Apr 20, 2018

For a typical weld joint a simple template and plasma cutting takes some serious beating, its easy to be accurate to under a 1/16" and its fast very fast and not abusive to anything.

Ries · Apr 20, 2018

Long term an abrasive belt is the way to go.
Even if you could afford annular cutters, they break when used like that, much more frequently than cutting in a nice flat, evenly supported sheet. The tubing will vibrate a bit, the cutter snaps. Been there, done that, and, even if its only 2" annulars, they cost big bucks.
Jancy, Scotchman, and various other companies make belt grinders with interchangeable contact wheels sized to make different size notches.

Cutting a 3in Cope on rectangular tubing - bridgeport production

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