How to Miter (Cope) a Round Tube by Hand

Intro: How to Miter (Cope) a Round Tube by Hand

There are many times when we need to miter tubes in order to fabricate various things. Motorcycle chassis, bicycle frames, rag and tube aircraft are things that immediately come to mind. My own experience is with bicycles, so the examples will come from that.

Hand mitering small (<1.5”) tubing is not terribly time consuming, but if I were in production environment I would definitely do this with machine tools. In either case, the accuracy and strength of the final joint is dependent on the skill and experience of the person doing the work. When I was learning, I bought several 6’ lengths of mild steel tubing similar in diameters and thickness to bicycle tubing. I cut miters and practiced making fillet joints with low fuming bronze (LFB) filler rod. Cutting up the joints you make is when you get to see if your mitering accuracy is good enough.

Things you will need:
Half round file to fit mating tube (8" for 1" dia, 10" for 1-1/8" dia, etc.)

torpedo level

small flat file

small round file for deburring

angle finder

tubing

vise

tubing blocks or 2 short length of 1” C-channel

hack saw with 32 tooth blade

paper pattern

Marking material: marking pens or fast drying spray paint

Prussian blue

Square

Computer

Printer

STEP 1: Get Joint Specs

From drawing or from model, get the following information:

1. Diameter of tube to be mitered

2. Diameter of mating tube

3. Angle of joint

4. Offset, if any. Offset is the distance between tube axes.

STEP 2: Get a Paper Pattern

Use a program to generate a paper pattern. I use the tube notching program at Nova Cycle Supply. I like this one because it gives a reference line that is 4 inches from the centerline of the mating tube. That's helpful when making mitered tubes of a specific length. Another program can be found at MetalGeek.

STEP 3: Mark a Centerline

Use the torpedo level with the flat file to mark a line on the top of the tube. While holding the torpedo level with the small flat file under it, pull the file along the top of the tube all the while keeping the bubble centered. The mark is pretty handy to have. I mark both ends. You can also use all the usual machine shop stuff if you have a surface plate and vee blocks. In that case I would mark top, bottom, left and right just because it’s so easy to do in one setup.

STEP 4: Apply Paper Pattern to Tube and Mark.

Cut out the pattern. Align one edge with centerline you just marked. Make sure the strike up marks on the pattern align. Now mark the edges with a marking pen or spray paint. Fast drying is what you’re going for here. I then remove the pattern, but I know some folks just leave in place.

STEP 5: Rough Cut

It is entirely possible to make the entire cut with a file. The guy that taught me how to do it insisted that I do it that way. Now I make rough cuts with a hacksaw. When guiding the cut at the start I recommend leaving your finger in place for longer than you think you need to do it. Those tiny teeth on the saw love to skitter out of the saw kerf and leave extra work at finishing time. Position the work so you can saw close to the lines. I usually make two cuts on either side and then bend the waste back and forth to break the section free. Be diligent in containing the waste pieces. If left on the floor, they can puncture a tire or a shoe.

STEP 6: File to Fit

The pattern on the tube should be pretty accurate, but you need a secondary method of making certain the tube fits, it is centered and at the proper angle. Place the tube in the vise so the angle of the tube is equal to the angle of the cut. That is to say, you want to file horizontally.

Check the angle of the tube using the angle finder. Now use the correct size file to file almost to the mark. When you’re close you can begin to check for fit. A piece of tubing of the correct size should sit horizontally, as checked by the angle finder, with no rocking and should have contact along the entire length of the miter circumference. In addition, for miters that have no offset, ears on either side of the cut should be the same height as measured by the square.

It may be helpful when beginning to take the test piece and apply some bluing. Place the test piece in the miter, rub it around and then take it away. After the test piece is taken away it will be easy to see the contact points. Then file away the blue. It’s possible to make accurate fits in this way. With some experience, you’ll be able to tell where the high spots are by rocking the test piece. The pivot point of the rocking is the high spot. And the high spots are always somewhere on the ears. Final fit is achieved by rubbing the file in a rotary motion.

STEP 7: Check Your Work

Test tube should be horizontal. There should be no appreciable gaps around the circumference and the test piece should be in the center of the miter.

This is only one way to accomplish this. I've seen grinding wheels and angle grinders used. If I were gas welding the tubes, my requirements for joint accuracy would be much less. Mostly I braze, so keeping the copper alloy layer thin is key to joint strength.

Comments

[david.lister.1671]

I wouldn't do it your way at all. I'd just get a hole saw the same size as the tube the first tube is fitting onto and then drill a hole at the appropriate angle.

It can't help but fit.

[General Shorstoff]

Working on a railing design with some 1" round tube that is 1.35" OD.
'Hello, Home Depot? Do you have a 1.35" diameter hole saw? What? No such thing?'
You would only be able to get close but some hand filing/grinding would ensue.

[mjenk20236]

What's the material? How are you joining the pieces? If you're welding, the requirements for accurate joints is much less. A 1-3/8 saw might be okay in that case as you could easily fill the gaps.

[mjenk20236]

Absolutely. I think it would be hard to be accurate without a drill press or a mill. Also, some sort of jig or fixture would be a good idea to maintain accuracy. There are also dedicated cutters available that last a lot longer than the usual hole saw and can be resharpened. See:

http://www.torchandfile.com/INTEGRAL-SHANK-CUTTER-286_p_1084.html

[david.lister.1671]

Hmm, looks like a nice piece of kit, but can't help wondering how many 'normal' hole cutters i could buy with $187.
Plus it isn't the sort of tool you can pop into a cordless drill chuck and drill with. No pilot drill. If you have the access to that sort of equipment, i wonder why you'd be looking at a site like this.

[mjenk20236]

Access to a wide variety of machine tools went away when I retired.

I have to say you're a better craftsman than I am. I don't think I could do this with a cordless drill at an angle of say 72 degrees. Even getting the pilot bit to stay in one place when drilling 0.028" wall 4130 is a challenge for me.

You would do the community a service was you to publish an Instructable demonstrating how you overcome the challenges of maintaining accuracy.

I like the instructables web site. While most of the content is not interesting to me, there are some gems I have stumbled upon.

[suncoaster2]

Exactly. This works every time and I've proved it countless times as an aluminum boat builder, where it's often a requirement for handrails, spars and so forth.

[mjenk20236]

I've used hole saws and cnc laser cutting in a production environment. The idea was to make the process available to anyone with a vise and $20 for a half round file.

BTW, how many miters on a typical boat rail? I wouldn't do it with a file either. Using TIG or spool gun?

[shannonlove]

If anyone wants to know how they did it back in the old days, here's a link to sheetmetal working book circa 1900. Translating from sheetmetal to paper will allow you to make the pattern used in this method.

https://play.google.com/books/reader?printsec=frontcover&output=reader&id=ywlaAAAAYAAJ&pg=GBS.PA75

[AndrewDouglasBird]

This is also a pretty nifty way to do it:

http://www.pirate4x4.com/forum/shop-tools/456800-chop-saw-notching-101-pictures.html

[mjenk20236]

I followed your link and agree it's a good, quick way to make the notches for welding where good penetration of the parent material will occur. The ability to fill small gaps without loss of joint strength when using a welding process has a lot of merits. One of my teachers didn't bother to miter at all when welding up projects out of 1/2" EMT. Tack and fill.

In brazing, I'm shooting for a very thin layer of filler between the cut edge of the mitered tube and outside surface of other tube. In the picture below, the joint fit-up on the left is preferred. When brazing, I use the file to shape the cut edge to the shape of the mating tube. This contouring is most pronounced on the "ears" of the miter as shown on the photograph on the pattern.

Thanks for the link.

[EricL17]

I love this cross-section photo of the mated surfaces you included. Not being a machinest or a welder, I think these fillets look pretty darned strong, nice smooth flow there. bravo!

[aideym]

Well the CMBST Notcher is finally completed and I am about to write the Instructable ( if it works properly)

[aideym]

Thank you for this instructable, I am about to get stuck into a load of bamboo poles to build a recumbent cycle. This was very helpful. I am just finishing building a cross mitre belt sanding tube notcher (got to think of a better name for it) but know I will have to hand finish my tubes due to the natural nature of the material. and this is a big help.

[deluges]

Are you kidding? This is a great name!

"Can you pass me the CMBST Notcher ?" is a very catchy question I think :)

[david.lister.1671]

Surely you'd ask for the CM-BSTN?

[deluges]

Much more ergonomic indeed

[clazman]

Being old school, when designers used pencil and paper to determine the intersection of two cylinders, I thought I'd try a few examples utilizing these sites mentioned herein.

I need to investigate further, the results obtained by a manual 2D layout

I entered a 1" tube with a 0.4 wall (approximating a solid bar) joined to a 1" tube at a 90 degree angle. The result was a square end.

Are the mentioned algorithms based on the ID as reference? Seems as though when treating the joining tubing that the ID would probably contact the adjoining surface before the OD.

[mjenk20236]

I don't have any insight into the algorithms used. Many times the patterns show both an inside and outside intersection line which I suppose to mean that both ID and OD are used.

I plugged your numbers into the notcher program and got the result shown. I couldn't repeat your result.

[clazman]

Hmmm?

I'll try it again. Maybe it was operator error?