How to bend tubing

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25 一 2010 18:16 #354 by Gregory Beckwith
How to bend tubing was created by Gregory Beckwith
Question:

I have a dream of being able to bend a tube for the F tuning branch of my Conn 11d that more closely resembles the "Geyer" bend, and learning the skills involved. Is there an alternative to going to school?

I imagine this is an advanced skill or the Conn men would have been able to do it. Do you know of a budding crafts person willing to take this on? I hate to bother some one like Chuck Ward.

Thanks, Rod Lowe

Greg Beckwith's answer:

Rod, thanks for the question.

The Skill Bending tubing is advanced skill and takes some time and repetition to achieve the bend and arc without flat spots, out of round portions and kinks. Some basic guidelines for how the tube behaves, and some tips for accomplishing the actual task are needed. Patience combined with some “trial by error” is required to advance in this skill. Technicians/repairers generally do bending by hand. Manufacturers and makers probably have fixtures or jigs made up for repeatability of the tubes/parts they need. Technicians and low volume makers often have something as simple as a 1”-2” wide block of hardwood cut to match the inside arc of the tube or part. Mass producing manufacturers have more costly jigs and devices for producing multiples with consistency. What they use and its affect on the part and acoustics of the instrument is another complete discussion.

Material inside- something must be used inside the part to maintain dimensions-roundness and bore.
  • Lead: The oldest but has been abandoned for obvious health hazard hazards.
  • Pitch: The most common and least expensive medium to use inside brass tubing.
    • It is a combination of wax and tar
    • It has to be burned out - It smells, smokes, and catches fire
    • There can be voids and bubbles of the material on the interior of the tube
    • Reusable over and over once obtained
    • The larger the diameter the part- the harder it is to bend
    • It needs to be kept cool while working or it begins to melt from handling
    • Not the best material for sharp bends- tends to fail (break apart) and cause flat spots.
    • Obtained from instrument repair technician suppliers- don’t sell to the public. Find a technician to get the pitch alone or included inside a universal part- leadpipes, branch tubing, and cylindrical tubing are available.Probably could find it somewhere on the web
    • Cheap and great to learn with
  • Soap and water: Inexpensive, solution is water + liquid ivory soap and then frozen until solid.
    • Ivory Liquid is the key- something about the detergent formula helps avoid air bubbles
    • Can freeze in a kitchen freezer, then bend part when solid
    • Has a short working time- melts quickly (can’t get cold enough with standard refrigeration)
    • Best for small corrections on tubes already in shape or to increase/decrease an area
    • Manufacturers use soaps + water too, but have capability to freeze 100’sº below zero to work with it and use a proprietary formula (they don’t say)
  • Cerrobend: ideal for small gauge tube bending
    • Is an alloy of bismuth, lead, tin and cadmium.
    • It has a melting point of approximately 160º F.
    • Conforms tightly to the inside of the tube allowing it to be bent as if it was solid
    • Cerrobend expands slightly instead of contracting as it becomes solid unlike pitch and others.
    • Expensive, not easily obtained
    • Unlike pitch, that has to be burned out, it is removed with hot water
    • Some good info on the web- ”how to bend tubing”
Learning:
There are technicians who bend tuning and you may be able to locate one that would be willing to give you some tips. The Universal parts mentioned above for pitch tubing are standard dimensions, not likely however the same dimensions (gauge, bore, diameter) that you will need for your Conn 11d. But you can certainly practice to get some experience and develop your skill.

Some questions:
Is your desire to use the existing part or do you want to start from scratch? You would want to practice and obtain an additional part to determine the exact bend you need and how to achieve it before you attempt to bend your original.

Getting a start:
If you find someone to assist you they will certainly have some advice and tips- below is some preparatory advice.
A horn leadpipe is a good tubing part to start learning how to bend. You will need to get a universal pitch filled horn leadpipe from your friendly technician who can purchase it for you. The leadpipe is good part to start with because it is small diameter and the curve is not “perfect” meaning a symmetrical, even spanned arc. Relate it to the “u” portion of a main tuning slide. A perfect ”u” is much harder to accomplish than a gradual arc. Obtaining or removing a decent condition leadpipe from an old horn and trying to copy its shape, is a good way to start. Or drawing an arc on a white piece of paper and trying to copy it can suffice. A white background works well enabling you to see where a bend begins and departs from the straight portion.

When I do a leadpipe I lay the old part flat on a white background. Sometimes I will trace around the part on the paper and then work from there. Either way- I take the new straight, tapered part and match up the small end of the new to the small end of the old. I then proceed determining where the first point of departure from a straight line is. This can be the “make or break” portion. Once a bend is made it is very difficult to reverse it without adverse outcome to the roundness of the part or creating a flat spot. This is where practice and the skill come in. Your eye and the ability to see minute bends and start points of curves are your most valuable tools. Hold the new part flat on the bench, hold the part with fingers wrapped around the tube, thumbs are touching in the middle at the point where you want to make the bend. Use a flexing motion, not a determined push to flex/bend the tube. It takes getting accustomed to the resistance and feel of a semisolid piece. You continue to eye the old part in relation to the new and try to copy its curve and shape and position. There are a lot of additional helps and troubleshooting that are difficult to explain unless you are “live” in the moment with your hands on the part and the teacher by your side. But I hope this will prove informing and helpful should you have the opportunity to attempt such a task. There is great reward in accomplishing the making of a part- especially for a musical instrument that you own and perform with. I wish you much success in finding someone to aid you in the endeavor and enjoyment in the craft.

Depending on where you are, we could help assist you locating a technician to contact and determine their willingness to work with you.

We can be reached at Email住址會使用灌水程式保護機制。你需要啟動Javascript才能觀看它 if you would like further contact.

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