Telescoping Pipes and Tubes, Interference Fits

This page started with the "Telescoping Pipe and Tube" page by Ron Dexter at http://www.rondexter.com/professional/rigging/telescoping_pipe_and_tube.htm. Ron is interested in pipes and tubing for film production and has a fascinating page on compatability at http://www.rondexter.com/professional/rigging/pipe_tube_conduit.htm. His site http://www.rondexter.com/ contains a wealth of useful information for the film maker and machine shop technicians.

Refer also:

http://www.steeltubeinstitute.org/

http://www.aisc.org/ Information rich site

Telescoping Pipe and Tube

Please refer to Pipe, Tube and Conduit for more information.

Tube, pipe, EMT and bolt manufacturers haven't gotten together and helped us much when it comes to telescoping their products inside one another. This is a survey of only part of what is available, but covers the more readily obtainable materials.

OD=Out Diameter
ID=Inner Diameter

STEEL, ALUMINUM and PVC PIPE always have the same OD regardless of wall thickness/schedule.
PIPE has a larger OD than its RATED SIZE.
PIPE SCHEDULE /Skd. refers to wall thickness (5,10,20,40,80 and 160)
PVC pipe is also rated in pressure.
TUBE always has the same OD regardless of wall thickness. ID= OD minus 2 times the wall thickness.
Most Square Perforated Square Steel Tubing telescopes and come in many sizes.

NOTES
All EMT sizes are telescoping, but a bit sloppy. Two EMT compression couplings can be joined to make an adjustable telescoping fitting. A lathe is helpful, but a sander, a file and some work will make them join together. If you put shrink tube on the end of the smaller tube, the fit can be very good. Layers of tape can work also but can jam if it unravels. If you find a ready made coupling that telescopes, please let me know. I will share it.

PVC which is made with many different ID's, makes many possibilities to make sleeves.

1/2" PVC Skd. 80 (Nipples) With a lengthwise saw cut will slip into 3/4 EMT and fairly tight fit for a 1/2" bolt or threaded rod.

Paddle wood bits can be sanded down to EMT and pipe sizes for boring wood and plastic. Make sure they taper smaller away from the cutting tip like they are originally. You can spin them in an electric drill against a belt sander to make them smaller. Keep drilling test holes before you take off too much metal. NOTES
All EMT sizes are telescoping, but a bit sloppy. Two EMT compression couplings can be joined to make an adjustable telescoping fitting. A lathe is helpful, but a sander, a file and some work will make them join together. If you put shrink tube on the end of the smaller tube, the fit can be very good. Layers of tape can work also but can jam if it unravels. If you find a ready made coupling that telescopes, please let me know. I will share it.

PVC which is made with many different ID's, make possible many possibilities to make sleeves.

1/2" PVC Sked. 80 (Nipples) With a lengthwise saw cut will slip into 3/4 EMT and fairly tight fit for a 1/2" bolt or threaded rod.

Paddle wood bits can be sanded down to EMT and pipe sizes for boring wood and plastic. Make sure they taper smaller away from the cutting tip like they are originally. You can spin them in an electric drill against a belt sander to make them smaller. Keep drilling test holes before you take off too much metal. See Making Homemade Grip Equipment

Paddle bits to reduce: 3/4" for 1/2" EMT, 15/16" for 3/4" EMT, 1-1/2" for 1" EMT

3/8"-16 nuts can be pressed into 1/2" EMT and 1/2"-13 nuts can be pressed into 3/4"EMT. Space the two nuts apart for more stability. Hammer over end of EMT to retain nut at end of EMT. If you use left-hand threads you can make your own turnbuckles if you braze the nuts in place. Don't breathe the zinc fumes from the galvanized EMT or water pipe when welding or brazing.

Paddle bits to reduce: 3/4" for 1/2" EMT, 15/16" for 3/4" EMT, 1-1/2" for 1" EMT

Pipe, Tube and Conduit

Searching for pipe/tube/conduit can be frustrating and confusing. You may not know the right language and the sales person may not know what he has or what it is called. Here are some definitions. The terms should be tailored to the person that you are talking to. A hardware store clerk will not know as much as a industrial pipe and tube salesperson. When your request is passed to a production person, then to the supplier it can get garbled in transmission. Talk to the supplier yourself if possible.

Pipe



Water Pipe- Galvanized steel with threaded ends max. 21'. Sold according to it's INSIDE DIAMETER (ID). Many people don't understand diameter, but only read what's printed on the rack or the pipe itself. For example, 1-1/4' pipe has an OD (OUTSIDE DIAMETER) OF 1-5/8" and 1-1/2" pipe has a OD of 1-7/8". 1-1/2" pipe is often mistaken for 2" "pipe". Tube goes by OD.

Galvanized water pipe is available in most places except in the tropics. It's heavy, but will do if it is all that's available. On flat surfaces is makes good dolly track with or without ties. To join two lengths you need to cut the threads off and file the ridges flat. A pipe cutter will cut it square, but will leave a ridge that you can file off with a flat file. Cutting it square with a hacksaw is difficult. It can be screwed to ties with effort. Water pipe can be used for rigging with Speed Rail (c). If you are asked what schedule you want say "schedule 40". Don't confuse people if they don't ask.

Gas Pipe- Steel usually rough and tar coated, cheaper, but usually too rough for track.

E.M.T., Electrical Conduit (Thin Wall) is available except in the tropics. Cheap, galvanized, 10' lengths and sold by inside diameter. (A bit larger). 1" E.M.T. has an O.D. of 1.160". E.M.T. is very useful. It telescopes inside each progressive size. It can be bent smoothly with an E.M.T. bender. 1/2" and 3/4" is good for rigging and 1-1/4" and 1-1/2" is good for short dolly track. Take your track couplers and a rat-tail file to notch the ends. Ties will attach easily with metal screws. E.M.T. doesn't fit any Speed Rail (c) fittings.

Aluminum Electrical Conduit is OK for one time rigging, but is soft, comes with threaded ends and is only 10' long.

Rigid Steel Electrical Conduit is thinner than water pipe, cheaper, but comes in 10' lengths. It has threads and is the same size as water pipe and Speed Rail (c)

PVC Plastic Pipe / PVC Electrical Conduit is good for curved track screwed to a wood floor or plywood. Lay it flat on flat surfaces with no ties. 1" and larger are OK. Make sure your dolly truck wheels clear the floor. Smaller sizes are very available. Larger sizes can be found at irrigation suppliers. You can make couplers out of dowel and layers of tape.

Tube

Tube is an exact language. Tube is always referred to by OUTSIDE DIAMETER (OD) and WALL THICKNESS. ie 2" by .065" has a diameter of 2" (plus or minus .002") The ID will be 2" minus two times the wall thickness or 1.870" Most camera cars uses 2" tube and have their own special fittings.

For aluminum dolly track you must find an industrial pipe and tube supplier. They will know all about pipe and tube. Their catalogs will help you understand pipe and tube. Your price will reflect the amount you buy. Get together with other potential users for a better price. It is wise to anodize your pipe to prevent oxidation and hair loss from aluminum poisoning through your hands. File the sharp edges off a little to prevent injury, but not enough to cause a bump at joints.

Some types of anodizing will damage Speed Rail© fittings.

For Dexter dolly track, I suggest 1-1/2", 6061-T6, Schedule 40 aluminum pipe. 6061 is a weldable alloy and T-6 means it is hard. Do not buy 6063 T-3 hand railing pipe. Pipe comes in various schedules: 5, 10, 20, 40, 80 and 160. Schedule 40 is the most common and cheapest.

Fence Post-comes in pipe sizes, is lighter, cheaper, but weaker. Don't fly people or equipment with it. There are a few fence fittings that are useful, but much weaker than Speed Rail©.