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fitting first and second sections of masts CS17


acreew

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Are you saying the 2 sections are different sizes, but so close one does not fit into the other?  If they were the same size a splice could be done with a sleeve going inside both, though some homework into what would be strong enough would need be done.  All I can think of is a splice with a sleeve that has custom bushings to meet the inside of each section. 

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Hey Will, 

 

Sorry about the collars and the grinding. As you've discovered, the telescope sections of the CS 17 masts use a lower tube that is 2.5" OD with an 1/8" wall thickness and the next tube is 2.25" OD meaning that they are a slip fit. We make sure every CS 17 mast kit fits together before we send them out because of this. Due to manufacturing tolerances in the drawn tubes they are not all that round from a micrometers point of view and sometimes the sections fall right in and sometimes we have to increase the ID of the lower tube and then we mark that end as "top" for assembly. 

 

It's important to inrease the ID of the larger tube and NOT take material off the smaller tube because where the smaller tube joins the larger is the point of maximum bending moment on the smaller tube. If you sand down the small tube to fit you're just making a weak point weaker. The larger tube is much larger and stronger than necessary at that point on the mast so we always take material from the inside of it to make the two fit together. 

 

To increase the ID of the lower tube, the elbow grease method is to just use rough sandpaper on a dowel. Initially the sandpaper scratches actually REDUCE the ID so it's important to go back in with some 150 or 220 to smooth it back down for test fitting. A cylindrical flap wheel on a drill with an extension would work as well. 

 

We came up with using a cylinder hone but with the honing stones replaced with carbide scrapers that take off a good amount of material and speed up the process but it's still a chore and sometimes it chatters. 

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I used a small drum sander on a drill extension, standard Stanley stuff from the hardware store.  I used the coarsest grit, 60 if I remember, but maybe 80.   I chucked it in the electric drill, and the extension was long enough to allow me to get inside to the required depth.  I just kept grinding away, back and forth, in and out, turn the tube, grind some more, try to keep it even. It took probably an hour or more of grinding on each of the big tubes.  I did find that if I applied heat to the larger tube, it helped get it over the small tube and saved some grinding time.  The epoxy helped lube the joint some, too, I found, and what had seemed like a tight fit dry actually slid in more nicely once it was epoxied and I worked it around some to find the best lineup.  Of course, you have to make sure it will dry fit first.  But try the heat gun on the larger tube, since that may help reduce the amount of grinding needed.  I got my tubes "raw" from B&B before they were doing any work on them, so your grinding time may be less.

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