How would you do this?

[Roger Long]

As discussed in earlier threads I'm replacing these tangs with a different design:

Here is the crazy way the mast was originally set up.

There was a hole for a compression tube but no tube. The through bolt bushings were bearing entirely on the S.S. spreader mount so all of the strain of the lower shrouds was being carried by the rivets.

I can't insert a compression tube taped to the end of a stick as is often done unless I totally un-wire the mast and remove all fittings. Even if I could, the tube would bear on the aluminum walls and the space between the spreader mount would let the wall deform and crack under heavy load and bolt tension. Not good.

I need to put the tube in like this with the ends shaped to bear against the S.S. It is both an angled and curved surface.

I've drilled out the rivets and removed one mount and can do the other. What now? There has got to be a better way than trial and fit of something I can't see. A tiny bit of over filing and I'll have to go back to Rig Rite for another $40 compression tube (couldn't find this size at the usual sources).

Any ideas?

(I already know how I'm going to do it but the mental exercise was so much fun I thought I'd give you folks a chance to experience it.)

 

[DannyS]

Mock it up

Could you remove the other mount, dust off your calipers (what am I saying and who am I talking to? I'm sure your calipers get polished every time they go back into their mohogany and satin lined storage box) and build yourself an open faced mock up so you can see what you are trying to fit?

 

[Witzend]

Well you know the width, setup a jig so you can carefully inspect as you file.

 

[All U Get]

As discussed in earlier threads I'm replacing these tangs with a different design:

Here is the crazy way the mast was originally set up.

There was a hole for a compression tube but no tube. The through bolt bushings were bearing entirely on the S.S. spreader mount so all of the strain of the lower shrouds was being carried by the rivets.

I can't insert a compression tube taped to the end of a stick as is often done unless I totally un-wire the mast and remove all fittings. Even if I could, the tube would bear on the aluminum walls and the space between the spreader mount would let the wall deform and crack under heavy load and bolt tension. Not good.

I need to put the tube in like this with the ends shaped to bear against the S.S. It is both an angled and curved surface.

I've drilled out the rivets and removed one mount and can do the other. What now? There has got to be a better way than trial and fit of something I can't see. A tiny bit of over filing and I'll have to go back to Rig Rite for another $40 compression tube (couldn't find this size at the usual sources).

Any ideas?

(I already know how I'm going to do it but the mental exercise was so much fun I thought I'd give you folks a chance to experience it.)

Hi Roger,
My backhoe has bushings and a pin with external snap rings for every ram. Your picture and drawings are kinda the same. These can take considerable force. Here's a picture, ignore the wrench. I can get you a better picture if you want.
All U Get

 

[MSter]

Roger,
Just a wide !@# guess from a rookie.
The mast OD mirrors the ID, If you hand prepare the compression tube to fit the mast OD and turn it 180 degrees it should then match the mast ID profile.
I guess then you'll have to fish the tube from the closest opening ( mast top ? ) to the spreader location and finesse it into place.
Mster

 

[kloudie1]

Pour wax into the spreader plate.. remove the wax mold when cool.. then slightly warm the tube and push through the wax.. carefully mark the tube... grind off the tip above the mark..??
I dunno..

 

[alexco38]

Why don't you use modern T-terminal

Most modern mast rigging use T-Terminal and leave the spreader tube alone. You can buy the SS plate or fabricate one to go on the mast.

 

[Roger Long]

When I reveal the answer, you folks are going to find out why I get the big bucks.

 

[woodster]

do they make ss hillside washers if so i might try useing them ....

regards

woody

 

[All U Get]

Drill the hole large enough for the bushing to go through. Push it out the other side and mark both ends with a marker. Take it to the bandsaw and cut it.
All U Get

 

[Roger Long]

Take it to the bandsaw and cut it.

It's got to fit very tightly so that the through bolt can be tightened up without distorting anything. The inside of the S.S. spreader mount is angled and curved. This has got to be done to very close tolerances.

 

[kenn]

In the above image, what are the thingies going into the holes on either side? If they were bushings and the bolt goes through, then that's all you'd need. Or, if you're upsizing, obtain or make the right-size flanged bushings for the new bolt. They only have to be long enough to bear on the ss and aluminum.

I don't see a need for a full tube taking the compression of the bolt; whether there's a tube or not, any lateral pull on one side get's borne by the mast wall on the other side anyway, tube or not. I would simply have the bolt reasonably tight without crushing the mast, and lock it (2nd nut, or loctite)

That's my initial impression, anyway.

 

[Roger Long]

In the above image, what are the thingies going into the holes on either side?

They are bushings for the through bolt. See here for the complete details:

http://www.facebook.com/album.php?aid=52981&id=1846284215

There actually is some significant compression here. The windward tang pulls on the head of the through bolt. There is nothing to hold that side to the mast so the load is transferred through to the leeward side. The bolt head on the leeward nut is actually holding up the mast. Meanwhile, the windward spreader is in compression from the upper shroud tension. At the knockdown design condition, there is about half a ton of force squeezing the mast walls together on my boat without even considering bolt pre-stress.

BTW I've designed a fair number of rigs, mostly for large sailing vessels. I also did the computer rigging structural analysis for the USCG certification of the Surprise in "Master and Commander" when she was a school ship.

 

[Witzend]

Make the compression tube out of plastic ..pvc...first by cutting it just a bit long and shaping one end to fit perfectly against the mount you have already removed. Insert it and apply some heat to melt the plastic as you turn the bolt down on the other end. Let cool, remove the squeezed out plastic with a knife and now you have a perfect model of what you need to make.

 

[MSter]

Roger,
After a second look at the diagram I see the compression tube does not support the mast wall, but butts up against the curved piece which must be part of the spreader base. ( ? )
That would suggest the tube can be inserted through the oversized opening in the mast.
If I'm correct then it's the profile of the ID of the spreader base you need to match not the Mast wall ID I originally assumed.
Sorry, I don't have access to Facebook, don't want to intrude on my kids !
Mster

 

[Sailm8]

Put back the original fittings. LOL

 

[LloydB]

"I've drilled out the rivets and removed one mount and can do the other. What now? There has got to be a better way than trial and fit of something I can't see"
I'm not sure I understand your problem as your rigging is now half apart with both front and back side of one spreader base in your hand to allow scribe fit both ends of the new compression tube.

 

[Ed Schenck]

If I understand the before and after drawings all forces are on the stainless plates. In the original state the bushing is loaded on the windward plate and trying to compress the mast. But that is spread over the size of the plate on some pretty heavy aluminum.

In your "after drawing" the new tube will distribute some of that load to the other stainless plate. But I guess your question is how to design that tube for an exact fit. The measuring of length and cutting of that angle just doesn't look that hard to me. As usual I am missing something.

 

[Witzend]

A better idea:
Why does the compression tube need to be one piece? Make each halve carefully fit to the mount you have already removed (assuming that they are both the same), but make them slightly longer than half. Now in order to make adjustments trim one of the halfs where it meets the other. That would be an easy square cut (or grind for finer adjustments against a wheel) to make a perfect fit.

 

[Roger Long]

Make each halve carefully fit to the mount you have already removed (assuming that they are both the same), but make them slightly longer than half.

That's not a half bad idea although I would have to add something in the middle to keep the ends aligned. My way is easier though. It's making me feel rather clever that no one has thought of it.