Flanged Bushings
 

Although I have a rough idea of what a "flanged bushing", looks like, I need confirmation from our moderators or forum members, on the specs, and descriptions of what a flanged bushing looks like, or even how it would be best, installed on a mast.

If you were installing a flanged bushing on an aluminum mast, what metal alloy should the bushing be made of ?

What is the best way to attach a flanged bushing to the mast, or is it necessary to attach it at all ?

If the bushing was to spread the load of a 5/8" through the mast bolt, for hanging shroud tangs on,,,,, just what would be the size of the hole, you would drill in the mast to receive the bushing ?

I guess that would be the same as asking, what are the dimentions, OD and ID of the bush and the flange dimentions ??? ,,,, and what about the insertion depth, and thickness of the flange itself ???

I suspect that a through the mast bolt would benifit significently, if it's down load was spread with a larger than the bolt, diameter bushing surrounding it .

Also, if the mast through bolt is ss , would an aluminum bushing be appropriate, or would a ss bushing be more desireable ???


Douglas

size matters
 

There is a little more to a bushing than just making the hole smaller...the major consideration is if the bushing can handle the load without deformation.
Three things come into play: Load (P) in psi, velocity(V) and load at velocity (PV). ergo:
P=bearing load/shaft dia x bearing length
V=shaft velocity x 0.262 constant x shaft dia
PV= P x V

Use the PV as a final check to ensure that the bearing can sustain the combined load and velocity requirements.

In all but the most extreme cases you will want to use Alloy 954 Bronze or SAE 841 Bronze-also called Oilite.

Hi Tom,
I believe Douglas is inquiring about a static bushing. Something to spread the load or compensate for a corroded area or spread a vibration load area, etc..

Regards, Russ

tube?
 

Hi Douglas,

If it's simple like a shroud tang or spreader base I suggest you consider a compression tube. Much easier to make and prevents overtightening. Simple S/S pipe has worked for me in the past.
If you require load spreading, consider aluminum doubler plates fastened permenantly and the compression tube.
If the bushing can stay put (not usually removed) I would go with S/S same as the bolt and TefGel the bolt to make the bolt much easier to remove years later.

Regards, Russ

Second that:

Russ L said
"If it's simple like a shroud tang or spreader base I suggest you consider a compression tube. Much easier to make and prevents overtightening. Simple S/S pipe has worked for me in the past.
If you require load spreading, consider aluminum doubler plates fastened permenantly and the compression tube.
If the bushing can stay put (not usually removed) I would go with S/S same as the bolt and TefGel the bolt to make the bolt much easier to remove years later. "

plates fastened with machine screws :)

Do you have a Kenyon Spar Douglas ?

Forespar Mast
 

Hi sailors, I have a Forespar mast,,, it has many welded on fittings,,,, in particular, on this subject, the mast has 1/4" thick X 2" OD aluminum washers welded all around,,,, attached to the outside, mast wall sides as "doublers" thus thickening the mast wall which a tang through bolt, goes through with a "thin" wall aluminum compression tube in which is the ss through tang bolt, passes through.

These 1/4" X 2" aluminum washer-doublers has some advantages and some disadvantages too.

We would have to consult with a naval engineering architect to find the load tolerances that Tom P , refered to , but just ball parking , I was hoping to find a way to use flanged aluminum bushings instead of copying the Forespar system of welding on doublers .

Brion has pointed out previously that a compression tube is not needed, if the through bolt nut bottoms out during tightening, before compressing the sides of the mast . This I have carefully done .

I think it was Brian that clued me in , that the flanged bushings do not need to be screwed , rivited, welded, or even attached to the mast wall in any way .

I think what we are trying to do is, spread the down loading through bolt loads, onto a bigger diameter bushing,,, so that the tang through bolt doesn't "sea-saw" an elicpital hole in the mast wall, during use.

I have been trying to guess what size through the mast hole would provide an adequate bushing bearing surface for say a 1/2" and or a 5/8" ss through tang bolt.

If I was machineing a stepped flange, I just may guess that an aluminum bushing of 1" OD , with an 1/2" or 5/8" ID ,,,, might be sufficient for the small end of the stepped flange, where as, a 1/4" thick X 2" OD might be acceptable for the large end of the flange,,,,, yes ,,, you say ,,, but what about the plunge depth through the mast wall ? How about 5/16" on that shoulder ?

Currently, I have great problems trying to communicate instructions to the welders here,,,,, seems that multi lingual welders are not available,,,,, sooo I am trying to build a mast with a bare minimum of any welding on it,,,, thus using the stepped bushing idea, instead of welding on doublers.

You ought to see the trouble I am having with my shieve box !!!!!!!!!!

Thank You Guys , for your help and patience,,,, counting to ten has helped me .

Douglas

Hi there,
I believe this wheel has already been invented. I'll be in touch with Douglas by PM with scantlings and sources. Meanwhile for general info the flanged bushings we use come in both stainless and aluminum. The aluminum ones are larger, and sit in the mast wall. The stainless ones nest in them, after going through their tangs. So the flange of the aluminum bushing holds the tang off the mast wall (good), while recruiting more aluminum molecules for the shroud load to bear on.
With sufficiently thick mast walls (a judgement call), one can use just the stainless bushings.
In cases where there's a combination of high loads and thin walls, a third component is an option: an insert, fastened above and below the tang hole, into which the bushings fit. All of these options distribute the load over more aluminum than even a very large throughbolt could hope to, and without the bother, potential deformation, or potential fatigue of welding doublers on.
We often retrofit bushings, and sometimes inserts, to older masts, where egg-shaped holes indicate the walls are not up to the loads.All you need is a tapered reamer, to get the hole big enough. If you don't have access to a tapered reamer, you can plug the hole with wood, then use a regular drill bit to enlarge the hole.
Because the stainless bushings go through the tang, the tang must be proportioned to have an unusually large hole for the throughbolt, so don't try retrofitting bushings to standard tangs. On the other hand, with the bushings, one can use an unusually small throughbolt, because you are counting on it only for the relatively minor lateral load; the bushings are taking the shear load.
We also use flanged bushings to fix point-loading issues on chainplates and tang clevis pin holes, in cases where they are sufficiently overbuilt to allow for limited reaming.

Fair leads,
Brion Toss

with respect
 

there is no such thing as a "static" bushing. By their very design, the bushing is subject to velocity vectors. Albeit miniscule, the velocity must be taken into consideration, for it is the velocity that amplifies the loads.

oh my
 

Hi Tom,

I did not intend to offend your comment, but when you specified an Oilite bronze bushing I assumed you were refering to rotating applications.
My comment intention was to reassure Douglas that he need not try to translate Oilite bronze specs to the mechanics in Singapore.
In my limited experience I believe the bronze bushing is best suited to running rigging aspects.
The velocity component is easily accounted for in the normal safety factor consideration of any standing rig arrangement, (and can therefore be ignored) for practical purposes. The safety factor itself can vary large and is a good start to a whole new thread.
Maybe even a Puzzler subject.

Kindest regards, Russ

So would something like this http://www.mcmaster.com/#2934t11 be appropriate? The bushing will be seated in a Gibb T-ball backing plate, and I'll be hanging standard tangs from it. All held in place with a 1/2" through bolt.