Cranse Iron mold needed

[Woodonwater]

I need to find a mold (or a finished one to buy) of a cranse iron for my bow sprit. It would be 3 1/2" I.D. at the aft end and perhaps 3 1/4" I.D. at the fore. It would be around 4 to 5" long, with four tangs for forestay, bobstay and sides.

I have a foundry which can cast it, but I need the mold(s).

Anyone have one?

Thanks,
James

[Bob Cleek]

Davey and Co. has them ready made. So does Toplicht. If galvanised works for you, it is an easy task to weld one up on a section of iron pipe or strap and have it hot dipped.

[StevenBauer]

It's the pattern you need, the mold would be made as needed and wouldn't be reused. You could make the pattern yourself or have it made. Places like Lunenburg Foundry or Port Townsend Foundry have thousands of patterns on 'file'.

www.porttownsendfoundry.com/id51.htm

[John B]

Yeah, make the pattern. .A mate made one for little Thelma by using filler on a tin can. I'd go looking for a piece of plumbing as Brian says. EG I have a plastic connector flange thing for gutter downpipes on my desk very close to that size . Four mdf/ timber tabs and some micro spheres to build it up and voila.

[PeterSibley]

James , it is a very easy pattern to make ,should you so choose .Just replicate the cranze iron you require but a small percentage larger.........to allow for the shrinkage of the metal as it cools from the molten state .Your foundry will give you that percentage figure , probably 3% . Just make sure your pattern is absolutely smooth and preferably painted or varnished .

[StevenBauer]

Have you read Moray from Classic Marine's take?:


http://www.classicmarine.co.uk/Articles/Bowsprits.PDF




Steven

[kc8pql]

Mine came from Toplicht. It's size is very close to what you're looking for and is very nicely cast. Even with the current exchange rate and postage it may be less expensive than making a pattern and having one cast. Worth checking anyway.
http://www.toplicht.de/product/l10839

http://www.toplicht.de/jpeg/1412050.JPG

[Woodonwater]

I was looking over the patterns they had at the Spaulding Boat Center in Sausalito and there seemed to be a separate interior pattern as well? The taper is the tricky part, right?

[kc8pql]

The pattern is "Free".. couldn't take more than an hour to make.


I can tell you never made a pattern.:rolleyes:

[PeterSibley]

I was looking over the patterns they had at the Spaulding Boat Center in Sausalito and there seemed to be a separate interior pattern as well? The taper is the tricky part, right?

If the inner has a taper more than about 4 degrees the foundryman should be able to withdraw it from the sand .If less than that or parallel you would need a core box( thats the other pattern you saw ).A core box is a mould the shape of the internal space ,the foundryman will fill it with a chemically bonded sand and use the piece produced inside the fitting ...a bit like the bowsprit .Horrible description but it's late .As to Brian's estimate of time ...yes , I might cut the inner taper out on my bandsaw after turning the outside, if I had a new blade and a steady hand .It would be quick and not very dirty .I have some long round drum sanders that would clean up the inside quickly enough .

Some of the old WB mag had articles on patternmaking that have PICTURES !! I strongly recommend them !:).

In your case I would not worry about a core box , make the interior with 4 degree taper and expect the foundryman to know his trade .Make it really beautifully smooth though , like your best varnish .

[kc8pql]

Go to the foundryman, show him a drawing or picture of the part and ask him exactly what he wants. I would also suggest that you add fillets where the tangs meet the body. Note the photo above. Sharp inside corners create stress risers that can cause the casting to crack. Make it pretty. It's one of the most prominent fittings on the boat. In most marinas bowsprits are novel enough to draw a lot of lookers.

[Tylerdurden]

PVC and ABS patterns are slick and easy to make. Could be a fun project. No specialty tools are needed and you can use you wifes hair dryer for forming to boot.

[Woodonwater]

You gotta be kidding...and this is the "Fancy" method...

I would never joke about something so serious...:)

1) Cut ABS pipe and chuck up in lathe, face end, cut taper, cut off part
20 minutes

OK smarty, my friend's lathe, an old Shopsmith likely can't fit a 4" pipe in the chuck can it? Also, is the wall thickness sufficient to be able to remove enough of it to get a taper? I am assuming the outside dia. will be a continuous 3 3/4" or 4". Perhaps only a 1/8" taper in 4 1/2" of length is sufficient with a minimum wall thickness of 1/4"? I don't recall off the shelf pipe to have this wall thickness. Am I still missing something here?


2) Trace flanges on ABS flatstock, bandsaw out shape, sand to smooth off saw marks, and bore and chamfer holes.

Sounds pretty straight forward. I suppose the big orange box might have this flatstock?

3) Take out yer pot of glue, no sniffin allowed, assemble.

What's a few sniffs among friends. geez.

4) Mix up 5minute epoxy, add microballoons to suit, fillet flanges.

Random Sanding.. DONE in 1 hour.

Ya know, in the time it will take to get me up to speed on this, you could be done and have it in the mail to me :)

[Tylerdurden]

If you have the form it fits on just cut a pvc pipe down one side slide it on and heat it with a heat gun. Once that shape is set you can finish it anyway you see fit. If you can heat weld on the split to help maintain the shape after it sets.

If you know someone with a pvc heat blanket you can roll out a soft sheet too.

[John B]

Thats a good idea.perfect fit/ taper matched to the spar.
If you can't weld it just glue it with the epoxy, maybe a narrow strip of glass, you're going to build it up with some balloons anyway. The flat stock can be anything... plastic is nice but ply or mdf would be fine.

Another way if you had the correct max ID pipe ,would be to take the pipe to the spar and using some food wrap on the spar end, bed the pipe in micro spheres/ balloons. Let it 3/4 set and knock it off.

[John Boone]

Afternoon James,

Do you have the original iron that you are replacing? If so, it might help to post a photo (I'll be happy to do that for you if you send me one). I looked at the previous photos you have sent but don't see the bowsprit and fitting in any of them.

If you have an old fitting it might be useful to take it to one of the foundries or send it to them and ask if they might have an existing pattern that will work for you.

Given your CAD skills have you taken the time to make a drawing that could be worked from ?

Just a thought.

John

[Tylerdurden]

Thats a good idea.perfect fit/ taper matched to the spar.
If you can't weld it just glue it with the epoxy, maybe a narrow strip of glass, you're going to build it up with some balloons anyway. The flat stock can be anything... plastic is nice but ply or mdf would be fine.

Another way if you had the correct max ID pipe ,would be to take the pipe to the spar and using some food wrap on the spar end, bed the pipe in micro spheres/ balloons. Let it 3/4 set and knock it off.

Once you have worked with PVC stock you will never go back.
Its faster than anything else and it looks good when done right.

[John B]

Glue it up with plastic gutter/downpipe cement too.;) I suppose you could use that.
I repaired a boat head with that. Stress crack in an elbow that required the whole pump body to be replaced, or repaired.

[Tylerdurden]

The plastic rod welders are cheap but yeah i would use PVC cement in a pinch. Scribe and buff the glue joints and use an acid brush instead of the big ball. The smoother the pattern the nicer it will look especially if you cast lost wax.

[Woodonwater]

John,
The one I am replacing is a straight mast band, galvy, and badly corroded. Not going to work, but thanks. I could CAD it all up, but I'd rather just fabricate it. This sounds like fun, and it really is a piece of jewelry that many people see. I'll paint the sprit tip white and put a bronze star in the middle of the end. It will be a thing of beauty!

I like the idea of splitting a pipe and sleeving it onto a tapered shape. My sprit end is not yet tapered, however. My boatwright wants to shape the sprit to fit exactly with the cranse iron I provide. I guess I could have him taper it anyway because the cast shape will apparently shrink slightly upon cooling, and then he or I can simply remove a little bit more wood if need be.

I assume we will do a lost wax casting. Is there another option? I have an old bronze drive shaft that I was planning to use/melt down. I assume this alloy will be strong enough...?

Thanks for all the input

[Thorne]

Sounds like you are having a lot of fun with the whole casting bit, but of course you do have the option to buy one new or used.

And you need not look for hardware just identified as a cranse iron, as apparently a heavy mast band is nearly identical in many ways -- see this thread:
http://www.woodenboat.com/forum/showthread.php?t=75461&highlight=cranse+iron+mast+band

[PeterSibley]

John,


I assume we will do a lost wax casting. Is there another option? I have an old bronze drive shaft that I was planning to use/melt down. I assume this alloy will be strong enough...?



He will use sand , either chemically bonded ,oil bonded or greensand .

I'll have to have a look at all this PVC stuff , I'm rather old fashioned with my patternmaking !:)

[Tylerdurden]

He will use sand , either chemically bonded ,oil bonded or greensand .

I'll have to have a look at all this PVC stuff , I'm rather old fashioned with my patternmaking !:)

I do a lot of off the wall projects or more like I used to. For quick patterns for machine type parts on/off or several, PVC works well.
I have used ABS too with good luck. If I was to reuse a pattern or planned to make more than a few wood is best.
I have done patterns in wax like the jewelry process but that is strictly one shot so if you blow a pour you are screwed.http://www.woodenboat.com/forum/images/icons/icon11.gif

[kc8pql]

I assume we will do a lost wax casting.
If it is lost wax (unlikely unless it's an art bronze foundry) you would be better off sculpting the pattern directly in wax. That would eliminate the need to make a rubber piece mold of your mock-up to pour the wax pattern but, as mentioned above, you only get one shot at it. Again , I urge you to talk to your foundry.

[Jim Ledger]

I've been reading up on bronze casting and patternmaking recently, trying to see if it's feasible to cast my own hardware.

Looking at that iron that KC8 posted I don't see how it could be cast without using a split pattern with a core. Split along two opposite flanges, half in the cope and half in the drag.

You all make it seem so simple, but I don't see how you could withdraw a one piece mold from the sand.

[kc8pql]

Looking at that iron that KC8 posted I don't see how it could be cast without using a split pattern with a core. Split along two opposite flanges, half in the cope and half in the drag.

Me either. A mock-up, which is what everyone is suggesting, won't work. You won't be able to withdraw it from the sand. It's going to take a split pattern and core. Also, the holes in the tangs have to be drilled after casting. There's no way to get the cores in to cast them in place.

[paladin]

I could send you the drawings that I made for my 44 footer, which are virtually identical with your requirements, but you would still have to make mold.......I made mine from wood, sanded, filled, varnished.......and I got the piece back finished even better. Mine is tapered to make a compression fit on the end of the sprit........and if you put a star on the end of the sprit...don't have it gold plated...someone will steal it for sure and bugger up the end of the pole.......if you want a copy of the drawings, send e-mail request...

[kc8pql]

Just to help explain what Ledger and I are talking about, these are the split patterns for my rudder fittings. The patterns are split down the centerline. Half goes in the drag and half in the cope. Small dowels locate the two halves. The draft angles taper from the center to the edge of each half so the can be withdrawn from the sand without breaking down the impression. I wouldn't have thought that these shapes would have needed to be split, except for the lower cranked fitting,but that's what the foundry wanted. It may have had to do with the size. The pattern on the right shows the two halves apart with the locater pins.

http://i28.tinypic.com/s13tjl.jpg

These are the finished parts. The straps are 3" wide, 3/8" thick about 18" long. Pins are 1" dia. Take the time to make nice smooth patterns. It will save you hours in finishing time.

http://i26.tinypic.com/2u6mvkw.jpg

[Jim Ledger]

Beautiful work, KC. No matter how many quick and dirty tricks there may be it's always most instructive, in the beginning, to see a carefully thought out and executed sample of the work.

So the pivot holes were drilled later? And it looks like the pins are turned. Are they permanently fixed to one half? Were you able to drill out the pivot holes or did you have a machine shop do it?

[kc8pql]

Beautiful work, KC. No matter how many quick and dirty tricks there may be it's always most instructive, in the beginning, to see a carefully thought out and executed sample of the work.

So the pivot holes were drilled later? And it looks like the pins are turned. Are they permanently fixed to one half? Were you able to drill out the pivot holes or did you have a machine shop do it?

Thanks Jim. No the pivot holes were cast in. In the photos you can see a small hole for a locater pin where the center of the holes would be. A 1/2" length of <1" dowel was attached there on both halves of the pattern to form pockets in the sand to accept the cores when the cope and drag are put together. The foundry then drilled the holes out to the finished dimension. The pins are loose at the suggestion of Pete at Port Townsend Foundry and were cast from patterns he already had. They make hanging a big heavy rudder like mine much easier to do. You don't have to drop 200 lbs. of rudder down on three pins all at once.

[PeterSibley]

I do a lot of off the wall projects or more like I used to. For quick patterns for machine type parts on/off or several, PVC works well.
I have used ABS too with good luck. If I was to reuse a pattern or planned to make more than a few wood is best.
I have done patterns in wax like the jewelry process but that is strictly one shot so if you blow a pour you are screwed.http://www.woodenboat.com/forum/images/icons/icon11.gif

If you want more ,cast the wax in that lovely blue mould making silicon first (with a feed etc attached) ....then you can make as many as you want .

The only time I've used acrylic sheet lately was to make up patterns for a few 2 and 3 sheave block frames ,big ones for a 65 footer .To get the frame legs perfectly straight, true and parallel ,(and with no draft ) I made up a pattern with a solid block of sodium silicate sand with sections of acrylic ( about 45mmx 8mm x200mm ) set up parallel inside .After the sand had gone off ,I withdrew the acrylic .The result was excellent ! :) Smooth ,fair and accurate .