core alignment

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gozaimaas
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core alignment

Post by gozaimaas »

I have built 5 boards now and have used dowels to locate the core and veneer top sheet. Where my dowels are I end up with a small low spot in the base.
I realise the core/top sheet can be aligned using dowels outside the edges so the end up cut off with the flash but I am at a loss as to how I can align the base/core outside the edges.
Gluing an insert to the base is the same as what Im doing now so not really a viable option.
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falls
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Post by falls »

I fix my bases with edges on to the aluminium sheet with spray adhesive (aluminium sheet has material centre marked also). Mark material centre on the edges when affixing them to the base using material centre mark on template. Then sit the core, which has material centre marked on it, on the edged base. I then glue with superglue a wood block (4 per ski) on either side of the core forward and back of the material centre. I use a 1/2mm thick washer in between the core and wood block to account for wetted out fibreglass thickness that gets draped over. During layup just wet the core out and make sure material centre on the core matches that marked on the cassette when you lay it on the lower glass layer. The wood blocks hold the core in the correct position laterally (the edge rebate also helps with this).
The alternative that others do is glue the blocks to the side of their core with a dowel hole drilled in them. then lay the core on the edged bases and place a dowel through the hole with superglue on its end so it sticks to the cassette. in layup you just slide the core down onto the dowels.

The benefit of my system if you are always building the same shapes is that if you use the same core template every time then you can replace the wood blocks with aluminium blocks (mold release coated) riveted to the aluminium and the core just goes in every time.

My system of registration is based on material centre (ie. centre of material length when flat). I use this for all stages and mark all templates and materials with material centre. (some people use boot centre instead). My cores have a centre line marked lengthwise and material centre line marked before I start shaping them with my templates. I then use these lines to place the core on my planer crib correctly (side to side and end to end). The lines remain then for lining up with the other materials during layup.
My base template has material centre and centre line marked too. When I route the base I then attach the edges and mark material centre on the top of the edges from the mark on the template. I also mark the centre line on the tip of the ptex for correct allignment on the aluminium cassette.

The only real failing with aligning the core is that I rely really on the L and R side material centre marks being in the correct position and I don't have a centre line marked on the ptex to make sure my core centre line is in line with the long axis of the ptex. However, I feel that with my templates I know the core is symmetrical and with the rebate for the edges the core sits pretty much correctly side to side and once you have the material centre marks lined up you can just eyeball the L to R placement.

I use one side of my aluminium sheet as a straight edge to reference all positioning from then mark lines with squares. On this side I rivet on 2 pieces of 90 degree aluminium angle either side of material centre on the lower side of the cassette. When I slide the cassette in these angle pieces sit against the side of the mold so I know my marks on the aluminium sheet are all square to the mould and all my lines run either perpendicular to or linearly along the mold. End result when materials are set down properly on these lines then they are also correctly aligned to the mold.

Sorry if a lot of this is preaching to the choir, but it seems an answer to your question. Although not 100% clear on what you are asking.

Edged base and wood blocks
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Wood blocks
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Wood blocks
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gozaimaas
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Post by gozaimaas »

Thanks for the awesome reply mate.
I dont do my lay up on the mold as I find its easier on a flat bench. I then transfer the entire lay up over to the mold. This method means I cant glue the base down.
I might try gluing a tab to the side of the steel edge that I can glue a dowel to and see if I can make that work
sammer
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Post by sammer »

gozaimaas wrote:Thanks for the awesome reply mate.
I dont do my lay up on the mold as I find its easier on a flat bench. I then transfer the entire lay up over to the mold. This method means I cant glue the base down.
I might try gluing a tab to the side of the steel edge that I can glue a dowel to and see if I can make that work
So let me get this straight....
You pick up the whole gooey mess then try to position it in your mold?
Sounds like an invitation to disaster.
How do you locate in your mold?
How do you avoid air pockets, etc.
I just can't imagine trying to pick up a fresh wet layup and moving it from point a>b.

sam
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gozaimaas
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Post by gozaimaas »

Yeah I do.
I have some strategically positioned screws in my mold that I push the steel edge into which ensures alignment of the whole thing. Its quite easy actually, much easier than having the core bounce around due to the fact that it wont conform to the shape of the molds and then hope it aligns with the dowels when I pressurize the hoses.
gozaimaas
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Post by gozaimaas »

I dont use tip fill. I use a full length wood core with a poured urethane sidewall/tip fill so if I lay my core on the mold it sits up by a few inches.
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vinman
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Post by vinman »

I hot glue MDF scrap blocks to my alu sheets for core stability. I use spray adhesive to stick the base to the alu sheet. I also lay up on a flat bench then slide my cassette into the mold.

The adhesive works fine for Keeping the bases in place. To align the cassette in the mold I just use some marks on the mold and on the cassette. To date after 19 pair, I've not had any cores shift with this method.
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JSquare
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Post by JSquare »

Goz-

I did a pretty heavy search on this last week. I switched to the guide block method recently after doing some reading and wrestling with issues with my base from using the guide insert method.

Here are the threads (now they can be linked in one place!)

viewtopic.php?t=73&highlight=core+alignment+methods (basic overview thread)

viewtopic.php?t=2310&highlight=core+locating (wooden alignment pins as guides)

viewtopic.php?t=825&highlight=core+locating (standoffs from mcmaster as guide pins instead of inserts--- as well as good explanations of other methods)

viewtopic.php?t=1806&highlight=core+locating (guide block method)
gozaimaas
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Post by gozaimaas »

Cheers JS
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skimann20
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Post by skimann20 »

hey Falls, how do you get the wood blocks to stick with mold release agent on your cassettes?
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falls
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Post by falls »

Just superglue. It seems to stick despite the mold release.
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skidesmond
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Post by skidesmond »

I realize this is an old thread and I think this method is one of the best approaches to keep the core in place.

I tried a new approach the other day that works very well and it gives folks another option.

First part of the process is the make sure you have center lines on everything (base, core, and cassette). This makes placing the materials easy and straight forward on to the cassette.

Instead of using wood blocks, I use medipore tape on the wood core and taped it to the cassette once I have everything in it's proper place. I don't tape across the full width of the core but you could. Epoxy will penetrate the tape. Make sure the tape is secure to the wood core on the top, side of the core and to the cassette so it doesn't move. I use medipore tape to attach the tip/tail spacers. I haven't had any issues with it.
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