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Saddle trees and changing back shape
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David Genadek
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 Posted: Tue May 25th, 2010 03:47 pm
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Adam,

    Alright some of the terminology is starting to make sense.  I'm starting to get a sense of what I'm doing. I don't understand how to know how much resin to use relative to the glass though.  I have three different resins here, one is very thin which is what the epoxy company recomended. The company I got my fabric sent me sample of two other resins that are more viscus. Originally I was told to use the least viscus to soak the wood and let it dry then add another coat with the glass but your suggestion of that creating a mechanical bond made sense so I'm going to try it all at once and see how that lay up works. 

     I'm trying a several fabrics in varying wieghts. The finer fabric seems to confom the  contours of the tree better. Does thicker = stronger?

     At the stage your at now you need to think attachments.  The attachments you plan to use will dictate your thickness in the areas where you will have an attachment.  This is some thing tree makers often neglect so when the saddle maker goes to put the saddle together he has to bend nails as he pounds and cut screws shorter.

David Genadek  

 

AdamTill
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 Posted: Tue May 25th, 2010 05:00 pm
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Hi David,

Epoxies are like leather - there are different "grades" and "curing methods" to suit different purposes. The broad categories to start with are laminating resins and structural resins, and the names are as you think they might be. There are some speciality resins (tooling resins for mold surfaces etc), but they tend to be much less common.

Laminating resins are intended for use in composites, and tend to be quite thin/non-viscous. They're intended to wet out fabrics, for the most part. Normally the only additive that's used on them is a pigment  - I have a few colours that I can use for aircraft fuselages, or the graphite mold additive that I used here is another popular one. The only other one that I know of that's used on occassion is aluminum powder, which gives a tougher finish at some cost in weight and sandability.
 
There are different cure times and strengths for resins, which can be tailored to purpose. I use a mid-grade resin with a slow hardener, so that when I', working on a hot day there's enough cure time. The other thing it helps is when I'm squeegeeing off resin in a lamination, it slows the hardening, so that working the resin doesn't cause it to kick off (also helps to avoid kicking off the resin in the mixing pot, which can cause fires).

One neat thing about higher quality resins is that you can sometimes UV-cure them dramtically quicker then standard quoted times - this might come in handy in a production situation. Where I might pesimistically keep my West System resin under vacuum for 24 hours, MGS resin in a UV/heat box can develop a fully cured part (AT FULL STRENGTH) in an hour. This seems to violate the rule that the quicker an epoxy cures, the weaker it will be, but the fancier resins are designed to accomplish this.

Structural resins are more for bonding components, tend to cure a little quicker, but are often more expensive per volume. There are lots of neat additives to use with these, depending on the joint type. My favorites are glass microspheres for bonding weight-senstive components or to make sanding easier, and milled glass fibre as a vicosity builder (to avoid having the glue run) and strength additive.

In terms of getting the resin component correctly, the worst thing you can do is to end up with a dry spot in a layup, where the glass is visibly white or starved. The second worst thing is to float the cloth in gallons of resin, since it results in a weak, brittle part. Just split the difference and you'll be fine :).

Seriously though, there's only so much you can do without getting really paranoid. If I'm laying up in a mold, then I generally wet the cloth out on an MDF board that I scrape clean before and after a project (easier to clean the loose strings up with a paper towel when wet then with a chisel when dry). Then I drizzle on a thin dolop of resin, and use an old credit card to spread it around. Any excess goes back into the pot. I use enough pressure that I'm really getting out the excess, but no so much so as to dry the glass out or distort the weave excessively. If I'm being dilligent/paranoid, then I might blot the cloth with paper towel, and then lay in into the mold. If I'm working on a wooden part, then the only other step is to rub a quick skim coat of resin over the wood, so the wood doesn't suck resin out of the first layer of cloth and result in a dry layup.

If your resin is too thick, then heat will sometimes work to thin it out, but will dramatically reduce the working time before curing. Xylene works okay as a thinner, as does denatured alcohol, but both will slightly reduce the final cure strength.

On the glass front, generally thicker/heavier = stronger, though only to a point. On the thicker cloth grades, especially on plain weaves, the kinks as the fabric weaves in and out can actually weaker the finished cloth. For our purposes, that's probably more detail then we need to worry about.

Thanks for the reminder on the fasteners. I think the safe play is to leave things as thick as possible without interfereing with rider fit and/or looking too odd. The thinner bars are lighter, but keeping the laminates as far apart as possible increases the stiffness of the part (helpful with carbon). I think I'll switch to balsa for the seat buildup anyway...should be plenty strong enough.

Val - glad you're enjoying this...at first I wasn't sure if I was boring everyone to tears :)

Cheers,
Adam

Val
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 Posted: Tue May 25th, 2010 05:03 pm
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I'm an engineer manquee.  No doubt there are more of us watching this thread who are embarrassed to out themselves.  ;-) 

Val

David Genadek
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 Posted: Tue May 25th, 2010 06:20 pm
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Adam,

    I don't know if you can tell from a picture but how does my ratio look? wink

If more real engineers got involved in the saddle industry it would stop all this crazy stuff like Flex trees and flexible panel systems from ripping the horse owner off.

Engineers WELCOME!!! Please speak up!!!!!

David Genadek

Attachment: fiberglass_resin_ratio.jpg (Downloaded 239 times)

AdamTill
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 Posted: Wed May 26th, 2010 08:05 pm
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Looks fine from here - no whiteish dry spots, and you can still see the weave of the cloth.

As for the gimmicks, those will only stop when the marketing folks back off...that still happens when engineers are involved!

The horse world is still BY FAR the worst that I know of in terms of useful info to BS/"Tradition" ratio.

AdamTill
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 Posted: Mon May 31st, 2010 02:35 am
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Did some work on the weekend...lots of sanding mainly, until the drive belt from my sander gave out <sigh>. Hope to pick up a new belt in the next couple of days, then I can finish off the rough sanding.

Next tasks are to size the stirrup leather gap, glue the cap on, sand it to shape, then do the upper carbon fibre layup. Only have four more weeks to go before the clinic - might be riding in a semi-finished rig :)

David Genadek
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 Posted: Mon May 31st, 2010 01:54 pm
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Adam,

    What did you use to stick everything together and to fill gaps?

David Genadek

AdamTill
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 Posted: Mon May 31st, 2010 04:20 pm
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Hi David,

The wooden blocks were seated in a generous dolop of structural epoxy and chopped fibre, and the excess squeezed out and disposed of.

The few little gaps that resulted or intentional/unintentional changes in shape afterwards are the blueish spots in the photo, and that's the same Icing Putty I mentioned a few pages back (polyester-based autobody filler). Most of that will go away on final sand.

Cheers,
Adam

David Genadek
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 Posted: Mon May 31st, 2010 04:47 pm
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In terms of attachments the balsa wood doesn't have much holding ability. Will the resins increase that or will the resins and fiber give enough holding power?

David Genadek

AdamTill
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 Posted: Mon May 31st, 2010 06:45 pm
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You're quite right, balsa is pretty useless at holding anything but a really coarse pitched screw. You can tap a hole and then reinforce it with cyanoacryalate/super glue, but that's probably more work then it's worth for more then a couple of fasteners.

That's why I decided to do this tree in basswood, in the end. Later on when I know where each of the fasteners will go it might make sense to do a full balsa tree with local basswood screw plates, but for now I'm just going to do the seat buildup in balsa. That way I can use longer attachements that reach into the bass for a firm grip.

The composite might have decent screw holding if a pilot or pilot/tap was used, but nails without a pilot would be a disaster. At best it would take a horrendous amound of force, and at worst you risk splitting the laminate.

AdamTill
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 Posted: Sun Jun 6th, 2010 02:38 pm
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Lots more progress, and so I might break this into two halves (waiting for the barn to open at 9:00 so I can get in a morning ride).

First off, this week I started by prepping the stirrup slot cover blocks and channels. That involved using a sanding block contoured to the desired shape, and a bit of filler here and there to build up some low spots.

Next, the two halves of the cover blocks were joined together at a slight bend, and the underside was sanded to shape.


The cover block was intentionally made about .25" wider on each side, and then sanded to a half round profile on the underside. The bar was given that same half round in relief, which provided lots of gluing area to bond the two together.

The cap block was then glued into place using structural epoxy and microfibre fill. I used a spacer to set the gap consisting of a scrap of 14oz leather, taped to a piece of cardboard for added clearance, all wrapped in waxed paper.



First side rough sanded, second side glued:



As you can see there was a lot of material to remove after, but the belt sander with an 80 grit belt made short work of that.

So, a few hours of sanding, checking, and more sanding, and this was the result:



(this was taken midway...before the tips were contoured to final shape)

Here you can see where the stirrup leather exits the bottom of the bar:



...and on top:



The leather would wrap around the upper surface of the bar and through the middle, rather then the upper and lower surfaces as is traditionally done. That (beating aside the marketing folks for a minute) has the advantage of no lower notch in the bar, which prevents both loss of strength and a possible lump under the saddle.


Last edited on Sun Jun 6th, 2010 02:52 pm by AdamTill

AdamTill
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 Posted: Sun Jun 6th, 2010 02:50 pm
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Since I was on a roll, and can feel the hot breath of the upcoming clinic, I soldiered on (and will do so further today).

Picked up some nice med weight Herman Oak skirting and a bark-tanned shearling last week, so that I have it on hand for later:



Next spent an hour or so setting up a new vac bag, and prepping all the rest of the carbon fibre. I got ripped off by my local fabric supplier on a supposed short cut of cloth, which was a weird irregular, tattered section (my fault for not checking), so I won't be sourcing locally to them for fabric again. As such, I had to use some uni-web material that I keep in reserve, which created some issues later on.

The moral of the story is, don't use carbon uniweb on highly contoured surfaces! It's unidrectional carbon fibre that's lightly stitched together using a binder, which means it won't contour and distort very easily in the same way that woven fabric will. I only found that out after I had started the layup, so there were some early profanities involved until I tamed the web into place.

The other layers were normal 80/20 and then plain weave, followed by a top layer of glass. I had wanted 14 layers, but only had enough mat'l for 12...such is life. I had originally planned on a balsa core, so this layup should still be fine.

Pre-bagging:


...and under vacuum:



Again, slight wrinkles were inevitable, but largely minimized by about a half hour of pressing, rolling and pushing most of the wrinkles and bubbles off the edges.

I learned something new as well - shears are great for cutting wet cloth. Normal heavy scissors just "smoosh" the wet cloth, but these short-blade snips will cut through 8-10 layers of wet cloth perfectly. They also seem to work on kelvar, which is notoriously tricky to cut any other way (special snips are generally sold for that...VERY expensive). It'll be interesting to see how long they hold their edge.

Anyway, barn time. This afternoon I'll start on the fork and cantle, since the bars won't be taken out of the bag until tomorrow.


 

David Genadek
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 Posted: Sun Jun 6th, 2010 03:03 pm
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Adam,

     What is the pen scribbling about? 

     Your arch keeps concerning me. It doesn't look like it has enough clearance underneath.

David Genadek

David Genadek
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 Posted: Sun Jun 6th, 2010 03:46 pm
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Adam,

     Here is a shot of three bars we did trying to standardize the top shape across differnt back shapes. I put the thicknesses they ended up on the top edge. One was 2.5 inches which I thought was just too much for a number of reasons, most of which were customer perception issues. Your shapes are looking pretty thick on that top edge how thick are they?

David Genadek

Attachment: bar-thickness.jpg (Downloaded 134 times)

AdamTill
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 Posted: Mon Jun 7th, 2010 01:45 pm
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>What is the pen scribbling about? 

That's the area where the fork will sit. Since I'm going to recess it into the gap a bit (notch the bottom of the fork to come down into the gullet area), I wanted to leave that part of the bar with a sharp upper edge. The rest got rounded off for appearance's sake.

>Your arch keeps concerning me. It doesn't look like it has enough clearance underneath.

I think it's mainly an optical illusion. There's lots of clearance under there:



>     Here is a shot of three bars we did trying to standardize the top shape across differnt back shapes. I put the thicknesses they ended up on the top edge. One was 2.5 inches which I thought was just too much for a number of reasons, most of which were customer perception issues. Your shapes are looking pretty thick on that top edge how thick are they?


I did jot the numbers down somewhere, but I can't find them right now. I'll measure tonight when I take things out of the bag, but it's somewhere around 1 3/4"-2 in the arch area tapering to about 1" up front.

It seemed to make sense to build a lot of the seat shape into the bar, rather then to have a thinner bar and make it up with leather thickness afterwards. My only customer is me :)

Spent the remainder of yesterday's work time making basswood dust...or taking a 3" lamination of wood and carving away anything that didn't look cantle-like. Even though I'm limited in shapes by the proposed laminate, this isn't looking too bad so far, I think (still very rough, obviously):



1/2" thick at the edge right now, 3" in the middle, 1 1/4" of dish on the front surface





Obviously still rough, but the general angles seem like they'll work:

 

Last edited on Mon Jun 7th, 2010 01:48 pm by AdamTill


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