concave vs convex form for bending strips for a laminated stem

[Ocean Spray]

When glueing up a laminated stem using eighth inch thick by one inch wide strips why do we bend the strips over a convex form versus pulling them in using a concave form? I should probably know the answer but I need a little refresher.
thanks

[John Meachen]

I would always wrap round a convex form.Others might not.

[George Roberts]

It is very hard to start with a concave form.

[Tom Lathrop]

Trying it with one strip on a convex form will teach you more than anything that can be said here.

[reeljob]

I made the stem for my Simmons using 12 1/4" laminates bent into a concave form. Worked fine for me.

[paladin]

depending on the jig arrangements...dunno see where it makes much difference...

[Rick Starr]

Among other things a convex form will usually use less wood. I've done it both ways and it is worthwhile having the ability to clamp the center of a lay-up on the center of the form and work out to the ends. Also you can use flat clamp pads, which you might not, depending on your clamps and bend, in a concave form.

good luck

[Tom Lathrop]

depending on the jig arrangements...dunno see where it makes much difference...

Well, for one thing, it takes many more clamps to make sure the laminate conforms to the jig shape on the inside. Laminates naturally tend to lay directly on teh jig on the convex side while they need to be pressed into the jig all along the inside. It will work either way but the convex is easier to get a fair curve on. All furniture makers of laminated goods use convex forms when possible.

[JimConlin]

Another reason for a convex form-
On a convex form, particularly if you start clamping in the center, as you tighten the clamps, the individual plies will be brought together will a lesser degree of being slid along one another. I'd think that the greater sliding action of a concave form would cause more squeeze-out.

[paladin]

Originally Posted by paladin
depending on the jig arrangements...

yes.....

[Tom Lathrop]

Chuck,

You are starting to talk to yourself.

[gert]

Done it both ways, convex is way easier

[paladin]

Tom....I wuz trying to point out that the comment was 6 of one half dozen t'other.."depending....." which meant the number of clamps involved, although I didn't use "clamps" as in commercial clamps...I used wedges....and lotsa rubber bands made from inner tubes.....and there's nothing inherently wrong with talking to yourself...as long as you aren't part of both sides of the conversation.......or having an open discussion with the dawg......or kat.......or another imaginary person in the room...talking to saws izz O.K. too......:D

[Ocean Spray]

Although I could have gone either way (I was making a couple of small laminated stems for a canoe)reading the pros and cons of each way, it will probably be easier with the convex form. Everyone's input was much appreciated!
It's going to be 58 degrees to be in Boston today.

[Tom Lathrop]

.and there's nothing inherently wrong with talking to yourself...as long as you aren't part of both sides of the conversation.......or having an open discussion with the dawg......or kat.......or another imaginary person in the room...talking to saws izz O.K. too......:D

My mother used to talk to herself all the time. I never heard the other side of the conversation though, so I'm sure you are right. I do talk to myself too but it is usually an expletive admonition resulting from some screw-up or other.:D

[erster]

And here in lies a potential disasterous problem. The component can be way out of wack given the thicknesses of the layup depending on witch;) side of the line that you wish to layup on if you also do not allow for the overall thickness, causing an increased exchange of words with the phantom helper. On some shapes, the parts can end up being useless. Concave seems to make a truer part. Personally I let one end be a bit wild, keeping the parts that have been wetted out on place by predrilling the dry fitted strips and run a fastener at the end after wetting out, making the sliding issue non existant Pieces have a way of jumping off your form when working by yourself sometimes..