Form width - does it need to perfect?

[EHK]

I've been thinking a lot about my first bow build and reflecting on what went right, and more importantly what went wrong as I prepare for my second build.  It got me thinking about my form.  thanks to Kenny's template, I'm happy with the shape and I know the surface is square.  Since my lams did slide during glue-up, I'm questioning the width of the form.

Since nobody makes 1/2" plywood that actually measures 1/2 or 3/4" plywood that measures 3/4", getting a form that measures exactly 1.5" is difficult if your tools are limited, like mine.  I believe I used 1 sheet of 11/32", 1 sheet of 25/32" and 1 sheet of 23/32" for a width of 49/32" - 1/32 over 1.5"  

Is that acceptable to turn out good results or do I need to shave 1/32 off of the form width?  How precise does the width of a form need to be?

[David Flanrey]

My opinion is that it is good at 1/32 over.  However, the lams slipping could be controlled somewhat with some washer guides attached to the sides of your form.  Say in 4 to 6 places along the sides.

Also, when you get your lams in place just put a little air in your hose and let some of the glue work its way out before you really put the pressure to it.  That way you can check to see if any lams slipped and make some adjustments.

Are you using pressure strips?  Air hose clamp?

[EHK]

I'm using an air hose with metal pressure strip on top.  I was thinking about trying the cable tie trick next time - at least to hold things in place while I tape - then removing them after getting some air in the hose.

[David Flanrey]

Yep.  Forgot to mention that.  I have holes drilled through my form for cable ties.  Use them every time.  Work very well for me.

All that mess is hard to hold by yourself.  I very rarely have help.

[monterey]

I had a bad exp with a form that swelled and ended up nearly 1/16" over on each side.  That made me a bit COD about width.  Have not built any new forms for a long time but need a new reflexed LB form to replace the swelled one.  This time I will use two pieces of 3/4" with some layers of roofing felt in between to get to exactly 1.5"

[fujimo]

i had the same problem with my first form, so what i did was chisel in a small recess, in top and bottom forms where my side stops are screwed into, so the form is wider, but the "side stoppers" are exactly 1.5' apart.- the lams never slid.
on my new form- my kenny m form- i just ran the laminated plywood chunk through my thickness sander,befor cutting to the template and routering, until it was the thickness i wanted. i never had a sander when i built the first one.

[EHK]

Roofing felt, eh?  Interesting idea.  Any other ways of taking up a small amount of space?

[monterey]

Depending on the amount of space, but luan board comes to mind.

The form that swelled was made of 3/4" chipboard T&G.  I went with it because it was a true 3/4" so therefore, my two pieces were exactly 1.5" for the LB form.  BUT, I stored the form up against the wall of my shed behind the hot box.  It sat there for several winters without use.  Somewhow it was able to take up enough moisture to swell it.  My regular flat bow form made from the same stuff was stored inside the hot box and remained stable.  Go figger?

In any case, I'd advise against using the chip board due to the potential for swelling, and it was also very hard on my router bit.

If you are going to make an LB, you can do pretty well with a good straight 2X6 or 2X8.  Only need one for a rubber band form and two for a hose form.

What seems to be popular here is the laminated veneer lumber (LVL) that you can order at the lumber yard.

[jess stuart]

Don't think a 1/32" would make much difference.  In fact I have built 1" wide bows for kids on my 11/2" wide longbow form. I just flushed everything up on one side.  Taped everything down really well I used rubber bands instead of a hose no worries.

[7 Lakes]

I like mine just a tad over 1.5".  I use washers on the edge to keep lams from slipping.  The tiny bit of extra width means I can tighten the washer without worry of binding the glass for a unsightly hump on the edge of a bow where the glass didn't make it all the way to the form.

[kennym]

I like Mikes way of thinkin, did one with the unsightly humps on the limb edges once....

[EHK]

Thanks for all the replies, guys.

[GentlemanArcher]

I have used a very dry 2x6, rough cut to shape, then use a edge bit with my router to follow a pattern (1/4 particle board).  Then I taped a 1.5 inch wide, 1/8 inch thick piece of aluminum stripping to the form.  Has worked well so far.  I have a few pieces of 1/16" thick as well that use on top of the stacked to help distribute the pressure from the clamps.  (no fire hose for me)