Form Question

[DoubleLung]

I recently built my first form for a take down longbow limb using two sheets of 3/4" MDF glued and screwed together and then glued and screwed 1/2" plywood to the outside of it to add strength.

I've read MDF is not optimal but I couldn't come up with another method to ensure I got an exact 1.5" form.

My question relates to the smoothness of the form? I used a template and a router to shape the MDF and then hand sanded what will be the back of the bow (bottom of the form). It looks smooth and dragging my square along the form it stays true the whole way but when I run my fingers down the form, I feel like there may be some slight "waves". I plan to attach a piece of glass to the form.

My question is, am I over concerned with the slight feeling of waves or do you always make sure that is gone? If so, how do you do it?

Thanks,
Tim

[beachbowhunter]

Check your template. My first one had some "waves" that I didnt notice until my first limb came off the form. If your template is good, your form will be good.

[DoubleLung]

I do believe that the template was not true but I just tried to get a nice curve on it with my rigid sander for 30 minutes and didn't seem that make any progress. Do you have tips or tricks for this? By the time I was done I as not matching the Bingham paper template.

[snapper1d]

They tell you to glue down some formica over it.It will help even it out.On my last form I used a 1/8" backing strip glued down and it really helped to even it all out.

[mikkekeswick]

I did what Snapper1d just said. I used a strip of ash about 2 -3 mm thick and glued it down using a pressure strip and my airhose.

[mikkekeswick]

Also make super sure there are no 'waves' these will only be transferred to the limbs so unless you want a 'character' glass bow....get them out! I made the mistake on my first glass bow of thinking that's close enough...it wasn't and gave me a flat spot out of the fades which looked awful in the finished bow but was hard to spot on the form.

[canopyboy]

Make some sanding blocks at the curve(s) you need and sand along the form. They will hit they high spots and smooth it out. This is something easier to do with your template as there is less to sand. Check the final surface(template and resulting form) by using a piece of glass as your batten. If you can't get a nice fit to the curve without gaps underneath your curve isn't fair enough.

[Crooked Stic]

I use regular automotive bondo to fill any voids in the plywood. Put a thin coat over the whole form surface and flat block sand to fill the waves before your formica or whatever you use.

[DoubleLung]

I'm using the Bingham TD LB template and it's set up so that the bottom of the form curves up and that is the side I've been trying to get smooth. It seems like it would be easier to get a nice smooth arc on the other side of the form (back of the bow). Would there be any problem with trying this and flipping the form upside down?

[canopyboy]

Make a curved sanding block to match the smallest radius of your "curve up". Should work great. Bondo is also a great idea.

You could flip the form over, but that sounds harder.

[Tim Finley]

glue a couple of lams over the forms in layers maybe .050 thick they will disappear.

[Mad Max]

Preparation is always the most important step.
ALWAYS