Bending Forms - sizing and construction

[Daniel P]

I'm starting to gear up for bending sides, and am wondering about bending form sizing vs final form.

Do you recommend making your bending form exactly the same as your body mold/form? Or is it wise to make it smaller my some factor to account for slight spring back?

If one is going to use a heating blanket, is there a need for the steel bars connecting the sides of the form - could the twos halves be joined with wood? I'm assuming they are, at least is part, for thermal mass. Or are they left unglued so one can break down the form, and store more easily?

These sides were a test cut with a CNC router over the weekend - wanted to see how well the 1/2 holes tangent to the perimeter would work with the router. Looks like it should work fine if I use a more suitable plywood- this was some rough stuff.

Yes, my desk is a mess right now...

[ken cierp]

Correct there is no need for the form to be hollow if you are using a heat blanket. I've made bending forms with and (mostly without) side relief thickness and over bend -- neither is necessary.

I'll give out the secret again !!!

Pre-bend the waist curve on a pipe -- after about 30 years of this bending stuff, now commercially I can tell you it is a "quantum" improvement in the bending process. Both in reducing waste (cracked sides) and the superior quality of the final product. These bone crushing inside clamps the hobbyist use are only necessary because the sides are not properly formed. It is not a coincidence that the major factories pre-bend the waist. $.02

[Daniel P]

Making a little progress on my bender.

[Kevin in California]

Alright! Way to go. You'll be bending soon!

[Jim Ball]

I just recently completed one of these. You will love it! :D

I made my mold to the exact dimensions as my Plantilla. I'm using a laminated side construction method, so the side laminations will be glued up and clamped in a side mold after bending. The minor shape differences will be taken care of in that step.

...and, yes, pre-bending the waist is a good idea.

[Daniel P]

For prebending the waist - are you guys just making a small mold that is the negative of the waist bend - essentially the caul from the end of the threaded waist section on this side bender?

How are you handling the exact placement/marking of the narrow point on the waist?

I have a 6"x6" heating blanket I can use for waisting bending, but want to make sure I'm thinking of the correct approach.

I might need to track down some practice wood for a few tests.

[John Link]

The easiest way to bend the waist is by hand, with a hot pipe. You can tell by the "feel" of the bend as it progresses whether it needs more heat. More heat is easily provided simply by lingering longer on the pipe as you bend. Try it on a scrap first. It really is not difficult to do.