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I just started to make a bending form and after i cut out the exact shape using my outside mold as a template I had a thought...
Do I actually make the bender form smaller by say 2-3mm for the thickness of the sides and heating blanket so as to arrive at the shape of the mold?

Does anyone take this into consideration when they have made a bender or just made it the size of the mold?
This hasn't been mentioned on any of the bender making websites I've seen but it makes sense to me that this would be worth doing...
what do you think?

cheers grant gratay39043.0405555556

Grant I did do that (make it smaller that is) on the last form the I made and I'm glad I did. It certainly fits the mold better.Rod True39043.0608449074

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Ditto for me, Grant. I found a small washer whose distance between the inside and outside diameter equalled the thickness of the wood and heating blanket. (or close)

I then put the body form over the bending form and, using a sharp pencil inside the washer, roll the washer around inside the body form to mark the bending form shape. Works like a charm.

I make the bending form out of the scraps cut out of the body form glued together, side by side. I glue pieces of wood on the top and bottom ends on what was the centerline of the body, so that it will stand high enough for the old curve to be completely removed after cutting the new shape.

Scott

Grant:

I made mine smaller also...

-Mark

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yep x the thickness of two slats + the wood + the blanket

I've been stumped on this one too. Do you get a better fit by reducing the bending form by the total thickness of the slats, wood, and blankets, or by just the wood and whatever you put under the wood (slat and maybe a blanket)?

Joe Volin

Yep, made mine smaller by two slats and wood thickness (I use bulbs).

Ron

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I've been cutting mine out this week as well. I'm using a coping saw, so it
takes me longer. I traced my body shape and eyeballed the thickness.
Occom's razor. Why spend all the time measuring to the thousandth of
an inch when you don't have a machine accurate to the thousandth of an
inch cutting it out?

EDIT: I joked in another thread about eyeballing things, but in reality I do
have a good eye for small distances. I can't tell you to the thousandth,
but if we're talking graphic design, I can tell you the difference between
21 and 22 pixels.James Orr39043.7451736111

Remember, your bending the inside of the wood to the inside shape of the body.

So what I did was this...

Depending on your "sandwich"; slat, blanket, wood.... or slat, wood... that's the amount you want to offset your line from the outside mold, so I take a piece of spruce (off cut from a piece of bracing) and thin it to that sandwich amount (I went slat, blanket, wood which worked out to about 0.17 or 3/16" for basic measurements. Than I held the tip of my pencil to the spruce and held the spruce to the inside of the mold and transfered the outline to the piece I was making my form with. Cut it out proud on the bandsaw and sand to the line with a robosander or post sander in the drill press. Use this as the template for the next piece(s) of the form.

Scott had a good idea with the washer if you have one that gives the right offset.

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"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Interesting, I always made mine a little smaller but wonder. Without realising it I accidentaly bent the sides for my L-00 model on my SJ form onece and it worked great. I checked it out and discovered I can use either mold and it will still work great even though the L-00 is significantly smaller tha the SJ.

Wow, that sure is "interesting" Richard.

that's some funny math you got goin' on in your shop.

So, how's the mayor?

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

thanks guys ....sounds like the way to go to me as well.

Greetings all – catching up with reading through last Wednesday. Got a question about how much smaller to make the bending form.

Seems like the consensus is to make them smaller by 2 slats, blanket, and wood. I’m not sure that it matters that much, but – for the sake of accuracy…

Isn’t it true that - when we take the wood from off of the bender form (outside) and place it into the building form (inside) – the blanket and 2nd slat are not there? And if it is true, then it would seem to me that we would only reduce the outside form by the thickness of the wood and 1 slat. The second slat is not significant in size (thickness) but the blanket is certainly thick enough to consider.

Of course with spring back and the use of spreaders – (like I said) this probably isn’t that big of an issue.

But, thought I’d throw it out there for comments. I would be interested to hear them – cause I’m going to be building a bender (hopefully) in the not to distant future.

Tony, I agree with you as long as the blanket is used on top of the wood. Add it of course if it's used under the wood.

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"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Your absolutely right Tony, you only need to reduce your form by the thickness of your sides and one slat unless you use the heating blanket on the inside of the side. I use a sandwhich of Slat/wood/slat/blanket/slat, from inside to outside. I use the outside slat because my bending jig pulls straight out from the ends of the sides and the springs are attached from the end of the outside slat to a swing arm that pulls the sandwich around the bout. I usually try to add in a little over bend in both bouts just for springback I don't usually worry about overbending the waist although that is probably the biggest need for overbending. It hasn't been a problem yet.John How39048.4768055556

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Rod, to clarify. about the SJ and L-00 being the same. I cut my sides to length after comming out of the bending form so obviously the L-00 sides are cut shorter but after cutting to length they will take the shape when put in the Mold. This means that if bent on the L-00 and used on the SJ there is a fair bit of spring back but it still fits perfect. If bent on the SJ and used on the L-00 it can be "sprung in" to the L-00 form and seems to fit perfectly. With this in mind I personally believe as long as the Basic shape is right (waist) it really doesn't matter if it is slightly smaller or larger.

As far as my new position as mayor, I am not sworn in for another week but am already busy. Have had a meeting with The premier already as well as Minister Of Natural Resources and all the local MP's and MPPs. Just came back from a weekend conference with all the other municiple leaders in our area...the scope of the job when one lives in a forestry dependent region trying to recover from the Soft wood lumber dispute and figure out a way to get back the billions of dollars illegally takenm from us by our "friends" to the south makes me wonder why I took the job. At the same time, I had my first Political cartoon a few weeks ago, I'll try to scan it in a post it here for everyone to see.

[QUOTE=tony] Greetings all – catching up with reading through last Wednesday. Got a question about how much smaller to make the bending form.

Seems like the consensus is to make them smaller by 2 slats, blanket, and wood. I’m not sure that it matters that much, but – for the sake of accuracy…

Isn’t it true that - when we take the wood from off of the bender form (outside) and place it into the building form (inside) – the blanket and 2nd slat are not there? And if it is true, then it would seem to me that we would only reduce the outside form by the thickness of the wood and 1 slat. The second slat is not significant in size (thickness) but the blanket is certainly thick enough to consider.

Of course with spring back and the use of spreaders – (like I said) this probably isn’t that big of an issue.

But, thought I’d throw it out there for comments. I would be interested to hear them – cause I’m going to be building a bender (hopefully) in the not to distant future.
[/QUOTE]
Tony, I havn't yet decided on what order of slat, blanket,wood works for me as yet but decided to go ahead and build the form anyway.....because you need the form before you can try different combinations anyway....
so i thought if i make it an off-set by around 3mm it would be in the ball park with the blanket under the wood ....but i thought that with the slat, wood, blanket combination it probably be ok as well because there probably be a bit of springback anyway.
cheers   

I make mine 3mm under with no springback allowance. I use blanket on top. However, I do take my sides back up to temperature and when hot take them out of the bender (with gloves!) and put them into the mould and tighten up the cauls. That way they set in the mould rather than on the bender.

Colin

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Great tip there Colin, thanks!

yeah thanks colin....that sounds like the smart way to do it.....I'll try that

I started my bending form at the exact shape, but found that the springback at the waist and ends was significant (I build classicals on a Solara, free assembly with no form). I made adjustments to the curves at waist and ends over the next few sides, eventually arriving at about 1 inch compensation at ends and 1/4 inch near the waist. For Madagascar at about 0.08 in. this gets me an exact fit to the Solera.