Bow form warping

[pditto613]

I would like to hear strategies to combat bow forms warping.  Living in Florida without climate control in my shop has left me with a bunch of useless forms.   I have been considering sandwiching MDF between plywood.  Also considered cutting plywood into 1 1/2” strips that would be stacked and glued into a 16” blank.  Share your collective wisdom please.

[Crooked Stic]

First off don't use MDF. It likes to draw moisture. I always try to seal the form right after making. What used to be good plywood nowadays is junk.

[Smguinnip]

i have been considering wrapping my next one with a counter top laminate on all sides. two pieces of 3/4" ply with .035 laminate on each side would put me really close to 1.50" and keep it sealed up, just not sure what kind of adhesive would hold up in the hot box.

[OldRawhide42]

I put some angle iron on the bottom to help and seal all of it.

[Kirkll]

i have been considering wrapping my next one with a counter top laminate on all sides. two pieces of 3/4" ply with .035 laminate on each side would put me really close to 1.50" and keep it sealed up, just not sure what kind of adhesive would hold up in the hot box.

I'm afraid that isn't going to help you much using P-lam. Your best bet is to find an LVL distributor. Finding a lumber yard that delivers supplies to construction sites is best. you get fresh material right from the mill that way.  Hope depot may have LVL materials too, but typically its old and picked over stuff..... Now the key to keeping LVL material from twisting is to leave it at the factory thickness of 1.75"  and seal it really well.

I've had laminated 3/4" plywood forms hold up well by laminating a hardwood edge band on the bottom form and the ends too. The cut out portion of your form can be capped by using a good hardwood lam and epoxy it in right after you build it using your air hose.

I had forms that i had a piece of angle iron on the bottom to keep it straight, but it was a seriously heavy form.  I also wouldn't recommend a steel edge band if you are using a hot box.  That steel moves when it heats up, and cools down.

Things you can do to keep forms from twisting besides using edge banding and a good sealer is storing them laying flat with weight on top of them if you are not using them often.

The bottom line is you are fighting a loosing battle putting your forms in a hot box and cooking them to death, them letting the humidity soak into them again and again. Wood moves!   If you want to get serious about this stuff, get a heat strip system going, and quit cooking your forms to death.  HUGE difference...

    Kirk

[Crooked Stic]

I have never had a form warping problem. My hot box 140 max. Usually for 6 hours. Smooth on claims 160 before it starts to break down. But would not test it at 160 to find out.   

[kennym]

A custom built aluminum form would be awesome if face was all square with sides . 

[Mad Max]

This is my 1-1/2" wide Recurve form, I use more plywood on the bottom (top on this picture) 6" wide and full length of the form, screwed and glued and 1/2" dowels also (6 or so).



This one has angle iron on both sides, 3/16" or 1/4"   x 1-1/2"

[Mad Max]

I try this before the angle iron if it's not to bad.
1" x 1/8" steel
this all thread is in the center of the form is pushing it back to straight



1/4" bolts all the way threw at each end

[Longcruise]

I had one that was warped a bit.  It was a 1.5 inch form and I wanted the bow to finish as close to that as possible.  So I used a spray bottle of water to wet the form down on the concave side.  Wet it three times over the course of a day and the swelling caused the form to go straight.  Layed the bow up next morning And cured at room temperature for 24 hours and everything just fine.

[Crooked Stic]

I have no idea if this matters but on all my long one piece forms after I get them marked and drilled I cut them in half for ease of bandsawing then fish plate them back together with 1/2 plywood glue and screws.

[Kirkll]

Hey Max, I had a one piece form like that with adjustable bolts and angle iron that I used for years before I finally replaced it with LVL material. Using that flat iron for a tension brace was pretty innovative.    I’ll bet it worked fine.

[pditto613]

This is the collective wisdom I was hoping for!  There are some good ideas here, thanks!

[Mad Max]

Hey Max, I had a one piece form like that with adjustable bolts and angle iron that I used for years before I finally replaced it with LVL material. Using that flat iron for a tension brace was pretty innovative.    I’ll bet it worked fine.

It was one of those, I don't have angle iron, so I tried it.
The 1/8" x 1" --It does work on some, a R/D form was straight and a few years later I put one of these on it and it was back to good again.
The angle Iron works much better, but you need to tighten the bolts more sometimes.

[Kirkll]

I had a customer that i was remodeling their house years ago that had this drop dead  gorgeous raised panel Black walnut front door. But.... It was warped so badly you couldn't hardly shut the door. This thing was in perfect condition too...  To replace the door and install it was going to run about 3 grand plus clear coating. 

So i told him to let me work some magic on it in my shop  and see if i can straighten it out for him.   That was an interesting project .... I sanded it down to bare wood, and wet down the crowned side first. Then set it out in the sun with a car battery on it for weight. It took 3 days of wetting it down and cooking it in the sun to get her straight again. Then i went just a wee bit further the other direction on the twist and let it set another day. Once i had it flat again and stabilized. I sprayed about 6 coats of marine spar varnish on it both sides.  She came out looking like a brand new door, and the customer was so happy he paid me an extra $500 in cash. I think i only charged him a grand for the project. I just kept track of my time and materials.
It took me a week in the evenings to get it done.

Kirk

[Mad Max]

Nice save

[Kirkll]

Nice save

Its amazing how many exterior wood doors get ruined just because the were not sealed after cutting off the bottom.

I've seen a lot of these weather stripping companies come in and put in the weather stripping in a new door and do not seal the bottom of the door or the mortise they dado into the door before putting the weather stripping and sweep on. Its a criminal act if you ask me...   

When we were setting interior finish we often had to cut pre finished doors off for carpet clearance and i always kept a can of shellac or poly uruithane handy to seal them. But most carpenters don't mess with it.
20 years down the road makes a difference....

[Mark R]

I use 4" wide pieces of doubled up 3/4" plywood full length of form and glue and screw to bottom of form to keep it straight, have not had any warping issues, kind of like a strong back for concrete forms, also doing it that way I can keep the height of the form a little shorter for less weight.

[pditto613]

That’s 2 people using perpendicular brace on the bottom. Seems like a simple inexpensive option.  All things I like in an option. 

[Mad Max]

That’s 2 people using perpendicular brace on the bottom. Seems like a simple inexpensive option.  All things I like in an option.

Yes for R/D and some recurves.
But some taller forms may need the angle Iron