Bow form problems

[VTer]

I've made two bows offf of my form, which is made of plywood laminated together and had the hardest time getting the riser area to release from the form. I took the precaution of coating the form with poly and even used johnson wax on the surface that the bow goes against. I laid saran wrap on the first one and a double layer of saran wrap on the second one. Same issue where i ended up forcing it off with a rubber mallett. Anyways, the bow shot great but eventually it delaminated in the lower riser area. Granted it was in my hottish truck when I noticed it but I feel the rubber mallett treatment was the culprit. I picked up a piece of formica to use as a surface between the form and bow. I'm just going to lay it on there as i'm not sure contact cement will work on the waxy surface. Any thoughts?

[Kirkll]

I use stainless steel myself. I’ve used Formica years ago, and it’s not bad, but doesn’t hold up real well over time.

But if you are having issues getting the bow out of the form, or limbs out of a form you may want to wrap your limbs in heavier plastic than Saran Wrap. I use a painters plastic from 1-3 mills thick. The thicker plastic is much easier to get off the limbs too.

Another issue may be eliminating washers or guides holding your glass in place on the edges. Just drill some 3/8” holes about an inch down from the edge of the form and use heavy duty zip ties to hold the bow in place. This is also really helpful to keep things from sliding around too much once you get your system down. It’s really nice getting recurve limbs into a form too.    Food for thought…

[chefrvitale]

Kirk, can I pre-order your future book of bow building tips? You need to put something out to print. Truly a wealth of knowledge, everytime I scroll through I pickup something from you.

[BigJim]

Is the bow actually sticking to the form or is the glue that surrounds the bow holding it in place?

The bow is formed as a perfect match to the form and will be hard to remove for that reason alone. The rubber mallet is not the issue unless you are beating the absolute hell out of the bow. Even then I doubt you could damage the bow with it... having said that, I could tear up an anvil with a rubber mallet..    We use a rubber mallet to remove ours and have always done so. The glue slag that forms down the side of the form as it is pressed from the bow does more to hold it in place than anything.

I like using stretch wrap on the roll and going all the way around the forms. We start with wrapping the form and then wrapping the bow on to the form. Some glue will still work its way through where we punch holes for pins but not enough to cause an issue.

We use aluminum strips for the surface on the forms and just tape them down.. makes them easily replaceable if they get damaged.
Good luck, Bigjim

[VTer]

I’m not sure about the slag. I had more ooze on the first bow and tried to do better and not waste glue on the second one. I’ve scored on a strip of free Formica so I will try that on the next one. Being a rook, I can’t really pinpoint what went wrong as there were so many things that I felt I could’ve done wrong. Thanks for some great answers guys.
Stikshooter Bows, appreciates it

[Kirkll]

If you use Formica, be sure and wipe it down with past wax in case you puncture your plastic wrap.

Typically if you are careful when you lay these up and wipe off the excess epoxy before putting the plastic around the limbs, you shouldn’t have any issues at all with them popping out of the form….

Then again…. I don’t use a hot box and cook the hell out of my forms for hours…. My limbs are cured in 30-40 minutes, and I pull them as soon as the temp drops below 90 degrees. Occasionally I need a chisel to pry the tip loose, but even that is rare.

[Kirkll]

Hey Jim,  are you using some kind of heat strip system on your bows?

[BigJim]

No Kirk, we use the hot box still. I have two rather large hot boxes... yet we still can barely fill one a day. One will hold at least 5 bows and a dozen risers at once. We are never in a hurry to get one cooked. By the time we've filled one hot box, the day is nearly over for my guys.
 I also have at least 3 forms for every model I make.  I tried the heat strips but found them to be a Pain... not to mention that they frequently failed. It also seemed to me that I had more issues with gassing/air between the glass and veneer.. that could be coincidence.
BigJim

[Kirkll]

I was just curious if you went high tech or not... I had a lot of issues with the old silicone heat strips myself. I was selling those at one point until they kept failing, and the company wouldn't replace them.
Over heating will definitely cause issues with clear glass over veneers. It critical to ramp up the heat gradually and keep the heat strips below 160-180 degrees and only heat it about 30-40 minutes.. I've done pretty well using the battery charger and stainless steel heat strips, but the chargers only take so much abuse before they puke. i get about 200 bows out of a charger.  So its only a buck a bow cost wise...

I may look into using a small welder to provide my power in the future. They may hold up better for that type heating system. But i'm going to need some help with engineering it so i don't light myself up like a Christmas tree.

[BigJim]

Using a hot box naturally and slowly ramps up the heat since it takes quite some time for the forms, hose, and bow to come to heat. Granted, it is a four hour process, but haste makes waste!

I get about 3500 bows and counting out of an oven... 

I tried the heat strips because i thought I should be using them.. you know, a professional shop. LOL. In reality, the  hot box is most certainly the safest and cheapest way.
BigJim

[VTer]

Guys, at what temps do you cure your riser blocks too vs curing the bow afterwards? Should the riser block be cured at a higher temp? Does leaving the bow in the form before going in the heat for an hour, let the bow gas off first? What’s your procedures?

[BigJim]

we never change the temperature and it is about 150 degrees. We used to leave our bows in the forms overnight before putting them in the hotbox and it seemed like it helped with gassing, but nothing helped more than doing away with the top of the form and going topless. .. form that is     
We also heat our risers during the footing process, then again when putting in the I-beam followed by heating the riser bow combo.
Once the bow is shaped out, the whole bow goes back in to cook the overlays for 2 hours, and then one more time to cook the horn overlays for two hours.

If you can't cook your bow that many times, there's something wrong.. I would expect that your wood is wet and it doesn't matter how long it has been drying, but more about where it has been drying for how long.

BigJim

[Kirkll]

Guys, at what temps do you cure your riser blocks too vs curing the bow afterwards? Should the riser block be cured at a higher temp? Does leaving the bow in the form before going in the heat for an hour, let the bow gas off first? What’s your procedures?

I rarely cook my riser blocks when doing footings, or I-beam construction. In warmer weather they just get put on the floor to dry overnight. In winter they go into the spray booth that I keep warm. EA 40 doesn’t require cooking the hell out of it to be strong.

But…. Depending on your climate, how you store your hardwoods, and the actual MC levels of your wood… there are certain advantages to heating your riser blocks as you build them. If you start getting above 10% MC level in winter time you can have issues with shrinkage down the road in summer weather, or sending them to a dry humidity climate.   The wood in my shop stays at 12% MC level pretty much year round, so I need to cook mine in the spray booth after the riser is shaped for a day or so at 80-90 degrees to insure the MC level has stabilized. But I do build my riser blocks ahead of time and let them set in the spray booth in warm temps for a few days prior to working with them.    Kirk

I’ll bet Jim doesn’t have any issues of his bows moving after all those cooking sessions, but I’d bet he’s had his share of MC level issues along the way. We all have at one time or another. The key is getting it stable and dry before you finish it.

[BigJim]

I have had an issue or two, but mostly in the beginning. All of my wood gets moved to a climate controlled building ..or two long before it gets used.

Unfortunately, just a few hours in the oven or even a day or two under 212 deg isn't enough to get moisture out of the core..
Before stabilizing wood, I bake dry wood about 8-10% in an industrial convection oven for 5 days at 220 deg to get it as dry as possible.. Still not enough for some of the woods. The shorter the pieces, the faster they dry.
BigJim

[garyschuler]

I built a mini kiln for drying wood years ago here on the Oregon Coast. I lose 3-4 percent daily. It uses 2 - 100 watt bulbs and 2 - 4” inline exhaust fans. I can run bulbs and fans, or just bulbs or fans. I shut off a night and run daily. Dried a lot of lams, Veneers, riser blocks over the years.

[Stagmitis]

Jim good to hear you talk about multiple cooks since my designs usually have several during the build- also thanks for inspiring me to invest in a quality moisture meter- this was an eye opener for knowing exactly what my MC is before glue-up- I mostly use natural bamboo that I temper myself and I have verified it’s hydrophobic after the process

[BigJim]

Garyschuler, i have a couple of old refrigerators with 120 watt bulbs (I think) that work well. I bought a warming oven that will hold a metric crap ton of wood and it is ready to use... fans and all. $100    I have left wood in it running for months and although it is dry, it will only go so low since the heat won't go over 180 deg. Dry enough to build with, but not stabilize with.

If while you are cooking bows or risers, you get moisture inside the plastic wrap.. you have a potential problem!

I would recommend the wagner pinless moisture meter. They are expensive, but allow for the most amount of adjustment for accurate readings. Also measures a fairly large area and 3/4" deep. They have several models.. look for the one they suggest for exotics.
bigJim

[garyschuler]

 

[Mark R]

Jim you mentioned you did away with the top form, what are you using on the top? pegs and fish tape? I've been thinking of doing all my forms that way, not sure yet but it does sound more versatile. What say yee all.

[BigJim]

Mark R, to be honest, we laughed at the idea at first thinking it would be slower without much benefit.. the weight wasn't a real issue at the time because we were all younger and bigger than the average bear. That has all changed!

We are no longer younger, and the decreased weight is a big advantage. Also, after doing a few, it turns out to be little to no disadvantage in time loss. What we did find is that we no longer wait for more than a few minutes to put bows in the oven. Also gassing and or foaming has all but dissappeared .. a real problem for us with some woods.

We went to half inch steel pegs so I would never have to worry about replacing them.. bought a "slightly" oversize drill bit to drill the holes so they would slide in and out with relative ease. Its also nice to have that bit to clean out the holes occasionally.  Mule tape can be had very reasonably and can be used many times over.

Forms are also much easier to build without top form and you can do a custom riser if you would choose to do so.
good luck, BigJim