When I am making a one piece bow with a laminated riser, how would I heat the riser differently in the hot box when laminating it? I want 170-180 degrees for the limbs, using 100 watt light bulbs. If I put in one more 50 watt bulb for the riser, then stick with the 100 watt bulbs without the additional 50w, would there be enough of a heat difference to keep the riser from delaminating? For overlays I will open the top of the box to hopefully get down ro 150 degrees.
Or I guess I could make an oven that gets to 200°F, and then use a thermostat to get three temps of 200°, 180°, and 150°. Does anyone have plans for a foam insulation hot box that can get to 200°F?
200 degrees may effect the glass as well as the smoothon. I've heard horror stories about higher heat on glass. I'd limit the highest temp to 180 and work down from there. But frankly if your riser has glass on the back and belly ramps and is under pressure when in your form there shouldn't be any problems with the riser glue joints and it may even strengthen them.
So I will:
1. glue up riser block with 2 wood blocks and a phenolic accent strip at 180 degrees
2. glue up entire bow at 180 degrees again
3. glue overlays on at 150 degrees
?
By the way, the bow is a longbow with fiberglass on the back but the bely glass lam will not reach all the way through the riser.
Right or wrong...When I glue up a wood/glass riser block I just heat it between 90 and 110 degrees for 4 hours, leave it clamped for another 12 or more hours , then cut and shape it. For bow glue up, I usually run my oven 160 to 170 degrees, I have a 180 degree F snap disc thermostat in my oven but I dont think temps have ever got to 180 degrees. I know some guys will cook their risers at 180 then after glue up cook bow blank at 160..
Oh, you said you are going to heat your overlays to 150 degrees. I would not do that, I believe you can soften the smooth on between your lams and ruin your bow. I have seen pictures of twisted limb tips when guys over heated the bow when gluing on the tip overlays.. When I use smooth on to glue riser overlays or tip overlays and it's over 75 degrees in the shop I use no heat or I put a 100 watt light bulb no closer than 1 foot from the overlay.. In the winter I have to run a little heater in my shop to get temp to 75 degrees.
i usually glue up my riser- put in a warm place for 24 hrs- then do the entire bow in the oven at the 180* then do another unheated( warm environment) glue up for tips and overlays- at 24 hrs.
takes a bit longer- but never had a failure yet. but then i am not into high speed production though!
On a one piece laminated riser mine don't get heat until the bow glue up. For TD risers about four hours in the hot box. Not even sure that is a must do. Because I have a few out there that never seen heat and are doing just fine.
I have done one piece risers both ways without incident. I now do not go much past 100 degrees for the riser glue up then about 180 for the entire bow. I wouldn't put my overlays on much past 100 degrees. I just unscrew all but one light bulb and leave them for 18-24 hours.
I typically don't use any heat with smooth-on, but I also don't use glass. Anyway, I would probably do as Fujimo said.
Smooth on will cure just fine at rooms temp or a little warmer. Remember that when you bake the whole bow the riser will also heat up so even if you think the heat is critical, the riser will get heated at least once.
Also consider that cured smooth on probably maintains its strength for like 100 years at ambient temps, but probably lasts like 2 weeks if kept at 200F, I'm being kinda sarcastic, but I think you get the point. I wouldnt expect the same life out of glue that I baked 25 times. I would bake it once like Fujimo .... Plus it's less work :-)
I've heated risers as many as 3 or 4 times at the same temp as what I did the whole bow no problem tip overlays also and I have done it hundreds of times . Don't heat smooth on to 200 degrees it will deteriorate, 160 degrees or about is best and you do need to heat it.
I do the risers in the Wife's kitchen oven, perfect 170 degrees.
everything you need to know--
https://www.smooth-on.com/tb/files/EA40.pdf
One of the guy's on here help me on this.
I use 4-150w and 2-100w with a insulated bow and a heat controller.
180* first glueup
170* second
ect.
https://www.amazon.com/gp/product/B00862G3TQ/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1
I mounted mine on the wall and put my door on the front side.
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=004433
I would listen to what Tim said. Kota are fine bows and he has built a lot of bows.
Good thread and I am with Tim I have heated my bows several times and have one I shoot that is 15 years old that is still going strong. Also you do need to heat Smooth on!!!
When heating the tip overlays..How do you keep the limb from twisting from the weight of the clamps?