I'm wondering what pressure some of you run on your hose forms? My last one it seems I ran at 80# but am wondering if maybe I've been running a bit high on the pressure?
75
60 here
60-70 on mine.
70 and a tad after the last check(not needed I'm sure but I feel better!)
Ok, just fired it up at right around 71 pounds. Thanks guys!
60 lbs is best,you don't want to squeeze all the glue out.
If you use 60# and dont very,your weights of finished limbs will stay more on mark.If you go to much over 60# you also have a good chance of over presure of the center of the limb.
Before I proceed...let me FIRST SAY...
I am NOT saying more pressure is necessary...I am only saying WHEN you go to higher pressures hoses, you need to BUILD the form and hose to handle it. Don't do it without the proper reinforcements. It is best to play it safe.
Now, that said...My mentor, Gary Sentman, glued bows up at 100-120 psi for 3 decades as a professional full time bowyer and he had an EXCELLENT track record for producing very durable bows. Even though he used more pressure than anyone else I ever discussed bow making with...and even though I use slightly less than he did...I can't argue with what Gary did...as over the years he made thousands of very durable bows. Additionally, he also made MANY VERY HEAVY pull weight bows. Being he personally held the world record for drawing 176# bow to a 28 1/4" draw, he produced MANY bows well over 100#. My point being, if anyone tested and proved what it takes for a bow to stay together in adverse and extreme conditions, he would be that person.
I personally will go up to 100 psi. I don't go over 100 psi because of how my compressor is set up. To use this level of pressure though, the form should be be reinforced so it doesn't flex. This is why both sides of my form is encased in 3/16" thick steel sheet metal from end to end and these sheets are bolted together with 3/8" and 1/2" bolts that run entirely THROUGH the form in many locations. While this makes my form extremely heavy, it also very consistent and safe. These sides reinforcements of sheet metal are NOT removed from the form at any time. As a result, my form is essentially encased by four I beams. The form is the foundation of the bow.
Gary also taught me that the end caps should not only be hosed clamped into place but also epoxied into the hose as well (prepare the rubber inside the hose prior). I followed his guidance and so far so good.
Additionally, my form has 5 pairs of brackets that join the upper and lower forms together during glue up instead of the typical 4 pairs. Additionally, my home made brackets are 50% wider than the Bingham brackets...and are therefore much stronger. I think the Bingham brackets are 1" wide, but with the OVERSIDED hole drilled into them to accept a 1/2" bolt they actually have LESS than 1/4" on each side...closer to 1/8." On my home made brackets, I used 1 & 1/2" steel and drilled a NON-oversized 1/2" hole in it...leaving a full 1/2" of steel on BOTH sides of the hole. This means EVERY bracket on my form is MORE THAN twice as strong as the "industry standard," and yet I still use 5 pairs instead of just 4. When it comes to a form, I believe overkill is a safety measure and consistency insurance.
Gary taught me that that one gets a dry glue joint by having a void (an empty area)...and a void is a result of not having enough glue or by having a poor fit of materials. He also believed one should never glue up with cold epoxy...that the epoxy should be at least room temp. If the glue is warm (not hot, but warm so it will spread easily), then more pressure will simply push more glue into the pores of the prepared surfaces. Additionally, any excess will be squeezed out which will reduce unnecessary limb mass and also help maintain limb dimensional consistency by keeping the stack depth consistent and relative to the materials being used by eliminating high/low spots in areas that had too much epoxy applied. All this said, the excess pressure should NOT be used to "force fit" materials. A good fit is obtained with careful craftsmanship and should be confirmed during a dry run with around only 20-30 psi (depending upon the curves in the riser and form) to look for a good fit between the laminations and the riser. I don't want to see any spaces even at such low pressures.
90 lbs here./
God bless you all, Steve
The blank came off from the 71 pounds quite nicely. I can see all the points made in favor of much higher pressures, but for sure my present forms will not withstand it.
Thanks for making this an interesting thread!
There have been many produced at 60 psi and many with much more. Use the same on each you build I guess to keep from having bow weight all over the charts.
I just pulled a tri lam out of the press, osage, boo, and osage. It has a flat spot in one area. I tried the 60 pounds, won't go that low ever again.