cracked riser, any thoughts??

[stykbow67]

Here are some pics of a riser that i had made for my son's bow. It was a Bingham design Hybrid 43@25 62" long and has been shot for over a year. I didn't think you could break a laminated riser  with a light poundage like this   . I guess I'll just have to build him another one this winter     I just don't want this to happen again if you think it's something i did wrong. I laid a quarter on the riser for size reference.

Thanks, Steve    

[rmorris]

Steve, the laminated riser should not crack like that unless there was a defect there( I assume you marked the crack with a red marker). I would have to say that the double threaded insert was not properly installed. If hole was not tapped deep enough and the insert was forced in that could cause that crack and if the hole was taped too narrow and the insert was once again forced in that crack could of been caused. I do not think you will have this problem again using laminated wood if the inserts were installed properly. My guess would be just a fluke.

[rmorris]

Just a FYI the correct drill size is a 27/64 and a 1/2 - 13 tap

[stykbow67]

Yes, red line is showing the crack, I'm pretty sure i used the correct drill bit and tap because that was the 2nd or 3rd bow i've built and hadn't experienced any problems before. That's why I think it was just a fluke or defect in material also. Thanks for the reply!

Steve

[LittleBen]

My only other comment would be that it could relate to moisture content of the wood and/or potentially contraction of the wood around the insert. What glue did you use?
TB I,II,III all tend to moisten wood substantially when gluing pieces together. Laminating a riser with TB would definately wet all the wood. If you then installed the insert soon after, the riser may have been shrinking imperceptibly.
This would concentrate stress at the insert, bc brass doesn;t swell or shrink.

Just one idiots thoughts ...

[stykbow67]

LittleBen, The riser was made from a piece of Actionwood, So all the glue joints are factory made.
Which still leads me to believe it was a defect in material or a oversized insert.
Thanks for your thoughts!
Steve

[GREG IN MALAD]

Steve, I think you made the riser too small. A quarter is only 7/8" in diameter so your riser is about 1" deep. Most risers are at least 1 3/4" deep at that point. You could try using a bunch of glass in the next one or make it deeper. How wide is the riser?

[stykbow67]

Greg, The riser is approx. 1 3/8" wide, I think your right about it being a little to narrow at that point also. I probably will start building a new next month sometime (way to much huntin to do right know!)Thanks for all the reply"s.

Steve

[LittleBen]

Steve sounds like you've got the problem pretty well nailed down. In engineering we tend to say that a failure results from not one problem but a series of problems, each of which doesn't produce a failure alone; only in combination. I'd bet it's all 3 things mentioned: oversized insert, narrow shallow riser and defective material

[HMlongbow]

The riser is to thin in that area you have the quarter.  There is alot of flexing there when pulling bow back and multiple times of shooting is what produces compression shock. The riser should be minimum of 1 1/2" any there in riser.  You could probably go a hair less but I wouldn't even with low poundage your asking for failure.
Dave

[HMlongbow]

Thats also the thinnest part of the riser and all your shock is going to least amount of resistant area.  I hope this helps and is this design from bingham with those measurements?  If so call them and ask there input on it.  I know John from Old Mastercrafters recommends at least 1 1/2".  He has been a mentor of sorts for me and has helped me out when I am stuck with something and we can usually come up with something that is going to work and work well.

Dave

[Sixby]

Pretty simple. Too much flex in the riser. you have to make it deeper or add a phenolic I beam.

God bless, Steve

[Jason Kendall]

It looks like Dymondwood, not actionwood? Either way there shouldnt be enough flex to worry about since it really is a bunch of i beams. I am developing a new 3 piece now and I highly recommend some type of overlay across the back, I use 1/8" phenolic.

I put limbs on a handle I had clamped in a vise and pulled the limb sideways as a riser strength test, it didnt take a lot of pressure to crack it like yours is. I couldnt crack the riser with the phenolic, just the all wood ones.

And like Hitman said, it is a little narrow. I like the shape though!

[Sixby]

I agree with Jaason, I either put phenolic or glass on the back of all my risers too.
I have seen several diamondwood and actionwood risers break right across the lams like that. You would not expect that. It just shows you how much pressure is actually being generated.
 
That break is a typical flex break though which in about 90 percnet of the cases runs from the bolt area to the back of the grip across the window. In those cases it is caused by too much flexing of that part of the riser where the forces of the two limbs being drawn concentrates against the fulcrim.

Personally I have found the I beam to be the pretty much fool proof answer.It adds about 15.00 to my costs and saves a ton of headaches and worry.

God bless , Steve