Ok, here’s a bit of a strange question with an obvious answer, but I’m looking for an opinion due to the materials available to me.
the situation is this: I’m building my free motion roller assembly and I’m about to drill and tap the legs for the bolts to hold the wheels on the roller frame. the legs are made out of Aluminum (I’m not sure which grade Al but I’m assuming it is pretty standard nothing aircraft grade or anything). Now obviously the right thing to do is to send the bolt all the way through the 1/4" leg and put a nut on the other side for the best results. So here is the rub, I don’t have alot of clearance on the other side of the leg for the nut due to the palcement of roller.
So the question is if I’m running four wheels am I going to have a big problems just screwing them into the 1/4" Al feet without running a nut on the other side? Obviously I’d loctite the bolts (5/16 x 18 thread grade 5) to keep them from working their way out, but am I running the risk of stripping out the threads on the soft Al without the backside nut?
I’m not sure what you call a nut-shaped countersink, but can you do that on the nut-side, so you can use a strong stainless “captured” nut, capturing enough threads and allowing you to shorten the protrusion on the roller side? Can you have the bolt enter from the roller side and use a very flat headed bolt?, and nut the other side?
1/4" is not adequate engagement for a 5/16" bolt. you’d need to be more like 1.5-2D. can you post a pic of the problem area, you may get better feedback.
What you want are rivet nuts or nut inserts. Start here, click Fasteners, then Thread Inserts, then RivetNuts/Nut Inserts. Both function in a similar manner: Drill an over-sized hole in your material, insert the insert, then crimp it upon itself using a puller tool (just like using pop-rivets). Select the diameter & grip length as needed for your application. The only drawback is that you’ll have to buy the puller tool.
Without knowing how much clearance you have on the inside of the aluminum rail, it’s hard to tell what type of fastener to use. You could countersink the inside of the rail or use a fat pan-head machine screw with the nut on the outside. If your material looks too thin, use another piece of aluminum as a stiffener between the frame & wheels.
Or you could go to Home Depot & pick up a pop-rivet kit…