My vote is the one on the right. I am not all that interested in drilling a huge hole through multiple 2x4’s, which would require a power-drill and a large bit. It would be cheaper to purchase a square, and go with the one on the right. Even though the option on the left feels rigid now, a small amount of wood will yield underneath the bolt over time, and it will become loose. If rigidity is an issue with the version on the right, there are a few options: glue; and double/triple 2x4’s, stacked either vertically or horizontally. I am a fan of wood glue.
If one bolt ended up at the top of the hole (1/8 inch high) and the other at the bottom of the hole (1/8 inch low) for a delta of 1/4 inch, will this very so slight tilt make an appreciable impact on accuracy?
I think the joint just needs to support the weight of the top beam, motors, chain and sled and any associated dynamics that might take place as the sled moves. It’s the top beam that’s taking the stress. The arm is just holding it there.
It would just be a regular 3/8ths drill bit and each hole would be drilled separately, then the parts would be bolted together so it shouldn’t require any special tools.
Would anyone else be willing to build both options and give feedback?
I think I’m biased because I found one simpler to build than the other, but that’s really a matter of opinion. It would be great to get a second perspective on ease of construction
@bar I have built a version using parts of both designs. I have the motors mounted on blocks bolted to the beam using your 3/8 inch 10 inch bolts. I can loosen the bolt and add in blocks of different thickness to adjust for project depth. I am going to do a calibration tonight and want to see what they do with the tension of the measuring between motors. If it flexes too much, I will swap the blocks to the back and use the front beam as the motor mount (if that all makes sense)
[quote=“bar, post:518, topic:2025, full:true”]
Thanks for illustrating this concern.
I think the key thing that we’re not agreeing on is that the hole the bolt passes through doesn’t matter. The hole could be 1/4 inch larger than the bolt if you want so that alignment there is not critical. In fact the holes HAVE to be too big to account for the human error of the person who is building the frame.
Imagine the case where the holes are 1/4 inch too big and the bolt hangs loose as shown in the picture. As the nut is tightened the bolt essentially becomes shorter and pulls itself into true.
[/quit]
This is part of where I disagree.
even if the bolt was straight, things can still be off by the amount of slop in the holes
I disagree that tightening the bolt will pull it true. It will pull it towards true, but never all the way
I think this is more a theoretical problem than a real one. I can’t imagine someone angling things so badly that it causes chain feed problems.
did you build the one on the right with glue, or just screws?
blocks moving the motor out from the beam will work (and work much better than the old winged frame), but are not quite as good as moving the entire beam out from the legs
the key is that you want to make sure the horizontal board doesn’t move at all, nailing these to the side of a joint is not as good as a glued/screwed wood-to-wood joint, because the nails through the holes have just a little give as the nails work loose over time.
Also, what diameter bolt and drill bit size should I test? I know I have a 3/8-inch bit… I don’t know that I have a 1/2-inch. I see earlier a 3/8-inch drill bit was required but then it was mentioned to oversize the hole by 1/4-inch… Maybe that was an example, but with a 3/8-inch hole - 1/4-inch is 1/8-inch. Should I try a 1/4-inch bolt through a 3/8-inch hole providing 1/8-inch oversize?
I used a 10 inch 3/8ths bolt. I think I just went one drill bit size larger than the bolt to make it slide in easily and the holes were drilled free-hand (no jigs to try to make everything perfectly square)
I can’t, however, commit to having it done tonight (life may get in the way)
