Just have to drill all the way through the 2x4 on edge and based on early discussions, sounded difficult to doā¦ Need a 10-inch carriage bolt to get all the way through it all. I donāt have a preference, was just āillustratingā for everyone.
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It might be possible to avoid drilling through the 2x4 long dimension by using a couple of smaller 2x4 blocks screwed into the vertical member and drilled through the short axis.
Here are my takeaways from having built this one.
Drilling through the 2x4 in the long way is really not as hard as I would have expected. I upped the size of bolt that I am using to a 3/8 carriage bolt which meant that my 25/64ths drill bit was more than long enough to reach all the way through. With the 1/4 inch bolts I was using before the bit was barely long enough.
Initially I tried to do two bolts, but drilling a perfectly straight hole through 10 inches of wood turned out to be nearly impossible so I switched to a single bolt.
With just one hole to line up all the way through alignment wasnāt an issue. If I could do it again I would switch to a hex head bolt (not available in 3/8 10" at the hardware store here) so that I could tighten everything better. Even using the carriage bolt I was able to get it pretty tight and there was very little play.
It was substantially (2x or 3x) stiffer than my frame right now, and because the motors are both anchored to a single piece of wood the only dynamic force on the connection comes from the force of the bit moving through the wood which is quite small.
This system is already much better than the old design, but I bet we can improve it further. I am going to try a 1/2" hex bolt so I can really squish everything tight, and I am also going to try flipping the outer board by 90 degrees to remove one of the 2x4 spacers since drilling the long way was not too difficult.
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That board I think you are talking about is the top beam for the motors to mount on. Iām not sure if it matters if its horizontal or verticalā¦ @dlang?
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that seems like itās very short.
if you have
3/4 main plywood
3/4 sled plywood
1/2" workpiece
(note, no wasteboard)
that uses up 2 inches of your 4.35 inches, so you have the chain 2 1/4" above the surface of the sled? everyone else Iāve been seeing post seems to have it significantly higher.
@madgrizzle pointed out your calculations to me and you are totally right that I was short
These 1/2" by 10" hex head bolts are beautiful. They arenāt cheap, but I want to use them just because they are so pretty!
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what a day for such a fast discussion to be going on. I only have 1 hour today that Iām not in meetings :-/
part of the question is how far out to the edges you are supporting it. If your legs are spaced widely, having it horizontal is best (best resistance to whatever bending forces exist from the chain)
If you space the legs a bit more narrowly (say the 54 inches I did) so that you can build the frame with less wood, then I would seriously consider putting it on edge (even if this needed another spacer)
If the board is on-edge, then unistrut or a 2x4 are pretty interchangeable (1 1/2" vs 1 5/8"), but if you put the 2x flat, thatās no longer the case (but you could add another spacer)
one note, the new motor brackets I designed will work perfectly well on either unistrut or 2x4 on edge, but you would have to cut a slot in the wood to use a flat 2x4. They wonāt be used for this third set of machines, but would be a possibility for the fourth.
Also, remember that almost all the force is going through the beam, the bolts/spacers are no longer handling nearly as much in the way of force
They only have to support the weight on the beam and sled, which is pretty static (call it 30-50 pounds even for a massive sled)
As opposed to the weight of the beam and sled, and the forces on the chains (call it 170 pounds at peak), with the force fluctuating significantly.
Thatās why I think that a threaded rod/bolt standoff would be āgood enoughā
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yeah, catching up after a few hours of meetings.
Yep, they are pretty, allthread is probably cheaper at that size.
I do want to point out the original alternate2 support where we glue/bolt a hunk of 2x material to the frame and then fasten the beam to it at the right distance. Eliminating adjustability would make this about 9.5" long (I used 12" in my images)
Also, donāt forget to level the top beam before tightening the bolts down. With so many spacers, one side or the other can droop.
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This is a really great point that we should keep in mind
Thanks for circling back to that. I agree that after having thought about it more and done more tests I think this is an idea we should test and I will test it
Note that the support boards will be FAR more stable if glued, but build it just screwed bolted initially to get a feel for it
If the support board is glued/screwed both to the top and the side it should be very stiff
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The 1/2 inch hex head bolt joint is rock solid with no flext at all. It was much easier to tighten down than the carriage bolt. Great recommendation @Keith
I think ultimately if we go this route a 3/8ths bolt would be plenty strong and my drill index only goes up to 1/2 inch so the holes were all a little bit more snug that I would have liked. The bolt is only under tension and the 3/8ths bolt will be plenty strong in that direction.
Next I will test the version with the cross brace 2x4 rotated to reduce the number of spacers needed.
@dlang will you show me a diagram of exactly what I should test? No rush, I will probably not be able to get two more tests in today.
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I will post a closeup in onshape on about 30 min
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The configuration with the both 2x4s drilled the long way is also rock solid, but Iām not sure I see any advantage over the other orientation.
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There are two variations
I am sure that the version on the right (2x4 on edge) will be strong enough if glued (and probably if you just use screws/lag bolts)
The version n the left gives more clearance, which only matters if you plan to have it extra long to allow the beam to move forward.
I would say try the version on the right (with a 10" long 2x4), and if you like it, we can try the version on the left, which is easier to attach the top beam to (as you only have to screw up through the narrow dimension of the 2x4)
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a quick note on this approach, the blocks donāt have to be at the corner, they could be moved inboard if needed (for example, to leave extra allthread to allow you to move it out, but not have the allthread get in the way of the chain when cutting in the top corner on the other side)
I would think that the version on the right with the yellow 2x4 screwed into the face of the short 2x4. I would think that if you screwed the short 2x4 into the top purple 2x and the gray right 2x that you would have one strong joint and there would be no need for glue.
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@bar, if you have some spare nuts that fit the bolt, can you test the stiffness without the spacer (i.e., the allthread design we kicked around)?
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The problem that Bar is going to have is he has 10" bolts with only about 1 1/2" of threads so not enough threads to check the stiffness if he fastens it to a 2x.
Yep, forgot threads didnāt go all the wayā¦ oh well.