given the moment arm that is going to be exerted on the top frame member in that instance, I don’t think that is the best placement for the threaded rod attachment as it is likely to twist the 2x4 and possibly lever it out of the vertical frame members. Screwing into the end grain of the vertical frame member will be the weakest way to attach that horizontal frame member. Whether blocks or U-channel, I think it would be much more rigid and less likely to move if the attachment was made on the side of the vertical member.
This? (if using block)
I’m loving seeing these designs progress. We’re making substantial progress very quickly. I love the no CNC cut parts for the legs.
I agree that I am worried about the threaded rods. I am not sure that they are needed in the first place because we currently operate without moving the motors. I know that the argument for them is “what if someone wanted to cut a very thick material like a tree slab”, but that seems like an exception rather than the rule. I think the stock frame should focus on sheet goods in the 1/4 to 3/4 inch thickness range that we know works well.
I am also worried that regular all thread would not be strong enough. Most all thread is made from very low quality metal and bends easily so we would need to find some which of a much higher quality possibly even stainless which would probably drive the cost up.
This is the force I am worried about.
Can we come up with a design which achieves the effect of moving the top bar out using 2x4s?
pretty much.
channel will work, even the sheet metal version if it’s wrapped around a piece
of 2x4 and the holes are on the other side from the metal.
P.S. this is a reason to have the ability to run the top beam out a ways, it
lets you use the CNC to cut through the edge of 2x material accurately 
exactly what I was thinking
This design will be simpler and stronger:
We could leave the option to use threaded rods to make it adjustable for those who want to be able to cut on 2by material.
1 Like
- most people (everyone?) will put the Maslow against a wall, so why bother with supports on the ground ? Just the 2 vertical beams extending above the frame, leaning against the wall, provide the best leveling and support. The angle can be changed anytime and sheets can be stored behind it. It doesn’t require cnc cut parts.
you need to keep it from slipping flat, so just leaning against the wall isn’t
safe.
Also, a lot of people don’t have room to operate inside, and so have to pull it
out to use it.
- when working with flexible materials, structural integrity and stiffness
are achieved by crossing and layering. A grid of beams (less large than 2x4)
achieves that. It makes the plywood sheet obsolete (any sheet will do as
cutting protection), it also allows for frames of any size. No particular
construction angles are required.
it’s a lot more work (and a lot more expensive) to make a grid of beams, and
they will still get cut up when the programming is wrong. better to use cheap,
simple stuff 
2 Likes
for the tensioner mounts, that’s a good idea (although it may make it more
painful to trip over them), no need for any special inserts, or even allthread,
just bolt it to the 2x4 and use a 8" bolt. The exact distance isn’t critical,
it’s just useful to pull it forward.
for material support, I think you really want something that won’t damage things
when your eventually run the bit into it.
1 Like
I concur. Much as I love the idea of the threaded rod, I think that simple is the way to go. That said, without the plywood motor supports of the current stock design, additional height beyond the one 2x4 may be needed to put the sprockets close to the same plane as the sled balance point, however, this may be able to be done by simply mounting the motors to the opposite side of the included metal mounts a la @mrfugu’s implementation (which I copied and is working great). The one reservation I have with that is the moment arm that will be created on the screws holding the mount into the frame. I think it would be fine with 4 screws to hold each mount, but I am not certain.
1 Like
I think the problem is that in that drawing, the motor isn’t far enough away from the frame (may need to be a couple more inches). I think this might work (showing two options). Not sure about the size of the blocks that @dlang proposes in order to screw together two joints… so adjust as needed.
I measure that we want the plane of the chain 4.35 inches in from the supports.
The sprockets are .6 inches out from the motor mount when used in the old configuration so we want that front of the motor bracket to be about 3.75 inches out from the supports which means the front of the top bar is moved out 3.75 inches. A 2x4 spacer would get us to 3" and adding a 3/4 inch plywood spacer would be right where we want to be.
I threw together a test joint to make sure that 1) It could be built using just a drill and that 2) There was no play in the joint.
There is no play at all and it wasn’t difficult to make once I realized that the way to do it is to drill holes in one piece first and use it as a template to drill the others.
5 Likes
Thank you for the definitive on that measurement!
2 Likes
The reason I like the inserts is because, in my experience, when finely threaded bolts interface with wood, wood is the weak sister, and if there’s any movement, the bolts acts as a rasp. Inserts eliminate that, act as a bearing, and can be used to take the slop out of hand drilled holes.
Good point on the supports. Could do the same idea with lengths of dowel, basically a vertical bench dog. It wouldn’t be as precise, but not sure that actually matters.
I think you would need 3 2x4 blocks between the top beam and the frame
The original alternate 2 frame used 2x4s to move the top beam out
I’m measuring just one 2x4 spacer and one spacer of 3/4 plywood, did I miss something in my calculations?
This is what @dlang calculated. I think the key is the 3-4 inches for the balance point.
1 Like
Thank you.
I absolutely missed the the thickness of the waste board and material being cut so I am off by .75 + .5 = 1.5 inches
The real answer is around 5.85 inches
1 Like
Would need something like an 8-inch lag screw
1 Like
To get to 5.85" we would need two 2x4 spacers just like @madgrizzle shows above.
What are the advantages and disadvantages of using a lag bolt vs using a carriage bolt with a nut on the back. No preference for either one, I was just imagining carriage bolts?
I would say carriage bolts would offer more long term stability and can be tightened again if need be (as well as being able to be easily disassembled). However, a long hex bolt might be better so that large fender washers can be used on both sides.
2 Likes