Does everyone agree that something should change in the Default frame design; either the specification of the ābeamā should be shortened to 6-6.5", or there should be some explicit text that says the ābeamā should be mounted with 1.5-2" spaced off the back?
@dlang do you remember the reason for the 8" length? I thought we went over this enough times that it would be right, but now Iām second guessing myself. I canāt see any issue with @Joshuaās math
by the way, this is the beam support, the beam is the 10ā long part 
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see post 151 and 197 in this thread which result in 6-8" from the front of the
leg to the front of the beam (in part depending on how heavy and tall the router
is, and therefor where the sled balance point is)
I used a 10" beam support to allow for 3.5" overlap with the legs and 1.5"
overlap with the top beam.
when we shifted the beam off the front, we shortened the beam supports by 2"
I double-checked my machine. The spacing between the ring and the sled is 2.5", and the sled balances well with this spacing. When I do the math again, the beam support length should be:
3.5 depth of vertical top beam
+ 0.75" thickness of frame plywood
+ 0.25" thickness of sacrificial plywood
+ 0.75" thickness of plywood being cut
+ 0.75" thickness of sled base
+ 2.5" distance between sled surface and ring
- 0.5" distance from front surface of top beam to sprocket center
- 1.5" width of 2x4 top beam
= 6.5" length of top beam support
This is 1.5" shorter than the current specification.
Hereās my tally working from the vertical beam as zero.
For the top beam it is 6.5 inches from 4.5 for the beam and 1.5 for the thickness of the top beam, .5 for the gear extending past that.
On the sled side it is 3 from the ring to the sled. .75 from the sled to the surface being cut. .75 for the sheet being cut, .5 for the sacrificial layer underneath, .75 for the back of the machine for a total of 3+.75+.75+.5+.75 = 5.75"
Now considering that we do not always have a 1/2 inch protective layer and we are not always cutting 3/4 plywood I think we could cut 3/4 inch off the length of that beam and be better off.
Any objections to shortening that top beam by 1"?
There will be some variation in how high the ring is mounted for different routers
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@bar, I am not sure I fully follow your logic. However, we arrive at a very similar number. For the distance between the ring and the sled surface, I have 2.5 and you have 3. For the beam support length, I got 6.5" and you got 7". I think weāre inside the system-to-system variation.
I do not object.
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Wondering if this is why I am having issues! With my setup,
I am having chronic issues with the chain jumping/skipping on the left sprocket. Also, both chains tend to wrap around the sprockets as well. This happens a lot. When the chain jumps, I then have to go back and re-calibrate the chain lengths, then try again.
I spent most of the evening last night trying to re-align the motors so the chains donāt bind. I also tried shortening the elastic string to add tension, but when I moved the sled to the far left, the string snapped. So, I had to order a new string but am using a series of rubber bands until the correct part arrives.
I have a .75 base, I donāt use a 1/4" sacrificial board (should I). and I have a .75 sled. I plan to be cutting (mostly) 5/8" plywood.
I have my Maslow hanging on the wall in the garage. Mine measures from the back of the front leg to the face of the 10ā beam 5 1/2". Then 1/2" from the face of the beam to the front of the chain sprocket. total 6"
I then have 3/4" ply for my base, 5/8" ply sled, then 2 7/8" from top of sled to top of the ring. That gives me 4 1/4". Right now, I have a piece of 1" foam I am using to test the machine. So that gives me 5 1/4". That would be 3/4" less than 6" that the beam is set to.
Would 3/4" make that much difference? Wouldnāt that mean I would have to readjust the sprocket or ring on the sled depths if I wanted to cut thinner or thicker material in order to keep the chains parallel?
It canāt be that sensitive can it???
I wouldnāt expect it to be that sensitive. Iāve never had to adjust it for a different thickness of material.
Which side are the chains wrapping from? Is it the side attached to the sled or the side which is slack which is getting stuck on the gear?
It is the side with the slack. Which is why I tightened the string hoping that would help but in the end it was too much tension and snapped. I also put those (chain guides) on to help keep it aligned with the sprocket better. See picture
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and if you look at my calculations, I planned for 3/4 spoilboard while you use
1/4" and I planned for 3-3.5" from the top of the sled to the level of the
chains.
so that would account for the 1.5" difference between our calculations.
you should be able to operate with some error, 1.5" would be pushing it, but
somewhere around 3/4" should be getting into reasonable.
so shortening the top beam support from 8" to 6.5-7" is very reasonable for your
setup.
If you plan to have 3/4" plywood be the thickest thing you work on, I would
consider going to to 6", if you plan to work on thicker stuff, keep them on the
long side.
Iāll point out that itās a lot easier to add a thicker spoilboard when you are
working on thin stuff than it is to remove thickness when working on thicker
stuff.
note that if you remove a brick from the sled, the CG will move away from the
sled, so you would want things a little taller in that case.
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So if we still are using the outdated original frame with no top bar design, what would be the easiest conversion to adding a top bar? Should I just bolt a 2x4x10 onto the [wings? ears? not sure what to call them] of the original frame and relocate the motors? I like the idea of reducing flex and increasing accuracy, but donāt feel like building a whole new frame. Making the CNC cut one was such an achievement for me!
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Sounds right. Even if there is flex parallel to the worksheet in the ārabbit earsā (what I called them), it should not effect accuracy to much and if, a few āstiffenersā will do.
In the original frame, there are two problems
-
the frame flexes in the middle. a 2x4 bolted between the wings solves this
problem even if you donāt move the motors. -
the motor mounts can flex (in a couple directions, āflappingā perpendicular
to the 2x4 they are mounted on, and ātwistingā as the chains pull roughtly
parallel to the 2x4 they are mounted on). This added distance from the support
also gives the motors more leverage to flex the entire frame, making problem #1
worse
the new frame solves this by bolting the motors to the top beam with as little
offset as possible, but this requires moving the beam forward of the frame. This
should probably be about 4.5" or so, so you could stack 3 layers of 2x4 between
the existing wings and the new top beam and be in the ballpark (see if your
chains are parallel to the workpiece with the sled balanced and change this
stack accordingly)
it wonāt be the prettiest thing, but it will work.
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Okay, Iāve already torn apart the default frame and re-designed it. Nothing wrong with the default frame. I have limited space in my garage and I desperately need a plywood storage cart. I decided to combine the default Maslow frame and a plywood cart. Itās only a small modification from the default frame. I also had to lower the overall height to allow for wheels. This is due to the height of my garage door.
The motors are 19" (482.6mm) above the plywood work space. I donāt know if this is too much, but I found in another post that 18" was what it was in Barās Bolt Together frame. And the work space is inclined at 13.5 degrees.
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Cool. Thatās pretty much the same thing I was thinking. It loses some of the cool look but I care more about function and accuracy. I will probably do the top bar modification when my triangulation kit comes in (since Iāll have to recalibrate then anyway).
Now, quick question in general: How have the big improvements to the frame and the triangulation setup helped yallās individual performance / accuracy on cutting parts that are near to the extents of the cutting surface? Iām talking mainly about the corners and the upper middle near the very edge. Whenever I try to cut somewhere besides the middle and lower middle 70% of the plywood, my machine struggles.
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Huh? Come again? 
If I try to cut a part all the way at one of the lower corners, I have to babysit the machine quite a bit, or the cuts will not be straight.
Likewise at the top edge, I have seen the flexing issue cause problems.
I get around these problems for now by pretty much only cutting parts in the lower middle section of the plywood (where the maslow seems to do the best job by itself) and avoiding the upper 30% of the plywood entirely. I rotate or shift around the plywood accordingly and have maybe 3 or 4 design files instead of 1 to cut parts on a full sheet. It works but itās not elegant.
I want to know how close to the edges of the plywood you guys with the latest and greatest builds are able to cut without worrying about it