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Why not completely vertical?

I was just musing about using the wall to mount my Maslow and I was curious whether there is any reason not to mount it entirely vertical?

Is there anything in the calcuations that adjust for frame angle or could it make it mildly more precise by being vertical?

Obviously there are considerations for workholding etc. But assuming the top beam es cantilevered off the wall to ensure the motors are in plane with the work surface, is there any reason this wouldn’t be an option?

-Jeff

when plunging the bit into the workpiece, it needs some force pushing it into
the material.

We had people test and find that if you were within ~5 degrees of vertical you
just couldn’t get the bit into the workpiece (and at 20 degrees, there is too
much friction)

I suspect that something closer to vertical will work better, but I haven’t got
my machine working well enough for a real comparison.

David Lang

I’m wondering if a four motor design will allow for something close to vertical. With two more cables on the bottom, the sled might not be able to push away from the board.

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it comes down to angles, the very flat angles of the cables will not produce
much force towards the workpiece

David Lang

If the sled is constrained from moving outwards because there are four cables, each under adequate tension to hold it in place, then the bit should go into the board. Are the four cables are going to be adequately taut to produce that force (i.e., sled doesn’t rise from the work surface in response to the bit being push into the work surface)? My money is on no, but I suspect it will at least lower the minimum angle… that is, if 15 degrees is required for two motors to work, then something less than 15 degrees would be required for four motors.

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remember that if the lines are perfectly parallel to the workpiece they will
apply zero force towards the workpiece. It’s only as they are angled out from
the workpiece (as you move towards the sled) that you will have any force at all
towards the workpiece.

David Lang

I got that, but let’s say there was so much tension on the cables that they were for all intents and purposes so rigid that the sled is unable to move. I could then turn the entire machine horizontal and upside down with the sled on the bottom and the bit still would go into the work surface because the sled cannot move.

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even if they were solid steel bars, there would be enough movement over several
feet that you would be able to pull the sled out an inch or so.

get a good heavy rope or chain, attach it between two cars that are on a hill
(the uphill car in park, the downhill car out of gear)

then pull on the center of the rope/chain and see how far you can move it before
you move the downhill car noticably (and note that you will be able to move it
noticably if you have a good long rope)

this is a similar problem to chain sag, you cannot pull a chain tight enough to
eliminate sag. some back-of-the-envelope numbers

if you have a 20 pound sled, with 5’ of line on each side (10’ total), a 1
degree sag would move the sled about 1", would put 280 pounds of tension on
the lines, and would strech the lines (or move the mounts) only about 0.02" Even
if we had a welded steel frame and brackets, you aren’t going to prevent the
mounts a few inches out from the main support behind the workpiece from flexing
that much.

you just cannot pull tight enough to eliminate sag, the multiplier as you get
closer and closer to zero sag just keeps going up. even solid steel bars will
strech

this isn’t exactly right, but do a chain sag calculation with tension of 4500N
(~1000 pounds), over 3.3m, with a total chain weight of 3Kg/M (~10Kg) and the
chain will sag ~9mm
https://www.spaceagecontrol.com/calccabm.htm?F=4500&a=3.3&q=3&g=9.81&Submit+Button=Calculate

in reality the sag will be a bit more as it would be a point load, not a heavy
chain as this calculates, but I couldn’t quickly find a proper calculator.

realistically, we are not going to get much above 100 pounds of tension, because
the wood will start flexing at that point (we already see it a little bit on the
current machines)

Insight into a problem is often gained by taking variables to the limits (0, infinity). If solid steel bars holding the sled in place doesn’t allow a router bit turning at 10k+ rpm to penetrate a sheet of plywood then you need to replace the router bit.

So, let me ask it this way… for a two motor design, if we somehow determine the optimal angle is 15 degrees, do you think attaching to motors to the bottom will affect the optimal angle by increasing it, decreasing it, or will have no effect? I think it will decrease it.

I’m in the ‘no effect’ camp on this. Add the cantilever effect of the z-axis and spindle/router to the things that tilt angle is used to offset…

I think it will have very little effect.

if you are at a 15 degree angle, each pound of sled weight will create ~.26
pounds of force towards the workpiece, so a 20 pound sled is about 5 pounds of
force

if you are vertical and have 100 pounds of tension on each of 4 lines, at 1/2"
deflection of the lines from parallel (i.e. the sled moving out 1/2") you will
have about 3.5 pounds of force towards the workpiece.

with the lines exactly parallel to the workpiece, you will have zero force
towards the workpiece.

the advantage that I see of going closer to vertical is reduced friction on the
sled (and therefor more of the small amount of force that’s available to move
the sled into the bottom corners). If the 4 motor version works, that eliminates
that bottlenec, but it won’t do anything for the cutting forces on the sled.

David Lang

I suspect with a four motor design that friction will not be an issue in the bottom corners and maybe this discussion is meaningless. I’d still keep the frame tilted to aid in keeping the plywood on the frame and the machine stable (don’t want it falling over). Perhaps if you had a wall mounted frame, you’d consider keeping it vertical advantageous. For standard frame designs, I do think you could reduce the angle to some extent if you wanted to because you are using four motors and still be able to penetrate into the plywood, but that’s where I’ll agree to disagree.

@madgrizzle You can believe whatever you like. What you are talking about is a thought experiment, @dlang is talking about real world data tested on actual working machines.
These angles have been tested quite a bit already (read through the threads). Also the chain cannot, for all intents and purposes, get any tighter.
A link chain provides almost zero lateral pressure, nor is it designed to. Four chains provide almost zero times four.
As stated above, even if you could tighten four chains well beyond the tension of this machine there would still be lateral slop due to their physical nature.
The Maslow works because gravity pulls the sled towards the workpiece, the chains are just essentially less stretchy string.
Would a vertical one take up less space and be more convenient, yes. Will the laws of physics allow that with this design, no.
Traditional (Cartesian) CNCs do not allow this either because the forces would be unequal depending on the direction of cut. I’m sure you could build one with modifications and beefier components to be vertical, but that would increase the price and complexity of those already expensive machines.
There are industrial examples of “vertical” CNCs but those are specialized and not really made for the materials we’re dealing with here, nor are anywhere near this class of machines.

No one has tested a four chain design to my knowledge so everyone, not just me, is doing a ‘thought experiment’.

All I’ve been arguing is that:

If I’m the only one that believes the earth is round… so be it :wink:

Again chain by design is not taut when working. Even much stouter chains such as those on motorcycles and industrial machinery must have slack or the chain does not function correctly and can fail.

And again they are in no way designed for lateral loads.

I get what you’re saying, and I like your outside of the box innovative thinking.
However chain does not function the way your supposition says it does.
Even if you tightened the chains well beyond working load spec they would still deflect quite a bit, even more so with your upside down thought.

I want a vertical Maslow too, that would of course be ideal from a space saving perspective.

Speaking of, have you seen this thread?:

It may be the answer to the vertical Maslow, might get us there.

The images on the left show the vertical two motor design. Doesn’t work well, completely agree, never argued otherwise… even though there is a component of force into the board for the right image of the pair due to gravity, albeit small and not enough to do anything worthwhile.

The images in the middle show a four motor design where the chains have elongated to accommodate the router being pushed away from the board, because no more chain was released during this z-axis move. This puts tension on the chains and there’s a component of the force the tension creates into the board (guy wires in radio towers put a significant compression force on the tower structure toward the ground in the very same way).

The images on the right is what I’m trying to get across. If 15 degrees turns out to be optimum for the two motor design, the effect of that extra force into the board in a four motor design results in something less than 15 degrees be optimum. I’m definitely not saying that 0 degrees is optimum… just that it will be less than 15 degrees… maybe it’s 10 degrees… or maybe its 14.9999 degrees… but it seems I’m being told it would still be precisely 15 degrees and that is what I disagree with.

And with ALL of that said, when I build my next four motor sled, I will still use a 15-degree frame.

I was mostly speaking to your question (title of this thread) as to why it would not work completely vertical and your comment about it working upside down.
I totally follow what you’re saying, I believe I get your logic.
What I’m saying is that I believe you’re grossly overestimating how mush force is applied laterally by the chain (in a four motor setup). This would be the same in even a 6 or 8 motor configuration.
I think it is negligible at best other than the extra gravity the chain applies when tilted towards the workpiece.
While the Maslow is new, bushing chain (aka “bicycle” chain), has been around for over 100 years and its function and limitations are well understood.
For the chain to function as designed it cannot be super tight. Also by design bushing chain has some lateral slop. Therefore there would be lateral slop and it would not be constrained in the perpendicular to the workpiece other than by gravity.

And since I too am just speculating based on experience, though NOT first hand knowledge with ANY Maslow in any configuration. I could be completely wrong and would welcome the opportunity to be proven wrong.
I love the healthy discussion on this board and especially respect those of you actually use one and especially those that iterate and innovate on it.

That being said I wonder if a four motor setup would be more accurate or could move quicker?
Something tells me time will tell.

Well, I didn’t start the topic, I only responded to it speculating that four motor design would reduce the optimum angle from a two motor design… my comment about upside down was predicated on solid bars or ‘infinite’ tension on cables, etc.

Whew…

I’m not claiming that it is any amount that makes a difference… just that it’s greater than zero. In practice, the bottom motors probably won’t be under much tension… especially compared to that of the top two motors.