Learning Curve? Time requied?

First off …fantastic piece of hardware/software, least wise from the video I have seen. As a retired designer I can not begin to admire the simplicity, of the the design and the concept. Please accept my thanks and I think many also would agree. Beautiful design and approach.

My problem …I am up to my eyeballs in another project, Design and Build of an aircraft. While this would be a useful tool to build my assembly fixture for my wing, I have to wonder what might be the amount of time to receive the kit, build it, hook it up and learn a cam software to accept a DXF closed polyline for 2d cutouts.

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The answer is 42… No, just kidding :grin:

The biggest unknow variable in your question is

as it is unclear when sales for the kit opens again. However, there have been people selling their kit here on the forum.
https://forums.maslowcnc.com/c/swap-meet

Building, assumed you have the router, cutters and a few tools 1 - 2 days.

CAM software depends highly on your requirements. If have your dxf already, for just 2d cutouts, you can get away with scripts like dxf2gcode. There are a couple of simple tools that can import dxf and generate the gcode. You will have to know what information to put in, for example like bit diameter, feedrate, material thickness, stepdown etc.
bCNC also opens dxf and generates gcode. It is very simple. All you need to learn is, in what order to click the buttons. If you get the order wrong the program like to crash.
FreeCAD requires a 3d model to generate gcode, I assume the same goes for fusion360. The learning curve for 3d modelling is quite steep. Took me like 2 months (~ 8 hours/week) to get along with FreeCAD, but now I do CAD/CAM in one go with one software.

Edit1: Thank you @Onelonedork for liking :slight_smile: I like!
The edit is that I changed the link to https://forums.maslowcnc.com/c/swap-meet
Edit2: and some spelling mistakes I discovered later

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Thanks much on the easy gcode software. I am highly proficient AutoCad V14 (rather old version but does what I need to do) This does not seem to be a 3D tool anyway, and I am too lazy to learn another more complicated software. As with your experience with FreeCad probably shows. I am up in the air as to weather to just design the assembly fixture and have it done outside because of the potential time this would take to de-bug for me, and I think I might get the contour boards cut for about the same amount of money. It really looks like a nice tool though. I wish I knew more about software so I could understand it better.

They claim a rather decent repeatability, which makes sense, but what about absolute accuracy? Have they cut say 12" squares on all portions of the board and measured them?

I would think if the angles of the chain mounting was just a little off it would effect the absolute accuracy.

right now we are working out the issues with the maslow accuracy. If you need
something immediately it’s probably not for you. But check back in a month and
things may have changed.

Converting it to use triangular kinematics will improve accuracy as well. This can be done a number of ways but right now the most economic ideas appear to be using a ring and rollers or using a set of linkages. You can make either solution yourself or you could buy a kit. There is not yet a ring/roller kit that I am aware of but there is a linkage kit.

This is a really long thread but there are loads of really great ideas here: Throwing my hat in the sled modification ring

Also there’s lots more information about linkages here: Linkage kits are now available! 🎉

so how is the location determined, is the whole board mapped or equations that do the same thing?

Solid linkages certainly seems like a good idea, but increases the complexity and adds tolerance buildup with the linkage. I would think a simple drawing of a simple fixture to locate the motors relative to the center of the router, and stick with the basic design which in theory is sound.

My plotter is ± .010 accurate, if the accurate is absolute of .04 (1 mm) or more I probably could use a jig saw from my plotter plots.

Holy batman just started that thread.

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Tried to find but so much stuff really hard. Is the accuracy problem software or hardware/design. Apparently with all the sled re-design talk most think it is a hardware/design problem. So are there software issues?

it’s a mass of equasions, and the problem with the stock design is that there
are just too many variables

you have

  1. the space between the motors
  2. the space from the top of the work area to the motors
  3. the space between the chains where they attach to the sled (note that this is
    where the chains pivot, not the end of the chain inside the bracket)
  4. how much chain you loose from the calibrated ‘end of the chain’ and where the
    chain pivots
  5. the distance down from the line connecting the chain mounts to the center of
    the bit
  6. the distance down from the bit to the center of gravity of the sled.

if any of these measurements are off by a few mm, you see noticable errors in
your accuracy.

This is because you have the question of what angles you have in many places.
Depending on the left-right position of the sled, and the values of 3-6, the
sled tilts different amounts left to right. and depending on this angle, the bit
cuts in a different place. This angle also affects the angle of the chains, and
depending on the angles of the chains, they wrap around the sprockets a
different amount, which changes where they stop being a circle and become a
straight line.

This calculation is so messy that we don’t actually know how to calculate it by
putting in either the chain lengths or the desired X/Y coordinates and get back
the other set. Instead we have to guess, and see how far off we are, tweak our
guess and try again. By default we do this up to 5000 times (down from 50,000 in
earlier versions) and it’s not uncommon for us to run into the condition where
we give up.

the triangular kinematics is far simpler

  1. the space between the motors
  2. the space from the top of the work area to the motors
  3. the distance to add to the chain to get from the calibrated ‘end of the
    chain’ to the center of the bit.

this still has the problem of chain wrap around the sprockets, but other than
that, this is simple trig.

we can measure #1 fairly accurately, the chain has very little stretch, and not
much sag, so we can start from a (fairly) known position, run the chain out
until it reaches the other motor in a (fairly) known position, and pull the
chain tight. Since we know how far the motors have rotated in this whole
process, the amount of chain between the two motors is known pretty accurately.

We may be able to improve this measurement if we can more accurately position
the motors to start with (manually setting one prong on the sprocket ‘straight
up’ when you are measuring to an accuracy of 0.044 degrees isn’t that accurate),
and if we measure the sag of the chain (impossible to do with the stock frame,
not hard with the alternate ‘top beam’ approach)

making sure the frame isn’t flexing while the chain is pulled tight is also
important.

#2 doesn’t really matter that much, it’s an offset value, if it’s wrong, the
work area is a little higher or lower than you think it is.

#3 is the only remaining thing, and this is here the linkage vs ring debate
starts.

A. Which is easier to mount accurately (so that the chain motion is truely
centered on the bit)

B. Which has less error in use (chain rollers not moving plus tolerances in the
rollers/bearings) vs slop in linkages). Both have the question of flex in the
materials and wear on whatever joints there are.

C. Which makes it easier to define the amount to add to the chain.

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Yes, we have some software issues as well as the hardware issues. Part of the
reason for the hardware work is to simplify the software.

One of the key problems is figureing out how to detect errors between what the
software thinks the machine dimensions are, and what they actually are. This is
the intent of the calibration process, but it doesn’t actually work very well.

We also have no planning in the firmware, so it runs full speed until it
realizes it is at the point it wanted to get to and tries to stop instantly.

There is currently a lot of work being done to try and get the control loops
correct to move the machine smoothly through the desired motion

there are other issues (only supporting a handful of g-codes), but they don’t
affect the accuracy.

I expect to get the metal link parts in the next day or two.

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Great answers, I am reminded of the joke when the guy says “you had to be there” . I will be watching and more reading here. Will look at the linkage kits and see if I understand what is trying to be done.

at some point people are going to add x-y ball slides and feedback, but it will not be cheap and easy to ship anymore

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@meddesign

I’m interested in your build. Where are you located? How has it progressed?

Thank you

Build Log Aluminum Dragon Glider

CNC routers are being used for thin alum sheet, and plywood in the homebuilt aircraft movement.

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Very cool stuff. I can se how making Jigs would come in handy.

Thank you

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