Hey all! Excited to get mine in September. Love the discussion on the forums.
I use 5x5 Baltic birch almost exclusively and garage space is at a premium so…
How can I calculate the frame size for:
A 5x5 piece with maybe a 6" border so the sled doesn’t hit or
A vertical 8’x5’setup that could use my 10’ ceiling.
I know someone posted a python script but I’m a programming newb. I have gc running on windows 7 for what it’s worth.
I’m pretty sure the 2 major considerations with regards to frame size are
(Disclaimer: I don’t yet have a maslowCNC)
accuracy: if the machine is of smaller outside dimensions than the default ratio of workspace to motor placement than it will not be as accurate as it can be. This doesn’t seem to be a problem in your case, keep at least the same ratio as a default machine. (where the motors are approx 24" @ 45deg from the 8’x4’workspace)
supplied chain length: the kit supplied chains are only so long, not a concern in a smaller build, but certainly a growing concern in a larger one, along with an ever growing chain weight and the resulting ‘sag’ and effort raising the sled to the top of a work surface.
In short, it shouldn’t be a problem to make a smaller machine, although currently GroundControl isn’t optimized for inputting a radically different machine size, it can be told that the machine size is different than expected and will accommodate your build. (common sense will be needed when operating GC with a different sized machine)
The concerns are:
- the sled needs to keep tension on both chains and if it gets too nearly beneath one motor, the other chain doesn’t have enough tension for accuracy. Space the motors wider if growing the work area wider.
- Great force is needed to pull the sled up near the top of the sheet where the chains become nearly horizontal. Move the motors higher to keep them well above the top of the work area to avoid the wide angle.
You can work on this in a CAD program (good practice for learning - pick one you’ll use for designing things to cut once the machine is built and running ) or with pencil and paper.
A good starting point might be the well-documented design in this thread. @dlang has put a lot of thought into the forces involved, and provided the software for exploring the geometry that you mentioned.
It looks to me like the beam across the top could be 12 feet long, and the verticals extended by a foot, and you would keep chain angles similar to the stock setup over a 5’x5’ panel. Getting to 8’x4’ portrait orientation while keeping the angle would probably grow beyond the 10’ height you mentioned.
Note that you’ll probably need longer chains for these modifications. Bar and Hannah don’t offer chain in their store - yet, nudge, nudge - but you’ve got time to calculate how much you’ll need to add and get some.
The concerns are:
- the sled needs to keep tension on both chains and if it gets too nearly
beneath one motor, the other chain doesn¢t have enough tension for accuracy.
Space the motors wider if growing the work area wider.
The current design lets the chain angles get as steep as 80 degrees (10 from
vertical), this is probably pushing it from what we are seeing.
Going to a 5’ tall machine, you would want to move the motors out a bit,
probably about 7’ spacing.
for a portrait mode 4x8 machine you may want to go a little wider, but may be
able to get by with 7’ spacing (check the accuracy in the bottom corners to see
if it satisfies you
- Great force is needed to pull the sled up near the top of the sheet where
the chains become nearly horizontal. Move the motors higher to keep them well
above the top of the work area to avoid the wide angle.
The stock design has them ~18" above the top of the cutting area, giving
yourself a few more inches will help
Note that you¢ll probably need longer chains for these modifications. Bar and Hannah don¢t offer chain in their store - yet, nudge, nudge - but you¢ve got time to calculate how much you¢ll need to add and get some.
#25 roller chain is readily available from many sources, usually in 10’ lengths,
but master links are cheap.
To add chain you’re going to need a Chain breaker and some chain which you can find here in colors. If you scroll down there is even a package that includes the Chain Tool $9.99 that’s needed to quickly and easily break the chain, add in links, push the pins back in to heal the chain. I can’t vouch for that particular brand Chain Tool. I’ve only ever used Park Chain Tool. $34.16,
Since you will be breaking chain anyway to add length. I’d get one of those colored chains even the Shiny Nickle one. That way you can use it to mark where your calibration is correct. Like people are doing with paint markers. Just seems like it would be much easier to see a brightly colored link than a lil mark.
I’ll also advise go slow. That pin is EASY to bend on the expensive heavy duty Park.
If you have never used a Chain Tool here’s a video on How to Replace a bicycle chain.
I think you missed my point in using a different colored link to mark on your chain where it’s residing on the motor drive sprocket when the sled properly centered on the material. That way the chains can be completely taken off the motors and put back on without having to run calibration again, also helps to see if the chain has jumped and caused the calibration to be off… I’m just expounding on something several people have done where they mark that link with a paint marker. It’s just much easier to find a completely different colored link than a link with a little paint mark on it. It’s a really simple hack with a lot of Pros and no Cons, but that’s just how I see it.