March 22, 2013 at 3:18 pm #2852
first of all thanks for sharing this great project!
I am considering to build a V2 in the not too distant future. Now I wonder about two details which may be obvious for others, but I could not find any answer on this forum or in the project documentation.
Why are all wooden parts bolted together? In many cases glueing should be fine. I understand of course that some parts may better be bolted for later maintenance access, let alone mounting the metal parts.
Many other homebrew CNC projects drive threaded rods for moving along the axes whereas here timing belts are used. What is the advantage of using the timing belt concept? Are there no disadvantages when it comes to accuracy?
TomMarch 25, 2013 at 2:46 pm #4231
We decided to design this rig for folks who want to learn and do everything themselves. We were also interested in folks who didn’t have access to awesome machine parts (which you can easily buy as an American with a large budget). With this in mind, we designed around the cheapest plywood you can buy. This means that our design must account for varying thickness that is inherent to inexpensive sheet goods. That said, once you bolt everything together, there’s no reason you couldn’t follow up with glue after you make fit adjustments.
Belt is useful because it is cheap. It also allows users to reset their bed size based on need. Belt can be run faster – threaded rod usually increases gear ratios significantly (leading to increased torque and decreased speed). Accuracy may drop slightly depending on how tight you run the belt, but the amount of loss is pretty small in our experience. Rod is also really hard to cut without bending, as it’s often very soft as metals go.March 26, 2013 at 7:55 am #4232
Thanks Taylor for the detailed explanation.
The glueing came to my mind since I wanted to take the low budget approach one step further by hand cutting the parts with a table saw offering sufficient precision. If you do that then of course you want to avoid all those T-shaped wholes where ever possible. So I keep your hint in mind and watch out for sheet material with constant thickness. Where we need the T-wholes I wanted get these done with a scroll saw. Let’s see how far I get this…
As to the belt I also found another Source (Post Jan 13, 2008. 8:51 AM) where a formerly belt driven design was modified into a threaded rod design for increased accuracy. However, the accuracy achieved already with the belt drive was reported to be 0.050mm which is probably way enough for my intended use of milling parts out of balsa and plywood. So I will stick with the belt looking forward to running the machine faster. I do indeed intend to extend the y-axis to accommodate up to 1m long balsa planks as available in Europe. Another pro for the belt.
Thanks again and greetings from *again* snowed in Bavaria.
ThomasMarch 27, 2013 at 8:22 pm #4233
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