Wow! I am wearing the ol’ brain cells down to the nub in the research of building a better CNC mousetrap, sometimes referred to as HB2. To the uninformed I am alluding to the next incarnation of a Home Brew CNC router, the design for which I am currently contemplating. What follows is an unexpected personal realization. I have found a very nice quality commercial CNC product line, the components and design of which I am presently admiring. The brand name is Techno Inc.. On their industrial CNC machines these folks have one of the best debris protection schemes for their ball style linear components. That is because the linear components are enclosed, using strong aluminum extrusions which include rubber-like dust seals. The majority of other brand machines let their linear components hang out in the breeze out in all the dust and contaminants, pretty much like I did with HB1.
The home brew design folks (me) are the worst at this lack of component protection. The plain truth is the linear components (especially ball glides) are not impervious to contamination. Dust shields and wipers are a must for long life. Enclosing these components is even better protection but more costly.
When using open construction with exposed linear components, the all-plastic sleeve type guides rather than ball guides actually perform better in contaminated environments. Yes, even ordinary sawdust is serious contamination that can “gum up” linear ball glides. The solid guides have no passageways to get filled with debris.
Mass or weight is a good thing in any machine tool that has rapidly and accurately moving parts. Not in the moving parts themselves but in the areas where the moving parts are attached. Weight is beneficial when it increases rigidity. The medium size machines I have considered building are in the many hundreds of pounds range. Yes, there are large light weight machines but they are far from accurate or consistent.
The downside to the good practice of using proper seals and wipers and heavy weight is that it makes the hardware costly. $10K for a well designed small to medium size commercial machine is a typical and necessary price for a high quality product.
For me, that much money must be a working “asset” class of investment. I can only justify that kind of money when I foresee a financial return. A more affluent person (than I) could make that kind of investment just for the fun or experience and not for financial gain; a definition of a true hobby. But the wealthy protect their investment even in a hobby by purchasing high quality, because it retains long term value.
For me, I may want to liquidate an asset that isn’t productive. To do that, there must be sufficient tangible value remaining that attracts a buyer. That is why I call it an asset.
The truth now so apparent to me is that larger, high quality home brew OR brand name CNC routing machines are not likely to be a financially reasonable out-of-pocket purchase for most just-for-fun hobbyist. I also see investing a lot of money into a medium to large one-off home built design as a huge risk. Even if the home made design actually works very well, such non-commercial machines will be nearly impossible to sell or trade up to a larger machine if the time comes. Buyers and dealers prefer brand name products for repurchase or trade-in. A home made machine will have to be impeccable to retain any long term resale value. Yes, it has been done by a few and if there were no reasonable (price or quality) alternatives, building would be the best path.
The hobbyists folks who don’t have a personal cache of cash to tap, may need to finance such a high cost tool and have a plan on how to make the payments. I think it would be very awkward for me to explain to the banker’s that I want to buy a bunch of components and build from scratch. So unless I have a great business plan or an existing open line of credit, the banker will want to have something tangible to attached to the loan. High interest credit cards are never a good financing alternative.
So my rule is: “I will only use available disposable funds when building any hobby project for the fun of it. I will stay within a budget. I will enjoy the process. I will keep the size down if it keeps accuracy and usability high and cost low.
If my goal is to produce a large but cheap machine, I will probably succeed in several unexpected ways. I will have no one to blame but myself if it does not perform as desired.”
If I want to actually invest in a quality medium to large CNC machine for making things accurately, then for me a home built design may be possible but may not be the best avenue to get there.