[Strix]

I just purchased two 3,000 mm sections of THK SSR35 rails. My original plan was to completely rebuild the motion and control on an old Shopbot frame using these instead of the grooved bearing system. However, as I have researched more and more DIY CNC designs, it seems that most people are getting good results with much smaller rails. I imagine weight could be an issue, which may reduce maximum speed, and the cost of the bearing blocks is impressive if I bought them all new. Aside from those negatives, are there other downsides I should be aware of before moving forward?

Thanks,

Andy

[awerby]

I don't think the extra weight of these rails is going to be a significant issue; they should work fine. Just make sure you get all the right scrapers and seals for the trucks, especially if you're not running them in bellows. They're a lot more sensitive to foreign matter getting in there than the grooved-wheel and V-rail system that Shopbot uses. https://technico.com/media/category/...l/LM_Guide.pdf

[peteeng]

Bigger is better in most regards when it comes to bearings. The main issue will be matching the stack heights of the drives to the cars as 35mm is quite tall. Plus they are longer so you will lose some travel unless you make the axes longer. Peter

[joeavaerage]

Hi,
if there is an item that you can go oversize and compromise your design is ballscrews. The rotational inertia of ballscrews is very significant, usually more than the linear bearings and axis weights.
This might seem counter intuitive, after all the axes are very VERY much heavier than the ballscrews right?........but ballscrews spin very fast, often 1000rpm or more, and that speed means that they have
a lot of momentum. If you get oversized ballscrews you will then need oversized servos or steppers to accelerate them....all in all you can spend a lot of money on overlarge ballscrews and servos. Sure they
are delightfully rigid but the cost and/or potential poor acceleration that results rather spoil that.

Craig