I bought one of these Chinese aluminium BDM frame with 4 probes. $95 shipped. General quality it’s good, very massive. Middle deck is wobbling all over the place, apart that, the item is very well built.
There to much play when you want to adjust. There is not linear bearing.
I find a solution to rework it. The ones that needed bearings was the ones without that middle windup mech.
Now the frame is smooth as anything. It is very cheap device, good for beginners. Hope it helps.
the rods are 13mm and 13mm linear bearings are not so common.
(so I will get 2 new longer 12+mm custom cut rods with minimal clearance possible and 12mm linear bearings. or just turn down the 13mm rods ~1mm)
I will eliminate the windup mech also cause the threads are way to large and the decent is not linear.
The bearings will eliminate this but the windup mech is also taking the place that can be used to rest the reading tool above the deck for easy operation.
I also get the set of 22 adapters. Quality is 7 of 10. Some pins needs reposition but for that price range is ok.
I mounted the bearings under the middle deck to facilitate the adapter insertion and to also have a “safety stop” in case of accidental deck collaps.
the new rods were cut to 12.02 for perfect matching of the bearings, there is zero play, proper centred,the deck is slinding just perfect.
the winding mechanism was deleted to make room for the reading tool, new lateral holes with M6 threads and ball-bearing stop for proper operation.
I put some LEDs also, need to put the wires + connector and job done.
for bearings I used: LMF12UU (12mm),
(13mm linear bearings can be also found to use with original rods. in my case I didn’t find any, so instead to import them I decided to go for 12mm system)
I use this bdm frame china rework with linear bearings 12-mm work very well…very stable after rework.