3DP linear bearing (recirculating) and DIY linear rail 4.5mm bb (Final version) by Baltojikale

Last crawled date: 3 years, 3 months ago

Attention: aluminium profiles not always up to spec thus model (cad fusion 360) should be eddited (added slimmer outer part model for under spec aluminum beam, in my case bought 15x2 m but actually it was 15x1.8mm)
DP linear bearing and DIY linear rail (4.5mm bb) (final version??)
Introduction
Been searching cheap alternative which can be 3d printable (partially) and made from easily acquirable materials from home depo or similar home improvement shops. Main challenge was to innovate linear rail design which could have mounting holes to flat surface. There are few recirculating linear bearing designs on thingiverse or other depositories. Most of them designed to be used with 3dp rails or V or T aluminum profiles. T or V slot aluminum profiles ware out of question as their not that accessible locally. Thus simple profiles were used to produce linear rail. For linear bearing prototype was made with 3mm steel ball bearings. Updated versions include 6mm airsoft bullet bb's and 4.5mm pneumatic gun bullet bb's. All mentioned bb's are also available and common sizes used for real bearings. One could try to find bbs in local stores which specializes in bearings for machinery, airsoft/gun/hunting equipment shop (pneumatic bullets).
BB
Main difference between real bb from steel bullets bb is the bb precision and price. Bullets precision usually two decimals places while real bb can be 3 and more (for example 6.00mm and real bb 6.0000mm). From price point difference is substantial: 4.5mm pneumatic steel bullet bbs 1500 bb/pack - 7euros ; 4.5000mm real ball bearings 100 bb/pack -3euros (local prices, internet/online prices can be lower but tendency is same). Plastic bb if available are very cheap.
Design
Linear rail
Rail was produced from rectangular 15x2 mm aluminum beam and from 10x10 mm aluminum square tube (10x10+15x2mm). Two pieces were center drilled and riveted to acquire shape which can provide rolling surface for BB’s. Making rail involves printing alignment jig (or jigs). For hole drilling best to use calipers and pointy punch to mark drilling holes.
Linear bearing
Design was improved upon few iterations. Design required to incorporate tensioning mechanics towards linear rail. Thus bearing is made up from 3 printable parts (hardware not accounted). Size is kept as small as possible but also leaving some thick zones for sturdiness. Left opening to manually access bb grooves/tracks. Sometimes some derby are left after printing thus openings allow to clean them with pointy files. "Outer" parts have designed holes for lubrication. Because bb grooves are open, grease(or oil) can reach all 4 tracks in linear bearing. For grease, personally I used petroleum gel (vaseline for machinery, at least that what was written on gel tube).
Contact points
This rail and bearing design incorporates at least 6 points of contact between rail and BB. At contact points were BB meats plastic round shape was changed to square or rounded square to minimize friction as round object cannot run in round groove as linear velocities at different points of spherical bb aren't the same as overall bb movement linear speed.
Printing
Used Pla with 25-35% infill, for dimensional accuracy printed outer walls first and very slowly (~10mm/s) 0.4mm nozzle. Printer slicing profile should be calibrated, at least for inner holes. For my set up I scale up models by 0.5% to compensate for part shrinking. Used 4.5 mm BB thus model has incorporated 4.8 mm diameter BB guide grooves.
Tensioning system
Current model has incorporated 10 degree tapered surface which also acts as tensioning mechanism when two meeting parts are bolted together. Parts during bolting slides one against other thus tensioning force are created at 10 degree angle which allows small (0.5mm) adjustment towards linear rail center. "Inner" parts have oval shaped holes thus M3 screws have space for sideways movement.
Why 4.5mm???
3mm version works the best. Smallest linear carriage most smooth performance. Due to small size sometimes is hard to get good bb groove as tolerances are small thus printer should be calibrated well. 3mm bb dont have any alternative(no airsoft/gun application or at least i dont know any at this moment) , thus only genuine ones can be used. Genuine bb price starts 1~2e per 100bb/pack. One linear bearing takes up about ~120bb.
6mm version is best for bb source because one can use airsoft steel or plastic bullets and genuine bb. Plastic bullets slide most quietly and are very cheap (5000bb/pack -7e). Steel bb either for airsoft or genuine ones are costly. Drawbacks are that printed bearing is quite big, thus longer printing time but its easier to clean up (stringing or similar 3dp artifacts).
Need wider linear rail as aluminum strip should be at least 6mm wider than aluminum square tube, thus first size starts at 15x15+25x2mm
4.5mm very cheap alternatives for genuine bb's with various surface finishes (1500bb/pack -7e). Size vise linear bearing isn't much bigger than 3mm version. can be made to fit 10x10+15x2 mm linear rail. Size vise easy to print and clean up. Many options for bb's.
Aluminium vs anodized aluminum
anodized aluminum should be used with steel bb as steel is much harder than aluminum thus protective coat should prolong work time of rail, as steel bb can grind in to aluminum. for 4.5mm version one can use copper coated lead core or plastic bbs. Copper and lead are quite soft metals, thus aluminum should not wear that much.
3mm versionhttps://www.thingiverse.com/thing:4671314
6mm versionhttps://www.thingiverse.com/thing:4672409
Short demonstrationhttps://youtu.be/ryh3pSujLEY
Further development
Application in cnc project. Currently working on test model of corexy laser cnc. Still testing.