Like several BigBox owners, my build platform wobbled in the horizontal (X-Y) plane. This mostly manifested near the top of tall prints where the Z-platform is down low near the couplers. This is because no leadscrews are perfectly straight, and the shorter the distance between the leadscrew nut and the coupler, the more that bends in the leadscrews transfer into undesired horizontal platform motion. My naive initial reaction was buy new leadscrews. So much disappointment I tried a domestic and three Far East suppliers and honestly, they were all over the map. In one case, two 'identical' leadscrews from a vendor were not the same 2 mm pitch! Long story short, some were better than others, and by picking the best two out of many I got slightly better results. Still it was frustrating to command the bed up or down and watch the top end of the leadscrews wobble about... Patrick Notton found THIS instructive video explaining how leadscrews are made. The rolling process is not intended to make perfectly straight leadscrews, but rather straight enough ones. On small sizes like we're interested in, manufacturers quote straightness numbers like 0.3 mm per 300 mm. Honestly, that's not good enough for the BigBox. What manufacturers will tell you is that, if you need better straightness, you need to have the manufacturer cut the leadscrews to length, have them do whatever machining you need on the ends, and then they will manually straighten them to meet your requirements. After doing a little research and following some leads suggested by Patrick, I decided another part of the problem was depending on Tr8x2 leadscrews which are basically 'miniature components' so not a lot of manufacturers bother with them. Tr10x2 seem to be the smallest standard size so I focused on them. I went back and forth with a few manufacturers, and found that Screw Technology Co., Ltd. was willing to make us a small batch of stainless steel Tr10x2 leadscrews with custom POM (Delrin) leadscrew nuts. They promised to hold the straightness to better than 0.1mm / 300 mm for a very reasonable price! I took a chance and wired Screw Technology the money. Two weeks later we had ten custom leadscrews and 20 custom plastic leadscrew nuts. The photo below shows original Tr8 and new Tr10 leadscrew/nut pairs. All ten were straighter than any of the original BigBox or aftermarket Tr8x2 leadscrews I had bought. So straight! Rolling them on a glass table was astounding! They were exactly the specified length and Screw Technology had machined the ends down to 8 mm so I could use our existing 8 mm couplers and constrain the tops using 8 mm pillow blocks (a plastic pillow block is shown in the photo above) Unfortunately, the BigBox Z-platform can not accommodate the larger Tr10x2 hardware. I modified my EphBox-3 frame drawings to make them fit. The next photo shows the redesigned EphBox-3 platform with the Tr10x2 hardware near the bottom travel limit. The advantage of the POM nuts mated to stainless steel leadscrews is that I can and do run the leadscrews dry with no grease or oil. The next photo shows the plastic Igus pillow blocks mounted to the Upper Support panels. What's amazing is the pillow blocks seem to be essentially unneeded. If I remove the pillow blocks, the top of the leadscrews barely move as the Z-platform travels. How well does it work? Here's a completed 290x50 mm test cylinder. The entire length is remarkably uniform. Here's a closeup of the top of the cylinder where the wobble would be expected to be worst. My straight edge has tic marks every 1/64" (0.4 mm). If you zoom in, you'll see there is some residual wobble with a 2 mm pitch and amplitude is about 100 micron as expected from the straightness specification. Whew! That's about it. Not a simple modification, but one I am very happy with
Nice! @Ephemeris what are you doing with the other 4 pairs? Depending on the price, I might be interested in a pair.
Patrick and I split the order so he has 5 for his two BigBox, and I have the other five. I could get another batch made but I assumed there wouldn't be much interest since it requires my redesigned Z-platform.
Ok - I'm just collecting ideas for my next update. X-Y is the priority for me though - my Z isn't too bad to be fare.
I have a second BigBox to allow me to make mods and still have a working printer and I would be interested in at least four, maybe six plus a spare. Mods to the Z-platform are not problem, that is what my extra printer is for, Duet etc. mods. Thanks for what was obviously a major exercise.
This should be doable. You might want to wait and see if anyone else in the UK is interested since in country shipping is probably reasonable and will spread the courier costs of getting the shipment to you. I can get you contact info and control drawings if you decide to do it I should have mentioned the quality of the POM nuts is remarkable! These are not the functional if skimpy cast bits like the Funssor Tr8x2 POM nuts I've used before. The nuts were beautifully machined to my specifications. I believe Patrick was likewise impressed.
Inspried by this... making a roller bearing (605zz) version for th 8mm rods to test... not sure if I need it though after looking at yours after picture. Not sure that I have more that that on my current set-up... But why not test. But I start getting the familiar stench of failure... The slack in the ball bearings are more than the wobble in the rods... So there seem to little hope for my idea well well... So far: Parts now available: Axel mounted: Missing is the acme rod extender... printing as I write... Seems like the sensible thing for us that have the 8mm rods is to see if a 8 mm version of the IGUS part exist and mount it on the underside of the holder. So I have proven that your way is the best at least.
