Hello Everybody! I'm in the process of putting together a Workbee Lead 1000x1000 CNC and when I tried to run the Z axis C-Beam trough the Z axis assembly it only fit with a little bit of "persuasion" as you can see in the following Video. Cue me taking every mesure that I possibly could and checking with the CAD files and the only dimension that was out of spec is the width of the v wheel groove on the C-Beam as shown below. Mine is the one to the right and as you can see the width is 6.22mm where it should be 6.79 and I'm guessing because of that the wheel doesn't go into the groove as much. If that is really the case I know that a possible solution would be to drill the plate and insert eccentric spacers on the fixed side of the assembly and according to what I've seen that would give me up to 0.79mm more of clearance but I'm not too excited about that option and I have no clue if that would be enough clearance. I was wondering if anyone has run into this issue and if there any other routes I could take. Thanks in advance
Some of the CAD models may be outdated compared to current part spec, so I wouldn't go by that alone (as designs get tweaked since inception) - Eccentrics in the open position? (if the eccentrics is all the way tight it will press the wheel too hard. Adjust them properly. Of if they are in the wide open position and still does that: - Is it Genuine OpenBuilds Parts? Contact the vendor you purchased from (or http://support.openbuilds.com/support/home if you bought from us directly) for replacements - If its not genuine, then consider replacing with genuine parts for guaranteed fitment
Thank you for the fast reply. Eccentrics are in the wide open position (forgot to mention that, sorry). I got almost everything from authorized vendors but I'm in Brasil and to import the aluminum rails would cost way too much so I tried to get some locally produced rails. I was considering buying genuine parts but I just don't have the money for it (between taxes, freight and devaluation of Brazilians currency I would be paying almost 10 times what I've paid on the ones I got) so I'll have to find a way to make this work with what I have in my hands right now.
About the only realistic option I can think of to modify the extrusion is to cut some wooden blocks to as perfect 90 degree angles as you can manage and use them with sandpaper to manually grind out the extra 0.1-0.2mm per side that you would need to get an adjustable fitment. Probably starting with US 180 grit and once it was near size, working up through 400, 800, 1000 grit (maybe higher, depending on how the wheels feel). This isn't an easy technique- it's effectively lapping- and could certainly lead to wobbly rails without a jig to keep you on track and a careful attention to pressure and varying of angle (maybe you could use the wheels themselves in the other grooves to make a sort of adjustable carriage?). The other option is to adjust the plates. You could extend the fixed wheel side screw holes out 0.3mm or so, which you could probably do with a small round file in a few seconds. Or you could re-drill the holes half-way between the existing holes, but a tiny bit further out. The advantage there is that presumably the plates are cheaper than the extrusion so damaging them wouldn't be as expensive a problem.
Thank you for your reply. I thought about making a jig and get a chamfer bit to widen the groove evenly but I lack the space and tools to make it. It's a great idea and I probably should spend more time on thinking how to make it happen. As to the plates they are very expensive down here due to taxes/currency devaluation that's why I'm looking for ways to fix the issue without messing with them.
I wouldn't use any rotary tools if at all possible- too much chatter and easy catastrophic error with both routers and Dremels. Some kind of scraping or grinding would likely be the way to go.
The Openbuilds Delrin (Black) v-wheels are 23.9mm in diameter. A quick look at Amazon and all the black Delrin wheels sold for 3D printers are 24mm in diameter so that may be where the tightness came from. You could try to drill out the bottom eccentric holes with a 9/32 (7.143mm) inch bit if you have access to one. The bottom holes are more forgiving since the eccentric can help cover up any error you may introduce while drilling. That may loosen them enough. If not then drill out the top holes with a 13/64 inch bit (5.159 mm).
That's a great idea, thank you for that! The wheels was one of the things that I bought original and I mesured it with my calipers and they seem to be sopt on (0.1mm seems to be inside the error margin). I'm still trying to think of a way to reliably route the grooves but if it's too much of a hassle I might end up drilling the bottom holes.
I would probably just default to drilling out the bottom holes. Routing the grooves will take off the hard smooth layer that the anodizing provides leaving behind a rough soft layer of bare aluminum. This will probably not wear well and will not be kind to the wheels. Start with the smallest possible increase in drill size and keep testing as you go for proper fit. On final assembly leave the fixed wheels slightly loose and then tighten them with the Cbeam in place where uniform pressure is holding them to their maximum outside position.
I think the dimensions given between the centres of the wheels (99.7mm) is just plain wrong. I drilled my own plates and everything was just too tight. Had to drill them out to 5.5 mm. Personally changing the C beam dimensions seems ludicrous. I suspect there are discrepancies in the dimensions of some Delrin wheels.
It is and this can be found in a number of threads over the years, most of them 8-10 years ago. There were a lot of problems with manufacturing tolerances of the extrusion during the early years and this lead to a bit of a moving target with wheel spacing. The best number is nominal extrusion depth + 20.0 mm (depth + 12.0 mm for mini-V wheels) as this is pretty much the sweet spot that covers all tolerance variations.
Yes. And if in doubt this is fairly easy to check with digital calipers. Set the wheels in place and measure between the inside edges of the bearings and then add 5mm.
Thanks. Another query if I may. What is the exact measurement for a spacer between two parallel wheels in two adjacent grooves of a C beam? I have measured it at 8.6mm. The nearest spacer I can find is 9mm. Are they made for this gap?
If you’re getting 8.6mm it sounds like your bearings are not properly seated. This is one of those items that is very consistent. A wheel with (2) 5mm wide bearings and a 1mm shoulder inside should be dead on 11.0mm. Anything else says you either got a bad wheel or your bearings aren’t seated. With a 20mm groove spacing this makes for a 9mm gap in between.
