Hey Guys: Just doing some upgrades to my C-Beam Machine (see C-Beam Machine Too thread), and taking some suggestions from Upgrading the C-Beam machine. I decided to do the belt drive upgrade to my Z axis, only to discover the parts have been pulled from the parts store. Apparently some issue with the system not quite working as advertised, I don't know what the problem was. Mark Carew didn't say what the issue was in his email, just that they were pulled temporarily. But, I managed to get the parts from a Canadian OB distributor, and got them in yesterday. It looked OK, but I thought what can I do to improve this? One issue I could see is that the top bearing on the axis would have a lot of sideways pull on it from the belt, and the length of the stub leadscrew sticking out may bend from the stress. The leadscrew is stainless and is fairly soft and easy to bend. So, I came up with a solution, based on Ronald van Arkel idea from the link above. I wanted to try some new bearings I got a while back, and this was the perfect opportunity. First order of business - beef up the shaft at the pulley end. The motor mount plate for the belt reduction just has a 10mm or so hole in it for the shaft to go through. Ronald's idea was to simply drill this out to 16mm so a bearing would fit in the hole. I decided to do this. I used a standard metric step drill, and carefully drilled out the hole on my drill press. Worked perfectly. The bearing was a nice tight fit. Next, I assembled the plate onto my Z axis, and installed the bearing. The bearing was just a hair thinner than the plate, which was perfect. As with the original hole, the hole in the end cap of the c-beam did not interfere with the bearing at all. Bonus! Next step was to mount the leadscrew. I had purchased some thrust type bearings off of Ebay a while back, and I wanted to try them out. The are a 3-piece design, with 2 flat washers and a ball bearing carrier in between. I figured they should work way better for c-beam applications since they are in compression anyway. Only issue is that they are not shielded, so may have a problem with dirt. However, they fit really nicely in the pocket for the regular bearing, and the outside washer fits partially into the pocket, so dirt should have a difficult time getting in anyway. No 8mm shims are needed with these bearings since they have a nice flat face. By the way, I have taken to grinding a flat spot on the leadscrew where the collar setscrew sits. Makes a much better fit for the setscrew, and eliminates damaging the threads so that they don't eat up your lead nut when you disassemble the system. Run the leadscrew carefully on a grinder, then use a power wire wheel to clean up the threads. I packed the thrust bearings with wheel bearing grease, and installed them into the pockets of the c-beam end caps in place of the old bearing. Putting a couple of 8mm shims on top of the outer bearing, and then installing the pulley, left a bit of space for pulley clearance, and the pulley lined up nicely with the motor pulley. The shims are mainly just to keep the bearing from coming out of its pocket. I put the 40T pulley on with the hub facing out. This should also minimize stress on the shaft by shortening the moment arm and reducing the side pull on the shaft. Sorry, that one's a bit blurry. Next, I mounted the belt and motor, and Voila! This should work really well, but I must admit I haven't tested it yet. The thrust bearings will also be a test, but they seem to work well and the axis action is nice and smooth and low friction. By the way, I have a pet peeve with these dang motor pulleys, both this high torque one and the ones used for the OX. THE SETSCREW IS TOO **** SMALL AND MADE OF SOFT MATERIAL! Every time I have installed one of these, I have stripped out the inner hex of the setscrew with the allen key, EVERY time! I thought at first it was just using cheap Allen keys, but now I think it is cheap setscrews! I am going to drill out the holes and tap them to 3mm (Correction, 4mm) setscrews in future. I hate cheap Chinese screws! The smaller they are the worse the quality. I'll keep youse guys posted on how it works out...
Maybe, my memory is far from faultless, but I'm pretty sure they are 2 or 2.5mm. They are **** tiny, anyway. I'll check when I get back to the shop. I think a 4mm setscrew would be too big. I know I ordered some setscrews from Amazon Supply to replace them, but I don't remember the size. Problem with panhead screws is that the head sticks out and often interferes with some other part. I know I tried screws on the 8mm lock collars and they hit the c-beam. I guess it depends on the head shape and size, and the length of the screw as well.
Yep, JustinTime you were right, they are M3's in the pulley. I got some M4 setscrews that I am going to replace them with. Sorry for the confusion. Still haven't got the hang of identifying metric screws on sight (especially the smaller ones) like I can with SAE's.
Was playing with the machine today, and finally I think I have figured out why the kit was pulled from the parts store. The 40T 8mm bore pulley has a tendency to slip on the lead screw under torque. I hadn't seen this before, but I was having problems with the Z axis not tracking properly. I thought one of the lock collars was loose, but it turns out that the pulley was slipping. Tighten the lock collar as much as I dared, I could not eliminate the slip. So, I decided it was time for a set screw. The pulley does not come equipped with one, and I thought this was a gross design flaw. So, I drilled and tapped the collar for an M3 setscrew, and then drilled through one of the 4 flanges on the pulley so the setscrew could protrude onto the shaft. I then filed a flat on the lead screw for the set screw to sit on, and reassembled the unit. Voila, no more slippage. Seems dumb to me that the pulley would not have a set screw to begin with, especially since it is advertised as "hi torque".
Nice idea, I do not care for clamp / collar style pulleys so just ordered a new pulley. I might give this a go while I wait for it to get here.
just wondering, instead of set-screw, why not just drill through all the way and use a tapered pin? Less likely to break, less likely to strip, just as effective...
I drilled holes through the existing collar/coupler holes into the threaded shafts. I then tapped those holes and screw through the collar/coupler and into the shaft. I use loktite and I have had great results. Broke a couple cheap drill bits trying, but it was worth it.
Yeah, MTO, that would likely be the better solution, but the setscrew seems to be holding, especially with a flat spot filed onto the lead screw. It would be difficult to drill all the way through as Giarc pointed out, especially with just a hand drill. The threads on the lead screw tend to catch the tip of the drill and break them, as Giarc said. If I had a fully equipped machine shop, it wouldn't be a problem, but then, if that was the case, I wouldn't really need a CNC Router either. I have found that the leadscrews currently being stocked by the OB Parts Store are a bit under as far as OD goes. Considering that they used to be a bit over, from some earlier posts, it does not bode well for their QC. This is likely why the clamping arrangement on the pulley doesn't hold. That, and the fact that because of the threads, it only has half the surface area of a smooth shaft to grip onto. I also find that I have to adjust the calibration a bit in the GRBL settings, with these lead screws, they are usually up to 2% under in pitch. That is, I have to set the GRBL steps/mm about 1-2% lower than the theoretical value to get proper movement calibration. At least with the current batch.
Actually, its not a QC issue. There were enough complaints regarding the fit of the original screws that the new ones are intentionally being rolled smaller. While is appears they overshot a bit on the new size, I'm not sure what's involved so it's hard to comment as to how close they can actually get with it.
That's a question for Mark but I probably wouldn't get my hopes up, at least not in the near term anyway. It's not as simple as just adding a 10mm screw. It involves integrating the 10mm screw into the existing systems and making sure everything ties together including having all the coordinating accessories and parts available to service a 10mm screw.
Shouldn't be too hard. The only issue is a lead nut, really. You can get 10x16x5 bearings that would easily fit into the existing C-Beam pockets, and it should only require a quick test to see if it works. I don't foresee any clearance issues, especially since the lead nuts are already spaced out from the gantry plate by 3mm anyway. A lead nut that is 2mm thicker should fit without issue. There is a company on eBay that sells 8, 10, and 12mm lead screws and nuts almost identical to the ones in the OB store, but their maximum length is 950mm. Kind of defeats the purpose if you can't get them longer than 1m.
New 40t is from Ebay, I do not have them in hand yet. So quality has not been confirmed. Here is the "link"
any chance of getting the old tighter size? We found the very early lead screw quite tight but made a small "tapp" by running a slitting disk down a short length of the lead screw to form a cutting surface. Run it down the nut once and the fit was AMAZING! A bit of extra work but the performance was outstanding!
Contact the shop to see if they still have any. http://support.openbuilds.com/support/home You might also check with the other distributors regarding their inventory.
Will do but this was more than a year ago, some of the first lead screw from the shop so guessing it's all gone.... Still I will check in with the part store next order as who know maybe there is a secret stash
Acme thread is not the same as 8mm metric trapeziodal thread. Acme is inch size and in this case would be 5/16"(.3125")diameter Tr8 is metric 8mm diameter (.3149") Hence 5/16 acme is approx .002" smaller. Also the thread pitch is different. Acme pitch is.071" Tr8 is.059". This would cause the travel per pulse discrepancy you are getting. These differences are not obvious to the naked eye and it would be easy to mix them up.
There is no mix up between the two. The TR8 threaded rod used here is a 4 start with a 2mm pitch (0.079") which makes for an 8mm lead (0.315"). 5/16-18 threaded rod is not even remotely similar and the closest thing I can find in a multi-start 5/16" acme would be a 2 start 5/16-8 which would also not be close enough to a TR8^8 that it would even remotely fit through a standard nut block.
Pardon my error I was refering to single start threads with info from Machinerys Hand book. My biggest annoyance is when Tr8 is called 8mm Acme. They are both trapezoidal threads but thats where the similarity ends. I am from the old school and am a little pedantic about using correct names. Cheers Phil Hopkins
