Centroid Community CNC Support Forum

JayCNC wrote: ↑Thu Apr 04, 2019 10:48 pm Ok, so I re-checked EVERYTHING on this machine and found that there was some play in the bearing block for the ballscrews. I took them apart and ended up shimming between the two bearings outer edges until they felt tight. I re-ran the same program with much better results but still not perfect. I’ve come to the conclusion that new better quality angular bearings are needed as I’m 99.9% positive this is the problem. Anyone know where to pick up a good quality angular bearings from? 12mm ID X 28mm OD X 8mm. I checked McMaster Carr but there’s no way I’m spending $204.32 EACH!!

JayCNC, thank your for reporting back.... (im really holding back here from saying i told ya so ) the fact that you reported back is a HUGE help to the rest of the Acorn/Centroid DIY community and i appreciate it. I think i'm going to copy this post into the tips and tricks section to make it permanent so other can learn from it. Good luck with your projects. -keith

PS real 0 lash (matched set) angular contact bearings cost money.. this is definitely a case of you get what you pay for and a place where you don't want to cheap it in this area. shimming is ok.. but you run the risk of over tightening a non matched set and introducing drag into the system.. a non matched set has either too much slop or too much drag..thats why matched set angular contact bearings exist.

JayCNC wrote: ↑Thu Apr 04, 2019 10:48 pm I checked McMaster Carr but there’s no way I’m spending $204.32 EACH!!

Check with the local bearing distributors - I use Alpine bearings here in Boston and they are usually quite a bit cheaper. Also check eBay. I picked up a set of matched bearings for a grinding spindle I was making for pennies on the dollar.

If you have rigidity problems, it will usually show up on the 45's on a circle. That's where you get the backlash of both X and Y combined as well as the lowest loads on each of the axis as well. On my machine, I notice a small amount of chatter at 135° and 215° when cutting a circle.

I've had good luck with VXB bearing. Looks like they have a variety of quality in that size:

https://www.vxb.com/searchresults.asp?s ... f-28mm=631

Keith, by all means say it!! I don't mind, I learned something new by this whole thing as in I never knew these bearings could cause so many issues! The only reason I kept going back to the smoothing thing is because I saw different results when I changed settings, so I really thought that could be part of my problem. I was wrong, and thank you for responding and helping me realize the real problem.

So let me ask you guys this, if I ordered bearings from VXB, 7001C P5 ABEC-5 12x28x8, am I going to have similar issues? Is the ABEC-7 bearings worth more money, or should I seriously be looking at the $200 plus bearings?

I honestly think the parts look pretty good as is for being done on a router. My big question is are the dimensions to spec? You will never get the finish that a VMC with a 30hp spindle gets.

So my opinion is if the parts work call it a day and make more parts. I've seen worse finishes on production parts, what you have looks like it would easily buff out if you really need a shiny edge. Like I was saying, if the parts are dimensionally right just roll with it. I'm sure they are more than sufficient it's not like you're making parts for a Bugatti. I've seen worse finishes on parts that were made for the military.

Dan

Dan M wrote: ↑Fri Apr 05, 2019 10:10 pm I honestly think the parts look pretty good as is for being done on a router. My big question is are the dimensions to spec? You will never get the finish that a VMC with a 30hp spindle gets.

So my opinion is if the parts work call it a day and make more parts. I've seen worse finishes on production parts, what you have looks like it would easily buff out if you really need a shiny edge. Like I was saying, if the parts are dimensionally right just roll with it. I'm sure they are more than sufficient it's not like you're making parts for a Bugatti. I've seen worse finishes on parts that were made for the military.

Dan

The parts I make are for performance boats ranging from 15-500K. I take pride in the things I make and I'm not willing to put my name on something I wouldn't put in my own boat. I know that this machine is DIY, but I know it's capable of perfection too. I'm within .0035" at it's worst and spot on at it's best, and I think with some time spent with ballscrew mapping, tool wear and runout it's capable of tenths or less. So... if it costs me a little more money to fix this issue, it'll be money well spent because like I said, I can't put my name on something that's not perfect.

Got it. Have you thought about using two ballscrews for the y-axis outside of the linear rails?

Dan

Dan M wrote: ↑Fri Apr 05, 2019 11:40 pm Got it. Have you thought about using two ballscrews for the y-axis outside of the linear rails?

Dan

No I haven’t, what would be the advantage to that? These Clearpath Servos are insanely strong, I bought nema 34s with 840oz or so power. I’m sure they are WAY oversized now that I have them. When I talked with Abe at Teknic we went through each axis individually and recommended the ones I bought. I had chose similar ones but we changed the Z axis to one with more torque vs speed.

tblough wrote: ↑Fri Apr 05, 2019 10:50 am

JayCNC wrote: ↑Thu Apr 04, 2019 10:48 pm I checked McMaster Carr but there’s no way I’m spending $204.32 EACH!!

Check with the local bearing distributors - I use Alpine bearings here in Boston and they are usually quite a bit cheaper.

Thanks for the tip, I called Alpine and spoke with Dave and he was a HUGE help! I'd recommend them to anyone looking for bearings or just information in general about them, they are more than willing to help you.