I built a 4′x8′ router from Patrick Hood-Daniel’s buildyourcnc.com. The router uses a chain drive for the long axis that is run by a central stepper motor. You can see the chain drive in this photo:
The 4'x'8' router uses a chain drive for the X axis.
You can see the x-axis motor and its mount in this photo (the black motor in the center of the photo is the x-axis stepper motor):
X-axis Motor in center of gantry - honkin' huge ass motor
Each side of the gantry has a chain, and the chains need to have the same tension for the router to track properly. Everyone tightens the chains too tight (okay, maybe just me). This flexes/bends/warps the long 1/4″ rods coming off the x-axis stepper motor, resulting in horrible stuttering/jerking/etc from the poor stepper motor. Somewhere there’s a law against it I’m sure. Anyway…
The 1/4″ rods needed some form of support across these lengthy spans. I finally got off my butt and created the supports, which are here:
I took an existing part and modified it a smidgen...
Long story short: Here is a pdf and a dxf of this support, should you need to do the same. The bearings were purchased at Fastenal, and weren’t too expensive (~$5.25USD):
1/4" Bearings Limited (R4 2RS PRX)
‘But wait wait Peter: how did you get everything lined up and square?’ Jigs young grasshoppa:
The Youtube video I created shows the jigs, the supports, and more important, the Blacktoe router’s vulnerable rods without these supports:
To drill accurate holes in the ends of the plywood pieces, I relied on kobbleit’s crude ‘end hole boring jig’ which is explained in detail on this website:
{ 10 comments… read them below or add one }
You change the motor for new one nema 34 ?
please specified the change and the comparing the old one whit the new one.
and the old one how many, oz are comparing with the new one. and now how is running you system with the change that you make.
thanks keep you great work and happy new year .
keep working.
I did not change the motor for the x-axis. This is the standard (1200 oz/in) motor that Daniel sent me. The x-axis uses/needs/requires/must have a much bigger motor to move the entire gantry. The other motors are 480 oz/in; the big x-axis motor is 1200 oz/in. Hope this helps you…
I’m using 425 oz motors on all three axises on my 4×4 v4.1 machine and the x axis works fine except the rods bending when I tighten the chains as much as the Y. I was going to do the exact same thing as you did with the supports but was only going to add one per side. I think I’m going to just add 2 to be safe. I hope it doesn’t make it skip steps. It’s probably smoother than the bending rods or loose chains though. Thanks for the DXF file, I’ll cut them tomorrow evening and install them this week.
Pete
Just a comment on these rod supports. If you would add a bearing to the outboard side of the shaft so that the sprocket is between 2 bearings it would completely eliminate the rod flex and you would not need the center supports.
Just my 2 cents worth
Thank you for the comment and visiting the site. The gantry side is only 3/4″ thick – there really is no room to add an outboard bearing. One bearing takes 3/8″ of that 3/4″ – another bearing would eat up the entire 3/4″, so you’d end up with two bearings back to back. I think that would help, but I still don’t think it would solve the issue. The only other solution is a much thicker rod – 3/8″ is what should have been used (the existing design uses 1/4″ rod. But… perhaps I am not following you.
I think what bruceb is talking about is not adding a second bearing where the current bearing is located, but adding an additional support and bearing on the outside of the sprocket like this: B-S-B where the B’s are bearings, and the S is the sprocket (and the dashes are the rod). It would make chain maintenance more difficult, but would solve the bending problem, which is occurring because the sprocket is only supported on the gantry side. One thing that concerns me is that big motor that’s confined inside of the gantry with almost no provision for cooling. Seems like you’re asking for overheating problems. If I owned one of these I’d put in as many cooling slots/holes as I could without compromising the strength of the gantry.
Thank you for clarifying this. You’re right: I didn’t really understand his suggestion. It would definitely run well this way but I’m not sure it would actually be any easier. Maybe it would be. Anyway, the whole chain-driven system is not that good. It really needs a re-design.
How much tension do you put on the X chain, and how do you measure this?
Cheers!
pr
Hi Paul – sorry to reply so late. I don’t have a system for measuring the correct amount of tension. But here is something that may help you: if you have the chain aligned to the sprockets correctly it shouldn’t matter. Aligning both sides is a pain but not impossible. It involves some jigs. I think I did a post on that. Maybe I didn’t. I’ll do one.
I have read that if the chains are loose they will bounce up and down considerably during a cut session, which can cause some problems as the bit cuts something. One solution was to put a glove on the chain as its cutting just to dampen the bouncing up and down.
Pkunhs … hopefully you still monitor this sight. The attached .dxf file is save as a “spline” type of file. The file should be saved as a .dxf with polylines instead. I think this would make the file much more useful for most users.