Chronicle of a Geek! (Part 2 A new dawn)

[Logon_Bob]

Hey Paul

I am glad you are still posting. :-) I ran across your initial I-beam drawing from quite some time ago but that thread quit. I am still in Over-thinking mode looking at all the designs out there trying to pull out what I like, will this work and can I do it. And I'll be dang, here's this drawing with the methods I am thinking of doing, sort of a cross between the buildyourcnc and Solslva. I have my eye on some 6x8.2 Steel channel instead of I-Beam but close. Fully supported X with THK rails. I see you switched.

I need around a 2 x 4 ft as well but I have not built a thing yet other than a CNCfoamcutter. So I wanted to find out just how the build went and find out about your chain stretch issues.

Looking at your pics, I would really check out the eye bolts for flex first. They're sticking out a ways a bound to bend under load. You could verify with a dial gauge.

I like the chain drive single motor as well and that is the plan at the moment. My issue is how much the connecting rod motor to sprocket is twisting, something else to check. I like the fact you placed the motor in the middle with 2 shorter shafts, longer shafts twist more. I don't know yet, at only 2 ft wide, so each shaft at 1 ft or less might be OK. Only thing you can do there is increase the diameter, increasing diameter just a little is a big gain in torsion stiffness. I have a bunch of ideas for the shafts. :-)

Plan A - This issue of a tighter chain over loads the motors. I still think it's the eye bolts but. Oh for a drawing.... mmmm The motor sprocket, since it's only support on one side by the bearing, what if you added a Cap Block with another bearing in it so the sprocket is supported on both sides. A lot more tension can be applied. But now you need a longer shaft as well.

Plan B - You have a lot of distance between the sprocket and the iders. What if you add a jack Shaft in between? Two Sprockets ( with a 9 tooth being the smallest practical, and now you can change gearing ) It's more friction but say you mounted an 18 tooth ( or what ever combo ) on the motor side and a 9 on the outside running the chain? Double resolution but of course less speed of which you said you have plenty. :-)

Regards
Dan

[Logon_Bob]

Sorry Rob, didn't mean to hijack your thread. I just followed a link and didn't realize.

Dan

[PaulRowntree]

Dan, you are spot on; I think the eye bolts are the source of weakness, and I may have been off-base in blaming the chain stretch. Let's move the discussion of my machine woes to my thread. Sorry Rob!

http://www.cnczone.com/forums/cnc_wo...tml#post945502

Cheers!

[voltsandbolts]

Its ok guys, it’s good to see some activity in my build thread … even if it’s not mine.

Rob.


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[voltsandbolts]

Well it’s been too long sense my last post, but the crappy economy caught up to me and I was out of work for a bit. Luckily I’m back to work with a great company and have reached the point I can think about hobbies again. :-)

I am working on setting up a PC to run the new router. I have an old Dell desk top without the case. I have all the parts plugged together and working and all my CAD software runs ok on this modest system so it should be ok to use as a controller.

Right now I run TurboCNC on an old Pentium 75 under DOS (hey it works)… the new or should I say newer PC is a P4 3Ghz with 2gig of ram. Not sure if I will spring for Mach3 or not (comments welcome) I have the new PC setup to dual boot Win XP / Ubuntu EMC2. I am also setting up a laptop to do the same, it will most likely become my design PC and back up for the controller PC.

Anyone doing the dual boot Windows / Linux EMC2 thing? How’s it working out? Any warnings for me?

Until next time…
Rob.

[ecurb5]

Anyone doing the dual boot Windows / Linux EMC2 thing? How’s it working out? Any warnings for me?
Rob.

Not a big fan of dual booting for this setup. I have a older P4, 2.4Ghz, 2gig ram that just runs EMC2 just fine. I tend to just leave it running but will shut down the electronics for the machine. I have a laptop running winblows for my design software. Both systems are on the network, so I just save the gcode file to the controller pc from the laptop.

[voltsandbolts]

Thanks for the info "ecurb5"

That’s also my plan. Windows for the design software, EMC for the controller. And both machines on the network for file transfers. I didn’t think I was charting new ground here, glad to know others have tried it successfully.

Rob.

[voltsandbolts]

Ok I have been back in the shop and making some parts for my G2 router (the big experiment), I’m working on the chain mount / tensioning assembly. Part cutting is being done on the old jgro.

[voltsandbolts]

Here are a few pic’s of the mount mocked up into place. The one with the ruler shows alignment of the eyebolt and chain idler sprockets.

[voltsandbolts]

I can only wonder how much tension I can put on the ¾” MDF before it “Pops” If I find it a flex issue I guess I can back it with a piece of angle for added rigidity.

[PaulRowntree]

For what it is worth, I would add the support now, since static tension is only part of the problem. Decent acceleration will add spikes to the tension too.
I found that my 3/8" steel eye-bolts were flexing too much under the chain tension, so I would think unsupported MDF would be too weak as well (although my bolts were mounted in the worst way ... at 90 degrees to the tension).
Cheers!

[voltsandbolts]

Hi Paul,
Thanks for the input. I have my eye bolts oriented inline with the chain pull. I have also added a stiffener along the front lower edge. It can easily be retrofit with angel along the backside, (I have some standing by)

[voltsandbolts]

Well the weathers finally getting chilly and it looks like I can get back into the garage and on with this project. I have spent the summer outdoors on other activities like building the chicken palace and figuring out how to hook up and use the tractor and implements I bought (instructions not included) It’s been an adventure. But now I can get back to the indoor stuff.
If this chain drive doesn’t work out for me, I will try something different. Maybe a rotating nut on ½-10 Acme… I haven’t seen too much talk of homemade rotating nuts on the Zone.

[CarveOne]

The DIY rotating nuts are around here if you search for the right terms. As far as I can recall, the ones that have them haven't changed them out because they weren't working as planned.

[voltsandbolts]

The DIY rotating nuts are around here if you search for the right terms. As far as I can recall, the ones that have them haven't changed them out because they weren't working as planned.

Carveone,

Thanks for that Tid-Bit. I have heard a lot of negative on the chain drive and I know it has it's weak points but I still want to give it a try. Then I can say I did it. I also want to try belt drive at some point but that will probably be on a PCB router (small scale). I have already acquired the parts to experiment with for the rotating nut idea I have and I haven't even got the chain drive running yet. Terrible I know....

[CarveOne]

Jason Marsha came up with a simple idea using a single pillow block. Search this forum for Rotating Nut. There is one other I have seen using two bearing supports with the nut and pulley between the supports. They are commonly driven with a timing belt. I suppose there are lots more out on the web.

Chains work, but if loose enough to be smooth they have backlash, or if tight enough to eliminate most of the backlash they have cogging problems.

[voltsandbolts]

Thanks CarevOne,

I can't believe I didn't find that thread, Jason is way ahead of me, with a similar idea. I have to read through his thread, it might save me some design time.

Ha ha, went back to read and found it to be very short! :-)

Rob.

[PaulRowntree]

I missed that one too. Interesting idea, but aren't pillow blocks / bearings designed for radial loads more than axial?

pr

[CarveOne]

I missed that one too. Interesting idea, but aren't pillow blocks / bearings designed for radial loads more than axial?

pr

I suppose they are, but they can handle some amount of axial loads within their ratings, and just have shortened service life if the rating is exceeded long term. DIY machine builders probably expect the machine to be repaired, upgraded, or replaced eventually. I know I do, and wouldn't worry too much about it. Use thrust washers on the lead screws to take excess axial loads off of the pillow block bearing.

[voltsandbolts]

Looks like Jason beat me to it by a few years... This is the concept I was working on. I modeled a v belt pulley because it it's easier to do. I would actually use a timing belt and pulley.

RotoNut