Have you considered a rack and pinion drive?
Hey Guys! Im still pretty new to the DIY CNC world, but I am a CNC programmer at one of the largest manufacturing companies in the US. Ive been lurking on the forums for about 6 months now, and I built a RockCliff machine about 5 months ago. I love the machine and it works awesome, but being a guy and such I wanted bigger and more power about a day after I got it running
So being that Im around giant machines all day, and working with some great mechanical minds Ive spent some time making up my own version of the fixed gantry, with some inspiration from alot of the other MDF and DIY builds.
Space was a big concern with this as my workspace is a one car garage, that the wife would still like to park a car in. But I wanted to be able to cut 48" wide boards at the least. So after some thought, I decided to place my gantry over the long axis of my machine. The axis will travel on v-groove bearings on angle aluminum and be driven by roller chain. The gantry is about 60" long so I thought chain would help me eliminate lead screw whip.
The X-axis will be set up much like the rockcliff design, except using .75" Thomson rails and Igus sleeve bearings.
I attached a couple preliminary CAD drawings to show the initial design. Let me hear some feed back.
Have you considered a rack and pinion drive?
I have considered rack and pinion, but It seems like theres less chance of backlash in a chain drive if tension is kept on the chain then with a rack and pinion drive. Also I have a source to get the roller chain components for basically free, so that's persuaded me haha.
Construction has officially started and is moving along swiftly. Some of my build plans have changed a bit, as they always do. But here are a few pictures. I have my torsion box for the base mostly built, the gantry bridge fully assembled, and lots of parts cut for the y and z axis. Its coming along slower then I thought,but coming and that's what counts. I even got to mock up the chain drive for the Y and drive it with a drill in place of the stepper motor. That was fun, made me feel like I have accomplished some thing.
Heres a link to a short vid of the Y axis too
[nomedia="http://www.youtube.com/watch?v=Az2K3HbYKpY"]YouTube - Eddi-P Y Axis travel[/nomedia]
Make sure you have lots of adjustment on your V bearings as it will wear the aluminium very quick until they are seated completly. Once seated they wont wear as much but they will wear.
as for adjustment, I gave myself 3/4" of play to make removing the board easier and for wear adjustment. I need to look at it and see if I need to give myself and more though. At this point remaking parts is super easy, so nows the time.
I used 1/8"
Just to seat the bearings you need about 1/16 on each side. Even more for long term wear. Another problem the aluminum has is that it does flex. I will probably eventualy replace all mine with steel. Its a simple problem to replace with out a tear down on my build. I simply loosen the vgroove so its nice and sloppy then remove the bolts holding the angle. I pull out one side and slip in a steel angle that has been drilled the same and reinsert the bolts.
Bottom line aluminum is ok for a first build and for learning but It does not work very well for a machine you dont want to constantly be tinkering with.
sounds good, and makes since. If I stick with v-grooves Ill probably replace with steel also. I will most likely replace them with THK Linear slides later on though.
Well another day off work and more progress has been completed!! I finished my Z axis slide today. complete with lead screw and all. When my motor couplers come later this week Ill make my motor mount for it too, but for now Ive left it off so when I get discouraged about this whole project, I can just go hook a drill to it and drive it back and forth lol!.
The z is comprised of Thomson 1/2" rails with Igus Sleeve bearings pressed into custom made sleeves. I then took HDPE and made blocks with my original CNC Router to hold the sleeve bearings into place and also to hold the rails and the actual carriage for the axis. A friend of mine made my bearing blocks and also helped me machine down the lead screw to fit in correctly.
Also Big news for the day, I now have THK HSR20 linear slides for both my X and Y axes! Super strong, Super Precise! Really stoked to get these on, but I bought the wrong size cap screw for them today so they will have to wait until later this week.
Heres the Pics!!!
Would love to see more info on the blocks and rails you chose. And lots of pics when you get them.
I have a big build in mind down the line and I Know I dont want to go with V bearings. Just too many issues.
Hi, would you mind posting some info on the chain drive parts and specs ?