Kim's - BTW 4x8 CNC Build

[peteeng]

Impressive work !! thanks for sharing.

I am designing a slightly smaller machine (1800x1250mm) and I hesitate between a ball screw or a rack. Are you satisfied with your rack and pignon system? Was it complex to implement and tune ? I have the impression that there is no spring which allows the pinion motor plate to be pressed onto the rack?

Hi Gustave - If a ballscrew works at your size then usually a ballscrew is better. They are available in cost/tolerance brackets are easy to set up and get to work.
A R&P gearset is designed for gear clearance. It's actually poor mechanics to have a system that pushes the two together. But DIY and others do not have the machines that can cut ways and registers to set the pinion/rack at the correct clearance so they use springs to deal with this issue. At a certain length or speed screws become problematic so then R&P takes over for "long" distances. Soon linear motors will take this over, they are available but too costly for the hobbyists.

Its your 1800mm that will be the issue with screws so look at the suppliers design sheets and that will determine if the 1800mm will work for you. Maybe the small axis are screws and the 1800mm is R&P .. Cheers Peter

[beartooth]

Impressive work !! thanks for sharing.

I am designing a slightly smaller machine (1800x1250mm) and I hesitate between a ball screw or a rack. Are you satisfied with your rack and pignon system? Was it complex to implement and tune ? I have the impression that there is no spring which allows the pinion motor plate to be pressed onto the rack?

Sorry, for the late reply, I have no spring tensioning on my rack system, the rack was placed and dowel pinned in place using a dial indicator and the traveling along the bearing rail sub-system. This provided a consistent and accurate level of tooth engagement to the pinion, the gear box is adjusted to the rack with light tension to the rack, thus having a zero backlash of tooth engagement. I keep a light coating of grease on the rack as well.

[beartooth]

Nice machine BT, Did you fabricate all the parts yourserf or sub it out?

Overall very clean work across the board.

Sorry, for the late reply,Thank you and yes I did all the fabrication work myself with the exception of the electrical control panel, I had the sheet metal cut and bent by a shop local to me. I did all the TIG and MIG welding as well.

[beartooth]

What mod size of rack you use ? How do u energize gearbox on rack ?

22x25 1.25Mod Gear Rack Straight Tooth and the pinion and is driven by a 550mm long timing belt with a 5:1 reduction. 90T to 18T timing pulleys in the reduction box.

[peteeng]

I can't remember who it was that posted the same thing I'm about to here (I believe they were in SC), but here in the south, humidity is something we just have to live with. After about 2 weeks this little bit of cloudiness showed up on top of the epoxy in just a few places. It was not measurable and nor could you feel it, so no harm and carried on

Hi -Thats an amine blush. Its the hardener combining with air moisture. Its water soluble so easily removed. Peter