Guest Book

          CNC Router

New CNC Router Project

The problems of my first CNC machine are detailed below and theirs a lot that can be done to improve its performance without breaking the bank and investing in linear guides, ball screws and proprietary stepper motor drives. This project is to see if I can make a low friction version of the existing machine using readily available parts or components that can be made on my Chester Model B lathe/miller and castings produced with the small furnace I made the other year.

Design Peramiters

  • Use as much of the old machine as possible. The Bed, 18mm BDMS guides etc.
  • Replace the guide bushes with V rollers to reduce friction.
  • Design a simple roller nut to remove the friction from the leadscrews.
  • Utilise 608 bearings wherever possible, available from skateboard suppliers much cheaper than bearings from mainstream bearing suppliers.
  • Keep the components simple and small enough to machine on my Chester Model B and using castings made in my home foundry.
  • Design the components and assembly using Blender producing a series of tutorials based around the machines components to help others get to grips with producing accurate 3D models and assemblies with Blender.
  • Investigate other drive electronics, possibly a bipolar chopper driver.

The problems with my first CNC Router

My first attempt at a CNC router detailed below has some major limitations in its design and performance. Notably it was built on a shoestring budget with the cheapest possible configuration. The bed was made from bonded aluminium box section.  These were architectural trims acquired at cost price.  This has proved to be sufficiently rigid and provides good fixing via the ‘T’ slot sections. This is possibly the most successful part of the machine. Most of the other parts of the structure were machined from a length of 3inch by 1 1/2 inch extruded aluminium bar, where this wasn't big enough sections were bolted together.
Aluminium Bed Section
Aluminium section bonded together to form the Bed

Slideways and Bushing

Guides and Slide Bushes

The guides are lengths of 18mm bright drawn mild steel rod with sintered bronze bushes as the slides. Again the 18mm diameter bar has proved amply rigid enough for this size of machine, however the friction from the bushes causes a sufficient “slip stick” effect to be a problem and light oil on the guides quickly becomes contaminated with dust binding up the slides and causing the stepper motors to lose steps. The machine then loses position and messes up the job.The positioning of the carriage is carried out using lead-screws made from threaded rod with brass nuts. To minimize backlash a split nut tightened by a small grub screw was used.
Leadscrew and Nut

Lead-screw and Phosphor Bronze nut

The threaded rod was easily accurate enough to position the router within 0.1mm of the intended position, but backlash was a problem and as the backlash was adjusted out friction increased again causing the stepper motors to lose steps. The electronics was also a problem. Not something I have a great deal of experience in I managed to trawl the web and put together a basic stepper drive but extremely inefficient and not capable of fast step rates. The motors relied on dropping resistors to regulate the power resulting in much poorer performance than could be achieved with better electronics.

My First CNC Router

The machine bed was made from epoxy bonded aluminium extrusions and the support components machined from 3 x 1 1/2 solid bars. The design of a traveling bridge and twin X-axis drives was chosen to allow larger pieces to be mounted on the table without requiring extra torque to drive them. The Y-axis guides can be raised within the frame to accommodate thicker pieces. The machine performed well on slow feed rates but occasionally missed steps on the X-axis when the feed rate was increased it seemed obvious larger motors were required. After some searching I found a suitable replacement with the same frame size but a substantial increase in torque. A slight modification was made to the coupling to accommodate the increased shaft diameter and the new motors fitted. The machine hasn't missed a beat since. The step generator circuit was built using a simple TTL logic circuit. This gave the correct 4-phase sequence of steps for the stepper motors from the serial step signal generated by the computer. The output from the TTL circuit was then used to control the power transistors to the motors.

CNC Engraver - Small Motors CNC Engraver - Large Motors

Old 486 Computer Electronics

Impress Stamps House Number

Terms of Use Site Map

All Content © 2007 - 2019 Robert Burke, unless otherwise stated.
Please contact me if you would like to use any of this content.